0000950170-23-057805 | 10-Q | XBRL Viewer

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Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (47,854)	$ 46,552	$ (71,174)	$ (60,002)	$ (64,735)	$ (56,624)	$ (72,476)	$ (181,361)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Leases [Abstract]
Operating lease costs	$ 5,544	$ 1,785	$ 16,496	$ 5,405
Short-term lease costs	362	326	1,102	1,035
Variable lease costs	1,699	1,135	5,643	3,437
Total lease costs	$ 7,605	$ 3,246	$ 23,241	$ 9,877

Fair Value Measurements - Schedule of Level 3 Inputs to Warrant Liabilities (Detail) - Warrant [Member]	Sep. 30, 2023	Apr. 27, 2023
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative Liability Expected Volatility	75.00%	83.00%
Derivative Liability Expected Term	1 year 3 months 18 days	1 year 8 months 12 days

Notes Payable (Tables)

9 Months Ended

Sep. 30, 2023

Debt Disclosure [Abstract]

Summary of Future Principal Payments Due Under the Oaktree Credit Arrangement, Excluding Interest and End of Term Charge

The future principal payments due under the Oaktree Credit Agreement, excluding interest and the end of term charge, are as follows:


Year Ending December 31,	Principal
2023 (remaining 3 months)	$	—
2024		—
2025		—
2026		24,750
2027		33,000
Thereafter		52,250
Total	$	110,000

Nature of the Business and Basis of Presentation	9 Months Ended
Sep. 30, 2023
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 commercial-stage microbiome therapeutics company focused on the development and commercialization of 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 product, VOWST (fecal microbiota spores, live brpk), formerly called SER-109, was approved by the U.S. Food and Drug Administration (“FDA”) on April 26, 2023 and is the first and only orally administered microbiome therapeutic. VOWST is indicated to prevent the recurrence of Clostridioides difficile infection (“CDI”) in patients 18 or older following antibacterial treatment for recurrent CDI. The Company launched VOWST in the United States with its collaborator, Nestlé Health Science (“Nestlé”), in June 2023. Building upon VOWST, the Company is progressing the Phase 1b clinical trial of SER-155, a microbiome therapeutic candidate consisting of a 16-strain consortium of cultivated bacteria designed to prevent enteric-derived infections and resulting blood stream infections, as well as induce immune tolerance responses to reduce the incidence of Graft versus Host Disease ("GvHD") in patients undergoing allogeneic hematopoietic stem cell transplantation (“allo-HSCT”). Gastrointestinal microbiome data from the first 100 days of SER-155 Phase 1b open-label study cohort 1 showed the successful engraftment of SER-155 bacterial strains, and a substantial reduction in the cumulative incidence of pathogen domination, a biomarker associated with the risk of serious enteric infections and resulting bloodstream infections, as well as GvHD. The tolerability profile observed was favorable, with no serious adverse events attributed to SER-155 administration. Enrollment in the placebo-controlled cohort 2 portion of the study is ongoing and 100-day topline results are anticipated in the third quarter of 2024. The Company has built and deploys a reverse translational platform for the discovery and development of microbiome therapeutics, and maintains extensive proprietary know-how that may be used to support future research and development efforts. 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. In addition, the Company owns a valuable intellectual property estate related to the development and manufacture of microbiome therapeutics. On October 29, 2023, the Company's Board of Directors approved a restructuring plan to prioritize the commercialization of VOWST and the completion of the SER-155 Phase 1b study, while significantly reducing costs and supporting longer-term business sustainability (the "Restructuring Plan"). The Restructuring Plan includes (i) a reduction of the Company's workforce by approximately 41% across the organization, resulting in the elimination of approximately 160 positions; (ii) significantly scaling back all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study; and (iii) reducing general and administrative expenses, including consolidating office space. For additional information on the Restructuring Plan, see Note 17, Subsequent Events. 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. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. Other than VOWST, the Company’s product candidates are in development, and will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to potential commercialization. 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 accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. As of September 30, 2023, the Company had an accumulated deficit of $936,987 and cash and cash equivalents of $169,912. Primarily as a result of the increased and costly efforts to commercialize VOWST and to continue the research and development efforts for other product candidates and preclinical programs, the Company incurred a net loss of $72,476 and had net operating cash outflows of $69,855 for the nine months ended September 30, 2023. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. 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 condensed consolidated financial statements, the Company believes it is reasonably likely that it will require additional funding to maintain commercial production of VOWST, continue its research and development efforts for other microbiome therapeutic product candidates and preclinical programs, and meet its operational obligations as they come due. These conditions raise substantial doubt about the Company's ability to continue as a going concern. Management's plans that are intended to mitigate the conditions that raise substantial doubt about the Company’s ability to continue as a going concern include (i) the recently announced Restructuring Plan, which is expected to result in cost savings in 2024 from the reduction in workforce of approximately 160 employees, or approximately 41% of the Company's current workforce, significant scaling back of all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study, as well as the reduction in general and administrative expenses; (ii) sharing equally in the commercial profits and losses with Nestle pursuant to the 2021 License Agreement; and (iii) plans to seek additional capital through financing or other transactions, including drawing the Tranche B Term Loan pursuant to the Oaktree Credit Agreement (see Note 9, Notes Payable), which is expected to become available within the next 12 months based on VOWST net sales forecasts. Management concluded these plans are probable of being effectively implemented and of mitigating the conditions that raised substantial doubt about the Company’s ability to continue as a going concern. The Company expects that its cash and cash equivalents as of September 30, 2023, in conjunction with the impact of the Restructuring Plan, sharing equally in commercial profits and losses of VOWST, and the expected availability of the Tranche B Term Loan from Oaktree, will be sufficient to fund its operating expenses, capital expenditure requirements, and debt service obligations for at least the next 12 months from issuance of these condensed consolidated financial statements. The Company may seek to raise additional capital through financing or other transactions, including through at the market equity offerings. The future viability of the Company beyond 12 months from issuance of these condensed consolidated financial statements is dependent on its ability to raise additional capital to finance its operations. Unaudited Interim Financial Information The accompanying unaudited condensed consolidated financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2022 included in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2022, which was filed with the SEC on March 7, 2023 (the “Annual Report”). The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited consolidated financial statements. The condensed consolidated balance sheet at December 31, 2022 was derived from audited annual financial statements, but does not contain all of the footnote disclosures from the annual financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position, results of operations, and cash flows for the periods presented. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023.

Nature of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2023

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 commercial-stage microbiome therapeutics company focused on the development and commercialization of 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 product, VOWST (fecal microbiota spores, live brpk), formerly called SER-109, was approved by the U.S. Food and Drug Administration (“FDA”) on April 26, 2023 and is the first and only orally administered microbiome therapeutic. VOWST is indicated to prevent the recurrence of Clostridioides difficile infection (“CDI”) in patients 18 or older following antibacterial treatment for recurrent CDI. The Company launched VOWST in the United States with its collaborator, Nestlé Health Science (“Nestlé”), in June 2023.

Building upon VOWST, the Company is progressing the Phase 1b clinical trial of SER-155, a microbiome therapeutic candidate consisting of a 16-strain consortium of cultivated bacteria designed to prevent enteric-derived infections and resulting blood stream infections, as well as induce immune tolerance responses to reduce the incidence of Graft versus Host Disease ("GvHD") in patients undergoing allogeneic hematopoietic stem cell transplantation (“allo-HSCT”). Gastrointestinal microbiome data from the first 100 days of SER-155 Phase 1b open-label study cohort 1 showed the successful engraftment of SER-155 bacterial strains, and a substantial reduction in the cumulative incidence of pathogen domination, a biomarker associated with the risk of serious enteric infections and resulting bloodstream infections, as well as GvHD. The tolerability profile observed was favorable, with no serious adverse events attributed to SER-155 administration. Enrollment in the placebo-controlled cohort 2 portion of the study is ongoing and 100-day topline results are anticipated in the third quarter of 2024.

The Company has built and deploys a reverse translational platform for the discovery and development of microbiome therapeutics, and maintains extensive proprietary know-how that may be used to support future research and development efforts. 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. In addition, the Company owns a valuable intellectual property estate related to the development and manufacture of microbiome therapeutics.

On October 29, 2023, the Company's Board of Directors approved a restructuring plan to prioritize the commercialization of VOWST and the completion of the SER-155 Phase 1b study, while significantly reducing costs and supporting longer-term business sustainability (the "Restructuring Plan"). The Restructuring Plan includes (i) a reduction of the Company's workforce by approximately 41% across the organization, resulting in the elimination of approximately 160 positions; (ii) significantly scaling back all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study; and (iii) reducing general and administrative expenses, including consolidating office space. For additional information on the Restructuring Plan, see Note 17, Subsequent Events.

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. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. Other than VOWST, the Company’s product candidates are in development, and will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to potential commercialization. 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 accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. As of September 30, 2023, the Company had an accumulated deficit of $936,987 and cash and cash equivalents of $169,912.

Primarily as a result of the increased and costly efforts to commercialize VOWST and to continue the research and development efforts for other product candidates and preclinical programs, the Company incurred a net loss of $72,476 and had net operating cash outflows of $69,855 for the nine months ended September 30, 2023. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. 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 condensed consolidated financial statements, the Company believes it is reasonably likely that it will require additional funding to maintain commercial production of VOWST, continue its research and development efforts for other microbiome therapeutic product candidates and preclinical programs, and meet its operational obligations as they come due. These conditions raise substantial doubt about the Company's ability to continue as a going concern.

Management's plans that are intended to mitigate the conditions that raise substantial doubt about the Company’s ability to continue as a going concern include (i) the recently announced Restructuring Plan, which is expected to result in cost savings in 2024 from the reduction in workforce of approximately 160 employees, or approximately 41% of the Company's current workforce, significant scaling back of all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study, as well as the reduction in general and administrative expenses; (ii) sharing equally in the commercial profits and losses with Nestle pursuant to the 2021 License Agreement; and (iii) plans to seek additional capital through financing or other transactions, including drawing the Tranche B Term Loan pursuant to the Oaktree Credit Agreement (see Note 9, Notes Payable), which is expected to become available within the next 12 months based on VOWST net sales forecasts.

Management concluded these plans are probable of being effectively implemented and of mitigating the conditions that raised substantial doubt about the Company’s ability to continue as a going concern. The Company expects that its cash and cash equivalents as of September 30, 2023, in conjunction with the impact of the Restructuring Plan, sharing equally in commercial profits and losses of VOWST, and the expected availability of the Tranche B Term Loan from Oaktree, will be sufficient to fund its operating expenses, capital expenditure requirements, and debt service obligations for at least the next 12 months from issuance of these condensed consolidated financial statements. The Company may seek to raise additional capital through financing or other transactions, including through at the market equity offerings. The future viability of the Company beyond 12 months from issuance of these condensed consolidated financial statements is dependent on its ability to raise additional capital to finance its operations.

Unaudited Interim Financial Information

The accompanying unaudited condensed consolidated financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2022 included in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2022, which was filed with the SEC on March 7, 2023 (the “Annual Report”).

The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited consolidated financial statements. The condensed consolidated balance sheet at December 31, 2022 was derived from audited annual financial statements, but does not contain all of the footnote disclosures from the annual financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position, results of operations, and cash flows for the periods presented. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023.

