Seres Therapeutics (MCRB) 10-K 7 Mar 23 2022 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2022	Mar. 03, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	MCRB
Entity Registrant Name	Seres Therapeutics, Inc.
Entity Central Index Key	0001609809
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity File Number	001-37465
Entity Tax Identification Number	27-4326290
Entity Address, Address Line One	200 Sidney Street – 4th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	945-9626
Entity Public Float			$ 239,918,450
Entity Common Stock Shares Outstanding		126,076,391
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Well Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement relating to its 2023 Annual Meeting of Stockholders to be filed with the SEC within 120 days after the end of the fiscal year ended December 31, 2022 are incorporated herein by reference in Part III.
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Boston, Massachusetts

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents		$ 163,030	$ 180,002
Short term investments		18,311	110,704
Prepaid expenses and other current assets		13,423	12,922
Total current assets		194,764	303,628
Property and equipment, net		22,985	17,938
Operating lease assets		110,984	18,208
Restricted cash		8,185	8,000
Restricted investments		1,401	1,401
Long term investments		0	495
Other non-current assets		10,465	5,189
Total assets		348,784	354,859
Current liabilities:
Accounts payable		17,440	13,735
Accrued expenses and other current liabilities	[1]	59,840	45,094
Operating lease liabilities		3,601	6,610
Short term portion of note payable, net of discount		456	0
Deferred revenue - related party		4,259	16,819
Total current liabilities		85,596	82,258
Long term portion of note payable, net of discount		50,591	24,643
Operating lease liabilities, net of current portion		107,942	17,958
Deferred revenue, net of current portion - related party		92,430	86,998
Other long-term liabilities	[2]	1,442	11,495
Total liabilities		338,001	223,352
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2022 and 2021; no shares issued and outstanding at December 31, 2022 and 2021, respectively		0	0
Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2022 and 2021; 125,222,273 and 91,889,418 shares issued and outstanding at December 31, 2022 and 2021, respectively		125	92
Additional paid-in capital		875,181	745,829
Accumulated other comprehensive loss		(12)	(60)
Accumulated deficit		(864,511)	(614,354)
Total stockholders' equity		10,783	131,507
Total liabilities and stockholders' equity		$ 348,784	$ 354,859
[1] Includes related party amounts of $ 34,770 and $ 21,098 at December 31, 2022 and December 31, 2021 , respectively (see Note 11) Includes related party amounts of $ 0 and $ 10,585 at December 31, 2022 and December 31, 2021 , respectively (see Note 11)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	125,222,273	91,889,418
Common stock, shares outstanding	125,222,273	91,889,418
Related party amounts included in accrued expenses and other current liabilities	$ 34,770	$ 21,098
Related party amounts included in other long-term liabilities	$ 0	$ 10,585

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue:
Collaboration revenue - related party	$ 7,128	$ 143,857	$ 11,897
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Grant revenue	$ 0	$ 1,070	$ 4,157
Collaboration revenue	0	0	17,161
Total revenue	7,128	144,927	33,215
Operating expenses:
Research and development expenses	172,920	141,891	90,570
General and administrative expenses	79,694	69,261	30,775
Collaboration (profit) loss sharing - related party	1,004	(1,732)	0
Total operating expenses	253,618	209,420	121,345
Loss from operations	(246,490)	(64,493)	(88,130)
Other (expense) income:
Interest income	3,058	2,870	946
Interest expense	(6,020)	(2,910)	(2,924)
Other (expense) income	(705)	(1,045)	981
Total other (expense) income, net	(3,667)	(1,085)	(997)
Net loss	$ (250,157)	$ (65,578)	$ (89,127)
Net loss per share attributable to common stockholders, basic	$ (2.31)	$ (0.72)	$ (1.12)
Net loss per share attributable to common stockholders, diluted	$ (2.31)	$ (0.72)	$ (1.12)
Weighted average common shares outstanding, basic	108,077,043	91,702,866	79,789,220
Weighted average common shares outstanding, diluted	108,077,043	91,702,866	79,789,220
Other comprehensive loss:
Unrealized gain (loss) on investments, net of tax of $0	$ 49	$ (12)	$ (47)
Currency translation adjustment	(1)	(1)	0
Total other comprehensive income (loss)	48	(13)	(47)
Comprehensive loss	$ (250,109)	$ (65,591)	$ (89,174)

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Unrealized (loss) gain on investment, tax	$ 0	$ 0	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2019	$ (48,324)	$ 70	$ 411,255		$ (459,649)
Beginning balance, shares at Dec. 31, 2019		70,143,252
Issuance of common stock, net of issuance costs, value	243,748	$ 12	243,736
Common stock, shares issued		12,075,000
Issuance of common stock from Securities Purchase Agreement, net of offering costs - related party, value	19,900	$ 1	19,899
Issuance of common stock from Securities Purchase Agreement, net of offering costs - related party, shares		959,002
Issuance of common stock from at the market equity offering, value	24,773	$ 6	24,767
Issuance of common stock from at the market equity offering, shares		5,787,681
Issuance of common stock upon exercise of stock options, value	14,421	$ 2	14,419
Issuance of common stock upon exercise of stock options, shares		2,214,011
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	120		120
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		125,000
Issuance of common stock under ESPP plan, value	462		462
Issuance of common stock under ESPP plan, shares		155,293
Stock-based compensation expense	8,824		8,824
Other comprehensive loss	(47)			$ (47)
Net loss	(89,127)				(89,127)
Ending balance at Dec. 31, 2020	174,750	$ 91	723,482	(47)	(548,776)
Ending balance, shares at Dec. 31, 2020		91,459,239
Issuance of common stock upon exercise of stock options, value	1,299	$ 1	1,298
Issuance of common stock upon exercise of stock options, shares		329,112
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		650
Issuance of common stock under ESPP plan, value	827		827
Issuance of common stock under ESPP plan, shares		100,417
Stock-based compensation expense	20,222		20,222
Other comprehensive loss	(13)			(13)
Net loss	(65,578)				(65,578)
Ending balance at Dec. 31, 2021	$ 131,507	$ 92	745,829	(60)	(614,354)
Ending balance, shares at Dec. 31, 2021	91,889,418	91,889,418
Issuance of common stock, net of issuance costs, value	$ 96,721	$ 32	96,689
Common stock, shares issued		31,746,030
Issuance of common stock from at the market equity offering, value	4,447	$ 1	4,446
Issuance of common stock from at the market equity offering, shares		655,000
Issuance of common stock upon exercise of stock options, value	$ 966		966
Issuance of common stock upon exercise of stock options, shares	326,864	326,864
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		282,401
Issuance of common stock under ESPP plan, value	$ 1,769		1,769
Issuance of common stock under ESPP plan, shares		322,560
Stock-based compensation expense	25,482		25,482
Other comprehensive loss	48			48
Net loss	(250,157)				(250,157)
Ending balance at Dec. 31, 2022	$ 10,783	$ 125	$ 875,181	$ (12)	$ (864,511)
Ending balance, shares at Dec. 31, 2022	125,222,273	125,222,273

Condensed Consolidated Statemen

Condensed Consolidated Statement of Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2020
Issuance costs	$ 3,279
Initial Public Offering ("IPO") [Member]
Issuance costs		$ 288
Market Equity Offering [Member]
Issuance costs	$ 310	673
Securities Purchase Agreement [Member]
Issuance costs		$ 100

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss		$ (250,157)	$ (65,578)	$ (89,127)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense		25,482	20,222	8,824
Depreciation and amortization expense		6,629	5,947	6,578
Non-cash operating lease cost		5,224	3,275	2,315
Accretion (amortization) of discount (premium) on issued debt securities		688	498	446
Amortization of debt issuance costs		705	2,526	551
Collaboration (profit) loss sharing - related party		1,004	(1,732)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets		(12,599)	(12,337)	(2,186)
Accounts receivable		0	9,387	(7,602)
Deferred revenue - related party		(7,128)	(4,357)	(11,565)
Accounts payable		2,203	9,362	(1,159)
Operating lease liabilities		(4,203)	(3,550)	(4,456)
Accrued expenses and other current and long-term liabilities	[1]	3,336	43,025	3,771
Net cash (used in) provided by operating activities		(228,816)	6,688	(93,610)
Cash flows from investing activities:
Purchases of property and equipment		(9,821)	(9,566)	(591)
Purchases of investments		(48,221)	(95,971)	(218,284)
Sales and maturities of investments		140,470	169,625	59,984
Net cash provided by (used in) investing activities		82,428	64,088	(158,891)
Cash flows from financing activities:
Proceeds from issuance of common stock		96,721	0	243,748
Proceeds from Securities Purchase Agreement, net of issuance costs - related party		0	0	19,900
Proceeds from issuance of note payable		27,606	0	0
Proceeds from at the market equity offering, net of commissions		4,447	0	24,773
Proceeds from exercise of stock options		966	1,299	14,421
Proceeds from issuance of common stock and restricted common stock		0	0	120
Issuance of common stock under ESPP		1,769	827	462
Repayment of notes payable		(1,907)	(948)	0
Net cash provided by financing activities		129,602	1,178	303,424
Net increase (decrease) in cash, cash equivalents and restricted cash		(16,786)	71,954	50,923
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(1)	(1)	0
Cash, cash equivalents and restricted cash at beginning of year		188,002	116,049	65,126
Cash, cash equivalents and restricted cash at end of year		171,215	188,002	116,049
Supplemental disclosure of cash flow information:
Cash paid for interest		4,926	2,446	2,453
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses		2,276	874	451
Lease liability arising from obtaining right-of-use assets		91,412	12,442	0
Prepaid rent reclassified to right-of-use assets		$ 6,822	$ 0	$ 0
[1] Includes related party amounts of $ 3,087 and $ 31,683 at December 31, 2022 and 2021 respectively (see Note 11)

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Statement of Cash Flows [Abstract]
Accrued expenses and other current and long-term liabilities, related party amounts	$ 3,087	$ 31,683

