Rubius Therapeutics (RUBY) 10-Q 8 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	001-38586
Entity Registrant Name	RUBIUS THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-2688109
Entity Address, Address Line One	399 Binney Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	679-9600
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RUBY
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		89,865,777
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001709401
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 264,017	$ 91,165
Investments	0	85,122
Prepaid expenses and other current assets	6,451	5,224
Total current assets	270,468	181,511
Operating lease, right-of-use-asset	36,296	40,447
Property, plant and equipment, net	52,727	53,952
Restricted cash	1,573	1,573
Other assets		311
Total assets	361,064	277,794
Current liabilities:
Accounts payable	8,492	5,478
Accrued expenses and other current liabilities	13,622	13,417
Operating lease liabilities	8,820	8,945
Total current liabilities	30,934	27,840
Long-term debt, net of discount	75,929	74,944
Other long-term liabilities	586	688
Operating lease liabilities, net of current portion	29,410	32,762
Total liabilities	136,859	136,234
Commitments and contingencies (see Note 9)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2021 and December 31, 2020; no shares issued or outstanding at September 30, 2021 and December 31, 2020
September 30, 2021 and December 31, 2020; 89,862,482 and 81,053,651 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively	90	81
Additional paid-in capital	846,112	621,946
Accumulated other comprehensive income		4
Accumulated deficit	(621,997)	(480,471)
Total stockholders' equity	224,205	141,560
Total liabilities and stockholders' equity	$ 361,064	$ 277,794

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
CONDENSED CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, share authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, share authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	89,862,482	81,053,651
Common stock, shares outstanding (in shares)	89,862,482	81,053,651

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 38,014	$ 28,209	$ 101,763	$ 90,491
General and administrative	12,035	11,976	39,126	36,241
Total operating expenses	50,049	40,185	140,889	126,732
Loss from operations	(50,049)	(40,185)	(140,889)	(126,732)
Other income (expense):
Interest income	23	223	75	1,682
Interest expense	(1,711)	(1,174)	(4,771)	(2,987)
Other income, net	2,721	284	4,059	845
Total other income (expense), net	1,033	(667)	(637)	(460)
Net loss	$ (49,016)	$ (40,852)	$ (141,526)	$ (127,192)
Net loss per share, basic and diluted	$ (0.55)	$ (0.51)	$ (1.62)	$ (1.58)
Weighted average common shares outstanding, basic and diluted	89,807,383	80,778,042	87,240,694	80,511,543
Comprehensive loss:
Net loss	$ (49,016)	$ (40,852)	$ (141,526)	$ (127,192)
Other comprehensive income (loss):
Unrealized (losses) on investments, net of tax of $0	(1)	(162)	(4)	(43)
Comprehensive loss	$ (49,017)	$ (41,014)	$ (141,530)	$ (127,235)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Unrealized gains (losses) on investments, tax	$ 0	$ 0	$ 0	$ 0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (141,526)	$ (127,192)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	26,428	24,725
Depreciation and amortization expense	4,331	5,176
Amortization of premium on investments	118	186
Non-cash interest expense	1,036	232
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,226)	(1,323)
Operating lease, right-of-use-asset	4,156	4,184
Accounts payable	2,773	2,095
Accrued expenses and other current liabilities	(416)	(2,425)
Other long-term liabilities	(102)	580
Operating lease liabilities	(3,477)	(3,338)
Net cash used in operating activities	(107,905)	(97,100)
Cash flows from investing activities:
Purchases of property, plant and equipment	(2,280)	(4,467)
Purchases of investments		(122,671)
Sales and maturities of investments	85,000	181,102
Net cash provided by investing activities	82,720	53,964
Cash flows from financing activities:
Proceeds from underwritten public offering of common stock, net of commissions and underwriting discounts	188,000
Payments of offering costs	(360)
Payments of debt issuance costs	(150)
Proceeds from borrowings under loan and security agreement		25,000
Proceeds from issuance of common stock upon exercise of stock options	10,547	1,412
Net cash provided by financing activities	198,037	26,412
Net increase in cash, cash equivalents and restricted cash	172,852	(16,724)
Cash, cash equivalents and restricted cash at beginning of period	92,901	93,633
Cash, cash equivalents and restricted cash at end of period	265,753	76,909
Supplemental cash flow information:
Cash paid for interest	3,635	2,740
Cash paid for leases	5,675	5,822
Supplemental disclosure of non-cash investing and financing information:
Purchases of property, plant and equipment included in accounts payable or accrued expenses	1,145	564
Lease assets obtained in exchange for new operating lease liabilities		90
Offering costs included in accounts payable and accrued expenses	$ 35
Lease asset derecognized upon lease cancellation		$ 982

