SQZ Biotechnologies (SQZB) S-1 9 Feb 21 IPO registration Financial data

Cover Page

Cover Page	9 Months Ended
	Sep. 30, 2020
Cover [Abstract]
Document Type	S-1
Amendment Flag	false
Entity Registrant Name	SQZ Biotechnologies Co
Entity Central Index Key	0001604477
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 107,060	$ 39,255	$ 59,570
Marketable securities	8,021	59,027	47,343
Accounts receivable	1,892	1,874	865
Prepaid expenses and other current assets	1,905	1,662	1,035
Total current assets	118,878	101,818	108,813
Property and equipment, net	3,850	5,163	4,429
Restricted cash	2,305	2,319	2,305
Deferred offering costs	1,132
Operating lease right-of-use assets	50,807	43,050
Total assets	176,972	152,350	115,547
Current liabilities:
Accounts payable	2,461	2,796	1,087
Accrued expenses	5,879	7,061	3,739
Current portion of deferred revenue	34,309	18,982	16,504
Current portion of operating lease liabilities	8,040	9,444
Total current liabilities	50,689	38,283	21,330
Deferred revenue, net of current portion	13,755	21,846	29,219
Deferred rent, net of current portion			1,282
Operating lease liabilities, net of current portion	41,323	32,887
Other liabilities	1,007	740	855
Total liabilities	106,774	93,756	52,686
Commitments and contingencies (Note 10)
Convertible preferred stock (Series Seed, A, B, C and D), $0.001 par value; 17,044,139 and 16,670,802 shares authorized at September 30, 2020 and December 31, 2019, respectively; 16,904,219 and 13,869,027 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively; liquidation preference of $169,648 and $127,348 at September 30, 2020 and December 31, 2019, respectively.	174,357	132,109	106,401
Stockholders' equity (deficit):
Common stock, $0.001 par value; 24,000,000 and 23,700,000 shares authorized at September 30, 2020 and December 31, 2019, respectively; 1,760,362 and 1,737,388 shares issued and outstanding at September 30, 2020 and December 31, 2019 respectively.	2	2	2
Additional paid-in capital	4,992	2,701	508
Accumulated other comprehensive income	15	30	(4)
Accumulated deficit	(109,168)	(76,248)	(44,046)
Total stockholders' deficit	(104,159)	(73,515)	(43,540)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 176,972	$ 152,350	$ 115,547

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Temporary equity, par value	$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized	17,044,139	16,670,802	12,057,951
Temporary equity, shares issued	16,904,219	13,869,027	12,006,791
Temporary equity, shares outstanding	16,904,219	13,869,027	12,006,791
Liquidation preference value	$ 169,648	$ 127,348	$ 101,395
Common stock, par value	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	24,000,000	23,700,000	18,500,000
Common stock, shares issued	1,760,362	1,737,388	1,691,129
Common stock, shares outstanding	1,760,362	1,737,388	1,691,129

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 6,121	$ 4,181	$ 18,511	$ 13,866	$ 20,109	$ 12,669
Operating expenses:
Research and development	13,910	8,489	37,815	26,324	36,102	24,379
General and administrative	4,612	4,065	14,139	11,191	18,272	8,694
Total operating expenses	18,522	12,554	51,954	37,515	54,374	33,073
Loss from operations	(12,401)	(8,373)	(33,443)	(23,649)	(34,265)	(20,404)
Other income (expense):
Interest income	56	492	533	1,711	2,070	978
Interest expense						(59)
Other income (expense), net	(6)	(2)	(10)	(5)	(7)	235
Total other income, net	50	490	523	1,706	2,063	1,154
Net loss	(12,351)	(7,883)	(32,920)	(21,943)	(32,202)	(19,250)
Accretion of redeemable convertible preferred stock to redemption value						(984)
Net loss attributable to common stockholders	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)	$ (32,202)	$ (20,234)
Net loss per share attributable to common stockholders, basic and diluted	$ (7.03)	$ (4.58)	$ (18.87)	$ (12.94)	$ (18.89)	$ (12.75)
Weighted-average common shares outstanding, basic and diluted	1,758,039	1,722,300	1,744,948	1,696,104	1,704,509	1,586,683
Comprehensive loss:
Net loss	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)	$ (32,202)	$ (19,250)
Other comprehensive income (loss):
Unrealized losses on marketable securities, net of tax of $0	(48)	(12)	(15)	(32)	34	(1)
Comprehensive loss	(12,399)	(7,895)	(32,935)	(21,975)	(32,168)	(19,251)
Collaboration Revenue [Member]
Revenue:
Total revenue	$ 6,121	4,050	$ 18,511	13,075	19,318	11,539
Grant Revenue [Member]
Revenue:
Total revenue		$ 131		$ 791	$ 791	$ 1,130

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Unrealized gains (losses) on marketable securities, net of tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumualted Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance, convertible preferred stock at Dec. 31, 2017		$ 34,314
Beginning balance, convertible preferred stock (Shares) at Dec. 31, 2017		5,996,651
Issuance of Series D convertible preferred stock, net of issuance costs of $43		$ 68,029
Issuance of Series D convertible preferred stock, net of issuance costs of $43 (Shares)		5,750,812
Conversion of convertible promissory note into Series C convertible preferred stock		$ 3,074
Conversion of convertible promissory note into Series C convertible preferred stock (Shares)		259,328
Ending balance, convertible preferred stock at Dec. 31, 2018	$ 106,401	$ 106,401
Ending balance, convertible preferred stock (Shares) at Dec. 31, 2018	12,006,791	12,006,791
Beginning balance at Dec. 31, 2017	$ (23,984)		$ 2		$ (3)	$ (23,983)
Beginning balance (Shares) at Dec. 31, 2017			1,657,627
Issuance of common stock upon exercise of stock options	89			$ 89
Issuance of common stock upon exercise of stock options (Shares)			48,638
Accretion of redeemable convertible preferred stock to redemption value	(984)	$ 984		(171)		(813)
Forfeiture of unvested restricted stock awards (Shares)			(15,136)
Stock-based compensation expense	590			590
Net loss	(19,250)					(19,250)
Unrealized losses on marketable securities, net of tax of $0	(1)				(1)
Ending balance at Dec. 31, 2018	(43,540)		$ 2	508	(4)	(44,046)
Ending balance (Shares) at Dec. 31, 2018			1,691,129
Ending balance, convertible preferred stock at Sep. 30, 2019		$ 106,401
Ending balance, convertible preferred stock (Shares) at Sep. 30, 2019		12,006,791
Issuance of common stock upon exercise of stock options	64			64
Issuance of common stock upon exercise of stock options (Shares)			34,626
Stock-based compensation expense	1,461			1,461
Net loss	(21,943)					(21,943)
Unrealized losses on marketable securities, net of tax of $0	32				32
Ending balance at Sep. 30, 2019	(63,926)		$ 2	2,033	28	(65,989)
Ending balance (Shares) at Sep. 30, 2019			1,725,755
Beginning balance, convertible preferred stock at Dec. 31, 2018	$ 106,401	$ 106,401
Beginning balance, convertible preferred stock (Shares) at Dec. 31, 2018	12,006,791	12,006,791
Issuance of Series D convertible preferred stock, net of issuance costs of $43		$ 25,708
Issuance of Series D convertible preferred stock, net of issuance costs of $43 (Shares)		1,862,236
Ending balance, convertible preferred stock at Dec. 31, 2019	$ 132,109	$ 132,109
Ending balance, convertible preferred stock (Shares) at Dec. 31, 2019	13,869,027	13,869,027
Beginning balance at Dec. 31, 2018	$ (43,540)		$ 2	508	(4)	(44,046)
Beginning balance (Shares) at Dec. 31, 2018			1,691,129
Issuance of common stock upon exercise of stock options	$ 85			85
Issuance of common stock upon exercise of stock options (Shares)	46,259		46,259
Stock-based compensation expense	$ 2,108			2,108
Net loss	(32,202)					(32,202)
Unrealized losses on marketable securities, net of tax of $0	34				34
Ending balance at Dec. 31, 2019	(73,515)		$ 2	2,701	30	(76,248)
Ending balance (Shares) at Dec. 31, 2019			1,737,388
Beginning balance, convertible preferred stock at Jun. 30, 2019		$ 106,401
Beginning balance, convertible preferred stock (Shares) at Jun. 30, 2019		12,006,791
Ending balance, convertible preferred stock at Sep. 30, 2019		$ 106,401
Ending balance, convertible preferred stock (Shares) at Sep. 30, 2019		12,006,791
Beginning balance at Jun. 30, 2019	(56,543)		$ 2	1,521	40	(58,106)
Beginning balance (Shares) at Jun. 30, 2019			1,715,214
Issuance of common stock upon exercise of stock options	21			21
Issuance of common stock upon exercise of stock options (Shares)			10,541
Stock-based compensation expense	491			491
Net loss	(7,883)					(7,883)
Unrealized losses on marketable securities, net of tax of $0	(12)				(12)
Ending balance at Sep. 30, 2019	(63,926)		$ 2	2,033	28	(65,989)
Ending balance (Shares) at Sep. 30, 2019			1,725,755
Beginning balance, convertible preferred stock at Dec. 31, 2019	$ 132,109	$ 132,109
Beginning balance, convertible preferred stock (Shares) at Dec. 31, 2019	13,869,027	13,869,027
Issuance of Series D convertible preferred stock, net of issuance costs of $43		$ 42,248
Issuance of Series D convertible preferred stock, net of issuance costs of $43 (Shares)		3,035,192
Ending balance, convertible preferred stock at Sep. 30, 2020	$ 174,357	$ 174,357
Ending balance, convertible preferred stock (Shares) at Sep. 30, 2020	16,904,219	16,904,219
Beginning balance at Dec. 31, 2019	$ (73,515)		$ 2	2,701	30	(76,248)
Beginning balance (Shares) at Dec. 31, 2019			1,737,388
Issuance of common stock upon exercise of stock options	$ 44			44
Issuance of common stock upon exercise of stock options (Shares)	22,974		22,974
Stock-based compensation expense	$ 2,247			2,247
Net loss	(32,920)					(32,920)
Unrealized losses on marketable securities, net of tax of $0	(15)				(15)
Ending balance at Sep. 30, 2020	(104,159)		$ 2	4,992	15	(109,168)
Ending balance (Shares) at Sep. 30, 2020			1,760,362
Beginning balance, convertible preferred stock at Jun. 30, 2020		$ 174,357
Beginning balance, convertible preferred stock (Shares) at Jun. 30, 2020		16,904,219
Ending balance, convertible preferred stock at Sep. 30, 2020	$ 174,357	$ 174,357
Ending balance, convertible preferred stock (Shares) at Sep. 30, 2020	16,904,219	16,904,219
Beginning balance at Jun. 30, 2020	$ (92,566)		$ 2	4,186	63	(96,817)
Beginning balance (Shares) at Jun. 30, 2020			1,756,018
Issuance of common stock upon exercise of stock options	10			10
Issuance of common stock upon exercise of stock options (Shares)			4,344
Stock-based compensation expense	796			796
Net loss	(12,351)					(12,351)
Unrealized losses on marketable securities, net of tax of $0	(48)				(48)
Ending balance at Sep. 30, 2020	$ (104,159)		$ 2	$ 4,992	$ 15	$ (109,168)
Ending balance (Shares) at Sep. 30, 2020			1,760,362

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Unrealized gains on marketable securities, net of tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Issuance of Series D convertible preferred stock, net of issuance costs of $43			$ 43		$ 245	$ 150

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (32,920)	$ (21,943)	$ (32,202)	$ (19,250)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	1,011	1,006	1,384	1,067
Amortization of operating lease right-of-use assets	7,154	929	2,972
Stock-based compensation expense	2,247	1,461	2,108	590
Accretion of discounts on marketable securities	(9)	(866)	(970)	(460)
Loss on disposal of property and equipment		51	51
Loss on termination of operating lease	108
Changes in operating assets and liabilities:
Accounts receivable	(18)	(1,612)	(1,009)	(365)
Prepaid expenses and other current assets	(243)	(5,617)	(628)	(724)
Accounts payable	(846)	1,186	1,709	434
Accrued expenses	(1,269)	1,380	3,381	2,232
Deferred revenue	7,236	606	(4,895)	36,950
Deferred rent				(232)
Operating lease liabilities	(6,630)	(1,231)	(5,275)
Other liabilities	267	189	(117)	855
Net cash used in operating activities	(23,912)	(24,461)	(33,491)	21,097
Cash flows from investing activities:
Purchases of property and equipment	(1,054)	(1,314)	(2,168)	(1,305)
Purchases of marketable securities		(99,797)	(115,880)	(74,905)
Sales and maturities of marketable securities	51,000	95,600	105,200	39,250
Net cash provided by (used in) investing activities	49,946	(5,511)	(12,848)	(36,960)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs paid in the period	42,248		25,953	68,029
Payments of initial public offering costs	(290)
Payments of issuance costs of convertible preferred stock issued in prior period	(245)
Proceeds from exercise of stock options	44	64	85	89
Net cash provided by financing activities	41,757	64	26,038	68,118
Net increase (decrease) in cash, cash equivalents and restricted cash	67,791	(29,908)	(20,301)	52,255
Cash, cash equivalents and restricted cash at beginning of period	41,574	61,875	61,875	9,620
Cash, cash equivalents and restricted cash at end of period	109,365	31,967	41,574	61,875
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accrued expenses and accounts payable at end of period	842
Conversion of convertible promissory note and accrued interest into Series C convertible preferred stock				3,074
Accretion of redeemable convertible preferred stock to redemption value				$ 984
Lease assets obtained in exchange for operating lease liabilities	$ 17,049	$ 14,716	43,326
Issuance costs for convertible preferred stock included in accrued expenses at end of period			$ 245