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Seres Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in October 2010 under the name Newco LS21, Inc. In October 2011, the Company changed its name to Seres Health, Inc., and in May 2015, the Company changed its name to Seres Therapeutics, Inc. The Company is a microbiome therapeutics company developing a novel class of biological drugs, which are designed to treat disease by modulating the microbiome to restore health by repairing the function of a disrupted microbiome to a non-disease state. The Company’s lead product candidate, SER-109, is designed to reduce further recurrences of Clostridioides difficile infection (“CDI”), a debilitating infection of the colon, in patients who have received antibiotic therapy for recurrent CDI by restructuring the colonic microbiome and changing its function. If approved by the U.S. Food and Drug Administration (“FDA”), the Company believes SER-109 will be a first-in-field oral microbiome drug. Building upon SER-109, the Company is developing therapeutic candidates, such as SER-155, to specifically target infections and antimicrobial resistance. SER-155, a microbiome therapeutic candidate consisting of a consortium of cultivated bacteria, is designed to reduce incidences of gastrointestinal infections, bloodstream infections and graft versus host disease ("GvHD”) in patients receiving allogeneic hematopoietic stem cell transplantation (“allo-HSCT”). The Company is progressing additional preclinical stage programs to evaluate how microbiome therapeutics may reduce incidence of infection, which the Company refers to as Infection Protection, in indications such as cancer neutropenia, chronic liver disease, solid organ transplant, and antimicrobial resistant infections more broadly in settings of high-risk such as intensive care units. The Company is also continuing its research activities in ulcerative colitis ("UC"), including evaluating the potential to utilize biomarker-based patient selection and stratification for future studies. In addition, the Company continues to leverage microbiome pharmacokinetic and pharmacodynamic data from across its clinical and preclinical portfolios, using its reverse translational microbiome therapeutic development platform to conduct research on various indications, including inflammatory and immune diseases, cancer, and metabolic diseases. The Company has built and deploys a reverse translational platform for the discovery and development of microbiome therapeutics. This platform incorporates high-resolution analysis of human clinical data to identify microbiome biomarkers associated with disease and non-disease states; preclinical screening using human cell-based assays and in vitro/ex vivo and in vivo disease models customized for microbiome therapeutics; and microbiological capabilities and a strain library that spans broad biological and functional breadth to both identify specific microbes and microbial metabolites that are associated with disease and to design consortia of bacteria with specific pharmacological properties. The accompanying consolidated financial statements have been prepared on a basis that assumes that the Company will continue as a going concern and that contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. As of December 31, 2022, the Company had an accumulated deficit of $ 864,511 and cash, cash equivalents and short- and long-term investments of $ 181,341 . 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. 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. 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 product candidate developed will obtain necessary government regulatory approval or that any approved product 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's primary focus in recent months has been and will continue to be supporting the Biologics License Application ("BLA") submission for our lead product candidate, SER-109, and continuing to prepare for potential commercialization, including the manufacture of SER-109, until and continuing after the Prescription Drug User Fee Act ("PDUFA") target action date set by the FDA of April 26, 2023. The Company has commenced manufacture of SER-109 in consideration of potential commercialization, which requires capital and resources. Successful execution of the pre-commercialization activities required by our collaboration agreement with Société des Produits Nestlé S.A., successor in interest to Nestec Ltd., and NHSc Rx License GmbH, a significant stockholder of the Company and successor in interest to NHSc Pharma Partners (collectively, and together with their affiliates and subsidiaries, “Nestlé”), requires continued investment in readying for launch. Still, there can be no assurance that the BLA for SER-109, which is currently under priority review by the FDA, will be approved, that the FDA will complete its review of the BLA in the anticipated timeline, or that, in the event of approval, the demand for SER-109 will be sufficient to meet the Company's forecasted cash needs without raising significant additional capital. The Company also has a credit facility (the "New Credit Facility") pursuant to a Loan and Security Agreement (the “Loan Agreement”) with Hercules Capital, Inc. ("Hercules," see Note 8, Notes Payable ), which is collateralized by substantially all of the Company’s assets excluding intellectual property. The Company is currently in compliance with the financial covenants in the New Credit Facility. The New Credit Facility includes a conditional liquidity covenant commencing on June 15, 2023, which ceases to apply if certain conditions are satisfied. Violation of any covenant under the New Credit Facility provides Hercules with the option to accelerate repayment of amounts borrowed and terminate its commitment to extend further credit, among other remedies as defined in the New Credit Facility. Primarily as a result of the increased and costly efforts to prepare for potential commercialization of SER-109, in conjunction with the Company's research and development efforts for other preclinical and product candidates, for the year ended December 31, 2022, the Company incurred a net loss of $ 250,157 , and had net operating cash outflows of $ 228,816 . The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. The Company is eligible to receive contingent milestone payments under its license agreement with Nestlé executed in July 2021 (see Note 11, Collaboration Revenue ) if certain development, regulatory approval or sales target milestones are achieved. Upon approval of the BLA, the Company is entitled to receive an additional $ 125,000 payment from Nestlé, and a $ 25,000 tranche under the New Credit Facility, which becomes available upon the satisfaction of certain conditions, including FDA approval of SER-109. Additionally, following FDA approval, the Company will be eligible to receive payments from Nestlé for the supply of SER-109. In the event of commercial sale of SER-109, the Company will be entitled to share equally in its commercial profits and losses. The payments under the 2021 License Agreement and the additional tranche under the New Credit Facility are uncertain and there is no assurance that the Company will receive any of them, because they are contingent upon approval of the Company's BLA, which is currently under priority review by the FDA. Based on the Company's currently available cash resources, current and forecasted level of operations, and forecasted cash flows for the 12 month period subsequent to the date of issuance of these consolidated financial statements, in the absence of approval of SER-109 by the FDA, and therefore, without the receipt of the approval milestone and other payments to which it is entitled to receive as a result thereof, the Company believes it is reasonably likely that it will require additional funding in early 2024. These factors raise substantial doubt about the Company’s ability to continue as a going concern. Management's plans to mitigate the conditions that raise substantial doubt about the Company’s ability to continue as a going concern include continuing to seek regulatory approval of the BLA for SER-109 and therefore earning the $ 125,000 milestone payment from Nestl é and becoming eligible for the $ 25,000 tranche under the New Credit Facility , as well as the ability to commercialize SER-109 and receive payments from Nestlé for the supply of SER-109, and share equally in commercial profits and losses with Nestlé pursuant to the 2021 License Agreement. Management may also seek to raise additional capital through financing or other transactions, including the Company's at the market equity offering. Because certain elements of the Company’s operating plan are outside of the Company’s control, primarily the approval of its BLA for SER-109, which has not occurred as of the issuance of these consolidated financial statements, and the ability to raise capital through an equity or other financing, those elements cannot be considered probable according to Accounting Standards Codification (“ASC”) 205-40, Going Concern ("ASC 205-40"), and therefore cannot be considered in the evaluation of mitigating factors. As a result, management has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for 12 months from the date these consolidated financial statements are issued. The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries after elimination of all intercompany accounts and transactions.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. In these consolidated financial statements, the Company uses estimates and assumptions related to revenue recognition and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, commercial paper and corporate bonds purchased with original maturities of less than 90 days from the date of purchase, are stated at fair value. Investments The Company classifies all of its marketable debt securities as available-for-sale securities. Accordingly, these marketable debt securities are recorded at fair value and unrealized gains and losses are reported as a separate component of accumulated other comprehensive loss in stockholders’ equity (deficit), unless the Company has determined that the security has experienced a credit loss, or the Company expects to sell the security prior to the recovery of its unrealized losses. In such cases a security is considered impaired, and adjusted through a charge to the consolidated statement of operations and comprehensive loss. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations and comprehensive loss. No credit losses were recorded during the years ended December 31, 2022, 2021, and 2020. The Company classifies its available-for-sale marketable debt securities as current assets on the consolidated balance sheet if they mature within one year from the balance sheet date. Any available-for-sale marketable debt securities with maturities greater than one year from the balance sheet date are classified as long-term assets on the consolidated balance sheet. Restricted Investments The Company held investments of $ 1,401 as of December 31, 2022 and 2021 , in a separate restricted bank account as a security deposit for the lease of the Company’s headquarters in Cambridge, Massachusetts. The Company has classified these deposits as long-term restricted investments on its consolidated balance sheet. Restricted Cash The Company held restricted cash of $ 8,185 and $ 8,000 as of December 31, 2022 and 2021, respectively, which represents cash held for the benefit of the landlord for the Company's other leases. The Company has classified the restricted cash as long-term on its consolidated balance sheet as the underlying leases are greater than 1 year. Cash, cash equivalents and restricted cash were comprised of the following (in thousands): December 31, 2022 2021 Cash and cash equivalents $ 163,030 $ 180,002 Restricted cash, non-current 8,185 8,000 Total cash, cash equivalents and restricted cash $ 171,215 $ 188,002 Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company has all cash, cash equivalents and investments balances at accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Fair Value Measurements Certain assets and liabilities are carried at fair value in accordance with GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above. The Company’s investments in certificates of deposit are carried at amortized cost, which approximates fair value. The carrying values of the Company’s prepaid expenses and other current and non-current assets, accounts payable and accrued expenses approximate their respective fair values due to the short-term nature of these assets and liabilities. The carrying value of the Company’s long-term debt approximates its fair value (a level 2 measurement) at each balance sheet date due to its variable interest rate, which approximates a market interest rate. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset, which are as follows: Estimated Useful Life (In Years) Laboratory equipment 5 Computer equipment, furniture and office equipment 3 Leasehold improvements Lesser of useful life Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and right-of-use assets associated with our lease agreements. All of the Company's long-lived assets are to be held and used and have definitive lives and accordingly are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has no t recorded any impairment losses on long-lived assets. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials. Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. Accounting for Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees, non-employees, and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options, restricted stock units and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. For stock options or restricted stock units issued with performance-based vesting conditions, the stock compensation expense related to these awards is recognized based on the grant date fair value when achievement of the performance condition is deemed probable. The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company accounts for forfeitures of stock-based awards as they occur rather than applying an estimated forfeiture rate to stock-based compensation expense. The fair value of each stock option grant is estimated on the date of grant using the Black- Scholes option-pricing model. The Company estimates its expected common stock volatility based on its historical common stock volatility for the same time period. The Company uses the simplified method prescribed by Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share-Based Payment , to calculate the expected term of options granted to employees, non-employees and directors. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Revenue Recognition The Company recognizes revenue in accordance with the guidance under ASC 606, Revenue from Contracts with Customers ("ASC 606"). ASC 606 applies to all contracts with customers, except those contracts that are within the scope of other guidance, such as leases, insurance, and financial instruments. The Company enters into agreements that are within the scope of ASC 606, under which the Company licenses certain of the Company’s product candidates and performs research and development services in connection with such arrangements. The terms of these arrangements typically include payment of one or more of the following: nonrefundable up-front fees, reimbursement of research and development costs, development, clinical, regulatory and commercial sales milestone payments, and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. When determining the timing and extent of revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: a. identify the contract(s) with a customer; b. identify the performance obligations in the contract; c. determine the transaction price; d. allocate the transaction price to the performance obligations in the contract; and e. recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services transferred to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within the contract to determine whether each promised good or service is a performance obligation. The promised goods or services in the Company’s arrangements typically consist of a license to the Company’s intellectual property and/or research and development services. The Company may provide options to additional items in such arrangements, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. Performance obligations are promises in a contract to transfer a distinct good or service to the customer that (i) the customer can benefit from on its own or together with other readily available resources, and (ii) is separately identifiable from other promises in the contract. Goods or services that are not individually distinct performance obligations are combined with other promised goods or services until such combined group of promises meet the requirements of a performance obligation. The Company determines the transaction price based on the amount of consideration the Company expects to receive for transferring the promised goods or services in the contract. Consideration may be fixed, variable, or a combination of both. At contract inception for arrangements that include variable consideration, the Company estimates the probability and extent of consideration it expects to receive under the contract utilizing either the most likely amount method or expected amount method, whichever best estimates the amount expected to be received. The Company then considers any constraints on the variable consideration and includes in the transaction price variable consideration to the extent it is deemed probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company then allocates the transaction price to each performance obligation based on the relative standalone selling price and recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) control is transferred to the customer and the performance obligation is satisfied. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company records amounts as accounts receivable when the right to consideration is deemed unconditional. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded for deferred revenue. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Incremental costs of obtaining a contract are expensed as and when incurred if the expected period over which the Company would have amortized the asset is one year or less, or the amount is immaterial. Collaboration Revenue Arrangements with collaborators may include licenses to intellectual property, research and development services, manufacturing services for clinical and commercial supply, and participation on joint steering committees. The Company evaluates the promised goods or services to determine which promises, or group of promises, represent performance obligations. In contemplation of whether a promised good or service meets the criteria required of a performance obligation, the Company considers the stage of development of the underlying intellectual property, the capabilities and expertise of the customer relative to the underlying intellectual property, and whether the promised goods or services are integral to or dependent on other promises in the contract. When accounting for an arrangement that contains multiple performance obligations, the Company must develop judgmental assumptions, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success to determine the stand-alone selling price for each performance obligation identified in the contract. When the Company concludes that a contract should be accounted for as a combined performance obligation and recognized over time, the Company must then determine the period over which revenue should be recognized and the method by which to measure revenue. The Company generally recognizes revenue using a cost-based input method. Licenses of intellectual property If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue associated with the bundled performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition. Milestone Payments At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service, otherwise it will be allocated to all performance obligations of the arrangement based on the initial allocation. The Company evaluates each milestone to determine when and how much of the milestone to include in the transaction price. The Company first estimates the amount of the milestone payment that the Company could receive using either the expected value or the most likely amount approach. The Company primarily uses the most likely amount approach as that approach is generally most predictive for milestone payments with a binary outcome. Then, the Company considers whether any portion of that estimated amount is subject to the variable consideration constraint (that is, whether it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty). The Company updates the estimate of variable consideration included in the transaction price at each reporting date which includes updating the assessment of the likely amount of consideration and the application of the constraint to reflect current facts and circumstances. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has no t recognized any revenue related to sales-based royalties or milestone payments based on the level of sales. Manufacturing supply services For arrangements that include a promise of supply of clinical or commercial product, the Company determines if the supply is a promise in the contract or a future obligation at the customer’s option. If determined to be a promise at inception of the contract, the Company evaluates the promise to determine whether it is a separate performance obligation or a component of a bundled performance obligation. If determined to be an option, the Company determines if the option provides a material right to the customer and if so, accounts for the option as a separate performance obligation. If determined to be an option but not a material right, the Company accounts for the option as a separate contract when the customer elects to exercise the option. Grant Revenue The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies, when the Company has concluded that it is the principal in conducting the research and development expenses, and where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. The Company has concluded to recognize funding received as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these contracts are central to its ongoing operations. Revenue is recognized as the qualifying expenses related to the contracts are incurred. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded in the Company’s consolidated balance sheet as accounts receivable. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss. Collaboration Profit and Loss We analyze our collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808"), which includes determining whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, we first determine which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, we apply the five-step model prescribed in ASC 606, as described above. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to ASC 606. In arrangements where we do not deem our collaborator to be our customer, up-front payments from our collaborator are presented in the consolidated balance sheets as liabilities, and adjusted as we perform activities pursuant to the collaboration arrangement. As the Company and its collaborator perform activities pursuant to the arrangement, amounts due to or from the Company or the collaborator, based on the relative contributions of activities of each party, are recognized in the consolidated statements of operations and comprehensive loss as an increase or reduction in operating expenses based on the nature of the payments. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The Company applies ASC 740-10, Accounting for Uncertain Tax Positions . The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 % likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing microbiome therapeutics to treat the modulation of the colonic microbiome. Revenue to date has been generated solely through the Company's agreements with its collaborators, all of which has been earned in the United States. All tangible assets are held in the United States. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2022, 2021 and 2020 , other comprehensive income (loss) consisted of changes in unrealized gains (losses) from available-for-sale investments and a currency translation adjustment. Net Loss per Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and unvested restricted stock. The Company applies the two-class method to calculate its basic and diluted net loss per share attributable to common stockholders. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method does not impact the net loss per share of common stock as the Company was in a net loss position for each of the periods presented. The Company’s convertible preferred stock contractually entitle the holders of such shares to participate in dividends but do not contractually require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Leases In accordance with ASC 842, Leases , the Company determines if an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records a right-of-use asset and a lease liability on the consolidated balance sheet for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded on the balance sheet, but payments are recognized as expense on a straight-line basis over the lease term. The Company has elected not to record a right-of-use asset or lease liability for leases with terms of 12 months or less. Right-of-use assets and lease liabilities are reassessed and remeasured when amendments to the terms of the lease agreement require reassessment and remeasurement of the lease payments and other inputs to the calculation of right-of-use assets and lease liabilities. The Company accounts for remeasurements and modifications to lease liabilities using the present value of remaining lease payments and estimated incremental borrowing rate at the date of remeasurement. The adjustment to the lease liability is recognized as a gain or loss in operating expenses, or as an adjustment to the right-of-use asset, as appropriate, based on the terms and conditions within the lease that are amended. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (‘‘ASU 2016-13’’), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. In November 2018, the FASB issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses , which na

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): Fair Value Measurements as of December 31, 2022 Using: Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 47,863 $ — $ — $ 47,863 Commercial paper — 11,691 — 11,691 Government securities — 4,966 — 4,966 Investments: Commercial paper $ — $ 2,465 $ — $ 2,465 Corporate bonds — 2,957 — 2,957 Government securities — 12,889 — 12,889 $ 47,863 $ 34,968 $ — $ 82,831 Fair Value Measurements as of December 31, 2021 Using: Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 70,322 $ — $ — $ 70,322 Commercial paper — 3,999 — 3,999 Investments: Commercial paper $ — $ 6,250 $ — $ 6,250 Corporate bonds — 40,095 — 40,095 Government securities — 64,854 — 64,854 $ 70,322 $ 115,198 $ — $ 185,520 Money market funds are valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. Commercial paper, corporate bonds, and government securities are valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. There were no transfers between Level 1 or Level 2 during the years ended December 31, 2022 and 2021. As of December 31, 2022 and 2021 the Company held a restricted investment of $ 1,401 , which represents a certificate of deposit that is classified as Level 2 in the fair value hierarchy.

Investments

Investments	12 Months Ended
	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Investments	4. Investments Investments by security type consisted of the following at December 31, 2022 and 2021 (in thousands): December 31, 2022 Amortized Gross Gross Fair Investments: Commercial paper $ 2,465 $ — $ — $ 2,465 Corporate bonds 2,958 — ( 1 ) 2,957 Government securities 12,898 3 ( 12 ) 12,889 $ 18,321 $ 3 $ ( 13 ) $ 18,311 December 31, 2021 Amortized Gross Gross Fair Investments: Commercial paper $ 6,250 $ — $ — $ 6,250 Corporate bonds 40,123 — ( 28 ) 40,095 Government securities 64,885 — ( 31 ) 64,854 $ 111,258 $ — $ ( 59 ) $ 111,199 Investments with original maturities of less than 90 days are included in cash and cash equivalents on the consolidated balance sheets and are not included in the table above. Investments with maturities of less than twelve months are considered current assets and those investments with maturities greater than twelve months are considered non-current assets. Excluded from the tables above at December 31, 2022 and 2021 are restricted investments of $ 1,401 , as the cost approximates current fair value. The amortized cost and fair value of investments in commercial paper, corporate bonds, and government securities by contractual maturity, as of December 31, 2022 and were as follows (in thousands): Available-for-Sale Cost Fair Value Due in 1-year or less $ 18,321 $ 18,311 Due after 1-year through 5-years — — $ 18,321 $ 18,311 The amortized cost and fair value of investments in commercial paper, corporate bonds, and government securities by contractual maturity, as of December 31, 2021 were as follows (in thousands): Available-for-Sale Cost Fair Value Due in 1-year or less $ 110,762 $ 110,704 Due after 1-year through 5-years 496 495 $ 111,258 $ 111,199

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2022 2021 Laboratory equipment $ 24,533 $ 19,137 Computer equipment 3,557 3,255 Furniture and office equipment 3,491 1,219 Leasehold improvements 32,474 32,925 Construction in progress 3,970 1,670 68,025 58,206 Less: Accumulated depreciation and amortization ( 45,040 ) ( 40,268 ) $ 22,985 $ 17,938 Depreciation and amortization expense was $ 6,629 , $ 5,947 and $ 6,578 for the years ended December 31, 2022, 2021 and 2020 , respectively. During the year ended December 31, 2022, the Company disposed of certain fully-depreciated assets with a cost basis of $ 1,857 .

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: December 31, 2022 2021 Development and manufacturing costs $ 6,717 $ 11,147 Payroll and payroll-related costs 14,709 9,216 Liability related to 2021 License Agreement (Note 11) 34,770 21,098 Facility and other 3,644 3,633 $ 59,840 $ 45,094

Leases

Leases	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Leases	7. Leases The Company leases real estate, primarily laboratory, office and manufacturing space. The Company’s leases have remaining terms ranging from approximately two to ten years . Certain leases include one or more options to renew, exercisable at the Company’s sole discretion, with renewal terms that can extend the lease from approximately one year to five years . The Company evaluated the renewal options in its leases to determine if it was reasonably certain that the renewal option would be exercised, given the Company’s current business structure, uncertainty of future growth, and the associated impact to real estate, the Company concluded that it is not reasonably certain that any renewal options would be exercised. Therefore, the operating lease assets and operating lease liabilities only contemplate the initial lease terms. All the Company’s leases qualify as operating leases. In July 2021, the Company entered into a lease agreement for a donor collection facility in Tempe, Arizona with a lease term of ten years , commencing in March 2022, subject to certain renewal options, which are not deemed reasonably certain. Minimum lease payments total $ 4,052 , net of tenant improvement allowance of $ 770 , through the lease term. At lease commencement, the Company recorded a right-of-use asset of $ 5,900 , which consists of the lease liability of $ 2,327 and $ 3,573 of leasehold improvements that revert back to the lessor at the termination of the lease. In August 2021, the Company entered into a lease for additional office and laboratory space in Waltham, Massachusetts with a lease term of ten years , commencing in two phases in October 2021 and March 2022, respectively, with a third and final phase for laboratory space, not yet commenced at December 31, 2022. Minimum lease payments for the two phases that commenced in 2022 total $ 12,125 and $ 2,449 , respectively, net of tenant improvement allowance of $ 767 for the laboratory space, through the lease term. At each lease commencement, the Company recorded right-of-use assets of $ 7,602 and $ 2,662 , respectively, which consist of the lease liability of $ 7,602 for the office space, and the lease liability of $ 1,273 and $ 1,389 of leasehold improvements that revert back to the lessor at the termination of the lease for the laboratory space. The lease is subject to certain renewal options, which are not deemed reasonably certain at commencement of the first two phases. In September 2021, the Company entered into a lease for additional laboratory and office space in Cambridge, Massachusetts with a lease term of ten years and a renewal option for an additional seven-year term. The lease commenced in December 2022, and the renewal option was not deemed reasonably certain of exercise. Minimum lease payments total $ 101,548 throughout the lease term. At lease commencement, the Company recorded a right-of-use asset of $ 56,065 , which consists of the lease liability of $ 54,206 and $ 1,859 of leasehold improvements that revert back to the lessor at the termination of the lease. In April 2022, the Company entered into a lease for additional laboratory and office space in Spring House, Pennsylvania, with a lease term of ten years and a renewal option, subject to certain conditions, for an additional five-year term. The undiscounted minimum lease payments are $ 2,980 , net of a tenant improvement allowance of $ 1,223 , over the original ten-year term. As of December 31, 2022, the lease has not yet commenced, and accordingly the Company has no t recorded a right-of-use asset or a lease liability with respect thereto. In December 2022, the Company amended its lease of its corporate headquarters in Cambridge, Massachusetts (the "Lease Amendment"). The Lease Amendment reduced the office space subject to the lease while maintaining the laboratory and manufacturing space and extended the term to begin in November 2023, when the term of the original lease concludes, and continue through January 2030. The Company accounted for the Lease Amendment as a modification to the existing lease and not a new contract separate from the existing contract, and accordingly increased the associated lease liability and right-of-use asset by $ 32,837 . Minimum lease payments total $ 60,022 throughout the term of the Lease Amendment, net of a tenant improvement allowance of $ 1,000 . The Company has committed to restore the leased space subject to the Lease Amendment to the condition specified in the original lease, and the Company updated its estimate of the costs required to fulfill this obligation in accordance with ASC 410, Asset Retirement Obligations , at the effective date of the modification. Based on current estimates, the Company recorded an additional asset retirement obligation of $ 452 in December 2022. The following table summarizes the presentation in the Company’s consolidated balance sheets of its operating leases: December 31, 2022 2021 Assets: Operating lease assets $ 110,984 $ 18,208 Liabilities: Operating lease liabilities $ 3,601 $ 6,610 Operating lease liabilities, net of current portion 107,942 17,958 Total operating lease liabilities $ 111,543 $ 24,568 The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss: Year Ended December 31, 2022 2021 2020 Operating lease costs $ 8,830 $ 5,170 $ 4,163 Short-term lease costs 1,375 1,452 1,457 Variable lease costs 4,547 3,300 2,890 Sublease income — ( 1,575 ) ( 1,813 ) Total lease costs $ 14,752 $ 8,347 $ 6,697 During the years ended December 31, 2022, 2021, and 2020, the Company made cash payments for operating leases of $ 7,809 , $ 6,821 and $ 6,302 , respectively. As of December 31, 2022, future payments of operating lease liabilities are as follows (in thousands): As of December 31, 2022 2023 $ 16,815 2024 19,055 2025 21,164 2026 21,755 2027 and thereafter 108,383 Total future payments of operating lease liabilities $ 187,172 Less: imputed interest ( 75,629 ) Present value of operating lease liabilities $ 111,543 As of December 31, 2022, the weighted average remaining lease term was 8.92 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13 % . As of December 31, 2021, the weighted average remaining lease term was 6.12 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 10 % .