Leases - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2023	Apr. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Apr. 01, 2022
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 ten years.
Lease renewal term (in years)								5 years
Lease term								10 years
Right-of-use asset			$ 108,105		$ 108,105		$ 110,984
Present value of operating lease liabilities			111,143		111,143		$ 111,543
Leases Payments			$ 4,399	$ 1,937	$ 11,687	$ 5,382
Weighted average remaining lease term			8 years 2 months 23 days	4 years 7 months 20 days	8 years 2 months 23 days	4 years 7 months 20 days
Weighted average incremental borrowing rate			13.00%	10.00%	13.00%	10.00%
Spring House, PA [Member]
Operating Leased Assets [Line Items]
Right-of-use asset								$ 3,546
Tenant improvement allowance		$ 1,184
Present value of operating lease liabilities								1,210
Leasehold Improvements								$ 2,336
Irvine, CA [Member]
Operating Leased Assets [Line Items]
Lease renewal term (in years)	5 years
Lease term	6 years
Right-of-use asset			$ 0		$ 0
Present value of operating lease liabilities
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease, remaining term					10 years
Lease renewal term (in years)			10 years		10 years
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease, remaining term					1 year
Lease renewal term (in years)			1 year		1 year
Minimum [Member] \| Spring House, PA [Member]
Operating Leased Assets [Line Items]
Leases Payments		$ 3,029
Minimum [Member] \| Irvine, CA [Member]
Operating Leased Assets [Line Items]
Leases Payments	$ 1,084

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Statement of Cash Flows [Abstract]
Accrued Expenses and Other current and Long-term Liabilities Related Party Amounts	$ (227)	$ (2,429)

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2023

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 (in thousands, except share and per share data):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss attributable to common stockholders	$	(47,854	)	$	(60,002	)	$	(72,476	)	$	(181,361	)
Denominator:
Weighted-average shares outstanding - basic and diluted		128,289,871			122,527,275			127,297,667			102,380,700
Net loss per share attributable to common stockholders - basic and diluted	$	(0.37	)	$	(0.49	)	$	(0.57	)	$	(1.77	)

Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:
Stock options to purchase common stock		16,370,123			14,908,709			16,370,123			14,908,709
Unvested restricted stock units		3,826,695			1,601,288			3,826,695			1,601,288
Shares issuable under employee stock purchase plan		139,649			62,010			47,061			20,897
Warrants to purchase common stock		1,177,433			—			1,177,433			—

Condensed Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss (Income) [Member]
Beginning balance at Dec. 31, 2021	$ 131,507	$ 92	$ 745,829	$ (614,354)	$ (60)
Beginning balance, shares at Dec. 31, 2021		91,889,418
Issuance of common stock upon exercise of stock options, value	257		257
Issuance of common stock upon exercise of stock options, shares		92,478
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		69,195
Issuance of common stock under ESPP, value	892		892
Issuance of common stock under ESPP, shares		159,214
Stock-based compensation expense	5,079		5,079
Other comprehensive income (loss)	(155)				(155)
Net income (loss)	(56,624)			(56,624)
Ending balance at Mar. 31, 2022	80,956	$ 92	752,057	(670,978)	(215)
Ending balance, shares at Mar. 31, 2022		92,210,305
Beginning balance at Dec. 31, 2021	131,507	$ 92	745,829	(614,354)	(60)
Beginning balance, shares at Dec. 31, 2021		91,889,418
Net income (loss)	(181,361)
Ending balance at Sep. 30, 2022	67,585	$ 124	863,294	(795,715)	(118)
Ending balance, shares at Sep. 30, 2022		124,410,917
Beginning balance at Mar. 31, 2022	80,956	$ 92	752,057	(670,978)	(215)
Beginning balance, shares at Mar. 31, 2022		92,210,305
Issuance of common stock upon exercise of stock options, value	130		130
Issuance of common stock upon exercise of stock options, shares		39,208
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		57,431
Stock-based compensation expense	6,748		6,748
Other comprehensive income (loss)	(41)				(41)
Net income (loss)	(64,735)			(64,735)
Ending balance at Jun. 30, 2022	23,058	$ 92	758,935	(735,713)	(256)
Ending balance, shares at Jun. 30, 2022		92,306,944
Issuance of common stock, net of issuance costs, value	96,721	$ 32	96,689
Issuance of common stock, net of issuance costs, shares		31,746,030
Issuance of common stock upon exercise of stock options, value	429		429
Issuance of common stock upon exercise of stock options, shares		150,477
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		44,120
Issuance of common stock under ESPP, value	877		877
Issuance of common stock under ESPP, shares		163,346
Stock-based compensation expense	6,364		6,364
Other comprehensive income (loss)	138				138
Net income (loss)	(60,002)			(60,002)
Ending balance at Sep. 30, 2022	67,585	$ 124	863,294	(795,715)	(118)
Ending balance, shares at Sep. 30, 2022		124,410,917
Beginning balance at Dec. 31, 2022	$ 10,783	$ 125	875,181	(864,511)	(12)
Beginning balance, shares at Dec. 31, 2022	125,222,273	125,222,273
Issuance of common stock upon exercise of stock options, value	$ 188		188
Issuance of common stock upon exercise of stock options, shares		56,523
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		259,023
Issuance of common stock under ESPP, value	1,229	$ 1	1,228
Issuance of common stock under ESPP, shares		267,615
Issuance of common stock from at the market equity offering, value	4,239	$ 1	4,238
Issuance of common stock from at the market equity offering, shares		787,170
Stock-based compensation expense	6,850		6,850
Other comprehensive income (loss)	14				14
Net income (loss)	(71,174)			(71,174)
Ending balance at Mar. 31, 2023	(47,871)	$ 127	887,685	(935,685)	2
Ending balance, shares at Mar. 31, 2023		126,592,604
Beginning balance at Dec. 31, 2022	$ 10,783	$ 125	875,181	(864,511)	(12)
Beginning balance, shares at Dec. 31, 2022	125,222,273	125,222,273
Issuance of common stock upon exercise of stock options, shares	260,640
Net income (loss)	$ (72,476)
Ending balance at Sep. 30, 2023	$ (15,123)	$ 129	921,735	(936,987)
Ending balance, shares at Sep. 30, 2023	128,630,689	128,630,689
Beginning balance at Mar. 31, 2023	$ (47,871)	$ 127	887,685	(935,685)	2
Beginning balance, shares at Mar. 31, 2023		126,592,604
Issuance of common stock upon exercise of stock options, value	168		168
Issuance of common stock upon exercise of stock options, shares		49,069
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		177,629
Issuance of common stock from at the market equity offering, value	7,491	$ 1	7,490
Issuance of common stock from at the market equity offering, shares		1,218,377
Issuance of warrants, Shares	2,785		2,785
Stock-based compensation expense	13,492		13,492
Other comprehensive income (loss)	(3)				(3)
Net income (loss)	46,552			46,552
Ending balance at Jun. 30, 2023	22,614	$ 128	911,620	(889,133)	(1)
Ending balance, shares at Jun. 30, 2023		128,037,679
Issuance of common stock upon exercise of stock options, value	521		521
Issuance of common stock upon exercise of stock options, shares		155,048
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		102,885
Issuance of common stock under ESPP, value	922	$ 1	921
Issuance of common stock under ESPP, shares		335,077
Stock-based compensation expense	8,673		8,673
Other comprehensive income (loss)	1				$ 1
Net income (loss)	(47,854)			(47,854)
Ending balance at Sep. 30, 2023	$ (15,123)	$ 129	$ 921,735	$ (936,987)
Ending balance, shares at Sep. 30, 2023	128,630,689	128,630,689

Common Stock and Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested Restricted Stock Units, Beginning Balance \| shares	1,549,540
Number of Shares, Granted \| shares	3,128,818
Number of Shares, Vested \| shares	(539,537)
Number of Shares, Forfeited \| shares	(312,126)
Number of Shares, Unvested Restricted Stock Units, Ending Balance \| shares	3,826,695
Weighted Average Grant Date Fair Value, Unvested Restricted Stock Units, Beginning Balance \| $ / shares	$ 9.37
Weighted Average Grant Date Fair Value, Granted \| $ / shares	5.45
Weighted Average Grant Date Fair Value, Vested \| $ / shares	9.62
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	8.13
Weighted Average Grant Date Fair Value, Unvested Restricted Stock Units, Ending Balance \| $ / shares	$ 6.23

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($)
$ in Thousands

Sep. 30, 2023

Dec. 31, 2022

Payables and Accruals [Abstract]

Clinical and development costs

$ 1,491

$ 6,717

Manufacturing and quality costs

1,719

Payroll and payroll-related costs

13,479

14,709

Collaboration payable - related party (Note 16)

34,543

34,770

Facility and other

2,926

3,644

Total accrued expenses and other current liabilities

^[1]

$ 54,158

$ 59,840

[1]	Includes related party amounts of $34,543 and $34,770 at September 30, 2023 and December 31, 2022, respectively (see Note 16)

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Sep. 30, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

The significant accounting policies and estimates used in preparation of the unaudited condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2022, and the notes thereto, which are included in the Annual Report. There have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2023, with the exception of those detailed below.

Inventories

Inventories are stated at the lower of cost or estimated net realizable value with cost based on the first-in first-out method. Inventory that can be used in either the production of clinical or commercial products is expensed as research and development costs when identified for use in clinical trials.

Prior to the regulatory approval of its product candidates, the Company incurs expenses for the manufacture of drug product supplies to support clinical development that could potentially be available to support the commercial launch of those drugs. Until the date at which regulatory approval has been received or is otherwise considered probable, the Company records all such costs as research and development expenses.

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 unaudited condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. In the unaudited condensed 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 those estimates.

Restricted Cash

The Company held restricted cash of $8,185 as of September 30, 2023 and December 31, 2022, which represents cash held for the benefit of the landlords for certain of the Company’s leases. The Company has classified the restricted cash as long-term on its condensed consolidated balance sheets as the terms of the underlying leases are greater than one year.

Cash, cash equivalents and restricted cash were comprised of the following (in thousands):


	September 30,		December 31,
	2023		2022
Cash and cash equivalents	$	169,912	$	163,030
Restricted cash, non-current		8,185		8,185
Total cash, cash equivalents and restricted cash	$	178,097	$	171,215

Net Loss per Share - Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss attributable to common stockholders	$ (47,854)	$ 46,552	$ (71,174)	$ (60,002)	$ (64,735)	$ (56,624)	$ (72,476)	$ (181,361)
Denominator:
Weighted-average shares outstanding - basic	128,289,871			122,527,275			127,297,667	102,380,700
Weighted-average shares outstanding - diluted	128,289,871			122,527,275			127,297,667	102,380,700
Net loss per share attributable to common stockholders - basic	$ (0.37)			$ (0.49)			$ (0.57)	$ (1.77)
Net loss per share attributable to common stockholders - diluted	$ (0.37)			$ (0.49)			$ (0.57)	$ (1.77)
Employee Stock Option
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:	16,370,123			14,908,709			16,370,123	14,908,709
Unvested Restricted Stock Units [Member]
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:	3,826,695			1,601,288			3,826,695	1,601,288
Shares Issuable under employee stock purchase plan [Member]
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:	139,649			62,010			47,061	20,897
Common Stock [Member] \| Warrants [Member]
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:	1,177,433						1,177,433

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
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	240,000,000	200,000,000
Common stock, shares issued	128,630,689	125,222,273
Common stock, shares outstanding	128,630,689	125,222,273
Related Party
Related parties, current	$ 34,543	$ 34,770

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Cash, Cash Equivalents and Restricted Cash

Cash, cash equivalents and restricted cash were comprised of the following (in thousands):


	September 30,		December 31,
	2023		2022
Cash and cash equivalents	$	169,912	$	163,030
Restricted cash, non-current		8,185		8,185
Total cash, cash equivalents and restricted cash	$	178,097	$	171,215

Inventories (Table)

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Schedule of Capitalized Inventories

Capitalized inventories consist of the following at September 30, 2023 (in thousands):


	September 30, 2023
Raw materials	$	3,532
Work in process		14,993
Finished goods		—
Total	$	18,525

