Cartesian Therapeutics (RNAC) 10-Q 8 Aug 22 2022 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2022	Aug. 02, 2022
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2022
Document Transition Report	false
Entity File Number	001-37798
Entity Registrant Name	Selecta Biosciences, Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1622110
Entity Address, Address Line One	65 Grove Street,
Entity Address, City or Town	Watertown,
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Local Phone Number	923-1400
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	SELB
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Smaller Reporting Company	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		152,713,211
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001453687
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 138,057	$ 114,057
Marketable securities	3,999	13,998
Accounts receivable	23,994	9,914
Prepaid expenses and other current assets	6,522	6,474
Total current assets	172,572	144,443
Property and equipment, net	2,833	2,142
Right-of-use asset, net	9,238	9,829
Long-term restricted cash	1,379	1,379
Investments	2,000	2,000
Other assets	46	90
Total assets	188,068	159,883
Current liabilities:
Accounts payable	693	224
Accrued expenses	12,366	10,533
Loan payable	3,285	5,961
Lease liability	1,125	1,049
Income taxes payable	320	601
Deferred revenue	15,974	53,883
Total current liabilities	33,763	72,251
Non-current liabilities:
Loan payable, net of current portion	22,634	19,673
Lease liability	8,018	8,598
Deferred revenue	7,113	11,417
Warrant liabilities	26,934	25,423
Total liabilities	98,462	137,362
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding as of June 30, 2022 and December 31, 2021	0	0
Common stock, $0.0001 par value; 350,000,000 shares authorized; 152,713,211 and 123,622,965 shares issued and outstanding as of June 30, 2022 and December 31, 2021, respectively	15	12
Additional paid-in capital	487,008	457,391
Accumulated deficit	(392,937)	(430,316)
Accumulated other comprehensive loss	(4,480)	(4,566)
Total stockholders’ equity	89,606	22,521
Total liabilities and stockholders’ equity	$ 188,068	$ 159,883

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares 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)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, shares issued (in shares)	152,713,211	123,622,965
Common stock, shares outstanding (in shares)	152,713,211	123,622,965

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Collaboration and license revenue	$ 39,273	$ 19,663	$ 73,272	$ 30,713
Operating expenses:
Research and development	19,182	14,463	36,871	27,467
General and administrative	6,231	4,748	11,768	9,952
Total operating expenses	25,413	19,211	48,639	37,419
Operating income (loss)	13,860	452	24,633	(6,706)
Investment income	207	12	222	24
Foreign currency transaction, net	(104)	(14)	(76)	(7)
Interest expense	(715)	(711)	(1,422)	(1,422)
Change in fair value of warrant liabilities	(4,647)	4,820	13,868	(11,927)
Other income, net	0	6	154	6
Net income (loss)	8,601	4,565	37,379	(20,032)
Other comprehensive income (loss):
Foreign currency translation adjustment	118	12	86	6
Unrealized gain on marketable securities	0	1	0	0
Total comprehensive income (loss)	$ 8,719	$ 4,578	$ 37,465	$ (20,026)
Net income (loss) per share:
Basic (in dollars per share)	$ 0.06	$ 0.04	$ 0.27	$ (0.18)
Diluted (in dollars per share)	$ 0.06	$ 0	$ 0.17	$ (0.18)
Weighted average common shares outstanding:
Basic (in shares)	148,505,729	113,524,110	136,436,316	112,140,815
Diluted (in shares)	148,505,729	121,177,998	136,966,312	112,140,815

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders’ (Deficit) Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive loss
Beginning balance (in shares) at Dec. 31, 2020		108,071,249
Beginning balance at Dec. 31, 2020	$ (18,006)	$ 11	$ 391,175	$ (404,629)	$ (4,563)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)		34,696
Issuance of common stock under Employee Stock Purchase Plan	72		72
Issuance of common stock upon exercise of options (in shares)		153,278
Issuance of common stock upon exercise of options	244		244
Issuance of vested restricted stock units (in shares)		10,937
Issuance of vested restricted stock units	0
Issuance of common stock through at-the-market offering, net (in shares)		4,706,844
Issuance of common stock through at-the-market offering, net	20,943		20,943
Stock-based compensation expense	1,780		1,780
Foreign currency translation adjustment	(6)				(6)
Unrealized gain on marketable securities	(1)				(1)
Net income	(24,597)			(24,597)
Ending balance (in shares) at Mar. 31, 2021		112,977,004
Ending balance at Mar. 31, 2021	(19,571)	$ 11	414,214	(429,226)	(4,570)
Beginning balance (in shares) at Dec. 31, 2020		108,071,249
Beginning balance at Dec. 31, 2020	(18,006)	$ 11	391,175	(404,629)	(4,563)
Increase (Decrease) in Stockholders' Equity
Foreign currency translation adjustment	6
Unrealized gain on marketable securities	0
Net income	(20,032)
Ending balance (in shares) at Jun. 30, 2021		115,079,292
Ending balance at Jun. 30, 2021	(4,222)	$ 12	424,984	(424,661)	(4,557)
Beginning balance (in shares) at Mar. 31, 2021		112,977,004
Beginning balance at Mar. 31, 2021	(19,571)	$ 11	414,214	(429,226)	(4,570)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options (in shares)		242,278
Issuance of common stock upon exercise of options	425		425
Issuance of vested restricted stock units (in shares)		10,938
Issuance of vested restricted stock units	0
Issuance of common stock through at-the-market offering, net (in shares)		1,849,072
Issuance of common stock through at-the-market offering, net	8,563	$ 1	8,562
Stock-based compensation expense	1,783		1,783
Foreign currency translation adjustment	12				12
Unrealized gain on marketable securities	1				1
Net income	4,565			4,565
Ending balance (in shares) at Jun. 30, 2021		115,079,292
Ending balance at Jun. 30, 2021	$ (4,222)	$ 12	424,984	(424,661)	(4,557)
Beginning balance (in shares) at Dec. 31, 2021	123,622,965	123,622,965
Beginning balance at Dec. 31, 2021	$ 22,521	$ 12	457,391	(430,316)	(4,566)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)		81,057
Issuance of common stock under Employee Stock Purchase Plan	127		127
Issuance of common stock upon exercise of options (in shares)		11,262
Issuance of common stock upon exercise of options	21		21
Issuance of vested restricted stock units (in shares)		89,142
Issuance of common stock through at-the-market offering, net (in shares)		576,418
Issuance of common stock through at-the-market offering, net	1,675		1,675
Other financing fees	(79)		(79)
Stock-based compensation expense	2,753		2,753
Foreign currency translation adjustment	(32)				(32)
Net income	28,778			28,778
Ending balance (in shares) at Mar. 31, 2022		124,380,844
Ending balance at Mar. 31, 2022	$ 55,764	$ 12	461,888	(401,538)	(4,598)
Beginning balance (in shares) at Dec. 31, 2021	123,622,965	123,622,965
Beginning balance at Dec. 31, 2021	$ 22,521	$ 12	457,391	(430,316)	(4,566)
Increase (Decrease) in Stockholders' Equity
Foreign currency translation adjustment	86
Unrealized gain on marketable securities	0
Net income	$ 37,379
Ending balance (in shares) at Jun. 30, 2022	152,713,211	152,713,211
Ending balance at Jun. 30, 2022	$ 89,606	$ 15	487,008	(392,937)	(4,480)
Beginning balance (in shares) at Mar. 31, 2022		124,380,844
Beginning balance at Mar. 31, 2022	55,764	$ 12	461,888	(401,538)	(4,598)
Increase (Decrease) in Stockholders' Equity
Issuance of vested restricted stock units (in shares)		10,938
Issuance of vested restricted stock units	0
Issuance of common stock, net (in shares)		27,428,572
Issuance of common stock	21,480	$ 3	21,477
Other financing fees	79		79
Issuance of common stock, license agreement (in shares)		892,857
Issuance of common stock, license agreement	1,000		1,000
Stock-based compensation expense	2,564		2,564
Foreign currency translation adjustment	118				118
Unrealized gain on marketable securities	0
Net income	$ 8,601			8,601
Ending balance (in shares) at Jun. 30, 2022	152,713,211	152,713,211
Ending balance at Jun. 30, 2022	$ 89,606	$ 15	$ 487,008	$ (392,937)	$ (4,480)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities
Net income (loss)	$ 37,379	$ (20,032)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	696	512
Amortization of premiums and discounts on marketable securities	0	28
Non-cash lease expense	591	549
(Gain) on disposal of property and equipment	(147)	0
Stock-based compensation expense	6,317	3,563
Non-cash interest expense	579	594
Warrant liabilities revaluation	(13,868)	11,927
Changes in operating assets and liabilities:
Accounts receivable	(14,080)	(1,241)
Prepaid expenses, deposits and other assets	(374)	(2,811)
Accounts payable	300	(289)
Income taxes payable	(280)	0
Deferred revenue	(42,213)	(11,046)
Accrued expenses and other liabilities	965	70
Net cash (used in) operating activities	(24,135)	(18,176)
Cash flows from investing activities
Proceeds from maturities of marketable securities	10,000	0
Purchases of marketable securities	0	(24,417)
Purchases of property and equipment	(554)	(643)
Net cash provided by (used in) investing activities	9,446	(25,060)
Cash flows from financing activities
Debt amendment fee included in debt discount	(110)	0
Net proceeds from issuance of common stock and common warrants	36,890	0
Proceeds from exercise of stock options	21	672
Proceeds from issuance of common stock under Employee Stock Purchase Plan	127	72
Net cash provided by financing activities	38,603	30,291
Effect of exchange rate changes on cash	86	9
Net change in cash, cash equivalents, and restricted cash	24,000	(12,936)
Cash, cash equivalents, and restricted cash at beginning of period	115,436	140,064
Cash, cash equivalents, and restricted cash at end of period	139,436	127,128
Supplemental cash flow information
Cash paid for interest	1,014	998
Noncash investing and financing activities
Issuance of common stock, license agreement in stock-based compensation expense	1,000	0
Purchase of property and equipment not yet paid	320	2
Equity offering costs in accrued liabilities	31	44
At-The-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 1,675	$ 29,547

Description of the Business

Description of the Business	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Business	Description of the Business Selecta Biosciences, Inc., or the Company, was incorporated in Delaware on December 10, 2007, and is based in Watertown, Massachusetts. The Company is a clinical-stage biopharmaceutical company. The Company’s ImmTOR ® platform encapsulates rapamycin, also known as sirolimus, an FDA approved immunomodulator, in biodegradable nanoparticles. ImmTOR is designed to induce antigen-specific immune tolerance. The Company believes, by combining ImmTOR with antigens of interest, the Company’s precision immune tolerance platform has the potential to restore self-tolerance to auto-antigens in autoimmune diseases, amplify the efficacy of biologics (including gene therapies) and mitigate the formation of anti-drug antibodies, or ADAs, against biologic drugs. Since inception, the Company has devoted its efforts principally to research and development of its technology and product candidates, recruiting management and technical staff, acquiring operating assets, and raising capital. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. 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 infrastructure and extensive compliance-reporting capabilities. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. Unaudited Interim Financial Information The accompanying unaudited consolidated financial statements for the three and six months ended June 30, 2022 and 2021 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. 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, 2021 included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 10, 2022. The unaudited interim financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments that are necessary for a fair statement of the Company’s financial position as of June 30, 2022, the consolidated results of operations for the three and six months ended June 30, 2022, and cash flows for the six months ended June 30, 2022. Such adjustments are of a normal and recurring nature. The results of operations for the three and six months ended June 30, 2022 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2022. Liquidity and Management’s Plan The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain and sustain profitable operations. The Company is subject to a number of risks similar to other early-stage life science companies, including, but not limited to, successful development of its product candidates, raising additional capital with favorable terms, protection of proprietary technology and market acceptance of any approved future products. The successful development of product candidates requires substantial working capital, which may not be available to the Company on favorable terms or at all. To date, the Company has financed its operations primarily through the initial public offering of its common stock, private placements of its common stock, issuances of common and preferred stock, debt, research grants, research collaborations and licenses. The Company currently has no source of product revenue, and it does not expect to generate product revenue for the foreseeable future. To date, the Company’s revenue has primarily been from collaboration and license agreements. The Company has devoted substantially all of its financial resources and efforts to developing its ImmTOR platform, identifying potential product candidates and conducting preclinical studies and clinical trials. The Company is in the early stages of development of its product candidates, and it has not completed development of any ImmTOR-enabled therapies. As of June 30, 2022, the Company’s cash, cash equivalents, restricted cash and marketable securities were $143.4 million, of which $1.4 million was restricted cash related to lease commitments and $0.3 million was held by its Russian subsidiary designated solely for use in its operations. The Company believes the cash, cash equivalents, restricted cash and marketable securities as of June 30, 2022 will enable it to fund its current planned operations for at least the next twelve months from the date of issuance of these financial statements, though it may realize additional cash resources upon the achievement of certain contingent collaboration milestones or it may pursue additional cash resources through public or private equity or debt financings or by establishing collaborations with other companies. Management’s expectations with respect to its ability to fund current and long term planned operations are based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional strategic or financing opportunities sooner than would otherwise be expected. However, there is no guarantee that any collaboration milestones will be achieved or that any of these strategic or financing opportunities will be executed on favorable terms, and some could be dilutive to existing stockholders. If the Company is unable to obtain additional funding on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations or otherwise capitalize on its commercialization of its product candidates. The Company anticipates operating losses to continue for the foreseeable future due to, among other things, costs related to research and development of its product candidates and its administrative organization. At this time, any impact of COVID-19 on the Company’s business, revenues, results of operations and financial condition will largely depend on future developments, which are highly uncertain and cannot be predicted with confidence, such as the duration of the pandemic, the emergence of new virus variants, travel restrictions and social distancing in the United States and other countries, business closures or disruptions, supply chain disruptions, the ultimate impact on financial markets and the global economy, and the effectiveness of actions taken in the United States and other countries to contain and treat the disease. Guarantees and Indemnifications As permitted under Delaware law, the Company indemnifies its officers, directors, consultants and employees for certain events or occurrences that happen by reason of the relationship with, or position held at the Company. Through June 30, 2022, the Company had not experienced any losses related to these indemnification obligations, and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The Company disclosed its significant accounting policies in Note 2 – Summary of Significant Accounting Policies included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021. There have been no material changes during the three months ended June 30, 2022, with the exception of the matters discussed in recent accounting pronouncements. Recent Accounting Pronouncements Recently Adopted In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt – Modifications and Extinguishments (Subtopic 470-50), Compensation – Stock Compensation (Topic 718), and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer's Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options . ASU 2021-04 provides guidance as to how entities should account for a modification of the terms or conditions or an exchange of a freestanding equity-classified written call option (i.e., a warrant) that remains equity-classified after modification or exchange as an exchange of the original instrument for a new instrument. An entity should apply the guidance provided in ASU 2021-04 prospectively to modifications or exchanges occurring on or after the effective date. This new standard was effective for all entities for fiscal years beginning after December 15, 2021. The adoption of ASU 2021-04 did not have an impact on the Company’s financial position or results of operations upon adoption. Not Yet Adopted In August 2020, the FASB issued ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) . ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. This new standard will be effective for smaller reporting companies for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years. The Company is assessing the impact this standard will have on its consolidated financial statements and disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit