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation SQZ Biotechnologies Company (the “Company”) is a clinical-stage biotechnology company developing cell therapies for patients with cancer, infectious diseases and other serious conditions. The Company uses its proprietary technology, Cell Squeeze, to physically squeeze cells through a microfluidic chip, temporarily opening the cell membrane and enabling biologic material of interest, or cargo, to diffuse into the cell. The Company is using Cell Squeeze to create multiple cell therapy platforms focused on directing specific immune responses. The Company was incorporated in March 2013 under the laws of the State of Delaware. The Company is subject to a number of risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, the ability to obtain additional financing, protection of proprietary technology, dependence on key personnel, the ability to attract and retain qualified employees, compliance with government regulations, the impact of the COVID-19 On November 3, 2020, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 4,411,765 shares of its common stock. On November 12, 2020, the Company issued and sold an additional 661,764 shares of its common stock pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate net proceeds received by the Company from the IPO were approximately $75.5 million, after deducting underwriting discounts and commissions, but before deducting offering costs payable by the Company, which are estimated to be $2.8 million. Upon the closing of the IPO, all of the shares of the Company’s convertible preferred stock then outstanding automatically converted into 17,800,084 shares of common stock (see Note 16). The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations primarily with proceeds from sales of convertible preferred stock, payments received in connection with collaboration agreements and proceeds from borrowings under a convertible promissory note, which converted into shares of convertible preferred stock, and, most recently, with proceeds from the IPO. The Company has incurred recurring losses since inception, including net losses of $32.2 million for the year ended December 31, 2019 and $32.9 million for the nine months ended September 30, 2020. As of September 30, 2020, the Company had an accumulated deficit of $109.2 million. The Company expects to continue to generate operating losses for the foreseeable future. As of December 7, 2020, the issuance date of these interim condensed consolidated financial statements, the Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of the interim consolidated financial statements. Impact of the COVID-19 In December 2019, a novel strain of coronavirus, which causes the disease known as COVID-19, COVID-19 COVID-19 The COVID-19 SQZ-PBMC-HPV COVID-19 COVID-19 The Company is monitoring the potential impact of the COVID-19 COVID-19 COVID-19, Basis of Presentation The Company’s consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, SQZ Biotechnologies Security Corporation. All intercompany accounts and transactions have been eliminated in consolidation.	1. Nature of the Business and Basis of Presentation SQZ Biotechnologies Company (the “Company”) is a clinical-stage biotechnology company developing cell therapies for patients with cancer, infectious diseases and other serious conditions. The Company uses its proprietary technology, Cell Squeeze, to physically squeeze cells through a microfluidic chip, temporarily opening the cell membrane and enabling biologic material of interest, or cargo, to diffuse into the cell. The Company is using Cell Squeeze to create multiple cell therapy platforms focused on directing specific immune responses. The Company was incorporated in March 2013 under the laws of the State of Delaware. The Company is subject to a number of risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, the ability to obtain additional financing, protection of proprietary technology, dependence on key personnel, the ability to attract and retain qualified employees, compliance with government regulations, the impact of the COVID-19 The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Through December 31, 2019, the Company has funded its operations primarily with proceeds from sales of convertible preferred stock, payments received in connection with collaboration agreements and proceeds from borrowings under a convertible promissory note, which converted into shares of convertible preferred stock. The Company has incurred recurring losses since inception, including net losses of $32.2 million for the year ended December 31, 2019. As of December 31, 2019, the Company had an accumulated deficit of $76.2 million. The Company expects to continue to generate operating losses in the foreseeable future. As of July 20, 2020, the issuance date of the annual consolidated financial statements for the year ended December 31, 2019, the Company expected that its cash, cash equivalents and marketable securities, including the $42.3 million of gross proceeds it received in January, February, May and June 2020 from the sale of Series D convertible preferred stock (see Notes 8 and 18), would be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of the annual consolidated financial statements. The Company is seeking to complete an initial public offering (“IPO”) of its common stock. Upon the completion of a qualified public offering on specified terms, the Company’s outstanding convertible preferred stock will automatically convert into shares of common stock (see Note 8). In the event the Company does not complete an IPO, the Company expects to seek additional funding through private equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company would be forced to delay, scale back or discontinue some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Impact of the COVID-19 In December 2019, a novel strain of coronavirus, which causes the disease known as COVID-19, COVID-19 COVID-19 The COVID-19 SQZ-PBMC-HPV COVID-19 COVID-19 The Company is monitoring the potential impact of the COVID-19 COVID-19 COVID-19, Basis of Presentation The Company’s consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, SQZ Biotechnologies Security Corporation. All intercompany accounts and transactions have been eliminated in consolidation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The accompanying consolidated balance sheet as of December 31, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2020 and for the three and nine months ended September 30, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2019 included in the Company’s final prospectus for the IPO filed pursuant to Rule 424(b)(4) under the Securities Act, with the SEC, on October 30, 2020. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2020 and consolidated results of operations for the three and nine months ended September 30, 2020 and 2019 and the consolidated cash flows for the nine months ended September 30, 2020 and 2019, have been made. The Company’s consolidated results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, the valuation of common stock and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. Recently Adopted Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”). non-employees 2018-07 2018-07 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) right-of-use No. 2018-11, Leases (Topic 842) Upon its adoption of ASC 842, the Company recognized right-of-use right-of-use Upon its adoption of ASC 842, the Company elected to apply the package of practical expedients permitted under the transition guidance to its entire lease portfolio as of January 1, 2019. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) whether the initial direct costs for any existing leases met the new definition of initial direct costs at the initial application date. In addition, the Company elected not to recognize a right-of-use The Company’s future commitments under lease obligations and additional disclosures are summarized in Note 11. Recently Issued Accounting Pronouncements The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement Topic 820 Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”), 2018-13 No. 2018-13 2018-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses Topic 326 Measurement of Credit Losses on Financial Instruments 2016-13”), 2016-13 available-for-sale No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief 2019-05”) , 2016-13. 2016-13 2019-05 In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 2018-18”). 2018-18 unit-of-account Collaborative Arrangements 2018-18 In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) 2019-12”), 2019-12. 2019-12	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, the valuation of common stock and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of accounts receivable and cash and cash equivalents. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. As of December 31, 2019, all of the Company’s accounts receivable were related to its collaboration agreements with Roche (see Note 14). The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and to process its product candidates for its development programs. These programs could be adversely affected by a significant interruption in the manufacturing process or supply chain. Cash Equivalents The Company considers all highly liquid investments in marketable securities with original maturities of three months or fewer at the date of purchase to be cash equivalents. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process paid-in in-process Accounts Receivable Allowance Accounts receivable are presented net of an allowance for doubtful accounts, which is an estimate of amounts that may not be collectible. The Company performs ongoing evaluations of its accounts receivable and, if necessary, provides an allowance for doubtful accounts and expected losses. The Company writes off accounts receivable against the allowance when it determines a balance is uncollectible and no longer actively pursues collection of the receivable. As of December 31, 2018 and 2019, the Company had no allowance for doubtful accounts. During the years ended December 31, 2018 and 2019, the Company did not record any provisions for doubtful accounts and did not write off any accounts receivable balances. Restricted Cash As of December 31, 2018 and 2019, the Company maintained letters of credit totaling $2.3 million for the benefit of the landlords of its leased properties. The Company was required to maintain separate cash balances of $2.3 million to secure the letters of credit. The Company classified these separate cash balances of $2.3 million as restricted cash (non-current) Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: ESTIMATED USEFUL LIFE Machinery and equipment 3 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of term of lease or 7 years Costs for capital assets not yet placed into service are capitalized as construction-in-progress Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. The Company continually evaluates long-lived assets for potential impairment whenever events or changes in circumstances indicate that the carrying value of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares the carrying values of the asset group to the expected future undiscounted cash flows that the asset group is expected to generate from the use and eventual disposition of the long-lived asset group. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. If such asset group is considered to be impaired, the impairment loss to be recognized would be based on the excess of the carrying value of the impaired asset group over its fair value. The Company did not recognize any impairment losses on long-lived assets during the years ended December 31, 2018 or 2019. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ∎ Level 1—Quoted prices in active markets for identical assets or liabilities. ∎ Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ∎ Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The fair value of the Company’s cash equivalents and marketable securities are determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts receivable, unbilled receivables, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities. Marketable Securities The Company’s marketable debt securities are classified as available-for-sale The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Leases Prior to January 1, 2019, the Company accounted for leases under Accounting Standards Codification (“ASC”) 840, Leases The Company adopted ASC 842, Leases , The Company has operating leases for office space as well as a contract for manufacturing under which the Company has a dedicated suite. The Company may enter into similar arrangements in the future. Under ASC 842, the Company determines whether such arrangements contain a lease at the inception of a contract by assessing whether there is an identified asset and whether a contract conveys the right to control the use of the identified asset in exchange for consideration and the right to obtain the economic benefits from the use of the identified asset. Upon commencement of an identified lease, the Company records a right-of-use Right-of-use After lease commencement and the establishment of a right-of-use As permitted by ASC 842, leases with an initial term of 12 months or fewer are not recorded in the consolidated balance sheets. The Company often enters into contracts that contain both lease and non-lease Non-lease non-lease right-of-use The Company’s lease terms often include renewal options. The amounts determined for the Company’s right-of-use Classification and Accretion of Convertible Preferred Stock The Company’s Series Seed, Series A, Series B, Series C and Series D convertible preferred stock are classified outside of stockholders’ equity (deficit) because the holders of such shares have liquidation rights in the event of a deemed liquidation that, in certain situations, is not solely within the control of the Company. Until May 2018, the carrying values of the Company’s Series A and Series B redeemable convertible preferred stock were being accreted to its redemption value from the date of issuance of such shares through the earliest required redemption date. However, in connection with the issuance of Series C convertible preferred stock in May 2018, the holders of Series A and Series B convertible preferred stock agreed to remove the redemption rights of the Series A and Series B redeemable convertible preferred stock, including rights to specified accruing interest (see Note 8), and as a result, the Company ceased recording adjustments to the carrying value of its outstanding convertible preferred stock for accretion to redemption value. Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is developing methods of engineering cell function and therapies for the treatment of patients across a range of indications. The Company has determined that its chief operating decision maker is its Chief Executive Officer. The Company’s chief operating decision maker reviews the Company’s financial information on a consolidated basis for purposes of allocating resources and assessing financial performance. All of the Company’s tangible assets are held in the United States, and all of the Company’s collaboration revenue is derived from its collaboration partner headquartered in Switzerland. Revenue Recognition for License and Collaboration Arrangements Effective January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract, determines which goods or services are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, that performance obligation is satisfied. The Company enters into licensing arrangements that are within the scope of ASC 606, under which it may exclusively license to third parties rights to research, develop, manufacture and commercialize its product candidates. The terms of these arrangements typically include payment to the Company of one or more of the following: nonrefundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and sales milestone payments; and royalties on net sales of licensed products. The payment terms under the Company’s existing licensing arrangements are 60 days. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its arrangements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the assessment of the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: (a) the performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above; and (c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company also uses judgment to determine whether milestone payments or other variable consideration, except for royalties and sales-based milestones, should be included in the transaction price, as described below. The transaction price is allocated to each performance obligation based on the relative standalone selling price of each performance obligation in the contract, and the Company recognizes revenue based on those amounts when, or as, the performance obligations under the contract are satisfied. The standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the standalone selling price of each of the identified performance obligations in the Company’s customer contracts, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis and there are no similar observable transactions in the marketplace, the Company estimates the standalone selling price of each performance obligation in its customer arrangements based on its estimate of costs to be incurred to fulfil its obligations associated with the performance, plus a reasonable margin. The Company has determined that its only contract liability under ASC 606 is deferred revenue. Amounts received prior to revenue recognition are recorded as deferred revenue in the consolidated balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion, in the consolidated balance sheets. Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from nonrefundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining promises, whether the value of the promise is dependent on the unsatisfied promises, whether there are other vendors that could provide the remaining promises, and whether it is separately identifiable from the remaining promises. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition. The measure of progress, and the resulting periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research, development and licensing arrangement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Under the Company’s existing license and collaboration agreements, the Company has concluded that the transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost Research and Development Services The promises under the Company’s license and collaboration arrangements often include research and development services to be performed by the Company on behalf of the partner. Payments or reimbursements resulting from the Company’s research and development efforts are estimated at the outset of the arrangement and considered part of the transaction price that is subsequently recognized as revenue because the Company is the principal in the arrangement for such efforts. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the Company evaluates the customer options to determine if they are material rights at the outset of each arrangement. Options to acquire additional goods or services for free or at a discount are deemed to be material rights. If the goods and services underlying the customer options are not determined to be material rights, these customer options are not considered to be performance obligations in the arrangement because they are contingent upon exercise of the option. If the customer options are determined to be a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. Milestone Payments At the inception of each arrangement that includes potential research, development or regulatory milestone payments, the Company evaluates whether the milestones are considered likely to be met and estimates the amount to be considered for inclusion in the transaction price using the most-likely-amount method. If it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur, the associated milestone payment value is included in the transaction price. For milestone payments due upon events that are not within the control of the Company or the licensee, such as regulatory approvals, the Company is not able to assert that it is likely that the regulatory approval will be granted and that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur until those approvals are received. In making this assessment, the Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the particular milestone. There is considerable judgment involved in determining whether it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price of the arrangement. Any such adjustments are recorded on a cumulative catch-up Royalties For arrangements that include sales-based royalties, including milestone payments due upon first commercial sales or based on a level of sales, that are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) the occurrence of the related sales or (ii) the date upon which the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue from any of its licensing arrangements. Revenue Recognition for Government Grants The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. Revenue from government grants is recognized as the qualifying expenses related to the contracts are incurred, provided that there is reasonable assurance of recoverability. The Company submits a budget, which outlines the expected project costs, to the funding government agency on a periodic basis. If the government agency approves the project proposed by the Company, the government agency funds the project upon receipt of the support for the costs incurred. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded as unbilled receivables, a component of prepaid expenses and other current assets, in the consolidated balance sheet. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and bonuses, stock-based compensation, employee benefits, facilities costs, laboratory supplies, depreciation, manufacturing expenses and external costs of vendors engaged to conduct preclinical development activities and clinical trials, as well as the costs of licensing technology and costs related to collaboration arrangements. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed in the period in which they are incurred. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed, or when it is no longer expected that the goods will be delivered or the services rendered. Research and Manufacturing Contract Costs and Accruals The Company has entered into various research, development and manufacturing contracts with research institutions and other companies in the United States. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research, development and manufacturing costs. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of period end. Any accrual estimates are based on a number of factors, including the Company’s knowledge of the progress towards completion of the research, development and manufacturing activities, invoicing to date under the contracts, communication from the research institutions and other companies of any actual costs incurred during the period that have not yet been invoiced and the costs included in the contracts. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. Stock-Based Compensation For stock-based awards granted to employees and directors, the Company estimates the grant-date fair value of each award using the Black-Scholes option-pricing model. Compensation expense for these awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. Following the Company’s adoption of ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”), non-employees, non-employee The Company accounts for forfeitures of stock-based awards as they occur rather than applying an estimated forfeiture rate to stock-based compensation expense. The Company classifies stock-based compensation expense in the consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2018 and 2019, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities. Net Income (Loss) per Share The Company follows the two-class two-class two-class Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents. The Company’s convertible preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders for each of the years ended December 31, 2018 and 2019. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step Recently Adopted Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”). non-employees 2018-07 2018-07 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) 2016-02”), right-of-use No. 2018-11, Leases (Topic 842) Upon its adoption of ASC 842, the Company recognized right-of-use right-of-use Upon its adoption of ASC 842, the Company elected to apply the package of practical expedients permitted under the transition guidance to its entire lease portfolio as of January 1, 2019. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) whether the initial direct costs for any existing leases met the new definition of initial direct costs at the initial application date. In addition, the Company elected not to recognize a right-of-use The Company’s future commitments under lease obligations and additional disclosures are summarized in Note 13. Recently Issued Accounting Pronouncements The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	3. Marketable Securities and Fair Value Measurements Marketable securities by security type consisted of the following (in thousands): SEPTEMBER 30, 2020 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 8,006 $ 15 $ — $ 8,021 $ 8,006 $ 15 $ — $ 8,021 DECEMBER 31, 2019 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 44,028 $ 24 $ — $ 44,052 U.S. Treasury bills 14,969 6 — 14,975 $ 58,997 $ 30 $ — $ 59,027 The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AT SEPTEMBER 30, 2020 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 106,997 $ — $ — $ 106,997 Marketable securities: U.S. government agency bonds — 8,021 — 8,021 $ 106,997 $ 8,021 $ — $ 115,018 FAIR VALUE MEASUREMENTS AT LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 37,071 $ — $ — $ 37,071 Marketable securities: U.S. government agency bonds — 44,052 — 44,052 U.S. Treasury bills — 14,975 — 14,975 $ 37,071 $ 59,027 $ — $ 96,098 Money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. U.S. government agency bonds and U.S. Treasury bills were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. There were no changes to the valuation methods during the three and nine months ended September 30, 2020 and 2019. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1 or Level 2 during the three and nine months ended September 30, 2020 and 2019.	Marketable securities by security type consisted of the following (in thousands): DECEMBER 31, 2018 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 13,986 $ — $ (1 ) $ 13,985 U.S. Treasury bills 33,361 — (3 ) 33,358 $ 47,347 $ — $ (4 ) $ 47,343 DECEMBER 31, 2019 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 44,028 $ 24 $ — $ 44,052 U.S. Treasury bills 14,969 6 — 14,975 $ 58,997 $ 30 $ — $ 59,027 The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2018 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 56,771 $ — $ — $ 56,771 U.S. Treasury bills — 2,799 — 2,799 Marketable securities: U.S. government agency bonds — 13,985 — 13,985 U.S. Treasury bills — 33,358 — 33,358 $ 56,771 $ 50,142 $ — $ 106,913 FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2019 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 37,071 $ — $ — $ 37,071 Marketable securities: U.S. government agency bonds — 44,052 — 44,052 U.S. Treasury bills — 14,975 — 14,975 $ 37,071 $ 59,027 $ — $ 96,098 Money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. U.S. government agency bonds and U.S. Treasury bills were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. There were no changes to the valuation methods during the years ended December 31, 2018 and 2019. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1 or Level 2 during the years ended December 31, 2018 and 2019.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid Expenses and Other Current Assets	4. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid expenses $ 1,844 $ 1,452 Interest receivable 61 206 Unbilled receivables — 4 $ 1,905 $ 1,662	4. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): DECEMBER 31, 2018 2019 Prepaid expenses $ 648 $ 1,452 Unbilled receivables 304 4 Interest receivable 83 206 $ 1,035 $ 1,662

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Machinery and equipment $ 6,037 $ 5,655 Leasehold improvements 436 2,650 Furniture and fixtures 579 353 7,052 8,658 Less: Accumulated depreciation and amortization (3,202 ) (3,495 ) $ 3,850 $ 5,163 Depreciation and amortization expense was $0.3 million and $0.4 million for the three months ended September 30, 2020 and 2019, respectively. Depreciation and amortization expense was $1.0 million for each of the nine months ended September 30, 2020 and 2019. In February 2020, as a result of the termination of the 2016 Lease (see Note 11), the Company removed from the consolidated balance sheet leasehold improvements with a cost of $2.7 million and accumulated depreciation related to those leasehold improvements of $1.3 million. The resulting $1.4 million loss was recognized as a component of the $0.1 million net loss recognized by the Company upon termination of the 2016 Lease (see Note 11).	5. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): DECEMBER 31, 2018 2019 Machinery and equipment $ 3,748 $ 5,655 Leasehold improvements 2,650 2,650 Furniture and fixtures 234 353 Construction-in-progress 22 — 6,654 8,658 Less: Accumulated depreciation and amortization (2,225 ) (3,495 ) $ 4,429 $ 5,163 Depreciation and amortization expense was $1.1 million and $1.4 million for the years ended December 31, 2018 and 2019, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, 2020 2019 Accrued external research, development and manufacturing costs $ 2,696 $ 3,220 Accrued employee compensation and benefits 1,880 1,878 Accrued licensing fees (Note 11) 777 697 Other 526 1,266 $ 5,879 $ 7,061	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): DECEMBER 31, 2018 2019 Accrued external research, development and manufacturing costs $ 673 $ 3,220 Accrued employee compensation and benefits 1,367 1,878 Accrued licensing fees (Note 12) 1,168 697 Current portion of deferred rent 303 — Other 228 1,266 $ 3,739 $ 7,061

Debt

Debt	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt	7. Debt As of December 31, 2018 and 2019, the Company had no debt outstanding. Loan and Security Agreement In October 2015, the Company entered into a loan and security agreement with a commercial bank, which provided for term loan borrowings of up to $1.0 million through June 2016. In connection with the agreement, the Company issued to the lender a warrant to purchase up to 7,114 shares of common stock at an exercise price of $2.11 per share. The warrant became exercisable as to 2,038 shares of common stock in connection with the Company’s borrowing of amounts under the agreement and expires on October 20, 2025. This warrant to purchase 2,038 shares of common stock remained outstanding as of December 31, 2018 and 2019. In July 2016, the Company entered into an amendment to the loan and security agreement with the commercial bank (the “amended agreement”), which amended and restated all terms of the prior loan and security agreement, except for the original warrant agreement. The amended agreement provided for term loan borrowings of up to $2.0 million under one or more term loans as well as additional borrowings of up to $3.0 million under one or more additional term loans, for aggregate maximum borrowings of $5.0 million through December 2017. In January 2018, the Company entered into a second amendment to the loan and security agreement with the commercial bank (the “second amended agreement”) in order to extend the draw periods and make certain other revisions. The second amended agreement extended the draw periods to June 30, 2018. The Company did not borrow any amounts under the second amended agreement, and the second amended agreement expired on June 30, 2018. In connection with the amended agreement, in July 2016, the Company issued to the lender a warrant to purchase up to 23,692 shares of common stock at an exercise price of $4.28 per share. This warrant would have become exercisable in proportion to and upon the Company’s borrowing of amounts under the amended agreement or the second amended agreement. However, this warrant never became exercisable as no amounts were borrowed by the Company under these agreements. Convertible Promissory Note In November 2017, the Company issued a convertible note (the “Note”) to a third party with an aggregate principal amount of $3.0 million. The Note bore interest at a rate of 6.0% per annum and was due and payable upon demand by the holder on or after the maturity date of February 28, 2019. In the event of a qualified sale of the Company’s preferred stock resulting in gross proceeds to the Company of at least $30.0 million, all principal and accrued interest under the Note would automatically convert into shares of the Company’s preferred stock issued in such financing. The Company assessed the embedded conversion and other features of the Note and concluded that any features that may have required bifurcation had an immaterial value, and, therefore, were not separately recognized. In May 2018, in connection with the Company’s issuance and sale of Series C convertible preferred stock (the “Series C Preferred Stock”), all outstanding principal of $3.0 million and accrued interest of $0.1 million under the Note was converted into 259,328 shares of Series C Preferred Stock at the same price paid by investors in the Series C financing (see Note 8).

Preferred Stock

Preferred Stock	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity [Abstract]
Preferred Stock	7. Preferred Stock The Company has issued Series Seed convertible preferred stock (the “Series Seed Preferred Stock”), Series A convertible preferred stock (the “Series A Preferred Stock”), Series B convertible preferred stock (the “Series B Preferred Stock”), Series C Preferred Stock and Series D convertible preferred stock (the “Series D Preferred Stock”), all of which are collectively referred to as the “Preferred Stock.” In March 2014, the Company issued and sold 350,858 shares of Series Seed Preferred Stock at a price of $2.85 per share for gross proceeds of $1.0 million. In June and July 2015, the Company issued and sold an aggregate of 1,490,035 shares of Series A Preferred Stock at a price of $3.41 per share for gross proceeds of $5.1 million. In September and November 2016, the Company issued and sold 4,155,758 shares of Series B Preferred Stock at a price of $5.79 per share for gross proceeds of $24.1 million. In May 2018, the Company issued and sold 4,354,122 shares of Series C Preferred Stock, consisting of (i) 4,094,794 shares sold at a price of $11.8555 per share for gross proceeds of $48.6 million and (ii) 259,328 shares issued upon the conversion of $3.1 million of principal and accrued interest on a convertible promissory note. From May through October 2018, the Company issued and sold an additional 1,656,018 shares of Series C Preferred Stock at a price of $11.8555 per share for gross proceeds of $19.6 million. The Company incurred issuance costs in connection with the Series C Preferred Stock of $0.2 million. In December 2019, the Company issued and sold 1,862,236 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $26.0 million. The Company incurred issuance costs in connection with this Series D Preferred Stock of $0.2 million. In January and February 2020, the Company issued and sold an aggregate of 1,094,247 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $15.2 million. In May and June 2020, the Company issued and sold an aggregate of 1,940,945 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $27.0 million. The Company incurred issuance costs in connection with these 2020 issuances of Series D Preferred Stock of less than $0.1 million. Upon issuance of each class of Preferred Stock, the Company assessed the embedded conversion and liquidation features of the shares and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance dates of each class of Preferred Stock. As of September 30, 2020 and December 31, 2019, Preferred Stock consisted of the following (in thousands, except share amounts): SEPTEMBER 30, 2020 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 5,037,348 4,897,428 67,956 68,253 5,156,975 17,044,139 16,904,219 $ 174,357 $ 169,648 17,800,084 DECEMBER 31, 2019 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 4,664,011 1,862,236 25,708 25,953 1,960,934 16,670,802 13,869,027 $ 132,109 $ 127,348 14,604,043 Upon the closing of the IPO in November 2020, all of the shares of the Company’s convertible preferred stock then outstanding automatically converted into 17,800,084 shares of common stock (see Note 16).	8. Preferred Stock The Company has issued Series Seed convertible preferred stock (the “Series Seed Preferred Stock”), Series A convertible preferred stock (the “Series A Preferred Stock”), Series B convertible preferred stock (the “Series B Preferred Stock”), Series C Preferred Stock and Series D convertible preferred stock (the “Series D Preferred Stock”), all of which are collectively referred to as the “Preferred Stock.” The Series A and Series B Preferred Stock had been redeemable at the option of the holder after five years from the issuance date of the Series B Preferred Stock. However, in connection with the issuance and sale of Series C Preferred Stock in May 2018, the holders of Series A and Series B Preferred Stock agreed to remove the redemption rights of the Series A and Series B Preferred Stock, including rights to specified accruing interest. The Company determined that the change to the terms of the Series A and Series B Preferred Stock should be accounted for as a modification, rather than an extinguishment, of the Series A and Series B Preferred Stock based on a comparison of the fair value of the stock immediately before and after the change in terms, which resulted in a fair value change of less than 10%. This modification did not have any impact on the Company’s consolidated financial statements because the Company concluded that the modification reflected a transfer of value from the existing preferred stockholders to the new preferred stockholders and did not constitute a transfer of value between the preferred stockholders and common stockholders. For periods after the May 2018 modification date of the Series A and Series B Preferred Stock, the Company no longer accretes the carrying value of the Series A and Series B Preferred Stock to redemption value as such shares are no longer mandatorily redeemable. In March 2014, the Company issued and sold 350,858 shares of Series Seed Preferred Stock at a price of $2.85 per share for gross proceeds of $1.0 million. In June and July 2015, the Company issued and sold an aggregate of 1,490,035 shares of Series A Preferred Stock at a price of $3.41 per share for gross proceeds of $5.1 million. In September and November 2016, the Company issued and sold 4,155,758 shares of Series B Preferred Stock at a price of $5.79 per share for gross proceeds of $24.1 million. In May 2018, the Company issued and sold 4,354,122 shares of Series C Preferred Stock, consisting of (i) 4,094,794 shares sold at a price of $11.8555 per share for gross proceeds of $48.6 million and (ii) 259,328 shares issued upon the conversion of $3.1 million of principal and accrued interest on a convertible promissory note (see Note 7). From May through October 2018, the Company issued and sold an additional 1,656,018 shares of Series C Preferred Stock at a price of $11.8555 per share for gross proceeds of $19.6 million. The Company incurred issuance costs in connection with the Series C Preferred Stock of $0.2 million. In December 2019, the Company issued and sold 1,862,236 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $26.0 million. The Company incurred issuance costs in connection with this Series D Preferred Stock of $0.2 million. In January and February 2020, the Company issued and sold an aggregate of 1,094,247 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $15.2 million. In May and June 2020, the Company issued and sold an aggregate of 1,940,945 shares of Series D Preferred Stock at a price of $13.9365 per share for gross proceeds of $27.0 million (see Note 18). The Company incurred issuance costs in connection with these 2020 issuances of Series D Preferred Stock of less than $0.1 million (see Note 18). Upon issuance of each class of Preferred Stock, the Company assessed the embedded conversion and liquidation features of the shares and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance dates of each class of Preferred Stock. As of December 31, 2018 and 2019, Preferred Stock consisted of the following (in thousands, except share amounts): DECEMBER 31, 2018 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,061,300 6,010,140 71,103 71,253 6,328,657 12,057,951 12,006,791 $ 106,401 $ 101,395 12,643,109 DECEMBER 31, 2019 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 4,664,011 1,862,236 25,708 25,953 1,960,934 16,670,802 13,869,027 $ 132,109 $ 127,348 14,604,043 The holders of Preferred Stock have various rights and preferences as follows: Voting The holders of the Preferred Stock are entitled to vote, together with the holders of common stock as a single class, on matters submitted to stockholders for a vote. The holders of Preferred Stock are entitled to the number of votes equal to the number of shares of common stock into which each share of Preferred Stock is convertible as of the record date for determining stockholders entitled to vote on such matters. The holders of Preferred Stock, voting exclusively and as a separate class, are entitled to elect three directors of the Company, and the holders of Preferred Stock, voting together with the holders of common stock as a single class, are entitled to elect three directors of the Company. Conversion Each share of Preferred Stock is convertible into shares of common stock at the option of the holder at any time after the date of issuance. Each share of Preferred Stock will be automatically converted into shares of common stock, at the applicable conversion ratio then in effect, upon either (i) the closing of a firm commitment public offering with at least $50.0 million of gross proceeds to the Company or (ii) the vote or written consent of the holders of at least a majority of the Preferred Stock, voting together as a single class. The conversion ratio of each series of Preferred Stock is determined by dividing the Original Issue Price of each series by the Conversion Price of each series. The Original Issue Price per share is $2.85 for Series Seed Preferred Stock, $3.41 for Series A Preferred Stock, $5.79 for Series B Preferred Stock, $11.8555 for Series C Preferred Stock and $13.9365 for Series D Preferred Stock. The Conversion Price per share is $2.7066 for Series Seed Preferred Stock, $3.2384 for Series A Preferred Stock, $5.4986 for Series B Preferred Stock, $11.2588 for Series C Preferred Stock and $13.2351 for Series D Preferred Stock, each subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization and other adjustments as set forth in the Company’s certificate of incorporation, as amended and restated. Dividends The holders of shares of Series A, Series B, Series C and Series D Preferred Stock are entitled to receive, when, as and if declared by the Company’s board of directors, noncumulative dividends at a rate of 6.0% per annum of the respective Original Issue Price on each outstanding share of that series of Preferred Stock. The Company shall not declare, pay or set aside any dividends on shares of any other class or series of stock of the Company unless the holders of the Preferred Stock then outstanding shall first receive, or simultaneously receive, a dividend on each outstanding share of Preferred Stock in an amount at least equal to the greater of: (i) for the Series A, Series B, Series C and Series D Preferred Stock, the amount of the aggregate preferred dividends then accrued on such shares and not previously paid and (ii) (A) in the case of a dividend on common stock or any class or series of stock that is convertible into common stock, a dividend per share of Preferred Stock that would equal the product of (1) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common stock and (2) the number of shares of common stock issuable upon conversion of a share of Preferred Stock; or (B) in the case of a dividend on any class or series of stock that is not convertible into common stock, at a rate per share of Preferred Stock determined by (1) dividing the amount of the dividend payable on each share of such class or series of stock by the Original Issue Price of such class or series of stock (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to such class or series) and (2) multiplying such fraction by an amount equal to the Original Issue Price of such class or series. If the Company declares, pays or sets aside, on the same date, a dividend on shares of more than one class or series of stock of the Company, the dividend payable to the holders of the Preferred Stock shall be calculated based upon the dividend on the class or series of stock that would result in the highest Preferred Stock dividend. Through December 31, 2019, no dividends had been declared on any series or class of shares. Liquidation In the event of any voluntary or involuntary liquidation, dissolution or winding-up winding-up Unless the holders of at least a majority of the Preferred Stock, voting together as a single class, elect otherwise, a Deemed Liquidation Event shall include a merger or consolidation (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation) or a sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Common Stock	9. Common Stock Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors. The holders of common stock, voting exclusively and as a separate class, are entitled to elect three directors of the Company.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation The Company’s 2014 Stock Incentive Plan (the “2014 Plan”) provides for the Company to grant incentive stock options, non-qualified The total number of shares of common stock that may be issued under the 2014 Plan was 4,853,361 shares as of September 30, 2020 and December 31, 2019. As of September 30, 2020 and December 31, 2019, 714,737 shares and 1,342,523 shares, respectively, remained available for future issuance under the 2014 Plan. Stock Option Valuation The fair value of each option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer public companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the option. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Fair value of common stock $ 10.36 $ 6.14 $ 9.07 $ 5.77 Expected term (years) 6.0 6.0 6.0 6.0 Expected volatility 76.7 % 69.5 % 75.2 % 69.1 % Risk-free interest rate 0.37 % 1.89 % 0.66 % 2.40 % Expected annual dividend yield 0 % 0 % 0 % 0 % The following table summarizes the Company’s stock option activity since December 31, 2019: NUMBER OF WEIGHTED- WEIGHTED- INTRINSIC (in years) (in thousands) Outstanding at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Granted 1,157,893 9.08 Exercised (22,974 ) 1.93 Forfeited or canceled (530,117 ) 4.62 Outstanding at September 30, 2020 3,744,451 $ 5.67 7.88 $ 20,620 Vested and expected to vest at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Vested and expected to vest at September 30, 2020 3,744,451 $ 5.67 7.88 $ 20,620 Options exercisable at December 31, 2019 870,219 $ 2.94 7.68 $ 4,235 Options exercisable at September 30, 2020 1,486,775 $ 3.69 6.08 $ 11,132 The weighted-average grant-date fair value of stock options granted during the three months ended September 30, 2020 and 2019 was $6.82 per share and $4.20 per share, respectively. The weighted-average grant-date fair value of stock options granted during the nine months ended September 30, 2020 and 2019 was $5.92 per share and $3.89 per share, respectively. Stock-Based Compensation Expense Stock-based compensation expense related to stock options and restricted stock awards was classified in the consolidated statements of operations as follows (in thousands): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Research and development expenses $ 296 $ 174 $ 811 $ 525 General and administrative expenses 500 317 1,436 936 $ 796 $ 491 $ 2,247 $ 1,461 As of September 30, 2020, total unrecognized stock-based compensation expense related to unvested stock-based awards was $10.6 million, which is expected to be recognized over a weighted-average period of 2.9 years.	10. Stock-Based Compensation The Company’s 2014 Stock Incentive Plan (the “2014 Plan”) provides for the Company to grant incentive stock options, non-qualified The total number of shares of common stock that may be issued under the 2014 Plan was 4,853,361 shares as of December 31, 2019. As of December 31, 2019, 1,342,523 shares remained available for future issuance under the 2014 Plan. The 2014 Plan is administered by the Company’s board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The board of directors, or its committee if so delegated, determines the types of stock awards to be granted, the provisions of each stock award, including the number of shares, exercise prices and vesting and other conditions and the fair market value of the common stock underlying stock-based awards. The exercise price per share for stock options granted may not be less than the fair market value of the common stock at the date of the grant. In the case of a more than 10% stockholder, an incentive stock option granted must have an exercise price of not less than 110% of the fair market value of the common stock and a term of not more than five years from the date of grant. In general, stock options expire ten years after the date of grant, unless the board of directors sets a shorter term. Stock options and restricted stock awards granted to employees and directors typically vest over a period of four years. Shares that are expired, terminated, surrendered or canceled under the 2014 Plan without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available under the 2014 Plan for the grant of awards. Stock Option Valuation The fair value of each option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer public companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the option. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted: YEAR ENDED 2018 2019 Fair value of common stock $ 4.65 $ 6.49 Expected term (years) 6.0 6.0 Expected volatility 66.5 % 69.3 % Risk-free interest rate 3.00 % 2.15 % Expected annual dividend yield 0 % 0 % The following table summarizes the Company’s stock option activity since December 31, 2018: NUMBER OF WEIGHTED- WEIGHTED- INTRINSIC (in years) (in thousands) Outstanding at December 31, 2018 2,013,769 $ 3.42 9.00 $ 3,595 Granted 1,340,467 5.14 Exercised (46,259 ) 1.84 Forfeited or canceled (168,328 ) 3.09 Outstanding at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Vested and expected to vest at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Options exercisable at December 31, 2019 870,219 $ 2.94 7.68 $ 4,235 The weighted-average grant-date fair value of stock options granted during the years ended December 31, 2018 and 2019 was $2.54 per share and $4.37 per share, respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2018 and 2019 was $0.1 million and $0.3 million, respectively. Restricted Common Stock The Company has entered into restricted stock agreements with certain employees, directors and consultants. Each restricted stock agreement contains restrictions on the sale or transfer of the shares of common stock. The following table summarizes the Company’s restricted stock award activity since December 31, 2018: NUMBER WEIGHTED- GRANT-DATE Unvested at December 31, 2018 25,880 $ 1.16 Vested (25,880 ) 1.16 Unvested at December 31, 2019 — $ — The aggregate intrinsic value of restricted stock awards that vested during the years ended December 31, 2018 and 2019 was $0.4 million and $0.2 million, respectively. The aggregate intrinsic value of restricted stock awards is calculated as the positive difference between the prices paid, if any, of the restricted stock awards and the fair value of the Company’s common stock. Stock-Based Compensation Expense Stock-based compensation expense related to stock options and restricted stock awards was classified in the consolidated statements of operations as follows (in thousands): YEAR ENDED 2018 2019 Research and development expenses $ 112 $ 718 General and administrative expenses 478 1,390 $ 590 $ 2,108 As of December 31, 2019, total unrecognized stock-based compensation expense related to unvested stock-based awards was $7.7 million, which is expected to be recognized over a weighted-average period of 3.0 years.