Revenue from Contracts with Customers - Additional Information (Detail) - USD ($)				1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 21, 2021	Jul. 01, 2021	Jan. 31, 2016	May 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2022	Nov. 30, 2018	Feb. 29, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement					$ 34,543,000		$ 34,543,000							$ 34,770,000
Upfront collaboration/license fee			$ 120,000,000
2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50.00%
Milestones payments received				$ 125,000,000			125,000,000
Nestle Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment					95,428,000		95,428,000							94,713,000		$ 120,000,000
Maximum development milestone payments to be received					285,000,000		285,000,000
Maximum regulatory payments to be received					375,000,000		375,000,000
Maximum amount to be received on achievement of certain commercial milestones					1,125,000,000		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		200,000,000
Collaboration revenue - related party					310,000	$ 1,947,000	(714,000)	$ 2,475,000
Deferred revenue					95,428,000		95,428,000							$ 96,689,000
Nestle Health Science [Member] \| 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50.00%
Upfront payment received	$ 175,000,000
Maximum Amount To Be Received On Achievement Of Regulatory and Sales Milestones		$ 235,000,000
Maximum amount to be received on achievement of sales milestones		225,000,000
Maximum regulatory payments to be received		10,000,000
Transaction price allocated to remaining performance obligations	$ 139,500,000
Termination notice period	60 days
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
License [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party									$ 131,343,000
Service [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to remaining performance obligations	$ 8,157,000
Collaboration revenue - related party					$ 0	$ 1,975,000	$ 1,497,000	$ 3,678,000
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	$ 35,500,000

Condensed Consolidated Statements of Stockholders' (Deficit) Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2023	Mar. 31, 2023
Market Equity Offering [Member]
Issuance costs	$ 304	$ 225

Inventories

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Inventories

5. Inventories

Capitalized inventories consist of the following at September 30, 2023 (in thousands):


	September 30, 2023
Raw materials	$	3,532
Work in process		14,993
Finished goods		—
Total	$	18,525

There were no inventories capitalized as of December 31, 2022, because the Company obtained approval for VOWST from the FDA on April 26, 2023. Prior to this approval, all costs for the manufacture of product supplies to support clinical development and commercial launch, including pre-launch inventory, were expensed as incurred or otherwise accounted for pursuant to the 2021 License Agreement. Pre-launch inventory manufactured prior to the FDA approval of VOWST, which was not capitalized into inventory but instead was expensed as research and development in previous periods, will be used in commercial production until it is depleted. Pre-launch inventory expensed as research and development totaled $0 and $26,794 for the three and nine months ended September 30, 2023, respectively.

Inventory amounts written down as a result of excess, obsolescence, or unmarketability and determined not to be recoverable pursuant to the 2021 License Agreement are expensed in the period in which they are identified. There were no such write-downs during the three and nine months ended September 30, 2023.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2023

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 September 30, 2023 Using:
	Level 1		Level 2		Level 3		Total
Warrant liabilities	$	—	$	—	$	956	$	956
Total liabilities	$	—	$	—	$	956	$	956


	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

Schedule Of Level 3 Inputs to Warrant Liabilities

On the Closing Date (as defined in Note 9, Notes Payable) and as of September 30, 2023, the Level 3 inputs to the warrant liabilities are as follows:



	Closing Date			September 30, 2023
Volatility		83.0	%		75.0	%
Term (in years)		1.7			1.3

Schedule of Reconciliation Company's Liabilities Measured at Fair Value on Recurring Basis

A reconciliation of the beginning and ending balances for the three and nine months ended September 30, 2023 for liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) is as follows (in thousands):


	Warrant Liabilities

Balance as of December 31, 2022	$	—
Issuance of warrants		2,100
Adjustment to fair value		(132	)
Balance as of June 30, 2023		1,968
Adjustment to fair value		(1,012	)
Balance as of September 30, 2023		956

Revenue from Contracts with Customers - Changes in Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Deductions	$ (310)	$ (3,444)	$ 714	$ (6,153)
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Balance at beginning of period			96,689	103,817
Deferred revenue - related party, Additions			1,644	0
Deferred revenue - related party, Deductions			(2,905)	(6,153)
Deferred revenue - related party, Balance at end of period	$ 95,428	$ 97,664	$ 95,428	$ 97,664

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):


	September 30, 2023			December 31, 2022
Laboratory equipment	$	29,133		$	24,533
Computer equipment		4,134			3,557
Furniture and office equipment		5,347			3,491
Leasehold improvements		32,963			32,474
Construction in progress		1,640			3,970
		73,217			68,025
Less: Accumulated depreciation and amortization		(49,651	)		(45,040	)
	$	23,566		$	22,985

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2023	Oct. 30, 2023
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
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
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 Common Stock Shares Outstanding		129,257,199
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ

Revenue from Contracts with Customers

9 Months Ended

Sep. 30, 2023

Revenue from Contract with Customer [Abstract]

Revenue from Contracts with Customers

12. Revenue from Contracts with Customers

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”) (the "2021 License Agreement"). Under the terms of the 2021 License 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 VOWST, previously 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) VOWST 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 was responsible for completing development of the first 2021 Collaboration Product, which is VOWST, in the 2021 Field in the United States until first regulatory approval, which was obtained on April 26, 2023.

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 is responsible for the manufacturing and supply for commercialization under a supply agreement that has been executed between the parties. Both parties performed pre-launch activities of VOWST prior to the first commercial sale in the United States, which occurred in June 2023. The Company was responsible for funding the pre-launch activities until first commercial sale of VOWST in the 2021 Licensed Territory and in accordance with a pre-launch plan, up to a specified cap. The Company is entitled to share equally in the commercial profits and losses of VOWST.

In connection with the 2021 License Agreement, the Company received an upfront payment of $175,000, and the Company received an additional $125,000 milestone payment in May 2023 after FDA approval of VOWST. The Company is eligible to receive additional payments of up to $235,000 if certain regulatory and sales milestones are achieved. The potential future milestone payments include up to $10,000 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 with twelve months’ prior written notice, effective only on or after the third anniversary of first commercial sale of VOWST in the 2021 Licensed Territory. 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) (see Note 13, Collaboration Profit and Loss), 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 VOWST 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 VOWST 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 VOWST and the services to obtain regulatory approval of VOWST 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 VOWST 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 VOWST were not complex or specialized, could be performed by another qualified third party, were not expected to significantly modify or customize the license given that VOWST was late-stage intellectual property that completed clinical development and the services were 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 up-front payment of $175,000 compensated the Company for: (i) the co-exclusive license for VOWST 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 VOWST in the United States and (iii) pre-launch activities performed by Nestlé and the Company until the first commercial sale of VOWST 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 VOWST 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 (see Note 13, Collaboration Profit and Loss).

The Topic 606 transaction price of $139,500 was allocated to the co-exclusive license for VOWST and the services performed in accordance with the development and regulatory activity plan to obtain regulatory approval of VOWST 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 was recognized over time as the Company performed the services, which it completed in April 2023. During the three and nine months ended September 30, 2023 and 2022 the Company recognized $0, $1,975, $1,497, and $3,678 of collaboration revenue - related party, respectively, related to the services performance obligation under the 2021 License Agreement.

The Company determined that any variable consideration related to the remaining 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 Company recognized the $125,000 regulatory milestone payment received in May 2023, which was fully allocated to the license performance obligation, as revenue in the consolidated statements of operations and comprehensive loss during the nine months ended September 30, 2023.

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 or commercialized, as applicable, for the treatment of CDI and IBD, including VOWST, 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 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 will be 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 VOWST, then 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 September 30, 2023, the aggregate amount of the transaction price allocated to the performance obligation of the 2016 License Agreement was approximately $200,000.

During the three and nine months ended September 30, 2023 and 2022, using the cost-to-cost method, which best depicts the transfer of control to the customer, the Company recognized $310, ($714), $1,947, and $2,475 of collaboration revenue – related party, respectively.

As of September 30, 2023 and December 31, 2022, there was $95,428 and $96,689, respectively, of deferred revenue related to the unsatisfied portion of the performance obligation under the Nestlé agreements. As of September 30, 2023 and December 31, 2022, the deferred revenue is classified as current or non-current in the condensed consolidated balance sheets based on the Company’s estimate of revenue that will be recognized within the next 12 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 condensed consolidated statements of operations and comprehensive loss.

Contract Balances from Contracts with Customers

The following table presents changes in the Company’s contract liabilities during the nine months ended September 30, 2023 and 2022 (in thousands):


	Balance as of December 31, 2022		Additions		Deductions			Balance as of September 30, 2023
Nine Months Ended September 30, 2023
Contract liabilities:
Deferred revenue - related party	$	96,689		1,644		(2,905	)	$	95,428


	Balance as of December 31, 2021		Additions		Deductions			Balance as of September 30, 2022
Nine Months Ended September 30, 2022
Contract liabilities:
Deferred revenue - related party	$	103,817		—		(6,153	)	$	97,664

During the three and nine months ended September 30, 2023 and 2022 the Company recognized the following revenues as a result of changes in the contract liability balances in the respective periods (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023			2022
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$	310	$	3,444	$	(714	)	$	6,153

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. During the three months ended March 31, 2023, the Company’s estimate of total costs expected to be incurred increased, resulting in a reversal of revenue based on its cost-to-cost methodology.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-9

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-10

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-15

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-13

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org//606/tableOfContent

+ Details

Common Stock and Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2022:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2022		14,940,034		$	10.03		7.25	$	11,608
Granted		2,507,053
Exercised		(260,640	)
Forfeited		(816,324	)
Outstanding as of September 30, 2023		16,370,123		$	9.47		6.78	$	135
Options exercisable as of September 30, 2023		10,000,136		$	10.05		5.67	$	—

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s restricted stock unit activity since December 31, 2022:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2022		1,549,540		$	9.37
Granted		3,128,818		$	5.45
Vested		(539,537	)	$	9.62
Forfeited		(312,126	)	$	8.13
Unvested restricted stock units as of September 30, 2023		3,826,695		$	6.23

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development expenses	$	4,744	$	3,474	$	16,326	$	9,500
General and administrative expenses		3,929		2,890		12,689		8,691
	$	8,673	$	6,364	$	29,015	$	18,191

Related Party Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	Jul. 31, 2022	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Feb. 29, 2016
Related Party Transaction [Line Items]
Transaction price allocated under collaborative arrangement		$ 34,543				$ 34,543		$ 34,770
Deferred income - related party		$ 9,465				9,465		$ 0
Proceeds from issuance of common stock						$ 0	$ 100,000
Common stock at a purchase price		$ 0.001				$ 0.001		$ 0.001
Nestle Health Science [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party		$ 310		$ 1,947		$ (714)	2,475
Deferred revenue		95,428				95,428		$ 94,713	$ 120,000
Due from related party		0				0		0
Nestle Health Science [Member] \| 2021 License Agreement [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party		0		$ 1,497		126,975	$ 3,678
Deferred revenue		0				0		1,976
Payment for collaboration receivable		14,387				14,387
Payments under agreements with related party		12,457				25,876
Due from related party		16,857				16,857		0
TPC, Inc. [Member] \| Research and Development Expenses [Member]
Related Party Transaction [Line Items]
Option Payment1			$ 833		$ 833
Accrued Expenses and Other Liabilities [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Related Party Transaction [Line Items]
Transaction price allocated under collaborative arrangement		$ 34,543				$ 34,543		$ 34,770
Other Noncurrent Assets [Member] \| TPC, Inc. [Member]
Related Party Transaction [Line Items]
Option Payment1	$ 833

