SQZ Biotechnologies (SQZB) 10-Q10 Dec 202020 Q3 Quarterly reportFinancial data

Company Profile

Cover Page

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2020	Dec. 04, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Registrant Name	SQZ Biotechnologies Co
Entity Central Index Key	0001604477
Entity Incorporation, State or Country Code	DE
Current Fiscal Year End Date	--12-31
Title of 12(b) Security	Common Stock
Trading Symbol	SQZ
Security Exchange Name	NYSE
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Shell Company	false
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		24,716,974
Entity Address, State or Province	MA
Entity Address, Country	US

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 107,060	$ 39,255
Marketable securities	8,021	59,027
Accounts receivable	1,892	1,874
Prepaid expenses and other current assets	1,905	1,662
Total current assets	118,878	101,818
Property and equipment, net	3,850	5,163
Restricted cash	2,305	2,319
Deferred offering costs	1,132
Operating lease right-of-use assets	50,807	43,050
Total assets	176,972	152,350
Current liabilities:
Accounts payable	2,461	2,796
Accrued expenses	5,879	7,061
Current portion of deferred revenue	34,309	18,982
Current portion of operating lease liabilities	8,040	9,444
Total current liabilities	50,689	38,283
Deferred revenue, net of current portion	13,755	21,846
Operating lease liabilities, net of current portion	41,323	32,887
Other liabilities	1,007	740
Total liabilities	106,774	93,756
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
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
Additional paid-in capital	4,992	2,701
Accumulated other comprehensive income	15	30
Accumulated deficit	(109,168)	(76,248)
Total stockholders' deficit	(104,159)	(73,515)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 176,972	$ 152,350

Condensed Consolidated Balanc_2

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

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue:
Total revenue	$ 6,121	$ 4,181	$ 18,511	$ 13,866
Operating expenses:
Research and development	13,910	8,489	37,815	26,324
General and administrative	4,612	4,065	14,139	11,191
Total operating expenses	18,522	12,554	51,954	37,515
Loss from operations	(12,401)	(8,373)	(33,443)	(23,649)
Other income (expense):
Interest income	56	492	533	1,711
Other income (expense), net	(6)	(2)	(10)	(5)
Total other income, net	50	490	523	1,706
Net loss	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)
Net loss per share attributable to common stockholders, basic and diluted	$ (7.03)	$ (4.58)	$ (18.87)	$ (12.94)
Weighted-average common shares outstanding, basic and diluted	1,758,039	1,722,300	1,744,948	1,696,104
Comprehensive loss:
Net loss	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)
Other comprehensive income (loss):
Unrealized losses on marketable securities, net of tax of $0	(48)	(12)	(15)	(32)
Comprehensive loss	(12,399)	(7,895)	(32,935)	(21,975)
Collaboration Revenue [Member]
Revenue:
Total revenue	$ 6,121	4,050	$ 18,511	13,075
Grant Revenue [Member]
Revenue:
Total revenue		$ 131		$ 791

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Unrealized gains (losses) on marketable securities, net of tax	$ 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, 2018		$ 106,401
Beginning balance, convertible preferred stock (Shares) at Dec. 31, 2018		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 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	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 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
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Stockholders' Equity [Abstract]
Unrealized gains on marketable securities, net of tax	$ 0	$ 0	$ 0	$ 0
Issuance of Series D convertible preferred stock, net of issuance costs of $43			$ 43