Income Taxes

Income Taxes	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes For the three and nine months ended September 30, 2020 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each period, due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States.	11. Income Taxes For the years ended December 31, 2018 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each period, due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States. A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: YEAR ENDED 2018 2019 Federal statutory income tax rate (21.0 )% (21.0 )% State income taxes, net of federal benefit (6.4 ) (6.4 ) Federal and state research and development tax credits (9.9 ) (8.0 ) Other 0.4 0.3 Change in deferred tax asset valuation allowance 36.9 35.1 Effective income tax rate 0.0 % 0.0 % The Company’s net deferred tax assets consisted of the following (in thousands): DECEMBER 31, 2018 2019 Deferred tax assets: Net operating loss carryforwards $ 9,598 $ 9,082 Research and development tax credit carryforwards 3,763 6,368 Deferred revenue 526 9,895 Deferred expenses 433 — Operating lease liabilities — 11,590 Stock-based compensation and other accrued expenses 180 603 Other 92 286 Total deferred tax assets 14,592 37,824 Deferred tax liabilities: Depreciation (541 ) (703 ) Operating lease right-of-use — (11,785 ) Total deferred tax liabilities (541 ) (12,488 ) Valuation allowance (14,051 ) (25,336 ) Net deferred tax assets $ — $ — As of December 31, 2019, the Company had U.S. federal net operating loss (“NOL”) carryforwards of $33.3 million, which may be available to offset future taxable income, of which $11.7 million begin to expire in 2035 and of which $21.6 million do not expire but are (for taxable years beginning after December 31, 2020) generally limited in their usage to an annual deduction equal to 80% of annual taxable income. In addition, as of December 31, 2019, the Company had state net operating loss carryforwards of $33.1 million, which may be available to offset future taxable income and begin to expire in 2035. As of December 31, 2019, the Company also had U.S. federal and state research and development tax credit carryforwards of $4.4 million and $2.5 million, respectively, each of which begin to expire in 2034. Utilization of the U.S. federal and state NOL carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and research and development tax credit carryforwards that can be utilized annually to offset future taxable income or tax liabilities. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. If a change in control has occurred at any time since the Company’s formation, utilization of its NOLs or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2018 and 2019. Management reevaluates the positive and negative evidence at each reporting period. For the years ended December 31, 2018 and 2019, the valuation allowance increased primarily due to increases in NOL carryforwards and research and development tax credit carryforwards as well as the increase in deferred revenue in 2019, and was as follows (in thousands): YEAR ENDED 2018 2019 Valuation allowance at beginning of year $ (6,953 ) $ (14,051 ) Increases recorded to income tax provision (7,098 ) (11,285 ) Valuation allowance at end of year $ (14,051 ) $ (25,336 ) On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was signed into United States law. The Tax Act made broad and complex changes to the Internal Revenue Code of 1986, which include, but are not limited to, (i) the reduction in the federal corporate income tax rate from a top marginal tax rate of 35% to a flat rate of 21%, effective as of January 1, 2018; (ii) the limitation of the deduction for net operating losses to 80% of annual taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2017 (though any such net operating losses may be carried forward indefinitely); and (iii) the limitation of the deduction of certain executive compensation amounts. On March 27, 2020, the Coronavirus Aid, Relief and Economic Security (“CARES”) Act was passed by the U.S. Congress and signed into United States law. The CARES Act, among other things, includes certain provisions for individuals and corporations (including a suspension on the application of the 80% limitation described above for taxable years beginning prior to January 1, 2021); however, these benefits did not impact the Company’s income tax provision in the periods presented. As of December 31, 2018 and 2019, the Company had not recorded any amounts for unrecognized tax benefits. Interest and penalties related to income taxes are recorded as a component of the income tax provision in the consolidated statements of operations and comprehensive loss. As of December 31, 2018 and 2019, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts had been recognized in the consolidated statements of operations and comprehensive loss. The Company files income tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. As of December 31, 2018 and 2019, there were no pending tax examinations. The Company is open to future tax examinations under statute from 2016 to the present; however, carryforward attributes that were generated prior to December 31, 2015 may still be adjusted upon examination by federal, state or local tax authorities if they either have been or will be used in a future period.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Leases The Company’s commitments under its leases are described in Note 11. License and Supply Agreements License Agreement with Massachusetts Institute of Technology In December 2015, the Company entered into an exclusive patent license agreement with the Massachusetts Institute of Technology (“MIT”) (the “MIT Agreement”). The MIT Agreement replaced a May 2013 exclusive agreement with MIT. Under the MIT Agreement, the Company received an exclusive license under the licensed patent rights to develop, manufacture and commercialize any products related to certain intracellular delivery methods that were developed at MIT. As of September 30, 2020 and December 31, 2019, the Company had liabilities of $1.5 million and $1.4 million, respectively, for amounts owed to MIT under the sublicense terms of the MIT Agreement, of which $0.8 million and $0.7 million, respectively, were included within accrued expenses (see Note 6) and of which $0.7 million and $0.7 million, respectively, were included in other liabilities (non-current). License Agreement with Erytech In June 2019, the Company entered into a license agreement with Erytech Pharma S.A. (“Erytech”), a French biopharmaceutical company developing therapies for severe forms of cancer and orphan diseases. Under the agreement, the Company received an exclusive worldwide license to develop red blood cell-based antigen-specific immune modulating therapies and has the right to grant sublicenses of its rights. During the nine months ended September 30, 2019, the Company paid the upfront fee of $1.0 million under the agreement and recorded this amount as a research and development expense in its consolidated statement of operations and comprehensive loss. As of September 30, 2020 and December 31, 2019, the Company had not made any additional payments and had not accrued for any contingent payments payable under the agreement as there were no development, regulatory or sales milestones that were probable of being achieved. Manufacturing Services Agreements During the years ended December 31, 2019 and 2018, the Company entered into agreements with a contract manufacturing organization to provide manufacturing services related to its product candidates as it began to prepare for a future clinical trial. The Company had no non-cancelable 401(k) Plan The Company sponsors a 401(k) defined contribution benefit plan (the “401(k) Plan”), which covers all employees who meet certain eligibility requirements as defined in the 401(k) Plan and allows participants to defer a portion of their annual compensation on a pre-tax Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to its vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its executive officers and members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnification agreements and is not currently aware of any indemnification claims. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.	12. Commitments and Contingencies Leases The Company’s commitments under its leases are described in Note 13. License and Supply Agreements License Agreement with Massachusetts Institute of Technology In December 2015, the Company entered into an exclusive patent license agreement with the Massachusetts Institute of Technology (“MIT”) (the “MIT Agreement”). The MIT Agreement replaced a May 2013 exclusive agreement with MIT. Under the MIT Agreement, the Company received an exclusive license under the licensed patent rights to develop, manufacture and commercialize any products related to certain intracellular delivery methods that were developed at MIT. Under the MIT Agreement, the Company also has the right to grant sublicenses of its rights during an exclusivity period that commences on the effective date of the MIT Agreement and expires on the date upon which all issued patents under the agreement have expired and all filed patent applications for the defined patent rights have been abandoned. Such sublicenses may extend past the expiration date of the exclusivity period; however, the exclusivity of such sublicenses expires at the end of the exclusivity period. During the exclusivity period, MIT may not grant any other license in the Company’s field of use under the licensed patent rights in the MIT Agreement, except that MIT may grant licenses under the agreement to specified parties. The Company is obligated to use diligent efforts to develop licensed products or licensed processes, to hire a specified number of employees to support the development effort to bring the licensed product or licensed process to commercialization, and to expend a minimum amount in the low single-digit millions annually that must be spent in support of this effort for the term of the MIT Agreement. There are also terms included in the MIT Agreement that require the Company to (i) reach certain thresholds of sublicense income within five years from the date of the amended effective date of the agreement or (ii) expend a minimum amount in the mid single-digit millions within five years on at least one fully funded project towards the development of a licensed product or licensed process. If the Company fails to meet these requirements, MIT may treat such failure as a material breach. Under the MIT Agreement, the Company is obligated to pay nonrefundable annual license maintenance fees of less than $0.1 million, which may be credited against royalties subsequently due on net sales of licensed products earned in the same calendar year, if any. In addition, the Company is obligated to make aggregate milestone payments to MIT of up to $1.8 million upon the achievement of specified milestones with respect to each licensed product, consisting of up to $0.8 million of development milestone payments and up to $1.0 million of regulatory milestone payments. The Company is also obligated to pay royalties of a low single-digit percentage to MIT based on (i) the Company’s, and any of its affiliates’ and sublicensees’, net sales of licensed products in the research field and (ii) the Company’s, and any of its affiliates’, net sales of licensed products in the therapeutic field. With respect to licensed products or licensed processes leased or sold by a sublicensee, the Company is required to pay MIT royalties equal to the lesser of a low single-digit percentage of each sublicensees’ net sales or a mid double-digit percentage of any royalty owed to the Company under a relevant sublicense agreement. The Company is also required to pay MIT a mid-teens The license granted by MIT to the Company is an exclusive license for the period from the effective date of the MIT Agreement through the date upon which all issued patents under the agreement have expired and all filed patent applications for the defined patent rights have been abandoned. MIT has the right to terminate the agreement if the Company fails to pay amounts when due or otherwise materially breaches the agreement and fails to cure such nonpayment or breach within specified cure periods or in the event the Company ceases to carry on its business related to the agreement. In the event of a termination due to the Company’s breach caused by a failure to meet its diligence requirements for a specified field, but where the Company has fulfilled its obligations with respect to a different specified field, MIT may not terminate the agreement with respect to the different specified field. MIT may immediately terminate the agreement if the Company or any of its affiliates brings specified patent challenges against MIT or assists others in bringing a patent challenge against MIT. The Company has the right to terminate the agreement for its convenience at any time on six months’ prior written notice to MIT and payment of all amounts due to MIT through the date of termination. During the year ended December 31, 2018, the Company made a payment to MIT of $0.9 million under a settlement agreement negotiated in 2018 related to 2017 sublicensee income. As of December 31, 2018 and 2019, the Company had accrued $2.0 million and $1.4 million for amounts owed to MIT under the sublicense terms of the MIT Agreement (see Note 6). During the years ended December 31, 2018 and 2019, the Company recognized research and development expense under the sublicense terms of the agreement of $2.8 million and $0.8 million, respectively. License Agreement with Erytech In June 2019, the Company entered into a license agreement with Erytech Pharma S.A. (“Erytech”), a French biopharmaceutical company developing therapies for severe forms of cancer and orphan diseases. Under the agreement, the Company received an exclusive worldwide license to develop red blood cell-based antigen-specific immune modulating therapies and has the right to grant sublicenses of its rights. Under the agreement, the Company paid an upfront fee of $1.0 million and is obligated to make aggregate milestone payments of up to $6.0 million upon the achievement of specified milestones, consisting of up to $1.0 million of development milestone payments and up to $5.0 million of regulatory milestone payments, for the first licensed product to achieve the specified milestones and payments of up to $50.0 million upon the achievement of specified sales milestones for all licensed products successfully developed under this agreement for each indication. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages of annual net sales for each licensed product or licensed indication sold by the Company or its affiliates. Royalties will be paid by the Company on a licensed product-by-licensed indication-by-indication country-by-country The Company has the right to terminate the agreement, in whole or on a country-by-country During the year ended December 31, 2019, the Company paid the upfront fee of $1.0 million and recorded this amount as a research and development expense in its consolidated statement of operations and comprehensive loss. As of December 31, 2019, the Company had not made any additional payments and had not accrued for any contingent payments as there were no development, regulatory or sales milestones that were probable of being achieved. Manufacturing Services Agreements During the years ended December 31, 2018 and 2019, the Company entered into agreements with a contract manufacturing organization to provide manufacturing services related to its product candidates as it began to prepare for a future clinical trial. As of December 31, 2018, the Company had non-cancelable non-cancelable 401(k) Plan The Company sponsors a 401(k) defined contribution benefit plan (the “401(k) Plan”), which covers all employees who meet certain eligibility requirements as defined in the 401(k) Plan and allows participants to defer a portion of their annual compensation on a pre-tax Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to its vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Leases