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Notes Payable	8. Notes Payable On October 29, 2019 (the “Closing Date”), the Company entered into the Loan Agreement with Hercules pursuant to which a term loan in an aggregate principal amount of up to $ 50,000 (the “Original Credit Facility”) was available to the Company in three tranches, subject to certain terms and conditions. The first tranche of $ 25,000 was advanced to the Company on the Closing Date. The Company did not meet the milestone requirements for the second tranche under the Original Credit Facility, and as such, the additional amount of up to $ 12,500 was not available for the Company to borrow. The Company elected not to borrow the third tranche of $ 12,500 , which was available upon Hercules’ approval until June 30, 2021. Advances under the Original Credit Facility will bear interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 4.40 %, and (ii) 9.65 %. Following an interest-only period of 24 months , principal payments are due in 24 equal monthly installments commencing December 1, 2021 and ending November 1, 2023 . Effective as of February 24, 2022 (the “Effective Date”), the Company entered into an Amendment to the Loan and Security Agreement (the “Amendment”), with the lenders party thereto (the “Lenders”), and Hercules in its capacity as the administrative agent and the collateral agent for the Lenders, which amended the Original Credit Facility. Pursuant to the Amendment, term loans in an aggregate principal amount of up to $ 100,000 (the “New Credit Facility”) became available to the Company in five tranches, subject to certain terms and conditions. The first tranche in an aggregate principal amount of $ 25,000 was outstanding as of the Effective Date, after taking into account reborrowing by the Company on the Effective Date of a previously-repaid principal amount of approximately $ 2,900 . The second tranche in an aggregate principal amount of $ 12,500 and the third tranche in an aggregate principal amount of $ 12,500 have been advanced to the Company and were outstanding as of the Effective Date. The fourth tranche in an aggregate principal amount of $ 25,000 is available upon satisfaction of certain conditions, including the approval by the FDA of a biologics license application in respect of SER-109 (the "Regulatory Approval Milestone") by no later than December 15, 2023. The fifth tranche in an aggregate principal amount of up to $ 25,000 is available through the Amortization Date (as defined below) upon satisfaction of certain conditions, including the Lenders’ investment committee approval. All advances outstanding under the New Credit Facility will bear interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 6.40 %, and (ii) 9.65 %. For all advances outstanding under the New Credit Facility, the Company will make interest only payments through December 31, 2023, extendable to December 31, 2024 upon satisfaction of certain conditions (such applicable date, the “Amortization Date”). The principal balance and interest of the advances will be repaid in equal monthly installments after the Amortization Date and continuing through October 1, 2024, extendable to October 1, 2025, upon satisfaction of certain conditions (such applicable date, the “Maturity Date”) . The Company may prepay advances under the New Credit Facility, in whole or in part, at any time subject to a prepayment charge equal to: (a) 2.0 % of amounts so prepaid, if such prepayment occurs during the first year following the Effective Date; (b) 1.5 % of the amount so prepaid, if such prepayment occurs during the second year following the Effective Date, and (c) 1.0 % of the amount so prepaid, if such prepayment occurs during the third year following the Effective Date. The Company will pay an end of term charge of 4.85 % of the aggregate amount of the advances made under the Original Credit Facility on the earliest date of (i) November 1, 2023; (ii) the date that the Company prepays all of the outstanding principal in full, or (iii) the date the loan payments are accelerated due to an event of default. The Company will pay an additional end of term charge of 1.75 % of the aggregate amount of the advances under the New Credit Facility (including the first tranche of $ 25,000 ) on the earliest date of (i) the Maturity Date; (ii) the date that the Company prepays all of the outstanding principal in full, or (iii) the date the loan payments are accelerated due to an event of default. Other terms of the New Credit Facility remain generally identical to those under the Original Credit Facility, with certain covenants amended by the Amendment to provide the Company with additional operational flexibility, including the ability for the Company to issue up to $ 350,000 in convertible notes. The New Credit Facility includes a conditional liquidity covenant commencing on June 15, 2023, which ceases to apply if certain conditions are satisfied. The New Credit Facility is secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company has agreed to not pledge or secure its intellectual property to others. The Company accounted for the New Credit Facility as a modification in accordance with the guidance in ASC 470-50, Debt . Amounts paid to the lenders were recorded as debt discount and a new effective interest rate was established. Upon issuance, the New Credit Facility was recorded as a liability with an initial carrying value of $ 50,586 , net of debt issuance costs. The initial carrying value will be accreted to the repayment amount, which includes the outstanding principal plus the end of term charge, through interest expense using the effective interest rate method over the term of the Loan Agreement. As of December 31, 2022, the carrying value of the New Credit Facility is $ 51,047 and the effective interest rate in effect is 15.01 %. As of December 31, 2021, the carrying value of the New Credit Facility was $ 24,643 , and the effective interest rate in effect was 11.47 %. The New Credit Facility is classified as a long-term liability on the consolidated balance sheet. The future principal payments due under the New Credit Facility, excluding interest and the end of term charge, are as follows: Year Ending December 31, Principal 2023 — 2024 $ 50,000 Total $ 50,000 During the years ended December 31, 2022 and 2021, the Company recognized $ 6,020 and $ 2,910 of interest expense related to the Loan Agreement, respectively, which is reflected in interest expense on the consolidated statement of operations and comprehensive loss.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Convertible Preferred Stock	9. Convertible Preferred Stock On July 1, 2015, in connection with the closing of the initial public offering of the Company’s common stock (“IPO”), the Company effected its Restated Certificate of Incorporation, which authorizes the Company to issue 10,000,000 shares of preferred stock, $ 0.001 par value per share.

Common Stock and Stock-Based Aw

Common Stock and Stock-Based Awards	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Common Stock and Stock-Based Awards	10. Common Stock and Stock-Based Awards On July 1, 2015, in connection with the closing of the IPO, the Company effected its Restated Certificate of Incorporation, which authorizes the Company to issue 200,000,000 shares of common stock, $ 0.001 par value per share. In November 2019, the Company entered into a common stock sales agreement, or the 2019 Sales Agreement, with Cowen to sell shares of the Company's common stock with aggregate gross sales proceeds of up to $ 25,000 , from time to time, through an "at the market" equity offering program, or ATM, under which Cowen acts as sales agent. In March 2020, in connection with filing an updated registration statement on Form S-3 (File No. 333-237033), the Company entered into a new common stock sales agreement, or the 2020 Sales Agreement, with Cowen on substantially the same terms as the 2019 Sales Agreement and terminated the 2019 Sales Agreement. In May 2021, the Company entered into a new common stock sales agreement, or the 2021 Sales Agreement, with Cowen to sell shares of its common stock with aggregate gross sales proceeds of up to $ 150,000 , from time to time, through an ATM under which Cowen acts as sales agent, and terminated the 2020 Sales Agreement. During the year ended December 31, 2022 , the Company sold approximately 655,000 shares of common stock under the 2021 Sales Agreement, at an average price of approximately $ 7.26 per share, raising aggregate net proceeds of approximately $ 4,447 after deducting an aggregate commission of approximately 3 % and other issuance costs. During the year ended December 31, 2021, the Company did no t sell any shares of common stock under the 2020 Sales Agreement or the 2021 Sales Agreement. During the year ended December 31, 2020, the Company sold approximately 5,788,000 shares of common stock under the 2019 Sales Agreement and the 2020 Sales Agreement, as applicable, at an average price of approximately $ 4.40 per share, raising aggregate net proceeds of approximately $ 24,773 after deducting an aggregate commission of approximately 3 % and other issuance costs. On August 12, 2020, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Cowen and Company, LLC and Piper Sandler & Co., as representatives of the several underwriters named therein (collectively, the “Underwriters”), in connection with the issuance and sale by the Company in a public offering of 10,500,000 shares of the Company’s common stock at a public offering price of $ 21.50 per share, less underwriting discounts and commissions, pursuant to an effective shelf registration statement on Form S-3 (Registration No. 333-244401) and a related prospectus supplement filed with the SEC (such public offering, the “offering”). Under the terms of the Underwriting Agreement, the Company granted the Underwriters an option exercisable for 30 days to purchase up to an additional 1,575,000 shares of its common stock at the public offering price, less underwriting discounts and commissions, which the underwriters exercised in full. The Company received aggregate net proceeds from the offering of approximately $ 243,748 after deducting underwriting discounts and commissions and offering expenses payable by the Company. Additionally on August 12, 2020, the Company entered into a Securities Purchase Agreement (the “Securities Agreement”) with Nestlé for the sale by the Company of 959,002 shares of the Company’s common stock at a purchase price of $ 20.855 per share (the “concurrent placement”). The Company received aggregate net proceeds from the concurrent placement of approximately $ 19,900 after deducting offering expenses payable by the Company. The consummation of the concurrent placement was contingent upon the closing of the offering and the satisfaction of certain other customary conditions. The shares were offered and sold to Nestlé pursuant to an effective registration statement on Form S-3 (File No. 333-237033) and a related prospectus supplement filed with the SEC. On June 29, 2022, the Company entered into securities purchase agreements with new and existing investors and certain directors and officers in a registered direct offering, or the Registered Direct Offering, of an aggregate of 31,746,030 shares of its common stock at a purchase price of $ 3.15 per share for total net proceeds of approximately $ 96,721 , after deducting placement agent’s fees and other estimated offering expenses. Net proceeds included an aggregate of $ 27,525 received from Flagship Pioneering Fund VII, L.P. and Nutritional Health LTP Fund, L.P., affiliates of Flagship Pioneering, or Flagship, one of its significant stockholders, in exchange for 8,738,243 shares. The closing date of the Registered Direct Offering was July 5, 2022. 2012 Stock Incentive Plan The Company’s 2012 Stock Incentive Plan, as amended, (the “2012 Plan”) provided for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2012 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100 % of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years . The Company generally granted stock-based awards with service conditions only (“service-based” awards). Stock options granted under the 2012 Plan generally vest over four years and expire after ten years , although options have been granted with vesting terms less than four years . As of December 31, 2022 , there were no shares available for future grant under the 2012 Plan. 2015 Incentive Award Plan On June 16, 2015, the Company’s stockholders approved the 2015 Incentive Award Plan (the “2015 Plan”), which became effective on June 25, 2015. The 2015 Plan was subsequently amended on December 14, 2022, and provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2015 Plan was the sum of (i) 2,200,000 shares of common stock and (ii) the number of shares subject to awards outstanding under the 2012 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company on or after the effective date of the 2015 Plan. In addition, the number of shares of common stock that may be issued under the 2015 Plan is subject to increase on the first day of each calendar year, beginning in 2016 and ending in 2025, equal to the lesser of (i) 4 % of the number of shares of the Company’s common stock outstanding on the last day of the preceding applicable calendar year and (ii) an amount determined by the Company’s board of directors. Stock awards granted under the 2015 Plan generally vest over four years and expire after ten years , although options have been granted with vesting terms less than four years . As of December 31, 2022, there were 967,206 shares available for future grant under the 2015 Plan. 2015 Employee Stock Purchase Plan On June 16, 2015, the Company’s stockholders approved the 2015 Employee Stock Purchase Plan (the “ESPP”), which became effective on June 25, 2015. A total of 365,000 shares of common stock were reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP automatically increase on the first day of each calendar year, beginning in 2016 and ending in 2025, by an amount equal to the lesser of (i) 400,000 shares, (ii) 1 % of the number of shares of the Company’s common stock outstanding on the last day of the applicable preceding calendar year and (iii) an amount determined by the Company’s board of directors. Offering periods under the ESPP will commence when determined by the plan administrator. During the year ended and as of December 31, 2022, there were 322,560 shares issued and 2,469,204 shares were reserved and available for issuance under the ESPP, respectively. The ESPP provides that eligible employees may contribute up to 15 % of their eligible earnings toward the semi-annual purchase of the Company's common stock. The ESPP is qualified under Section 423 of the Internal Revenue Code. The employee's purchase price is derived from a formula based on the closing price of the common stock on the first day of the offering period versus the closing price on the date of purchase (or, if not a trading day, on the immediately preceding trading day). The offering period under the ESPP has a duration of six months , and the purchase price with respect to each offering period beginning on or after such date is, until otherwise amended, equal to 85 % of the lesser of (i) the fair market value of the Company's common stock at the commencement of the applicable six-month offering period or (ii) the fair market value of the Company's common stock on the purchase date. 2022 Employment Inducement Award Plan On December 14, 2022, the Company’s board of directors approved the 2022 Employment Inducement Award Plan (the "2022 Plan"), which became effective on such date without stockholder approval pursuant to Rule 5635(c)(4) of The Nasdaq Stock Market LLC listing rules (“Rule 5635(c)(4)”). The 2022 Plan provides for the grant of nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock- or cash-based awards. In accordance with Rule 5635(c)(4), awards under the 2022 Plan may only be made to a newly hired employee who has not previously been a member of our board of directors, or an employee who is being rehired following a bona fide period of non-employment by us as a material inducement to the employee’s entering into employment with us. A total of 2,500,000 shares of common stock were reserved for issuance under the 2022 Plan. Any shares subject to awards previously granted under the 2022 Plan that expire, terminate or are otherwise surrendered, canceled, or forfeited in any case, in a manner that results in the Company acquiring the shares covered by the award at a price not greater than the price (as adjusted to reflect any equity restructuring) paid by the Participant for such shares or not issuing any shares covered by the award, the unused shares covered by the award will again be available for award grants under the 2022 Plan. As of December 31, 2022, there were no awards outstanding and 2,500,000 shares available for future grant under the 2022 Plan. Stock Options The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Number of Weighted Weighted Aggregate (in years) Outstanding as of December 31, 2021 11,517,189 $ 11.10 7.42 $ 28,007 Granted 4,527,897 6.89 Exercised ( 326,864 ) 2.96 Forfeited ( 778,188 ) 10.62 Outstanding as of December 31, 2022 14,940,034 $ 10.03 7.25 $ 11,608 Options exercisable as of December 31, 2022 7,441,253 $ 10.38 5.88 $ 8,115 The weighted average grant-date fair value of stock options granted during the years ended December 31, 2022, 2021 and 2020 was $ 5.53 , $ 15.33 , and $ 5.08 per share, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2022, 2021, and 2020 was $ 981 , $ 4,727 , and $ 37,255 , respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. During the year ended December 31, 2021, the Company granted performance-based stock options to employees for the purchase of an aggregate of 562 thousand shares of common stock with a grant date fair value of $ 5.53 per share. These stock options are exercisable only upon achievement of specified performance targets. As of December 31, 2022 , none of these options were exercisable because none of the specified performance targets had been achieved. Because achievement of the specified performance targets was not deemed probable as of December 31, 2022 , the Company did no t record any expense for these stock options from the dates of issuance through December 31, 2022. Restricted Stock Units The Company has granted restricted stock units ("RSUs") with service-based vesting conditions. RSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Restricted stock units may not be sold or transferred by the holder and vest according to the vesting conditions of each award. The table below summarizes the Company’s RSU activity for the year ended December 31, 2022: Number Weighted Unvested restricted stock units as of December 31, 2021 734,755 $ 17.68 Granted 1,302,844 $ 6.95 Forfeited ( 205,658 ) $ 11.82 Vested ( 282,401 ) $ 18.06 Unvested restricted stock units as of December 31, 2022 1,549,540 $ 9.37 During the years ended December 31, 2022, 2021 and 2020, the Company granted 1,302,844 , 768,998 and 6,500 RSUs, respectively. RSUs generally vest over four years , with 25 % vesting after one year, and the remaining 75 % vesting quarterly over the next 3 years, subject to continued service to the Company through the applicable vesting date. The aggregate intrinsic value of restricted stock units that vested during the years ended December 31, 2022, 2021 and 2020 was $ 1,809 , $ 16 , and $ 532 , respectively. During the year ended December 31, 2021, the Company granted performance-based restricted stock awards to two employees for the purchase of an aggregate of 85,000 shares of common stock with a grant date fair value of $ 9.59 per share and 40,000 shares with a grant date fair value of $ 20.35 per share. These restricted stock awards vest only upon achievement of specified performance targets. As of December 31, 2021, these awards were no t vested because the specified performance targets had not been achieved. In addition, the performance targets were not deemed probable of achievement. Accordingly, the Company did no t record any expense for these awards from the dates of issuance through December 31, 2021. In October 2022, 42,500 of the awards with a grant date fair value of $ 9.59 , and 20,000 of the awards with a grant date fair value of $ 20.35 , vested fully, as the associated performance targets were achieved. Accordingly, the Company recorded $ 815 in compensation expense during the year ended December 31, 2022, with respect to these awards. As of December 31, 2022, the remaining performance-based restricted stock awards in these grants were not vested because the associated targets had not been achieved. In addition, the performance targets were not deemed probable of achievement. Accordingly, the Company did no t record any expense for these remaining awards from the dates of issuance through December 31, 2022. Stock-based Compensation Valuation The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis: Year Ended December 31, 2022 2021 2020 Risk-free interest rate 1.67 % 0.73 % 1.26 % Expected term (in years) 6.0 5.4 6.0 Expected volatility 104.0 % 106.5 % 73.3 % Expected dividend yield 0 % 0 % 0 % The Company estimates the fair value of rights to acquire common stock under the ESPP using a Black-Scholes valuation model on the date of grant and the straight-line attribution approach to recognize the expense. The assumptions that the Company used to determine the fair value of rights to acquire common stock under the ESPP were as follows, presented on a weighted average basis: Year Ended December 31, 2022 2021 2020 Risk-free interest rate 2.11 % 0.97 % 1.20 % Expected term (in years) 0.5 0.5 0.5 Expected volatility 99.0 % 123.8 % 74.9 % Expected dividend yield 0 % 0 % 0 % Stock-based Compensation The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its consolidated statements of operations and comprehensive loss: Year Ended December 31, 2022 2021 2020 Research and development expenses $ 13,429 $ 10,146 $ 4,760 General and administrative expenses 12,053 10,076 4,064 $ 25,482 $ 20,222 $ 8,824 As of December 31, 2022, the Company had an aggregate of $ 57,005 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 1.8 years.

