0000950170-24-055159 | 10-Q | XBRL Viewer

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Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
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	240,000,000
Common stock, shares issued	151,442,034	135,041,467
Common stock, shares outstanding	151,442,034	135,041,467
Bacthera Agreement [Member]
Prepayments on long term contract	$ 38,877	$ 38,877
Related Party [Member]
Related parties, current	$ 36,211	$ 28,053

Fair Value Measurements

3 Months Ended

Mar. 31, 2024

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 March 31, 2024 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	82	$	—	$	—	$	82
Total assets	$	82	$	—	$	—	$	82

Warrant liabilities	$	—	$	—	$	130	$	130
Total liabilities	$	—	$	—	$	130	$	130


	Fair Value Measurements as of December 31, 2023 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	81	$	—	$	—	$	81
Total assets	$	81	$	—	$	—	$	81

Warrant liabilities	$	—	$	—	$	546	$	546
Total liabilities	$	—	$	—	$	546	$	546

Money market funds are valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy.

As of both March 31, 2024 and December 31, 2023, 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.

As of March 31, 2024 and December 31, 2023, the Level 3 inputs to the warrant liabilities are as follows:



	March 31, 2024			December 31, 2023
Volatility		100.2	%		101.0	%
Term (in years)		1.3			1.3

A reconciliation of the beginning and ending balances for the three months ended March 31, 2024 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, 2023	$	546
Issuance of warrants		—
Adjustment to fair value		(416	)
Balance as of March 31, 2024		130

There were no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the three months ended March 31, 2023. There were no transfers between Level 1, Level 2, or Level 3 during the three months ended March 31, 2024 and 2023.

- 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

Leases - Summary of Operating Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Operating lease assets	$ 105,669	$ 109,793
Liabilities:
Operating lease liabilities	8,833	6,677
Operating lease liabilities, net of current portion	103,341	105,715
Total operating lease liabilities	$ 112,174	$ 112,392

Leases

3 Months Ended

Mar. 31, 2024

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 nine 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 were $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 $1,079 over the original term. The lease commenced in December 2023, at which point, the Company recorded a right-of-use asset of $1,830, which consists of the lease liability of $768, and $1,062 of leasehold improvements that revert back to the lessor at the termination of the lease.

In January 2024, the Company entered into a sublease agreement with an unrelated third party to sublease a portion of its office and laboratory space in Cambridge, Massachusetts. The term of the sublease agreement commenced in March 2024 and ends on January 13, 2030. The Company will receive lease payments over the sublease term totaling $10,400. The sublessee is obligated to pay all real estate taxes and costs related to the subleased premises, including cost of operations, maintenance, repair, replacement and property management.

As of March 31, 2024, the Company identified an indicator of impairment of its donor collection facility in Cambridge, Massachusetts, as the facility is no longer being used by the Company as a result of operational efficiencies implemented related to the production process and is being marketed for sublease. The Company determined that this represents a significant adverse change in the extent in which the long-lived asset was being used. The Company determined that the location contains multiple asset groups for the purpose of the long-lived asset impairment assessment. The Company concluded that the carrying value of each asset group was not recoverable as it exceeded the future net undiscounted cash flows that are expected to be generated from the assets within the asset group. For the three months ended March 31, 2024, the Company recognized an impairment loss of $3,267, consisting of $1,731 on the operating lease right-of-use asset and $1,536 on the leasehold improvements. $2,727 of the total impairment loss is included in research and development expenses and the remaining $540 is included in general and administrative expenses in the accompanying condensed consolidated statements of operations and comprehensive loss.

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


	March 31, 2024		December 31, 2023
Assets:
Operating lease assets	$	105,669	$	109,793

Liabilities:
Operating lease liabilities	$	8,833	$	6,677
Operating lease liabilities, net of current portion		103,341		105,715
Total operating lease liabilities	$	112,174	$	112,392

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 March 31,
	2024			2023
Operating lease costs	$	5,771		$	5,410
Short-term lease costs		374			368
Variable lease costs		1,967			1,763
Sublease income		(376	)		—
Total lease costs	$	7,736		$	7,541

During the three months ended March 31, 2024 and 2023, the Company made cash payments for operating leases of $3,596 and $3,413 respectively.

As of March 31, 2024, future payments of operating lease liabilities are as follows (in thousands):


	As of March 31, 2024
2024 (remaining 9 months)	$	16,273
2025	$	22,062
2026	$	22,674
2027	$	23,347
2028	$	23,580
2029 and thereafter	$	65,819
Total future minimum lease payments	$	173,755
Less: interest		(61,581	)
Present value of operating lease liabilities	$	112,174

As of March 31, 2024, the weighted average remaining lease term was 7.70 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%. As of March 31, 2023, the weighted average remaining lease term was 8.68 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%.