Leases	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Leases	11. Leases As of September 30, 2020, the Company leases its office and laboratory facilities under a non-cancelable 2018 Lease In December 2018, the Company entered into a lease for office and laboratory space in Watertown, Massachusetts (the “2018 Lease”). The 2018 Lease term commenced in December 2019 and expires in November 2029. Under the 2018 Lease, the Company has one five-year option to extend the term of the lease. The initial annual base rent was $3.8 million upon entering into the lease, with such base rent increasing during the initial term by 3% annually on the anniversary of the commencement date. The Company is obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement and management of the new leased premises. In connection with the lease, the Company maintains a letter of credit for the benefit of the landlord in the amount of $2.3 million, for which the Company is required to maintain a separate cash balance of the same amount. The 2018 Lease Agreement includes a landlord-provided tenant improvement allowance of $9.8 million that was applied to the costs of the construction of leasehold improvements. 2016 Lease In September 2016, the Company entered into a lease for office and laboratory space in Watertown, Massachusetts (the “2016 Lease”). Under the 2016 Lease, the initial annual base rent was $0.9 million upon entering into the lease, with such base rent increasing during the initial term by 3% annually. The Company was obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement and management of the leased premises. The 2016 Lease included a landlord-provided tenant improvement allowance of $2.1 million that was applied to the costs of the construction of leasehold improvements. The 2016 Lease was set to expire in September 2023; however, in February 2020, the Company and the landlord jointly terminated the 2016 Lease. Accordingly, as of February 2020, the Company had no further obligations under the 2016 Lease. Accounting under ASC 842 2016 Lease As discussed in Note 2, the Company adopted ASC 842 effective January 1, 2019 using the modified retrospective transition method. Upon its adoption of ASC 842, the Company recognized a right-of-use right-of-use In February 2020, as a result of the termination of the 2016 Lease described above, the Company removed from the consolidated balance sheet the associated operating lease right-of-use 2018 Lease As described above, the 2018 Lease Agreement includes a landlord-provided tenant improvement allowance of $9.8 million that was applied to the costs of the construction of leasehold improvements. The lessor owns the tenant improvements related to the 2018 Lease and such improvements are not specialized and can be utilized by a future tenant. Accordingly, amounts paid by the Company during the year ended December 31, 2019 that were due to be reimbursed by the lessor were recorded as amounts reimbursable from the landlord. In the period from December 2018 to November 2019, the Company was not considered the accounting owner due to (i) the Company not having the right to obtain or control the leased premises during the construction period, (ii) the lessor having no right of payment for the partially constructed assets, and the leased premises not being of a specialized nature and, thus, could potentially be leased to another tenant, and (iii) the Company not legally owning or controlling the land on which the property improvements were being constructed. The lease commenced for accounting purposes in December 2019 when the Company took control of the facility under the 2018 Lease. Upon such commencement date, the Company assessed and determined the accounting treatment for the asset and corresponding liability and recorded a right-of-use Embedded Lease The Company evaluated its vendor contracts to identify embedded leases, if any, and noted that an agreement entered into in April 2019 with a contract manufacturing supplier constituted a lease under ASC 842 because the Company has the right to substantially all of the economic benefits from the use of the asset and can direct the use of the asset. The embedded lease commenced in September 2019 and expires 24 months from commencement date, with no stated option to extend the term. Upon the commencement date, the Company recorded right-of-use right-of-use one-year right-of-use The Company’s lease agreements, including the embedded lease, have terms ranging from three years to ten years. Some of the Company’s lease agreements include options to extend the leases for up to five years. These options are only included in the determination of the amount of the lease liability when it is reasonably certain that the option will be exercised. When determining if a renewal option is reasonably certain of being exercised, the Company considers several economic factors, including, but not limited to, the significance of leasehold improvements incurred on the property, whether the asset is difficult to replace, underlying contractual obligations or specifics unique to that particular lease that would make it reasonably certain that the Company would exercise such option. Renewal and termination options were not included in the lease term for the Company’s new and existing operating leases as these options were not reasonably certain of being exercised. Right-of-use The components of lease cost and other information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Lease cost: Operating lease cost $ 3,231 $ 823 $ 9,345 $ 1,189 Variable lease cost 306 121 908 383 Short-term lease cost — 39 21 72 $ 3,537 $ 983 $ 10,274 $ 1,644 SEPTEMBER 30, DECEMBER 31, Other information: Weighted-average remaining lease term (in years) 6.9 7.9 Weighted-average discount rate 7.1 % 8.2 % Supplemental cash flow information related to the Company’s operating leases was as follows (in thousands): NINE MONTHS ENDED 2020 2019 Cash paid for amounts included in the measurement of operating lease liabilities: Operating cash flows from operating leases $ 8,820 $ 1,701 Lease assets obtained in exchange for lease obligations: Operating leases $ 17,049 $ 14,716	13. Leases As of December 31, 2019, the Company leased its office and laboratory facilities under two non-cancelable 2016 Lease In September 2016, the Company entered into a lease for office and laboratory space in Watertown, Massachusetts (the “2016 Lease”). Under the 2016 Lease, the initial annual base rent was $0.9 million upon entering into the lease, with such base rent increasing during the initial term by 3% annually. The Company was obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement and management of the leased premises. The 2016 Lease included a landlord-provided tenant improvement allowance of $2.1 million that was applied to the costs of the construction of leasehold improvements. The 2016 Lease was set to expire in September 2023; however, in February 2020, the Company and the landlord jointly terminated the 2016 Lease. Accordingly, as of February 2020, the Company had no further obligations under the 2016 Lease. 2018 Lease In December 2018, the Company entered into a lease for office and laboratory space in Watertown, Massachusetts (the “2018 Lease”). The 2018 Lease term commenced in December 2019 and expires in November 2029. Under the 2018 Lease, the Company has one five-year option to extend the term of the lease. The initial annual base rent was $3.8 million upon entering into the lease, with such base rent increasing during the initial term by 3% annually on the anniversary of the commencement date. The Company is obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement and management of the new leased premises. In connection with the lease, the Company maintains a letter of credit for the benefit of the landlord in the amount of $2.3 million, for which the Company is required to maintain a separate cash balance of the same amount. The 2018 Lease Agreement includes a landlord-provided tenant improvement allowance of $9.8 million that was applied to the costs of the construction of leasehold improvements. Accounting under ASC 840 As of December 31, 2018, the Company concluded that construction activities had not commenced for the 2018 Lease, and, therefore, the Company did not recognize an asset for a build-to-suit As of December 31, 2018, future minimum commitments under the Company’s operating leases were as follows (in thousands): YEAR ENDING DECEMBER 31, 2019 $ 1,312 2020 4,840 2021 4,983 2022 5,130 2023 4,905 Thereafter 27,370 $ 48,540 Total rent expense for the year ended December 31, 2018 was $1.0 million. Accounting under ASC 842 2016 Lease As discussed in Note 2, the Company adopted ASC 842 effective January 1, 2019 using the modified retrospective transition method. Upon its adoption of ASC 842, the Company recognized a right-of-use right-of-use 2018 Lease As described above, the 2018 Lease Agreement includes a landlord-provided tenant improvement allowance of $9.8 million that was applied to the costs of the construction of leasehold improvements. The lessor owns the tenant improvements related to the 2018 Lease and such improvements are not specialized and can be utilized by a future tenant. Accordingly, amounts paid by the Company during the year ended December 31, 2019 that were due to be reimbursed by the lessor were recorded as amounts reimbursable from the landlord. In the period from December 2018 to November 2019, the Company was not considered the accounting owner due to (i) the Company not having the right to obtain or control the leased premises during the construction period, (ii) the lessor having no right of payment for the partially constructed assets, and the leased premises not being of a specialized nature and, thus, could potentially be leased to another tenant, and (iii) the Company not legally owning or controlling the land on which the property improvements were being constructed. The lease commenced for accounting purposes in December 2019 when the Company took control of the facility under the 2018 Lease. Upon such commencement date, the Company assessed and determined the accounting treatment for the asset and corresponding liability and recorded a right-of-use Embedded Lease The Company evaluated its vendor contracts to identify embedded leases, if any, and noted that an agreement entered into in April 2019 with a contract manufacturing supplier constituted a lease under ASC 842 because the Company has the right to substantially all of the economic benefits from the use of the asset and can direct the use of the asset. The embedded lease commenced in September 2019 and expires 24 months from commencement date, with no stated option to extend the term. Upon the commencement date, the Company recorded right-of-use The Company’s lease agreements, including the embedded lease, have terms ranging from two years to ten years. Some of the Company’s lease agreements include options to extend the leases for up to five years. These options are only included in the determination of the amount of the lease liability when it is reasonably certain that the option will be exercised. When determining if a renewal option is reasonably certain of being exercised, the Company considers several economic factors, including, but not limited to, the significance of leasehold improvements incurred on the property, whether the asset is difficult to replace, underlying contractual obligations or specifics unique to that particular lease that would make it reasonably certain that the Company would exercise such option. Renewal and termination options were not included in the lease term for the Company’s new and existing operating leases as these options were not reasonably certain of being exercised. Right-of-use Future minimum lease payments for operating leases with initial or remaining terms in excess of one year at December 31, 2019 were as follows (in thousands): YEAR ENDING DECEMBER 31, 2020 $ 12,546 2021 8,840 2022 5,130 2023 4,905 2024 4,297 Thereafter 23,072 Total lease payments 58,790 Less: Imputed interest (16,459 ) Total operating lease liabilities $ 42,331 Lease Portfolio The components of lease cost and supplemental balance sheet information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): YEAR ENDED Lease cost: Operating lease cost $ 3,667 Variable lease cost 619 Short-term lease cost 112 $ 4,398 DECEMBER 31, Operating leases: Assets: Operating lease right-of-use $ 43,050 Liabilities: Current portion of operating lease liabilities $ 9,444 Operating lease liabilities, net of current portion 32,887 Total operating lease liabilities $ 42,331 Other information: Weighted-average remaining lease term (in years) 7.9 Weighted-average discount rate 8.2 % Supplemental cash flow information related to the Company’s operating leases was as follows (in thousands):​​​​​​​ YEAR ENDED Cash paid for amounts included in the measurement of operating lease liabilities: Operating cash flows from operating leases $ 5,161 Lease assets obtained in exchange for lease obligations: Operating leases $ 43,326

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Research and Development [Abstract]
License and Collaboration Agreements	12. License and Collaboration Agreements 2017 License and Collaboration Agreement with Roche In April 2017, the Company entered into a license and collaboration agreement with Roche (the “2017 Roche Agreement”) to allow Roche to use the Company’s Cell Squeeze technology to enable gene editing of immune cells to discover new targets in cancer immunotherapy. The 2017 Roche Agreement includes several licenses granted by Roche to the Company and by the Company to Roche in order to conduct a specified research program in accordance with a specified research plan. The 2017 Roche Agreement has a term that ends upon the earlier to occur of (i) the completion of all work under the research plan or (ii) two years after the effective date of the agreement. The collaboration term is subject to Roche’s right to extend the collaboration term for up to two additional one-year workstream-by-workstream Under the agreement, the Company received an upfront payment of $5.0 million as a technology access fee and is entitled to (i) payments of up to $1.0 million, in two tranches of $0.5 million, as reimbursement for the Company’s research costs; (ii) milestone payments of up to $7.0 million upon the achievement of specified development milestones; and (iii) annual maintenance fees ranging from $0.5 million to $0.9 million for each year following the fifth anniversary of the effective date, subject to specified prepayment discounts. The Company assessed its accounting for the 2017 Roche Agreement under ASC 606 as the transactions underlying the agreement were deemed to be transactions with a customer. The Company identified the following promises under the 2017 Roche Agreement: (i) a non-exclusive The Company recognizes revenue associated with the performance obligation as the research, development and manufacturing services are provided using an input method, based on the cumulative costs incurred compared to the total estimated costs expected to be incurred to satisfy the performance obligation. The transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost During the three and nine months ended September 30, 2020 and 2019, there were no significant changes in the total estimated costs expected to be incurred to satisfy the performance obligation under the 2017 Roche Agreement. The Company recognized revenue of $0.1 million during each of the three months ended September 30, 2020 and 2019 under the 2017 Roche Agreement. During the nine months ended September 30, 2020 and 2019, the Company recognized revenue of $0.4 million and $0.6 million, respectively, under the 2017 Roche Agreement. As of September 30, 2020, the Company recorded as a contract liability deferred revenue related to the 2017 Roche Agreement of $1.3 million, of which $0.6 million was a current liability. As of September 30, 2020, the research and development services related to the performance obligation were expected to be performed over a remaining period of approximately 1.8 years. 2018 License and Collaboration Agreement with Roche In October 2018, the Company entered into a license and collaboration agreement with Roche (the “2018 Roche Agreement”) to jointly develop certain products based on mononuclear antigen presenting cells (“APCs”), including human papilloma virus (“HPV”), using the SQZ APC platform for the treatment of oncology indications. The Company granted Roche a non-exclusive non-exclusive product-by-product Under the 2018 Roche Agreement, Roche was granted option rights to obtain an exclusive license to develop APC products or products derived from the collaboration programs on a product-by-product product-by-product Under the 2018 Roche Agreement, the Company received an upfront payment of $45.0 million and is eligible to receive (i) reimbursement of a mid double-digit percentage of its development costs; (ii) aggregate milestone payments on a product-by-product Roche will pay tiered royalties based on annual net sales of APC and TCL products. If Roche exercises its option to obtain a license to commercialize an APC product, Roche will pay the Company tiered royalties on annual net sales of that licensed product at rates ranging from a mid single-digit percentage to a mid-teens mid-teens mid-teens mid-single low-teens The Company assessed its accounting for the 2018 Roche Agreement in accordance with ASC 606 and concluded that Roche is a customer prior to the exercise of any of its options under the agreement. The Company also identified the following promises under the 2018 Roche Agreement: (i) a non-exclusive The Company concluded that, in the case of each performance obligation, the license to its intellectual property was not distinct as a result of Roche being unable to benefit from the license on its own or with other resources reasonably available in the marketplace because the license to its intellectual property requires significant specialized capabilities in order to be further developed. The Company concluded that the license to its intellectual property, research and development activities related to HPV, and manufacturing of the Company’s SQZ APC platform and equipment related to HPV were not distinct from each other because the research and manufacturing activities together customize and significantly modify the underlying technology. As such, the Company determined that each of these related promises under the agreement was not distinct from the others in this group and should be combined into a single performance obligation. The Company also concluded that the license to its intellectual property and the research and development activities on next-generation APCs were not distinct from each other because the research and development activities customize and significantly modify the underlying technology. As such, the Company determined that these related promises should be combined into a single performance obligation. Further, the Company concluded that the license to its intellectual property and the research and development activities on TCL were not distinct from each other because the research and development activities customize and significantly modify the underlying technology. As such, the Company determined that these related promises should be combined into a single performance obligation. The Company concluded that the three performance obligations were distinct from each other as they are separate programs and are unrelated. In addition, the Company determined that the impact of participation on the JSC was insignificant and had an immaterial impact on the accounting model. Finally, the Company evaluated the option rights for licenses to develop, manufacture and commercialize the collaboration targets to determine whether these options provide Roche with any material rights for accounting purposes. The Company concluded that the option exercise prices were not below respective standalone selling prices, and, therefore, the options were marketing offers that do not provide material rights under ASC 606. Accordingly, the options were excluded as performance obligations at the outset of the 2018 Roche Agreement and will be accounted for as separate accounting contracts if and when each option exercise occurs. Based on these assessments, the Company identified three performance obligations at the outset of the 2018 Roche Agreement: (1) the license to the Company’s intellectual property, the research and development activities related to HPV through Phase 1 clinical trials under a specified research plan, and the manufacturing of the Company’s SQZ APC platform and equipment in order to support the HPV research plan (the “first performance obligation”); (2) the license to the Company’s intellectual property and the research and development activities on next-generation APCs (the “second performance obligation”); and (3) the license to the Company’s intellectual property and the research and development activities on TCL (the “third performance obligation”). As of entering into the 2018 Roche Agreement, the Company assessed whether the 2018 Roche Agreement was, for accounting purposes, a modification of the two prior Roche agreements or a separate contract and concluded that it was a modification of the 2015 Roche Agreement. At the termination of the 2015 Roche Agreement, all deliverables were submitted to Roche for review, and as such, the Company completed all of its obligations under the 2015 Roche Agreement. Because the obligations under the 2015 Roche Agreement were completed at its termination and all arrangement consideration had been recognized as revenue, the accounting treatment as a modification determined by the Company would result in the same measurement and recognition patterns as would a separate contract. Further, the Company concluded that the 2018 Roche Agreement was a separate contract from the 2017 Roche Agreement because (i) the Company contracted to provide distinct goods and services associated with its gene editing platform to discover new targets in cancer immunotherapy, (ii) the 2018 Roche Agreement and 2017 Roche Agreement were not negotiated together as a package with a single commercial objective and (iii) the amount of consideration paid under the 2018 Roche Agreement and 2017 Roche Agreement are not dependent on the price or performance under the other agreement. In addition, the Company determined that the upfront payment of $45.0 million as well as the reimbursable costs of $10.8 million estimated by the Company constituted the entirety of the consideration to be included in the transaction price. This transaction price of $55.8 million was initially allocated to the three performance obligations based on the relative standalone selling price of each obligation. The potential milestone payments that the Company may be eligible to receive were excluded from the transaction price at the outset of the arrangement because (i) all development and regulatory milestone payments did not meet the criteria for inclusion using the most-likely-amount method and (ii) the Company recognizes as revenue sales-based royalties and milestone payments at the later of the occurrence of the related sales or the date upon which the performance obligation has been satisfied because the Company believes that the license is the predominant item to which the royalties relate and has applied the sales-based royalty exception. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, the Company will adjust its estimate of the transaction price. The Company determined the standalone selling price of each performance obligation under the 2018 Roche Agreement based on its estimate of its costs to be incurred to fulfil the research, development and manufacturing obligations associated with each of the three performance obligations, plus a reasonable margin. During the first quarter of 2019, the Company became entitled to receive a payment of $10.0 million upon the achievement of the first development milestone under the 2018 Roche Agreement, which was related to submission by the Company of preclinical data to the FDA. The $10.0 million amount was added to the Company’s estimate of the transaction price as of the first quarter of 2019, when the Company determined that achievement of the milestone was “most likely” and that it was probable that a significant reversal in the amount of cumulative revenue recognized would not occur, and, as a result, the Company recorded a cumulative catch-up In October 2019, the Company received clearance from the FDA for its investigational new drug application (“IND”) for its lead clinical program under the 2018 Roche Agreement. As a result of this IND clearance and progress made toward beginning clinical trials, the Company concluded as of December 31, 2019 that the achievement in the first quarter of 2020 of a milestone resulting in receipt of a payment of $20.0 million due upon first-patient dosing in a Phase 1 clinical trial under the 2018 Roche Agreement was “most likely” and that it was probable that a significant reversal in the amount of cumulative revenue recognized would not occur. The Company therefore included the $20.0 million payment in the estimate of the transaction price for the 2018 Roche Agreement in the fourth quarter of 2019 and recorded a cumulative catch-up During the fourth quarter of 2019, the Company evaluated its overall program priorities and determined that in 2020 it would continue to focus its resources on progressing the specified APC programs related to the 2018 Roche Agreement as well as its Activating Antigen Carriers (“AAC”) and Tolerizing Antigen Carriers (“TAC”) platforms. As a result of its continuing focus on these specific programs, the Company reduced the level of priority of the TCL research activities under the 2018 Roche Agreement and expects to perform such TCL research activities over a longer time period than as originally expected under the specified research plan of the agreement. Consequently, in the fourth quarter of 2019, the Company reclassified $5.3 million of its current deferred revenue to non-current non-current The Company separately recognizes revenue associated with each of the three performance obligations as the research, development and manufacturing services are provided using an input method, based on the cumulative costs incurred compared to the total estimated costs expected to be incurred to satisfy each performance obligation. The transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost During the three months ended September 30, 2020 and 2019 as well as the nine months ended September 30, 2020, there were no significant changes in the total estimated costs expected to be incurred to satisfy the performance obligations under the 2018 Roche Agreement. During the nine months ended September 30, 2019, the total estimated costs expected to be incurred to satisfy the performance obligations increased by $2.3 million. The Company recognized revenue of $6.0 million and $3.9 million during the three months ended September 30, 2020 and 2019, respectively, under the 2018 Roche Agreement. The Company recognized revenue of $18.1 million and $12.5 million during the nine months ended September 30, 2020 and 2019, respectively, under the 2018 Roche Agreement. As of September 30, 2020, the Company recorded as a contract liability deferred revenue related to the 2018 Roche Agreement of $46.4 million, of which $33.3 million was a current liability. As of September 30, 2020, the research and development services related to the performance obligations were expected to be performed over remaining periods ranging from 1.0 year to 1.3 years. As of December 31, 2019, the Company recorded as a contract liability deferred revenue related to the 2018 Roche Agreement of $38.7 million, of which $17.9 million was a current liability. As of December 31, 2019, the research and development services related to the first and second performance obligations were expected to be performed over remaining periods ranging from 1.8 years to 2.0 years. As of September 30, 2020 and December 31, 2019, the expected remaining period of performance of the Company’s research and development services related to the third performance obligation was not determinable, and it will not become determinable until TCL research activities resume or the 2018 Roche Agreement is modified by the Company and Roche. Contract Liability The changes in the total contract liability (deferred revenue) balances related to the Company’s license and collaboration agreements with Roche were as follows (in thousands): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Balance at beginning of period $ 51,917 $ 48,873 $ 40,453 $ 45,598 Deferral of revenue 1,891 1,255 25,746 13,555 Recognition of deferred revenue (6,120 ) (4,050 ) (18,511 ) (13,075 ) Balance at end of period $ 47,688 $ 46,078 $ 47,688 $ 46,078	14. License and Collaboration Agreements 2015 License and Collaboration Agreement with Roche In December 2015, the Company entered into a license and collaboration agreement with Hoffman-La non-exclusive non-exclusive The 2015 Roche Agreement provided that the parties would conduct a research program for a term of five years from the effective date of agreement. During the collaboration term, the parties agreed to a research cross-license where the two parties had certain exclusive and non-exclusive Under the 2015 Roche Agreement, the Company received a $12.0 million upfront payment from Roche. In addition, the Company was entitled to receive aggregate milestone payments of up to $486.0 million upon the achievement of specified milestones, which were not achieved. The Company received the upfront payment of $12.0 million in 2015. No other payments were due or received in connection with the 2015 Roche Agreement prior to its termination. The Company evaluated the 2015 Roche Agreement under ASC 606 as the transactions underlying the agreement were considered transactions with a customer. The Company identified the following promises under the arrangement: (i) an exclusive license granted to develop, manufacture and commercialize the licensed product; (ii) research and development services through Phase 1 clinical studies related to the use of B Cells to treat cancer; (iii) manufacturing activities related to development supply of the licensed products; and (iv) participation on a JRC. The Company determined that each of the promises was not distinct from the other promises in the contract. The research license was determined to not be distinct from the research and manufacturing activities primarily as a result of Roche being unable to benefit on its own or with other resources reasonably available in the marketplace because the license to the Company’s intellectual property requires significant specialized capabilities in order to be further developed, the research services necessary to develop the product are highly specialized, and the Company’s proprietary Cell Squeeze technology is a key capability of that development. The research and manufacturing services were determined not to be distinct because they customize and significantly modify the underlying technology. In addition, the Company determined that the impact of participation on the JRC was insignificant and had an immaterial impact on the accounting model. As such, the Company determined that the first three promises should be combined into a single performance obligation. Based on these assessments, the Company identified one distinct performance obligation at the outset of the 2015 Roche Agreement. Upon entering into the 2015 Roche Agreement, the Company determined that the upfront payment of $12.0 million constituted the entirety of the consideration to be included in the transaction price. The potential milestone payments that the Company may have been eligible to receive were initially excluded from the transaction price at the outset of the arrangement because (i) all development and regulatory milestone payments did not meet the criteria for inclusion using the most-likely-amount method and (ii) the Company recognizes as revenue sales-based royalties and milestone payments at the later of the occurrence of the related sales or the date upon which the performance obligation has been satisfied because the Company believes that the license is the predominant item to which the royalties relate and has applied the sales-based royalty exception. The Company reevaluated the transaction price at the end of each reporting period until the 2015 Roche Agreement was terminated. No adjustments were made to the transaction price from the inception of the 2015 Roche Agreement through its termination in October 2018. The Company recognized revenue associated with the performance obligation as the research and development services were provided using an input method, based on the cumulative costs incurred compared to the total estimated costs that were expected to be incurred to satisfy the performance obligation. The transfer of control to the customer occurs over the time period that the research and development services were to be provided by the Company, and this cost-to-cost During the year ended December 31, 2018, the Company recognized revenue of $5.3 million under the 2015 Roche Agreement. The Company had completed its required obligations as of the termination of this agreement, and all revenue related to the 2015 Roche Agreement was fully recognized as of December 31, 2018 using an input method. 2017 License and Collaboration Agreement with Roche In April 2017, the Company entered into a second license and collaboration agreement with Roche (the “2017 Roche Agreement”) to allow Roche to use the Company’s Cell Squeeze technology to enable gene editing of immune cells to discover new targets in cancer immunotherapy. The 2017 Roche Agreement includes several licenses granted by Roche to the Company and by the Company to Roche in order to conduct a specified research program in accordance with a specified research plan. The 2017 Roche Agreement has a term that ends upon the earlier to occur of (i) the completion of all work under the research plan or (ii) two years after the effective date of the agreement. The collaboration term is subject to Roche’s right to extend the collaboration term for up to two additional one-year workstream-by-workstream Under the agreement, the Company received an upfront payment of $5.0 million as a technology access fee and is entitled to (i) payments of up to $1.0 million, in two tranches of $0.5 million, as reimbursement for the Company’s research costs; (ii) milestone payments of up to $7.0 million upon the achievement of specified development milestones; and (iii) annual maintenance fees ranging from $0.5 million to $0.9 million for each year following the fifth anniversary of the effective date, subject to specified prepayment discounts. The Company assessed its accounting for the 2017 Roche Agreement under ASC 606 as the transactions underlying the agreement were deemed to be transactions with a customer. The Company identified the following promises under the 2017 Roche Agreement: (i) a non-exclusive As of entering into the 2017 Roche Agreement, the Company assessed whether the 2017 Roche Agreement was, for accounting purposes, a modification of the 2015 Roche Agreement or a separate contract and concluded that it was a separate contract because (i) the programs under the 2017 Roche Agreement were entirely new and distinct and are separate from programs under the 2015 Roche Agreement, (ii) the 2017 Roche Agreement and 2015 Roche Agreement were not negotiated together as a package with a single commercial objective and (iii) the amount of consideration paid under the 2017 Roche Agreement and 2015 Roche Agreement are not dependent on the price or performance under the other agreement. In addition, the Company determined that the upfront payment of $5.0 million as well as the expected reimbursable costs of $1.0 million constituted the entirety of the consideration to be included in the transaction price. The potential milestone payments that the Company may be eligible to receive were initially excluded from the transaction price of the arrangement as all development milestone payments did not meet the criteria for inclusion using the most-likely-amount method. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, the Company will adjust its estimate of the transaction price. The Company received the upfront payment of $5.0 million in April 2017 upon execution of the agreement. The Company also received the payments of $0.5 million in each of 2017 and 2018 related to its reimbursable research costs. In addition, during the third quarter of 2018, the Company received a payment of $2.0 million following the achievement of the first development milestone under the agreement related to Roche’s validation of preclinical proof of concept. This amount was added to the Company’s estimate of the transaction price as of the second quarter of 2018, when the Company determined that achievement of the milestone was “most likely” and that it was probable that a significant reversal in the amount of cumulative revenue recognized would not occur, and as a result, the Company recorded a cumulative catch-up The Company recognizes revenue associated with the performance obligation as the research, development and manufacturing services are provided using an input method, based on the cumulative costs incurred compared to the total estimated costs expected to be incurred to satisfy the performance obligation. The transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost During the years ended December 31, 2018 and 2019, there were no significant changes in the total estimated costs expected to be incurred to satisfy the performance obligation under the 2017 Roche Agreement and the Company recognized revenue of $3.6 million and $0.7 million, respectively, under the 2017 Roche Agreement. As of December 31, 2018 and 2019, the Company recorded as a contract liability deferred revenue related to the 2017 Roche Agreement of $2.4 million and $1.7 million, respectively, of which $0.9 million and $0.7 million, respectively, were current liabilities. As of December 31, 2018 and 2019, the research and development services related to the performance obligation were expected to be performed over a remaining period of approximately 3.5 years and 2.5 years, respectively. 2018 License and Collaboration Agreement with Roche In October 2018, the Company entered into a third license and collaboration agreement with Roche (the “2018 Roche Agreement”) to jointly develop certain products based on mononuclear antigen presenting cells (“APCs”), including human papilloma virus (“HPV”), using the SQZ APC platform for the treatment of oncology indications. The Company granted Roche a non-exclusive non-exclusive product-by-product Under the 2018 Roche Agreement, Roche was granted option rights to obtain an exclusive license to develop APC products or products derived from the collaboration programs on a product-by-product product-by-product Under the 2018 Roche Agreement, the Company received an upfront payment of $45.0 million and is eligible to receive (i) reimbursement of a mid double-digit percentage of its development costs; (ii) aggregate milestone payments on a product-by-product Roche will pay tiered royalties based on annual net sales of APC and TCL products. If Roche exercises its option to obtain a license to commercialize an APC product, Roche will pay the Company tiered royalties on annual net sales of that licensed product at rates ranging from a mid single-digit percentage to a mid-teens mid-teens mid-teens mid-single low-teens The Company assessed its accounting for the 2018 Roche Agreement in accordance with ASC 606 and concluded that Roche is a customer prior to the exercise of any of its options under the agreement. The Company also identified the following promises under the 2018 Roche Agreement: (i) a non-exclusive The Company concluded that, in the case of each performance obligation, the license to its intellectual property was not distinct as a result of Roche being unable to benefit from the license on its own or with other resources reasonably available in the marketplace because the license to its intellectual property requires significant specialized capabilities in order to be further developed. The Company concluded that the license to its intellectual property, research and development activities related to HPV, and manufacturing of the Company’s SQZ APC platform and equipment related to HPV were not distinct from each other because the research and manufacturing activities together customize and significantly modify the underlying technology. As such, the Company determined that each of these related promises under the agreement was not distinct from the others in this group and should be combined into a single performance obligation. The Company also concluded that the license to its intellectual property and the research and development activities on next-generation APCs were not distinct from each other because the research and development activities customize and significantly modify the underlying technology. As such, the Company determined that these related promises should be combined into a single performance obligation. Further, the Company concluded that the license to its intellectual property and the research and development activities on TCL were not distinct from each other because the research and development activities customize and significantly modify the underlying technology. As such, the Company determined that these related promises should be combined into a single performance obligation. The Company concluded that the three performance obligations were distinct from each other as they are separate programs and are unrelated. In addition, the Company determined that the impact of participation on the JSC was insignificant and had an immaterial impact on the accounting model. Finally, the Company evaluated the option rights for licenses to develop, manufacture and commercialize the collaboration targets to determine whether these options provide Roche with any material rights for accounting purposes. The Company concluded that the option exercise prices were not below respective standalone selling prices, and, therefore, the options were marketing offers that do not provide material rights under ASC 606. Accordingly, the options were excluded as performance obligations at the outset of the 2018 Roche Agreement and will be accounted for as separate accounting contracts if and when each option exercise occurs. Based on these assessments, the Company identified three performance obligations at the outset of the 2018 Roche Agreement: (1) the license to the Company’s intellectual property, the research and development activities related to HPV through Phase 1 clinical trials under a specified research plan, and the manufacturing of the Company’s SQZ APC platform and equipment in order to support the HPV research plan (the “first performance obligation”); (2) the license to the Company’s intellectual property and the research and development activities on next-generation APCs (the “second performance obligation”); and (3) the license to the Company’s intellectual property and the research and development activities on TCL (the “third performance obligation”). As of entering into the 2018 Roche Agreement, the Company assessed whether the 2018 Roche Agreement was, for accounting purposes, a modification of the two prior Roche agreements or a separate contract and concluded that it was a modification of the 2015 Roche Agreement. At the termination of the 2015 Roche Agreement, all deliverables were submitted to Roche for review, and as such, the Company completed all of its obligations under the 2015 Roche Agreement. Because the obligations under the 2015 Roche Agreement were completed at its termination and all arrangement consideration had been recognized as revenue, the accounting treatment as a modification determined by the Company would result in the same measurement and recognition patterns as would a separate contract. Further, the Company concluded that the 2018 Roche Agreement was a separate contract from the 2017 Roche Agreement because (i) the Company contracted to provide distinct goods and services associated with its gene editing platform to discover new targets in cancer immunotherapy, (ii) the 2018 Roche Agreement and 2017 Roche Agreement were not negotiated together as a package with a single commercial objective and (iii) the amount of consideration paid under the 2018 Roche Agreement and 2017 Roche Agreement are not dependent on the price or performance under the other agreement. In addition, the Company determined that the upfront payment of $45.0 million as well as the reimbursable costs of $10.8 million estimated by the Company constituted the entirety of the consideration to be included in the transaction price. This transaction price of $55.8 million was initially allocated to the three performance obligations based on the relative standalone selling price of each obligation. The potential milestone payments that the Company may be eligible to receive were excluded from the transaction price at the outset of the arrangement because (i) all development and regulatory milestone payments did not meet the criteria for inclusion using the most-likely-amount method and (ii) the Company recognizes as revenue sales-based royalties and milestone payments at the later of the occurrence of the related sales or the date upon which the performance obligation has been satisfied because the Company believes that the license is the predominant item to which the royalties relate and has applied the sales-based royalty exception. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, the Company will adjust its estimate of the transaction price. The Company determined the standalone selling price of each performance obligation under the 2018 Roche Agreement based on its estimate of its costs to be incurred to fulfil the research, development and manufacturing obligations associated with each of the three performance obligations, plus a reasonable margin. During the first quarter of 2019, the Company became entitled to receive a payment of $10.0 million upon the achievement of the first development milestone under the 2018 Roche Agreement, which was related to submission by the Company of preclinical data to the FDA. The $10.0 million amount was added to the Company’s estimate of the transaction price as of the first quarter of 2019, when the Company determined that achievement of the milestone was “most likely” and that it was probable that a significant reversal in the amount of cumulative revenue recognized would not occur, and, as a result, the Company recorded a cumulative catch-up In October 2019, the Company received clearance from the FDA for its investigational new drug application (“IND”) for its lead clinical program under the 2018 Roche Agreement. As a result of this IND clearance and progress made toward beginning clinical trials, the Company concluded as of December 31, 2019 that the achievement in the first quarter of 2020 of a milestone resulting in receipt of a payment of $20.0 million due upon first-patient dosing in a Phase 1 clinical trial under the 2018 Roche Agreement was “most likely” and that it was probable that a significant reversal in the amount of cumulative revenue recognized would not occur. The Company therefore included the $20.0 million payment in the estimate of the transaction price for the 2018 Roche Agreement in the fourth quarter of 2019 and recorded a cumulative catch-up During the fourth quarter of 2019, the Company evaluated its overall program priorities and determined that in 2020 it would continue to focus its resources on progressing the specified APC programs related to the 2018 Roche Agreement as well as its Activating Antigen Carriers (“AAC”) and Tolerizing Antigen Carriers (“TAC”) platforms. As a result of its continuing focus on these specific programs, the Company reduced the level of priority of the TCL research activities under the 2018 Roche Agreement and expects to perform such TCL research activities over a longer time period than as originally expected under the specified research plan of the agreement. Consequently, in the fourth quarter of 2019, the Company reclassified $5.3 million of its current deferred revenue to non-current non-current The Company separately recognizes revenue associated with each of the three performance obligations as the research, development and manufacturing services are provided using an input method, based on the cumulative costs incurred compared to the total estimated costs expected to be incurred to satisfy each performance obligation. The transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost During the year ended December 31, 2018, there were no significant changes in the total estimated costs expected to be incurred to satisfy the performance obligations under the 2018 Roche Agreement. During the year ended December 31, 2019, the total estimated costs expected to be incurred to satisfy the performance obligations increased by $21.0 million. The Company recognized revenue of $2.7 million and $18.6 million during the years ended December 31, 2018 and 2019, respectively, under the 2018 Roche Agreement. As of December 31, 2018, the Company recorded as a contract liability deferred revenue related to the 2018 Roche Agreement of $43.2 million, of which $15.7 million was a current liability. As of December 31, 2018, the research and development services related to the performance obligations were expected to be performed over remaining periods ranging from 2.8 years to 3.0 years. As of December 31, 2019, the Company recorded as a contract liability deferred revenue related to the 2018 Roche Agreement of $38.7 million, of which $17.9 million was a current liability. As of December 31, 2019, the research and development services related to the first and second performance obligations were expected to be performed over remaining periods ranging from 1.8 years to 2.0 years. As of December 31, 2019, the expected remaining period of performance of the Company’s research and development services related to the third performance obligation was not determinable, and it will not become determinable until TCL research activities resume or the 2018 Roche Agreement is modified by the Company and Roche. Contract Liability The changes in the total contract liability (deferred revenue) balances related to the Company’s license and collaboration agreements with Roche were as follows (in thousands): YEAR ENDED 2018 2019 Balance at beginning of period $ 8,773 $ 45,598 Deferral of revenue 48,364 14,173 Recognition of deferred revenue (11,539 ) (19,318 ) Balance at end of period $ 45,598 $ 40,453 During the years ended December 31, 2018 and 2019, the Company recognized revenue of $7.5 million and $10.1 million, respectively, related to deferred revenue that was recorded as a contract liability at the beginning of each respective year.