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit	Total
Balances at Beginning of period (in shares) at Dec. 31, 2019	80,016,245
Balances at Beginning of period at Dec. 31, 2019	$ 80	$ 586,798	$ 75	$ (312,740)	$ 274,213
Issuance of common stock upon exercise of stock options		486			486
Issuance of common stock upon exercise of stock options (in shares)	413,721
Stock-based compensation expense		8,488			8,488
Unrealized gains (losses) on investments			456		456
Net loss				(48,486)	(48,486)
Balances at End of period (in shares) at Mar. 31, 2020	80,429,966
Balances at End of period at Mar. 31, 2020	$ 80	595,772	531	(361,226)	235,157
Balances at Beginning of period (in shares) at Dec. 31, 2019	80,016,245
Balances at Beginning of period at Dec. 31, 2019	$ 80	586,798	75	(312,740)	274,213
Net loss					(127,192)
Balances at End of period (in shares) at Sep. 30, 2020	80,923,820
Balances at End of period at Sep. 30, 2020	$ 81	612,934	32	(439,932)	173,115
Balances at Beginning of period (in shares) at Dec. 31, 2019	80,016,245
Balances at Beginning of period at Dec. 31, 2019	$ 80	586,798	75	(312,740)	274,213
Net loss					(167,700)
Balances at End of period (in shares) at Dec. 31, 2020	81,053,651
Balances at End of period at Dec. 31, 2020	$ 81	621,946	4	(480,471)	141,560
Balances at Beginning of period (in shares) at Mar. 31, 2020	80,429,966
Balances at Beginning of period at Mar. 31, 2020	$ 80	595,772	531	(361,226)	235,157
Issuance of common stock upon exercise of stock options		256			256
Issuance of common stock upon exercise of stock options (in shares)	115,553
Stock-based compensation expense		8,252			8,252
Unrealized gains (losses) on investments			(337)		(337)
Net loss				(37,854)	(37,854)
Balances at End of period (in shares) at Jun. 30, 2020	80,545,519
Balances at End of period at Jun. 30, 2020	$ 80	604,280	194	(399,080)	205,474
Issuance of common stock upon exercise of stock options	$ 1	669			670
Issuance of common stock upon exercise of stock options (in shares)	378,301
Stock-based compensation expense		7,985			7,985
Unrealized gains (losses) on investments			(162)		(162)
Net loss				(40,852)	(40,852)
Balances at End of period (in shares) at Sep. 30, 2020	80,923,820
Balances at End of period at Sep. 30, 2020	$ 81	612,934	32	(439,932)	173,115
Balances at Beginning of period (in shares) at Dec. 31, 2020	81,053,651
Balances at Beginning of period at Dec. 31, 2020	$ 81	621,946	4	(480,471)	141,560
Issuance of common stock from public offering, net of commissions, underwriting discounts and offering costs of $800	$ 7	187,193			187,200
Issuance of common stock from public offering, net of commissions, underwriting discounts and offering costs (in shares)	6,896,552
Issuance of common stock upon exercise of stock options	$ 1	5,907			5,908
Issuance of common stock upon exercise of stock options (in shares)	1,237,324
Stock-based compensation expense		8,642			8,642
Unrealized gains (losses) on investments			3		3
Net loss				(42,330)	(42,330)
Balances at End of period (in shares) at Mar. 31, 2021	89,187,527
Balances at End of period at Mar. 31, 2021	$ 89	823,688	7	(522,801)	300,983
Balances at Beginning of period (in shares) at Dec. 31, 2020	81,053,651
Balances at Beginning of period at Dec. 31, 2020	$ 81	621,946	4	(480,471)	141,560
Net loss					(141,526)
Balances at End of period (in shares) at Sep. 30, 2021	89,862,482
Balances at End of period at Sep. 30, 2021	$ 90	846,112		(621,997)	224,205
Balances at Beginning of period (in shares) at Mar. 31, 2021	89,187,527
Balances at Beginning of period at Mar. 31, 2021	$ 89	823,688	7	(522,801)	300,983
Issuance of common stock upon exercise of stock options	$ 1	3,719			3,720
Issuance of common stock upon exercise of stock options (in shares)	532,400
Stock-based compensation expense		9,597			9,597
Unrealized gains (losses) on investments			(6)		(6)
Net loss				(50,180)	(50,180)
Balances at End of period (in shares) at Jun. 30, 2021	89,719,927
Balances at End of period at Jun. 30, 2021	$ 90	837,004	1	(572,981)	264,114
Issuance of common stock upon exercise of stock options		919			919
Issuance of common stock upon exercise of stock options (in shares)	142,555
Stock-based compensation expense		8,189			8,189
Unrealized gains (losses) on investments			$ (1)		(1)
Net loss				(49,016)	(49,016)
Balances at End of period (in shares) at Sep. 30, 2021	89,862,482
Balances at End of period at Sep. 30, 2021	$ 90	$ 846,112		$ (621,997)	$ 224,205

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Net of commissions, underwriting discounts and offering costs	$ 800