Marketable Securities and Inves

Marketable Securities and Investments	6 Months Ended
	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Marketable Securities and Investments	Marketable Securities and Investments The following table summarizes the marketable securities held as of June 30, 2022 and December 31, 2021 (in thousands): Amortized Unrealized gains Unrealized losses Fair June 30, 2022 Commercial paper 3,999 — — 3,999 Total $ 3,999 $ — $ — $ 3,999 December 31, 2021 Corporate bonds $ 2,007 $ — $ (1) $ 2,006 Commercial paper 11,992 — — 11,992 Total $ 13,999 $ — $ (1) $ 13,998 All marketable securities held at June 30, 2022 and December 31, 2021 had maturities of less than 12 months when purchased and are classified as short-term marketable securities on the accompanying consolidated balance sheet. During the six months ended June 30, 2022, there were no marketable securities adjusted for other than temporary declines in fair value. The Company does not intend to sell its investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity. Investments As of June 30, 2022 and December 31, 2021, the Company has a $2.0 million investment in Cyrus Biotechnology, Inc., or Cyrus, pursuant to an investment agreement entered into in connection with the Collaboration and License Agreement with Cyrus. The Company’s maximum exposure to loss related to this variable interest entity is limited to the carrying value of the investment.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	6 Months Ended
	Jun. 30, 2022
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) Per Share The following table sets forth the computation of basic and diluted net income (loss) per share for the three and six months ended June 30, 2022 and 2021 (in thousands, except share and per-share data): Three Months Ended Six Months Ended 2022 2021 2022 2021 Numerator: Net income (loss) $ 8,601 $ 4,565 $ 37,379 $ (20,032) Less: Change in fair value of liability warrants — (4,820) (13,868) — Adjusted net income (loss) $ 8,601 $ (255) $ 23,511 $ (20,032) Denominator: Weighted-average common shares outstanding - basic 148,505,729 113,524,110 136,436,316 112,140,815 Dilutive effect of employee equity incentive plans and — 7,653,888 529,996 — Weighted-average common shares used in per share calculations - diluted 148,505,729 121,177,998 136,966,312 112,140,815 Net income (loss) per share: Basic $ 0.06 $ 0.04 $ 0.27 $ (0.18) Diluted $ 0.06 $ — $ 0.17 $ (0.18) The following table represents the potential dilutive shares of common stock excluded from the computation of the diluted net loss per share for all periods presented, as the effect would have been anti-dilutive: Three Months Ended Six Months Ended 2022 2021 2022 2021 Options, RSUs and ESPP shares 16,422,488 10,574,133 16,660,700 10,574,133 Warrants to purchase common stock 31,307,409 292,469 20,863,898 12,378,016 Total 47,729,897 10,866,602 37,524,598 22,952,149

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables present the Company’s assets and liabilities that are measured at fair value on a recurring basis as of June 30, 2022 and December 31, 2021 (in thousands): June 30, 2022 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 76,686 $ 76,686 $ — $ — Marketable securities: Commercial paper 3,999 — 3,999 — Total assets $ 80,685 $ 76,686 $ 3,999 $ — Liabilities: Warrant liabilities $ 26,934 $ — $ — $ 26,934 Total liabilities $ 26,934 $ — $ — $ 26,934 December 31, 2021 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 66,563 $ 66,563 $ — $ — Marketable securities: Corporate bonds 2,006 — 2,006 — Commercial paper 11,992 — 11,992 — Total assets $ 80,561 $ 66,563 $ 13,998 $ — Liabilities: Warrant liabilities $ 25,423 $ — $ — $ 25,423 Total liabilities $ 25,423 $ — $ — $ 25,423 There were no transfers within the fair value hierarchy during the six months ended June 30, 2022 or year ended December 31, 2021. Cash, Cash Equivalents, and Restricted Cash As of June 30, 2022 and December 31, 2021, money market funds were classified as cash and cash equivalents on the accompanying consolidated balance sheets as they mature within 90 days from the date of purchase. As of June 30, 2022, the Company had restricted cash balances relating to a secured letter of credit in connection with its lease for the Company’s headquarters. The Company’s consolidated statements of cash flows include the following as of June 30, 2022 and 2021 (in thousands): June 30, 2022 2021 Cash and cash equivalents $ 138,057 $ 125,749 Long-term restricted cash 1,379 1,379 Total cash, cash equivalents, and restricted cash $ 139,436 $ 127,128 Marketable Securities As of June 30, 2022, marketable securities classified as Level 2 within the valuation hierarchy consist of commercial paper which are available-for-sale securities in accordance with the Company’s investment policy. The Company estimates the fair value of these marketable securities by taking into consideration valuations that include market pricing based on real-time trade data for the same or similar securities, and other observable inputs. The amortized cost of available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to the earliest call date for premiums or to maturity for discounts. Loans Payable At June 30, 2022, in light of the issuance of the first tranche under the Company’s term loan pursuant the Loan and Security Agreement, dated August 31, 2020, as amended, among the Company, Oxford Finance LLC, or Oxford, as Collateral Agent and a Lender, and Silicon Valley Bank, or SVB, as a Lender, or the Loan and Security Agreement, the Company believes the carrying value approximates the fair value of the loan. Warrants In December 2019, the Company issued warrants in connection with a private placement of shares of common stock, or the 2019 Warrants. Pursuant to the terms of the 2019 Warrants, the Company could be required to settle the 2019 Warrants in cash in the event of certain acquisitions of the Company and, as a result, the 2019 Warrants are required to be measured at fair value and reported as a liability on the balance sheet. In April 2022, the Company issued warrants in connection with an underwritten offering of shares of common stock and warrants to purchase shares of common stock, or the 2022 Warrants. Pursuant to the terms of the 2022 Warrants, the Company could be required to settle the 2022 Warrants in cash in the event of an acquisition of the Company under certain circumstances and, as a result, the 2022 Warrants are required to be measured at fair value and reported as a liability on the balance sheet. The Company recorded the fair value of the 2019 Warrants and the 2022 Warrants upon issuance using the Black-Scholes valuation model and is required to revalue the 2019 Warrants and the 2022 Warrants at each reporting date, with any changes in fair value recorded in the statement of operations and comprehensive income (loss). The valuations of the 2019 Warrants and the 2022 Warrants are considered Level 3 of the fair value hierarchy due to the need to use assumptions in the valuations that are both significant to the fair value measurement and unobservable; including the stock price volatility and the expected life of the 2019 Warrants and the 2022 Warrants. Generally, increases (decreases) in the fair value of the underlying stock and estimated term would result in a directionally similar impact to the fair value measurement. The changes in the fair values of the Level 3 warrant liability are reflected in the statement of operations and comprehensive income (loss) for the three and six months ended June 30, 2022 and 2021. The estimated fair values of the 2019 Warrants and the 2022 Warrants are determined using the following inputs to the Black-Scholes simulation valuation: Estimated fair value of the underlying stock . The Company estimates the fair value of the common stock based on the closing stock price at the end of each reporting period. Risk-free interest rate . The risk-free interest rate is based on the U.S. Treasury at the valuation date commensurate with the expected remaining life assumption. Dividend rate . The dividend rate is based on the historical rate, which the Company anticipates will remain at zero. Expected life . The expected life of the 2019 Warrants and the 2022 Warrants is assumed to be equivalent to their remaining contractual terms which expire on December 23, 2024 and April 11, 2027, respectively. Volatility . The Company estimates stock price volatility based on the Company’s historical volatility and the historical volatility of peer companies for a period of time commensurate with the expected remaining life assumption. A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2019 Warrants liability is as follows: June 30, December 31, 2022 2021 Risk-free interest rate 2.92 % 0.97 % Dividend yield — — Expected life (in years) 2.48 2.98 Expected volatility 96.95 % 96.10 % A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2022 Warrants liability is as follows: At Issuance June 30, April 11, 2022 2022 Risk-free interest rate 3.01 % 2.79 % Dividend yield — — Expected life (in years) 4.78 5.00 Expected volatility 99.88 % 96.00 % Changes in Level 3 Liabilities Measured at Fair Value on a Recurring Basis The following table reflects a roll-forward of fair value for the Company’s Level 3 warrant liabilities (see Note 10), for the six months ended June 30, 2022 (in thousands): Warrant liabilities Fair value as of December 31, 2021 $ 25,423 Issuances 15,379 Exercises — Change in fair value (13,868) Fair value as of June 30, 2022 $ 26,934

Property and Equipment

Property and Equipment	6 Months Ended
	Jun. 30, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consists of the following (in thousands): June 30, December 31, 2022 2021 Laboratory equipment $ 6,074 $ 5,134 Computer equipment and software 695 731 Leasehold improvements 57 45 Furniture and fixtures 341 332 Office equipment 190 163 Construction in process 310 534 Total property and equipment 7,667 6,939 Less accumulated depreciation (4,834) (4,797) Property and equipment, net $ 2,833 $ 2,142 Depreciation expense was $0.2 million and $0.3 million, and $0.2 million and $0.3 million for the three and six months ended June 30, 2022 and 2021, respectively.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2022
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consist of the following (in thousands): June 30, December 31, 2022 2021 Payroll and employee related expenses $ 2,223 $ 3,179 Collaboration and licensing 500 — Accrued patent fees 885 309 Accrued external research and development costs 6,701 4,339 Accrued professional and consulting services 547 815 Accrued interest 184 170 Other 1,326 1,721 Accrued expenses $ 12,366 $ 10,533 Other accrued expenses as of June 30, 2022 and December 31, 2021 include a $0.9 million estimated liability for the settlement of litigation relating to the two lawsuits described further within Note 17.

Leases

Leases	6 Months Ended
	Jun. 30, 2022
Leases [Abstract]
Leases	Leases For the three and six months ended June 30, 2022 and 2021, the components of lease costs were as follows (in thousands): Three Months Ended Six Months Ended 2022 2021 2022 2021 Operating lease cost $ 505 $ 454 $ 1,011 $ 898 Variable lease cost 205 182 425 470 Short-term lease cost 2 2 5 5 Total lease cost $ 712 $ 638 $ 1,441 $ 1,373 The maturity of the Company’s operating lease liabilities as of June 30, 2022 were as follows (in thousands): June 30, 2022 2022 (remainder) $ 942 2023 1,922 2024 1,980 2025 2,039 2026 2,101 Thereafter 2,844 Total future minimum lease payments 11,828 Less imputed interest 2,685 Total operating lease liabilities $ 9,143 The supplemental disclosure for the statement of cash flows related to operating leases were as follows (in thousands): June 30, 2022 2021 Cash paid for amounts included in the measurement of lease liabilities: $ 924 $ 898 Other than the initial recording of the right-of-use asset and lease liability for the Headquarters Lease in 2020, which was non-cash, the changes in the Company’s right-of-use asset and lease liability for the six months ended June 30, 2022 and 2021 are reflected in the non-cash lease expense and accrued expenses and other liabilities, respectively, in the consolidated statements of cash flows. The following summarizes additional information related to operating leases: June 30, 2022 2021 Weighted-average remaining lease term 5.9 years 6.9 years Weighted-average discount rate 8.9 % 8.9 %

Debt

Debt	6 Months Ended
	Jun. 30, 2022
Debt Disclosure [Abstract]
Debt	Debt 2020 Term Loan On March 21, 2022, the Company entered into a Second Amendment to its 2020 Term Loan. The Second Amendment extended the date on which amortization payments in respect of the 2020 Term Loan will commence by twelve months to April 1, 2023. Thereafter, amortization payments will be paid monthly in equal installments of principal and interest to fully amortize the outstanding principal over the remaining term of the 2020 Term Loan, subject to recalculation upon a change in the prime rate. The Second Amendment was determined to be a loan modification, and the $0.1 million fee was recorded as an addition to the debt discount on the effective date. As of June 30, 2022 and December 31, 2021, the outstanding principal balance under the 2020 Term Loan was $25.0 million. Total 2020 Term Loan and unamortized debt discount balances as of June 30, 2022 are as follows (in thousands): Face value $ 25,000 Venture debt termination fee 2,250 Less: Debt discount (1,331) Less: Current portion of loan payable (3,285) Loan payable, net of current portion $ 22,634 Future minimum principal payments on the 2020 Term Loan as of June 30, 2022 are as follows (in thousands): Year ended: 2023 7,759 2024 10,345 2025 6,896 Total minimum principal payments $ 25,000