Research Funding Agreements wit

Research Funding Agreements with Government Agencies	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Research and Development [Abstract]
Research Funding Agreements with Government Agencies	13. Research Funding Agreements with Government Agencies Through October 2020, the Company generated revenue from government contracts with the National Institutes of Health (“NIH”) and the National Science Foundation (“NSF”), which reimbursed the Company for certain allowable costs for funded projects. The Company’s contracts with the NIH and NSF were awarded to support specified research projects. Amounts received from these government agencies were based on a budget submitted by the Company to the agencies, and such budgets were approved in advance by the agencies. The Company was reimbursed for allowable costs upon receipt by the agencies of the supporting information for the costs incurred. The term for work to be performed under the government contracts expired in October 2020.	15. Research Funding Agreements with Government Agencies The Company generates revenue from government contracts with the National Institutes of Health (“NIH”) and the National Science Foundation (“NSF”), which reimburse the Company for certain allowable costs for funded projects. The Company’s contracts with the NIH and NSF are awarded to support specified research projects. Amounts received from these government agencies are based on a budget submitted by the Company to the agencies, and such budgets are approved in advance by the agencies. The Company is reimbursed for allowable costs upon receipt by the agencies of the supporting information for the costs incurred. The government contracts expire by the end of October 2020 unless renewed by the parties. As of December 31, 2018 and 2019, aggregate future funding, excluding unbilled receivables, available to the Company under its existing government contracts totaled up to $1.4 million and $0.6 million, respectively, which, if received, will be recognized by the Company as revenue in accordance with the policy above (see Note 2). As of December 31, 2018 and 2019, the Company had $0.1 million and $0.4 million, respectively, of deferred revenue recorded under these government contracts. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded as unbilled receivables, a component of prepaid expenses and other current assets, in the consolidated balance sheet (see Note 4).

Related Parties

Related Parties	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Parties	14. Related Parties In October 2015, the Company entered into a consulting agreement with Klavs Jensen, Ph.D., a member of the Company’s board of directors. The director had agreed to perform consulting and advisory services as specified in the agreement in exchange for consulting fees, and the Company could terminate the consulting agreement for any reason. Effective as of October 1, 2019, the consulting agreement with the director was terminated. During the three and nine months ended September 30, 2019, the Company paid less than $0.1 million to the director under the terms of the consulting agreement and recorded general and administrative expenses of less than $0.1 million related to this consulting agreement. As of September 30, 2020 and December 31, 2019, there were no amounts due to the related party under this consulting agreement.	16. Related Parties In October 2015, the Company entered into a consulting agreement with Klavs Jensen, Ph.D., a member of the Company’s board of directors. The director had agreed to perform consulting and advisory services as specified in the agreement in exchange for consulting fees, and the Company could terminate the consulting agreement for any reason. Effective as of October 1, 2019, the consulting agreement with the director was terminated. During each of the years ended December 31, 2018 and 2019, the Company paid $0.1 million to the director under the terms of the consulting agreement and recorded general and administrative expenses of $0.1 million related to this consulting agreement. As of December 31, 2018 and 2019, there were no amounts due to the related party under this consulting agreement.

Net Loss per Share

Net Loss per Share	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Loss per Share	15. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Numerator: Net loss attributable to common stockholders $ (12,351 ) $ (7,883 ) $ (32,920 ) $ (21,943 ) Denominator: Weighted-average common shares outstanding, basic and diluted 1,758,039 1,722,300 1,744,948 1,696,104 Net loss per share attributable to common stockholders, basic and diluted $ (7.03 ) $ (4.58 ) $ (18.87 ) $ (12.94 ) The Company’s potential dilutive securities, which include convertible preferred stock, a warrant to purchase common stock and common stock options, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: SEPTEMBER 30, 2020 2019 Convertible preferred stock (as converted to common stock) 17,800,084 12,643,109 Warrant to purchase common stock 2,038 2,038 Stock options to purchase common stock 3,744,451 2,715,875 21,546,573 15,361,022	17. Net Loss per Share Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): YEAR ENDED DECEMBER 31, 2018 2019 Numerator: Net loss $ (19,250 ) $ (32,202 ) Accretion of redeemable convertible preferred stock to redemption value (984 ) — Net loss attributable to common stockholders $ (20,234 ) $ (32,202 ) Denominator: Weighted-average common shares outstanding, basic and diluted 1,586,683 1,704,509 Net loss per share attributable to common stockholders, basic and diluted $ (12.75 ) $ (18.89 ) The Series A and Series B preferred stock were redeemable at the option of the holder (see Note 8). In connection with the issuance and sale of Series C Preferred Stock in May 2018, the holders of Series A and Series B Preferred Stock agreed to remove the redemption rights of the Series A and Series B Preferred Stock, including rights to specified accruing interest. Accordingly, for periods prior to May 2018, the calculation of net loss attributable to common stockholders included the accretion of Series A and Series B redeemable convertible preferred stock to redemption value. The Company’s potential dilutive securities, which include convertible preferred stock, a warrant to purchase common stock, common stock options and unvested restricted common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: YEAR ENDED DECEMBER 31, 2018 2019 Convertible preferred stock (as converted to common stock) 12,643,109 14,604,043 Warrant to purchase common stock 2,038 2,038 Stock options to purchase common stock 2,013,769 3,139,649 Unvested restricted common stock 25,880 — 14,684,796 17,745,730

Subsequent Events

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events 2020 Incentive Award Plan On October 20, 2020, the Company’s board of directors adopted, and on October 22, 2020 its stockholders approved, the 2020 Incentive Award Plan (the “2020 Plan”), which became effective on October 29, 2020. The 2020 Plan provides for the grant of incentive stock options, stock appreciation rights, restricted stock awards, restricted stock units, and other stock-based awards. A total of 2,690,415 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2020 Plan will automatically increase on the first day of each calendar year, beginning on January 1, 2021 and ending on and including January 1, 2030, equal to the lesser of (i) 5% of the aggregate number of shares of common stock outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the board of directors. The shares of common stock underlying any awards that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, repurchased or are otherwise terminated by the Company under the 2020 Plan will be added back to the shares of common stock available for issuance under the 2020 Plan. 2020 Employee Stock Purchase Plan On October 20, 2020, the Company’s board of directors adopted, and on October 22, 2020 its stockholders approved, the 2020 Employee Stock Purchase Plan (the ‘‘2020 ESPP’’), which became effective on October 29, 2020. A total of 275,886 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2020 ESPP will automatically increase on the first day of each calendar year, beginning on January 1, 2021 and ending on and including January 1, 2030, equal to the lesser of (i) 1% of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the board of directors, provided that not more than 3,724,461 shares of common stock may be issued under the 2020 ESPP. Stock Split On October 23, 2020, the Company effected a 1.0530-for-one Initial Public Offering On November 3, 2020, the Company completed its IPO, pursuant to which it issued and sold 4,411,765 shares of its common stock. On November 12, 2020, the Company issued and sold an additional 661,764 shares of its common stock pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate net proceeds received by the Company from the IPO were approximately $75.5 million, after deducting underwriting discounts and commissions, but before deducting offering costs payable by the Company, which are estimated to be $2.8 million. Upon the closing of the IPO, all of the shares of the Company’s convertible preferred stock then outstanding automatically converted into 17,800,084 shares of common stock. Upon the conversion of the convertible preferred stock, the Company reclassified the carrying value of the convertible preferred stock to common stock (at par value) and additional paid-in Increase in Authorized Number of Shares of Common Stock and Changes in Authorized Preferred Stock On November 3, 2020, in connection with the closing of the IPO, the Company filed a restated certificate of incorporation, which amended and restated the Company’s certificate of incorporation to, among other things: (i) increase the number of authorized shares of common stock from 24,000,000 shares to 200,000,000 shares, (ii) eliminate all references to the previously existing series of convertible preferred stock, and (iii) authorize 10,000,000 shares of undesignated preferred stock that may be issued from time to time by the Company’s board of directors in one or more series.	18. Subsequent Events For its annual consolidated financial statements as of December 31, 2019 and for the year then ended, the Company evaluated subsequent events through July 20, 2020, the date on which those financial statements were issued, and, with respect to the stock split described below, through October 26, 2020. Issuance and Sale of Series D Preferred Stock In January and February 2020, the Company issued and sold an aggregate of 1,094,247 shares of Series D Preferred Stock, at a price of $13.9365 per share, for gross proceeds of $15.2 million (see Note 8). In May and June 2020, the Company issued and sold an aggregate of 1,940,945 shares of Series D Preferred Stock, at a price of $13.9365 per share, for gross proceeds of $27.0 million (see Note 8). The Company incurred issuance costs in connection with these 2020 issuances of Series D Preferred Stock of less than $0.1 million (see Note 8). Upon issuance of these shares of Series D Preferred Stock, the Company assessed the embedded conversion and liquidation features of the shares and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed as of the issuance dates of these shares of Series D Preferred Stock. Termination of the 2016 Lease In February 2020, the Company and the landlord jointly terminated the 2016 Lease. Accordingly, as of February 2020, the Company had no further obligations under the 2016 Lease (see Note 13). Grants of Stock Options under the 2014 Plan On February 27, 2020, the Company granted options for the purchase of an aggregate of 402,521 shares of common stock, at an exercise price of $7.93 per share, to employees. The aggregate grant-date fair value of these options was $2.0 million, which is expected to be recognized as stock-based compensation expense over a period of 4.0 years. Receipt of Milestone Payment under the 2018 Roche Agreement In March 2020, the Company received from Roche the $20.0 million milestone payment due under the 2018 Roche Agreement upon the first patient being dosed in a Phase 1 clinical trial (see Note 14). Stock Split On October 23, 2020, the Company effected a 1.0530-for-one