Common Stock and Stock-Based Awards - Additional Information (Details) $ / shares in Units, $ in Thousands		3 Months Ended
	May 21, 2021 USD ($)	Mar. 31, 2024 USD ($) $ / shares shares	Mar. 31, 2023 USD ($) $ / shares shares	Feb. 22, 2024 shares	Feb. 21, 2024 shares	Dec. 31, 2023 shares
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized \| shares		240,000,000		360,000,000	240,000,000	240,000,000
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		15,366,630	787,170
Common stock, average share price \| $ / shares		$ 1.23	$ 5.67
Proceeds from issuance of common stock \| $		$ 18,409	$ 4,238
Percentage of commission on sale of common stock		3

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

Mar. 31, 2024

Dec. 31, 2023

Payables and Accruals [Abstract]

Clinical and development costs

$ 1,405

$ 1,404

Manufacturing and quality costs

30,574

31,917

Payroll and payroll-related costs

6,137

16,465

Collaboration payable - related party (Note 17)

36,211

28,053

Facility and other

1,990

2,772

Total accrued expenses and other current liabilities

^[1]

$ 76,317

$ 80,611

[1]	Includes related party amounts of $36,211 and $28,053 at March 31, 2024 and December 31, 2023, respectively (see Note 17)

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
Operating lease costs	$ 5,771	$ 5,410
Short-term lease costs	374	368
Variable lease costs	1,967	1,763
Sublease income	(376)	0
Total lease costs	$ 7,736	$ 7,541

Common Stock and Stock-Based Awards - Stock Options - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average exercise price of stock options granted		$ 1.07
Weighted average grant-date fair value of stock options		$ 0.95	$ 4.56
Number of stock options granted		6,743,362
Stock-based compensation expense		$ 6,489	$ 6,850
Employee Stock Option Market Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options granted		2,550,010
Stock-based compensation expense		$ 142
Stock option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average exercise price of stock options granted		$ 1.1
Expiration period of stock options granted		10 years
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
Number of stock options granted				562,000
Stock-based compensation expense		$ 45	$ 0

Related Party Transactions

3 Months Ended

Mar. 31, 2024

Related Party Transactions

17. Related Party Transactions

As described in Notes 13 and 14, 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 months ended March 31, 2024 and 2023, the Company recognized $0 and $1,122, respectively, of related party revenue associated with the 2021 License Agreement. As of both March 31, 2024 and December 31, 2023, there was $0 of deferred revenue related to the 2021 License Agreement. As of March 31, 2024 and December 31, 2023, there was $36,211 and $28,053 included in accrued expenses related to the 2021 License Agreement, which represents amounts due to Nestlé pursuant to the 2021 License Agreement. As of March 31, 2024 and December 31, 2023 there was $8,109 and $7,730 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 months ended March 31, 2024 and 2023, the Company paid Nestlé $0 and $13,419, respectively, for Nestlé’s share of the collaboration losses pursuant to the 2021 License Agreement. During the three months ended March 31, 2024 and 2023, the Company received $8,674 and $0, respectively in payments from Nestlé for the transfer of VOWST to Nestlé. As of March 31, 2024 and December 31, 2023, there is $7,418 and $8,674 in Collaboration receivable - related party due from Nestlé pursuant to the 2021 License Agreement.

As described in Note 13, 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 months ended March 31, 2024 and 2023, the Company recognized $0 and ($1,644), respectively, of related party revenue associated with the 2016 License Agreement. As of March 31, 2024 and December 31, 2023, there was $95,364 and $95,364 of deferred revenue related to the 2016 License Agreement, which is classified as 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 months ended March 31, 2024 and 2023 pursuant to the 2016 License Agreement. There is no amount due from Nestlé pursuant to the 2016 License Agreement as of March 31, 2024 or December 31, 2023.

- 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
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-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
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-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
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-Name Accounting Standards Codification
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-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-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
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-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
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-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
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Leases - Schedule of Future Payments of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
2024 (remaining 9 months)	$ 16,273
2025	22,062
2026	22,674
2027	23,347
2028	23,580
2029 and thereafter	65,819
Total future minimum lease payments	173,755
Less: interest	(61,581)
Present value of operating lease liabilities	$ 112,174	$ 112,392

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2024

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

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


	March 31, 2024		December 31, 2023
Clinical and development costs	$	1,405	$	1,404
Manufacturing and quality costs		30,574		31,917
Payroll and payroll-related costs		6,137		16,465
Collaboration payable - related party (Note 17)		36,211		28,053
Facility and other		1,990		2,772
	$	76,317	$	80,611

Inventories (Tables)

3 Months Ended

Mar. 31, 2024

Inventory Disclosure [Abstract]

Schedule of Capitalized Inventories

Capitalized inventories consist of the following (in thousands):


	March 31, 2024		December 31, 2023
Raw materials	$	4,224	$	4,426
Work in process		37,265		25,221
Finished goods		484		—
Total	$	41,973	$	29,647

Revenue from Contracts with Customers (Tables)

3 Months Ended

Mar. 31, 2024

Revenue from Contract with Customer [Abstract]