Equity

Equity	6 Months Ended
	Jun. 30, 2022
Equity [Abstract]
Equity	Equity On June 17, 2022, at the 2022 Annual Meeting of Stockholders, the Company’s stockholders approved an amendment to the Company’s Restated Certificate of Incorporation, or the Charter, to increase the number of authorized shares of common stock, par value $0.0001 per share, from 200,000,000 to 350,000,000 shares. On June 21, 2022, the Company filed a Certificate of Amendment to the Charter with the Secretary of State of the State of Delaware, which became effective upon filing. Equity Financings Underwritten Offering On April 6, 2022, the Company entered into an underwriting agreement with SVB Securities LLC, as representative of the several underwriters named therein, relating to an underwritten offering of 27,428,572 shares, or the Shares, of the Company’s common stock and warrants to purchase up to 20,571,429 shares of common stock, or the 2022 Warrants. The offering of the Shares and the 2022 Warrants is referred to as the Offering. Each Share and accompanying 2022 Warrant to purchase 0.75 shares of common stock was sold at a combined offering price of $1.41. The exercise price for the 2022 Warrants is $1.55 per share. The Company received net proceeds from the Offering of approximately $36.9 million. The 2022 Warrants are subject to adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the Company’s common stock and also upon any distributions for no consideration of assets to the Company’s stockholders. Each 2022 Warrant is exercisable at any time and from time to time after issuance. In the event of certain corporate transactions, the holders of the 2022 Warrants will be entitled to receive the kind and amount of securities, cash or other property that the holders would have received had they exercised the Warrants immediately prior to such transaction. Therefore, the Company is required to account for the 2022 Warrants as liabilities and record the 2022 Warrants at fair value. The 2022 Warrants do not entitle the holders thereof to any voting rights or any of the other rights or privileges to which holders of Common Stock are entitled. “At-the-Market” Offerings On October 25, 2021, the Company entered into a Sales Agreement, or the 2021 Sales Agreement, with SVB Leerink LLC (now known as SVB Securities LLC), or SVB Leerink, pursuant to which the Company may sell shares of the Company’s common stock, from time to time, through an “at the market” equity offering program under which SVB Leerink will act as sales agent. The shares of common stock sold pursuant to the 2021 Sales Agreement will be issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-241692), aggregate gross sales proceeds of up to $75.0 million. During the six months ended June 30, 2022, the Company sold 576,418 shares of its common stock pursuant to the 2021 Sales Agreement for aggregate net proceeds of $1.7 million, after deducting commissions and other transaction costs. Warrants During the six months ended June 30, 2022, there were 20,571,429 warrants issued, no warrants exercised, and 79,130 warrants canceled. Refer to Note 10 to the consolidated financial statements within our 2021 Annual Report on Form 10-K for further discussion of the terms related to the Company’s 2019 Warrants. Number of Warrants Equity Liability classified Total Weighted average Outstanding at December 31, 2021 292,469 10,443,511 10,735,980 $ 1.62 Issuance — 20,571,429 20,571,429 1.55 Canceled (79,130) — (79,130) 17.71 Outstanding at June 30, 2022 213,339 31,014,940 31,228,279 $ 1.53 Reserved Shares The Company has authorized shares of common stock for future issuance as follows: As of June 30, 2022 December 31, 2021 Exercise of warrants 31,228,279 10,735,980 Shares available for future stock incentive awards 6,830,244 6,039,564 Unvested restricted stock units 1,097,483 394,450 Outstanding common stock options 15,536,170 11,039,873 Total 54,692,176 28,209,867

Stock Incentive Plans

Stock Incentive Plans	6 Months Ended
	Jun. 30, 2022
Share-Based Payment Arrangement [Abstract]
Stock Incentive Plans	Stock Incentive Plans The Company maintains the 2008 Stock Incentive Plan, or the 2008 Plan, for employees, consultants, advisors, and directors. The 2008 Plan provided for the granting of incentive and non-qualified stock option and restricted stock awards as determined by the Board. In June 2016, the Company’s stockholders approved the 2016 Incentive Award Plan, or the 2016 Plan, which authorized 1,210,256 shares of common stock for future issuance under the 2016 Plan and the Company ceased granting awards under the 2008 Plan. Upon the effective date of the 2016 Plan, awards issued under the 2008 Plan remain subject to the terms of the 2008 Plan. Awards granted under the 2008 Plan that expire, lapse or terminate become available under the 2016 Plan as shares available for future grants. Additionally, pursuant to the terms of the 2016 Plan, the Board is authorized to grant awards with respect to common stock, and may delegate to a committee of one or more members of the Board or executive officers of the Company the authority to grant options and restricted stock units. On December 9, 2020, the Board established a Stock Option Committee authorized to grant awards to certain employees and consultants subject to conditions and limitations within the 2016 Plan. In January 2022, the number of shares of common stock that may be issued under the 2016 Plan was increased by 4,944,919 shares. As of June 30, 2022, 1,561,045 shares remain available for future issuance under the 2016 Plan. In September 2018, the Company’s 2018 Employment Inducement Incentive Award Plan, or the 2018 Inducement Incentive Award Plan was adopted by the Board without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Stock Market LLC listing rules, which authorized 1,175,000 shares of its common stock for issuance. In March 2019, the Board approved the amendment and restatement of the 2018 Inducement Incentive Award Plan to reserve an additional 2,000,000 shares of the Company’s common stock for issuance thereunder. As of June 30, 2022, there are 1,591,661 shares available for future grant under the 2018 Inducement Incentive Award Plan. Stock-based Compensation Expense Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive income (loss), including $1.0 million recognized as stock-based compensation expense upon the issuance of common stock to Ginkgo Bioworks Holdings, Inc. during the three and six months ended June 30, 2022 as described in Note 14, was as follows (in thousands): Three Months Ended Six Months Ended 2022 2021 2022 2021 Research and development $ 2,021 $ 786 $ 3,039 $ 1,540 General and administrative 1,543 997 3,278 2,023 Total stock-based compensation expense $ 3,564 $ 1,783 $ 6,317 $ 3,563 Stock Options The estimated grant date fair values of employee stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model, based on the following weighted-average assumptions: Three Months Ended Six Months Ended 2022 2021 2022 2021 Risk-free interest rate 3.26 % 1.12 % 1.63 % 0.72 % Dividend yield — — — — Expected term 6.05 6.05 6.03 6.02 Expected volatility 92.03 % 94.96 % 91.85 % 95.52 % Weighted-average fair value of common stock $ 1.29 $ 4.16 $ 3.10 $ 3.39 The weighted average grant date fair value of stock options granted to employees during the three and six months ended June 30, 2022 and 2021 was $0.99 and $3.19, $2.33 and $2.59 respectively. As of June 30, 2022, total unrecognized compensation expense related to unvested employee stock options was $16.9 million, which is expected to be recognized over a weighted average period of 2.8 years. The following table summarizes the stock option activity under the 2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan: Weighted-average remaining Aggregate Number of Weighted-average contractual term intrinsic value options exercise price ($) (in years) (in thousands) Employees Outstanding at December 31, 2021 10,616,800 $ 3.99 8.19 $ 4,982 Granted 4,884,200 $ 3.10 Exercised (10,000) $ 2.10 Forfeited (221,069) $ 5.03 Outstanding at June 30, 2022 15,269,931 $ 3.69 8.30 $ 17,260 Vested at June 30, 2022 6,085,326 $ 4.35 7.17 $ — Vested and expected to vest at June 30, 2022 14,055,754 $ 3.73 8.22 $ 14,045 Non-employee consultants Outstanding at December 31, 2021 423,073 $ 6.34 3.85 $ 42 Granted — $ — Exercised — $ — Forfeited (156,834) $ 3.44 Outstanding at June 30, 2022 266,239 $ 8.05 5.58 $ — Vested at June 30, 2022 266,239 $ 8.05 5.58 $ — Vested and expected to vest at June 30, 2022 266,239 $ 8.05 5.58 $ — Restricted Stock Units During the six months ended June 30, 2022, the Company granted 813,200 restricted stock awards with a weighted average fair value of $3.31 per share based on the closing price of the Company’s common stock on the date of grant to employees under the 2016 Plan, which will vest over a four-year term. Forfeitures are estimated at the time of grant and are adjusted, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company has estimated a forfeiture rate of 10% for restricted stock awards to employees based on historical attrition trends. Unrecognized compensation expense for all restricted stock units was $2.6 million as of June 30, 2022, which is expected to be recognized over a weighted average period of 3.2 years. The following table summarizes the Company’s restricted stock units under the 2016 Plan and 2018 Inducement Incentive Award Plan: Number of shares Weighted average Unvested at December 31, 2021 394,450 $ 3.45 Granted 813,200 3.31 Vested (100,080) 3.65 Forfeited (10,087) 3.22 Unvested at June 30, 2022 1,097,483 $ 3.33 Employee Stock Purchase Plan In June 2016, the Company approved the 2016 Employee Stock Purchase Plan, or the ESPP, which authorized 173,076 shares of common stock for future issuance under the ESPP to participating employees. In January 2022, the number of shares of common stock authorized for issuance under the ESPP was increased by 1,236,229 shares. During the six months ended June 30, 2022, the Company issued 81,057 shares of common stock under the ESPP. As of June 30, 2022, 3,677,538 shares remain available for future issuance under the ESPP.