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying consolidated balance sheet as of December 31, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2020 and for the three and nine months ended September 30, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2019 included in the Company’s final prospectus for the IPO filed pursuant to Rule 424(b)(4) under the Securities Act, with the SEC, on October 30, 2020. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2020 and consolidated results of operations for the three and nine months ended September 30, 2020 and 2019 and the consolidated cash flows for the nine months ended September 30, 2020 and 2019, have been made. The Company’s consolidated results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, the valuation of common stock and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions.	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, the valuation of common stock and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions.
Concentrations of Credit Risk and of Significant Suppliers		Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of accounts receivable and cash and cash equivalents. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. As of December 31, 2019, all of the Company’s accounts receivable were related to its collaboration agreements with Roche (see Note 14). The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and to process its product candidates for its development programs. These programs could be adversely affected by a significant interruption in the manufacturing process or supply chain.
Cash Equivalents		Cash Equivalents The Company considers all highly liquid investments in marketable securities with original maturities of three months or fewer at the date of purchase to be cash equivalents.
Deferred Offering Costs		Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process paid-in in-process
Accounts Receivable Allowance		Accounts Receivable Allowance Accounts receivable are presented net of an allowance for doubtful accounts, which is an estimate of amounts that may not be collectible. The Company performs ongoing evaluations of its accounts receivable and, if necessary, provides an allowance for doubtful accounts and expected losses. The Company writes off accounts receivable against the allowance when it determines a balance is uncollectible and no longer actively pursues collection of the receivable. As of December 31, 2018 and 2019, the Company had no allowance for doubtful accounts. During the years ended December 31, 2018 and 2019, the Company did not record any provisions for doubtful accounts and did not write off any accounts receivable balances.
Restricted Cash		Restricted Cash As of December 31, 2018 and 2019, the Company maintained letters of credit totaling $2.3 million for the benefit of the landlords of its leased properties. The Company was required to maintain separate cash balances of $2.3 million to secure the letters of credit. The Company classified these separate cash balances of $2.3 million as restricted cash (non-current)
Property and Equipment		Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: ESTIMATED USEFUL LIFE Machinery and equipment 3 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of term of lease or 7 years Costs for capital assets not yet placed into service are capitalized as construction-in-progress
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. The Company continually evaluates long-lived assets for potential impairment whenever events or changes in circumstances indicate that the carrying value of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares the carrying values of the asset group to the expected future undiscounted cash flows that the asset group is expected to generate from the use and eventual disposition of the long-lived asset group. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. If such asset group is considered to be impaired, the impairment loss to be recognized would be based on the excess of the carrying value of the impaired asset group over its fair value. The Company did not recognize any impairment losses on long-lived assets during the years ended December 31, 2018 or 2019.
Fair Value Measurements		Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ∎ Level 1—Quoted prices in active markets for identical assets or liabilities. ∎ Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ∎ Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The fair value of the Company’s cash equivalents and marketable securities are determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts receivable, unbilled receivables, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.
Marketable Securities		Marketable Securities The Company’s marketable debt securities are classified as available-for-sale The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Leases		Leases Prior to January 1, 2019, the Company accounted for leases under Accounting Standards Codification (“ASC”) 840, Leases The Company adopted ASC 842, Leases , The Company has operating leases for office space as well as a contract for manufacturing under which the Company has a dedicated suite. The Company may enter into similar arrangements in the future. Under ASC 842, the Company determines whether such arrangements contain a lease at the inception of a contract by assessing whether there is an identified asset and whether a contract conveys the right to control the use of the identified asset in exchange for consideration and the right to obtain the economic benefits from the use of the identified asset. Upon commencement of an identified lease, the Company records a right-of-use Right-of-use After lease commencement and the establishment of a right-of-use As permitted by ASC 842, leases with an initial term of 12 months or fewer are not recorded in the consolidated balance sheets. The Company often enters into contracts that contain both lease and non-lease Non-lease non-lease right-of-use The Company’s lease terms often include renewal options. The amounts determined for the Company’s right-of-use
Classification of Convertible Preferred Stock		Classification and Accretion of Convertible Preferred Stock The Company’s Series Seed, Series A, Series B, Series C and Series D convertible preferred stock are classified outside of stockholders’ equity (deficit) because the holders of such shares have liquidation rights in the event of a deemed liquidation that, in certain situations, is not solely within the control of the Company. Until May 2018, the carrying values of the Company’s Series A and Series B redeemable convertible preferred stock were being accreted to its redemption value from the date of issuance of such shares through the earliest required redemption date. However, in connection with the issuance of Series C convertible preferred stock in May 2018, the holders of Series A and Series B convertible preferred stock agreed to remove the redemption rights of the Series A and Series B redeemable convertible preferred stock, including rights to specified accruing interest (see Note 8), and as a result, the Company ceased recording adjustments to the carrying value of its outstanding convertible preferred stock for accretion to redemption value.
Segment Information		Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is developing methods of engineering cell function and therapies for the treatment of patients across a range of indications. The Company has determined that its chief operating decision maker is its Chief Executive Officer. The Company’s chief operating decision maker reviews the Company’s financial information on a consolidated basis for purposes of allocating resources and assessing financial performance. All of the Company’s tangible assets are held in the United States, and all of the Company’s collaboration revenue is derived from its collaboration partner headquartered in Switzerland.
Revenue Recognition for License and Collaboration Arrangements		Revenue Recognition for License and Collaboration Arrangements Effective January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract, determines which goods or services are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, that performance obligation is satisfied. The Company enters into licensing arrangements that are within the scope of ASC 606, under which it may exclusively license to third parties rights to research, develop, manufacture and commercialize its product candidates. The terms of these arrangements typically include payment to the Company of one or more of the following: nonrefundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and sales milestone payments; and royalties on net sales of licensed products. The payment terms under the Company’s existing licensing arrangements are 60 days. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its arrangements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the assessment of the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: (a) the performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above; and (c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company also uses judgment to determine whether milestone payments or other variable consideration, except for royalties and sales-based milestones, should be included in the transaction price, as described below. The transaction price is allocated to each performance obligation based on the relative standalone selling price of each performance obligation in the contract, and the Company recognizes revenue based on those amounts when, or as, the performance obligations under the contract are satisfied. The standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the standalone selling price of each of the identified performance obligations in the Company’s customer contracts, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis and there are no similar observable transactions in the marketplace, the Company estimates the standalone selling price of each performance obligation in its customer arrangements based on its estimate of costs to be incurred to fulfil its obligations associated with the performance, plus a reasonable margin. The Company has determined that its only contract liability under ASC 606 is deferred revenue. Amounts received prior to revenue recognition are recorded as deferred revenue in the consolidated balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion, in the consolidated balance sheets. Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from nonrefundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining promises, whether the value of the promise is dependent on the unsatisfied promises, whether there are other vendors that could provide the remaining promises, and whether it is separately identifiable from the remaining promises. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition. The measure of progress, and the resulting periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research, development and licensing arrangement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Under the Company’s existing license and collaboration agreements, the Company has concluded that the transfer of control to the customer occurs over the time period that the research and development services are to be provided by the Company, and this cost-to-cost Research and Development Services The promises under the Company’s license and collaboration arrangements often include research and development services to be performed by the Company on behalf of the partner. Payments or reimbursements resulting from the Company’s research and development efforts are estimated at the outset of the arrangement and considered part of the transaction price that is subsequently recognized as revenue because the Company is the principal in the arrangement for such efforts. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the Company evaluates the customer options to determine if they are material rights at the outset of each arrangement. Options to acquire additional goods or services for free or at a discount are deemed to be material rights. If the goods and services underlying the customer options are not determined to be material rights, these customer options are not considered to be performance obligations in the arrangement because they are contingent upon exercise of the option. If the customer options are determined to be a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. Milestone Payments At the inception of each arrangement that includes potential research, development or regulatory milestone payments, the Company evaluates whether the milestones are considered likely to be met and estimates the amount to be considered for inclusion in the transaction price using the most-likely-amount method. If it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur, the associated milestone payment value is included in the transaction price. For milestone payments due upon events that are not within the control of the Company or the licensee, such as regulatory approvals, the Company is not able to assert that it is likely that the regulatory approval will be granted and that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur until those approvals are received. In making this assessment, the Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the particular milestone. There is considerable judgment involved in determining whether it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price of the arrangement. Any such adjustments are recorded on a cumulative catch-up Royalties For arrangements that include sales-based royalties, including milestone payments due upon first commercial sales or based on a level of sales, that are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) the occurrence of the related sales or (ii) the date upon which the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue from any of its licensing arrangements.
Revenue Recognition for Government Grants		Revenue Recognition for Government Grants The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. Revenue from government grants is recognized as the qualifying expenses related to the contracts are incurred, provided that there is reasonable assurance of recoverability. The Company submits a budget, which outlines the expected project costs, to the funding government agency on a periodic basis. If the government agency approves the project proposed by the Company, the government agency funds the project upon receipt of the support for the costs incurred. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded as unbilled receivables, a component of prepaid expenses and other current assets, in the consolidated balance sheet. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss.
Research and Development Costs		Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and bonuses, stock-based compensation, employee benefits, facilities costs, laboratory supplies, depreciation, manufacturing expenses and external costs of vendors engaged to conduct preclinical development activities and clinical trials, as well as the costs of licensing technology and costs related to collaboration arrangements. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed in the period in which they are incurred. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed, or when it is no longer expected that the goods will be delivered or the services rendered.
Research and Manufacturing Contract Costs and Accruals		Research and Manufacturing Contract Costs and Accruals The Company has entered into various research, development and manufacturing contracts with research institutions and other companies in the United States. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research, development and manufacturing costs. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of period end. Any accrual estimates are based on a number of factors, including the Company’s knowledge of the progress towards completion of the research, development and manufacturing activities, invoicing to date under the contracts, communication from the research institutions and other companies of any actual costs incurred during the period that have not yet been invoiced and the costs included in the contracts. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs.
Patent Costs		Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
Stock-Based Compensation		Stock-Based Compensation For stock-based awards granted to employees and directors, the Company estimates the grant-date fair value of each award using the Black-Scholes option-pricing model. Compensation expense for these awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. Following the Company’s adoption of ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”), non-employees, non-employee The Company accounts for forfeitures of stock-based awards as they occur rather than applying an estimated forfeiture rate to stock-based compensation expense. The Company classifies stock-based compensation expense in the consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Comprehensive Loss		Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2018 and 2019, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities.
Net Income (Loss) per Share		Net Income (Loss) per Share The Company follows the two-class two-class two-class Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents. The Company’s convertible preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders for each of the years ended December 31, 2018 and 2019.
Income Taxes		Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”). non-employees 2018-07 2018-07 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) right-of-use No. 2018-11, Leases (Topic 842) Upon its adoption of ASC 842, the Company recognized right-of-use right-of-use Upon its adoption of ASC 842, the Company elected to apply the package of practical expedients permitted under the transition guidance to its entire lease portfolio as of January 1, 2019. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) whether the initial direct costs for any existing leases met the new definition of initial direct costs at the initial application date. In addition, the Company elected not to recognize a right-of-use The Company’s future commitments under lease obligations and additional disclosures are summarized in Note 11.	Recently Adopted Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting 2018-07”). non-employees 2018-07 2018-07 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) 2016-02”), right-of-use No. 2018-11, Leases (Topic 842) Upon its adoption of ASC 842, the Company recognized right-of-use right-of-use Upon its adoption of ASC 842, the Company elected to apply the package of practical expedients permitted under the transition guidance to its entire lease portfolio as of January 1, 2019. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) whether the initial direct costs for any existing leases met the new definition of initial direct costs at the initial application date. In addition, the Company elected not to recognize a right-of-use The Company’s future commitments under lease obligations and additional disclosures are summarized in Note 13.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement Topic 820 Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”), 2018-13 No. 2018-13 2018-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses Topic 326 Measurement of Credit Losses on Financial Instruments 2016-13”), 2016-13 available-for-sale No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief 2019-05”) , 2016-13. 2016-13 2019-05 In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 2018-18”). 2018-18 unit-of-account Collaborative Arrangements 2018-18 In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) 2019-12”), 2019-12. 2019-12	Recently Issued Accounting Pronouncements The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement Topic 820 Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”), 2018-13 No. 2018-13 2018-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses Topic 326 Measurement of Credit Losses on Financial Instruments 2016-13”), 2016-13 available-for-sale No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief 2019-05”) , 2016-13. 2016-13 2019-05 In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 2018-18”). 2018-18 unit-of-account Collaborative Arrangements 2018-18 No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) 2019-12”),

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of property plant and equipment useful life	Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: ESTIMATED USEFUL LIFE Machinery and equipment 3 to 5 years Furniture and fixtures 7 years Leasehold improvements Shorter of term of lease or 7 years

Marketable Securities and Fai_2

Marketable Securities and Fair Value Measurements (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of marketable securities by security type	Marketable securities by security type consisted of the following (in thousands): SEPTEMBER 30, 2020 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 8,006 $ 15 $ — $ 8,021 $ 8,006 $ 15 $ — $ 8,021 DECEMBER 31, 2019 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 44,028 $ 24 $ — $ 44,052 U.S. Treasury bills 14,969 6 — 14,975 $ 58,997 $ 30 $ — $ 59,027	Marketable securities by security type consisted of the following (in thousands): DECEMBER 31, 2018 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 13,986 $ — $ (1 ) $ 13,985 U.S. Treasury bills 33,361 — (3 ) 33,358 $ 47,347 $ — $ (4 ) $ 47,343 DECEMBER 31, 2019 AMORTIZED GROSS GROSS FAIR VALUE U.S. government agency bonds $ 44,028 $ 24 $ — $ 44,052 U.S. Treasury bills 14,969 6 — 14,975 $ 58,997 $ 30 $ — $ 59,027
Summary of fair value hierarchy for assets and liabilities	The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AT SEPTEMBER 30, 2020 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 106,997 $ — $ — $ 106,997 Marketable securities: U.S. government agency bonds — 8,021 — 8,021 $ 106,997 $ 8,021 $ — $ 115,018 FAIR VALUE MEASUREMENTS AT LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 37,071 $ — $ — $ 37,071 Marketable securities: U.S. government agency bonds — 44,052 — 44,052 U.S. Treasury bills — 14,975 — 14,975 $ 37,071 $ 59,027 $ — $ 96,098	The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2018 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 56,771 $ — $ — $ 56,771 U.S. Treasury bills — 2,799 — 2,799 Marketable securities: U.S. government agency bonds — 13,985 — 13,985 U.S. Treasury bills — 33,358 — 33,358 $ 56,771 $ 50,142 $ — $ 106,913 FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2019 USING: LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Cash equivalents: Money market funds $ 37,071 $ — $ — $ 37,071 Marketable securities: U.S. government agency bonds — 44,052 — 44,052 U.S. Treasury bills — 14,975 — 14,975 $ 37,071 $ 59,027 $ — $ 96,098

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense and Other Assets, Current [Abstract]
Summary of prepaid expenses and other current assets	Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid expenses $ 1,844 $ 1,452 Interest receivable 61 206 Unbilled receivables — 4 $ 1,905 $ 1,662	Prepaid expenses and other current assets consisted of the following (in thousands): DECEMBER 31, 2018 2019 Prepaid expenses $ 648 $ 1,452 Unbilled receivables 304 4 Interest receivable 83 206 $ 1,035 $ 1,662

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net [Abstract]
Summary of property and equipment, net	Property and equipment, net consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Machinery and equipment $ 6,037 $ 5,655 Leasehold improvements 436 2,650 Furniture and fixtures 579 353 7,052 8,658 Less: Accumulated depreciation and amortization (3,202 ) (3,495 ) $ 3,850 $ 5,163	Property and equipment, net consisted of the following (in thousands): DECEMBER 31, 2018 2019 Machinery and equipment $ 3,748 $ 5,655 Leasehold improvements 2,650 2,650 Furniture and fixtures 234 353 Construction-in-progress 22 — 6,654 8,658 Less: Accumulated depreciation and amortization (2,225 ) (3,495 ) $ 4,429 $ 5,163

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Summary of accrued expenses	Accrued expenses consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, 2020 2019 Accrued external research, development and manufacturing costs $ 2,696 $ 3,220 Accrued employee compensation and benefits 1,880 1,878 Accrued licensing fees (Note 11) 777 697 Other 526 1,266 $ 5,879 $ 7,061	Accrued expenses consisted of the following (in thousands): DECEMBER 31, 2018 2019 Accrued external research, development and manufacturing costs $ 673 $ 3,220 Accrued employee compensation and benefits 1,367 1,878 Accrued licensing fees (Note 12) 1,168 697 Current portion of deferred rent 303 — Other 228 1,266 $ 3,739 $ 7,061

Preferred Stock (Tables)

Preferred Stock (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity [Abstract]
Summary of preferred stock	As of September 30, 2020 and December 31, 2019, Preferred Stock consisted of the following (in thousands, except share amounts): SEPTEMBER 30, 2020 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 5,037,348 4,897,428 67,956 68,253 5,156,975 17,044,139 16,904,219 $ 174,357 $ 169,648 17,800,084 DECEMBER 31, 2019 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 4,664,011 1,862,236 25,708 25,953 1,960,934 16,670,802 13,869,027 $ 132,109 $ 127,348 14,604,043	As of December 31, 2018 and 2019, Preferred Stock consisted of the following (in thousands, except share amounts): DECEMBER 31, 2018 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,061,300 6,010,140 71,103 71,253 6,328,657 12,057,951 12,006,791 $ 106,401 $ 101,395 12,643,109 DECEMBER 31, 2019 SHARES ISSUED AND CARRYING LIQUIDATION COMMON STOCK Series Seed 350,858 350,858 $ 975 $ 1,000 369,452 Series A 1,490,035 1,490,035 6,469 5,081 1,569,001 Series B 4,155,758 4,155,758 27,854 24,061 4,375,999 Series C 6,010,140 6,010,140 71,103 71,253 6,328,657 Series D 4,664,011 1,862,236 25,708 25,953 1,960,934 16,670,802 13,869,027 $ 132,109 $ 127,348 14,604,043

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Schedule of Fair Value of Stock Option Awards on the Grant Date Using the Black-Scholes Option Valuation Model	The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Fair value of common stock $ 10.36 $ 6.14 $ 9.07 $ 5.77 Expected term (years) 6.0 6.0 6.0 6.0 Expected volatility 76.7 % 69.5 % 75.2 % 69.1 % Risk-free interest rate 0.37 % 1.89 % 0.66 % 2.40 % Expected annual dividend yield 0 % 0 % 0 % 0 %	The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted: YEAR ENDED 2018 2019 Fair value of common stock $ 4.65 $ 6.49 Expected term (years) 6.0 6.0 Expected volatility 66.5 % 69.3 % Risk-free interest rate 3.00 % 2.15 % Expected annual dividend yield 0 % 0 %
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since December 31, 2019: NUMBER OF WEIGHTED- WEIGHTED- INTRINSIC (in years) (in thousands) Outstanding at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Granted 1,157,893 9.08 Exercised (22,974 ) 1.93 Forfeited or canceled (530,117 ) 4.62 Outstanding at September 30, 2020 3,744,451 $ 5.67 7.88 $ 20,620 Vested and expected to vest at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Vested and expected to vest at September 30, 2020 3,744,451 $ 5.67 7.88 $ 20,620 Options exercisable at December 31, 2019 870,219 $ 2.94 7.68 $ 4,235 Options exercisable at September 30, 2020 1,486,775 $ 3.69 6.08 $ 11,132	The following table summarizes the Company’s stock option activity since December 31, 2018: NUMBER OF WEIGHTED- WEIGHTED- INTRINSIC (in years) (in thousands) Outstanding at December 31, 2018 2,013,769 $ 3.42 9.00 $ 3,595 Granted 1,340,467 5.14 Exercised (46,259 ) 1.84 Forfeited or canceled (168,328 ) 3.09 Outstanding at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Vested and expected to vest at December 31, 2019 3,139,649 $ 4.20 8.69 $ 11,303 Options exercisable at December 31, 2019 870,219 $ 2.94 7.68 $ 4,235
Summary of Restricted Common Stock		The following table summarizes the Company’s restricted stock award activity since December 31, 2018: NUMBER WEIGHTED- GRANT-DATE Unvested at December 31, 2018 25,880 $ 1.16 Vested (25,880 ) 1.16 Unvested at December 31, 2019 — $ —
Summary of Stock-Based Compensation Expense	Stock-based compensation expense related to stock options and restricted stock awards was classified in the consolidated statements of operations as follows (in thousands): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Research and development expenses $ 296 $ 174 $ 811 $ 525 General and administrative expenses 500 317 1,436 936 $ 796 $ 491 $ 2,247 $ 1,461	Stock-based compensation expense related to stock options and restricted stock awards was classified in the consolidated statements of operations as follows (in thousands): YEAR ENDED 2018 2019 Research and development expenses $ 112 $ 718 General and administrative expenses 478 1,390 $ 590 $ 2,108

Income Taxes (Table)

Income Taxes (Table)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
A reconciliation of the U.S. federal statutory income tax rate	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: YEAR ENDED 2018 2019 Federal statutory income tax rate (21.0 )% (21.0 )% State income taxes, net of federal benefit (6.4 ) (6.4 ) Federal and state research and development tax credits (9.9 ) (8.0 ) Other 0.4 0.3 Change in deferred tax asset valuation allowance 36.9 35.1 Effective income tax rate 0.0 % 0.0 %
Net deferred tax assets	The Company’s net deferred tax assets consisted of the following (in thousands): DECEMBER 31, 2018 2019 Deferred tax assets: Net operating loss carryforwards $ 9,598 $ 9,082 Research and development tax credit carryforwards 3,763 6,368 Deferred revenue 526 9,895 Deferred expenses 433 — Operating lease liabilities — 11,590 Stock-based compensation and other accrued expenses 180 603 Other 92 286 Total deferred tax assets 14,592 37,824 Deferred tax liabilities: Depreciation (541 ) (703 ) Operating lease right-of-use — (11,785 ) Total deferred tax liabilities (541 ) (12,488 ) Valuation allowance (14,051 ) (25,336 ) Net deferred tax assets $ — $ —
Summary of Valuation Allowance	For the years ended December 31, 2018 and 2019, the valuation allowance increased primarily due to increases in NOL carryforwards and research and development tax credit carryforwards as well as the increase in deferred revenue in 2019, and was as follows (in thousands): YEAR ENDED 2018 2019 Valuation allowance at beginning of year $ (6,953 ) $ (14,051 ) Increases recorded to income tax provision (7,098 ) (11,285 ) Valuation allowance at end of year $ (14,051 ) $ (25,336 )

Leases (Tables)

Leases (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases		As of December 31, 2018, future minimum commitments under the Company’s operating leases were as follows (in thousands): YEAR ENDING DECEMBER 31, 2019 $ 1,312 2020 4,840 2021 4,983 2022 5,130 2023 4,905 Thereafter 27,370 $ 48,540
Summary of Components of Lease Cost and Other Information	The components of lease cost and other information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Lease cost: Operating lease cost $ 3,231 $ 823 $ 9,345 $ 1,189 Variable lease cost 306 121 908 383 Short-term lease cost — 39 21 72 $ 3,537 $ 983 $ 10,274 $ 1,644
Summary of Operating Lease Lessee Balance Sheet and Related Disclosures	SEPTEMBER 30, DECEMBER 31, Other information: Weighted-average remaining lease term (in years) 6.9 7.9 Weighted-average discount rate 7.1 % 8.2 %
Summary of Supplementary Cash Flow Information Relating to Operating Leases	Supplemental cash flow information related to the Company’s operating leases was as follows (in thousands): NINE MONTHS ENDED 2020 2019 Cash paid for amounts included in the measurement of operating lease liabilities: Operating cash flows from operating leases $ 8,820 $ 1,701 Lease assets obtained in exchange for lease obligations: Operating leases $ 17,049 $ 14,716	Supplemental cash flow information related to the Company’s operating leases was as follows (in thousands): YEAR ENDED Cash paid for amounts included in the measurement of operating lease liabilities: Operating cash flows from operating leases $ 5,161 Lease assets obtained in exchange for lease obligations: Operating leases $ 43,326
Disclosure Of Components Of Lease Cost And Balance Sheet Details Related To Leases [Table Text Block]		The components of lease cost and supplemental balance sheet information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): YEAR ENDED Lease cost: Operating lease cost $ 3,667 Variable lease cost 619 Short-term lease cost 112 $ 4,398 DECEMBER 31, Operating leases: Assets: Operating lease right-of-use $ 43,050 Liabilities: Current portion of operating lease liabilities $ 9,444 Operating lease liabilities, net of current portion 32,887 Total operating lease liabilities $ 42,331 Other information: Weighted-average remaining lease term (in years) 7.9 Weighted-average discount rate 8.2 %
Schedule of Future Minimum lease Payments for Operating Leases		Future minimum lease payments for operating leases with initial or remaining terms in excess of one year at December 31, 2019 were as follows (in thousands): YEAR ENDING DECEMBER 31, 2020 $ 12,546 2021 8,840 2022 5,130 2023 4,905 2024 4,297 Thereafter 23,072 Total lease payments 58,790 Less: Imputed interest (16,459 ) Total operating lease liabilities $ 42,331