Collaboration Revenue

Collaboration Revenue	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Collaboration Revenue	11. Collaboration Revenue License Agreement with NHSc Rx License GmbH (Nestlé) Summary of Agreement In July 2021, the Company entered into the 2021 License Agreement with NHSc Pharma Partners, succeeded by NHSc Rx License GmbH (together with Société des Produits Nestlé S.A., their affiliates, and their subsidiaries, "Nestlé"). Under the terms of the Agreement, the Company granted Nestlé a co-exclusive, sublicensable (under certain circumstances) license to develop, commercialize and conduct medical affairs activities for (i) therapeutic products based on the Company's microbiome technology (including the Company's SER-109 product candidate) that are developed by the Company or on the Company's behalf for the treatment of CDI and recurrent CDI, as well as any other indications pursued for the products upon mutual agreement of the parties (the “2021 Field”) in the United States and Canada (the “2021 Licensed Territory”), and (ii) the Company's SER-109 product candidate and any improvements and modifications thereto developed pursuant to the terms of the 2021 License Agreement (the "2021 Collaboration Products") for any indications in the 2021 Licensed Territory. The Company is responsible for completing development of SER-109 in the 2021 Field in the United States until first regulatory approval for SER-109 is obtained. Nestlé has the sole right to commercialize the 2021 Collaboration Products in the 2021 Licensed Territory in accordance with a commercialization plan. Both parties will perform medical affairs activities in the 2021 Licensed Territory in accordance with a medical affairs plan. The Company will be responsible for the manufacturing and supply for commercialization under a supply agreement that will be entered into between the parties. Both parties will perform pre-launch activities of 2021 Collaboration Products prior to the first commercial sale in the United States. The Company is responsible for funding the pre-launch activities until first commercial sale of 2021 Collaboration Products in the 2021 Licensed Territory and in accordance with a pre-launch plan, up to a specified cap. Following first commercial sale of the first 2021 Collaboration Product, the Company will be entitled to share equally in its commercial profits and losses. In connection with the 2021 License Agreement, the Company received an upfront payment of $ 175,000 . The Company is eligible to receive additional payments of up to $ 360,000 if certain regulatory and sales milestones are achieved. The potential future milestone payments include up to $ 135,000 for the achievement of specified regulatory milestones and up to $ 225,000 for the achievement of specified net sales milestones. The 2021 License Agreement continues in effect until all development and commercialization activities for all 2021 Collaboration Products in the 2021 Licensed Territory have permanently ceased. The 2021 License Agreement may be terminated by either party upon sixty days ’ written notice for the other party’s material breach that remains uncured during such sixty-day period, or immediately upon written notice for the other party’s insolvency. Nestlé may also terminate the 2021 License Agreement at-will (i) with twelve months’ prior written notice, effective only on or after the third anniversary of first commercial sale of the first 2021 Collaboration Product in the 2021 Licensed Territory, (ii) if first commercial sale of the first 2021 Collaboration Product in the 2021 Licensed Territory has not occurred by the fifth anniversary of the effective date of the 2021 License Agreement, with one hundred eighty days’ prior written notice, which must be provided during a specified period set forth in the 2021 License Agreement, or (iii) if regulatory approval for SER-109 is not granted after submission by the Company of a filing seeking first regulatory approval as set forth in the development and regulatory activity plan, and the parties fail to agree on further development of SER-109 in accordance with the terms of the 2021 License Agreement, with one hundred eighty days’ prior written notice, which must be provided within a specified period set forth in the 2021 License Agreement. The Company may also terminate the 2021 License Agreement immediately upon written notice if Nestlé challenges any licensed patent in the 2021 Licensed Territory. Upon termination of the 2021 License Agreement, all licenses granted to Nestlé by the Company will terminate. If the Company commits a material breach of the 2021 License Agreement, Nestlé may elect not to terminate the 2021 License Agreement but instead apply specified adjustments to the payment terms and other terms and conditions of the 2021 License Agreement. Accounting Analysis The 2021 License Agreement represents a separate contract between Nestlé and the Company. The 2021 License Agreement is within the scope of Accounting Standard Update 2018-18, Collaborative Arrangements (Topic 808), and has elements that are within the scope of ASC 606 - Revenue From Contracts with Customers (Topic 606) and Topic 808. The Company identified the following promises in the 2021 License Agreement that were evaluated under the scope of Topic 606: (i) delivery of a co-exclusive license for SER-109 to develop, commercialize and conduct medical affairs in the United States and Canada; (ii) services to be performed in accordance with the development and regulatory activity plan to obtain regulatory approval of SER-109 in the United States. The Company also evaluated whether certain options outlined within the 2021 License Agreement represented material rights that would give rise to a performance obligation and concluded that none of the options convey a material right to Nestlé and therefore are not considered separate performance obligations within the 2021 License Agreement. The Company assessed the above promises and determined that the co-exclusive license for SER-109 and the services to obtain regulatory approval of SER-109 in the United States are reflective of a vendor-customer relationship and therefore represent performance obligations within the scope of Topic 606. The co-exclusive license for SER-109 in the United States and Canada is considered functional intellectual property and distinct from other promises under the contract as Nestlé can benefit from the license on its own or together with other readily available resources. The services performed by the Company to obtain regulatory approval of SER-109 are not complex or specialized, could be performed by another qualified third party, are not expected to significantly modify or customize the license given that SER-109 is late-stage intellectual property that has completed clinical development and the services are expected to be performed over a short period of time. Therefore, the license and the services each represents a separate performance obligation within a contract with a customer under the scope of Topic 606 at contract inception. The Company considers the collaborative pre-launch activities and commercialization activities to be separate units of account within the scope of Topic 808 and are not deliverables under Topic 606. The Company and Nestlé are both active participants in the pre-launch activities and commercialization activities and are exposed to significant risks and rewards that are dependent on the commercial success of the activities in the arrangement. The up-front payment of $ 175,000 compensated the Company for: (i) the co-exclusive license for SER-109 to develop, commercialize and conduct medical affairs in the United States and Canada, (ii) services performed in accordance with the development and regulatory activity plan to obtain regulatory approval of SER-109 in the United States and (iii) pre-launch activities performed by Nestlé and the Company until the first commercial sale of SER-109 in the United States. The commercialization activities, which include the commercial manufacturing, participation on joint steering committees and medical affairs work, that occur after regulatory approval of SER-109 in the United States, are part of the 50 / 50 sharing of commercial profits. Therefore, the up-front payment of $ 175,000 does not compensate the Company for these activities. The Company allocated the $ 175,000 between the Topic 606 unit of account and the Topic 808 unit of account by determining the standalone selling price (SSP) of each good or service. The selling price of each good or service was determined based on the Company’s SSP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company determined the transaction price under Topic 606 to be $ 139,500 and the Topic 808 amount to be $ 35,500 at the inception of the 2021 License Agreement. The Company determined that any variable consideration related to regulatory milestones is deemed to be fully constrained and therefore excluded from the transaction price due to the high degree of uncertainty and risk associated with these potential payments, as the Company determined that it could not assert that it was probable that a significant reversal in the amount of cumulative revenue recognized will not occur. The Company also determined that sales milestones relate solely to the license of intellectual property and are therefore excluded from the transaction price under the sales- or usage-based royalty exception of Topic 606. Revenue related to these sales milestones will only be recognized when the associated sales occur, and relevant thresholds are met. The Topic 606 transaction price of $ 139,500 has been allocated to the co-exclusive license for SER-109 and the services performed in accordance with the development and regulatory activity plan to obtain regulatory approval of SER-109 in the United States based on the Company’s SSP. The Company recognized revenue for the license performance obligation at a point in time, that is upon transfer of the license to Nestlé. As control of the license was transferred in July 2021, the Company recognized $ 131,343 of collaboration revenue - related party during the year ended December 31, 2021 pertaining to the license performance obligation. The remaining amount of the Topic 606 transaction price of $ 8,157 was allocated to the services performance obligation and is being recognized over time as the services are performed. During the years ended December 31, 2022 and 2021 , the Company recognized $ 4,114 and $ 2,068 , of collaboration revenue - related party, respectively, related to the services performance obligation under the 2021 License Agreement. The amount allocated to the Topic 808 unit of accounting relates to the pre-launch activities performed prior to the first commercial sale of SER-109 and was determined to be $ 35,500 based on standalone selling price. The Company recorded the $ 35,500 in total liabilities on its consolidated balance sheet at the inception of the arrangement. On a quarterly basis, the Company and Nestlé will provide financial information about the pre-launch activities performed by both parties. The Company reduces the $ 35,500 liability as the pre-launch activities are performed and it makes payments to Nestlé for the pre-launch costs Nestlé incurs. As of December 31, 2022 and 2021, there is $ 34,770 and $ 21,098 included in accrued expenses and other current liabilities and $ 0 and $ 10,585 included in other long-term liabilities, respectively. The cost associated with pre-launch activities performed by the Company is recorded within total operating expenses in the Company’s consolidated statements of operations and comprehensive loss. In the years ended December 31, 2022 and 2021 , the Company recognized $ 6,102 and $ 2,168 in research and development expenses and $ 8,953 and $ 3,383 in general and administrative expenses, respectively, associated with pre-launch activities performed. As the Company and Nestlé are both active participants in the pre-launch activities, the sharing of 50 % of the pre-launch costs will be recognized in collaboration (profit) loss sharing - related party in the Company’s consolidated statements of operations and comprehensive loss. The Company recorded $ 1,004 of expense and $ 1,732 of income in the collaboration (profit) loss sharing line for the years ended December 31, 2022 and 2021, respectively. Collaboration and License Agreement with Société des Produits Nestlé S.A. (Nestlé) Summary of Agreement In January 2016, the Company entered into a collaboration and license agreement with Nestec Ltd., succeeded by Société des Produits Nestlé S.A. (together with NHSc Rx License GmbH, their affiliates and their subsidiaries, “Nestlé”) (the “2016 License Agreement”) for the development and commercialization of certain product candidates for the treatment and management of CDI and inflammatory bowel disease (“IBD”), including UC and Crohn’s disease. The 2016 License Agreement supports the development of the Company’s portfolio of products for CDI and IBD in markets outside of the United States and Canada (the “2016 Licensed Territory”). Under the 2016 License Agreement, the Company granted to Nestlé an exclusive, royalty-bearing license to develop and commercialize, in the 2016 Licensed Territory, certain products based on its microbiome technology that are being developed for the treatment of CDI and IBD, including SER-109, SER-262, SER-287 and SER-301 (collectively, the “2016 Collaboration Products”). The 2016 License Agreement sets forth the Company’s and Nestlé’s respective obligations for development, commercialization, regulatory and manufacturing and supply activities for the 2016 Collaboration Products with respect to the licensed fields and the 2016 Licensed Territory. Under the 2016 License Agreement, Nestlé agreed to pay the Company an upfront cash payment of $ 120,000 , which the Company received in February 2016. The Company is eligible to receive up to $ 285,000 in development milestone payments, $ 375,000 in regulatory payments and up to an aggregate of $ 1,125,000 for the achievement of certain commercial milestones related to the sales of the 2016 Collaboration Products. Nestlé also agreed to pay the Company tiered royalties, at percentages ranging from the high single digits to high teens, of net sales of 2016 Collaboration Products in the 2016 Licensed Territory. Under the 2016 License Agreement, the Company is entitled to receive a $ 20,000 milestone payment from Nestlé following initiation of a SER-287 Phase 2 study and a $ 20,000 milestone payment from Nestlé following the initiation of a SER-287 Phase 3 study. In November 2018, the Company entered into a letter agreement with Nestlé which modified the 2016 License Agreement to address the current clinical plans for SER-287. Pursuant to the letter agreement, the Company and Nestlé agreed that following initiation of the SER-287 Phase 2b study, the Company would be entitled to receive $ 40,000 in milestone payments from Nestlé, which represent the milestone payments due to the Company for the initiation of a SER-287 Phase 2 study and a Phase 3 study. The SER-287 Phase 2b study was initiated and the $ 40,000 of milestone payments were received in December 2018. The letter agreement also provides scenarios under which Nestlé’s reimbursement to the Company for certain Phase 3 development costs would be reduced or delayed depending on the outcomes of the SER-287 Phase 2b study. The 2016 License Agreement continues in effect until terminated by either party on the following bases: (i) Nestlé may terminate the 2016 License Agreement in the event of serious safety issues related to any of the 2016 Collaboration Products; (ii) the Company may terminate the 2016 License Agreement if Nestlé challenges the validity or enforceability of any of the Company’s licensed patents; and (iii) either party may terminate the 2016 License Agreement in the event of the other party’s uncured material breach or insolvency. Upon termination of the 2016 License Agreement, all licenses granted to Nestlé by the Company will terminate, and all rights in and to the 2016 Collaboration Products in the 2016 Licensed Territory will revert to the Company. If the Company commits a material breach of the 2016 License Agreement, Nestlé may elect not to terminate the 2016 License Agreement but instead apply specified adjustments to its payment obligations and other terms and conditions of the 2016 License Agreement. Accounting Analysis The Company assessed the 2016 License Agreement in accordance with Topic 606 and concluded that Nestlé is a customer. The Company identified the following promises under the contract: (i) a license to develop and commercialize the 2016 Collaboration Products in the 2016 Licensed Territory, (ii) obligation to perform research and development services, (iii) participation on a joint steering committee, and (iv) manufacturing services to provide clinical supply to complete future clinical trials. In addition, the Company identified a contingent obligation to perform manufacturing services to provide commercial supply if commercialization occurs, which is contingent upon regulatory approval. This contingent obligation is not a performance obligation at inception and has been excluded from the initial allocation as it represents a separate buying decision at market rates, rather than a material right in the contract. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that Nestlé cannot benefit from the promised goods and services separately from the others as they are highly interrelated and therefore not distinct. Accordingly, the promised goods and services represent one combined performance obligation and the entire transaction price was allocated to that single combined performance obligation. At contract inception, the Company determined that the $ 120,000 non-refundable upfront amount constituted the entirety of the consideration to be included in the transaction price as the development, regulatory, and commercial milestones were fully constrained. During the year ended December 31, 2016, the Company received $ 10,000 from Nestlé in connection with the initiation of the Phase 1b study for SER-262 in CDI. During the year ended December 31, 2017, the Company received $ 20,000 from Nestlé in connection with the initiation of the Phase 3 study for SER-109. During the year ended December 31, 2018, the Company received $ 40,000 from Nestlé in connection with the initiation of the Phase 2b study for SER-287. During the year ended December 31, 2020, the Company received $ 10,000 from Nestlé in connection with the initiation of the Phase 1b SER-301 study. As of December 31, 2022 , the aggregate amount of the transaction price allocated to the performance obligation of the 2016 License Agreement was approximately $ 200,000 . During the years ended December 31, 2022, 2021, and 2020 using the cost-to-cost method, which best depicts the transfer of control to the customer, the Company recognized $ 3,014 , $ 10,446 , and $ 11,897 of Collaboration revenue – related party, respectively, relating to the 2016 License Agreement. As of December 31, 2022 and 2021, there was $ 96,689 , and $ 103,817 of deferred revenue related to the unsatisfied portion of the performance obligation under the Nestlé agreements. As of December 31, 2022, deferred revenue is classified as current or non-current in the consolidated balance sheets based on the Company’s estimate of revenue that will be recognized within the next twelve months, which is determined by the cost-to-cost method which measures the extent of progress towards completion based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the performance obligation. All costs associated with the 2016 License Agreement are recorded in research and development expense in the consolidated statements of operations and comprehensive loss. AstraZeneca Research Collaboration and Option Agreement Summary of the Agreement In March 2019, the Company entered into a Research Collaboration and Option Agreement (the “Research Agreement”) with MedImmune, LLC, a wholly owned subsidiary of AstraZeneca Inc. (“AstraZeneca”), to advance the mechanistic understanding of the microbiome in augmenting the efficacy of cancer immunotherapy. Under the Research Agreement, the Company and AstraZeneca would conduct certain research and development activities as set forth on a research plan focused on the role of the microbiome in certain cancers and cancer immunotherapies, including furthering the research program for SER-401, in combination with AstraZeneca compounds targeting various cancers. Pursuant to the Research Agreement, the Company agreed not to conduct research or development on any microbiome products specifically designed by the Company during the term of the Research Agreement for the treatment of cancer (“Microbiome Oncology Products”), with or on behalf of any third-party without the prior approval of the joint steering committee for the Research Agreement for at least three years after the effective date (the “Exclusivity Period”). Additionally, AstraZeneca was to pay to the Company a total of $ 20,000 in three equal installments, the first of which the Company received in April 2019, the second of which the Company received in December 2019, and the third of which the Company received in January 2021. Additionally, AstraZeneca was to bear its costs of conducting activities under the research plan and to reimburse the Company for all activities performed under the research plan based on actual full-time employee (“FTE”) time and certain third-party costs incurred by the Company in connection therewith. Under the Research Agreement, the Company granted to AstraZeneca an exclusive option to negotiate a worldwide, sublicensable exclusive license under relevant intellectual property rights controlled by the Company to exploit Microbiome Oncology Products for the treatment of cancer. Additionally, the Company granted to AstraZeneca an additional exclusive option to obtain a worldwide, sublicensable, license under certain intellectual property rights arising out of the Agreement or coming into the control of the Company during the term of the Agreement, which AstraZeneca did not exercise. In December 2020, the Company received written notice from AstraZeneca that AstraZeneca elected to terminate the Research Agreement by and in accordance with its terms. The termination of the Research Agreement was effective on April 2, 2021 (the “Termination Date”), which was 120 days from the date of the termination notice. Accounting Analysis The Company assessed the Research Agreement in accordance with ASC 606 and concluded that AstraZeneca was a customer, and that the promised goods and services in the Research Agreement represented one combined performance obligation to which the entire transaction price was allocated. The Company also concluded that each option does not constitute a performance obligation at inception and was therefore excluded from the initial allocation since each option represents a separate buying decision at market rates, rather than a material right in the contract. At contract inception, the Company determined that the transaction price was comprised of: (i) the $ 20,000 fee, which represents fixed consideration, and (ii) the estimated reimbursement of research and development costs incurred, which totaled approximately $ 13,900 , which represents variable consideration. The Company included the variable consideration in the transaction price at contract inception because the Company had determined it was not probable that a significant reversal of cumulative revenue would occur. The Company determined that revenue under the Research Agreement should be recognized over time, using a cost-to-cost input method, as AstraZeneca simultaneously receives the benefit from the Company as the Company performs under the single performance obligation over time. In December 2020, the Company received written notice that AstraZeneca elected to terminate the Research Agreement. As a result of AstraZeneca’s decision to terminate the Research Agreement, the Company’s performance obligations under the Research Agreement ended as of December 31, 2020. The final transaction price of $ 23,377 is comprised of the $ 20,000 fixed consideration and $ 3,376 for the reimbursed research and development costs. The Company recognized its remaining deferred revenue of $ 15,145 in collaboration revenue in the year ended December 31, 2020. No collaboration revenue was recognized for the years ended December 31, 2022 and 2021, as the Company's performance obligations under the Research Agreement ended December 31, 2020. Contract Balances from Contracts with Customers The following tables present changes in the Company’s contract liabilities during the year ended December 31, 2022 and 2021: Balance as of December 31, 2021 Additions Deductions Balance as of December 31, 2022 Year ended December 31, 2022 Contract liabilities: Deferred revenue - related party $ 103,817 — ( 7,128 ) $ 96,689 Balance as of December 31, 2020 Additions Deductions Balance as of December 31, 2021 Year ended December 31, 2021 Contract liabilities: Deferred revenue - related party $ 108,174 8,157 ( 12,514 ) $ 103,817 During the year ended December 31, 2022, the Company recognized the following revenues as a result of changes in the contract liability balances in the respective periods: Year Ended December 31, 2022 2021 Revenue recognized in the period from: Amounts included in the contract liability at the beginning of the period $ 7,128 $ 10,446 When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Revenue is recognized from the contract liability over time using the cost-to-cost method.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Net Loss per Share	12. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Year Ended December 31, 2022 2021 2020 Numerator: Net loss attributable to common stockholders $ ( 250,157 ) $ ( 65,578 ) $ ( 89,127 ) Denominator: Weighted average common shares outstanding, basic and diluted 108,077,043 91,702,866 79,789,220 Net loss per share attributable to common stockholders, basic and diluted $ ( 2.31 ) $ ( 0.72 ) $ ( 1.12 ) The Company’s potential dilutive securities, which include stock options, unvested restricted common stock and shares issuable under the ESPP, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share and therefore been anti-dilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Year Ended December 31, 2022 2021 2020 Stock options to purchase common stock 14,940,034 11,517,189 10,037,130 Unvested restricted stock units 1,549,540 734,755 6,500 Shares issuable under employee stock purchase plan 89,593 165,047 10,786 16,579,167 12,416,991 10,054,416