Common Stock and Stock-Based Awards - Restricted Stock Units - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Oct. 31, 2024 USD ($)	Oct. 31, 2022 $ / shares shares	Sep. 30, 2023 USD ($) shares	Mar. 31, 2023 $ / shares shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($) shares	Dec. 31, 2022 USD ($)	Dec. 31, 2021 Employee $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense for stock options \| $			$ 8,673		$ 6,364	$ 29,015	$ 18,191
Performance Based Restricted Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee share based compensation expense \| $						815		$ 815
Weighted average grant-date fair value of stock options \| $ / shares				$ 5.5
Stock based compensation expense for stock options \| $			$ 1,610			$ 4,378
Number of employees granted \| Employee									2
Number of shares granted			0	1,322,715		1,322,715
Service Based Restricted Stock Units (RSUs)[Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted			85,308		114,600	1,806,103	1,224,494
Vesting period						4 years
Service Based Restricted Stock Units (RSUs)[Member] \| Vesting After One Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage						25.00%
Service Based Restricted Stock Units (RSUs)[Member] \| Vesting Quarterly Over Next 3 Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage						75.00%
Forecast [Member] \| Performance Based Restricted Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense for stock options \| $	$ 2,459
Employee One [Member] \| Performance Based Restricted Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options \| $ / shares									$ 9.59
Number of shares, vested		42,500
Weighted average grant date fair value, vested \| $ / shares		$ 9.59
Number of shares granted									85,000
Employee Two [Member] \| Performance Based Restricted Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options \| $ / shares									$ 20.35
Number of shares, vested		20,000
Weighted average grant date fair value, vested \| $ / shares		$ 20.35
Number of shares granted									40,000

Property and Equipment, Net

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

6. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):


	September 30, 2023			December 31, 2022
Laboratory equipment	$	29,133		$	24,533
Computer equipment		4,134			3,557
Furniture and office equipment		5,347			3,491
Leasehold improvements		32,963			32,474
Construction in progress		1,640			3,970
		73,217			68,025
Less: Accumulated depreciation and amortization		(49,651	)		(45,040	)
	$	23,566		$	22,985

Depreciation and amortization expense was $1,684, $4,611, $1,747, and $5,002 for the three and nine months ended September 30, 2023 and 2022, respectively.

Notes Payable - Summary of Future Principal Payments Due Under the Oaktree Credit Arrangement, Excluding Interest and End of Term Charge (Detail) $ in Thousands	Sep. 30, 2023 USD ($)
Debt Disclosure [Abstract]
2023 (remaining 3 months)	$ 0
2024	0
2025	0
2026	24,750
2027	33,000
Thereafter	52,250
Total	$ 110,000

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Revenue from Contracts with Customers - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 310	$ 3,444	$ (714)	$ 6,153

Leases

9 Months Ended

Sep. 30, 2023

Leases [Abstract]

Leases

8. Leases

The Company leases real estate, primarily laboratory, office and manufacturing space. The Company’s leases have remaining terms ranging from approximately one 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 ten 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 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 $3,029, net of a tenant improvement allowance of $1,184, over the original ten-year term. The lease

commenced in April 2023, at which point, the Company recorded a right-of-use asset of $3,546, which consists of the lease liability of $1,210, and $2,336 of leasehold improvements that revert back to the lessor at the termination of the lease.

In June 2023, the Company entered into a lease for a donor collection facility in Irvine, California, with a lease term of approximately six years and a renewal option, subject to certain conditions, for an additional five-year term. The undiscounted minimum lease payments are $1,084 over the original seven-year term. As of September 30, 2023, the lease has not yet commenced, and accordingly the Company has not recorded a right-of-use asset or a lease liability with respect thereto.

The following table summarizes the presentation in the Company’s condensed consolidated balance sheets of its operating leases (in thousands):


	September 30, 2023		December 31, 2022
Assets:
Operating lease assets	$	108,105	$	110,984

Liabilities:
Operating lease liabilities	$	6,280	$	3,601
Operating lease liabilities, net of current portion		104,863		107,942
Total operating lease liabilities	$	111,143	$	111,543

The following table summarizes the effect of lease costs in the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Operating lease costs	$	5,544	$	1,785	$	16,496	$	5,405
Short-term lease costs		362		326		1,102		1,035
Variable lease costs		1,699		1,135		5,643		3,437
Total lease costs	$	7,605	$	3,246	$	23,241	$	9,877

During the three and nine months ended September 30, 2023 and 2022, the Company made cash payments for operating leases of $4,399, $11,687, $1,937, and $5,382 respectively.

As of September 30, 2023, future payments of operating lease liabilities are as follows (in thousands):


	As of September 30, 2023
2023 (remaining 3 months)	$	4,221
2024	$	19,437
2025	$	21,555
2026	$	22,155
2027 and thereafter	$	111,164
Total future minimum lease payments	$	178,532
Less: interest		(67,389	)
Present value of operating lease liabilities	$	111,143

As of September 30, 2023, the weighted average remaining lease term was 8.23 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%. As of September 30, 2022, the weighted average remaining lease term was 4.64 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 10%.

Investments (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Schedule of Investments by Security Type

Investments by security type consisted of the following at December 31, 2022 (in thousands):


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
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

Excluded from the table above are restricted investments of $1,401, as the cost approximated fair value as of December 31, 2022.

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Commitments and Contingencies

9 Months Ended

Sep. 30, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

14. Commitments and Contingencies

Leases

Refer to Note 8, 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 not accrued any liabilities related to such obligations in its consolidated financial statements as of September 30, 2023 or December 31, 2022.

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 not accrue any liabilities related to legal contingencies in its consolidated financial statements as of September 30, 2023 or December 31, 2022.

Income Taxes

9 Months Ended

Sep. 30, 2023

Income Tax Disclosure [Abstract]

Income Taxes

15. Income taxes

The Company did not provide for any income taxes in its condensed consolidated statement of operations and comprehensive loss for the three and nine months ended September 30, 2023 and 2022. Management has considered the Company’s history of cumulative net losses incurred since inception, its early stage of commercialization of VOWST, and its projection of book and tax losses for the twelve months ended December 31, 2023. Based on its evaluation of the positive and negative evidence bearing upon its ability to realize its deferred tax assets, the Company determined that it is more likely than not that it will not realize such benefits. Accordingly, the Company has recorded a full valuation allowance against its deferred tax assets as of September 30, 2023 and December 31, 2022, and has not recorded any income taxes for the three and nine months ended September 30, 2023 and 2022. Management reevaluates the positive and negative evidence at each reporting period.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Investments

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Investments

4. Investments

As of September 30, 2023, the Company held restricted investments of $1,401, the cost of which approximates current fair value. The Company did not hold any other investments as of September 30, 2023.

Investments by security type consisted of the following at December 31, 2022 (in thousands):


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
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

Excluded from the table above are restricted investments of $1,401, as the cost approximated fair value as of December 31, 2022. Investments with original maturities of less than 90 days are included in cash and cash equivalents on the condensed consolidated balance sheets and are not included in the table above. Investments with maturities of less than 12 months are considered current assets and those investments with maturities greater than 12 months are considered non-current assets. As of December 31, 2022, all of the Company’s investments were classified as available-for-sale and mature within 12 months of the balance sheet date.

Condensed Consolidated Statements of Cash Flows - USD ($)
$ in Thousands

9 Months Ended

Sep. 30, 2023

Sep. 30, 2022

Cash flows from operating activities:

Net income (loss)

$ (72,476)

$ (181,361)

Adjustments to reconcile net loss to net cash provided by (used in) operating activities:

Stock-based compensation expense

29,015

18,191

Depreciation and amortization expense

4,611

5,002

Non-cash operating lease cost

6,450

3,558

Net (accretion) amortization of (discounts) premiums on investments

(236)

676

Amortization of debt issuance costs

730

553

Loss on extinguishment of debt

1,625

Change in fair value of warrant liabilities

(1,144)

Collaboration (profit) loss sharing - related party

5,158

346

Changes in operating assets and liabilities:

Prepaid expenses and other current and other non-current assets

2,504

(12,899)

Collaboration receivable - related party

(16,857)

Inventories

(18,525)

Deferred income - related party

9,465

Deferred revenue - related party

(1,261)

(6,153)

Accounts payable

(6,539)

(3,250)

Operating lease liabilities

(1,635)

(3,520)

Accrued expenses and other current and long-term liabilities (3)

^[1]

(10,740)

2,933

Net cash used in operating activities

(69,855)

(175,924)

Cash flows from investing activities:

Purchases of property and equipment

(7,098)

(6,360)

Purchases of investments

(4,426)

(36,138)

Sales and maturities of investments

22,983

119,000

Net cash provided by investing activities

11,459

76,502

Cash flows from financing activities:

Proceeds from exercise of stock options

877

816

Proceeds from issuance of common stock

100,000

Issuance costs paid for common stock

(3,279)

Proceeds from issuance of common stock from at the market equity offering, net of issuance costs

11,730

Issuance of common stock under ESPP

2,151

1,769

Proceeds from issuance of debt, net of issuance costs

103,378

27,606

Repayment of notes payable

(52,860)

(1,907)

Net cash provided by financing activities

65,276

125,005

Net increase (decrease) in cash, cash equivalents, and restricted cash

6,880

25,583

Effect of exchange rate changes on cash, cash equivalents, and restricted cash

(2)

Cash, cash equivalents and restricted cash at beginning of period

171,215

188,002

Cash, cash equivalents and restricted cash at end of period

178,097

213,583

Supplemental disclosure of cash flow information:

Cash paid for interest

8,966

3,282

Supplemental disclosure of non-cash investing and financing activities:

Property and equipment purchases included in accounts payable and accrued expenses

370

1,061

Prepaid rent reclassified to right-of-use assets

2,336

4,962

Lease liability arising from obtaining right-of-use assets

1,235

4,370

Recognition of warrant liabilities

2,100

Warrants issued related to Term Loan and recorded as debt discount

$ 2,785

$ 0

[1]	Includes related party amounts of $227 and $2,429 at September 30, 2023 and 2022, respectively (see Note 16)

Inventories - Schedule of Capitalized Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials	$ 3,532
Work in process	14,993
Finished goods	0
Total	$ 18,525	$ 0

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Restricted cash	$ 8,185	$ 8,185

Revenue from Contracts with Customers (Tables)

9 Months Ended

Sep. 30, 2023

Revenue from Contract with Customer [Abstract]

Changes in Contract Liabilities

The following table presents changes in the Company’s contract liabilities during the nine months ended September 30, 2023 and 2022 (in thousands):


	Balance as of December 31, 2022		Additions		Deductions			Balance as of September 30, 2023
Nine Months Ended September 30, 2023
Contract liabilities:
Deferred revenue - related party	$	96,689		1,644		(2,905	)	$	95,428


	Balance as of December 31, 2021		Additions		Deductions			Balance as of September 30, 2022
Nine Months Ended September 30, 2022
Contract liabilities:
Deferred revenue - related party	$	103,817		—		(6,153	)	$	97,664


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023			2022
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$	310	$	3,444	$	(714	)	$	6,153

Fair Value Measurements - Schedule of Reconciliation Company's Liabilities Measured at Fair Value on Recurring Basis (Detail) - Warrant [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Sep. 30, 2023	Jun. 30, 2023
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,968	$ 0
Issuance of warrants		2,100
Adjustment to fair value	(1,012)	(132)
Ending Balance	$ 956	$ 1,968

Investments - Schedule of Investments by Security Type (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 18,321
Gross Unrealized Gain	3
Gross Unrealized Loss	(13)
Fair Value	18,311
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,465
Gross Unrealized Gain	0
Gross Unrealized Loss	0
Fair Value	2,465
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,958
Gross Unrealized Gain	0
Gross Unrealized Loss	(1)
Fair Value	2,957
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,898
Gross Unrealized Gain	3
Gross Unrealized Loss	(12)
Fair Value	$ 12,889