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Research and Development [Abstract]
Summary of Changes in the Total Contract Liability	Contract Liability The changes in the total contract liability (deferred revenue) balances related to the Company’s license and collaboration agreements with Roche were as follows (in thousands): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Balance at beginning of period $ 51,917 $ 48,873 $ 40,453 $ 45,598 Deferral of revenue 1,891 1,255 25,746 13,555 Recognition of deferred revenue (6,120 ) (4,050 ) (18,511 ) (13,075 ) Balance at end of period $ 47,688 $ 46,078 $ 47,688 $ 46,078	The changes in the total contract liability (deferred revenue) balances related to the Company’s license and collaboration agreements with Roche were as follows (in thousands): YEAR ENDED 2018 2019 Balance at beginning of period $ 8,773 $ 45,598 Deferral of revenue 48,364 14,173 Recognition of deferred revenue (11,539 ) (19,318 ) Balance at end of period $ 45,598 $ 40,453

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Summary of basic and diluted net loss per share attributable to common stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Numerator: Net loss attributable to common stockholders $ (12,351 ) $ (7,883 ) $ (32,920 ) $ (21,943 ) Denominator: Weighted-average common shares outstanding, basic and diluted 1,758,039 1,722,300 1,744,948 1,696,104 Net loss per share attributable to common stockholders, basic and diluted $ (7.03 ) $ (4.58 ) $ (18.87 ) $ (12.94 )	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): YEAR ENDED DECEMBER 31, 2018 2019 Numerator: Net loss $ (19,250 ) $ (32,202 ) Accretion of redeemable convertible preferred stock to redemption value (984 ) — Net loss attributable to common stockholders $ (20,234 ) $ (32,202 ) Denominator: Weighted-average common shares outstanding, basic and diluted 1,586,683 1,704,509 Net loss per share attributable to common stockholders, basic and diluted $ (12.75 ) $ (18.89 )
Summary of potentially dilutive shares excluded from the calculation of diluted net loss	The Company’s potential dilutive securities, which include convertible preferred stock, a warrant to purchase common stock and common stock options, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: SEPTEMBER 30, 2020 2019 Convertible preferred stock (as converted to common stock) 17,800,084 12,643,109 Warrant to purchase common stock 2,038 2,038 Stock options to purchase common stock 3,744,451 2,715,875 21,546,573 15,361,022	The Company’s potential dilutive securities, which include convertible preferred stock, a warrant to purchase common stock, common stock options and unvested restricted common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: YEAR ENDED DECEMBER 31, 2018 2019 Convertible preferred stock (as converted to common stock) 12,643,109 14,604,043 Warrant to purchase common stock 2,038 2,038 Stock options to purchase common stock 2,013,769 3,139,649 Unvested restricted common stock 25,880 — 14,684,796 17,745,730

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Nov. 30, 2020	Nov. 12, 2020	Nov. 03, 2020	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Income (loss) from continuing operations					$ (32,900)	$ (32,200)
Accumulated deficit					109,168	76,248	$ 44,046
Proceeds from temporary equity shares issued					$ 42,248	$ 25,953	$ 68,029
Subsequent Event [Member]
Common stock shares issued upon conversion	17,800,084
Proceeds from temporary equity shares issued				$ 42,300
Subsequent Event [Member] | Redeemable Convertible Preferred Stock [Member]
Common stock shares issued upon conversion		17,800,084
Subsequent Event [Member] | IPO [Member]
Stock shares issued during the period new issues shares			4,411,765
Proceeds from initial public offer net of underwriting discounts and before payment of offering costs		$ 75,500
Offering costs payable		$ 2,800	$ 2,800
Subsequent Event [Member] | Over-Allotment Option [Member]
Stock shares issued during the period new issues shares		661,764

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017	Jan. 01, 2017
Summary of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 0	$ 0
Accounts Receivable, Allowance for Credit Loss	0	0
Letter of credit outstanding	2,300	2,300
Restricted cash, noncurrent	2,300	2,300
Cash and cash equivalents, at carrying value	39,255	59,570	$ 107,060
Operating lease right-of-use assets	43,050		50,807
Operating lease, liability	42,331
Decrease to accumulated deficit						$ (400)
Provision For Doubtful Accounts	0	0
Cash Balance To Be Maintained	2,300
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	41,574	61,875	109,365	$ 31,967	$ 9,620
Impairment losses on long-lived assets	$ 0	$ 0
Income Tax Examination, Likelihood Percentage	50.00%
Accounting Standards Update 2016-02 [Member]
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 2,700		2,700
Operating lease, liability	$ 4,200		$ 4,200

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Property Plant and Equipment Useful Life (Detail)	12 Months Ended
	Dec. 31, 2019
Machinery and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Machinery and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	Shorter of term of lease or 7 years

Marketable Securities and Fai_3

Marketable Securities and Fair Value Measurements - Summary of Marketable Securities by Security Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 8,006	$ 58,997	$ 47,347
Gross Unrealized Gains	15	30
Gross Unrealized Losses			(4)
Fair Value	8,021	59,027	47,343
U.S. Government Agency Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,006	44,028	13,986
Gross Unrealized Gains	15	24
Gross Unrealized Losses			(1)
Fair Value	$ 8,021	44,052	13,985
U.S. Treasury Bills [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		14,969	33,361
Gross Unrealized Gains		6
Gross Unrealized Losses			(3)
Fair Value		$ 14,975	$ 33,358

Marketable Securities and Fai_4

Marketable Securities and Fair Value Measurements - Summary of Fair Value Hierarchy for Assets and Liabilities (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets:
Assets, fair value disclosure	$ 115,018	$ 96,098	$ 106,913
Level 1 [Member]
Assets:
Assets, fair value disclosure	106,997	37,071	56,771
Level 2 [Member]
Assets:
Assets, fair value disclosure	8,021	59,027	50,142
Cash equivalents [Member] | Money Market Funds [Member]
Assets:
Assets, fair value disclosure	106,997	37,071	56,771
Cash equivalents [Member] | Money Market Funds [Member] | Level 1 [Member]
Assets:
Assets, fair value disclosure	106,997	37,071	56,771
Cash equivalents [Member] | U.S. Treasury Bills [Member]
Assets:
Assets, fair value disclosure			2,799
Cash equivalents [Member] | U.S. Treasury Bills [Member] | Level 2 [Member]
Assets:
Assets, fair value disclosure			2,799
Marketable securities [Member] | U.S. Government Agency Bonds [Member]
Assets:
Assets, fair value disclosure	8,021	44,052	13,985
Marketable securities [Member] | U.S. Government Agency Bonds [Member] | Level 2 [Member]
Assets:
Assets, fair value disclosure	$ 8,021	44,052	13,985
Marketable securities [Member] | U.S. Treasury Bills [Member]
Assets:
Assets, fair value disclosure		14,975	33,358
Marketable securities [Member] | U.S. Treasury Bills [Member] | Level 2 [Member]
Assets:
Assets, fair value disclosure		$ 14,975	$ 33,358

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 1,844	$ 1,452	$ 648
Unbilled receivables		4	304
Interest receivable	61	206	83
Total prepaid expenses and other current assets	$ 1,905	$ 1,662	$ 1,035

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net [Abstract]
Machinery and equipment	$ 6,037	$ 5,655	$ 3,748
Leasehold improvements	436	2,650	2,650
Furniture and fixtures	579	353	234
Construction in Progress			22
Total property and equipment, gross	7,052	8,658	6,654
Less: Accumulated depreciation and amortization	(3,202)	(3,495)	(2,225)
Total property and equipment, net	$ 3,850	$ 5,163	$ 4,429

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Depreciation and amortization expense		$ 300	$ 400	$ 1,011	$ 1,006	$ 1,384	$ 1,067
Leasehold improvements gross		436		436		2,650	2,650
Accumulated depreciation related to those leasehold improvements		3,202		3,202		3,495	2,225
Property and equipment, net		$ 3,850		3,850		$ 5,163	$ 4,429
Gain loss on termination of lease				$ (108)
2016 Lease [Member]
Leasehold improvements gross	$ 2,700
Accumulated depreciation related to those leasehold improvements	1,300
Gain loss on termination of lease	(100)
2016 Lease [Member] | Leasehold Improvements [Member]
Property and equipment, net	$ 1,400

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued external research, development and manufacturing costs	$ 2,696	$ 3,220	$ 673
Accrued employee compensation and benefits	1,880	1,878	1,367
Accrued licensing fees (Note 11)	777	697	1,168
Current portion of deferred rent			303
Other	526	1,266	228
Total accrued expenses	$ 5,879	$ 7,061	$ 3,739

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	Nov. 30, 2017	Oct. 30, 2015	May 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2016
Short-term Debt [Line Items]
Debt outstanding				$ 0	$ 0
Series C Convertible Preferred Stock [Member]
Short-term Debt [Line Items]
Borrowings face amount			$ 3,000,000
Covertible promissory notes accrued interest write off			$ 100,000
Shares issued on convertible promissory note			259,328
Warrant [Member]
Short-term Debt [Line Items]
Borrowings face amount		$ 1,000,000
Number of shares issued as warrant		7,114
Number of shares issued as warrant price per share		$ 2.11
Number of shares as warrant exercisable		2,038
Warrants and rights expiry date		Oct. 20, 2025
Warrants outstanding				2,038	2,038
Warrant [Member] | Amendment Two [Member]
Short-term Debt [Line Items]
Number of shares issued as warrant						23,692
Number of shares issued as warrant price per share						$ 4.28
Warrants and rights expiry date						Jun. 30, 2018
Warrant [Member] | Amendment One [Member]
Short-term Debt [Line Items]
Borrowings face amount						$ 2,000,000
Additional borrowings						3,000,000
Warrant [Member] | Amendment One [Member] | Maximum [Member]
Short-term Debt [Line Items]
Borrowings face amount						$ 5,000,000
Convertible Notes Payable [Member]
Short-term Debt [Line Items]
Borrowings face amount	$ 3,000,000
Debt instrument interest rate percentage	6.00%
Proceeds from conertible promissory note	$ 30,000,000
Debt instrument maturity date	Feb. 28, 2019

Preferred Stock - Summary of Pr

Preferred Stock - Summary of Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Shares Authorized	17,044,139	16,670,802	12,057,951
Shares issued	16,904,219	13,869,027	12,006,791
Shares outstanding	16,904,219	13,869,027	12,006,791
Carrying Amount	$ 174,357	$ 132,109	$ 106,401
Liquidation Preference	$ 169,648	$ 127,348	$ 101,395
Common stock issuable upon conversion	17,800,084	14,604,043	12,643,109
Series Seed
Temporary Equity [Line Items]
Shares Authorized	350,858	350,858	350,858
Shares issued	350,858	350,858	350,858
Shares outstanding	350,858	350,858	350,858
Carrying Amount	$ 975	$ 975	$ 975
Liquidation Preference	$ 1,000	$ 1,000	$ 1,000
Common stock issuable upon conversion	369,452	369,452	369,452
Series A
Temporary Equity [Line Items]
Shares Authorized	1,490,035	1,490,035	1,490,035
Shares issued	1,490,035	1,490,035	1,490,035
Shares outstanding	1,490,035	1,490,035	1,490,035
Carrying Amount	$ 6,469	$ 6,469	$ 6,469
Liquidation Preference	$ 5,081	$ 5,081	$ 5,081
Common stock issuable upon conversion	1,569,001	1,569,001	1,569,001
Series B
Temporary Equity [Line Items]
Shares Authorized	4,155,758	4,155,758	4,155,758
Shares issued	4,155,758	4,155,758	4,155,758
Shares outstanding	4,155,758	4,155,758	4,155,758
Carrying Amount	$ 27,854	$ 27,854	$ 27,854
Liquidation Preference	$ 24,061	$ 24,061	$ 24,061
Common stock issuable upon conversion	4,375,999	4,375,999	4,375,999
Series C
Temporary Equity [Line Items]
Shares Authorized	6,010,140	6,010,140	6,061,300
Shares issued	6,010,140	6,010,140	6,010,140
Shares outstanding	6,010,140	6,010,140	6,010,140
Carrying Amount	$ 71,103	$ 71,103	$ 71,103
Liquidation Preference	$ 71,253	$ 71,253	$ 71,253
Common stock issuable upon conversion	6,328,657	6,328,657	6,328,657
Series D
Temporary Equity [Line Items]
Shares Authorized	5,037,348	4,664,011
Shares issued	4,897,428	1,862,236
Shares outstanding	4,897,428	1,862,236
Carrying Amount	$ 67,956	$ 25,708
Liquidation Preference	$ 68,253	$ 25,953
Common stock issuable upon conversion	5,156,975	1,960,934

Preferred Stock - Additional In

Preferred Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands	Nov. 30, 2020shares	Jun. 30, 2020$ / sharesshares	May 31, 2020USD ($)$ / sharesshares	Feb. 29, 2020$ / sharesshares	Jan. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	May 31, 2018USD ($)$ / sharesshares	Nov. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Jul. 31, 2015USD ($)$ / sharesshares	Jun. 30, 2015USD ($)$ / sharesshares	Mar. 31, 2014USD ($)$ / sharesshares	Jun. 30, 2020USD ($)$ / sharesshares	Feb. 29, 2020USD ($)$ / sharesshares	Jul. 31, 2015$ / sharesshares	Jun. 30, 2020USD ($)$ / shares	Oct. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)
Temporary Equity [Line Items]
Proceeds from temporary equity shares issued | $																		$ 42,248	$ 25,953	$ 68,029
Issuance costs | $																		43	$ 245	$ 150
Percentage of change in fair value of stock																			1,000
Preferred Stock, Voting Rights																			The holders of Preferred Stock are entitled to the number of votes equal to the number of shares of common stock into which each share of Preferred Stock is convertible as of the record date for determining stockholders entitled to vote on such matters.
Preferred Stock, Dividends Per Share, Declared																			$ 0
Temporary equity Non - cumulative dividend percentage rate																			6.00%
Payments of initial public offering costs | $																		$ (290)
Subsequent Event [Member]
Temporary Equity [Line Items]
Proceeds from temporary equity shares issued | $																$ 42,300
Common stock shares issued upon conversion | shares	17,800,084
Minimum [Member]
Temporary Equity [Line Items]
Percentage of change in fair value of stock																			10
Payments of initial public offering costs | $																			$ 50,000
Series Seed Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price												$ 2.85
Proceeds from temporary equity shares issued | $												$ 1,000
Temporary Equity, Shares Issued During Period | shares												350,858
Original Issue Price per share						$ 2.85													$ 2.85
Conversion price per share						2.7066													2.7066
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price										$ 3.41	$ 3.41				$ 3.41
Proceeds from temporary equity shares issued | $										$ 5,100	$ 5,100
Temporary Equity, Shares Issued During Period | shares										1,490,035	1,490,035				1,490,035
Original Issue Price per share						3.41													3.41
Conversion price per share						3.2384													3.2384
Series B Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price								$ 5.79	$ 5.79
Proceeds from temporary equity shares issued | $								$ 24,100	$ 24,100
Temporary Equity, Shares Issued During Period | shares								4,155,758	4,155,758
Original Issue Price per share						5.79													5.79
Conversion price per share						5.4986													5.4986
Series C Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price							$ 11.8555										$ 11.8555
Proceeds from temporary equity shares issued | $							$ 48,600										$ 19,600
Shares issued on convertible promissory note | shares							259,328
Shares issued on convertible promissory note value | $							$ 3,100
Issuance costs | $																	$ 200
Temporary Equity, Shares Issued During Period | shares							4,094,794										1,656,018
Original Issue Price per share						11.8555													11.8555
Conversion price per share						11.2588													11.2588
Series C Convertible Preferred Stock [Member] | Maximum [Member]
Temporary Equity [Line Items]
Temporary Equity, Shares Issued During Period | shares							4,354,122
Series D Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price		$ 13.9365	$ 13.9365	$ 13.9365	$ 13.9365	$ 13.9365							$ 13.9365	$ 13.9365		$ 13.9365			13.9365
Proceeds from temporary equity shares issued | $			$ 27,000		$ 15,200	$ 26,000							$ 27,000	$ 15,200
Issuance costs | $						$ 200							$ 100	$ 100
Temporary Equity, Shares Issued During Period | shares		1,940,945	1,940,945	1,094,247	1,094,247	1,862,236							1,940,945	1,094,247
Original Issue Price per share						$ 13.9365													13.9365
Conversion price per share						$ 13.2351													$ 13.2351

Common Stock - Additional Infor

Common Stock - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019Directors
Stockholders' Equity Note [Abstract]
Common stock description of voting rights	one vote
Number Of Directors Entitled To Elect	3

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Fair Value of Stock Option Awards on the Grant Date Using the Black-Scholes Option Valuation Model (Detail) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Fair value of common stock	$ 10.36	$ 6.14	$ 9.07	$ 5.77	$ 6.49	$ 4.65
Expected term (years)	6 years	6 years	6 years	6 years	6 years	6 years
Expected volatility	76.70%	69.50%	75.20%	69.10%	69.30%	66.50%
Risk-free interest rate	0.37%	1.89%	0.66%	2.40%	2.15%	3.00%
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Shares - Outstanding at December 31, 2018	3,139,649	2,013,769
Granted	1,157,893	1,340,467
Exercised	(22,974)	(46,259)
Forfeited or canceled	(530,117)	(168,328)
Number Of Shares - Outstanding at September 30, 2019	3,744,451	3,139,649	2,013,769
Number Of Shares - Vested and expected to vest at December 31, 2019	3,139,649	3,139,649
Number Of Shares - Vested and expected to vest at September 30, 2020	3,744,451	3,139,649	3,139,649
Number Of Shares - Options exercisable at December 31, 2019	870,219	870,219
Number Of Shares - Options exercisable at September 30, 2020	1,486,775	870,219	870,219
Weighted Average Exercise price - Outstanding at December 31, 2018	$ 4.20	$ 3.42
Granted	9.08	5.14
Exercised	1.93	1.84
Forfeited or canceled	4.62	3.09
Weighted Average Exercise price - Outstanding at September 30, 2019	5.67	4.20	$ 3.42
Weighted Average Exercise price - Vested and expected to vest at December 31, 2019	4.20	4.20
Weighted Average Exercise price - Vested and expected to vest at September 30, 2020	5.67	4.20	4.20
Weighted Average Exercise price - Options exercisable at December 31, 2019	2.94	2.94
Weighted Average Exercise price - Options exercisable at September 30, 2020	$ 3.69	$ 2.94	$ 2.94
Weighted-Average Remaining Contractual Term	7 years 10 months 17 days	8 years 8 months 8 days	9 years
Weighted-Average Remaining Contractual Term - Vested and expected to vest	7 years 10 months 17 days	8 years 8 months 8 days
Weighted-Average Remaining Contractual Term - Options exercisable	6 years 29 days	7 years 8 months 4 days
Aggregate Intrinsic Value - Outstanding	$ 20,620	$ 11,303	$ 3,595
Aggregate Intrinsic Value - Vested and expected to vest	20,620	11,303
Aggregate Intrinsic Value - Options exercisable	$ 11,132	$ 4,235

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Restricted Common Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Number of shares Unvested at December 31, 2018	0	25,880
Number of shares Vested	(25,880)
Number of shares Unvested at December 31, 2019	0	25,880
Weighted average grant date fair value Unvested at December 31, 2018	$ 0	$ 1.16
Weighted average grant date fair value Vested	1.16
Weighted average grant date fair value Unvested at December 31, 2019	$ 0	$ 1.16

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 796	$ 491	$ 2,247	$ 1,461	$ 2,108	$ 590
Research and Development Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	296	174	811	525	718	112
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 500	$ 317	$ 1,436	$ 936	$ 1,390	$ 478

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
StockBased Compensation [Line Items]
Unrecognized compensation expense related to unvested stock based awards	$ 10.6		$ 10.6		$ 7.7
Unrecognized compensation expense expected period for recognition			2 years 10 months 24 days		3 years
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Weighted-average grant-date fair value of stock options granted	$ 6.82	$ 4.20	$ 5.92	$ 3.89	$ 4.37	$ 2.54
Percentage of change in fair value of stock					1,000
Purchase price of common stock expressed as a percentage of its fair value.					110.00%
Share based payments expiry period					4 years
Share based payments aggregate intrinsic value of stock options exercised					$ 0.3	$ 0.1
Share based payment aggregate intrinsic value of restricted stock awards vested					$ 200,000	$ 400,000
Twenty Fourteen Stock Incentive Plan [Member]
StockBased Compensation [Line Items]
Number of shares of common stock authorised for issue	4,853,361		4,853,361		4,853,361
Common stock shares reserved for future issuance	714,737		714,737		1,342,523

Income Taxes - A reconciliation

Income Taxes - A reconciliation of the U.S. federal statutory income tax rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)
State income taxes, net of federal benefit	(6.40%)	(6.40%)
Federal and state research and development tax credits	(8.00%)	(9.90%)
Other	0.30%	0.40%
Change in deferred tax asset valuation allowance	35.10%	36.90%
Effective income tax rate	0.00%	0.00%

Income Taxes - Net deferred tax

Income Taxes - Net deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 9,082	$ 9,598
Research and development tax credit carryforwards	6,368	3,763
Deferred revenue	9,895	526
Deferred expenses	0	433
Operating lease liabilities	11,590	0
Stock-based compensation and other accrued expenses	603	180
Other	286	92
Total deferred tax assets	37,824	14,592
Deferred tax liabilities:
Depreciation	(703)	(541)
Operating lease right-of-use assets	(11,785)
Total deferred tax liabilities	(12,488)	(541)
Valuation allowance	$ (25,336)	$ (14,051)	$ (6,953)