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	RUBIUS THERAPEUTICS, INC. NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (Unaudited) 1. Nature of the Business and Basis of Presentation Rubius Therapeutics, Inc. (“Rubius” or the “Company”) is a biopharmaceutical company that is using its platform to genetically engineer red blood cells into medicines, called Red Cell Therapeutics, for the treatment of cancer and autoimmune diseases. Rubius was incorporated in April 2013 as VL26, Inc. under the laws of the State of Delaware. In January 2015, the Company changed its name to Rubius Therapeutics, Inc. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes and the ability to secure additional capital to fund operations. In addition, the Company is subject to uncertainty regarding the performance and safety of its product candidates in humans. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. T he Company is continuing to monitor the impact of the novel coronavirus (“COVID-19”), if any, on the carrying value of certain assets. Although the Company has experienced some impacts to its business as a result of COVID-19, such impacts, to date, have not been material, nor has the Company incurred impairment of any assets as a result of COVID-19. The extent to which these events have impacted, and may continue to impact, the Company’s business will depend on future developments, which are highly uncertain and cannot be predicted at this time. The duration and intensity of these impacts and resulting disruption to the Company’s operations is uncertain and the Company will continue to assess the financial impact. On July 20, 2018, the Company completed its initial public offering (“IPO”), pursuant to which it issued and sold 12,055,450 shares of common stock, inclusive of 1,572,450 shares sold by the Company pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate net proceeds received by the Company from the IPO were $254.3 million, after deducting underwriting discounts and commissions and other offering costs. Upon the closing of the IPO, all of the shares of the Company’s outstanding convertible preferred stock then outstanding automatically converted into 51,845,438 shares of common stock. On March 18, 2021, the Company completed an underwritten public offering (the “March 2021 Offering”), pursuant to which it issued and sold 6,896,552 shares of common stock. The aggregate net proceeds received by the Company from the March 2021 Offering were $187.2 million, after deducting underwriting discounts and commissions and other offering costs. The accompanying condensed 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. The Company has incurred recurring losses since inception, including net losses of $141.5 million for the nine months ended September 30, 2021 and $167.7 million for the year ended December 31, 2020. As of September 30, 2021, the Company had an accumulated deficit of $622.0 million. The Company expects to continue to generate operating losses in the foreseeable future. As of November 8, 2021, the issuance date of the interim condensed consolidated financial statements, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses, capital expenditure requirements and debt service payments for at least 12 months from the issuance date of the interim condensed consolidated financial statements. The Company has financed its operations to date primarily through private placements, proceeds from its IPO and the March 2021 Offering and borrowings under credit facilities. The Company has devoted substantially all of its financial resources and efforts to research and development, including preclinical studies and clinical trials, and developing manufacturing capabilities. The Company will need to raise additional funds through public or private equity financings, debt financings, collaborations, strategic alliances or marketing, distribution or licensing arrangements to fund operations. The Company may not be able to obtain financing, or enter into collaboration or other arrangements, on acceptable terms, or at all. Furthermore, the terms of any financing may adversely affect the holdings or the rights of the Company's stockholders. If the Company is unable to obtain funding, the Company may need to delay, scale back or discontinue some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. The Company’s condensed 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. All intercompany accounts and transactions have been eliminated in consolidation. Certain prior period amounts have been reclassified to conform to the current year presentation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The condensed consolidated balance sheet at December 31, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 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 condensed 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, 2020 included in the Company’s Annual Report on Form 10-K for the year-ended December 31, 2020, on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s condensed consolidated financial position as of September 30, 2021 and condensed consolidated results of operations for the three and nine months ended September 30, 2021 and 2020 and the condensed consolidated cash flows for the nine months ended September 30, 2021 and 2020 have been made. The Company’s condensed consolidated results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021 . 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 financial statements and the reported amounts of revenue and expenses during the reporting periods. In the condensed consolidated financial statements, the Company uses estimates and assumptions related to the accrual of research and development expenses 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. ​ The full extent to which the ongoing COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19. ​ Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company’s cash and cash equivalents, as of September 30, 2021, consisted of U.S. government money market funds. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials. Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Restricted Cash As of both September 30, 2021 and December 31, 2020, the Company maintained letters of credit totaling $1.7 million for the benefit of the landlords of its leased properties. The Company was required to maintain separate cash balances of these amounts to secure the letters of credit. Related to these separate cash balances, the Company included $0.1 million in prepaid expenses and other current assets and $1.6 million in restricted cash (non-current) in its condensed consolidated balance sheet as of September 30, 2021 and December 31, 2020. Cash, cash equivalents and restricted cash presented in the accompanying condensed consolidated statement of cash flows was $265.8 million and $76.9 million for the nine months ended September 30, 2021 and 2020, respectively, of which $1.7 million and $1.7 million was restricted cash, respectively. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ● Level 1—Quoted prices in active markets for identical assets or liabilities. ● Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ● Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The carrying value of the Company’s long-term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate. Investments The Company’s investments are classified as available-for-sale and are carried at fair value. Realized gains and losses and declines in value are based on the specific identification method and are included as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company classifies its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such investments are available for current operations. In June 2016, issued 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses , which changes the impairment model for most financial assets, including the Company’s investments. The Company adopted the standard effective January 1, 2020 using a prospective transition method. The Company evaluates its investments with unrealized losses for impairment. When assessing investments for unrealized declines in value, the Company considers whether the decline in value is related to a credit loss or non-credit loss. For credit losses, the Company reduces the investment to fair value through an allowance for credit losses recorded to the balance sheet and corresponding charge to the statement of operations. The allowance for credit losses and corresponding impairment charge is adjusted each period for changes in fair value. For non-credit losses, the Company reduces the investment to fair value through a charge to the statement of comprehensive loss, reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. No such credit losses were recorded during the periods presented. Leases At the inception of an arrangement as lessee or lessor, the Company determines whether the arrangement is or contains a lease. Operating lease cost is recognized over the lease term on a straight-line basis. Variable lease cost and short-term leases (lease terms less than 12 months) are recognized as incurred. For both lessee and lessor arrangements, variable lease payments are the amounts owed by the Company to a lessor that are not fixed, such as reimbursement for common area maintenance and utilities costs, and are expensed when incurred. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that it will exercise that option. For lessee arrangements, operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current. The Company has elected the following lease policies at the inception of a lease: (1) for lessee and lessor arrangements within all asset classes, combine lease and non-lease components as a single component, with the lease expense recognized over the expected term on a straight-line basis and (2) for lessee arrangements, apply short-term lease exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for leases with terms of one year or less. ​ Recently Adopted Accounting Pronouncements ASU No. 2019-12, Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (ASC 740). interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. This guidance is effective for the Company for annual and interim periods beginning after December 31, 2020; however, early adoption is permitted. The Company adopted this standard as of January 1, 2021 on a prospective basis. The adoption did not have an impact on the Company’s condensed consolidated financial statements.