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (32,920)	$ (21,943)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	1,011	1,006
Amortization of operating lease right-of-use assets	7,154	929
Stock-based compensation expense	2,247	1,461
Accretion of discounts on marketable securities	(9)	(866)
Loss on disposal of property and equipment		51
Loss on termination of operating lease	108
Changes in operating assets and liabilities:
Accounts receivable	(18)	(1,612)
Prepaid expenses and other current assets	(243)	(5,617)
Accounts payable	(846)	1,186
Accrued expenses	(1,269)	1,380
Deferred revenue	7,236	606
Operating lease liabilities	(6,630)	(1,231)
Other liabilities	267	189
Net cash used in operating activities	(23,912)	(24,461)
Cash flows from investing activities:
Purchases of property and equipment	(1,054)	(1,314)
Purchases of marketable securities		(99,797)
Sales and maturities of marketable securities	51,000	95,600
Net cash provided by (used in) investing activities	49,946	(5,511)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs paid in the period	42,248
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
Net cash provided by financing activities	41,757	64
Net increase (decrease) in cash, cash equivalents and restricted cash	67,791	(29,908)
Cash, cash equivalents and restricted cash at beginning of period	41,574	61,875
Cash, cash equivalents and restricted cash at end of period	109,365	31,967
Supplemental disclosure of non-cash investing and financing activities:
Lease assets obtained in exchange for operating lease liabilities	17,049	$ 14,716
Deferred offering costs included in accrued expenses and accounts payable at end of period	$ 842

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2020
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 shares of its common stock. On November 12, 2020, the Company issued and sold an additional shares of its common stock pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate million, after deducting underwriting discounts and commissions , but before deducting million. U p 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 million for the year ended December 31, 2019 and million for the nine months ended September 30, 2020. As of September 30, 2020, the Company had an accumulated deficit of 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 hospitals, The COVID-19 SQZ-PBMC-HPV COVID-19 COVID-19 or at third-party vendors The Company is monitoring the potential impact of the COVID-19 pandemic on its business and financial statements. To date, the Company has not incurred impairment losses in the carrying values of its assets as a result of the pandemic and it is not aware of any specific related event or circumstance that would require it to revise its estimates reflected in these interim condensed consolidated financial statements. The extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations, financial condition and liquidity, including planned and future clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19, the actions taken to contain or treat it, and the duration and intensity of the related effects. 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2020
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) 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

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	9 Months Ended
Marketable Securities and Fair Value Measurements	Sep. 30, 2020
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 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 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.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
Prepaid Expenses and Other Current Assets	Sep. 30, 2020
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, 2020 2019 Prepaid expenses $ 1,844 $ 1,452 Interest receivable 61 206 Unbilled receivables — 4 $ 1,905 $ 1,662

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
Property and Equipment, Net	Sep. 30, 2020
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, 2020 2019 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 million net loss recognized by the Company upon termination of the 2016 Lease (see Note 11).

Accrued Expenses

Accrued Expenses	9 Months Ended
Accrued Expenses	Sep. 30, 2020
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

Preferred Stock

Preferred Stock	9 Months Ended
Preferred Stock	Sep. 30, 2020
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).

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
Stock-Based Compensation	Sep. 30, 2020
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 shares as of September 30, 2020 and December 31, 2019. As of September 30, 2020 and December 31, 2019, 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 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.

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9 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.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10 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 million , respect ively, and of which , respectively, were included in other liabilities (non - the three months ended September 30, 2020 and 2019, the Company recognized research and development expense under the sublicense terms of the agreement of $0 and $0.1 million, respectively. During the nine months ended September 30, 2020 and 2019, the Company recognized research and development expense under the sublicense terms of the agreement of $0 and $0.6 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. 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 each of 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 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
Leases	Sep. 30, 2020
Leases [Abstract]
Leases	11 As of September 30, 2020, the Company leases its office and laboratory facilities under a non-cancelable p 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 In September 2020, the Company further amended the agreement with its contract manufacturing supplier to extend the term of the agreement, which had the effect of extending the term of the embedded lease by one year through The amendment increased the Company’s contractual payment obligations by $9.9 million, representing the monthly fees payable over that extension. The amendment also included an option of the Company to further extend the term of the manufacturing services agreement by one additional year. The Company evaluated the probability of its exercising the option to extend the term of the agreement and concluded that it was reasonably certain that it would occur. The Company therefore recorded increases in right-of-use assets and operating liabilities in equal amounts of million as of September 30, 2020 , 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 assets under operating leases at September 30, 2020 and December 31, 2019 totaled million, respectively. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance. 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 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