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Leases Refer to Note 7 “Leases” for discussion of the commitments associated with the Company’s lease portfolio. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third-parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has no t accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2022 or 2021. Legal Contingencies The Company accrues a liability for legal contingencies when it believes that it is both probable that a liability has been incurred and that the Company can reasonably estimate the amount of the loss. The Company reviews these accruals and adjusts them to reflect ongoing negotiations, settlements, rulings, advice of legal counsel and other relevant information. To the extent new information is obtained and the views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in the Company’s accrued liabilities would be recorded in the period in which such determination is made. In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, the Company will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, the Company will provide disclosure to that effect. The Company expenses legal costs as they are incurred. The Company did no t accrue any liabilities related to legal contingencies in its consolidated financial statements as of December 31, 2022 and 2021. Bacthera Long Term Manufacturing Agreement On November 8, 2021, the Company entered into a Long Term Manufacturing Agreement with BacThera AG (“Bacthera”), a joint venture between Chr. Hansen and a Lonza Group affiliate, which was amended on December 14, 2022 (the "Bacthera Agreement"). The Bacthera Agreement governs the general terms under which Bacthera, or one of its affiliates, will (i) construct a dedicated full-scale production suite for the Company at Bacthera’s Microbiome Center of Excellence in Visp, Switzerland, which is currently under construction; and (ii) provide manufacturing services to the Company for its SER-109 product and other products, as agreed to by the parties. Under the terms of the Bacthera Agreement, the Company agreed to pay Bacthera a total of at least 256,000 CHF (or approximately $ 277,000 ) for the initial term of the agreement, inclusive of the construction fees and annual operating fees. Bacthera is funding the majority of the construction costs and will own and control the manufacturing suite during construction. The construction fees that the Company is responsible for represent a small percentage of the overall construction costs and are payable upon the achievement of certain milestones related to the construction of the dedicated manufacturing suite. The annual operating fee includes the cost of a baseline annual batch production volume. The Company has also agreed to pay certain other ancillary fees and a per-batch fee in excess of the baseline batches. These fees are subject to adjustment during construction for certain items outside of Bacthera’s control and annually against an agreed index. The Company will supply the active pharmaceutical ingredients to Bacthera to enable it to perform the services and pay for certain other raw materials and manufacturing components, which will be acquired by Bacthera. The Bacthera Agreement has an initial term that continues until the tenth anniversary of the earlier of (a) successful completion of construction and demonstration of Bacthera’s readiness for commercial production or (b) the commencement of manufacturing. The initial term is subject to renewals, which could extend the term to 16 years , and additional three-year terms thereafter. Each party has the ability to terminate the Bacthera Agreement upon the occurrence of certain customary conditions. The Company may also terminate the Bacthera Agreement for convenience after a defined period. In the event of a termination, the Company has certain financial obligations that would apply, and Bacthera has agreed to grant a license to Bacthera-developed manufacturing know how, if any, and provide technical assistance to the Company, so that the Company could transfer the manufacturing operations to itself or a third party. The Bacthera Agreement also contains representations, warranties and indemnity obligations as well as limitations of liability that are customary for agreements of this type. The Bacthera Agreement represents a lease as the Company will have the right to use the dedicated manufacturing suite for a period of time following completion of the construction of the manufacturing suite and approval by regulatory authorities. As of December 31, 2022 , the lease commencement date has not occurred and therefore the Company has not recorded an operating lease asset or an operating lease liability on its consolidated balance sheets. As of December 31, 2022, the Company has paid Bacthera $ 12,276 , of which $ 3,448 was expensed in the year ended December 31, 2021, and $ 8,828 relate to the construction of the dedicated manufacturing suite and are included in other non-current assets in the accompanying consolidated balance sheet.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes During the years ended December 31, 2022, 2021 and 2020 , the Company recorded no income tax benefits for the net operating losses incurred in each year or interim period, due to its uncertainty of realizing a benefit from those items. A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2022 2021 2020 Federal statutory income tax rate ( 21.0 )% ( 21.0 )% ( 21.0 )% Research and development tax credits ( 3.1 ) ( 16.6 ) ( 6.4 ) State taxes, net of federal benefit ( 4.3 ) ( 2.8 ) ( 7.8 ) Stock-based compensation 0.6 ( 0.4 ) ( 5.8 ) Uncertain tax position reserves 4.6 — — Other 0.3 0.4 0.2 Change in deferred tax asset valuation allowance 22.9 40.4 40.8 Effective income tax rate — % — % — % Net deferred tax assets as of December 31, 2022 and 2021 consisted of the following: December 31, 2022 2021 Deferred tax assets: Net operating loss carryforwards $ 132,560 $ 108,189 Research and development tax credit carryforwards 48,854 53,133 Section 174 capitalized research and development expenses 38,894 — Stock-based compensation expense 20,048 16,045 Lease liability 29,717 6,635 Deferred revenue 29,922 36,666 Accrued expenses 4,044 2,475 Section 163(j) limitation 2,303 1,368 Depreciation and amortization 396 247 Other 200 274 Total deferred tax assets $ 306,938 $ 225,032 Deferred tax liabilities: Depreciation and amortization — — Right of use assets ( 29,568 ) ( 4,918 ) Total deferred tax liabilities ( 29,568 ) ( 4,918 ) Valuation allowance $ ( 277,370 ) $ ( 220,114 ) Net deferred tax assets $ — $ — The Tax Cuts and Jobs Act ("TCJA") requires taxpayers to capitalize and amortize research and experimental expenditures under IRC Section 174 for tax years beginning after December 31, 2021. This rule became effective for the Company during the year ended December 31, 2022 and resulted in the capitalization of research and development costs of $ 160,586 . The Company will amortize these costs for tax purposes over five years if the research and development was performed in the U.S. and over 15 years if the research and development was performed outside the U.S. As of December 31, 2022, the Company had net operating loss carryforwards (“NOLs”) for federal and state income tax purposes of $ 501,789 and $ 481,862 , respectively. Federal NOLs of $ 119,800 , generated before 2018, will begin expiring in varying amounts in 2035 unless utilized. The remaining federal NOLs of $ 381,989 , generated after 2017, will be carried forward indefinitely and could be used to offset up to 80 % of taxable income in future tax years. The Company's state NOLs will expire at various times starting in 2035 . As of December 31, 2022, the Company also had available gross research and development tax credit carryforwards for federal and state income tax purposes of $ 50,248 and $ 12,925 , respectively, which begin to expire in 2031 and 2028 , respectively. The federal research and development tax credits include an orphan drug credit carryforward of $ 25,623 . Utilization of the NOLs and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code ("IRC") of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. Since its formation, the Company has raised capital through the issuance of capital stock on several occasions. These financings, combined with the purchasing shareholders' subsequent disposition of those shares, may have resulted in a change of control or could result in a change of control in the future upon subsequent disposition. The Company conducted an analysis to determine if historical changes in ownership through December 31, 2020 would limit or otherwise restrict its ability to utilize these NOLs and research and development credit carryforwards. As a result of this analysis, the Company does not believe there are any significant limitations on its ability to utilize these carryforwards. However, future changes in ownership after December 31, 2020 could affect the limitation in future years. Any limitation may result in expiration of a portion of the NOLs or research and development credit carryforwards before utilization. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2022 and 2021. Management reevaluates the positive and negative evidence at each reporting period. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2022, 2021 and 2020 related primarily to the increases in NOLs, research and development tax credit carryforwards and capitalized research and development expenses pursuant to IRC Section 174, and stock-based compensation were as follows: Year Ended December 31, 2022 2021 2020 Valuation allowance at beginning of year $ ( 220,114 ) $ ( 193,736 ) $ ( 157,346 ) Decreases recorded as benefit to income tax provision — — — Increases recorded to income tax provision ( 57,256 ) ( 26,378 ) ( 36,390 ) Valuation allowance as of end of year $ ( 277,370 ) $ ( 220,114 ) $ ( 193,736 ) The Company is currently under examination by the Internal Revenue Service ("IRS") for the period ended December 31, 2018 related to its 2018 research and development tax credits ("R&D Credit(s)"). The Company has adjusted its 2018 R&D Credits and its overall federal and state R&D Credit carryforward balance from the Company's inception to December 31, 2022, based on the most recent information received from the IRS regarding the examination. Also, the Company has reviewed each of its overall filing positions since inception and has not identified any additional positions that do not meet the more likely than not threshold. The Company does not anticipate a material change to its uncertain tax position reserves in the next 12 months. The changes in the Company's unrecognized tax benefits for the years ended December 31, 2022, 2021, and 2020 were as follows: Year Ended December 31, 2022 2021 2020 Balance at beginning of year $ — $ — $ — Increase in unrecognized tax benefits as a result of tax positions taken 12,528 — — Reduction to unrecognized tax benefits — — — Increases in unrecognized tax benefits as a result of tax positions taken $ 12,528 $ — $ — The Company has not yet conducted a study of its research and development credit carry forwards. This study may result in further adjustment to the Company’s R&D Credits; however, a full valuation allowance has been provided against the Company’s R&D Credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheet or statement of operations if an adjustment were required. The Company had no other unrecognized tax benefits accrued for the years ended December 31, 2022 and 2021, or related interest and penalties as of such dates. The Company will recognize any interest and penalties related to uncertain tax positions in income tax expense. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. The Company's tax years are still open under statute from 2011 to present. All years may be examined to the extent the tax credit or net operating loss carryforwards are used in future periods.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	15. Related Party Transactions As described in Note 11, in July 2021, the Company entered into the 2021 License Agreement with NHSc Pharma Partners (together with Société des Produits Nestlé S.A., “Nestlé”). NHSc Pharma Partners is an affiliate of two of the Company's significant stockholders, Société des Produits Nestlé S.A. and Nestlé Health Science U.S. Holdings, Inc. During the years ended December 31, 2022 and 2021, the Company recognized $ 4,114 and $ 133,411 of related party revenue, respectively, associated with the 2021 License Agreement. As of the years ended December 31, 2022 and 2021, there was $ 1,976 and $ 6,089 of deferred revenue related to the 2021 License Agreement, which is classified as current or non-current in the consolidated balance sheets. As of December 31, 2022 and 2021 there was $ 34,770 and $ 21,098 included in accrued expenses and other liabilities and $ 0 and $ 10,585 included in other long term liabilities, respectively, related to the 2021 License Agreement. The Company has made no payments to Nestlé during the years ended December 31, 2022 and 2021 . There was no amount due from Nestlé as of December 31, 2022 and 2021. As described in Note 11, in January 2016, the Company entered into the 2016 License Agreement with Société des Produits Nestlé S.A. (successor in interest to Nestec, Ltd.) for the development and commercialization of certain product candidates in development for the treatment and management of CDI and IBD, including UC and Crohn’s disease. Société des Produits Nestlé S.A. and its affiliate Nestlé Health Science U.S. Holdings, Inc. are two of the Company's significant stockholders. During the years ended December 31, 2022, 2021, and 2020, the Company recognized $ 3,014 , $ 10,446 , and $ 11,897 , respectively, of related party revenue associated with the 2016 License Agreement. As of December 31, 2022 and 2021, there was $ 94,713 and $ 97,728 , respectively, of deferred revenue related to the 2016 License Agreement, which is classified as current or non-current in the consolidated balance sheets. The Company has made no payments to Nestlé during the years ended December 31, 2022 and 2021 . There was no amount due from Nestlé as of December 31, 2022 and 2021. As described in Note 10, the Company entered into a securities purchase agreement with Flagship Pioneering Fund VII, L.P. and Nutritional Health LTP Fund, L.P., affiliates of Flagship, one of the Company's significant stockholders, for the sale of 8,738,243 shares of its common stock at a purchase price of $ 3.15 per share as part of the Registered Direct Offering, which closed on July 5, 2022. The Company received proceeds from Flagship of $ 27,525 . In July 2022, the Company entered into a Pledge and Utilization Agreement with Flagship Pioneering Labs TPC, Inc., an affiliate of Flagship, for an option to lease certain manufacturing space. The Company paid $ 833 for this option which is classified in other non-current assets on the Company's condensed consolidated balance sheet as of December 31, 2022. In July 2019, the Company entered into a sublease agreement with Flagship to sublease a portion of its office and laboratory space in Cambridge, Massachusetts. The term of the sublease agreement commenced in July 2019 and ended in November 2021 . Under this agreement, the Company recorded other income of $ 0 and $ 1,575 during the years ended December 31, 2022 and 2021. The Company received cash payments of $ 0 and $ 1,575 during the years ended December 31, 2022 and 2021 .