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Condensed Consolidated Balance Sheets - USD ($)
$ in Thousands

Sep. 30, 2023

Dec. 31, 2022

Current assets:

Cash and cash equivalents

$ 169,912

$ 163,030

Short term investments

18,311

Collaboration receivable - related party

16,857

Inventories

18,525

Prepaid expenses and other current assets

9,100

13,423

Total current assets

214,394

194,764

Property and equipment, net

23,566

22,985

Operating lease assets

108,105

110,984

Restricted cash

8,185

Restricted investments

1,401

Other non-current assets

12,048

10,465

Total assets

367,699

348,784

Current liabilities:

Accounts payable

8,958

17,440

Accrued expenses and other current liabilities

^[1]

54,158

59,840

Operating lease liabilities

6,280

3,601

Short term portion of note payable, net of discount

456

Deferred income - related party

9,465

Deferred revenue - related party

364

4,259

Total current liabilities

79,225

85,596

Long term portion of note payable, net of discount

101,135

50,591

Operating lease liabilities, net of current portion

104,863

107,942

Deferred revenue, net of current portion - related party

95,064

92,430

Warrant liabilities

956

Other long-term liabilities

1,579

1,442

Total liabilities

382,822

338,001

Commitments and contingencies (Note 14)

Stockholders' (deficit) equity:

Preferred stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2023 and December 31, 2022; no shares issued and outstanding at September 30, 2023 and December 31, 2022

Common stock, $0.001 par value; 240,000,000 and 200,000,000 shares authorized at September 30, 2023 and December 31, 2022, respectively; 128,630,689 and 125,222,273 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively

129

125

Additional paid-in capital

921,735

875,181

Accumulated other comprehensive loss

(12)

Accumulated deficit

(936,987)

(864,511)

Total stockholders' (deficit) equity

(15,123)

10,783

Total liabilities and stockholders' (deficit) equity

$ 367,699

$ 348,784

[1]	Includes related party amounts of $34,543 and $34,770 at September 30, 2023 and December 31, 2022, respectively (see Note 16)

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ in Thousands		3 Months Ended						9 Months Ended
	Oct. 29, 2023 Employee	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
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		$ 936,987						$ 936,987		$ 864,511
Cash and cash equivalents		169,912						169,912		$ 163,030
Net operating cash outflows								(69,855)	$ (175,924)
Net Income (Loss)		$ (47,854)	$ 46,552	$ (71,174)	$ (60,002)	$ (64,735)	$ (56,624)	$ (72,476)	$ (181,361)
Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Reduction in workforce, percentage	41.00%
Number of positions eliminated \| Employee	160

Common Stock and Stock-Based Awards

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Common Stock and Stock-Based Awards

10. Common Stock and Stock-Based Awards

On March 29, 2023, the Company’s board of directors adopted a resolution to amend the Restated Certificate of Incorporation, subject to stockholder approval, by increasing the number of authorized shares of the Company’s Common Stock from 200,000,000 shares to 240,000,000 shares (the “Share Increase Amendment”). At the Company’s annual meeting of stockholders held on June 22, 2023, the Company’s stockholders approved the Share Increase Amendment. On June 27, 2023, the Company amended its Restated Certificate of Incorporation to reflect the Share Increase Amendment.

On May 21, 2021, the Company entered into a Sales Agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock, with aggregate gross sales proceeds of up to $150,000, from time to time, through an “at the market” equity offering program under which Cowen acts as sales agent. During the nine months ended September 30, 2023, the Company sold 2,005,547 shares of common stock under the Sales Agreement, at an average price of approximately $6.11 per share, raising aggregate net proceeds of approximately $11,730, after deducting an aggregate commission of approximately 3% and other issuance costs. During the three and nine months ended September 30, 2022, the Company did not sell any shares of common stock under the Sales Agreement.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2022:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2022		14,940,034		$	10.03		7.25	$	11,608
Granted		2,507,053
Exercised		(260,640	)
Forfeited		(816,324	)
Outstanding as of September 30, 2023		16,370,123		$	9.47		6.78	$	135
Options exercisable as of September 30, 2023		10,000,136		$	10.05		5.67	$	—

The weighted average grant date fair value of stock options granted during the three and nine months ended September 30, 2023 and 2022 was $3.14, $4.52, $4.07, and $5.53 per share, respectively.

During the year ended December 31, 2021, the Company granted performance-based stock options to employees for the purchase of an aggregate of approximately 562,000 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. In April 2023, the performance target associated with 50% of the performance-based stock options was achieved. Accordingly, the Company recorded $109 and $2,481 of compensation expense during the three and nine months ended September 30, 2023, respectively, with respect to these performance-based stock options, which represents a cumulative catch-up from the grant date through the achievement of the performance targets, and vesting of the remaining 50% of the options beginning in April 2023. The remaining compensation expense associated with these performance-based stock options will be recognized ratably through April 2024, for all such options for which ongoing performance targets are achieved and service requirements are met.

Restricted Stock Units

The following table summarizes the Company’s restricted stock unit activity since December 31, 2022:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2022		1,549,540		$	9.37
Granted		3,128,818		$	5.45
Vested		(539,537	)	$	9.62
Forfeited		(312,126	)	$	8.13
Unvested restricted stock units as of September 30, 2023		3,826,695		$	6.23

The Company has granted restricted stock units with service-based vesting conditions (“RSUs”) and performance-based vesting conditions (“PSUs”). RSUs and PSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. RSUs and PSUs may not be sold or transferred by the holder and vest according to the service-based or performance-based vesting conditions of the award. During the three and nine months ended September 30, 2023 and 2022, the Company granted 85,308, 1,806,103, 114,600, and 1,224,494 RSUs, respectively. During the three and nine months ended September 30, 2023, the Company granted 0 and 1,322,715 PSUs, respectively. The Company did not grant any PSUs during the three and nine months ended September 30, 2022. 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. PSUs vest according to the performance requirements of the awards, generally when the Company has determined that the specified performance targets have been achieved.

During the year ended December 31, 2021, the Company granted PSUs 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 of common stock with a grant date fair value of $20.35 per share. These PSUs vest only upon achievement of specified performance targets. In October 2022, 42,500 of the PSUs with a grant date fair value of $9.59, and 20,000 of the PSUs 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 PSUs. In April 2023, the remaining PSUs underlying these awards vested because the associated targets were achieved. Accordingly, the Company recorded the remaining $815 in compensation expense during the nine months ended September 30, 2023, with respect to these PSUs.

During the three months ended March 31, 2023, the Company granted PSUs to employees for the purchase of an aggregate of 1,322,715 shares of common stock with a grant date fair value of $5.50. These PSUs begin to vest ratably only upon achievement of specified performance targets, which were achieved in April 2023. Accordingly, the Company recorded $1,610 and $4,378 in compensation expense during the three and nine months ended September 30, 2023, respectively, with respect to these PSUs. The remaining $2,459 in compensation expense associated with these PSUs will be recognized ratably through October 2024.

Stock-based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development expenses	$	4,744	$	3,474	$	16,326	$	9,500
General and administrative expenses		3,929		2,890		12,689		8,691
	$	8,673	$	6,364	$	29,015	$	18,191

Common Stock and Stock-Based Awards - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Equity [Abstract]
Number of Shares, Beginning Balance	14,940,034
Number of Shares, Granted	2,507,053
Number of Shares, Exercised	(260,640)
Number of Shares, Forfeited	(816,324)
Number of Shares, Ending Balance	16,370,123	14,940,034
Number of Shares, Options Exercisable	10,000,136
Weighted Average Exercise Price, Beginning Balance \| $ / shares	$ 10.03
Weighted Average Exercise Price, Ending Balance \| $ / shares	9.47	$ 10.03
Weighted Average Exercise Price, Options Exercisable \| $ / shares	$ 10.05
Weighted Average Remaining Contractual Term, Outstanding	6 years 9 months 10 days	7 years 3 months
Weighted Average Remaining Contractual Term, Options Exercisable	5 years 8 months 1 day
Aggregate Intrinsic Value, Outstanding \| $	$ 135	$ 11,608
Aggregate Intrinsic Value, Options Exercisable \| $	$ 0

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Unrealized (loss) gain on investments, net of tax	$ 0	$ 0	$ 0	$ 0

Notes Payable

9 Months Ended

Sep. 30, 2023

Debt Disclosure [Abstract]

Notes Payable

9. Notes Payable

On October 29, 2019 (“Hercules Closing Date”), the Company entered into a Loan and Security Agreement (the “Hercules Loan Agreement”) with Hercules Capital, Inc. (“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. Effective as of February 24, 2022 (the “Effective Date”), the Company entered into an Amendment to the Hercules Loan Agreement (the “Amendment”), with the lenders party thereto (the “Hercules Lenders”), and Hercules in its capacity as the administrative agent and the collateral agent for the Hercules Lenders, which amended the Original Credit Facility. Pursuant to the Amendment, term loans

in an aggregate principal amount of up to $100,000 (the “Hercules 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 and fifth tranches, in aggregate principal amounts of $25,000 each, were available upon satisfaction of certain conditions, but were not drawn before the repayment and extinguishment of the Hercules Credit Facility.

All advances outstanding under the Hercules Credit Facility bore 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%. The Company had the option to prepay advances under the Hercules Credit Facility, in whole or in part, at any time subject to a prepayment charge, and the Hercules Loan Agreement included an end of term charge of 4.85% of the aggregate amount of the advances made under the Original Credit Facility, as well as an additional end of term charge of 1.75% of the aggregate amount of the advances under the Hercules Credit Facility (including the first tranche of $25,000), each due as specified in the Amendment.

The Hercules Credit Facility was secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company agreed to not pledge or secure its intellectual property to others.

The Company accounted for the Amendment as a modification in accordance with the guidance in ASC 470-50, Debt ("ASC 470"). Amounts paid to the Hercules Lenders were recorded as debt discount and a new effective interest rate was established. Upon issuance, the Hercules Credit Facility was recorded as a liability with an initial carrying value of $50,586, net of debt issuance costs. The initial carrying value was 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 debt. As of December 31, 2022, the carrying value of the debt was $51,047.

On April 27, 2023 (the “Closing Date”), the Company entered into the Credit Agreement and Guaranty (the “Oaktree Credit Agreement”) among the Company, the subsidiary guarantors from time to time party thereto, the lenders from time to time party thereto (the “Lenders”), and Oaktree Fund Administration, LLC, in its capacity as administrative agent for the Lenders (in such capacity, the “Agent”). The Oaktree Credit Agreement establishes a term loan facility of $250,000 (the “Term Loan”) consisting of (i) $80,000 (“Tranche A-1”) and (ii) $30,000 (“Tranche A-2” and collectively, “Tranche A Loan”), funded on the Closing Date. The Term Loan also consists of (i) $45,000 (the “Tranche B Loan”) and (iii) $45,000 (the “Tranche C Loan”), each of which the Company may borrow subject to certain conditions, and (iv) $50,000 (the “Tranche D Loan”) available in Oaktree’s sole discretion. The Tranche B Loan may be drawn by the Company until September 30, 2024, if VOWST net sales for the trailing six consecutive months are at least $35,000 and at least 4.5% greater in the calendar quarter prior to the Applicable Funding Date (as defined in the Oaktree Credit Agreement) over the calendar quarter immediately preceding it. The Tranche C Loan may be drawn until September 30, 2025, if VOWST net sales for the trailing 12 consecutive months are at least $120,000 and at least 4.5% greater in each of the two calendar quarters prior to the Applicable Funding Date relative, in each case, to the calendar quarter immediately preceding it. The Term Loan has a maturity date of April 27, 2029 (the “Maturity Date”).