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
License and Collaboration Agreements	Sep. 30, 2020
Research and Development [Abstract]
License and Collaboration Agreements	12 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 license granted to Roche to perform research related to and use of the Company’s Cell Squeeze technology for gene editing of immune cells; (ii) specified research and development services related to gene editing of immune cells through the research term; (iii) manufacturing activities to support the specified research plan; and (iv) participation on a joint research committee (“JRC”). The s 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 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 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 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 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 license to its intellectual property, and Roche granted the Company a non-exclusive license to its and its affiliates’ intellectual property for the purpose of performing research activities. In connection with this agreement, the parties terminated an earlier agreement. The 2018 Roche Agreement has a term that extends until all royalty, profit-share and other payment obligations expire or have been satisfied. Roche has the right to terminate the 2018 Roche Agreement, in whole or on a product-by-product basis, upon a specified amount of notice to the Company. The Company or Roche may terminate the agreement if the other party fails to cure its material breach within a specified period after receiving notice of such breach. 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 the 2018 Roche Agreement. the 2018 Roche Agreement. 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

Research Funding Agreements wit

Research Funding Agreements with Government Agencies	9 Months Ended
Research Funding Agreements with Government Agencies	Sep. 30, 2020
Research and Development [Abstract]
Research Funding Agreements with Government Agencies	13 Through The term for work to be performed under the

Related Parties

Related Parties	9 Months Ended
Related Parties	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Parties	14 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.

Net Loss per Share

Net Loss per Share	9 Months Ended
Net Loss per Share	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss per Share	15 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 SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 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

Subsequent Events

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	16 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 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) 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 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) 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 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 split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock (see Note 8). Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the Preferred Stock conversion ratios. Initial Public Offering On November 3, 2020, the Company completed its IPO, pursuant to which it issued and sold shares of its common stock. On November 12, 2020, the Company issued and sold an additional shares of its common stock pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate $ million, after deducting underwriting discounts and commissions , but before deducting million. Upon the closing of the IPO, all of the shares of the Company’s convertible preferred stock then outstanding automatically converted into 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 capit a 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

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2020
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.
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) 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	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

Marketable Securities and Fai_2

Marketable Securities and Fair Value Measurements (Tables)	9 Months Ended
Marketable Securities and Fair Value Measurements (Tables)	Sep. 30, 2020
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
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 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
Prepaid Expenses and Other Current Assets (Tables)	Sep. 30, 2020
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, 2020 2019 Prepaid expenses $ 1,844 $ 1,452 Interest receivable 61 206 Unbilled receivables — 4 $ 1,905 $ 1,662

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
Property and Equipment, Net (Tables)	Sep. 30, 2020
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, 2020 2019 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

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
Accrued Expenses (Tables)	Sep. 30, 2020
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

Preferred Stock (Tables)

Preferred Stock (Tables)	9 Months Ended
Preferred Stock (Tables)	Sep. 30, 2020
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

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
Stock-Based Compensation (Tables)	Sep. 30, 2020
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 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 %
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
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

Leases (Tables)

Leases (Tables)	9 Months Ended
Leases (Tables)	Sep. 30, 2020
Leases [Abstract]
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 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

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	9 Months Ended
License and Collaboration Agreements (Tables)	Sep. 30, 2020
Research and Development [Abstract]
Summary of Changes in the Total 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

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
Net Loss per Share (Tables)	Sep. 30, 2020
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 SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 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 )
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

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	Sep. 30, 2020	Dec. 31, 2019
Income (loss) from continuing operations				$ (32,900)	$ (32,200)
Accumulated deficit				$ 109,168	$ 76,248
Subsequent Event [Member]
Common stock shares issued upon conversion	17,800,084
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_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Jan. 01, 2017
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 50,807	$ 43,050
Decrease to accumulated deficit			$ (400)
Accounting Standards Update 2016-02 [Member]
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	2,700
Operating lease, liability	$ 4,200