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
401(k) Savings Plan	16. 401(k) Savings Plan The Company has a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Effective January 1, 2016, the Company elected to match 50 % of the first 6 % of an employee’s deferral. Company contributions are expensed in the year for which they are declared. During the years ended December 31, 2022, 2021, and 2020 the Company recorded expense of $ 1,921 , $ 1,087 , and $ 586 , respectively, for 401(k) match contributions.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. In these consolidated financial statements, the Company uses estimates and assumptions related to revenue recognition and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Cash Equivalents	Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, commercial paper and corporate bonds purchased with original maturities of less than 90 days from the date of purchase, are stated at fair value.
Investments	Investments The Company classifies all of its marketable debt securities as available-for-sale securities. Accordingly, these marketable debt securities are recorded at fair value and unrealized gains and losses are reported as a separate component of accumulated other comprehensive loss in stockholders’ equity (deficit), unless the Company has determined that the security has experienced a credit loss, or the Company expects to sell the security prior to the recovery of its unrealized losses. In such cases a security is considered impaired, and adjusted through a charge to the consolidated statement of operations and comprehensive loss. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations and comprehensive loss. No credit losses were recorded during the years ended December 31, 2022, 2021, and 2020. The Company classifies its available-for-sale marketable debt securities as current assets on the consolidated balance sheet if they mature within one year from the balance sheet date. Any available-for-sale marketable debt securities with maturities greater than one year from the balance sheet date are classified as long-term assets on the consolidated balance sheet.
Restricted Investments	Restricted Investments The Company held investments of $ 1,401 as of December 31, 2022 and 2021 , in a separate restricted bank account as a security deposit for the lease of the Company’s headquarters in Cambridge, Massachusetts. The Company has classified these deposits as long-term restricted investments on its consolidated balance sheet.
Restricted Cash	Restricted Cash The Company held restricted cash of $ 8,185 and $ 8,000 as of December 31, 2022 and 2021, respectively, which represents cash held for the benefit of the landlord for the Company's other leases. The Company has classified the restricted cash as long-term on its consolidated balance sheet as the underlying leases are greater than 1 year. Cash, cash equivalents and restricted cash were comprised of the following (in thousands): December 31, 2022 2021 Cash and cash equivalents $ 163,030 $ 180,002 Restricted cash, non-current 8,185 8,000 Total cash, cash equivalents and restricted cash $ 171,215 $ 188,002
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company has all cash, cash equivalents and investments balances at accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value in accordance with GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above. The Company’s investments in certificates of deposit are carried at amortized cost, which approximates fair value. The carrying values of the Company’s prepaid expenses and other current and non-current assets, accounts payable and accrued expenses approximate their respective fair values due to the short-term nature of these assets and liabilities. The carrying value of the Company’s long-term debt approximates its fair value (a level 2 measurement) at each balance sheet date due to its variable interest rate, which approximates a market interest rate.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset, which are as follows: Estimated Useful Life (In Years) Laboratory equipment 5 Computer equipment, furniture and office equipment 3 Leasehold improvements Lesser of useful life Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and right-of-use assets associated with our lease agreements. All of the Company's long-lived assets are to be held and used and have definitive lives and accordingly are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has no t recorded any impairment losses on long-lived assets.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees, non-employees, and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options, restricted stock units and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. For stock options or restricted stock units issued with performance-based vesting conditions, the stock compensation expense related to these awards is recognized based on the grant date fair value when achievement of the performance condition is deemed probable. The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company accounts for forfeitures of stock-based awards as they occur rather than applying an estimated forfeiture rate to stock-based compensation expense. The fair value of each stock option grant is estimated on the date of grant using the Black- Scholes option-pricing model. The Company estimates its expected common stock volatility based on its historical common stock volatility for the same time period. The Company uses the simplified method prescribed by Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share-Based Payment , to calculate the expected term of options granted to employees, non-employees and directors. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with the guidance under ASC 606, Revenue from Contracts with Customers ("ASC 606"). ASC 606 applies to all contracts with customers, except those contracts that are within the scope of other guidance, such as leases, insurance, and financial instruments. The Company enters into agreements that are within the scope of ASC 606, under which the Company licenses certain of the Company’s product candidates and performs research and development services in connection with such arrangements. The terms of these arrangements typically include payment of one or more of the following: nonrefundable up-front fees, reimbursement of research and development costs, development, clinical, regulatory and commercial sales milestone payments, and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. When determining the timing and extent of revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: a. identify the contract(s) with a customer; b. identify the performance obligations in the contract; c. determine the transaction price; d. allocate the transaction price to the performance obligations in the contract; and e. recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration to which it is entitled in exchange for the goods or services transferred to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within the contract to determine whether each promised good or service is a performance obligation. The promised goods or services in the Company’s arrangements typically consist of a license to the Company’s intellectual property and/or research and development services. The Company may provide options to additional items in such arrangements, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. Performance obligations are promises in a contract to transfer a distinct good or service to the customer that (i) the customer can benefit from on its own or together with other readily available resources, and (ii) is separately identifiable from other promises in the contract. Goods or services that are not individually distinct performance obligations are combined with other promised goods or services until such combined group of promises meet the requirements of a performance obligation. The Company determines the transaction price based on the amount of consideration the Company expects to receive for transferring the promised goods or services in the contract. Consideration may be fixed, variable, or a combination of both. At contract inception for arrangements that include variable consideration, the Company estimates the probability and extent of consideration it expects to receive under the contract utilizing either the most likely amount method or expected amount method, whichever best estimates the amount expected to be received. The Company then considers any constraints on the variable consideration and includes in the transaction price variable consideration to the extent it is deemed probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company then allocates the transaction price to each performance obligation based on the relative standalone selling price and recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) control is transferred to the customer and the performance obligation is satisfied. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company records amounts as accounts receivable when the right to consideration is deemed unconditional. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded for deferred revenue. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Incremental costs of obtaining a contract are expensed as and when incurred if the expected period over which the Company would have amortized the asset is one year or less, or the amount is immaterial.
Collaborative Revenue	Collaboration Revenue Arrangements with collaborators may include licenses to intellectual property, research and development services, manufacturing services for clinical and commercial supply, and participation on joint steering committees. The Company evaluates the promised goods or services to determine which promises, or group of promises, represent performance obligations. In contemplation of whether a promised good or service meets the criteria required of a performance obligation, the Company considers the stage of development of the underlying intellectual property, the capabilities and expertise of the customer relative to the underlying intellectual property, and whether the promised goods or services are integral to or dependent on other promises in the contract. When accounting for an arrangement that contains multiple performance obligations, the Company must develop judgmental assumptions, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success to determine the stand-alone selling price for each performance obligation identified in the contract. When the Company concludes that a contract should be accounted for as a combined performance obligation and recognized over time, the Company must then determine the period over which revenue should be recognized and the method by which to measure revenue. The Company generally recognizes revenue using a cost-based input method. Licenses of intellectual property If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue associated with the bundled performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition. Milestone Payments At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service, otherwise it will be allocated to all performance obligations of the arrangement based on the initial allocation. The Company evaluates each milestone to determine when and how much of the milestone to include in the transaction price. The Company first estimates the amount of the milestone payment that the Company could receive using either the expected value or the most likely amount approach. The Company primarily uses the most likely amount approach as that approach is generally most predictive for milestone payments with a binary outcome. Then, the Company considers whether any portion of that estimated amount is subject to the variable consideration constraint (that is, whether it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty). The Company updates the estimate of variable consideration included in the transaction price at each reporting date which includes updating the assessment of the likely amount of consideration and the application of the constraint to reflect current facts and circumstances. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has no t recognized any revenue related to sales-based royalties or milestone payments based on the level of sales. Manufacturing supply services For arrangements that include a promise of supply of clinical or commercial product, the Company determines if the supply is a promise in the contract or a future obligation at the customer’s option. If determined to be a promise at inception of the contract, the Company evaluates the promise to determine whether it is a separate performance obligation or a component of a bundled performance obligation. If determined to be an option, the Company determines if the option provides a material right to the customer and if so, accounts for the option as a separate performance obligation. If determined to be an option but not a material right, the Company accounts for the option as a separate contract when the customer elects to exercise the option.
Grant Revenue	Grant Revenue The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies, when the Company has concluded that it is the principal in conducting the research and development expenses, and where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. The Company has concluded to recognize funding received as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these contracts are central to its ongoing operations. Revenue is recognized as the qualifying expenses related to the contracts are incurred. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded in the Company’s consolidated balance sheet as accounts receivable. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss.
Collaboration Profit and Loss	Collaboration Profit and Loss We analyze our collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808"), which includes determining whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, we first determine which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, we apply the five-step model prescribed in ASC 606, as described above. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to ASC 606. In arrangements where we do not deem our collaborator to be our customer, up-front payments from our collaborator are presented in the consolidated balance sheets as liabilities, and adjusted as we perform activities pursuant to the collaboration arrangement. As the Company and its collaborator perform activities pursuant to the arrangement, amounts due to or from the Company or the collaborator, based on the relative contributions of activities of each party, are recognized in the consolidated statements of operations and comprehensive loss as an increase or reduction in operating expenses based on the nature of the payments.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The Company applies ASC 740-10, Accounting for Uncertain Tax Positions . The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 % likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing microbiome therapeutics to treat the modulation of the colonic microbiome. Revenue to date has been generated solely through the Company's agreements with its collaborators, all of which has been earned in the United States. All tangible assets are held in the United States.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2022, 2021 and 2020 , other comprehensive income (loss) consisted of changes in unrealized gains (losses) from available-for-sale investments and a currency translation adjustment.
Net Loss per Share	Net Loss per Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and unvested restricted stock. The Company applies the two-class method to calculate its basic and diluted net loss per share attributable to common stockholders. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method does not impact the net loss per share of common stock as the Company was in a net loss position for each of the periods presented. The Company’s convertible preferred stock contractually entitle the holders of such shares to participate in dividends but do not contractually require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Leases	Leases In accordance with ASC 842, Leases , the Company determines if an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records a right-of-use asset and a lease liability on the consolidated balance sheet for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded on the balance sheet, but payments are recognized as expense on a straight-line basis over the lease term. The Company has elected not to record a right-of-use asset or lease liability for leases with terms of 12 months or less. Right-of-use assets and lease liabilities are reassessed and remeasured when amendments to the terms of the lease agreement require reassessment and remeasurement of the lease payments and other inputs to the calculation of right-of-use assets and lease liabilities. The Company accounts for remeasurements and modifications to lease liabilities using the present value of remaining lease payments and estimated incremental borrowing rate at the date of remeasurement. The adjustment to the lease liability is recognized as a gain or loss in operating expenses, or as an adjustment to the right-of-use asset, as appropriate, based on the terms and conditions within the lease that are amended.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (‘‘ASU 2016-13’’), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. In November 2018, the FASB issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses , which narrowed the scope and changed the effective date for non-public entities for ASU 2016-13. The FASB subsequently issued supplemental guidance within ASU No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief (‘‘ASU 2019-05’’). ASU 2019-05 provides an option to irrevocably elect the fair value option for certain financial assets previously measured at amortized cost basis. For public entities that are Securities and Exchange Commission ("SEC") filers, excluding entities eligible to be smaller reporting companies, ASU 2016-13 is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. For all other entities, ASU 2016-13 is effective for annual periods beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted the new standard using a modified retrospective approach as of January 1, 2022. The adoption of this standard did not have a material impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements The Company has considered all recent accounting pronouncements issued. The Company’s management believes that these recent pronouncements will not have a material effect on the Company’s financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash	Cash, cash equivalents and restricted cash were comprised of the following (in thousands): December 31, 2022 2021 Cash and cash equivalents $ 163,030 $ 180,002 Restricted cash, non-current 8,185 8,000 Total cash, cash equivalents and restricted cash $ 171,215 $ 188,002
Schedule of Property and Equipment Estimated Useful Life	Depreciation expense is recognized using the straight-line method over the useful life of the asset, which are as follows: Estimated Useful Life (In Years) Laboratory equipment 5 Computer equipment, furniture and office equipment 3 Leasehold improvements Lesser of useful life

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis (in thousands): Fair Value Measurements as of December 31, 2022 Using: Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 47,863 $ — $ — $ 47,863 Commercial paper — 11,691 — 11,691 Government securities — 4,966 — 4,966 Investments: Commercial paper $ — $ 2,465 $ — $ 2,465 Corporate bonds — 2,957 — 2,957 Government securities — 12,889 — 12,889 $ 47,863 $ 34,968 $ — $ 82,831 Fair Value Measurements as of December 31, 2021 Using: Level 1 Level 2 Level 3 Total Cash Equivalents: Money market funds $ 70,322 $ — $ — $ 70,322 Commercial paper — 3,999 — 3,999 Investments: Commercial paper $ — $ 6,250 $ — $ 6,250 Corporate bonds — 40,095 — 40,095 Government securities — 64,854 — 64,854 $ 70,322 $ 115,198 $ — $ 185,520

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Schedule of Investments by Security Type	Investments by security type consisted of the following at December 31, 2022 and 2021 (in thousands): December 31, 2022 Amortized Gross Gross Fair Investments: Commercial paper $ 2,465 $ — $ — $ 2,465 Corporate bonds 2,958 — ( 1 ) 2,957 Government securities 12,898 3 ( 12 ) 12,889 $ 18,321 $ 3 $ ( 13 ) $ 18,311 December 31, 2021 Amortized Gross Gross Fair Investments: Commercial paper $ 6,250 $ — $ — $ 6,250 Corporate bonds 40,123 — ( 28 ) 40,095 Government securities 64,885 — ( 31 ) 64,854 $ 111,258 $ — $ ( 59 ) $ 111,199
Schedule of Amortized Cost and Fair Value of Investments by Contractual Maturity	The amortized cost and fair value of investments in commercial paper, corporate bonds, and government securities by contractual maturity, as of December 31, 2022 and were as follows (in thousands): Available-for-Sale Cost Fair Value Due in 1-year or less $ 18,321 $ 18,311 Due after 1-year through 5-years — — $ 18,321 $ 18,311 The amortized cost and fair value of investments in commercial paper, corporate bonds, and government securities by contractual maturity, as of December 31, 2021 were as follows (in thousands): Available-for-Sale Cost Fair Value Due in 1-year or less $ 110,762 $ 110,704 Due after 1-year through 5-years 496 495 $ 111,258 $ 111,199

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31, 2022 2021 Laboratory equipment $ 24,533 $ 19,137 Computer equipment 3,557 3,255 Furniture and office equipment 3,491 1,219 Leasehold improvements 32,474 32,925 Construction in progress 3,970 1,670 68,025 58,206 Less: Accumulated depreciation and amortization ( 45,040 ) ( 40,268 ) $ 22,985 $ 17,938

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, 2022 2021 Development and manufacturing costs $ 6,717 $ 11,147 Payroll and payroll-related costs 14,709 9,216 Liability related to 2021 License Agreement (Note 11) 34,770 21,098 Facility and other 3,644 3,633 $ 59,840 $ 45,094

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Summary of Operating Lease Assets and Liabilities	The following table summarizes the presentation in the Company’s consolidated balance sheets of its operating leases: December 31, 2022 2021 Assets: Operating lease assets $ 110,984 $ 18,208 Liabilities: Operating lease liabilities $ 3,601 $ 6,610 Operating lease liabilities, net of current portion 107,942 17,958 Total operating lease liabilities $ 111,543 $ 24,568
Summary of Lease Costs	The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss: Year Ended December 31, 2022 2021 2020 Operating lease costs $ 8,830 $ 5,170 $ 4,163 Short-term lease costs 1,375 1,452 1,457 Variable lease costs 4,547 3,300 2,890 Sublease income — ( 1,575 ) ( 1,813 ) Total lease costs $ 14,752 $ 8,347 $ 6,697
Schedule of Future Payments of Operating Lease Liabilities	As of December 31, 2022, future payments of operating lease liabilities are as follows (in thousands): As of December 31, 2022 2023 $ 16,815 2024 19,055 2025 21,164 2026 21,755 2027 and thereafter 108,383 Total future payments of operating lease liabilities $ 187,172 Less: imputed interest ( 75,629 ) Present value of operating lease liabilities $ 111,543

Notes Payable (Tables)

Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Summary of Future Principal Payments Due Under Arrangement, Excluding Interest and End of Term Charge	The future principal payments due under the New Credit Facility, excluding interest and the end of term charge, are as follows: Year Ending December 31, Principal 2023 — 2024 $ 50,000 Total $ 50,000

Common Stock and Stock-Based _2

Common Stock and Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2022
Subsidiary, Sale of Stock [Line Items]
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Number of Weighted Weighted Aggregate (in years) Outstanding as of December 31, 2021 11,517,189 $ 11.10 7.42 $ 28,007 Granted 4,527,897 6.89 Exercised ( 326,864 ) 2.96 Forfeited ( 778,188 ) 10.62 Outstanding as of December 31, 2022 14,940,034 $ 10.03 7.25 $ 11,608 Options exercisable as of December 31, 2022 7,441,253 $ 10.38 5.88 $ 8,115
Summary of Restricted Stock Activity	The Company has granted restricted stock units ("RSUs") with service-based vesting conditions. The table below summarizes the Company’s RSU activity for the year ended December 31, 2022: Number Weighted Unvested restricted stock units as of December 31, 2021 734,755 $ 17.68 Granted 1,302,844 $ 6.95 Forfeited ( 205,658 ) $ 11.82 Vested ( 282,401 ) $ 18.06 Unvested restricted stock units as of December 31, 2022 1,549,540 $ 9.37
Summary of Stock Based Compensation Expense	The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its consolidated statements of operations and comprehensive loss: Year Ended December 31, 2022 2021 2020 Research and development expenses $ 13,429 $ 10,146 $ 4,760 General and administrative expenses 12,053 10,076 4,064 $ 25,482 $ 20,222 $ 8,824
Employee Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Summary of Estimated Fair Value of Employee Stock Options	The assumptions that the Company used to determine the fair value of rights to acquire common stock under the ESPP were as follows, presented on a weighted average basis: Year Ended December 31, 2022 2021 2020 Risk-free interest rate 2.11 % 0.97 % 1.20 % Expected term (in years) 0.5 0.5 0.5 Expected volatility 99.0 % 123.8 % 74.9 % Expected dividend yield 0 % 0 % 0 %
Employees Stock Option [Member]
Subsidiary, Sale of Stock [Line Items]
Summary of Estimated Fair Value of Employee Stock Options	The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis: Year Ended December 31, 2022 2021 2020 Risk-free interest rate 1.67 % 0.73 % 1.26 % Expected term (in years) 6.0 5.4 6.0 Expected volatility 104.0 % 106.5 % 73.3 % Expected dividend yield 0 % 0 % 0 %

Collaboration Revenue (Tables)

Collaboration Revenue (Tables)	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Changes in Contract Liabilities	The following tables present changes in the Company’s contract liabilities during the year ended December 31, 2022 and 2021: Balance as of December 31, 2021 Additions Deductions Balance as of December 31, 2022 Year ended December 31, 2022 Contract liabilities: Deferred revenue - related party $ 103,817 — ( 7,128 ) $ 96,689 Balance as of December 31, 2020 Additions Deductions Balance as of December 31, 2021 Year ended December 31, 2021 Contract liabilities: Deferred revenue - related party $ 108,174 8,157 ( 12,514 ) $ 103,817 During the year ended December 31, 2022, the Company recognized the following revenues as a result of changes in the contract liability balances in the respective periods: Year Ended December 31, 2022 2021 Revenue recognized in the period from: Amounts included in the contract liability at the beginning of the period $ 7,128 $ 10,446