Revenue Arrangements

Revenue Arrangements	6 Months Ended
	Jun. 30, 2022
Revenue from Contract with Customer [Abstract]
Revenue Arrangements	Revenue Arrangements Takeda Pharmaceuticals USA, Inc. License and Development Agreement In October 2021, the Company entered into a License Agreement, or the Takeda Agreement, with Takeda Pharmaceuticals USA, Inc., or Takeda. Under the Takeda Agreement, the Company granted Takeda an exclusive license to the Company’s ImmTOR technology initially for two specified disease indications within the field of lysosomal storage disorders. Takeda paid a $3.0 million upfront payment to the Company upon signing of the Takeda Agreement, and the Company is entitled to receive up to $1.124 billion in future additional payments over the course of the partnership that are contingent on the achievement of development or commercial milestones or Takeda’s election to continue its activities at specified development stages. The Company is also eligible for tiered royalties on future commercial sales of any licensed products. The Company determined the Takeda Agreement represents a service arrangement under the scope of ASC 606, and given the reversion of the rights under the Takeda Agreement represents a penalty in substance for a termination by Takeda, the contract term would remain the stated term of the Takeda Agreement. The Company determined that the research license, the licensed know-how, and the manufactured supply and delivery of materials represent a single promise and performance obligation to be transferred to Takeda over time due to the nature of the promises in the contract. The delivery of the manufactured supply is the predominant promise within the arrangement, as it is essential to the utility of the licensed intellectual property. The material to be supplied by the Company to Takeda is unique to the Company and cannot be obtained by other vendors. As such, consideration in the initial transaction price will be allocated to the single performance obligation and the recognition period would not extend beyond the initial contractual period. The Company will recognize the revenue associated with the upfront payment and combined single performance obligation utilizing the output method over the term that manufactured supply is delivered to Takeda. In determining the transaction price, the Company concluded the payment associated with all the performance milestones will be fully constrained and only be included in the transaction price when the respective milestone is deemed probable of achievement. Each of these variable consideration items were evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt and timing of such study milestones is outside the control of the Company and probability of success criteria is estimated. The Company will re-evaluate the transaction price in each reporting period, as uncertain events are resolved, or as other changes in circumstances occur. Takeda has the right to exercise covenant release rights on a field-by-field basis. If Takeda exercises its covenant release rights, we could receive exercise payments per indication and would be entitled to significant development and commercial milestone payments and tiered royalties on commercial sales. The Company determined that a significant financing component does not exist in its arrangement with Takeda. The Company also determined the options to negotiate additional fields, pursue other products, enter into a supply agreement explore additional fields, and pursue additional development under the initial fields do not represent material rights under the agreement. Takeda has the right to terminate the Takeda Agreement in its entirety or on a field-by-field basis, upon 90 days’ written notice to the Company. As of June 30, 2022, the Company recorded $1.0 million as a short-term contract liability, representing deferred revenue associated with this agreement. Revenue of $1.0 million related to the Takeda Agreement was recognized during the six months ended June 30, 2022. No revenue related to the Takeda Agreement was recognized during the three months ended June 30, 2022. As of December 31, 2021, the Company recorded $1.0 million as a short term contract liability and $1.0 million as a long-term contract liability, respectively, representing deferred revenue associated with this agreement. Swedish Orphan Biovitrum License and Development Agreement In June 2020, the Company and Sobi entered into the Sobi License. Pursuant to the Sobi License, the Company agreed to grant Sobi an exclusive, worldwide (except as to Greater China) license to develop, manufacture and commercialize the Company’s SEL-212 drug candidate, which is currently in development for the treatment of chronic refractory gout. The SEL-212 drug candidate is a pharmaceutical composition containing a combination of SEL-037, or the Compound, and ImmTOR. Pursuant to the Sobi License, in consideration of the license, Sobi agreed to pay the Company a one-time, upfront payment of $75.0 million. Sobi has also agreed to make milestone payments totaling up to $630.0 million to the Company upon the achievement of various development and regulatory milestones and, if commercialized, sales thresholds for annual net sales of SEL-212, and tiered royalty payments ranging from the low double digits on the lowest sales tier to the high teens on the highest sales tier. Pursuant to the Sobi License, the Company has agreed to supply (at cost) quantities of the Compound and ImmTOR as necessary for completion of the two Phase 3 clinical trials of SEL-212 (DISSOLVE I and DISSOLVE II) and a 6-month placebo extension. The Company is required to supply quantities of the Compound until all rights to the Compound and any materials needed to manufacture the Compound are transferred to Sobi. Sobi has agreed to reimburse the Company for all budgeted costs incurred to complete development of SEL-212, including but not limited to costs incurred while conducting and completing the Phase 3 DISSOLVE trials, except for any costs of additional development activities required that are related to ImmTOR and that are unrelated to SEL-212. Sobi will have control and responsibility over all regulatory filings, including any investigational drug applications, biologics license applications, and marketing authorization applications relating to the licensed product. Sobi may terminate the Sobi License for any reason upon 180 days’ written notice to the Company, whereby all rights granted under the Sobi License would revert back to the Company. In addition, if Sobi were to terminate the Sobi License, the Company has the option to obtain a license to all patents and know-how necessary to exploit SEL-212 in existence as of the termination date from Sobi in return for making an equitable royalty payment to Sobi. Additionally, on June 11, 2020, the Company entered into the Sobi Purchase Agreement for the sale of 5,416,390 shares of common stock for aggregate gross proceeds of $25.0 million in connection with the Sobi License. The closing of the Sobi Private Placement occurred on July 31, 2020, following the closing of the transactions contemplated under the Sobi License. The Company determined that the Sobi License represents a service arrangement under the scope of ASC 606. In addition, given the Sobi License and Sobi Purchase Agreement were executed contemporaneously and negotiated as a package with a single commercial objective, the Company will account for the two agreements as a single contract. The term of the Sobi License commenced upon the effective date of July 28, 2020 and will continue on a product-by-product basis until the royalty terms for each country have expired. The royalty term for a given product begins upon the first commercial sale of the product in a country and ends at the later of ten years from the first commercial sale, expiration of the last valid patent claim covering the product and expiration of all regulatory exclusivity periods for the product in a country. Given the reversion of the rights under the Sobi License represents a penalty in substance for a termination by Sobi, the contract term would remain the stated term of the Sobi License. The Company determined that the Sobi License contains three distinct performance obligations due to the nature of the promises in the contract, which includes conducting the Phase 3 DISSOLVE trials, Sobi’s option to set-up a second source supplier, and a combined obligation comprised of the delivery of the license to SEL-212, transfer of the know-how and the manufacturing and delivery of SEL-212 supply for development, or the Combined License Obligation. As the set-up of a second source supplier is optional for Sobi and the Company will be reimbursed at cost for its efforts in the subsequent set-up and technology transfer, the option for this future service was determined to be at a significant and incremental discount to its standalone selling price and treated as a material right in the arrangement, namely a distinct performance obligation. In determining the transaction price, the Company concluded the upfront payment of $75.0 million and the $5.0 million development milestone associated with the dosing of the first patient in the Phase 3 DISSOLVE trials will be included in the transaction price. All other development milestones will be fully constrained and only be included in the transaction price when the respective milestone is deemed probable of achievement. Each of these variable consideration items was evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of the evaluation of the constraint, the Company considered numerous factors, including that receipt of such milestones is outside the control of the Company and probability of success criteria is estimated. The Company will re-evaluate the transaction price in each reporting period, as uncertain events are resolved. In accordance with ASC 606, the Company will only recognize revenue associated with sales-based milestones and royalties when the subsequent sales thresholds are reached and underlying sales occur, respectively. In connection with the Sobi Purchase Agreement, the Company determined that the gross proceeds of $25.0 million from the Sobi Private Placement included a premium to the fair value of the Company’s shares as of July 28, 2020 equal to approximately $14.5 million. The premium amount will be included in the transaction price for revenue recognition. The Company will estimate and include in the transaction price the total reimbursements to be received from Sobi for both the manufacturing and delivery of the Compound and ImmTOR as well as conducting the Phase 3 DISSOLVE trials. The Company determined that a significant financing component does not exist in its arrangement with Sobi. The Company allocated the transaction price based on the relative standalone selling prices of the three distinct performance obligations. The Company estimated the standalone selling price of conducting the Phase 3 DISSOLVE trials by forecasting its anticipated costs and applying a margin reflective of the industry. The Company determined the standalone selling price of the second source supplier option by determining the discount given to Sobi multiplied by the likelihood that Sobi will exercise the option in the future. Similar to the Phase 3 program estimate, the Company estimated the discount of the option by forecasting the set-up costs and applying a margin that is reflective of the industry. As the Company will be providing the set-up and technology transfer services and the future supply at cost, the discount of the option is equal to the margin amount. The Company considered discussions with Sobi as well as probability of regulatory success of SEL-212 in determining the likelihood of exercise. The Company estimated the standalone selling price of the Combined License Obligation by utilizing a discounted cash flow model. The Company determined that the delivery of the supply to Sobi best represents the pattern of delivery of the Combined License Obligation as the supply is essential to the utility of the license and know-how. The Company will recognize the revenue allocated to the Combined License Obligation by utilizing the output method. The Company estimated the total supply of the Compound and ImmTOR to be required during the clinical trial period and will recognize revenue as this supply is shipped for use in the clinical trials. The Company will recognize the revenue allocated to the conducting of the Phase 3 DISSOLVE trials obligation by utilizing the input method. The Company estimated the total budgeted costs to be incurred over the Phase 3 DISSOLVE trials and will recognize revenue as these costs are incurred. The Company’s costs best represent the pattern of transfer as these will capture all performance of the trials completed to date and can be readily measured. The Company will recognize the revenue allocated to the second source supplier option when the future services and goods are transferred. On June 29, 2022, the Company completed enrollment of the DISSOLVE II trial. The completion of enrollment of the DISSOLVE II trial has resulted in the achievement of a development milestone and a $10.0 million payment obligation from Sobi to the Company. This amount was added to the overall transaction price during the three months ended June 30, 2022. As of June 30, 2022 and December 31, 2021, the Company recorded $12.9 million and $37.5 million, respectively, as a short-term contract liability and $1.8 million and $5.1 million, respectively, as a long-term contract liability, representing deferred revenue associated with this agreement. In addition, as of June 30, 2022, the Company has recorded $0.3 million of contract assets related to incremental costs that would not have been incurred if the Sobi License had not been obtained, of which $0.3 million is presented in prepaid expenses and other current assets and less than $0.1 million is presented in other assets in the accompanying unaudited consolidated balance sheets. As of June 30, 2022 and December 31, 2021, the Company recorded a total outstanding receivable of $17.9 million and $9.9 million, respectively, representing billings for the Phase 3 DISSOLVE program that are subject to reimbursement by Sobi. Revenue of $29.2 million and $52.9 million related to the Sobi License was recognized during the three and six months ended June 30, 2022, respectively, inclusive of $4.1 million of revenue recognized from performance obligations related to prior periods as a result of the change in transaction price during the three months ended June 30, 2022. Revenue of $19.5 million and $30.6 million related to the Sobi License was recognized during the three and six months ended June 30, 2021, respectively. Sarepta Therapeutics, Inc. Research License and Option Agreement In June 2020, the Company and Sarepta Therapeutics, Inc., or Sarepta, entered into a Research License and Option Agreement, or the Sarepta Agreement. Pursuant to the Sarepta Agreement, the Company agreed to grant Sarepta a license under the Company’s intellectual property rights covering the Company’s antigen-specific biodegradable nanoparticle encapsulating ImmTOR to research and evaluate ImmTOR in combination with Sarepta’s adeno-associated virus gene therapy technology, or gene editing technology, using viral or non-viral delivery, to treat Duchenne Muscular Dystrophy and certain Limb-Girdle Muscular Dystrophy subtypes, or the Indications. Sarepta will have an option term of 24 months during which it can opt-in to obtain an exclusive license to further develop and commercialize the Product to treat at least one Indication, with a potential to extend the option term for an additional fee. The Company will supply ImmTOR to Sarepta for clinical supply on a cost-plus basis. Sarepta paid a $2.0 million upfront payment to the Company upon signing of the Sarepta Agreement, and the Company is eligible to receive additional preclinical payments during the option term. If Sarepta opts-in to an exclusive license agreement, the Company could receive option exercise payments per Indication upon execution of the exclusive license, and the Company would be entitled to significant development and commercial milestone payments and tiered royalties ranging from the mid-to-high single digits based on net sales. Pursuant to the Sarepta Agreement, the Company determined the Sarepta Agreement represents a service arrangement under the scope of ASC 606, with a 24 month contract duration. Given the reversion of the rights under the Sarepta Agreement represents a penalty in substance for a termination by Sarepta, the contract term would remain the stated term of the Sarepta Agreement. The Company determined that the Sarepta Agreement and supply obligation including the delivery of the research license, the licensed know-how, the manufactured supply and delivery of materials represent a single promise and performance obligation to be transferred to Sarepta over time due to the nature of the promises in the contract. The delivery of the manufactured supply is the predominant promise within the arrangement, as it is essential to the utility of the licensed intellectual property. As such, consideration in the initial transaction price will be allocated to the single performance obligation based on the contractual price. In determining the transaction price, the Company concluded the payment associated with all the performance milestones will be fully constrained and only be included in the transaction price when the respective milestone is deemed probable of achievement. Each of these variable consideration items was evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of such study milestones is outside the control of the Company and probability of success criteria is estimated. The Company also determined the option to enter into a future commercial license agreement and extend the term of the option does not represent a material right since it was not priced at an incremental discount. Sarepta may terminate the Sarepta Agreement for any reason upon 30 days’ written notice to the Company. The Sarepta Agreement contains other customary terms and conditions, including representations and warranties, covenants, termination, and indemnification obligations in favor of each party. During the year ended December 31, 2020, the Company and Sarepta entered into two amendments relating to an additional feasibility study. During the year ended December 31, 2021, the Company and Sarepta entered into a third amendment relating to the additional feasibility study. On April 13, 2021, the Company was notified by Sarepta of the achievement of the milestone event related to the completion of a non-clinical study for Duchenne muscular dystrophy and certain limb-girdle muscular dystrophies under the Sarepta Agreement. Accordingly, the Company received a milestone payment of $3.0 million during the three months ended June 30, 2021. On June 10, 2022, the Company was notified by Sarepta that Sarepta would be extending their options under the Sarepta Agreement. In exchange for a nine-month extension to Sarepta’s options to both Duchenne muscular dystrophy and certain limb-girdle muscular dystrophies, Sarepta is obligated to pay, and the Company recorded a receivable of, $2.0 million as of June 30, 2022. On June 15, 2022, the Company was notified by Sarepta of the achievement of a milestone event related to certain preclinical study milestones under the Sarepta Agreement. Accordingly, the Company recorded a receivable of $4.0 million as of June 30, 2022. As of June 30, 2022, one milestone remained constrained. The Company will re-evaluate the transaction price in each reporting period, as uncertain events are resolved. The Company will recognize the revenue associated with the upfront payment and combined single performance obligation utilizing the output method, over the 33-month term as the manufactured supply is delivered to Sarepta. As of June 30, 2022, the Company recorded a total outstanding receivable of $6.0 million related to the Sarepta Agreement. No outstanding receivable was recorded as of December 31, 2021. The Company recorded $0.5 million and $4.6 million as a short-term contract liability representing deferred revenue associated with this agreement at June 30, 2022 and December 31, 2021, respectively. Revenue of $10.1 million and $10.2 million related to the Sarepta Agreement was recognized during the three and six months ended June 30, 2022, respectively, inclusive of $0.9 million of revenue recognized from performance obligations related to prior periods as a result of the change in transaction price during the three months ended June 30, 2022. Revenue of less than $0.1 million related to the Sarepta Agreement was recognized during each of the three and six months ended June 30, 2021. Asklepios Biopharmaceutical, Inc. License Agreement for Pompe Disease In December 2019, the Company and Asklepios Biopharmaceutical, Inc., or AskBio, entered into a license agreement, or the AskBio License Agreement. Pursuant to the AskBio License Agreement, AskBio has exercised its option to exclusively license the Company’s intellectual property rights covering the Company’s ImmTOR platform to research, develop, and commercialize certain adeno-associated viral, or AAV, gene therapy products utilizing ImmTOR, and targeting the lysosomal alpha-glucosidase, or GAA, gene, or derivatives thereof, to treat Pompe Disease. Pursuant to the AskBio License Agreement and ancillary documents, AskBio agreed to pay to the Company upfront fees of an aggregate of $7.0 million. Assuming successful development and commercialization, the Company could receive up to an additional $237.0 million in development, regulatory, and sales milestone payments. If commercialized, the Company would be eligible to receive tiered royalties on global net sales at percentages ranging from mid-to-high single digits. Under the terms of the agreement, the Company will be eligible to receive these royalties commencing on the first commercial sale of the licensed product until the expiration of the later of (i) ten years after the first commercial sale and (ii) expiration of the last to expire valid claim on patents covering the licensed product. Pursuant to the AskBio License Agreement, the Company will supply AskBio with its ImmTOR platform, or the Supply Obligation, and AskBio will be responsible for all preclinical, clinical and commercial manufacture and supply of licensed products (other than ImmTOR) and carry out all other activities related to the research, development, and commercialization of licensed products at its sole expense, including all regulatory activities related thereto. The Company determined that the AskBio License Agreement and Supply Obligation represent a single promise and performance obligation. This is because AskBio cannot derive benefit from the license without the simultaneous transfer of the patent protected ImmTOR supply. Therefore, the License Obligation and Supply Obligation represent the only promise in the arrangement and are combined as a single performance obligation. In determining the transaction price, the Company concluded that the future development milestones, regulatory milestones, sales milestones, and sales royalties all represent variable consideration. Each of these variable consideration items was evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of such milestones is outside the control of the Company. Consideration related to sales-based milestones as well as royalties on net sales upon commercialization by AskBio, will be recognized when the related sales occur, as they were determined to relate predominantly to the intellectual property granted to AskBio and, therefore, have also been excluded from the transaction price in accordance with the royalty recognition constraint. As of June 30, 2022 and December 31, 2021, all milestones were constrained. The Company will re-evaluate the transaction price in each reporting period, as uncertain events are resolved, or as other changes in circumstances occur. The total initial transaction price of the contract on the effective date was $7.0 million, comprised of a $2.0 million initial upfront payment upon agreement of terms, and a $5.0 million initial upfront execution fee. At each of June 30, 2022 and December 31, 2021, the Company recorded $1.7 million as short-term contract liability and $5.3 million as a long-term contract liability, representing deferred revenue associated with this agreement. Revenue will be recognized over the period in which the particles are delivered. No revenue related to the AskBio License Agreement was recognized during the three and six months ended June 30, 2022 and 2021 as no deliveries were made during these periods. Spark Therapeutics, Inc. Spark License Agreement In December 2016, the Company entered into a License and Option Agreement, or the Spark License Agreement, with Spark Therapeutics, Inc., or Spark, pursuant to which the Company and Spark agreed to collaborate on the development of gene therapies for certain targets utilizing the ImmTOR platform. The Spark License Agreement provides Spark with certain exclusive, worldwide, royalty bearing licenses to the Company’s intellectual property, allowing Spark to develop and commercialize gene therapies in combination with ImmTOR for Factor VIII, an essential blood clotting protein relevant to the treatment of hemophilia A, the initial target. On January 18, 2022, both parties agreed to mutually terminate the Spark License Agreement. Therefore, the short-term contract liability of $9.2 million as of December 31, 2021 was recognized as revenue during the six months ended June 30, 2022. No revenue was recognized during the three months ended June 30, 2022. Transaction Price Allocated to Future Performance Obligations Remaining performance obligations represent the transaction price of contracts for which work has not been performed, or has been partially performed. As of June 30, 2022, the aggregate amount of the transaction price allocated to remaining performance obligations was $23.1 million. Contract Balances from Contracts with Customers ( Takeda, Sobi, Sarepta, and AskBio ) The following table presents changes in the Company’s contract liabilities during the six months ended June 30, 2022 (in thousands): Balance at Balance at beginning of period Additions Deductions end of period Six Months Ended June 30, 2022 Contract liabilities: Deferred revenue $ 65,300 $ 16,000 $ (58,213) $ 23,087 Total contract liabilities $ 65,300 $ 16,000 $ (58,213) $ 23,087

Related-party Transactions

Related-party Transactions	6 Months Ended
	Jun. 30, 2022
Related Party Transactions [Abstract]
Related-party Transactions	Related-party Transactions April 2022 Offering During the three and six months ended June 30, 2022, the Company completed the Offering as described in Note 10. The following table sets forth the number of shares of Common Stock and 2022 Warrants purchased in the Offering by directors and executive officers, as of the time of the Offering, and related parties thereto: Name Shares of Common Stock purchased 2022 Warrants purchased Total aggregate purchase price TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.) 6,681,600 5,011,200 $ 9,421,056 Consulting Services The Company incurred expenses for consulting services provided by its founders to serve on its Scientific Advisory Board, totaling less than $0.1 million during each of the three and six months ended June 30, 2021.