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
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 8,006	$ 58,997
Gross Unrealized Gains	15	30
Gross Unrealized Losses
Fair Value	8,021	59,027
U.S. Government Agency Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,006	44,028
Gross Unrealized Gains	15	24
Gross Unrealized Losses
Fair Value	$ 8,021	44,052
U.S. Treasury Bills [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		14,969
Gross Unrealized Gains		6
Gross Unrealized Losses
Fair Value		$ 14,975

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
Assets:
Assets, fair value disclosure	$ 115,018	$ 96,098
Level 1 [Member]
Assets:
Assets, fair value disclosure	106,997	37,071
Level 2 [Member]
Assets:
Assets, fair value disclosure	8,021	59,027
Money Market Funds [Member]
Assets:
Assets, fair value disclosure	106,997	37,071
Money Market Funds [Member] \| Level 1 [Member]
Assets:
Assets, fair value disclosure	106,997	37,071
U.S. Government Agency Bonds [Member]
Assets:
Assets, fair value disclosure	8,021	44,052
U.S. Government Agency Bonds [Member] \| Level 2 [Member]
Assets:
Assets, fair value disclosure	$ 8,021	44,052
U.S. Treasury Bills [Member]
Assets:
Assets, fair value disclosure		14,975
U.S. Treasury Bills [Member] \| Level 2 [Member]
Assets:
Assets, fair value disclosure		$ 14,975

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
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 1,844	$ 1,452
Interest receivable	61	206
Unbilled receivables		4
Total prepaid expenses and other current assets	$ 1,905	$ 1,662

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
Property, Plant and Equipment, Net [Abstract]
Machinery and equipment	$ 6,037	$ 5,655
Leasehold improvements	436	2,650
Furniture and fixtures	579	353
Total property and equipment, gross	7,052	8,658
Less: Accumulated depreciation and amortization	(3,202)	(3,495)
Total property and equipment, net	$ 3,850	$ 5,163

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Depreciation and amortization expense		$ 300	$ 400	$ 1,011	$ 1,006
Leasehold improvements gross		436		436		$ 2,650
Accumulated depreciation related to those leasehold improvements		3,202		3,202		3,495
Property and equipment, net		$ 3,850		3,850		$ 5,163
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
Payables and Accruals [Abstract]
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
Total accrued expenses	$ 5,879	$ 7,061

Preferred Stock - Summary of Pr

Preferred Stock - Summary of Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares Authorized	17,044,139	16,670,802
Shares issued	16,904,219	13,869,027
Shares outstanding	16,904,219	13,869,027
Carrying Amount	$ 174,357	$ 132,109
Liquidation Preference	$ 169,648	$ 127,348
Common stock issuable upon conversion	17,800,084	14,604,043
Series Seed
Temporary Equity [Line Items]
Shares Authorized	350,858	350,858
Shares issued	350,858	350,858
Shares outstanding	350,858	350,858
Carrying Amount	$ 975	$ 975
Liquidation Preference	$ 1,000	$ 1,000
Common stock issuable upon conversion	369,452	369,452
Series A
Temporary Equity [Line Items]
Shares Authorized	1,490,035	1,490,035
Shares issued	1,490,035	1,490,035
Shares outstanding	1,490,035	1,490,035
Carrying Amount	$ 6,469	$ 6,469
Liquidation Preference	$ 5,081	$ 5,081
Common stock issuable upon conversion	1,569,001	1,569,001
Series B
Temporary Equity [Line Items]
Shares Authorized	4,155,758	4,155,758
Shares issued	4,155,758	4,155,758
Shares outstanding	4,155,758	4,155,758
Carrying Amount	$ 27,854	$ 27,854
Liquidation Preference	$ 24,061	$ 24,061
Common stock issuable upon conversion	4,375,999	4,375,999
Series C
Temporary Equity [Line Items]
Shares Authorized	6,010,140	6,010,140
Shares issued	6,010,140	6,010,140
Shares outstanding	6,010,140	6,010,140
Carrying Amount	$ 71,103	$ 71,103
Liquidation Preference	$ 71,253	$ 71,253
Common stock issuable upon conversion	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) - USD ($) $ / shares in Units, $ in Thousands	Nov. 30, 2020	Jun. 30, 2020	May 31, 2020	Feb. 29, 2020	Jan. 31, 2020	Dec. 31, 2019	May 31, 2018	Nov. 30, 2016	Sep. 30, 2016	Jul. 31, 2015	Jun. 30, 2015	Mar. 31, 2014	Jun. 30, 2020	Feb. 29, 2020	Oct. 31, 2018	Sep. 30, 2020
Temporary Equity [Line Items]
Proceeds from temporary equity shares issued																$ 42,248
Issuance costs																$ 43
Subsequent Event [Member]
Temporary Equity [Line Items]
Common stock shares issued upon conversion	17,800,084
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												350,858
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Share price										$ 3.41	$ 3.41
Proceeds from temporary equity shares issued										$ 5,100	$ 5,100
Temporary Equity, Shares Issued During Period										1,490,035	1,490,035
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								4,155,758	4,155,758
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							259,328
Shares issued on convertible promissory note value							$ 3,100
Issuance costs															$ 200
Temporary Equity, Shares Issued During Period							4,094,794								1,656,018
Series C Convertible Preferred Stock [Member] \| Maximum [Member]
Temporary Equity [Line Items]
Temporary Equity, Shares Issued During Period							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
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		1,940,945	1,940,945	1,094,247	1,094,247	1,862,236