Investments and Fair Value of F

Investments and Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2021
Investments and Fair Value of Financial Assets and Liabilities
Investments and Fair Value of Financial Assets and Liabilities	3. Investments and Fair Value of Financial Assets and Liabilities The Company had no investments as of September 30, 2021. As of December 31, 2020, investments by security type consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Amortized Cost ​ Gross ​ Gross ​ Credit Losses ​ Fair Value U.S. treasury bills and notes (due within one year) $ 85,118 $ 6 $ (2) ​ $ — ​ $ 85,122 ​ ​ $ 85,118 ​ $ 6 ​ $ (2) ​ $ — ​ $ 85,122 ​ The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value measurements at September 30, 2021 using: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ U.S. money market funds $ 256,034 $ — $ — ​ $ 256,034 ​ ​ $ 256,034 ​ $ — ​ $ — ​ $ 256,034 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value measurements at December 31, 2020 using: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ U.S money market funds $ 88,814 $ — $ — ​ $ 88,814 Investments: ​ ​ ​ ​ ​ ​ ​ U.S. treasury bills and notes ​ — ​ 85,122 ​ — ​ 85,122 ​ ​ $ 88,814 ​ $ 85,122 ​ $ — ​ $ 173,936 ​ U.S. government 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. treasury notes and U.S. government agency bonds 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 have been no changes to the valuation methods during the nine months ended September 30, 2021. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1, Level 2 or Level 3 during the nine months ended September 30, 2021.

Property, Plant and Equipment,

Property, Plant and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment, Net.
Property, Plant and Equipment, Net	4. Property, Plant and Equipment, Net Property, plant and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 December 31, 2020 Land ​ $ 1,300 ​ $ 1,300 ​ Manufacturing facility ​ ​ 31,235 ​ ​ 30,969 ​ Manufacturing equipment ​ ​ 8,804 ​ ​ 8,782 ​ Laboratory equipment ​ 17,370 ​ ​ 16,639 Computer equipment 2,480 ​ 2,118 Furniture and fixtures ​ ​ 1,228 ​ ​ 1,228 ​ Leasehold improvements 444 ​ 444 Construction-in-progress 4,330 ​ 2,605 ​ 67,191 ​ 64,085 Less: Accumulated depreciation and amortization (14,464) ​ (10,133) ​ ​ $ 52,727 ​ $ 53,952 ​ ​

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Accrued Expenses and Other Current Liabilities
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 December 31, 2020 Accrued employee compensation and benefits $ 5,978 ​ $ 8,124 Accrued external research and development expenses 4,430 ​ 3,156 Accrued manufacturing facility expenses 1,331 ​ 339 Accrued general and administrative expenses ​ ​ 1,019 ​ ​ 1,244 Other 864 ​ 554 ​ ​ $ 13,622 ​ $ 13,417 ​

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt
Debt	6. Debt On December 21, 2018 (the “Closing Date”), the Company entered into a loan and security agreement (as amended, the “Loan Agreement”) with Solar Capital Ltd., now SLR Investment Corp., as collateral agent for the lenders party thereto for an aggregate principal amount of $75.0 million. The aggregate principal amount was funded in three tranches of term loans of $25.0 million each. On the Closing Date, the Company made an initial borrowing of $25.0 million. In June 2019, the Company made a second borrowing of $25.0 million and in June 2020, the Company made a third and final borrowing of $25.0 million. On June 22, 2021 (the “Amendment Closing Date”), the Company entered into an amendment (the “Amendment”) to its Loan Agreement. Pursuant to the Amendment, the Company and its lenders agreed to extend the interest-only period applicable to borrowings under the Loan Agreement from December 21, 2021 until July 1, 2024 and the final maturity date from December 21, 2023 until June 1, 2026. An additional tranche in the amount of $35.0 million is available at the request of the Company prior to the final maturity date, to be provided at the sole discretion of the lenders. The Amendment increases the LIBOR interest rate floor from 0.00% to 2.10%. Interest on the outstanding loan balance will accrue at a rate of 5.50%, plus the greater of 2.10% or the one-month U.S. LIBOR rate. Certain back-end fees are due to the lender at the time of final repayment based on the total funded term loans. The Company accrues the back-end fees that will be due at final repayment to outstanding debt by charges to interest expense over the term of the loans using the effective interest method. The term loans are subject to a prepayment fee of 1.00% if prepayment occurs within the first year subsequent to the Amendment Closing Date, 0.50% in the second year and 0.25% in the third year through final maturity date. As the terms of the Amendment were not substantially different than the terms of the Loan Agreement, the Amendment was accounted for as a debt modification. In conjunction with the Amendment, the Company incurred issuance costs of $0.2 million payable to the lenders, which were recorded as an additional debt discount and will be amortized to interest expense over the remaining term, together with unamortized original issuance costs as of the Amendment Closing Date, using the effective interest method. The Loan Agreement contains financial covenants that require the Company to maintain either a certain minimum cash balance or a minimum market capitalization threshold. The Company was in compliance with all such financial covenants as of September 30, 2021. The Loan Agreement contains customary representations, warranties and covenants and also includes customary events of default, including payment defaults, breaches of covenants, change of control and a material adverse change default. Upon the occurrence of an event of default, a default interest rate of an additional 4.00% per annum may be applied to the outstanding loan balances, and the lenders may declare all outstanding obligations immediately due and payable. Borrowings under the Loan Agreement are collateralized by substantially all of the Company’s assets, other than its intellectual property. As of September 30, 2021, the estimated future principal payments due were as follows (in thousands): ​ ​ ​ ​ Year ending December 31, ​ 2021 (three months ending December 31) ​ $ — 2022 ​ — 2023 ​ ​ — 2024 ​ ​ 18,750 2025 and thereafter ​ ​ 56,250 ​ ​ $ 75,000 ​