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Year Ended December 31, 2022 2021 2020 Numerator: Net loss attributable to common stockholders $ ( 250,157 ) $ ( 65,578 ) $ ( 89,127 ) Denominator: Weighted average common shares outstanding, basic and diluted 108,077,043 91,702,866 79,789,220 Net loss per share attributable to common stockholders, basic and diluted $ ( 2.31 ) $ ( 0.72 ) $ ( 1.12 )
Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share	The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Year Ended December 31, 2022 2021 2020 Stock options to purchase common stock 14,940,034 11,517,189 10,037,130 Unvested restricted stock units 1,549,540 734,755 6,500 Shares issuable under employee stock purchase plan 89,593 165,047 10,786 16,579,167 12,416,991 10,054,416

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of U.S Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2022 2021 2020 Federal statutory income tax rate ( 21.0 )% ( 21.0 )% ( 21.0 )% Research and development tax credits ( 3.1 ) ( 16.6 ) ( 6.4 ) State taxes, net of federal benefit ( 4.3 ) ( 2.8 ) ( 7.8 ) Stock-based compensation 0.6 ( 0.4 ) ( 5.8 ) Uncertain tax position reserves 4.6 — — Other 0.3 0.4 0.2 Change in deferred tax asset valuation allowance 22.9 40.4 40.8 Effective income tax rate — % — % — %	Year Ended December 31, 2022 2021 2020 Federal statutory income tax rate ( 21.0 )% ( 21.0 )% ( 21.0 )% Research and development tax credits ( 3.1 ) ( 16.6 ) ( 6.4 ) State taxes, net of federal benefit ( 4.3 ) ( 2.8 ) ( 7.8 ) Stock-based compensation 0.6 ( 0.4 ) ( 5.8 ) Uncertain tax position reserves 4.6 — — Other 0.3 0.4 0.2 Change in deferred tax asset valuation allowance 22.9 40.4 40.8 Effective income tax rate — % — % — %
Schedule of Net Deferred Tax Assets	Net deferred tax assets as of December 31, 2022 and 2021 consisted of the following: December 31, 2022 2021 Deferred tax assets: Net operating loss carryforwards $ 132,560 $ 108,189 Research and development tax credit carryforwards 48,854 53,133 Section 174 capitalized research and development expenses 38,894 — Stock-based compensation expense 20,048 16,045 Lease liability 29,717 6,635 Deferred revenue 29,922 36,666 Accrued expenses 4,044 2,475 Section 163(j) limitation 2,303 1,368 Depreciation and amortization 396 247 Other 200 274 Total deferred tax assets $ 306,938 $ 225,032 Deferred tax liabilities: Depreciation and amortization — — Right of use assets ( 29,568 ) ( 4,918 ) Total deferred tax liabilities ( 29,568 ) ( 4,918 ) Valuation allowance $ ( 277,370 ) $ ( 220,114 ) Net deferred tax assets $ — $ —
Summary of Changes In Valuation Allowance for Deferred Tax Assets	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2022, 2021 and 2020 related primarily to the increases in NOLs, research and development tax credit carryforwards and capitalized research and development expenses pursuant to IRC Section 174, and stock-based compensation were as follows: Year Ended December 31, 2022 2021 2020 Valuation allowance at beginning of year $ ( 220,114 ) $ ( 193,736 ) $ ( 157,346 ) Decreases recorded as benefit to income tax provision — — — Increases recorded to income tax provision ( 57,256 ) ( 26,378 ) ( 36,390 ) Valuation allowance as of end of year $ ( 277,370 ) $ ( 220,114 ) $ ( 193,736 )
Schedule of change in unrecognized tax benefits roll forward	The changes in the Company's unrecognized tax benefits for the years ended December 31, 2022, 2021, and 2020 were as follows: Year Ended December 31, 2022 2021 2020 Balance at beginning of year $ — $ — $ — Increase in unrecognized tax benefits as a result of tax positions taken 12,528 — — Reduction to unrecognized tax benefits — — — Increases in unrecognized tax benefits as a result of tax positions taken $ 12,528 $ — $ —

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporated month and year	2010-10
Entity incorporation, state or country code	DE
Accumulated deficit	$ 864,511	$ 614,354
Cash, cash equivalents and short and long-term investments	181,341
Net loss	(250,157)	(65,578)	$ (89,127)
Net operating cash outflows	(228,816)	$ 6,688	$ (93,610)
Line of credit facility	25,000
2021 License Agreement [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Milestones payments	$ 125,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents	90 days	90 days	90 days
Restricted investments	$ 1,401,000	$ 1,401,000
Restricted cash	8,185,000	8,000,000
Credit losses	0	$ 0	$ 0
Impairment losses on long lived assets	0
Revenue related to sales-based royalties	$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement	50%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 163,030	$ 180,002
Restricted cash, non-current	8,185	8,000
Total cash, cash equivalents and restricted cash	$ 171,215	$ 188,002	$ 116,049	$ 65,126

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Life (Details)	12 Months Ended
	Dec. 31, 2022
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment Useful Lives (in years)	5 years
Computer Equipment, Furniture and Office Equipment
Property, Plant and Equipment [Line Items]
Property and Equipment Useful Lives (in years)	3 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Estimated Useful Lives	Lesser of useful lifeor lease term

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Investments:
Investments	$ 18,311	$ 111,199
Fair Value, Measurements, Recurring [Member]
Investments:
Investments	82,831	185,520
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Cash Equivalents:
Cash Equivalents	47,863	70,322
Commercial Paper [Member]
Investments:
Investments	2,465	6,250
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]
Cash Equivalents:
Cash Equivalents	11,691	3,999
Investments:
Investments	2,465	6,250
Corporate Bonds [Member]
Investments:
Investments	2,957	40,095
Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Investments:
Investments	2,957	40,095
Government Securities [Member]
Investments:
Investments	12,889	64,854
Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Cash Equivalents:
Cash Equivalents	4,966
Investments:
Investments	12,889	64,854
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Investments:
Investments	47,863	70,322
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Cash Equivalents:
Cash Equivalents	47,863	70,322
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Investments:
Investments	34,968	115,198
Level 2 [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]
Cash Equivalents:
Cash Equivalents	11,691	3,999
Investments:
Investments	2,465	6,250
Level 2 [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Investments:
Investments	2,957	40,095
Level 2 [Member] | Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Cash Equivalents:
Cash Equivalents	4,966
Investments:
Investments	$ 12,889	$ 64,854

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair value, assets transfers from Level 1 to Level 2 measurement	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1 measurement	0	0
Restricted investment	$ 1,401	$ 1,401

Investments - Schedule of Inves

Investments - Schedule of Investments by Security Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 18,321	$ 111,258
Gross Unrealized Gain	3
Gross Unrealized Loss	(13)	(59)
Fair Value	18,311	111,199
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,465	6,250
Gross Unrealized Gain	0
Gross Unrealized Loss	0	0
Fair Value	2,465	6,250
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,958	40,123
Gross Unrealized Gain	0
Gross Unrealized Loss	(1)	(28)
Fair Value	2,957	40,095
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,898	64,885
Gross Unrealized Gain	3
Gross Unrealized Loss	(12)	(31)
Fair Value	$ 12,889	$ 64,854

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investments [Abstract]
Maximum maturity days for cash equivalents	90 days	90 days	90 days
Restricted investment	$ 1,401	$ 1,401

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost and Fair Value of Investments by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available-for-sale, amortized cost
Due in 1-year or less	$ 18,321	$ 110,762
Due after 1-year through 5-years	0	496
Amortized Cost	18,321	111,258
Available-for-sale, fair value
Due in 1-year or less	18,311	110,704
Due after 1-year through 5-years	0	495
Fair value	$ 18,311	$ 111,199

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 68,025	$ 58,206
Less: Accumulated depreciation and amortization	(45,040)	(40,268)
Property and equipment, net	22,985	17,938
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	24,533	19,137
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,557	3,255
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,491	1,219
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	32,474	32,925
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,970	$ 1,670

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 6,629	$ 5,947	$ 6,578
Disposal of fully depreciated assets cost basis	$ 1,857

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands		Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Development and clinical manufacturing costs		$ 6,717	$ 11,147
Payroll and payroll-related costs		14,709	9,216
Liability related to 2021 License Agreement (Note 11)		34,770	21,098
Facility and other		3,644	3,633
Total accrued expenses and other current liabilities	[1]	$ 59,840	$ 45,094
[1] Includes related party amounts of $ 34,770 and $ 21,098 at December 31, 2022 and December 31, 2021 , respectively (see Note 11)

Leases - Additional Information

Leases - Additional Information (Details) - USD ($)

1 Months Ended

12 Months Ended

Dec. 31, 2022

Apr. 30, 2022

Sep. 30, 2021

Aug. 31, 2021

Jul. 31, 2021

Dec. 31, 2022

Dec. 31, 2021

Dec. 31, 2020

Dec. 01, 2022

Apr. 01, 2022

Sep. 01, 2021

Aug. 01, 2021

Jul. 01, 2021

Operating Leased Assets [Line Items]

Existence of option to extend

true

Option to extend, description

Certain leases include one or more options to renew, exercisable at the Company’s sole discretion, with renewal terms that can extend the lease from approximately one year to five years.

Lease renewal term (in years)

5 years

7 years

Lease term

10 years

10 years

10 years

Right-of-use asset

$ 110,984,000

$ 110,984,000

$ 18,208,000

$ 56,065,000

$ 5,900,000

Tenant improvement allowance

$ 1,223,000

$ 770,000

Present value of operating lease liabilities

111,543,000

111,543,000

24,568,000

54,206,000

2,327,000

Leasehold Improvements

$ 1,859,000

$ 3,573,000

Leases Payments

7,809,000

$ 6,821,000

$ 6,302,000

Asset retirement obligation

$ 452,000

$ 452,000

Weighted average remaining lease term

8 years 11 months 1 day

8 years 11 months 1 day

6 years 1 month 13 days

Weighted average incremental borrowing rate

13%

13%

10%

October 2021 [Member]

Operating Leased Assets [Line Items]

Right-of-use asset

$ 7,602,000

March 2022 [Member]

Operating Leased Assets [Line Items]

Right-of-use asset

2,662,000

Lease Amendment [Member]

Operating Leased Assets [Line Items]

Right-of-use asset

$ 32,837,000

Present value of operating lease liabilities

$ 32,837,000

Spring House, PA

Operating Leased Assets [Line Items]

Right-of-use asset

$ 0

$ 0

Present value of operating lease liabilities

$ 0

$ 0

Office Space [Member]

Operating Leased Assets [Line Items]

Present value of operating lease liabilities

7,602,000

Laboratory Space [Member]

Operating Leased Assets [Line Items]

Tenant improvement allowance

$ 767,000

Present value of operating lease liabilities

1,273,000

Leasehold Improvements

$ 1,389,000

Office and Laboratory Space [Member]

Operating Leased Assets [Line Items]

Lease term

10 years

Maximum [Member]

Operating Leased Assets [Line Items]

Operating lease, remaining term

10 years

Lease renewal term (in years)

5 years

5 years

Minimum [Member]

Operating Leased Assets [Line Items]

Operating lease, remaining term

2 years

Lease renewal term (in years)

1 year

1 year

Leases Payments

$ 2,980,000

$ 101,548,000

$ 4,052,000

Minimum [Member] | October 2021 [Member]

Operating Leased Assets [Line Items]

Leases Payments

12,125,000

Minimum [Member] | March 2022 [Member]

Operating Leased Assets [Line Items]

Leases Payments

$ 2,449,000

Minimum [Member] | Lease Amendment [Member]

Operating Leased Assets [Line Items]

Tenant improvement allowance

$ 1,000,000

Leases Payments

$ 60,022,000

Leases - Summary of Operating L

Leases - Summary of Operating Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Sep. 01, 2021	Jul. 01, 2021
Assets:
Operating lease assets	$ 110,984	$ 18,208	$ 56,065	$ 5,900
Liabilities:
Operating lease liabilities	3,601	6,610
Operating lease liabilities, net of current portion	107,942	17,958
Total operating lease liabilities	$ 111,543	$ 24,568	$ 54,206	$ 2,327

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease costs	$ 8,830	$ 5,170	$ 4,163
Short-term lease costs	1,375	1,452	1,457
Variable lease costs	4,547	3,300	2,890
Sublease income	0	(1,575)	(1,813)
Total lease costs	$ 14,752	$ 8,347	$ 6,697

Leases - Schedule of Future Pay

Leases - Schedule of Future Payments of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Sep. 01, 2021	Jul. 01, 2021
Leases [Abstract]
2023	$ 16,815
2024	19,055
2025	21,164
2026	21,755
2027 and thereafter	108,383
Total future payments of operating lease liabilities	187,172
Less: imputed interest	(75,629)
Present value of operating lease liabilities	$ 111,543	$ 24,568	$ 54,206	$ 2,327

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) $ in Thousands			12 Months Ended
	Feb. 24, 2022 USD ($)	Oct. 29, 2019 USD ($)	Dec. 31, 2022 USD ($) Installment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Interest expense			$ 6,020	$ 2,910	$ 2,924
Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument, Face amount	$ 350,000
Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, payment terms			For all advances outstanding under the New Credit Facility, the Company will make interest only payments through December 31, 2023, extendable to December 31, 2024 upon satisfaction of certain conditions (such applicable date, the “Amortization Date”). The principal balance and interest of the advances will be repaid in equal monthly installments after the Amortization Date and continuing through October 1, 2024, extendable to October 1, 2025, upon satisfaction of certain conditions (such applicable date, the “Maturity Date”)
Previously repaid principal amount of debt	$ 2,900
Additional advance prepayment or repayment percentage	1.75%
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Interest expense			$ 6,020	$ 2,910
Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate		9.65%
Credit facility, payment terms			Following an interest-only period of 24 months, principal payments are due in 24 equal monthly installments commencing December 1, 2021 and ending November 1, 2023
Notes payable interest-only period				24 months
Notes payable principal payments equal monthly installments | Installment			24
Percentage of prepayment amount during first year		2%
Percentage of prepayment amount during second year		1.50%
Percentage of prepayment amount during third year		1%
Prepayment or repayment percentage		4.85%
Loan and Security Agreement [Member] | Original Credit Facility [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate		4.40%
Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate			9.65%
Carrying value of debt			$ 51,047	$ 24,643
Debt instrument, interest rate effective percentage			15.01%	11.47%
Loan and Security Agreement [Member] | New Credit Facility [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate			6.40%
Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	$ 100,000
Hercules Capital, Inc. [Member] | Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 50,000
First Tranche [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	25,000
First Tranche [Member] | Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Carrying value of debt			$ 50,586
First Tranche [Member] | Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	25,000
First Tranche [Member] | Hercules Capital, Inc. [Member] | Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Gross proceeds from debt		25,000
Second Tranche [Member] | Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	12,500
Second Tranche [Member] | Hercules Capital, Inc. [Member] | Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		12,500
Third Tranche [Member] | Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	12,500
Third Tranche [Member] | Hercules Capital, Inc. [Member] | Loan and Security Agreement [Member] | Original Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 12,500
Fourth Tranche Available Upon Satisfaction of Conditions Including Approval by U.S. Food and Drug Administration [Member] | Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	25,000
Fifth Tranche Available Through Amortization Date Including Lenders' Investment Committee Approval [Member] | Lenders [Member] | Second Amendment to Loan and Security Agreement [Member] | New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	$ 25,000

Notes Payable - Summary of Futu

Notes Payable - Summary of Future Principal Payments Due Under Arrangement, Excluding Interest and End of Term Charge (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
2023	$ 0
2024	50,000
Total	$ 50,000

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2022	Dec. 31, 2021	Jul. 01, 2015
Equity [Abstract]
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001

Common Stock and Stock-Based _3

Common Stock and Stock-Based Awards - Additional Information (Detail) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended
	Jun. 29, 2022 USD ($) $ / shares shares	Aug. 12, 2020 USD ($) $ / shares shares	May 31, 2021 USD ($)	Nov. 30, 2019 USD ($)	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Jul. 01, 2015 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized					200,000,000	200,000,000
Common stock, par value | $ / shares	$ 3.15				$ 0.001	$ 0.001
Common stock, shares issued	8,738,243
Net proceeds from sale of common stock | $	$ 27,525				$ 96,721	$ 0	$ 243,748
Common stock, shares issued					125,222,273	91,889,418
Flagship Pioneering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from sale of common stock | $	$ 27,525
Underwriting Agreement [Member] | Cowen and Company, LLC and Piper Sandler & Co. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from sale of common stock | $		$ 243,748
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued					31,746,030		12,075,000
Common Stock [Member] | Underwriting Agreement [Member] | Cowen and Company, LLC and Piper Sandler & Co. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued		10,500,000
Common stock, share price | $ / shares		$ 21.50
Option exercisable period for purchase additional shares		30 days
Common Stock [Member] | Maximum [Member] | Underwriting Agreement [Member] | Cowen and Company, LLC and Piper Sandler & Co. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option to purchase additional shares of common stock		1,575,000
Initial Public Offering ("IPO") [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized								200,000,000
Common stock, par value | $ / shares	$ 3.15							$ 0.001
Common stock, shares issued	31,746,030
Additional net proceeds from the registered direct offering | $	$ 96,721
At The Market Equity Offering Program [Member] | 2019 Sales Agreement [Member] | Cowen And Company, LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Gross proceeds from sale of common stock | $				$ 25,000,000
At The Market Equity Offering Program [Member] | 2019 and 2020 Sales Agreement [Member] | Cowen And Company, LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued							5,788,000
Common stock, share price | $ / shares							$ 4.40
Net proceeds from sale of common stock | $							$ 24,773
Percentage of commission on sale of common stock							3
At The Market Equity Offering Program [Member] | 2020 and 2021 Sales Agreement [Member] | Cowen And Company, LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued						0
At The Market Equity Offering Program [Member] | 2021 Sales Agreement [Member] | Cowen And Company, LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued					655,000
Common stock, share price | $ / shares					$ 7.26
Net proceeds from sale of common stock | $					$ 4,447
Gross proceeds from sale of common stock | $			$ 150,000,000
Percentage of commission on sale of common stock					3
Concurrent Placement [Member] | Securities Purchase Agreement [Member] | Nestlé [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued		959,002
Common stock, share price | $ / shares		$ 20.855
Net proceeds from sale of common stock | $		$ 19,900