Of the $110,000 Tranche A Loan advanced by the Lenders at closing, approximately $53,380 repaid the Company’s existing credit facility with Hercules. After deducting other transaction expenses and fees, the Company received net proceeds of approximately $50,446. The Company accounted for the repayment of the Hercules Credit Facility as an extinguishment in accordance with the guidance in ASC 470-50, and recognized a loss on extinguishment of $1,625 in other income (expense) in the accompanying condensed consolidated statements of operations and comprehensive loss for the nine months ended September 30, 2023.

Borrowings under the Term Loan bear interest at a rate per annum equal to the three-month term Secured Overnight Financing Rate (“SOFR”) (subject to a 2.50% floor and a 5.00% cap), plus an applicable margin of 7.875%, payable quarterly in arrears. If certain VOWST net sales targets are met, the applicable margin will be reduced from 7.875% to 7.50% through the Maturity Date. The Company is permitted to make quarterly interest-only payments on the Term Loan for the first three years after the Closing Date. Beginning on June 30, 2026, the Company will be required to make quarterly payments of interest, plus repay 7.50% of the outstanding principal of the Term Loan in quarterly installments until the Maturity Date, unless the interest only period is extended based upon the achievement of certain VOWST net sales targets.

The Company is obligated to pay the Lenders an exit fee equal to 1.50% of the aggregate amount of the Term Loan funded, such exit fee to be due and payable upon the earliest to occur of (1) the Maturity Date, (2) the acceleration of the outstanding Term Loan, and (3) the prepayment of the outstanding Term Loan. The Company may voluntarily prepay the outstanding Term Loan, subject to a customary make-whole for the first two years following the Closing Date plus 4.0% of the principal amount of the Term Loan prepaid, and thereafter a prepayment premium equal to (i) 4.0% of the principal amount of the Term Loan prepaid, if prepaid after the second anniversary of the Closing Date through and including the third anniversary of the Closing Date, (ii) 2.0% of the principal amount of

the Term Loan if prepaid after the third anniversary of the Closing Date through and including the fourth anniversary of the Closing Date, (iii) 1.0% of the principal amount of the Term Loan if prepaid after the fourth anniversary of the Closing Date through and including the fifth anniversary of the Closing Date, with no prepayment premium due after the fifth anniversary of the Closing Date through the Maturity Date.

The Company’s obligations under the Oaktree Credit Agreement and the other Loan Documents (as defined in the Oaktree Credit Agreement) will be guaranteed by any domestic subsidiaries of the Company that become Guarantors (as defined in the Oaktree Credit Agreement), subject to certain exceptions. The Company’s and the Guarantors’ (collectively, the “Loan Parties”) respective obligations under the Oaktree Credit Agreement and the other Loan Documents are secured by first priority security interests in substantially all assets of the Loan Parties, including intellectual property, subject to certain customary thresholds and exceptions. As of September 30, 2023, there are no Guarantors.

The Oaktree Credit Agreement contains customary representations, warranties and affirmative and negative covenants, including a financial covenant requiring the Company to maintain certain levels of cash and cash equivalents in accounts subject to a control agreement in favor of the Agent of at least $30,000 at all times commencing from 30 days after the Closing Date and decreasing to $25,000 of cash and cash equivalents in such controlled accounts after the Company borrows any Tranche B Loan. As of September 30, 2023, the Company is in compliance with all financial covenants pursuant to the Oaktree Credit Agreement.

In addition, the Oaktree Credit Agreement contains certain events of default that entitle the Agent to cause the Company’s indebtedness under the Oaktree Credit Agreement to become immediately due and payable, and to exercise remedies against the Loan Parties and the collateral securing the Term Loan, including cash. In an event of default and for its duration, as defined in the Oaktree Credit Agreement, an additional default interest rate equal to 2.0% per annum may apply to all obligations owed under the Oaktree Credit Agreement.

On the Closing Date, the Company issued to the Lenders warrants to purchase 647,589 shares (subject to certain adjustments) of the Company’s common stock (the “Tranche A Warrant”), at an exercise price per share of $6.69. The Tranche A Warrant is immediately exercisable and the exercise period expires on April 26, 2030. Upon the funding of each of the Tranche B Loan and the Tranche C Loan, the Company is required to issue to the Lenders warrants to purchase 264,922 shares (subject to certain adjustments) of the Company’s common stock on each such funding date at an exercise price equal to the trailing volume weighted average price of the Company’s common stock for the 30 trading days prior to the funding date for each tranche (the “Tranche B Warrant” and the “Tranche C Warrant,” respectively, and together the “Additional Warrants”). The Additional Warrants will be immediately exercisable upon issuance, and the exercise period will expire seven years from the date of issuance.

The Company determined that the Tranche A Loan, the Tranche A Warrant, the commitment by the Lenders to fund the Tranche B Loan and the Tranche C Loan, and the Tranche B Warrant and Tranche C Warrant, are all freestanding financial instruments. On the Closing Date, the Company evaluated the Tranche A Warrant and determined that it meets the requirements for equity classification under ASC 815, Derivatives and Hedging (“ASC 815”). The net proceeds from the Tranche A Loan were allocated to the Tranche A Warrant and the Tranche A Loan using the relative fair value method, and the relative fair value of the Tranche A Warrant, $2,785, is recorded as an increase to additional paid-in-capital on the consolidated statements of stockholder’s equity (deficit), and as a discount to the Tranche A Loan that will be amortized over the life of the Tranche A Loan using the effective interest method. The Company used the Black-Scholes option pricing model to determine the fair value of the Tranche A Warrant. Assumptions used in the Black-Scholes model included the fair market value per share of common stock on the valuation date of $5.32, the exercise price per warrant equal to $6.69, the expected volatility of 111.6%, the risk-free interest rate of 3.57%, the expected term of 7 years and the absence of a dividend.

The Additional Warrants are considered outstanding instruments at the Closing Date of the Oaktree Credit Agreement and in accordance with ASC 815, are initially recognized at their respective fair values as derivative liabilities given the variable settlement amount of their respective aggregate exercise prices. The Company adjusts the carrying values of the Additional Warrants to their respective fair values at each reporting period, until such time that the Additional Warrants are issued and their respective exercise prices become fixed, and the value of the Additional Warrants is reclassified to additional paid-in capital. The Company uses a simulation model to determine the fair value of the Additional Warrants, as described in Note 3, Fair Value Measurements. The fair value of the Tranche B Warrant and Tranche C Warrant derivative liabilities was $1,077, $1,023, $506, and $450 on the Closing Date and at September 30, 2023, respectively.

Changes in the fair values of the Additional Warrants are recorded as other income (expense) in the consolidated statements of operations and comprehensive loss. In addition to the relative fair value of the Tranche A Warrant, the original issue discount and certain debt issuance costs were recorded as a discount to the Tranche A Loan, the total of which will be accreted to the Tranche A Loan as interest expense over the life of the Tranche A Loan using the effective interest method. The fair values of the derivative liabilities associated with the Tranche B Warrant and Tranche C Warrant are recorded as loan commitment prepaid assets on the Closing Date, which are included in the condensed consolidated balance sheets in other non-current assets, and will be reclassified as discounts to the associated Term Loan balances at such time that they are drawn.

The effective interest rate in effect as of September 30, 2023 was 15.9%. As of September 30, 2023, the carrying value of the Term Loan was $101,135, which is classified as a long-term liability on the condensed consolidated balance sheets. The future principal payments due under the Oaktree Credit Agreement, excluding interest and the end of term charge, are as follows:


Year Ending December 31,	Principal
2023 (remaining 3 months)	$	—
2024		—
2025		—
2026		24,750
2027		33,000
Thereafter		52,250
Total	$	110,000

During the three and nine months ended September 30, 2023 and 2022, the Company recognized $4,012, $9,147, $1,727, and $4,140 of interest expense, which is reflected in interest expense on the condensed consolidated statements of operations and comprehensive loss.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Common Stock and Stock-Based Awards - Additional Information (Details) $ / shares in Units, $ in Thousands		3 Months Ended	9 Months Ended
	May 21, 2021 USD ($)	Sep. 30, 2022 shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares	Mar. 29, 2023 shares	Mar. 28, 2023 shares	Dec. 31, 2022 shares
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized \| shares			240,000,000		240,000,000	200,000,000	200,000,000
Proceeds from issuance of common stock			$ 0	$ 100,000
At The Market Equity Offering Program [Member] \| Sales Agreement [Member] \| Cowen And Company, LLC [Member]
Subsidiary, Sale of Stock [Line Items]
Gross proceeds from sale of common stock	$ 150,000,000
Common stock, shares issued \| shares		0	2,005,547	0
Common stock, average share price \| $ / shares			$ 6.11
Proceeds from issuance of common stock			$ 11,730
Percentage of commission on sale of common stock			3

Investments - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Investments [Abstract]
Maximum maturity days for cash equivalents	90 days	90 days
Restricted investments	$ 1,401	$ 1,401

Net Loss per Share

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Net Loss per Share

11. Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss attributable to common stockholders	$	(47,854	)	$	(60,002	)	$	(72,476	)	$	(181,361	)
Denominator:
Weighted-average shares outstanding - basic and diluted		128,289,871			122,527,275			127,297,667			102,380,700
Net loss per share attributable to common stockholders - basic and diluted	$	(0.37	)	$	(0.49	)	$	(0.57	)	$	(1.77	)

Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:
Stock options to purchase common stock		16,370,123			14,908,709			16,370,123			14,908,709
Unvested restricted stock units		3,826,695			1,601,288			3,826,695			1,601,288
Shares issuable under employee stock purchase plan		139,649			62,010			47,061			20,897
Warrants to purchase common stock		1,177,433			—			1,177,433			—

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 be 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. Additionally, for the three and nine months ended September 30, 2023, the warrants to purchase common stock were excluded because the exercise price of the Tranche A Warrants is greater than the average fair value of the Company's common shares, and the necessary conditions for exercise of the Tranche B and Tranche C Warrants had not been met.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Inventories

Use of Estimates

Restricted Cash

Cash, cash equivalents and restricted cash were comprised of the following (in thousands):


	September 30,		December 31,
	2023		2022
Cash and cash equivalents	$	169,912	$	163,030
Restricted cash, non-current		8,185		8,185
Total cash, cash equivalents and restricted cash	$	178,097	$	171,215

- Definition

Disclosure of inventory accounting policy for inventory classes, including, but not limited to, basis for determining inventory amounts, methods by which amounts are added and removed from inventory classes, loss recognition on impairment of inventories, and situations in which inventories are stated above cost.