Equity

Equity	9 Months Ended
	Sep. 30, 2021
Equity
Equity	7. Equity On July 20, 2018, the Company filed a restated certificate of incorporation in the State of Delaware, which, among other things, restated the number of shares of all classes of stock that the Company has authority to issue to 160,000,000 shares, consisting of (i) 150,000,000 shares of common stock, $0.001 par value per share, and (ii) 10,000,000 shares of preferred stock, $0.001 par value per share. The preferred stock will have such rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, as shall be determined by the Company’s board of directors upon issuance. The shares of preferred stock are currently undesignated. On August 1, 2019, the Company entered into a Distribution Agreement (the “Distribution Agreement”) with J.P. Morgan Securities LLC, Jefferies LLC and SVB Leerink LLC (the “Sales Agents”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $100.0 million through the Sales Agents. The Company’s registration statement on Form S-3 filed on August 1, 2019 was declared effective on August 21, 2019. The Sales Agents may sell common stock by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended, including sales made directly on or through the Nasdaq Global Select Market or any other existing trade market for the common stock, in negotiated transactions at market prices prevailing at the time of sale or at prices related to prevailing market prices, or any other method permitted by law. The Sales Agents will be entitled to receive 3.0% of the gross sales price per share of common stock sold pursuant to the Distribution Agreement. As of September 30, 2021, no shares of common stock have been issued and sold pursuant to the Distribution Agreement. On March 18, 2021, the Company completed the March 2021 Offering, pursuant to which it issued and sold 6,896,552 shares of common stock. The aggregate net proceeds received by the Company from the March 2021 Offering were $187.2 million, after deducting underwriting discounts and commissions and other offering costs.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Stock-Based Compensation
Stock-Based Compensation	​ ​ 8. Stock-Based Compensation Service-Based Stock Options During the nine months ended September 30, 2021, the Company granted options with service-based vesting conditions for the purchase of 3,942,080 shares of common stock with a weighted average exercise price of $16.01 per share and a weighted average grant-date fair value of $10.69 per share. Stock-Based Compensation The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Research and development expenses ​ $ 3,408 ​ $ 1,996 $ 8,995 ​ $ 6,165 General and administrative expenses ​ 4,781 ​ 5,989 ​ 17,433 ​ 18,560 ​ ​ $ 8,189 ​ $ 7,985 ​ $ 26,428 ​ $ 24,725 ​ ​ As of September 30, 2021, total unrecognized compensation cost related to the unvested stock-based awards was $67.0 million, which is expected to be recognized over a weighted average period of 2.6 years.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies
Commitments and Contingencies	9. Commitments and Contingencies License Agreement with the Whitehead Institute for Biomedical Research The Company has a license agreement with the Whitehead Institute for Biomedical Research (“WIBR”) under which the Company has been granted an exclusive, sublicensable, nontransferable license under certain patent families related to the development of the Company’s red cell therapies (as amended, the “WIBR License”). The Company is obligated to pay WIBR annual license maintenance fees of less than $0.1 million, as well as patent-related costs, including legal fees, and low single-digit royalties based on annual net sales of licensed products and licensed services by the Company and its sublicensees. Based on the progress the Company makes in the advancement of products covered by the licensed patent rights, the Company is required to make aggregate milestone payments of up to $1.6 million upon the achievement of specified preclinical, clinical and regulatory milestones. In addition, the Company is required to pay to WIBR a percentage of the non-royalty payments that it receives from sublicensees of the patent rights licensed by WIBR. This percentage varies from low single-digit to low double-digit percentages and will be based upon the clinical stage of the product that is the subject of the sublicense. Royalties shall be paid by the Company on a licensed product-by-licensed product and country-by-country basis, beginning on the first commercial sale of such licensed product in such country until expiration of the last valid patent claim covering such licensed product in such country. The Company has the right to terminate the WIBR License in its entirety, on a patent-by-patent or country-by-country basis, at will upon three months’ notice to WIBR. WIBR may terminate the agreement upon breach of contract or in the event of the Company’s bankruptcy, liquidation, insolvency or cessation of business related to the license. 401(k) Plan In January 2018, the Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company will make matching contributions at a rate of 50% of each employee’s contribution up to a maximum employee contribution of 6% of eligible plan compensation. For the three and nine months ended September 30, 2021, the Company made matching contributions of $0.2 million and $0.7 million, respectively. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and executive officers 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 or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2021
Net Loss per Share
Net Loss per Share	10. Net Loss per Share Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Numerator: ​ ​ ​ ​ Net loss ​ $ (49,016) ​ $ (40,852) ​ $ (141,526) ​ $ (127,192) ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ Weighted average common shares outstanding, basic and diluted ​ 89,807,383 ​ 80,778,042 ​ 87,240,694 ​ 80,511,543 ​ Net loss per share, basic and diluted ​ $ (0.55) ​ $ (0.51) ​ $ (1.62) ​ $ (1.58) ​ ​ The Company’s potential dilutive securities 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 from the periods in the table above, 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, ​ ​ 2021 2020 Unvested restricted common stock 985,364 252,000 Stock options to purchase common stock 17,782,603 16,541,112 ​ 18,767,967 16,793,112 ​ ​ ​ ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated balance sheet at December 31, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 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 condensed 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, 2020 included in the Company’s Annual Report on Form 10-K for the year-ended December 31, 2020, on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s condensed consolidated financial position as of September 30, 2021 and condensed consolidated results of operations for the three and nine months ended September 30, 2021 and 2020 and the condensed consolidated cash flows for the nine months ended September 30, 2021 and 2020 have been made. The Company’s condensed consolidated results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021 .
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 financial statements and the reported amounts of revenue and expenses during the reporting periods. In the condensed consolidated financial statements, the Company uses estimates and assumptions related to the accrual of research and development expenses 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. ​ The full extent to which the ongoing COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19.
Concentrations of Credit Risk and of Significant Suppliers	Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company’s cash and cash equivalents, as of September 30, 2021, consisted of U.S. government money market funds. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.
Restricted Cash	Restricted Cash As of both September 30, 2021 and December 31, 2020, the Company maintained letters of credit totaling $1.7 million for the benefit of the landlords of its leased properties. The Company was required to maintain separate cash balances of these amounts to secure the letters of credit. Related to these separate cash balances, the Company included $0.1 million in prepaid expenses and other current assets and $1.6 million in restricted cash (non-current) in its condensed consolidated balance sheet as of September 30, 2021 and December 31, 2020. Cash, cash equivalents and restricted cash presented in the accompanying condensed consolidated statement of cash flows was $265.8 million and $76.9 million for the nine months ended September 30, 2021 and 2020, respectively, of which $1.7 million and $1.7 million was restricted cash, respectively.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ● Level 1—Quoted prices in active markets for identical assets or liabilities. ● Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ● Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The carrying value of the Company’s long-term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate.
Investments	Investments The Company’s investments are classified as available-for-sale and are carried at fair value. Realized gains and losses and declines in value are based on the specific identification method and are included as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company classifies its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such investments are available for current operations. In June 2016, issued 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses , which changes the impairment model for most financial assets, including the Company’s investments. The Company adopted the standard effective January 1, 2020 using a prospective transition method. The Company evaluates its investments with unrealized losses for impairment. When assessing investments for unrealized declines in value, the Company considers whether the decline in value is related to a credit loss or non-credit loss. For credit losses, the Company reduces the investment to fair value through an allowance for credit losses recorded to the balance sheet and corresponding charge to the statement of operations. The allowance for credit losses and corresponding impairment charge is adjusted each period for changes in fair value. For non-credit losses, the Company reduces the investment to fair value through a charge to the statement of comprehensive loss, reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. No such credit losses were recorded during the periods presented.
Leases	Leases At the inception of an arrangement as lessee or lessor, the Company determines whether the arrangement is or contains a lease. Operating lease cost is recognized over the lease term on a straight-line basis. Variable lease cost and short-term leases (lease terms less than 12 months) are recognized as incurred. For both lessee and lessor arrangements, variable lease payments are the amounts owed by the Company to a lessor that are not fixed, such as reimbursement for common area maintenance and utilities costs, and are expensed when incurred. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that it will exercise that option. For lessee arrangements, operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current. The Company has elected the following lease policies at the inception of a lease: (1) for lessee and lessor arrangements within all asset classes, combine lease and non-lease components as a single component, with the lease expense recognized over the expected term on a straight-line basis and (2) for lessee arrangements, apply short-term lease exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for leases with terms of one year or less.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements ASU No. 2019-12, Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (ASC 740). interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. This guidance is effective for the Company for annual and interim periods beginning after December 31, 2020; however, early adoption is permitted. The Company adopted this standard as of January 1, 2021 on a prospective basis. The adoption did not have an impact on the Company’s condensed consolidated financial statements.