Common Stock and Stock-Based _4

Common Stock and Stock-Based Awards - 2012 Stock Incentive plan - Additional Information (Detail) - 2012 Stock Incentive Plan [Member]	12 Months Ended
	Dec. 31, 2022 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan description	The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The Company generally granted stock-based awards with service conditions only (“service-based” awards).
Shares available for future grant	0
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price per share of common stock expressed as a percentage	100%
Stock option granted vesting period	4 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option term	10 years
Stock option granted vesting period	4 years
Stock option expiration period	10 years

Common Stock and Stock-Based _5

Common Stock and Stock-Based Awards - 2015 Incentive Award Plan - Additional Information (Detail) - 2015 Incentive Award Plan [Member] - shares		12 Months Ended
	Jun. 16, 2015	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares initially reserved for issuance	2,200,000
Percentage of common stock shares outstanding	4%
Stock incentive plan description		The number of shares initially reserved for issuance under the 2015 Plan was the sum of (i) 2,200,000 shares of common stock and (ii) the number of shares subject to awards outstanding under the 2012 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company on or after the effective date of the 2015 Plan. In addition, the number of shares of common stock that may be issued under the 2015 Plan is subject to increase on the first day of each calendar year, beginning in 2016 and ending in 2025, equal to the lesser of (i) 4% of the number of shares of the Company’s common stock outstanding on the last day of the preceding applicable calendar year and (ii) an amount determined by the Company’s board of directors.
Shares available for future grant		967,206
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period		4 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period		4 years
Stock option expiration period		10 years

Common Stock and Stock-Based _6

Common Stock and Stock-Based Awards - 2015 Employee Stock Purchase Plan - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jun. 16, 2015	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 25,482	$ 20,222	$ 8,824
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate shares of common stock reserved for issuance	365,000	2,469,204
Shares issued under ESPP	400,000	322,560
Percentage of common stock shares outstanding	1%
Percentage of eligible earning contributed toward semi-annual purchase of common stock		15%
Offering period under the plan		6 months
Percentage of purchase price with respect to each offering period		85%

Common Stock and Stock-Based _7

Common Stock and Stock-Based Awards - 2022 Employment Inducement Award Plan - Additional Information (Detail) - 2022 Employment Inducement Award Plan [Member] - shares	12 Months Ended
	Dec. 31, 2022	Dec. 14, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Stock incentive plan description	2,500,000 shares of common stock were reserved for issuance under the 2022 Plan. Any shares subject to awards previously granted under the 2022 Plan that expire, terminate or are otherwise surrendered, canceled, or forfeited in any case, in a manner that results in the Company acquiring the shares covered by the award at a price not greater than the price (as adjusted to reflect any equity restructuring) paid by the Participant for such shares or not issuing any shares covered by the award, the unused shares covered by the award will again be available for award grants under the 2022 Plan.
Number of shares initially reserved for issuance		2,500,000
Shares available for future grant	2,500,000

Common Stock and Stock-Based _8

Common Stock and Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Equity [Abstract]
Number of Shares, Beginning Balance	11,517,189
Number of Shares, Granted	4,527,897
Number of Shares, Exercised	(326,864)
Number of Shares, Forfeited	(778,188)
Number of Shares, Ending Balance	14,940,034	11,517,189
Number of Shares, Options exercisable	7,441,253
Weighted Average Exercise Price, Beginning Balance	$ 11.10
Weighted Average Exercise Price, Granted	6.89
Weighted Average Exercise Price, Exercised	2.96
Weighted Average Exercise Price, Forfeited	10.62
Weighted Average Exercise Price, Ending Balance	10.03	$ 11.10
Weighted Average Exercise Price, Options exercisable	$ 10.38
Weighted Average Remaining Contractual Term, Outstanding	7 years 3 months	7 years 5 months 1 day
Weighted Average Remaining Contractual Term, Options exercisable	5 years 10 months 17 days
Aggregate Intrinsic Value, Outstanding	$ 11,608	$ 28,007
Aggregate Intrinsic Value, Options exercisable	$ 8,115

Common Stock and Stock-Based _9

Common Stock and Stock-Based Awards - Stock Options - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options	$ 5.53	$ 15.33	$ 5.08
Intrinsic Value, Stock options exercised	$ 981	$ 4,727	$ 37,255
Performance-based stock options to granted	4,527,897
Stock based compensation expense for stock options	$ 25,482	$ 20,222	$ 8,824
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options		$ 5.53
Performance-based stock options to granted		562,000
Stock options exercisable	0
Stock based compensation expense for stock options	$ 0	$ 0

Common Stock and Stock-Based_10

Common Stock and Stock-Based Awards - Summary of Restricted Stock Activity (Detail) - Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested restricted stock units, Beginning balance	734,755
Number of Shares, Granted	1,302,844	768,998	6,500
Number of Shares, Forfeited	(205,658)
Number of Shares, Vested	(282,401)
Number of Shares, Unvested restricted stock units, Ending balance	1,549,540	734,755
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Beginning balance	$ 17.68
Weighted Average Grant Date Fair Value, Granted	6.95
Weighted Average Grant Date Fair Value, Forfeited	11.82
Weighted Average Grant Date Fair Value, Vested	18.06
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Ending balance	$ 9.37	$ 17.68

Common Stock and Stock-Based_11

Common Stock and Stock-Based Awards - Restricted Stock Units - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2022 $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) Employee $ / shares shares	Dec. 31, 2020 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees granted | Employee			2
Stock-based compensation expense | $		$ 25,482	$ 20,222	$ 8,824
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value, vested | $		$ 1,809	$ 16	$ 532
Performance-based stock options to granted		1,302,844	768,998	6,500
Stock option granted vesting period		4 years
Weighted average grant-date fair value of stock options | $ / shares		$ 6.95
Number of Shares, Vested		(282,401)
Restricted Stock Units [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage		25%
Restricted Stock Units [Member] | Share-Based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage		75%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $		$ 0	$ 0
Employee share based compensation expense | $		$ 815
Number of Shares, Vested			0
Performance Shares [Member] | Employee 1 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance-based stock options to granted	42,500		85,000
Weighted average grant-date fair value of stock options | $ / shares	$ 9.59		$ 9.59
Performance Shares [Member] | Employee 2 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance-based stock options to granted	20,000		40,000
Weighted average grant-date fair value of stock options | $ / shares	$ 20.35		$ 20.35

Common Stock and Stock-Based_12

Common Stock and Stock-Based Awards - Summary of Estimated Fair Value of Employee Stock Options (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.11%	0.97%	1.20%
Expected term (in years)	6 months	6 months	6 months
Expected volatility	99%	123.80%	74.90%
Expected dividend yield	0%	0%	0%
Employees Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.67%	0.73%	1.26%
Expected term (in years)	6 years	5 years 4 months 24 days	6 years
Expected volatility	104%	106.50%	73.30%
Expected dividend yield	0%	0%	0%

Common Stock and Stock-Based_13

Common Stock and Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 25,482	$ 20,222	$ 8,824
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	13,429	10,146	4,760
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 12,053	$ 10,076	$ 4,064

Common Stock and Stock-Based_14

Common Stock and Stock-Based Awards - Stock Based Compensation - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Equity [Abstract]
Unrecognized stock-based compensation cost	$ 57,005
Weighted average period over which unrecognized compensation cost is expected to be recognized	1 year 9 months 18 days

Collaboration Revenue - Additio

Collaboration Revenue - Additional Information (Detail)				1 Months Ended		3 Months Ended	12 Months Ended
	Jul. 21, 2021 USD ($)	Jul. 01, 2021 USD ($)	Jan. 31, 2016 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2019 USD ($) Installment	Dec. 31, 2020 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 30, 2018 USD ($)	Feb. 29, 2016 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration (profit) loss sharing - related party							$ (1,004,000)	$ 1,732,000	$ 0
Upfront collaboration/license fee			$ 120,000,000
Collaboration revenue - related party							7,128,000	143,857,000	11,897,000
Collaboration revenue							0	0	17,161,000
2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50%
Collaborative arrangement, sharing of pre-launch costs, percentage		50%
Research Agreement [Member] | AstraZeneca Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable					$ 20,000,000
Transaction price allocated to remaining performance obligations				$ 23,377,000		$ 23,377,000			23,377,000
Minimum exclusivity period					3 years
Number of installments | Installment					3
Termination date				Apr. 02, 2021
Termination notice period				120 days
Research and development fixed consideration				$ 20,000,000		20,000,000	20,000,000		20,000,000
Research and development estimated reimbursement costs							13,900,000
Reimbursement of research and development costs incurred									3,376,000
Collaboration revenue						$ 15,145,000	0
Nestle Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment							94,713,000	97,728,000						$ 120,000,000
Maximum development milestone payments to be received							285,000,000
Maximum regulatory payments to be received							375,000,000
Maximum amount to be received on achievement of certain commercial milestones							1,125,000,000
Proceeds on achievement of development milestone									10,000,000	$ 40,000,000	$ 20,000,000	$ 10,000,000
Transaction price allocated to remaining performance obligations							200,000,000
Collaboration revenue - related party							3,014,000	10,446,000	$ 11,897,000
Deferred revenue							96,689,000	103,817,000
Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50%
Upfront payment received	$ 175,000,000
Maximum amount to be received on achievement of regulatory and sales milestones		$ 360,000,000
Maximum amount to be received on achievement of sales milestones		225,000,000
Collaboration (profit) loss sharing - related party							(1,004,000)	1,732,000
Maximum regulatory payments to be received		$ 135,000,000
Transaction price allocated to remaining performance obligations	$ 139,500,000
Termination notice period	60 days
Nestle Health Science [Member] | 2021 License Agreement [Member] | License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party								131,343,000
Nestle Health Science [Member] | 2021 License Agreement [Member] | Service [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to remaining performance obligations	$ 8,157,000
Collaboration revenue - related party							4,114,000	2,068,000
Nestle Health Science [Member] | Phase 2 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable			20,000,000
Nestle Health Science [Member] | Phase 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable			$ 20,000,000
Nestle Health Science [Member] | Phase 2b [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable													$ 40,000,000
Proceeds on achievement of development milestone										$ 40,000,000
Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement	35,500,000
Topic 808 [Member] | Total Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement	$ 35,500,000
Topic 808 [Member] | Other Long-term Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement							0	10,585,000
Topic 808 [Member] | Accrued Expenses and Other Current Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement							34,770,000	21,098,000
Research and development expenses [Member] | Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cost associated with pre-launch activities							6,102,000	2,168,000
General and administrative expenses [Member] | Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cost associated with pre-launch activities							$ 8,953,000	$ 3,383,000

Collaboration Revenue - Changes

Collaboration Revenue - Changes in Contract Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Deductions	$ 7,128	$ 10,446
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Balance at beginning of period	103,817	108,174
Deferred revenue - related party, Additions	0	8,157
Deferred revenue - related party, Deductions	(7,128)	(12,514)
Deferred revenue - related party, Balance at end of period	$ 96,689	$ 103,817

Collaboration Revenue - Schedul

Collaboration Revenue - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 7,128	$ 10,446

Net Loss per Share - Basic and

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net loss attributable to common stockholders	$ (250,157)	$ (65,578)	$ (89,127)
Denominator:
Weighted average common shares outstanding, basic	108,077,043	91,702,866	79,789,220
Weighted average common shares outstanding, diluted	108,077,043	91,702,866	79,789,220
Net loss per share attributable to common stockholders, basic	$ (2.31)	$ (0.72)	$ (1.12)
Net loss per share attributable to common stockholders, diluted	$ (2.31)	$ (0.72)	$ (1.12)

Net Loss per Share - Summary of

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	16,579,167	12,416,991	10,054,416
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	14,940,034	11,517,189	10,037,130
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	1,549,540	734,755	6,500
Shares Issuable under Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	89,593	165,047	10,786

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) SFr in Thousands	Nov. 08, 2021 USD ($)	Nov. 08, 2021 CHF (SFr)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Construction
Other Commitments [Line Items]
Prepayments on long term contract				$ 8,828,000
Bacthera Agreement [Member]
Other Commitments [Line Items]
Payments to acquire under agreement	$ 277,000,000	SFr 256,000
Long-term manufacturing agreement, additional term period thereafter	3 years	3 years
Payments on long-term contract			$ 12,276,000
Bacthera Agreement [Member] | Maximum [Member]
Other Commitments [Line Items]
Long-term manufacturing agreement term period	16 years	16 years
Bacthera Agreement [Member] | Research and development expenses [Member]
Other Commitments [Line Items]
Prepayments on long term contract				3,448,000
Indemnification Agreement [Member]
Other Commitments [Line Items]
Obligations accrued			0	0
Legal Contingencies [Member]
Other Commitments [Line Items]
Obligations accrued			$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Capitalized research and development costs	160,586,000
Unrecognized tax benefits	$ 0	$ 0	$ 0	$ 0
Massachusetts [Member]
Income Tax Disclosure [Line Items]
Net operating loss carry forwards, expiration year, start	2035
Future Tax Years [Member] | Maximum [Member]
Income Tax Disclosure [Line Items]
Taxable income on NOL	80%
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 501,789,000
Research and development performance period	5 years
Federal [Member] | Before 2018 [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 119,800,000
Net operating loss carry forwards, expiration year, start	2035
Federal [Member] | After 2017 [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 381,989,000
Federal [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 50,248,000
Tax credit carryforwards, expiration year, start	2031
Federal [Member] | Orphan Drug Credit Carryforwards [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 25,623,000
Foreign [Member]
Income Tax Disclosure [Line Items]
Research and development performance period	15 years
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 481,862,000
State [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 12,925,000
Tax credit carryforwards, expiration year, start	2028

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of U.S Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)	(21.00%)
Research and development tax credits	(3.10%)	(16.60%)	(6.40%)
State taxes, net of federal benefit	(4.30%)	(2.80%)	(7.80%)
Stock-based compensation	0.60%	(0.40%)	(5.80%)
Uncertain tax position reserves	4.60%	0%	0%
Other	0.30%	0.40%	0.20%
Change in deferred tax asset valuation allowance	22.90%	40.40%	40.80%
Effective income tax rate	0%	0%	0%

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 132,560	$ 108,189
Research and development tax credit carryforwards	48,854	53,133
Section 174 capitalized research and development expenses	38,894	0
Stock-based compensation expense	20,048	16,045
Lease Liability	29,717	6,635
Deferred revenue	29,922	36,666
Accrued expenses	4,044	2,475
Section 163(j) limitation	2,303	1,368
Depreciation and amortization	396	247
Other	200	274
Total deferred tax assets	306,938	225,032
Deferred tax liabilities:
Depreciation and amortization	0	0
Right of use assets	(29,568)	(4,918)
Total deferred tax liabilities	(29,568)	(4,918)
Valuation allowance	(277,370)	(220,114)	$ (193,736)	$ (157,346)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Summary of Chang

Income Taxes - Summary of Changes In Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Valuation Allowance [Abstract]
Valuation allowance at beginning of year	$ (220,114)	$ (193,736)	$ (157,346)
Increases recorded to income tax provision	(57,256)	(26,378)	(36,390)
Valuation allowance as of end of year	$ (277,370)	$ (220,114)	$ (193,736)

Income Taxes - Schedule of chan

Income Taxes - Schedule of change in unrecognized tax benefits roll forward (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 0	$ 0	$ 0
Increase in unrecognized tax benefits as a result of tax positions taken during the year	12,528,000	0	0
Reduction to unrecognized tax benefits	0	0	0
Increases in unrecognized tax benefits as a result of tax positions taken during current period	$ 12,528,000	$ 0	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Jun. 29, 2022	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Feb. 29, 2016
Related Party Transaction [Line Items]
Collaboration revenue - related party			$ 7,128,000	$ 143,857,000	$ 11,897,000
Common stock, shares issued	8,738,243
Common stock, par value	$ 3.15		$ 0.001	$ 0.001
Proceeds from issuance of common stock	$ 27,525,000		$ 96,721,000	$ 0	243,748,000
Payment for the lease option			0	10,585,000
Nestle Health Science [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party			3,014,000	10,446,000	$ 11,897,000
Deferred revenue			94,713,000	97,728,000		$ 120,000,000
Payments under agreements with related party			0	0
Due from related party for the reimbursement of development costs			0	0
Nestle Health Science [Member] | 2021 License Agreement [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party			4,114,000	133,411,000
Deferred revenue			1,976,000	6,089,000
Payments under agreements with related party			0	0
Due from related party for the reimbursement of development costs			0	0
Nestle Health Science [Member] | 2021 License Agreement [Member] | Accrued Expenses and Other Current Liabilities [Member]
Related Party Transaction [Line Items]
Transaction price allocated under collaborative arrangement			34,770,000	21,098,000
Nestle Health Science [Member] | 2021 License Agreement [Member] | Other Long-term Liabilities [Member]
Related Party Transaction [Line Items]
Transaction price allocated under collaborative arrangement			$ 0	10,585,000
Flagship Pioneering [Member]
Related Party Transaction [Line Items]
Proceeds from issuance of common stock	$ 27,525,000
Flagship Pioneering [Member] | Sublease Agreement [Member]
Related Party Transaction [Line Items]
Lessee, term of operating sublease, description			The term of the sublease agreement commenced in July 2019 and ended in November 2021
Sub lease commencement date		2019-07
Cash received from related party transaction			$ 0	1,575,000
Flagship Pioneering [Member] | Sublease Agreement [Member] | Other Income [Member]
Related Party Transaction [Line Items]
Sublease income			0	$ 1,575,000
Flagship Pioneering [Member] | Pledge and Utilization Agreement [Member]
Related Party Transaction [Line Items]
Payment for the lease option			$ 833,000

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2016	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Retirement Benefits [Abstract]
Employer match of employee contributions	50%
Employee deferral subject to employer match	6%
Employer contribution expenses		$ 1,921	$ 1,087	$ 586