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Net of Valuation Allowance [Abstract]
Valuation allowance at beginning of year	$ (14,051)	$ (6,953)
Increases recorded to income tax provision	(11,285)	(7,098)
Valuation allowance at beginning of year	$ (25,336)	$ (14,051)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Mar. 27, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax benefits		$ 0	$ 0	$ 0	$ 0
Income Tax Disclosure [Line Items]
Percentage of net operating loss carryforwards eligible for deduction							80.00%
Miniumum ownership percentage to be maintanied by the existing owners						50.00%
Period for which minimum shareholding percentage shall be maintained						3 years
Corporate statutory tax rate						21.00%	21.00%
Accrued interest and penalties on unrecognised tax position						$ 0	$ 0
Unrecognised tax penalties income tax penalties and interest expense						0	0
Unrecognized Tax Benefits						0	$ 0
Covid Nineteen | Annual Limitation On Deduction Rolled Back
Income Tax Disclosure [Line Items]
Percentage of net operating loss carryforwards eligible for deduction	80.00%
Maximum [Member]
Income Tax Disclosure [Line Items]
Corporate statutory tax rate							35.00%
Minimum [Member]
Income Tax Disclosure [Line Items]
Corporate statutory tax rate							21.00%
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards						33,300,000
Domestic Tax Authority [Member] | Tax Year 2035
Income Tax Disclosure [Line Items]
Operating loss carryforwards						11,700,000
Domestic Tax Authority [Member] | Can Be Indefinitely Carried Forward [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards						$ 21,600,000
Domestic Tax Authority [Member] | Maximum [Member]
Income Tax Disclosure [Line Items]
Percentage of net operating loss carryforwards eligible for deduction						80.00%
Domestic Tax Authority [Member] | Research [Member] | Tax Year 2035
Income Tax Disclosure [Line Items]
Research and development tax credit forwards						$ 4,400,000
State and Local Jurisdiction [Member] | Tax Year 2035
Income Tax Disclosure [Line Items]
Operating loss carryforwards						33,100,000
State and Local Jurisdiction [Member] | Research [Member] | Tax Year 2035
Income Tax Disclosure [Line Items]
Research and development tax credit forwards						$ 2,500,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Commitments and contingencies liabilities
Accrued license fees, current	$ 777		$ 777		697	1,168
Research and development expense	13,910	$ 8,489	37,815	$ 26,324	36,102	24,379
Research and development	13,910	8,489	37,815	26,324	36,102	24,379
Discretionary contribution by the employer to defined contribution benefit plan			300	200	300	200
Sublicense Agreement [Member]
Other Commitments [Line Items]
Research and development expense					800	2,800
Research and development					800	2,800
Accrued expenses
Other Commitments [Line Items]
Accrued license fees, current	800		800		700
Other liabilities
Other Commitments [Line Items]
Accrued License Fees, Noncurrent	700		700		700
Massachusetts Institute of Technology [Member]
Other Commitments [Line Items]
Commitments and contingencies liabilities	1,500		1,500		1,400
Accrued license fees, current	800		800		700
Research and development expense	0	100	0	600	1,000
Milestone payment payable					1,800
Research and development	0	100	0	600	1,000
Annual license maintanance fee payable					100
Massachusetts Institute of Technology [Member] | Sublicense Agreement [Member]
Other Commitments [Line Items]
Payment made pursuant to settlement agreement						900
Accrued license fees					1,400	2,000
Massachusetts Institute of Technology [Member] | Regulatory Milestone [Member]
Other Commitments [Line Items]
Milestone payment payable					1,000
Massachusetts Institute of Technology [Member] | Development Milestone [Member]
Other Commitments [Line Items]
Milestone payment payable					800
Maximum [Member]
Other Commitments [Line Items]
Discretionary contribution by the employer to defined contribution benefit plan	100	$ 100
Manufacturing Services Agreements [Member]
Other Commitments [Line Items]
Non cancellable purchase commitements	$ 0		$ 0		0	$ 400
Erytech [Member] | License Agreement With Erytech [Member]
Other Commitments [Line Items]
Research and development expense				1,000	1,000
Milestone payment payable					6,000
Research and development				$ 1,000	1,000
Specified milestone payment payable					$ 50,000
Number of days notice for agreement termination					60 days
Erytech [Member] | License Agreement With Erytech [Member] | Regulatory Milestone [Member]
Other Commitments [Line Items]
Milestone payment payable					$ 5,000
Erytech [Member] | License Agreement With Erytech [Member] | Development Milestone [Member]
Other Commitments [Line Items]
Milestone payment payable					$ 1,000

Leases - Summary of Components

Leases - Summary of Components of Lease Cost and Other Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 3,231	$ 823	$ 9,345	$ 1,189	$ 3,667
Variable lease cost	306	121	908	383	112
Short-term lease cost		39	21	72	619
Lease, Cost	$ 3,537	$ 983	$ 10,274	$ 1,644	$ 4,398

Leases - Summary of Operating L

Leases - Summary of Operating Lease Lessee Balance Sheet and Related Disclosures (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lease cost:
Operating lease cost	$ 3,231	$ 823	$ 9,345	$ 1,189	$ 3,667
Variable lease cost		39	21	72	619
Short-term lease cost	306	121	908	383	112
Lease Cost	3,537	$ 983	10,274	$ 1,644	4,398
Operating leases:
Operating lease right-of-use assets	50,807		50,807		43,050
Current portion of operating lease liabilities	8,040		8,040		9,444
Operating lease liabilities, net of current portion	$ 41,323		$ 41,323		32,887
Total operating lease liabilities					$ 42,331
Other Information [Abstract]
Weighted-average remaining lease term (in years)	6 years 10 months 24 days		6 years 10 months 24 days		7 years 10 months 24 days
Weighted-average discount rate	7.10%		7.10%		8.20%

Leases - Summary of Supplementa

Leases - Summary of Supplementary Cash Flow Information Relating to Operating Leases (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Leases [Abstract]
Operating cash flows from operating leases	$ 8,820	$ 1,701	$ 5,161
Operating leases	$ 17,049	$ 14,716	$ 43,326

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($)	Jun. 01, 2020	Sep. 01, 2019	Jan. 01, 2019	Feb. 29, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2016	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Sep. 01, 2020
Lessee, Lease, Description [Line Items]
Lessee operating lease renewal term					5 years					5 years		5 years
Letter of credit outstanding					$ 2,300,000	$ 2,300,000						$ 2,300,000	$ 2,300,000
Cost of construction of leasehold improvements					2,650,000	2,650,000				$ 436,000		2,650,000	2,650,000
Operating lease right-of-use assets					$ 43,050,000					50,807,000		43,050,000
Operating lease liability										17,049,000	$ 14,716,000	$ 43,326,000
Gain (loss) on termination of operating lease										$ (108,000)
Operating lease rental expense													$ 1,000,000
Minimum [Member]
Lessee, Lease, Description [Line Items]
Operating lease term					3 years					3 years		3 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Operating lease term					10 years					10 years		10 years
Accounting Standards Update 2016-02 [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					$ 2,700,000					$ 2,700,000		$ 2,700,000
Office Building [Member] | Watertown Massauchets [Member] | Two Thousand And Sixteen Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Lessee operating lease month of expiry									2023-09
Initial annual base rent						$ 3.8	$ 900,000	$ 900,000
Initial annual base rent escalation percentage						3.00%	3.00%	3.00%
Cost of construction of leasehold improvements								$ 2,100,000	$ 2,100,000
Increase (decrease) in operating lease right of use assets				$ (2,100,000)
Increase (decrease) in leasehold improvements operating lease				(1,400,000)
Increase (decrease) in operating lease liability				$ (3,400,000)
Gain (loss) on termination of operating lease										(100,000)
Office Building [Member] | Watertown Massauchets [Member] | Two Thousand And Eighteen Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Lessee operating lease month of expiry						2029-11
Lessee operating lease renewal term						5 years							5 years
Initial annual base rent						$ 3,800,000
Initial annual base rent escalation percentage						3.00%
Letter of credit outstanding					2,300,000	$ 2,300,000						2,300,000	$ 2,300,000
Cash in escrow account					2,300,000	2,300,000						2,300,000	2,300,000
Cost of construction of leasehold improvements						$ 9,800,000							$ 9,800,000
Office Building [Member] | Watertown Massauchets [Member] | Deferred Rent [Member] | Two Thousand And Sixteen Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets								2,700,000	2,700,000
Incentive from lessor								2,100,000	2,100,000
Office Building [Member] | Watertown Massauchets [Member] | Accounting Standards Update 2016-02 [Member] | Two Thousand And Sixteen Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Cost of construction of leasehold improvements								$ 2,100,000	$ 2,100,000
Operating lease right-of-use assets			$ 2,700,000
Operating lease liability			$ 4,200,000
Office Building [Member] | Watertown Massauchets [Member] | Accounting Standards Update 2016-02 [Member] | Two Thousand And Eighteen Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					28,600,000							$ 28,600,000
Operating lease liability					$ 27,600,000
Machinery and Equipment [Member] | Embedded Lease [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 14,700,000
Operating lease liability		$ 14,700,000
Operating lease term		24 months
Machinery and Equipment [Member] | Embedded Lease Amendment Agreement One [Member] | Embedded Lease [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 900,000
Operating lease liability	$ 900,000
Machinery and Equipment [Member] | Embedded Lease Amendment Agreement Two [Member] | Embedded Lease [Member]
Lessee, Lease, Description [Line Items]
Lessee operating lease renewal term														1 year
Operating lease right-of-use assets										16,200,000
Operating lease liability										$ 16,200,000
Operating lease date of expiry										Aug. 31, 2022
Contractual payment obligations										$ 9,900,000

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Rental Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 1,312
2020	4,840
2021	4,983
2022	5,130
2023	4,905
Thereafter	27,370
Total lease payments	$ 48,540

Leases - Schedule of Future M_2

Leases - Schedule of Future Minimum lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 12,546
2021	8,840
2022	5,130
2023	4,905
2024	4,297
Thereafter	23,072
Total lease payments	58,790
Less: Imputed interest	(16,459)
Total operating lease liabilities	$ 42,331

License and Collaboration Agr_3

License and Collaboration Agreements - Summary of Changes in the Total Contract Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Research and Development [Abstract]
Balance at beginning of period	$ 51,917	$ 48,873	$ 40,453	$ 45,598	$ 45,598	$ 8,773
Deferral of revenue	1,891	1,255	25,746	13,555	14,173	48,364
Recognition of deferred revenue	(6,120)	(4,050)	(18,511)	(13,075)	(19,318)	(7,500)
Balance at end of period	$ 47,688	$ 46,078	$ 47,688	$ 46,078	$ 40,453	$ 45,598

License and Collaboration Agr_4

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	Dec. 31, 2015	Mar. 31, 2020	Oct. 31, 2018	Apr. 30, 2017	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015	Jun. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
License And Collaboration Agreements [Line Items]
Contract with customer liability revenue recognised					$ 6,120,000			$ 4,050,000				$ 18,511,000	$ 13,075,000	$ 19,318,000	$ 7,500,000
Contract with customer liability					47,688,000		$ 40,453,000	46,078,000		$ 51,917,000	$ 46,078,000	47,688,000	46,078,000	40,453,000	45,598,000		$ 48,873,000		$ 8,773,000
Milestone payment received		$ 20,000,000
Performance obligation revenue recognized					6,120,000			4,050,000				18,511,000	13,075,000	19,318,000	7,500,000
Two Thousand And Fifteen License And Collobration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Term Of Agreement	5 years
Contract with customer liability revenue recognised																$ 12,000,000
Performance obligation revenue recognized																12,000,000
2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Upfront payment received towards technology access fee												5,000,000		5,000,000
Reimbursement receivable for research and development costs incurred					1,000,000		1,000,000					1,000,000		1,000,000
2018 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable on exercise of option rights					100,000,000							100,000,000
Tranche One [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Reimbursement receivable for research and development costs incurred							500,000							500,000
Tranche Two [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Reimbursement receivable for research and development costs incurred							500,000							500,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | APC [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license					15,000,000							15,000,000
Roche [Member] | Maximum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | TCL [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license					100,000,000							100,000,000
Roche [Member] | Minimum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | TCL [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license					50,000,000							$ 50,000,000
Roche [Member] | Two Thousand And Fifteen License And Collobration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable	$ 486,000,000															486,000,000
Contract with customer liability revenue recognised															5,300,000
Performance obligation transaction price	$ 12,000,000															$ 12,000,000
Performance obligation revenue recognized															5,300,000
Roche [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Term of license and collaboration agreement												2 years
Renewal term of license and collaboration agreement												1 year
Upfront payment received towards technology access fee				$ 5,000,000
Reimbursement receivable for research and development costs incurred															500,000				500,000
Milestone payment receivable					7,000,000		7,000,000					$ 7,000,000		7,000,000				$ 2,000,000
Contract with customer liability revenue recognised					100,000			100,000				400,000	600,000	700,000	3,600,000
Contract with customer liability					1,300,000		1,700,000					1,300,000		1,700,000	2,400,000
Contract with customer liability current					600,000		$ 700,000					600,000		700,000	900,000
Cumulative catch up adjustment to revenue															1,100,000
Performance obligation revenue recognized					$ 100,000			100,000				$ 400,000	600,000	$ 700,000	$ 3,600,000
Roche [Member] | 2017 License and Collaboration Agreement With Roche [Member] | Technology Access Fee [Member]
License And Collaboration Agreements [Line Items]
Performance obligation transaction price																			5,000,000
Roche [Member] | 2017 License and Collaboration Agreement With Roche [Member] | Reimbursement Of Research And Development Costs [Member]
License And Collaboration Agreements [Line Items]
Performance obligation transaction price																			$ 1,000,000
Roche [Member] | 2017 License and Collaboration Agreement With Roche [Member] | Performance Obligation First And Second [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-09-30
License And Collaboration Agreements [Line Items]
Remaining period over which the performance obligation is to be satisfied					1 year 9 months 18 days		2 years 6 months					1 year 9 months 18 days		2 years 6 months	3 years 6 months
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Upfront payment received towards technology access fee			$ 45,000,000
Contract with customer liability revenue recognised												$ 18,100,000	$ 12,500,000	$ 18,600,000	$ 2,700,000
Contract with customer liability revenue recognised					$ 6,000,000			3,900,000
Contract with customer liability					46,400,000		$ 38,700,000					46,400,000		38,700,000	43,200,000
Contract with customer liability current					33,300,000		17,900,000					33,300,000		17,900,000	15,700,000
Milestone payment receivable based on product					1,600,000		1,600,000,000					1,600,000		1,600,000,000
Performance obligation transaction price																		55,800,000
Estimated costs to be incurred to satisfy performance obligation												2,300,000		21,000,000
Performance obligation revenue recognized					6,000,000			$ 3,900,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | APC [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license															15,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | TCL [Member]
License And Collaboration Agreements [Line Items]
Contract liabilities current reclassified to non current							5,300,000		$ 5,300,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Upfront Payment [Member]
License And Collaboration Agreements [Line Items]
Performance obligation transaction price			$ 45,000,000															45,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Reimbursable Costs [Member]
License And Collaboration Agreements [Line Items]
Performance obligation transaction price																		$ 10,800,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Development Milestone [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable based on product							217,000,000							217,000,000
Performance obligation transaction price									10,000,000
Cumulative catch up adjustment to revenue									1,100,000					1,100,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Development Milestone [Member] | First Patient Doosing Phase One Clinical Trial [Member]
License And Collaboration Agreements [Line Items]
Milestone payment received					20,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Regulatory Milestone [Member] | First Patient Doosing Phase One Clinical Trial [Member]
License And Collaboration Agreements [Line Items]
Performance obligation transaction price									20,000,000
Cumulative catch up adjustment to revenue									5,000,000					5,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Regulatory Milestone [Member] | Preclinical Data Submitted To FDA For Approval [Member]
License And Collaboration Agreements [Line Items]
Milestone payment received										$ 10,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Development Milestone [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable based on product					217,000,000							217,000,000
Performance obligation transaction price									10,000,000
Cumulative catch up adjustment to revenue									1,100,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Development Milestone [Member] | First Patient Doosing Phase One Clinical Trial [Member]
License And Collaboration Agreements [Line Items]
Milestone payment received					20,000,000	$ 20,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Regulatory Milestone [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable based on product					240,000,000							240,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Regulatory Milestone [Member] | First Patient Doosing Phase One Clinical Trial [Member]
License And Collaboration Agreements [Line Items]
Milestone payment received						$ 20,000,000
Performance obligation transaction price									$ 20,000,000
Cumulative catch up adjustment to revenue							5,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Regulatory Milestone [Member] | Preclinical Data Submitted To FDA For Approval [Member]
License And Collaboration Agreements [Line Items]
Milestone payment received											$ 10,000,000
Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Sales Milestone [Member]
License And Collaboration Agreements [Line Items]
Milestone payment receivable based on product					1,200,000		1,200,000,000					1,200,000		1,200,000,000
Roche [Member] | Maximum [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Annual maintenance fee receivable later than Five years					$ 900,000		$ 900,000					$ 900,000		$ 900,000
Roche [Member] | Maximum [Member] | 2018 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Remaining period over which the performance obligation is to be satisfied					1 year 3 months 18 days							1 year 3 months 18 days
Roche [Member] | Maximum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Performance Obligation First And Second [Member]
License And Collaboration Agreements [Line Items]
Remaining period over which the performance obligation is to be satisfied							2 years							2 years
Roche [Member] | Maximum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | TCL [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license															100,000,000
Roche [Member] | Minimum [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Annual maintenance fee receivable later than Five years					$ 500,000		$ 500,000					$ 500,000		$ 500,000
Roche [Member] | Minimum [Member] | 2018 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Remaining period over which the performance obligation is to be satisfied					1 year							1 year
Roche [Member] | Minimum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Performance Obligation First And Second [Member]
License And Collaboration Agreements [Line Items]
Remaining period over which the performance obligation is to be satisfied							1 year 9 months 18 days							1 year 9 months 18 days
Roche [Member] | Minimum [Member] | 2018 License and Collaboration Agreement With Roche [Member] | TCL [Member]
License And Collaboration Agreements [Line Items]
Amount payable on exercise of option rights to use the license															$ 50
Roche [Member] | Tranche One [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Reimbursement receivable for research and development costs incurred					$ 500,000							$ 500,000
Roche [Member] | Tranche Two [Member] | 2017 License and Collaboration Agreement With Roche [Member]
License And Collaboration Agreements [Line Items]
Reimbursement receivable for research and development costs incurred					$ 500,000							$ 500,000

Research Funding Agreements w_2

Research Funding Agreements with Government Agencies-Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Performance obligation revenue recognized	$ 6,120	$ 4,050	$ 18,511	$ 13,075	$ 19,318	$ 7,500
Research Funding Agreement With Government Agencies [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate Future Funding Available To The Company					600	1,400
Performance obligation revenue recognized					$ 400	$ 100

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Klavs Jensen [Member] - Consulting Agreement [Member] - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Related Party Transaction [Line Items]
Due from related party			$ 0	$ 0	$ 0
General and Administrative Expense [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Increase (decrease) in accrued expenses related party	$ (100,000)	$ (100,000)	100,000	100,000
Related party transaction general and administration expenses	$ 100,000	$ 100,000	$ 100,000	$ 100,000

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of basic and diluted net loss per share attributable to common stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)	$ (32,202)	$ (19,250)
Accretion of redeemable convertible preferred stock to redemption value						(984)
Net loss attributable to common stockholders	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)	$ (32,202)	$ (20,234)
Weighted-average common shares outstanding, basic and diluted	1,758,039	1,722,300	1,744,948	1,696,104	1,704,509	1,586,683
Net loss per share attributable to common stockholders, basic and diluted	$ (7.03)	$ (4.58)	$ (18.87)	$ (12.94)	$ (18.89)	$ (12.75)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of potentially dilutive shares excluded from the calculation of diluted net loss (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	21,546,573	15,361,022	17,745,730	14,684,796
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	17,800,084	12,643,109	14,604,043	12,643,109
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	2,038	2,038	2,038	2,038
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	3,744,451	2,715,875	3,139,649	2,013,769
Unvested Restricted Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount				25,880

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Millions

Nov. 30, 2020shares

Nov. 12, 2020USD ($)shares

Nov. 03, 2020USD ($)shares

Oct. 23, 2020

Oct. 20, 2020shares

Feb. 27, 2020USD ($)$ / sharesshares

Mar. 31, 2020USD ($)

Jun. 30, 2020shares

Feb. 29, 2020USD ($)$ / sharesshares

Jun. 30, 2020USD ($)

Sep. 30, 2020$ / sharesshares

Dec. 31, 2019$ / sharesshares

Dec. 31, 2018shares

Subsequent Event [Line Items]

Common stock, shares authorized

24,000,000

23,700,000

18,500,000

Temporary equity, shares authorized

17,044,139

16,670,802

12,057,951

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross

1,157,893

1,340,467

Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | $ / shares

$ 9.08

$ 5.14

Milestone Payment Received | $

$ 20

Unrecognized compensation expense expected period for recognition

2 years 10 months 24 days

3 years

Twenty Fourteen Stock Incentive Plan [Member]

Subsequent Event [Line Items]

Share based compensation by share based payment arrangement number of shares authorised for grant

4,853,361

4,853,361

Common stock shares reserved for future issuance

714,737

1,342,523

Subsequent Event [Member]

Subsequent Event [Line Items]

Stock split ratio

1.0530

Common stock shares issued upon conversion

17,800,084

Common stock, shares authorized

24,000,000

Temporary equity, shares authorized

200,000,000

Preferred Stock, Shares Authorized

10,000,000

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross

402,521

Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | $ / shares

$ 7.93

Share Based Compensation By Share Based Payment Arrangement Grant Date Aggregate Fair Value Of Options Granted | $

$ 2

Subsequent Event [Member] | Redeemable Convertible Preferred Stock [Member]

Subsequent Event [Line Items]

Common stock shares issued upon conversion

17,800,084

Subsequent Event [Member] | Series D Redeemable Convertible Preferred Stock [Member]

Subsequent Event [Line Items]

Temporary Equity Shares Issued During The Period Shares

1,940,945

1,094,247

Temporary Equity Issue Price Per Share | $ / shares

$ 13.9365

Proceeds from Issuance of Redeemable Convertible Preferred Stock | $

$ 15.2

Temporary Equity Stock Issuance Costs | $

$ 27

Subsequent Event [Member] | IPO [Member]

Subsequent Event [Line Items]

Stock shares issued during the period new issues shares

4,411,765

Proceeds from initial public offer net of underwriting discounts and before payment of offering costs | $

$ 75.5

Offering costs payable | $

$ 2.8

$ 2.8

Subsequent Event [Member] | Over-Allotment Option [Member]

Subsequent Event [Line Items]

Stock shares issued during the period new issues shares

661,764

Subsequent Event [Member] | 2020 Incentive Plan [Member]

Subsequent Event [Line Items]

Share based compensation by share based payment arrangement number of shares authorised for grant

2,690,415

Share based compensation by share based payment arrangement number of additional shares authorised as a percentage of common stock outstanding

5.00%

Subsequent Event [Member] | 2020 Employee Stock Purchase Plan [Member]

Subsequent Event [Line Items]

Share based compensation by share based payment arrangement number of shares authorised for grant

275,886

Share based compensation by share based payment arrangement number of additional shares authorised as a percentage of common stock outstanding

1.00%

Subsequent Event [Member] | 2020 Employee Stock Purchase Plan [Member] | Maximum [Member]

Subsequent Event [Line Items]

Common stock shares reserved for future issuance

3,724,461

Subsequent Event [Member] | Twenty Fourteen Stock Incentive Plan [Member]

Subsequent Event [Line Items]

Unrecognized compensation expense expected period for recognition

4 years