Collaboration and License Agree

Collaboration and License Agreements	6 Months Ended
	Jun. 30, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Collaboration and License Agreements	Collaboration and License Agreements Ginkgo Bioworks Holdings, Inc. Collaboration and License Agreement On January 3, 2022, the Company entered into a Collaboration and License Agreement, or the Second Ginkgo Agreement, with Ginkgo Bioworks Holdings, Inc., or Ginkgo. Under this agreement, the Company will engage with Ginkgo to develop AAV capsids designed to enhance transduction efficiency and transgene expression. In return, Ginkgo is eligible to earn both upfront research and development fees and milestone payments, including certain milestone payments in the form of shares of the Company’s common stock, clinical and commercial milestone payments of up to $207 million in cash. The Second Ginkgo Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the Second Ginkgo Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company is accounting for the contingently issuable shares of common stock to be issued in exchange for the license obtained from Ginkgo as a liability-classified, stock-based compensation arrangement with a non-employee which will be recognized when achievement of the milestones is probable. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Ginkgo tiered royalties ranging from low-single digit to high-single digit percentages of annual net sales of collaboration products which will be expensed as the commercial sales occur. In October 2021, the Company entered into a Collaboration and License Agreement, or the First Ginkgo Agreement, with Ginkgo. Under the First Ginkgo Agreement, Ginkgo will design next generation IgA proteases with potentially transformative therapeutic potential. In return, Ginkgo is eligible to earn research and development fees, clinical and commercial milestone payments of up to $85.0 million in cash, as well as certain milestone payments for fixed fair values in the form of shares of the Company’s common stock. The First Ginkgo Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the First Ginkgo Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company is accounting for the contingently issuable shares of common stock to be issued in exchange for the license obtained from Ginkgo as a liability-classified, stock-based compensation arrangement with a non-employee which will be recognized when achievement of the milestones is probable. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Ginkgo tiered royalties ranging from low-single digit to high-single digit percentages of annual net sales of collaboration products which will be expensed as the commercial sales occur. On June 13, 2022, the Company was notified of the achievement of the midpoint of the technical development plan under the First Ginkgo Agreement by Ginkgo. This milestone resulted in the payment of $0.5 million and issuance of 892,857 shares of the Company’s common stock valued at $1.0 million to Ginkgo during the three months ended June 30, 2022. Genovis AB (publ.) License Agreement In October 2021, the Company entered into an Exclusive License Agreement, or the Genovis Agreement, with Genovis AB (publ.), or Genovis. Under the Genovis Agreement, the Company paid to Genovis an upfront payment in exchange for an exclusive license to Genovis’ IgG protease, or Xork, enzyme technology across all therapeutic uses in humans, excluding research, preclinical, diagnostic and other potential non-therapeutic applications of the enzyme. Genovis is eligible to earn development and sales-based milestones. The Genovis Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the Genovis Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Genovis tiered royalties of low double-digit percentages of worldwide annual net sales of collaboration products which will be expensed as the commercial sales occur. Cyrus Biotechnology, Inc. Collaboration and License Agreement In September 2021, the Company and Cyrus entered into a collaboration and license agreement, or the Cyrus Agreement. Pursuant to the Cyrus Agreement, Cyrus agreed to grant the Company an exclusive, worldwide license to certain intellectual property to form a protein engineering collaboration combining the Company’s ImmTOR platform with Cyrus’ ability to redesign protein therapeutics. The lead program is a proprietary interleukin-2, or IL-2, protein agonist designed to selectively promote expansion of regulatory T cells for treatment of patients with autoimmune diseases and other deleterious immune conditions. In return for the licensed intellectual property, the Company made an upfront payment and is obligated to pay certain discovery, development, and sales-based milestones which could total up to approximately $1.5 billion across multiple programs. The Cyrus Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the Cyrus Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Cyrus tiered royalties ranging from mid-single digit to low-double digit percentages of annual net sales of collaboration products which will be expensed as the commercial sales occur. Additionally, on September 7, 2021, the Company entered into a stock purchase agreement, or the Series B Preferred Stock Purchase Agreement, in connection with the Cyrus Agreement. Pursuant to the Series B Preferred Stock Purchase Agreement, the Company purchased 2,326,934 shares of Cyrus’ Series B Preferred Stock, par value $0.0001 per share, at a purchase price of $0.8595 per share for an aggregate purchase price of $2.0 million. In accordance with ASC 810, the Company has a variable interest in Cyrus resulting from its equity investment. The Company will share in Cyrus’ expected losses or receive a portion of its expected returns and absorb the variability associated with changes in the entity’s net assets. However, the Company is not the primary beneficiary as it does not have the power to direct the activities most significant to Cyrus, and therefore it is not required to consolidate Cyrus. The Company determined its equity interest to be within the scope of ASC 321 and elected to record the $2.0 million investment of Cyrus’ Series B Preferred Stock at cost on the purchase date. On June 13, 2022, the Company and Cyrus mutually agreed that the preclinical key in-vitro success milestone had been achieved. As of June 30, 2022, no impairment indicators are present and therefore the carrying value of the investment in Cyrus is $2.0 million on the accompanying consolidated balance sheet. The Company’s maximum exposure to loss related to this variable interest entity is limited to the carrying value of the investment. The Company has not provided financing to Cyrus other than the amount contractually required by the Series B Preferred Stock Purchase Agreement. Asklepios Biopharmaceutical, Inc. Feasibility Study and License Agreement In August 2019, the Company entered into a Feasibility Study and License Agreement with AskBio, or the AskBio Collaboration Agreement. Pursuant to the AskBio Collaboration Agreement, the Company and AskBio agreed to license intellectual property rights to each other as part of a collaboration to research, develop, and commercialize certain AAV gene therapy products utilizing the Company’s ImmTOR platform to enable re-dosing of such AAV gene therapy products to treat serious rare and orphan genetic diseases for which there is a significant unmet medical need. Pursuant to the AskBio Collaboration Agreement, the Company and AskBio agreed to conduct proof of concept studies to potentially validate the use of ImmTOR in conjunction with AskBio’s AAV gene therapy, or SEL-302 (previously disclosed as MMA-101, in combination with ImmTOR), for the treatment of MMA, to mitigate the formation of neutralizing anti-AAV capsid antibodies, or the POC Studies. On April 29, 2021, the Company was notified by AskBio that it intended to opt-out of development of the MMA indication. The feasibility study and license agreement with AskBio, or AskBio Collaboration Agreement, otherwise remains in effect. Consequently, the Company has assumed all rights to the MMA program and intends to continue to progress the SEL-302 program through clinical development. The Company filed an IND to conduct a Phase 1/2 clinical trial of its SEL-302 product candidate in pediatric patients with methylmalonic acidemia in the third quarter of 2021. On November 23, 2021, this trial was placed on clinical hold by the FDA, with questions specifically relating to chemistry, manufacturing and controls, or CMC, of the AAV vector. On March 9, 2022, the Company received a letter from the FDA indicating the clinical hold was removed and the trial may proceed. The SEL-399 program combined an empty AAV capsid (EMC-101), which is an AAV capsid containing no transgene, with ImmTOR and was conducted in partnership with AskBio. Building on the preclinical data the Company has generated showing ImmTOR’s effect on mitigating or reducing the formation of neutralizing antibodies to AAV gene therapies, the Company completed a clinical trial of SEL-399 in healthy adult volunteers in Belgium. The goal of the SEL-399 clinical trial was to demonstrate the appropriate dose of ImmTOR in humans to mitigate the formation of antibodies to AAV capsids used in gene therapies. The Company believes this promising study in healthy volunteers provides support for the potential use of ImmTOR for the inhibition of neutralizing antibodies to AAV8 in gene therapy clinical trials. The Company and AskBio will share responsibility for the research and development of products developed under the SEL-399 program collaboration. The parties will also share research, development, and commercialization costs equally for all collaboration products, but with a right of either party to opt out of certain products, and thereby no longer be required to share costs for such products. Each party will receive a percentage of net profits under the collaboration equal to the percentage of shared costs borne by such party in the development of such product. Pursuant to the AskBio Collaboration Agreement, AskBio is responsible for manufacturing the AAV capsids and AAV vectors and the Company is responsible for manufacturing ImmTOR. The AskBio Collaboration Agreement is considered to be within the scope of ASC 808, as both parties are active participants and exposed to the risks and rewards of the collaborative activity. The Company evaluated the terms of the AskBio Collaboration Agreement and have identified the following promises in the arrangement (1) conducting research and development activities to develop and commercialize products under the collaboration, or the R&D Services, (2) granting a non-exclusive, non-transferable, royalty-free, fully paid up, worldwide license to certain intellectual property of the Company, or the IP Rights, for the purpose of performing the POC Studies, or the Research License, (3) granting an exclusive, nontransferable, worldwide license to the IP Rights for use in certain indications, or the Collaboration License, (4) providing manufactured supply of preclinical and clinical ImmTOR, or the Manufactured Supply, (5) participation on identified steering committees responsible for the oversight of the collaboration, or the JSC Participation, and (6) granting an exclusive option to obtain a license under the IP Rights to research, develop and commercialize Licensed Products. The Company determined that the R&D Services, Research License, Collaboration License, Manufactured Supply, and JSC Participation were not capable of being distinct, and therefore must be combined into a single performance obligation. Therefore, promises (1) through (5) identified above were combined into a single performance obligation. Furthermore, the Company evaluated the Option Agreement and determined that it does not provide AskBio with a material right under ASC 606 as the option was not priced at a discount. The Company noted that AskBio did not meet the definition of a customer within the scope of ASC 606 for any distinct performance obligations as the Company concluded that such items were not an output of the Company’s ordinary activities. As such, the Company determined that the entire arrangement would be accounted for within the scope of ASC 808. In accordance with ASC 808, collaboration expenses are recognized within research and development expense and selling, general and administrative expense on the Company’s condensed consolidated statements of operations. Under certain collaborative arrangements, the Company is entitled to reimbursement of certain research and development expense. Activities under collaborative arrangements for which the Company is entitled to reimbursement are considered to be collaborative activities under the scope of ASC 808. For these units of account, the Company does not analogize to ASC 606 or recognize revenue. Rather, the Company analogizes to the guidance in ASC 730, which requires that reimbursements from counterparties be recognized as an offset to the related costs. In accordance with ASC 730, the Company records reimbursement payments received from collaborators as reductions to research and development expense. For the three and six months ended June 30, 2022, the Company recognized $0.2 million and $0.6 million, respectively, of collaboration expense under the AskBio Collaboration Agreement in which actual costs incurred by both parties approximate a 50% cost share. For the three and six months ended June 30, 2021, the Company recognized $0.5 million and $1.7 million, respectively, of collaboration expense under the AskBio Collaboration Agreement. Massachusetts Institute of Technology In November 2008, the Company entered into an Exclusive Patent License Agreement, or the MIT License, with the Massachusetts Institute of Technology, or MIT, under which the Company received an exclusive royalty-bearing license to utilize patents held by MIT in exchange for upfront consideration and annual license maintenance fees. Such fees are expensed as incurred and have not been material to any period presented. In June 2020, the Company entered into a Fifth Amendment, or the MIT Amendment, to the MIT License, which is effective as of May 15, 2020. Pursuant to the MIT Amendment, certain of the Company’s diligence obligations were extended. The extension included the obligation to commence a Phase 3 trial for a licensed product by the second quarter of 2021 or to file an IND (or equivalent) with the FDA or comparable European regulatory agency for a licensed product by the second quarter of 2023. Additionally, certain of the Company’s development and regulatory milestones and payments upon achievement of such milestones were adjusted. As of June 30, 2022, and in connection with the execution of the Spark License Agreement, the Company has made contractual payments pursuant to the MIT License totaling $2.2 million for the sublicense granted to Spark and $0.4 million relative to the calculated premium paid by Spark for the equity investments made under the Spark Purchase Agreement. The Company made no additional payments during the three and six months ended June 30, 2022. Shenyang Sunshine Pharmaceutical Co., Ltd In May 2014, the Company entered into a license agreement, or the 3SBio License, with Shenyang Sunshine Pharmaceutical Co., Ltd., or 3SBio. The Company has paid to 3SBio an aggregate of $7.0 million in upfront and milestone-based payments under the 3SBio License as of June 30, 2022. The Company is required to make future payments to 3SBio contingent upon the occurrence of events related to the achievement of clinical and regulatory approval milestones of up to an aggregate of $15.0 million for products containing the Company’s ImmTOR platform.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company provides for income taxes under ASC 740. Under ASC 740, the Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax bases of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. The Company has provided a full valuation allowance against its net deferred tax assets, as the Company believes that it is more likely than not that the deferred tax assets will not be realized. Effective for tax years beginning on or after January 1, 2022, research and experimental expenditures under IRC Section 174 must be capitalized over five years when performed in the U.S. and 15 years for research and experimental expenditures performed outside of the U.S. As of June 30, 2022, the Company has performed a high-level analysis of the impact of this legislation enactment and determined the projected taxable loss position for 2022 does not result in income tax due. As of December 31, 2021, the Company has $51.1 million of federal net operating losses available, subject to an 80% limitation. The Company also has $1.2 million of federal tax credits, subject to a 75% limitation. The Company maintains its full valuation allowance. Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 and 383 of the Internal Revenue Code due to ownership change limitations that have occurred previously, or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. As of December 31, 2021, the Company completed both a Section 382 and R&D tax credit study. The statute of limitations for assessment by the Internal Revenue Service and Massachusetts tax authorities is open for tax years since inception as the Company claimed research tax credits on its 2020 tax return which remains open for examination for the 2020 year as well as for any year in which a credit has been claimed. The Company files income tax returns in the United States and Massachusetts. There are currently no federal, state or foreign audits in progress.