Investments and Fair Value of_2

Investments and Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Investments and Fair Value of Financial Assets and Liabilities
Schedule of investments by security type	The Company had no investments as of September 30, 2021. As of December 31, 2020, investments by security type consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Amortized Cost ​ Gross ​ Gross ​ Credit Losses ​ Fair Value U.S. treasury bills and notes (due within one year) $ 85,118 $ 6 $ (2) ​ $ — ​ $ 85,122 ​ ​ $ 85,118 ​ $ 6 ​ $ (2) ​ $ — ​ $ 85,122
Schedule of financial assets and liabilities measured at fair value on a recurring basis	The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value measurements at September 30, 2021 using: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ U.S. money market funds $ 256,034 $ — $ — ​ $ 256,034 ​ ​ $ 256,034 ​ $ — ​ $ — ​ $ 256,034 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value measurements at December 31, 2020 using: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ U.S money market funds $ 88,814 $ — $ — ​ $ 88,814 Investments: ​ ​ ​ ​ ​ ​ ​ U.S. treasury bills and notes ​ — ​ 85,122 ​ — ​ 85,122 ​ ​ $ 88,814 ​ $ 85,122 ​ $ — ​ $ 173,936

Property, Plant and Equipment_2

Property, Plant and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment, Net.
Schedule of property, plant and equipment, Net	Property, plant and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 December 31, 2020 Land ​ $ 1,300 ​ $ 1,300 ​ Manufacturing facility ​ ​ 31,235 ​ ​ 30,969 ​ Manufacturing equipment ​ ​ 8,804 ​ ​ 8,782 ​ Laboratory equipment ​ 17,370 ​ ​ 16,639 Computer equipment 2,480 ​ 2,118 Furniture and fixtures ​ ​ 1,228 ​ ​ 1,228 ​ Leasehold improvements 444 ​ 444 Construction-in-progress 4,330 ​ 2,605 ​ 67,191 ​ 64,085 Less: Accumulated depreciation and amortization (14,464) ​ (10,133) ​ ​ $ 52,727 ​ $ 53,952 ​