+ References + Details

Collaboration Profit and Loss - Schedule of Collaboration Profit (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Business Combinations [Abstract]
Share of VOWST net loss	$ 6,463	$ 0	$ 8,604	$ 0
Profit on transfer of VOWST inventory to Nestle	(7,295)	0	(8,568)	0
Collaboration (profit)/loss related to pre-launch activities	313	1,051	5,158	346
Collaboration (profit) loss sharing - related party	$ (519)	$ 1,051	$ 5,194	$ 346

Leases - Schedule of Future Payments of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Leases [Abstract]
2023 (remaining 3 months)	$ 4,221
2024	19,437
2025	21,555
2026	22,155
2027 and thereafter	111,164
Total future minimum lease payments	178,532
Less: interest	(67,389)
Present value of operating lease liabilities	$ 111,143	$ 111,543

Leases - Summary of Operating Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets:
Operating lease assets	$ 108,105	$ 110,984
Liabilities:
Operating lease liabilities	6,280	3,601
Operating lease liabilities, net of current portion	104,863	107,942
Total operating lease liabilities	$ 111,143	$ 111,543

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

7. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Clinical and development costs	$	1,491	$	6,717
Manufacturing and quality costs		1,719		—
Payroll and payroll-related costs		13,479		14,709
Collaboration payable - related party (Note 16)		34,543		34,770
Facility and other		2,926		3,644
	$	54,158	$	59,840

Collaboration Profit and Loss - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Jul. 21, 2021	Jul. 01, 2021
Business Acquisition [Line Items]
Transaction price allocated under collaborative arrangement	$ 34,543		$ 34,543		$ 34,770
Collaboration (profit)/loss related to pre-launch activities	313	$ 1,051	5,158	$ 346
Topic 808 [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Business Acquisition [Line Items]
Transaction price allocated under collaborative arrangement						$ 35,500
Topic 808 [Member] \| Total Liabilities [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Business Acquisition [Line Items]
Transaction price allocated under collaborative arrangement						$ 35,500	$ 35,500
Topic 808 [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Business Acquisition [Line Items]
Transaction price allocated under collaborative arrangement	15,791		15,791		$ 34,770
Research and Development Expenses [Member] \| Topic 808 [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Business Acquisition [Line Items]
Cost associated with pre-launch activities	0	1,182	1,446	4,355
General and Administrative Expenses [Member] \| Topic 808 [Member] \| Nestle Health Science [Member] \| 2021 License Agreement [Member]
Business Acquisition [Line Items]
Cost associated with pre-launch activities	$ 0	$ 1,676	$ 4,242	$ 6,290

Subsequent Events - Additional Information (Detail) $ in Thousands		3 Months Ended
	Oct. 29, 2023 Employee	Dec. 31, 2023 USD ($)
Maximum [Member]
Subsequent Event [Line Items]
Restructuring costs		$ 5,500
Minimum [Member]
Subsequent Event [Line Items]
Restructuring costs		$ 5,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Workforce reduction rate	41.00%
Reduction in workforce, percentage	41.00%
Number of positions eliminated \| Employee	160

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Related Party Transactions

9 Months Ended

Sep. 30, 2023

Related Party Transactions

16. Related Party Transactions

As described in Notes 12 and 13, 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”). NHSc Rx License GmbH is an affiliate of one of the Company’s significant stockholders, Société des Produits Nestlé S.A. During the three and nine months ended September 30, 2023 and 2022, the Company recognized $0, $126,975, $1,497, and $3,678, respectively, of related party revenue associated with the 2021 License Agreement. As of September 30, 2023 and December 31, 2022, there was $0 and $1,976 of deferred revenue related to the 2021 License Agreement, respectively, which is classified as current in the condensed consolidated balance sheets. As of September 30, 2023 and December 31, 2022, there was $34,543 and $34,770 included in accrued expenses related to the 2021 License Agreement, which represents amounts due to Nestlé pursuant to the 2021 License Agreement. As of September 30, 2023 and December 31, 2022 there was $9,465 and $0 of deferred income - related party included on the accompanying condensed consolidated balance sheets, which represents the inventory transferred to Nestlé that Nestlé has not yet sold through to customers or transferred as free goods. The Company recognizes deferred income - related party as collaboration profit upon Nestlé's sale or transfer of such inventory to third parties. During the three and nine months ended September 30, 2023, the Company paid Nestlé $12,457 and $25,876, respectively, for Nestlé’s share of the collaboration expenses pursuant to the 2021 License Agreement. During the three and nine months ended September 30, 2023, the Company received $14,387 in payments from Nestlé for the transfer of VOWST to Nestlé. The Company did not make any payment to or receive any payments from Nestlé during the three and nine months ended September 30, 2022 pursuant to the 2021 License Agreement. As of September 30, 2023, there is $16,857 in Collaboration receivable - related party due from Nestlé pursuant to the 2021 License Agreement. There is no amount due from Nestlé pursuant to the 2021 License Agreement as of December 31, 2022.

As described in Note 12, Revenue from Contracts with Customers, in January 2016, the Company entered into the 2016 License Agreement with Nestec, Ltd, succeeded by Société des Produits Nestlé S.A. 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. is one of the Company’s significant stockholders. During the three and nine months ended September 30, 2023 and 2022, the Company recognized $310, ($714), $1,947, and $2,475, respectively, of related party revenue associated with the 2016 License Agreement. As of September 30, 2023 and December 31, 2022, there was $95,428 and $94,713 of deferred revenue related to the 2016 License Agreement, which is classified as current or non-current in the condensed consolidated balance sheets. The Company did not make any payment to or receive any payments from Nestlé during the three and nine months ended September 30, 2023 pursuant to the 2016 License Agreement. There is no amount due from Nestlé pursuant to the 2016 License Agreement as of September 30, 2023 or December 31, 2022.

In July 2022, the Company entered into a Pledge and Utilization Agreement with Flagship Pioneering Labs TPC, Inc., an affiliate of Flagship Pioneering, one of its significant stockholders, 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 June 2023, the Company elected not to renew the option and accordingly at such time, expensed the $833 option payment.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Fair Value Measurements - Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	$ 956	$ 0
Investments:
Investments		18,311
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	956
Equity, Fair Value Disclosure [Abstract]
Total liabilities	956
Investments:
Investments		82,831
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents		47,863
Commercial Paper [Member]
Investments:
Investments		2,465
Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		11,691
Investments:
Investments		2,465
Corporate Bonds [Member]
Investments:
Investments		2,957
Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Investments:
Investments		2,957
Government Securities [Member]
Investments:
Investments		12,889
Government Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		4,966
Investments:
Investments		12,889
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	0
Equity, Fair Value Disclosure [Abstract]
Total liabilities	0
Investments:
Investments		47,863
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents		47,863
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	0
Equity, Fair Value Disclosure [Abstract]
Total liabilities	0
Investments:
Investments		34,968
Level 2 [Member] \| Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		11,691
Investments:
Investments		2,465
Level 2 [Member] \| Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Investments:
Investments		2,957
Level 2 [Member] \| Government Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		4,966
Investments:
Investments		$ 12,889
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	956
Equity, Fair Value Disclosure [Abstract]
Total liabilities	$ 956

Subsequent Events

9 Months Ended

Sep. 30, 2023

Subsequent Events [Abstract]

Subsequent Events

17. Subsequent Events

On October 29, 2023, the Company’s Board of Directors approved the Restructuring Plan to prioritize the commercialization of VOWST and the completion of the SER-155 Phase 1b study, while significantly reducing costs and supporting longer-term business sustainability. The Restructuring Plan includes (i) a reduction of the Company’s workforce by approximately 41% across the organization, resulting in the elimination of approximately 160 positions; (ii) significantly scaling back all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study; and (iii) reducing general and administrative expenses, including consolidating office space. The Company expects the Restructuring Plan to be substantially implemented on or around the end of fiscal 2023.

In connection with the Restructuring Plan, the Company estimates that it will incur approximately $5,000 to $5,500 in restructuring costs, primarily related to the workforce reduction, all of which are expected to result in cash expenditures. These costs are anticipated to be incurred primarily in the fourth quarter of 2023.

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 73,217	$ 68,025
Less: Accumulated depreciation and amortization	(49,651)	(45,040)
Property and equipment, net	23,566	22,985
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	29,133	24,533
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,134	3,557
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,347	3,491
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	32,963	32,474
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,640	$ 3,970

Leases (Tables)

9 Months Ended

Sep. 30, 2023

Leases [Abstract]

Summary of Operating Lease Assets and Liabilities

The following table summarizes the presentation in the Company’s condensed consolidated balance sheets of its operating leases (in thousands):


	September 30, 2023		December 31, 2022
Assets:
Operating lease assets	$	108,105	$	110,984

Liabilities:
Operating lease liabilities	$	6,280	$	3,601
Operating lease liabilities, net of current portion		104,863		107,942
Total operating lease liabilities	$	111,143	$	111,543

Summary of Lease Costs

The following table summarizes the effect of lease costs in the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Operating lease costs	$	5,544	$	1,785	$	16,496	$	5,405
Short-term lease costs		362		326		1,102		1,035
Variable lease costs		1,699		1,135		5,643		3,437
Total lease costs	$	7,605	$	3,246	$	23,241	$	9,877

Schedule of Future Payments of Operating Lease Liabilities

As of September 30, 2023, future payments of operating lease liabilities are as follows (in thousands):


	As of September 30, 2023
2023 (remaining 3 months)	$	4,221
2024	$	19,437
2025	$	21,555
2026	$	22,155
2027 and thereafter	$	111,164
Total future minimum lease payments	$	178,532
Less: interest		(67,389	)
Present value of operating lease liabilities	$	111,143

Notes Payable - Additional Information (Detail) $ / shares in Units, $ in Thousands					3 Months Ended			9 Months Ended
	Jun. 30, 2026	Apr. 27, 2023 USD ($) TradingDays $ / shares shares	Feb. 24, 2022 USD ($)	Oct. 29, 2019 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Net proceeds received from credit facility		$ 50,446
Loss on extinguishment								$ (1,625)	$ 0
Trading days prior to the funding date \| TradingDays		30
Adjustments To Additional Paid In Capital, Warrant Issued						$ 2,785
Interest expense					$ 4,012		$ 1,727	$ 9,147	4,140
Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate		7.875%
Percentage of prepayment amount after the first year		4.00%
Percentage of prepayment amount after the second year		4.00%
Percentage of prepayment amount after the third year		2.00%
Percentage of prepayment amount after the fourth year		1.00%
Line of credit facility exit fee percentage		1.50%
Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Repayments of Debt			$ 2,900
Additional advance prepayment or repayment percentage			1.75%
Loan and Security Agreement [Member] \| Original Credit Facility [Member]
Debt Instrument [Line Items]
Prepayment or repayment percentage				4.85%
Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate								9.65%
Carrying value of debt										$ 51,047
Loan and Security Agreement [Member] \| Hercules Credit Facility [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate								6.40%
Hercules Lenders [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount			$ 100,000
Oaktree Credit Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Interest expense					$ 4,012		$ 1,727	$ 9,147	$ 4,140
Oaktree Credit Agreement [Member] \| Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Debt instrument interest rate					15.90%			15.90%
Oaktree Credit Agreement [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Carrying value of debt					$ 101,135			$ 101,135
Oaktree Fund Administration, LLC [Member]
Debt Instrument [Line Items]
Additional default interest rate		2.00%
Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 250,000
Hercules Capital, Inc. [Member] \| Loan and Security Agreement [Member] \| Original Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount				$ 50,000
Debt Instrument Tranche Four [Member] \| Hercules Lenders [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount			25,000
Tranche A Loan [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Loss on extinguishment		(1,625)
Tranche A Loan [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		110,000
Tranche A Loan [Member] \| Hercules Capital, Inc. [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Repayments of existing credit facility		53,380
Tranche B Loan [Member]
Debt Instrument [Line Items]
Net sales target		$ 35,000
Percentage increase in net sales rate		4.50%
Tranche B Loan [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 45,000
Tranche C Loan [Member]
Debt Instrument [Line Items]
Net sales target		$ 120,000
Percentage increase in net sales rate		4.50%
Tranche C Loan [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 45,000
Tranche D Loan [Mmeber] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		50,000
First Tranche [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules 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			50,586
First Tranche [Member] \| Hercules Lenders [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount			25,000
First Tranche [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		80,000
Second Tranche Unavailable to Borrow Due to Not Met Milestone Requirements [Member] \| Hercules Lenders [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount			12,500
Second Tranche Unavailable to Borrow Due to Not Met Milestone Requirements [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 30,000
Third Tranche Available Upon Approval Until June 30, 2021 [Member] \| Hercules Lenders [Member] \| Second Amendment to Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount			$ 12,500
Interest Rate Floor [Member] \| Term Loan Facility [Member] \| SOFR [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate		2.50%
Interest rate cap [Member] \| Term Loan Facility [Member] \| SOFR [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate		5.00%
Maximum [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate		7.875%
Minimum [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate		7.50%
Minimum [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Cash		$ 30,000
Minimum [Member] \| Tranche B Loan [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Cash		25,000
Forecast [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Percentage of the outstanding principal amount repaid	7.50%
Tranche A Warrant [Member]
Debt Instrument [Line Items]
Adjustments To Additional Paid In Capital, Warrant Issued		$ 2,785
Volatility		111.60%
Term (in years)		7 years
Risk free interest rate		3.57%
Fair value of common stock price per share on the valuation date \| $ / shares		$ 5.32
Warrants exercise price \| $ / shares		$ 6.69
Tranche A Warrant [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt instrument conversion warrants or options issued \| shares		647,589
Warrants exercise price \| $ / shares		$ 6.69
Tranche B Warrant [Member]
Debt Instrument [Line Items]
Debt instrument conversion warrants or options issued \| shares		264,922
Derivative liabilities		$ 1,077			506			506
Tranche C Warrant [Member]
Debt Instrument [Line Items]
Debt instrument conversion warrants or options issued \| shares		264,922
Derivative liabilities		$ 1,023			$ 450			$ 450