Defined Contribution Plan

Defined Contribution Plan	6 Months Ended
	Jun. 30, 2022
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution PlanThe Company maintains a defined contribution plan, or the 401(k) Plan, under Section 401(k) of the Internal Revenue Code. 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 pretax basis. The 401(k) Plan provides for matching contributions on a portion of participant contributions pursuant to the 401(k) Plan’s matching formula. As of January 2022, all matching contributions vest ratably over 2 years and participant contributions vest immediately. Contributions by the Company totaled less than $0.1 million during each of the three months ended June 30, 2022 and 2021, and $0.2 million and $0.1 million during the six months ended June 30, 2022 and 2021, respectively.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies As of June 30, 2022, the Company was not a party to any litigation that could have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. On August 3, 2020, a stockholder of Selecta filed a stockholder derivative action, purportedly on behalf of Selecta and against certain current and former members of the Company’s Board of Directors, as well as one affiliated company owned by a current board member, in the Court of Chancery of the State of Delaware, namely Franchi v. Barabe, et al. The complaint alleges that the individual defendants breached their fiduciary duties and committed corporate waste when they authorized a private placement transaction, announced on December 19, 2019, at a price allegedly below fair value. The complaint further alleges that the four defendant directors who participated in the private placement were unjustly enriched in connection with the transaction. On September 25, 2020, the defendants filed a motion to dismiss the lawsuit. On November 6, 2020, the plaintiff filed an amended complaint, and the defendants filed a second motion to dismiss on January 8, 2021. On December 31, 2020, the Company received a litigation demand letter from two other putative stockholders relating to the same private placement transaction. On April 12, 2021, the Court of Chancery in the State of Delaware granted a motion to stay the litigation pending a review by a Special Committee appointed by the Company’s Board of Directors. While the litigation was stayed, the parties reached an agreement in principle to settle the matter, and on March 18, 2022, they submitted a Stipulation and Agreement of Settlement and other documentation to the Court for its approval of the settlement. As of June 30, 2022, the Company accrued an estimated liability of $0.9 million for the litigation, as the liability has been determined to be probable. Other As permitted under Delaware law, the Company indemnifies its directors and officers for certain events or occurrences while the director or officer is, or was, serving at the Company’s request in such capacity. The term of the indemnification is for the director’s or officer’s lifetime. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ and officers’ insurance coverage that limits its exposure and enables it to recover a portion of any future amounts paid. The Company also has indemnification arrangements under certain of its facility leases that require it to indemnify the landlord against certain costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from certain breaches, violations, or non-performance of any covenant or condition of the Company’s lease. The term of the indemnification is for the term of the related lease agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. To date, the Company had not experienced any material losses related to any of its indemnification obligations, and no material claims with respect thereto were outstanding. The Company is a party in various other contractual disputes and potential claims arising in the ordinary course of business. The Company does not believe that the resolution of these matters will have a material adverse effect the Company’s business, financial position, results of operations or cash flows.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2022
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsThe Company has evaluated subsequent events through the date on which the consolidated financial statements were issued. The Company has concluded that no subsequent events have occurred that require disclosure to the consolidated financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2022
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt – Modifications and Extinguishments (Subtopic 470-50), Compensation – Stock Compensation (Topic 718), and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer's Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options . ASU 2021-04 provides guidance as to how entities should account for a modification of the terms or conditions or an exchange of a freestanding equity-classified written call option (i.e., a warrant) that remains equity-classified after modification or exchange as an exchange of the original instrument for a new instrument. An entity should apply the guidance provided in ASU 2021-04 prospectively to modifications or exchanges occurring on or after the effective date. This new standard was effective for all entities for fiscal years beginning after December 15, 2021. The adoption of ASU 2021-04 did not have an impact on the Company’s financial position or results of operations upon adoption. Not Yet Adopted In August 2020, the FASB issued ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) . ASU 2020-06 simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. This new standard will be effective for smaller reporting companies for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years. The Company is assessing the impact this standard will have on its consolidated financial statements and disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit

Marketable Securities and Inv_2

Marketable Securities and Investments (Tables)	6 Months Ended
	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Marketable Securities	The following table summarizes the marketable securities held as of June 30, 2022 and December 31, 2021 (in thousands): Amortized Unrealized gains Unrealized losses Fair June 30, 2022 Commercial paper 3,999 — — 3,999 Total $ 3,999 $ — $ — $ 3,999 December 31, 2021 Corporate bonds $ 2,007 $ — $ (1) $ 2,006 Commercial paper 11,992 — — 11,992 Total $ 13,999 $ — $ (1) $ 13,998

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	6 Months Ended
	Jun. 30, 2022
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of basic and diluted net income (loss) per share for the three and six months ended June 30, 2022 and 2021 (in thousands, except share and per-share data): Three Months Ended Six Months Ended 2022 2021 2022 2021 Numerator: Net income (loss) $ 8,601 $ 4,565 $ 37,379 $ (20,032) Less: Change in fair value of liability warrants — (4,820) (13,868) — Adjusted net income (loss) $ 8,601 $ (255) $ 23,511 $ (20,032) Denominator: Weighted-average common shares outstanding - basic 148,505,729 113,524,110 136,436,316 112,140,815 Dilutive effect of employee equity incentive plans and — 7,653,888 529,996 — Weighted-average common shares used in per share calculations - diluted 148,505,729 121,177,998 136,966,312 112,140,815 Net income (loss) per share: Basic $ 0.06 $ 0.04 $ 0.27 $ (0.18) Diluted $ 0.06 $ — $ 0.17 $ (0.18)
Schedule of Potential Common Shares Issuable Upon Conversion of Warrants	The following table represents the potential dilutive shares of common stock excluded from the computation of the diluted net loss per share for all periods presented, as the effect would have been anti-dilutive: Three Months Ended Six Months Ended 2022 2021 2022 2021 Options, RSUs and ESPP shares 16,422,488 10,574,133 16,660,700 10,574,133 Warrants to purchase common stock 31,307,409 292,469 20,863,898 12,378,016 Total 47,729,897 10,866,602 37,524,598 22,952,149

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2022
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on a Recurring Basis	The following tables present the Company’s assets and liabilities that are measured at fair value on a recurring basis as of June 30, 2022 and December 31, 2021 (in thousands): June 30, 2022 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 76,686 $ 76,686 $ — $ — Marketable securities: Commercial paper 3,999 — 3,999 — Total assets $ 80,685 $ 76,686 $ 3,999 $ — Liabilities: Warrant liabilities $ 26,934 $ — $ — $ 26,934 Total liabilities $ 26,934 $ — $ — $ 26,934 December 31, 2021 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 66,563 $ 66,563 $ — $ — Marketable securities: Corporate bonds 2,006 — 2,006 — Commercial paper 11,992 — 11,992 — Total assets $ 80,561 $ 66,563 $ 13,998 $ — Liabilities: Warrant liabilities $ 25,423 $ — $ — $ 25,423 Total liabilities $ 25,423 $ — $ — $ 25,423
Schedule of Cash and Cash Equivalents	The Company’s consolidated statements of cash flows include the following as of June 30, 2022 and 2021 (in thousands): June 30, 2022 2021 Cash and cash equivalents $ 138,057 $ 125,749 Long-term restricted cash 1,379 1,379 Total cash, cash equivalents, and restricted cash $ 139,436 $ 127,128
Schedule of Restricted Cash and Cash Equivalents	The Company’s consolidated statements of cash flows include the following as of June 30, 2022 and 2021 (in thousands): June 30, 2022 2021 Cash and cash equivalents $ 138,057 $ 125,749 Long-term restricted cash 1,379 1,379 Total cash, cash equivalents, and restricted cash $ 139,436 $ 127,128
Schedule of Fair Value Measurement Inputs and Valuation Techniques	A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2019 Warrants liability is as follows: June 30, December 31, 2022 2021 Risk-free interest rate 2.92 % 0.97 % Dividend yield — — Expected life (in years) 2.48 2.98 Expected volatility 96.95 % 96.10 % A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2022 Warrants liability is as follows: At Issuance June 30, April 11, 2022 2022 Risk-free interest rate 3.01 % 2.79 % Dividend yield — — Expected life (in years) 4.78 5.00 Expected volatility 99.88 % 96.00 %
Schedule Of Changes In The Warrant Liabilities	The following table reflects a roll-forward of fair value for the Company’s Level 3 warrant liabilities (see Note 10), for the six months ended June 30, 2022 (in thousands): Warrant liabilities Fair value as of December 31, 2021 $ 25,423 Issuances 15,379 Exercises — Change in fair value (13,868) Fair value as of June 30, 2022 $ 26,934

Property and Equipment (Tables)

Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consists of the following (in thousands): June 30, December 31, 2022 2021 Laboratory equipment $ 6,074 $ 5,134 Computer equipment and software 695 731 Leasehold improvements 57 45 Furniture and fixtures 341 332 Office equipment 190 163 Construction in process 310 534 Total property and equipment 7,667 6,939 Less accumulated depreciation (4,834) (4,797) Property and equipment, net $ 2,833 $ 2,142

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2022
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): June 30, December 31, 2022 2021 Payroll and employee related expenses $ 2,223 $ 3,179 Collaboration and licensing 500 — Accrued patent fees 885 309 Accrued external research and development costs 6,701 4,339 Accrued professional and consulting services 547 815 Accrued interest 184 170 Other 1,326 1,721 Accrued expenses $ 12,366 $ 10,533

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2022
Leases [Abstract]
Schedule of Lease, Cost	For the three and six months ended June 30, 2022 and 2021, the components of lease costs were as follows (in thousands): Three Months Ended Six Months Ended 2022 2021 2022 2021 Operating lease cost $ 505 $ 454 $ 1,011 $ 898 Variable lease cost 205 182 425 470 Short-term lease cost 2 2 5 5 Total lease cost $ 712 $ 638 $ 1,441 $ 1,373 The following summarizes additional information related to operating leases: June 30, 2022 2021 Weighted-average remaining lease term 5.9 years 6.9 years Weighted-average discount rate 8.9 % 8.9 %
Schedule of Lessee, Operating Lease, Liability, Maturity	The maturity of the Company’s operating lease liabilities as of June 30, 2022 were as follows (in thousands): June 30, 2022 2022 (remainder) $ 942 2023 1,922 2024 1,980 2025 2,039 2026 2,101 Thereafter 2,844 Total future minimum lease payments 11,828 Less imputed interest 2,685 Total operating lease liabilities $ 9,143
Schedule of Operating Lease, Lease Income	The supplemental disclosure for the statement of cash flows related to operating leases were as follows (in thousands): June 30, 2022 2021 Cash paid for amounts included in the measurement of lease liabilities: $ 924 $ 898

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2022
Debt Disclosure [Abstract]
Schedule of Term Loan And Unamortized Debt Discount Balances	Total 2020 Term Loan and unamortized debt discount balances as of June 30, 2022 are as follows (in thousands): Face value $ 25,000 Venture debt termination fee 2,250 Less: Debt discount (1,331) Less: Current portion of loan payable (3,285) Loan payable, net of current portion $ 22,634
Schedule of Future Minimum Payments on the Term Loans	Future minimum principal payments on the 2020 Term Loan as of June 30, 2022 are as follows (in thousands): Year ended: 2023 7,759 2024 10,345 2025 6,896 Total minimum principal payments $ 25,000

Equity (Tables)

Equity (Tables)	6 Months Ended
	Jun. 30, 2022
Equity [Abstract]
Schedule of Stockholders' Equity Note, Warrants or Rights	During the six months ended June 30, 2022, there were 20,571,429 warrants issued, no warrants exercised, and 79,130 warrants canceled. Refer to Note 10 to the consolidated financial statements within our 2021 Annual Report on Form 10-K for further discussion of the terms related to the Company’s 2019 Warrants. Number of Warrants Equity Liability classified Total Weighted average Outstanding at December 31, 2021 292,469 10,443,511 10,735,980 $ 1.62 Issuance — 20,571,429 20,571,429 1.55 Canceled (79,130) — (79,130) 17.71 Outstanding at June 30, 2022 213,339 31,014,940 31,228,279 $ 1.53
Schedule of Authorized Shares of Common Stock for Future Issuance	The Company has authorized shares of common stock for future issuance as follows: As of June 30, 2022 December 31, 2021 Exercise of warrants 31,228,279 10,735,980 Shares available for future stock incentive awards 6,830,244 6,039,564 Unvested restricted stock units 1,097,483 394,450 Outstanding common stock options 15,536,170 11,039,873 Total 54,692,176 28,209,867