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Expenses and Other Current Liabilities
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 December 31, 2020 Accrued employee compensation and benefits $ 5,978 ​ $ 8,124 Accrued external research and development expenses 4,430 ​ 3,156 Accrued manufacturing facility expenses 1,331 ​ 339 Accrued general and administrative expenses ​ ​ 1,019 ​ ​ 1,244 Other 864 ​ 554 ​ ​ $ 13,622 ​ $ 13,417

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt
Schedule of estimated future principal payments due	As of September 30, 2021, the estimated future principal payments due were as follows (in thousands): ​ ​ ​ ​ Year ending December 31, ​ 2021 (three months ending December 31) ​ $ — 2022 ​ — 2023 ​ ​ — 2024 ​ ​ 18,750 2025 and thereafter ​ ​ 56,250 ​ ​ $ 75,000

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Stock-Based Compensation
Schedule of allocation of share based compensation	The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Research and development expenses ​ $ 3,408 ​ $ 1,996 $ 8,995 ​ $ 6,165 General and administrative expenses ​ 4,781 ​ 5,989 ​ 17,433 ​ 18,560 ​ ​ $ 8,189 ​ $ 7,985 ​ $ 26,428 ​ $ 24,725 ​

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Net Loss per Share
Schedule of calculation of basic and diluted net loss per share attributable to common stockholders	Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Numerator: ​ ​ ​ ​ Net loss ​ $ (49,016) ​ $ (40,852) ​ $ (141,526) ​ $ (127,192) ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ Weighted average common shares outstanding, basic and diluted ​ 89,807,383 ​ 80,778,042 ​ 87,240,694 ​ 80,511,543 ​ Net loss per share, basic and diluted ​ $ (0.55) ​ $ (0.51) ​ $ (1.62) ​ $ (1.58) ​
Schedule of dilutive securities excluded from computations of diluted weighted average shares outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ ​ 2021 2020 Unvested restricted common stock 985,364 252,000 Stock options to purchase common stock 17,782,603 16,541,112 ​ 18,767,967 16,793,112

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details) - USD ($) $ in Thousands	Mar. 18, 2021	Jul. 20, 2018	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Sale of Equity
Net proceeds after deducting underwriting discounts and commissions									$ 188,000
Net Loss			$ (49,016)	$ (50,180)	$ (42,330)	$ (40,852)	$ (37,854)	$ (48,486)	(141,526)	$ (127,192)	$ (167,700)
Accumulated deficit			$ (621,997)						$ (621,997)		$ (480,471)
Common stock
Sale of Equity
Shares issued (in shares)					6,896,552
Conversion of redeemable convertible preferred stock to common stock (in shares)		51,845,438
IPO
Sale of Equity
Shares issued (in shares)		12,055,450
Net proceeds after deducting underwriting discounts and commissions		$ 254,300
Offering
Sale of Equity
Shares issued (in shares)	6,896,552
Net proceeds after deducting underwriting discounts and commissions	$ 187,200
Overallotment
Sale of Equity
Shares issued (in shares)		1,572,450

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies
Restricted cash for the benefit of its leased properties	$ 1,700	$ 1,700
Restricted cash (current)	$ 100	$ 100
Current restricted cash included in prepaid expense and other current assets	Prepaid expenses and other current assets	Prepaid expenses and other current assets
Restricted cash (non-current)	$ 1,573	$ 1,573
Cash, cash equivalents and restricted cash	265,753	$ 92,901	$ 76,909	$ 93,633
Restricted cash	$ 1,700		$ 1,700

Investments and Fair Value of_3

Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable securities
Amortized Cost		$ 85,118
Gross Unrealized Gains		6
Gross Unrealized Losses		(2)
Investments	$ 0	85,122
Assets:
Investments	0	85,122
Transfers between Level 1, Level 2 or Level 3
Transfer from Level 1 to Level 2, assets	0
U.S. treasury bills and notes
Marketable securities
Amortized Cost		85,118
Gross Unrealized Gains		6
Gross Unrealized Losses		(2)
Investments		85,122
Assets:
Investments		85,122
Recurring
Assets:
Assets	256,034	173,936
Recurring | U.S. money market funds
Assets:
Cash equivalents	256,034	88,814
Recurring | U.S. treasury bills and notes
Marketable securities
Investments		85,122
Assets:
Investments		85,122
Recurring | Level 1
Assets:
Assets	256,034	88,814
Recurring | Level 1 | U.S. money market funds
Assets:
Cash equivalents	$ 256,034	88,814
Recurring | Level 2
Assets:
Assets		85,122
Recurring | Level 2 | U.S. treasury bills and notes
Marketable securities
Investments		85,122
Assets:
Investments		$ 85,122

Property, Plant and Equipment_3

Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment, Net
Property, plant and equipment, gross	$ 67,191	$ 64,085
Less: Accumulated depreciation and amortization	(14,464)	(10,133)
Property, plant and equipment, net	52,727	53,952
Land
Property, Plant and Equipment, Net
Property, plant and equipment, gross	1,300	1,300
Manufacturing facility
Property, Plant and Equipment, Net
Property, plant and equipment, gross	31,235	30,969
Manufacturing equipment
Property, Plant and Equipment, Net
Property, plant and equipment, gross	8,804	8,782
Laboratory equipment
Property, Plant and Equipment, Net
Property, plant and equipment, gross	17,370	16,639
Computer equipment
Property, Plant and Equipment, Net
Property, plant and equipment, gross	2,480	2,118
Furniture and fixtures
Property, Plant and Equipment, Net
Property, plant and equipment, gross	1,228	1,228
Leasehold improvements
Property, Plant and Equipment, Net
Property, plant and equipment, gross	444	444
Construction-in-progress
Property, Plant and Equipment, Net
Property, plant and equipment, gross	$ 4,330	$ 2,605