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
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
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
Expected term (years)	6 years	6 years	6 years	6 years
Expected volatility	76.70%	69.50%	75.20%	69.10%
Risk-free interest rate	0.37%	1.89%	0.66%	2.40%
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Shares - Outstanding at December 31, 2019 \| shares	3,139,649
Granted \| shares	1,157,893
Exercised \| shares	(22,974)
Forfeited or canceled \| shares	(530,117)
Number Of Shares - Outstanding at September 30, 2020 \| shares	3,744,451	3,139,649
Number Of Shares - Vested and expected to vest at December 31, 2019 \| shares	3,139,649
Number Of Shares - Vested and expected to vest at September 30, 2020 \| shares	3,744,451	3,139,649
Number Of Shares - Options exercisable at December 31, 2019 \| shares	870,219
Number Of Shares - Options exercisable at September 30, 2020 \| shares	1,486,775	870,219
Weighted Average Exercise price - Outstanding at December 31, 2019 \| $ / shares	$ 4.20
Granted \| $ / shares	9.08
Exercised \| $ / shares	1.93
Forfeited or canceled \| $ / shares	4.62
Weighted Average Exercise price - Outstanding at September 30, 2020 \| $ / shares	5.67	$ 4.20
Weighted Average Exercise price - Vested and expected to vest at December 31, 2019 \| $ / shares	4.20
Weighted Average Exercise price - Vested and expected to vest at September 30, 2020 \| $ / shares	5.67	4.20
Weighted Average Exercise price - Options exercisable at December 31, 2019 \| $ / shares	2.94
Weighted Average Exercise price - Options exercisable at September 30, 2020 \| $ / shares	$ 3.69	$ 2.94
Weighted-Average Remaining Contractual Term	7 years 10 months 17 days	8 years 8 months 8 days
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
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 Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 796	$ 491	$ 2,247	$ 1,461
Research and Development Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	296	174	811	525
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 500	$ 317	$ 1,436	$ 936

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
StockBased Compensation [Line Items]
Unrecognized compensation expense related to unvested stock based awards	$ 10.6		$ 10.6
Unrecognized compensation expense expected period for recognition			2 years 10 months 24 days
Expected annual dividend yield	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
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 - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax benefits	$ 0	$ 0	$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Other Commitments [Line Items]
Commitments and contingencies liabilities
Accrued license fees, current	777		777		697
Research and development expense	13,910	$ 8,489	37,815	$ 26,324
Research and development	13,910	8,489	37,815	26,324
Discretionary contribution by the employer to defined contribution benefit plan			300	200
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
Research and development	0	100	0	600
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
Erytech [Member] \| License Agreement With Erytech [Member]
Other Commitments [Line Items]
Research and development expense				1,000
Research and development				$ 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
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 3,231	$ 823	$ 9,345	$ 1,189
Variable lease cost	306	121	908	383
Short-term lease cost		39	21	72
Lease, Cost	$ 3,537	$ 983	$ 10,274	$ 1,644