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	6 Months Ended
	Jun. 30, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation	Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive income (loss), including $1.0 million recognized as stock-based compensation expense upon the issuance of common stock to Ginkgo Bioworks Holdings, Inc. during the three and six months ended June 30, 2022 as described in Note 14, was as follows (in thousands): Three Months Ended Six Months Ended 2022 2021 2022 2021 Research and development $ 2,021 $ 786 $ 3,039 $ 1,540 General and administrative 1,543 997 3,278 2,023 Total stock-based compensation expense $ 3,564 $ 1,783 $ 6,317 $ 3,563
Schedule of Weighted Average Assumptions Used	The estimated grant date fair values of employee stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model, based on the following weighted-average assumptions: Three Months Ended Six Months Ended 2022 2021 2022 2021 Risk-free interest rate 3.26 % 1.12 % 1.63 % 0.72 % Dividend yield — — — — Expected term 6.05 6.05 6.03 6.02 Expected volatility 92.03 % 94.96 % 91.85 % 95.52 % Weighted-average fair value of common stock $ 1.29 $ 4.16 $ 3.10 $ 3.39
Summary of Options Activity	The following table summarizes the stock option activity under the 2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan: Weighted-average remaining Aggregate Number of Weighted-average contractual term intrinsic value options exercise price ($) (in years) (in thousands) Employees Outstanding at December 31, 2021 10,616,800 $ 3.99 8.19 $ 4,982 Granted 4,884,200 $ 3.10 Exercised (10,000) $ 2.10 Forfeited (221,069) $ 5.03 Outstanding at June 30, 2022 15,269,931 $ 3.69 8.30 $ 17,260 Vested at June 30, 2022 6,085,326 $ 4.35 7.17 $ — Vested and expected to vest at June 30, 2022 14,055,754 $ 3.73 8.22 $ 14,045 Non-employee consultants Outstanding at December 31, 2021 423,073 $ 6.34 3.85 $ 42 Granted — $ — Exercised — $ — Forfeited (156,834) $ 3.44 Outstanding at June 30, 2022 266,239 $ 8.05 5.58 $ — Vested at June 30, 2022 266,239 $ 8.05 5.58 $ — Vested and expected to vest at June 30, 2022 266,239 $ 8.05 5.58 $ —
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award	The following table summarizes the Company’s restricted stock units under the 2016 Plan and 2018 Inducement Incentive Award Plan: Number of shares Weighted average Unvested at December 31, 2021 394,450 $ 3.45 Granted 813,200 3.31 Vested (100,080) 3.65 Forfeited (10,087) 3.22 Unvested at June 30, 2022 1,097,483 $ 3.33

Revenue Arrangements (Tables)

Revenue Arrangements (Tables)	6 Months Ended
	Jun. 30, 2022
Revenue from Contract with Customer [Abstract]
Schedule of Changes in Contract Liabilities	The following table presents changes in the Company’s contract liabilities during the six months ended June 30, 2022 (in thousands): Balance at Balance at beginning of period Additions Deductions end of period Six Months Ended June 30, 2022 Contract liabilities: Deferred revenue $ 65,300 $ 16,000 $ (58,213) $ 23,087 Total contract liabilities $ 65,300 $ 16,000 $ (58,213) $ 23,087

Related-Party Transactions - (T

Related-Party Transactions - (Tables)	6 Months Ended
	Jun. 30, 2022
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	The following table sets forth the number of shares of Common Stock and 2022 Warrants purchased in the Offering by directors and executive officers, as of the time of the Offering, and related parties thereto: Name Shares of Common Stock purchased 2022 Warrants purchased Total aggregate purchase price TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.) 6,681,600 5,011,200 $ 9,421,056

Description of the Business (De

Description of the Business (Details) $ in Millions	Jun. 30, 2022 USD ($)
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, restricted cash and marketable securities	$ 143.4
Restricted cash and cash equivalents	1.4
Russian subsidiary
Cash and Cash Equivalents [Line Items]
Cash maintained in Russian bank accounts	$ 0.3

Marketable Securities and Inv_3

Marketable Securities and Investments - Summary of Available-for-Sale Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 3,999	$ 13,999
Unrealized gains	0	0
Unrealized losses	0	(1)
Fair value	3,999	13,998
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized cost	3,999	11,992
Unrealized gains	0	0
Unrealized losses	0	0
Fair value	$ 3,999	11,992
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized cost		2,007
Unrealized gains		0
Unrealized losses		(1)
Fair value		$ 2,006

Marketable Securities and Inv_4

Marketable Securities and Investments - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021	Sep. 07, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Marketable securities adjusted for other than temporary declines in fair value	$ 0
Investments	2,000,000	$ 2,000,000
Cyrus Biotechnology, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investments	$ 2,000,000	$ 2,000,000	$ 2,000,000

Net Income (Loss) Per Share- Co

Net Income (Loss) Per Share- Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator:
Net income (loss)	$ 8,601	$ 28,778	$ 4,565	$ (24,597)	$ 37,379	$ (20,032)
Less: Change in fair value of liability warrants			(4,820)		(13,868)	0
Adjusted net income (loss)	8,601		(255)		23,511	(20,032)
Adjusted net income (loss)	$ 8,601		$ (255)		$ 23,511	$ (20,032)
Denominator:
Weighted-average common shares outstanding, basic (in shares)	148,505,729		113,524,110		136,436,316	112,140,815
Dilutive effect of employee equity incentive plans and outstanding warrants (in shares)	0		7,653,888		529,996	0
Weighted‑average common shares outstanding—diluted (in shares)	148,505,729		121,177,998		136,966,312	112,140,815
Net income (loss) per share:
Basic (in dollars per share)	$ 0.06		$ 0.04		$ 0.27	$ (0.18)
Diluted (in dollars per share)	$ 0.06		$ 0		$ 0.17	$ (0.18)

Net Income (Loss) Per Share - S

Net Income (Loss) Per Share - Schedule of Potential Common Shares Issuable Upon Conversion of Warrants (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Potential common shares
Total (in shares)	47,729,897	10,866,602	37,524,598	22,952,149
Employees
Potential common shares
Total (in shares)	16,422,488	10,574,133	16,660,700	10,574,133
Warrants to purchase common stock
Potential common shares
Total (in shares)	31,307,409	292,469	20,863,898	12,378,016

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Assets:
Marketable securities:	$ 3,999	$ 13,998
Liabilities:
Warrant liabilities	26,934	25,423
Commercial paper
Assets:
Marketable securities:	3,999	11,992
Corporate bonds
Assets:
Marketable securities:		2,006
Recurring
Assets:
Total assets	80,685	80,561
Liabilities:
Warrant liabilities	26,934	25,423
Total liabilities	26,934	25,423
Recurring | Level 1
Assets:
Total assets	76,686	66,563
Liabilities:
Warrant liabilities	0	0
Total liabilities	0	0
Recurring | Level 2
Assets:
Total assets	3,999	13,998
Liabilities:
Warrant liabilities	0	0
Total liabilities	0	0
Recurring | Level 3
Assets:
Total assets	0	0
Liabilities:
Warrant liabilities	26,934	25,423
Total liabilities	26,934	25,423
Recurring | Commercial paper
Assets:
Marketable securities:	3,999	11,992
Recurring | Commercial paper | Level 1
Assets:
Marketable securities:	0	0
Recurring | Commercial paper | Level 2
Assets:
Marketable securities:	3,999	11,992
Recurring | Commercial paper | Level 3
Assets:
Marketable securities:	0	0
Recurring | Corporate bonds
Assets:
Marketable securities:		2,006
Recurring | Corporate bonds | Level 1
Assets:
Marketable securities:		0
Recurring | Corporate bonds | Level 2
Assets:
Marketable securities:		2,006
Recurring | Corporate bonds | Level 3
Assets:
Marketable securities:		0
Recurring | Money market funds (included in cash equivalents)
Assets:
Money market funds (included in cash equivalents)	76,686	66,563
Recurring | Money market funds (included in cash equivalents) | Level 1
Assets:
Money market funds (included in cash equivalents)	76,686	66,563
Recurring | Money market funds (included in cash equivalents) | Level 2
Assets:
Money market funds (included in cash equivalents)	0	0
Recurring | Money market funds (included in cash equivalents) | Level 3
Assets:
Money market funds (included in cash equivalents)	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Disclosures [Abstract]
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, transfers, net	$ 0
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability, transfers, net		$ 0
Dividend yield | Valuation technique, option pricing model
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants and rights outstanding, measurement input	0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Cash and cash equivalents	$ 138,057	$ 114,057	$ 125,749
Long-term restricted cash	1,379	1,379	1,379
Total cash, cash equivalents, and restricted cash	$ 139,436	$ 115,436	$ 127,128	$ 140,064

Fair Value Measurements - Assum

Fair Value Measurements - Assumptions used to record the fair value of the warrants (Details) - Valuation technique, option pricing model	Jun. 30, 2022	Apr. 11, 2022	Dec. 31, 2021
Risk-free interest rate | 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.0292		0.0097
Risk-free interest rate | 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.0301	0.0279
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0
Dividend yield | 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0		0
Dividend yield | 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0	0
Expected life (in years) | 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, term	2 years 5 months 23 days		2 years 11 months 23 days
Expected life (in years) | 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, term	4 years 9 months 10 days	5 years
Expected volatility | 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.9695		0.9610
Expected volatility | 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.9988	0.9600

Fair Value Measurements - Chang

Fair Value Measurements - Change in the warrant liabilities (Details) - Warrant liabilities $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of December 31, 2021	$ 25,423
Issuances	15,379
Exercises	0
Change in fair value	(13,868)
Fair value as of June 30, 2022	$ 26,934

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 7,667	$ 6,939
Less accumulated depreciation	(4,834)	(4,797)
Property and equipment, net	2,833	2,142
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	6,074	5,134
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	695	731
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	57	45
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	341	332
Office equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	190	163
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 310	$ 534

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 0.2	$ 0.2	$ 0.3	$ 0.3

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Payroll and employee related expenses	$ 2,223	$ 3,179
Collaboration and licensing	500	0
Accrued patent fees	885	309
Accrued external research and development costs	6,701	4,339
Accrued professional and consulting services	547	815
Accrued interest	184	170
Other	1,326	1,721
Accrued expenses	$ 12,366	$ 10,533

Accrued Expenses - Narrative (D

Accrued Expenses - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($) lawsuit	Dec. 31, 2021 USD ($)
Payables and Accruals [Abstract]
Loss contingency accrual | $	$ 0.9	$ 0.9
Number of claims settled | lawsuit	2

Leases - Components of lease co

Leases - Components of lease costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Leases [Abstract]
Operating lease cost	$ 505	$ 454	$ 1,011	$ 898
Variable lease cost	205	182	425	470
Short-term lease cost	2	2	5	5
Total lease cost	$ 712	$ 638	$ 1,441	$ 1,373

Leases - Operating Lease, Liabi

Leases - Operating Lease, Liability, Maturity (Details) $ in Thousands	Jun. 30, 2022 USD ($)
Leases [Abstract]
2022 (remainder)	$ 942
2023	1,922
2024	1,980
2025	2,039
2026	2,101
Thereafter	2,844
Total future minimum lease payments	11,828
Less imputed interest	2,685
Lease liabilities	$ 9,143

Leases - Other Information (Det

Leases - Other Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities:	$ 924	$ 898

Leases - Lease Term and Discoun

Leases - Lease Term and Discount Rate (Details)	Jun. 30, 2022	Jun. 30, 2021
Leases [Abstract]
Operating lease, weighted average remaining lease term	5 years 10 months 24 days	6 years 10 months 24 days
Operating lease, weighted average discount rate, percent	8.90%	8.90%

Debt - Term Loans (Narrative) (

Debt - Term Loans (Narrative) (Details) - 2020 Term Loans - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021	Aug. 31, 2020
Line of Credit Facility [Line Items]
Debt discount			$ 0.1
Term loan facility	$ 25	$ 25

Debt - Term Loan And Unamortize

Debt - Term Loan And Unamortized Debt Discount Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Loan payable, net of current portion	$ 22,634	$ 19,673
2020 Term Loans
Debt Instrument [Line Items]
Face value	25,000
Venture debt termination fee	2,250
Less: Debt discount	(1,331)
Less: Current portion of loan payable	(3,285)
Loan payable, net of current portion	$ 22,634

Debt - Schedule of Future Minim

Debt - Schedule of Future Minimum Payments on the Term Loans (Details) - 2020 Term Loans $ in Thousands	Jun. 30, 2022 USD ($)
Long-term Debt, Fiscal Year Maturity [Abstract]
2023	$ 7,759
2024	10,345
2025	6,896
Total minimum principal payments	$ 25,000

Equity - Narrative (Details)

Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Apr. 06, 2022	Oct. 25, 2021	Jun. 30, 2022	Jun. 30, 2021	Jun. 17, 2022	Dec. 31, 2021	Dec. 30, 2021
Subsidiary, Sale of Stock [Line Items]
Common stock, par value (in dollars per share)			$ 0.0001		$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)			350,000,000		350,000,000	350,000,000	200,000,000
Exercise price (in dollars per share)			$ 1.53			$ 1.62
Issuances (in shares)			20,571,429
Exercise of warrants (in shares)			0
Canceled (in shares)			79,130
Underwriting Agreement
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	27,428,572
Sale common stock	$ 36,900
Underwriting Agreement - 2022 Warrants
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	20,571,429
Class of warrant or right, number of securities called by warrants or rights (in shares)	0.75
Share price (in dollars per share)	$ 1.41
Exercise price (in dollars per share)	$ 1.55
At-The-Market Offering
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)			576,418
Sale common stock		$ 75,000
Shares issued, value			$ 1,675	$ 29,547

Equity - Warranty Activity (Det

Equity - Warranty Activity (Details)	6 Months Ended
	Jun. 30, 2022 $ / shares shares
Number of Warrants
Class of warrant or right, outstanding, beginning balance (in shares)	10,735,980
Issuances (in shares)	20,571,429
Canceled (in shares)	(79,130)
Class of warrant or right, outstanding, ending balance (in shares)	31,228,279
Weighted average exercise price
Exercise price, beginning balance (in dollars per share) | $ / shares	$ 1.62
Issuance (in dollars per share) | $ / shares	1.55
Canceled (in dollars per share) | $ / shares	17.71
Exercise price, ending balance (in dollars per share) | $ / shares	$ 1.53
Warrants to purchase common stock
Number of Warrants
Class of warrant or right, outstanding, beginning balance (in shares)	10,443,511
Issuances (in shares)	20,571,429
Class of warrant or right, outstanding, ending balance (in shares)	31,014,940
Warrants to purchase common stock
Number of Warrants
Class of warrant or right, outstanding, beginning balance (in shares)	292,469
Canceled (in shares)	(79,130)
Class of warrant or right, outstanding, ending balance (in shares)	213,339