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses and Other Current Liabilities
Accrued employee compensation and benefits	$ 5,978	$ 8,124
Accrued external research and development expenses	4,430	3,156
Accrued manufacturing facility expenses	1,331	339
Accrued general and administrative expenses	1,019	1,244
Other	864	554
Accrued expenses and other current liabilities	$ 13,622	$ 13,417

Debt (Details)

Debt (Details) $ in Thousands	Jun. 23, 2021	Jun. 22, 2021USD ($)	Dec. 21, 2018USD ($)tranche	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Sep. 30, 2021USD ($)
Estimated future principal payments due
2024						$ 18,750
2025 and thereafter						56,250
Total debt						$ 75,000
2018 Credit Facility
Debt
Number of tranche | tranche			3
Maximum amount outstanding			$ 75,000
Debt default interest rate addition (as a percent)						4
Term loan
Debt
Principal amount of each tranche of term loans			25,000
Borrowing			$ 25,000	$ 25,000	$ 25,000
2018 Credit Facility Amendment
Debt
Interest rate (as a percent)		5.50%
Prepayment fee in first year		1.00%
Prepayment fee in second year		0.50%
Prepayment fee in third year		0.25%
2018 Credit Facility Amendment | Lenders
Debt
Issuance costs		$ 200
2018 Credit Facility Amendment | Minimum
Debt
Variable interest rate		2.10%
2018 Credit Facility Amendment | One-month U.S. LIBOR
Debt
Variable interest rate	2.10%	0.00%
One-month LIBOR		one-month
Principal Amount To Be Funded Per Tranche, Second Amendment, Including Additional Limit [Member]
Debt
Principal amount		$ 35,000

Equity (Details)

Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 18, 2021	Jul. 20, 2018	Mar. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Aug. 01, 2019
Equity
Shares authorized		160,000,000
Common stock, authorized (in shares)		150,000,000		150,000,000	150,000,000
Common stock, par value (in dollars per share)		$ 0.001		$ 0.001	$ 0.001
Preferred stock, share authorized (in shares)		10,000,000		10,000,000	10,000,000
Preferred stock, par value (in dollars per share)		$ 0.001		$ 0.001	$ 0.001
Net proceeds after deducting underwriting discounts and commissions				$ 188,000
Common stock
Equity
Shares issued (in shares)			6,896,552
IPO
Equity
Shares issued (in shares)		12,055,450
Net proceeds after deducting underwriting discounts and commissions		$ 254,300
Overallotment
Equity
Shares issued (in shares)		1,572,450
At the market offering
Equity
Aggregate offering price						$ 100,000
Percentage of commission						3.00%
Shares issued (in shares)				0
Offering
Equity
Shares issued (in shares)	6,896,552
Net proceeds after deducting underwriting discounts and commissions	$ 187,200

Stock-Based Compensation - Comp

Stock-Based Compensation - Compensation expense (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-based compensation expense
Stock-based compensation expense	$ 8,189	$ 7,985	$ 26,428	$ 24,725
Research and development expenses
Stock-based compensation expense
Stock-based compensation expense	3,408	1,996	8,995	6,165
General and administrative expenses
Stock-based compensation expense
Stock-based compensation expense	4,781	$ 5,989	17,433	$ 18,560
Stock options.
Stock-based compensation expense
Unrecognized compensation cost	$ 67,000		$ 67,000
Unrecognized compensation cost expected to be recognized over a weighted average period			2 years 7 months 6 days
Service Based Stock Options
Stock-based compensation expense
Purchase of an aggregate shares of common stock			3,942,080
Options exercise price			$ 16.01
Weighted average grant-date fair value (per share)			$ 10.69

Commitments and Contingencies -

Commitments and Contingencies - Collaborative Arrangements and Non-collaborative Arrangement (Details) - WIBR $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Collaborative Arrangements and Non-collaborative Arrangement
Aggregate milestone payments	$ 1.6
Maximum | License maintenance fees
Collaborative Arrangements and Non-collaborative Arrangement
License costs	$ 0.1

Commitments and Contingencies_2

Commitments and Contingencies - Defined Contribution Plan (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2018	Sep. 30, 2021	Sep. 30, 2021
Commitments and Contingencies
Employer matching contribution (as a percent)	50.00%
Company matching contribution		$ 0.2	$ 0.7
Maximum
Commitments and Contingencies
Percentage of employee's gross pay match	6.00%

Net Loss per Share - Weighted A

Net Loss per Share - Weighted Average Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Numerator:
Net Loss	$ (49,016)	$ (50,180)	$ (42,330)	$ (40,852)	$ (37,854)	$ (48,486)	$ (141,526)	$ (127,192)	$ (167,700)
Denominator:
Weighted average common shares outstanding, basic and diluted	89,807,383			80,778,042			87,240,694	80,511,543
Net loss per share, basic and diluted	$ (0.55)			$ (0.51)			$ (1.62)	$ (1.58)

Net Loss per Share - Antidiluti

Net Loss per Share - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	18,767,967	16,793,112
Unvested restricted common stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	985,364	252,000
Stock options to purchase common stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	17,782,603	16,541,112