Leases - Summary of Operating L

Leases - Summary of Operating Lease Lessee Balance Sheet and Related Disclosures (Detail)	Sep. 30, 2020	Dec. 31, 2019
Other Information [Abstract]
Weighted-average remaining lease term (in years)	6 years 10 months 24 days	7 years 10 months 24 days
Weighted-average discount rate	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
	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating cash flows from operating leases	$ 8,820	$ 1,701
Operating leases	$ 17,049	$ 14,716

Leases - Additional Information

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

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
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Research and Development [Abstract]
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

License and Collaboration Agr_4

License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands

1 Months Ended

3 Months Ended

6 Months Ended

9 Months Ended

12 Months Ended

Oct. 31, 2018

Sep. 30, 2020

Sep. 30, 2019

Mar. 31, 2019

Sep. 30, 2019

Sep. 30, 2020

Sep. 30, 2019

Dec. 31, 2019

Jun. 30, 2020

Jun. 30, 2019

Dec. 31, 2018

Sep. 30, 2018

License And Collaboration Agreements [Line Items]

Contract with customer liability revenue recognised

$ 6,120

$ 4,050

$ 18,511

$ 13,075

Contract with customer liability

47,688

46,078

$ 46,078

47,688

46,078

$ 40,453

$ 51,917

$ 48,873

$ 45,598

2017 License and Collaboration Agreement With Roche [Member]

License And Collaboration Agreements [Line Items]

Upfront payment received towards technology access fee

5,000

Reimbursement receivable for research and development costs incurred

1,000

2018 License and Collaboration Agreement With Roche [Member]

License And Collaboration Agreements [Line Items]

Milestone payment receivable on exercise of option rights

100,000

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

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

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

$ 50,000

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

Milestone payment receivable

7,000

$ 7,000

Contract with customer liability revenue recognised

100

400

600

Contract with customer liability

1,300

Contract with customer liability current

$ 600

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

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

Contract with customer liability revenue recognised

$ 18,100

$ 12,500

Contract with customer liability revenue recognised

$ 6,000

$ 3,900

Contract with customer liability

46,400

38,700

Contract with customer liability current

33,300

17,900

Milestone payment receivable based on product

1,600

Performance obligation transaction price

$ 55,800

Estimated costs to be incurred to satisfy performance obligation

2,300

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

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

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

Roche [Member] | 2018 License and Collaboration Agreement With Roche [Member] | Development Milestone [Member]

License And Collaboration Agreements [Line Items]

Performance obligation transaction price

10,000

Cumulative catch up adjustment to revenue

1,100

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

Cumulative catch up adjustment to revenue

$ 5,000

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

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

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

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

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

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

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

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

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

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

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

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

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

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Klavs Jensen [Member] - Consulting Agreement [Member] - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Due from related party			$ 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)
Related party transaction general and administration expenses	$ 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
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (12,351)	$ (7,883)	$ (32,920)	$ (21,943)
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)

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
	Sep. 30, 2020	Sep. 30, 2019
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
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
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
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

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ in Millions	Nov. 30, 2020shares	Nov. 12, 2020USD ($)shares	Nov. 03, 2020USD ($)shares	Oct. 23, 2020	Oct. 20, 2020shares	Sep. 30, 2020shares	Dec. 31, 2019shares
Subsequent Event [Line Items]
Common stock, shares authorized						24,000,000	23,700,000
Temporary equity, shares authorized						17,044,139	16,670,802
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
Subsequent Event [Member] \| Redeemable Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Common stock shares issued upon conversion		17,800,084
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