Equity - Schedule of Authorized

Equity - Schedule of Authorized Shares of Common Stock for Future Issuance (Details) - shares	Jun. 30, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Total (in shares)	54,692,176	28,209,867
Shares available for future stock incentive awards
Class of Stock [Line Items]
Total (in shares)	6,830,244	6,039,564
Unvested restricted stock units
Class of Stock [Line Items]
Total (in shares)	1,097,483	394,450
Outstanding common stock options
Class of Stock [Line Items]
Total (in shares)	15,536,170	11,039,873
Exercise of warrants
Class of Stock [Line Items]
Total (in shares)	31,228,279	10,735,980

Stock Incentive Plans - Narrati

Stock Incentive Plans - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)		54,692,176		54,692,176		28,209,867
Employee stock option grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)		6,830,244		6,830,244		6,039,564
Weighted average grant date fair value of stock options (in dollars per share)		$ 0.99	$ 2.33	$ 3.19	$ 2.59
Unrecognized compensation expense related to unvested employee stock options		$ 16.9		$ 16.9
Weighted average period for recognition				2 years 9 months 18 days
Estimated forfeitures rate				10%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)				813,200
Grants in period (in dollars per share)				$ 3.31
2016 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grants (in shares)									1,210,256
Number of shares authorized, increase (in shares)	4,944,919
Common stock authorized and reserved for future issuance (in shares)		1,561,045		1,561,045
2016 Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)				813,200
Grants in period (in dollars per share)				$ 3.31
Award vesting term				4 years
Employment Inducement Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grants (in shares)		1,591,661		1,591,661
Common stock authorized and reserved for future issuance (in shares)							2,000,000	1,175,000
Employment Inducement Incentive Award Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for recognition				3 years 2 months 12 days
Unrecognized compensation expense		$ 2.6		$ 2.6
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized, increase (in shares)	1,236,229
Common stock authorized and reserved for future issuance (in shares)		3,677,538		3,677,538					173,076

Stock Incentive Plans - Schedul

Stock Incentive Plans - Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 3,564	$ 1,783	$ 6,317	$ 3,563
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	2,021	786	3,039	1,540
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 1,543	$ 997	$ 3,278	$ 2,023

Stock Incentive Plans - Sched_2

Stock Incentive Plans - Schedule of Assumptions (Details) - Shares available for future stock incentive awards - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	3.26%	1.12%	1.63%	0.72%
Dividend yield	0%	0%	0%	0%
Expected term	6 years 18 days	6 years 18 days	6 years 10 days	6 years 7 days
Expected volatility	92.03%	94.96%	91.85%	95.52%
Weighted-average fair value of common stock (in dollars per share)	$ 1.29	$ 4.16	$ 3.10	$ 3.39

Stock Incentive Plans - Summary

Stock Incentive Plans - Summary of Options Activity (Details) - 2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Employees
Number of Options
Beginning balance (in shares)	10,616,800
Granted (in shares)	4,884,200
Exercised (in shares)	(10,000)
Forfeited (in shares)	(221,069)
Ending balance (in shares)	15,269,931	10,616,800
Vested (in shares)	6,085,326
Vested and expected to vest (in shares)	14,055,754
Weighted-average exercise price
Beginning balance (in dollars per share)	$ 3.99
Granted (in dollars per share)	3.10
Exercised (in dollars per share)	2.10
Forfeited (in dollars per share)	5.03
Ending balance (in dollars per share)	3.69	$ 3.99
Vested (in dollars per share)	4.35
Vested and expected to vest (in dollars per share)	$ 3.73
Weighted-average remaining contractual term
Outstanding, term	8 years 3 months 18 days	8 years 2 months 8 days
Vested, term	7 years 2 months 1 day
Vested and expected to vest, term	8 years 2 months 19 days
Aggregate intrinsic value
Outstanding	$ 17,260	$ 4,982
Vested	0
Vested and expected to vest	$ 14,045
Non-employee consultants
Number of Options
Beginning balance (in shares)	423,073
Granted (in shares)	0
Exercised (in shares)	0
Forfeited (in shares)	(156,834)
Ending balance (in shares)	266,239	423,073
Vested (in shares)	266,239
Vested and expected to vest (in shares)	266,239
Weighted-average exercise price
Beginning balance (in dollars per share)	$ 6.34
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Forfeited (in dollars per share)	3.44
Ending balance (in dollars per share)	8.05	$ 6.34
Vested (in dollars per share)	8.05
Vested and expected to vest (in dollars per share)	$ 8.05
Weighted-average remaining contractual term
Outstanding, term	5 years 6 months 29 days	3 years 10 months 6 days
Vested, term	5 years 6 months 29 days
Vested and expected to vest, term	5 years 6 months 29 days
Aggregate intrinsic value
Outstanding	$ 0	$ 42
Vested	0
Vested and expected to vest	$ 0

Stock Incentive Plans - Restric

Stock Incentive Plans - Restricted Stock Units (Details) - Restricted Stock Units (RSUs)	6 Months Ended
	Jun. 30, 2022 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested at beginning of period (in shares) | shares	394,450
Grants in period (in shares) | shares	813,200
Vested in period (in shares) | shares	(100,080)
Forfeited in period (in shares) | shares	(10,087)
Unvested at end of period (in shares) | shares	1,097,483
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Unvested at beginning of period (in dollars per share) | $ / shares	$ 3.45
Grants in period (in dollars per share) | $ / shares	3.31
Vested in period (in dollars per share) | $ / shares	3.65
Forfeited in period (in dollars per share) | $ / shares	3.22
Unvested at end of period (in dollars per share) | $ / shares	$ 3.33

Stock Incentive Plans - Employe

Stock Incentive Plans - Employee Stock Purchase Plan (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)		54,692,176		54,692,176		28,209,867
Stock-based compensation expense		$ 3,564	$ 1,783	$ 6,317	$ 3,563
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)		3,677,538		3,677,538			173,076
Number of shares authorized, increase (in shares)	1,236,229
Shares of common stock issued to employees under the ESPP (in shares)				81,057
Stock-based compensation expense		$ 100	$ 100	$ 100	$ 100

Revenue Arrangements - Narrativ

Revenue Arrangements - Narrative (Details)							1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 29, 2022 USD ($)	Jun. 10, 2022	Jul. 28, 2020 USD ($)	Jun. 11, 2020 USD ($) obligation shares	Dec. 17, 2019 USD ($)	Oct. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 amendment	Dec. 31, 2021 USD ($)
Disaggregation of Revenue [Line Items]
Short-term contract liability	$ 15,974,000									$ 15,974,000		$ 15,974,000			$ 53,883,000
Revenue recognized												58,213,000
Long-term contract liability	7,113,000									7,113,000		7,113,000			11,417,000
Accounts receivable	23,994,000									23,994,000		23,994,000			9,914,000
Collaboration and license revenue										39,273,000	$ 19,663,000	73,272,000	$ 30,713,000
Deferred revenue related to agreement	23,087,000									23,087,000		23,087,000			65,300,000
Remaining performance obligation	23,100,000									23,100,000		23,100,000
SOBI Purchase Agreement
Disaggregation of Revenue [Line Items]
Short-term contract liability	12,900,000									12,900,000		12,900,000			37,500,000
Revenue recognized											19,500,000		30,600,000
Long-term contract liability	1,800,000									1,800,000		1,800,000			5,100,000
Sale of stock, number of shares issued in transaction (in shares) | shares					5,416,390
Sale common stock					$ 25,000,000
Redemption premium				$ 14,500,000
Payment obligation		$ 10,000,000
Contract assets	300,000									300,000		300,000
Contract assets, current	300,000									300,000		300,000
Contract assets, noncurrent	100,000									100,000		100,000
Accounts receivable	17,900,000									17,900,000		17,900,000			9,900,000
Collaboration and license revenue										29,200,000		52,900,000
Revenue recognized from performance obligations related to prior periods as a result of the change in transaction price										4,100,000
Takeda Agreement
Disaggregation of Revenue [Line Items]
Upfront cash payment							$ 3,000,000
Future additional payments, expected							$ 1,124,000,000
Short-term contract liability	1,000,000									1,000,000		1,000,000			1,000,000
Revenue recognized										0		1,000,000
Long-term contract liability															1,000,000
Collaborative Arrangement
Disaggregation of Revenue [Line Items]
Upfront cash payment					$ 75,000,000			$ 75,000,000
Sales milestone payments								630,000,000
License and option agreement, written day notice period before cancellation					180 days
Period after first commercial sale when the Company is eligible to receive royalties					10 years
Number of obligations | obligation					3
Development milestone					$ 5,000,000
Sarepta Therapeutics, Inc.
Disaggregation of Revenue [Line Items]
Upfront cash payment								$ 2,000,000
Short-term contract liability	500,000									500,000		500,000			4,600,000
Revenue recognized											100,000		100,000
Sales milestone payments											3,000,000
License and option agreement, written day notice period before cancellation								30 days
Accounts receivable	$ 6,000,000									6,000,000		6,000,000			0
Collaboration and license revenue										10,100,000		10,200,000
Revenue recognized from performance obligations related to prior periods as a result of the change in transaction price										900,000
Option term	33 months							24 months
Number of amendments | amendment														2
Extension term			9 months
Extension receivable	$ 2,000,000									2,000,000		2,000,000
Milestone receivable	4,000,000									4,000,000		4,000,000
License Agreement For Pompe Disease
Disaggregation of Revenue [Line Items]
Upfront cash payment									$ 7,000,000
Short-term contract liability	1,700,000									1,700,000		1,700,000			1,700,000
Revenue recognized										0	$ 0	0	$ 0
Long-term contract liability	$ 5,300,000									5,300,000		$ 5,300,000			5,300,000
Sales milestone payments									$ 237,000,000
Period after first commercial sale when the Company is eligible to receive royalties									10 years
Initial up-front cash payment						$ 2,000,000
Initial upfront execution fee payment						$ 5,000,000
Spark License Agreement
Disaggregation of Revenue [Line Items]
Revenue recognized										$ 0
Deferred revenue related to agreement															$ 9,200,000

Revenue Arrangements - Schedule

Revenue Arrangements - Schedule of Changes in Contract Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)
Contract liabilities:
Deferred revenue, beginning of period	$ 65,300
Deferred revenue, additions	16,000
Deferred revenue, deductions	(58,213)
Deferred revenue, end of period	23,087
Contract liabilities, beginning of period	65,300
Contract liabilities, additions	16,000
Contract liabilities, deductions	(58,213)
Contract liabilities, end of period	$ 23,087

Related-Party Transactions - Nu

Related-Party Transactions - Number of Shares of Common Stock Purchased (Details) - TAS Partners, LLC (affiliate of Timothy A. Springer, Ph.D.) - Affiliated Entity	Apr. 06, 2022 USD ($) shares
Related Party Transaction [Line Items]
Shares issued, value | $	$ 9,421,056
Common stock
Related Party Transaction [Line Items]
Stock issued (in shares)	6,681,600
Exercise of warrants
Related Party Transaction [Line Items]
Stock issued (in shares)	5,011,200

Related-party Transactions - Na

Related-party Transactions - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Founders
Related Party Transaction [Line Items]
Consulting services expenses (less than)	$ 0.1	$ 0.1

Collaboration and License Agr_2

Collaboration and License Agreements - Ginkgo Agreement (Details) - Ginkgo Agreement - USD ($) $ in Millions			1 Months Ended	3 Months Ended
	Jun. 13, 2022	Jan. 03, 2022	Oct. 31, 2021	Jun. 30, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Clinical and commercial milestone payment, expected		$ 207	$ 85
Milestone payment	$ 0.5
Sale of stock, number of shares issued in transaction (in shares)	892,857
Sale common stock				$ 1

Collaboration and License Agr_3

Collaboration and License Agreements - Cyrus Biotechnology, Inc. (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 07, 2021	Jun. 30, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity securities without readily determinable fair value, amount		$ 2,000	$ 2,000
Cyrus Biotechnology, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment	$ 1,500,000
Equity securities, stock purchase agreement, shares purchased (in shares)	2,326,934
Equity securities without readily determinable fair value, amount	$ 2,000	$ 2,000	$ 2,000
Cyrus Biotechnology, Inc. | Series B Preferred Stock Purchase Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity securities, stock purchase agreement, par value per share (in dollars per share)	$ 0.0001
Equity securities, stock purchase agreement, purchase price per share (in dollars per share)	$ 0.8595

Collaboration and License Agr_4

Collaboration and License Agreements - AskBio (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration expense	$ 25,413	$ 19,211	$ 48,639	$ 37,419
AskBio License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration expense	$ 200	$ 500	$ 600	$ 1,700
Cost share percentage			50%

Collaboration and License Agr_5

Collaboration and License Agreements - MIT (Narrative) (Details) - Spark License Agreement - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contractual payments defined in the Exclusive Patent License agreement	$ 0	$ 0
MIT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contractual payments defined in the Exclusive Patent License agreement		2,200,000
License and option agreement, payments made relative to calculated premium paid for initial equity investment made under the purchase agreement		$ 400,000

Collaboration and License Agr_6

Collaboration and License Agreements - Shenyang Sunshine Pharmaceutical Co., Ltd (Narrative) (Details) - 3SBio License $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate amount of upfront and milestone-based payments	$ 7
Aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for products containing ImmTOR platform	$ 15

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) $ in Millions	Dec. 31, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Federal operating loss carryforwards	$ 51.1
Domestic Tax Authority
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development credits	$ 1.2

Defined Contribution Plan - Nar

Defined Contribution Plan - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Retirement Benefits [Abstract]
Vesting period			2 years
Employer contribution made	$ 0.1	$ 0.1	$ 0.2	$ 0.1

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Loss contingency accrual	$ 0.9	$ 0.9