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 1,684	$ 1,747	$ 4,611	$ 5,002

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Indemnification Agreement [Member]
Other Commitments [Line Items]
Obligations accrued	$ 0	$ 0
Legal Contingencies [Member]
Other Commitments [Line Items]
Obligations accrued	$ 0	$ 0

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Cash and cash equivalents	$ 169,912	$ 163,030
Restricted cash, non-current	8,185	8,185
Total cash, cash equivalents and restricted cash	$ 178,097	$ 171,215	$ 213,583	$ 188,002

Collaboration Profit and Loss

9 Months Ended

Sep. 30, 2023

Nestle Health Science [Member]

Business Combinations [Abstract]

Collaboration profit and loss

13. Collaboration Profit and Loss

License Agreement with NHSc Rx License GmbH (Nestlé)

Accounting Analysis

The 2021 License Agreement represents a separate contract between Nestlé and the Company. The 2021 License Agreement is within the scope of Topic 808, and has elements that are within the scope of Topic 606 (see Note 12, Revenue from Contracts with Customers) and Topic 808.

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 performance obligations under Topic 606. The Company and Nestlé were both active participants in the pre-launch activities and commercialization activities and were exposed to significant risks and rewards that were dependent on the commercial success of the activities in the arrangement. The amount allocated to the Topic 808 unit of accounting

relates to the pre-launch activities performed prior to the first commercial sale of VOWST 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 sheets at the inception of the arrangement. On a quarterly basis, the Company and Nestlé provided financial information about the pre-launch activities performed by both parties. The Company reduced the $35,500 liability as the pre-launch activities were performed and it made payments to Nestlé for the pre-launch costs Nestlé incurred. As of September 30, 2023 and December 31, 2022, there was $15,791 and $34,770, respectively, included in accrued expenses and other current liabilities which represents costs incurred by Nestlé for pre-launch activities that have not yet been reimbursed by Seres.

The cost associated with pre-launch activities performed by the Company is recorded within total operating expenses in the Company’s condensed consolidated statements of operations and comprehensive loss. In the three and nine months ended September 30, 2023 and 2022, the Company recognized $0, $1,446, $1,182 and $4,355 respectively, in research and development expenses and $0, $4,242, $1,676 and $6,290 respectively, in general and administrative expenses associated with pre-launch activities performed. The pre-launch activities were completed prior to the first commercial sale of VOWST, which occurred in June 2023.

Under the 2021 License Agreement with Nestlé, beginning with the first commercial sale of VOWST, which occurred in June 2023, net sales of VOWST are recorded by Nestlé and include gross sales net of discounts, rebates, allowances, and other applicable deductions. These amounts include the use of estimates and judgments, which could be adjusted based on actual results in the future. The Company records its share of the profits or losses from the sales of VOWST, including commercial and medical affairs expenses incurred by the Company, on a net basis, as collaboration (profit) loss sharing - related party. This treatment is in accordance with the Company’s revenue recognition and collaboration policy, given that Nestlé and the Company are both active participants in commercialization activities and are exposed to significant risks and rewards that are dependent on the commercial success of the activities in the 2021 License Agreement. Nestlé provides the Company with reporting related to net sales of VOWST in accordance with U.S. generally accepted accounting principles in order to calculate and record collaboration profit or loss.

The collaboration (profit) loss sharing - related party line item also includes the Company's profit on the transfer of VOWST inventory to Nestlé, which represents the excess of the supply price paid by Nestlé over the Company's cost to manufacture VOWST, subject to a supply price cap applicable to product manufactured prior to commercial launch.

The collaboration (profit) loss sharing - related party line item also includes the collaboration loss related to pre-launch activities, which were completed prior to the first commercial sale of VOWST. In the three months ended September 30, 2023, the Company recognized $313 for the remaining pre-launch costs incurred by Nestlé.

The components of the collaboration profit (loss) sharing for the three and nine months ended September 30, 2023 are as follows:


	Three Months Ended September 30,					Nine Months Ended September 30,
	2023			2022		2023			2022
Share of VOWST net loss	$	6,463		$	—	$	8,604		$	—
Profit on transfer of VOWST inventory to Nestlé		(7,295	)		—		(8,568	)		—
Collaboration (profit)/loss related to pre-launch activities		313			1,051		5,158			346
Total collaboration (profit) loss sharing - related party	$	(519	)	$	1,051	$	5,194		$	346

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Fair Value Disclosures [Abstract]
Assets measured at fair value			$ 0
Liabilities measured at fair value			0
Fair value, assets transfers from Level 1 to Level 2 measurement	$ 0		30
Fair value, assets transfers from Level 2 to Level 1 measurement	0		2,023
Fair value, assets transfers from Level 1 to Level 3 measurement	0		30
Fair value, assets transfers from Level 2 to Level 3 measurement	30		2,023
Fair value, assets transfers from Level 3 to Level 1 measurement	0		2,023
Fair value, assets transfers from Level 3 to Level 2 measurement	30		$ 2,023
Restricted investments	$ 1,401	$ 1,401

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue:
Collaboration revenue - related party	$ 310	$ 3,444	$ 126,261	$ 6,153
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Total revenue	$ 310	$ 3,444	$ 126,261	$ 6,153
Operating expenses:
Research and development expenses	28,253	43,116	119,014	126,700
General and administrative expenses	19,989	18,384	70,510	57,290
Collaboration (profit) loss sharing - related party	(519)	1,051	5,194	346
Total operating expenses	47,723	62,551	194,718	184,336
Loss from operations	(47,413)	(59,107)	(68,457)	(178,183)
Other income (expense):
Interest income	2,572	865	5,330	1,644
Interest expense	(4,012)	(1,727)	(9,147)	(4,140)
Other income (expense)	999	(33)	(202)	(682)
Total other expense, net	(441)	(895)	(4,019)	(3,178)
Net loss	$ (47,854)	$ (60,002)	$ (72,476)	$ (181,361)
Net income (loss) per share attributable to common stockholders, basic	$ (0.37)	$ (0.49)	$ (0.57)	$ (1.77)
Net income (loss) per share attributable to common stockholders, diluted	$ (0.37)	$ (0.49)	$ (0.57)	$ (1.77)
Weighted-average common shares outstanding, basic	128,289,871	122,527,275	127,297,667	102,380,700
Weighted average common shares outstanding, diluted	128,289,871	122,527,275	127,297,667	102,380,700
Other comprehensive income (loss) :
Unrealized gain (loss) on investments, net of tax of $0	$ 0	$ 140	$ 10	$ (56)
Currency translation adjustment	1	(2)	2	(2)
Total other comprehensive income (loss)	1	138	12	(58)
Comprehensive loss	$ (47,853)	$ (59,864)	$ (72,464)	$ (181,419)

Collaboration Profit and Loss (Tables)

9 Months Ended

Sep. 30, 2023

Business Combinations [Abstract]

Schedule of Collaboration Profit (Loss)

The components of the collaboration profit (loss) sharing for the three and nine months ended September 30, 2023 are as follows:


	Three Months Ended September 30,					Nine Months Ended September 30,
	2023			2022		2023			2022
Share of VOWST net loss	$	6,463		$	—	$	8,604		$	—
Profit on transfer of VOWST inventory to Nestlé		(7,295	)		—		(8,568	)		—
Collaboration (profit)/loss related to pre-launch activities		313			1,051		5,158			346
Total collaboration (profit) loss sharing - related party	$	(519	)	$	1,051	$	5,194		$	346

Fair Value Measurements

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

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 September 30, 2023 Using:
	Level 1		Level 2		Level 3		Total
Warrant liabilities	$	—	$	—	$	956	$	956
Total liabilities	$	—	$	—	$	956	$	956


	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

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.

As of both September 30, 2023 and December 31, 2022, 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.

Level 3 financial liabilities consist of the warrant liabilities for which there is no current market such that the determination of fair value requires significant judgment or estimation. Changes in fair value measurements categorized within Level 3 of the fair value hierarchy are analyzed each period based on changes in estimates or assumptions and recorded through other income (expense). The Company uses a Monte-Carlo simulation model which includes the Black-Scholes option pricing model to value the Level 3 warrant liabilities at inception and on each subsequent reporting date. This model incorporates transaction details such as the Company’s stock price, contractual terms of the underlying warrants, maturity, risk free rates, volatility, as well as the term to achievement of estimated

sales targets. The unobservable inputs for all of the Level 3 warrant liabilities are volatility and the term to achievement of estimated sales targets. The Company utilizes its historical and implied volatility, using its closing common stock prices and market data, to reflect future volatility over the expected term of the warrants. The Company estimates the time to achievement of sales targets of VOWST using information and forecasts generated by the Company in consideration of the terms of the 2021 License Agreement.

On the Closing Date (as defined in Note 9, Notes Payable) and as of September 30, 2023, the Level 3 inputs to the warrant liabilities are as follows:



	Closing Date			September 30, 2023
Volatility		83.0	%		75.0	%
Term (in years)		1.7			1.3


	Warrant Liabilities

Balance as of December 31, 2022	$	—
Issuance of warrants		2,100
Adjustment to fair value		(132	)
Balance as of June 30, 2023		1,968
Adjustment to fair value		(1,012	)
Balance as of September 30, 2023		956

There were no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the three and nine months ended September 30, 2022. There were no transfers between Level 1, Level 2, or Level 3 during the three and nine months ended September 30, 2023 and 2022.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	September 30, 2023		December 31, 2022
Clinical and development costs	$	1,491	$	6,717
Manufacturing and quality costs		1,719		—
Payroll and payroll-related costs		13,479		14,709
Collaboration payable - related party (Note 16)		34,543		34,770
Facility and other		2,926		3,644
	$	54,158	$	59,840

Common Stock and Stock-Based Awards - Stock Options - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2024	Apr. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options			$ 3.14	$ 4.07	$ 4.52	$ 5.53
Performance-based stock options to granted					2,507,053
Stock based compensation expense for stock options			$ 8,673	$ 6,364	$ 29,015	$ 18,191
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance-based stock options		50.00%
Percentage of Performance-Based Stock Options Vesting	50.00%
Weighted average grant-date fair value of stock options							$ 5.53
Performance-based stock options to granted							562,000
Stock based compensation expense for stock options			$ 109		$ 2,481

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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+ Details

Common Stock and Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 8,673	$ 6,364	$ 29,015	$ 18,191
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,744	3,474	16,326	9,500
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,929	$ 2,890	$ 12,689	$ 8,691

Inventories - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Inventories	$ 18,525	$ 18,525	$ 0
Pre-launch inventory research and development expense	0	26,794
Inventory Write-down	$ 0	$ 0