Changes in Contract Liabilities

The following tables present changes in the Company’s contract liabilities during the three months ended March 31, 2024 and 2023 (in thousands):


	Balance as of December 31, 2023		Additions		Deductions		Balance as of March 31, 2024
Three Months Ended March 31, 2024
Contract liabilities:
Deferred revenue - related party	$	95,364		—		—	$	95,364


	Balance as of December 31, 2022		Additions		Deductions			Balance as of March 31, 2023
Three Months Ended March 31, 2023
Contract liabilities:
Deferred revenue - related party	$	96,689		1,644		(1,122	)	$	97,211

During the three months ended March 31, 2024 and 2023 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 March 31,
	2024		2023
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$	—	$	(522	)

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2024

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):


	March 31, 2024		December 31, 2023
Clinical and development costs	$	1,405	$	1,404
Manufacturing and quality costs		30,574		31,917
Payroll and payroll-related costs		6,137		16,465
Collaboration payable - related party (Note 17)		36,211		28,053
Facility and other		1,990		2,772
	$	76,317	$	80,611

As of March 31, 2024, the Company accrued a total of $28,046 payable to Bacthera for the substantial completion of the Company’s dedicated production suite for long-term supply of VOWST. This amount is included in the Manufacturing and quality costs category above.

Additionally, included within payroll and payroll-related costs as of March 31, 2024 and December 31, 2023 is $564 and $5,080, respectively, of accrued severance related to the Restructuring Plan. See Note 12, Restructuring, for further details.

Common Stock and Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - RSU and PSU [Member]	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested restricted stock units, Beginning balance \| shares	3,377,804
Number of Shares, Granted \| shares	1,282,941
Number of Shares, Vested \| shares	(329,981)
Number of Shares, Forfeited \| shares	(178,039)
Number of Shares, Unvested restricted stock units, Ending balance \| shares	4,152,725
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Beginning balance \| $ / shares	$ 4.26
Weighted Average Grant Date Fair Value, Granted \| $ / shares	1.09
Weighted Average Grant Date Fair Value, Vested \| $ / shares	6.24
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	3.35
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Ending balance \| $ / shares	$ 3.16

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Indemnification Agreement [Member]
Other Commitments [Line Items]
Obligations accrued	$ 0	$ 0
Legal Contingencies [Member]
Other Commitments [Line Items]
Obligations accrued	$ 0	$ 0

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenue:
Collaboration revenue - related party	$ 0	$ (522)
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Total revenue	$ 0	$ (522)
Operating expenses:
Research and development expenses	21,702	43,969
General and administrative expenses	15,466	22,470
Collaboration (profit) loss sharing - related party	2,418	3,607
Total operating expenses	39,586	70,046
Loss from operations	(39,586)	(70,568)
Other income (expense):
Interest income	1,648	1,032
Interest expense	(4,663)	(1,948)
Other income	2,468	310
Total other expense, net	(547)	(606)
Net loss	$ (40,133)	$ (71,174)
Net loss per share attributable to common stockholders, basic	$ (0.27)	$ (0.57)
Net loss per share attributable to common stockholders, diluted	$ (0.27)	$ (0.57)
Weighted-average common shares outstanding, basic	146,101,581	125,862,975
Weighted average common shares outstanding, diluted	146,101,581	125,862,975
Other comprehensive income (loss) :
Unrealized gain (loss) on investments, net of tax of $0	$ 0	$ 12
Currency translation adjustment	0	2
Total other comprehensive income (loss)	0	14
Comprehensive loss	$ (40,133)	$ (71,160)

Collaboration Profit and Loss (Tables)

3 Months Ended

Mar. 31, 2024

Business Combinations [Abstract]

Schedule of Collaboration Profit (Loss)

The components of the collaboration profit (loss) sharing for the three months ended March 31, 2024 and 2023 are as follows:


	Three Months Ended March 31,
	2024			2023
Share of VOWST net loss	$	7,128		$	—
Profit on transfer of VOWST inventory to Nestlé		(4,710	)		—
Collaboration (profit)/loss related to pre-launch activities		—			3,607
Total collaboration (profit) loss sharing - related party	$	2,418		$	3,607

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 71,511	$ 73,595
Less: Accumulated depreciation and amortization	(52,396)	(51,138)
Property and equipment, net	19,115	22,457
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	29,003	29,081
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,142	4,142
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,188	5,430
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	32,039	33,549
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,139	$ 1,393

Investments

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Investments

4. Investments

As of March 31, 2024 and December 31, 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 March 31, 2024 and December 31, 2023.

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.

Common Stock and Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2023:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2023		14,844,112		$	9.64		5.71	$	-
Granted		6,743,362		$	1.07
Exercised		—		$	—
Forfeited		(2,428,857	)	$	8.93
Outstanding as of March 31, 2024		19,158,617		$	6.72		7.59	$	—
Vested or expected to vest as of March 31, 2024		19,158,617		$	6.72		7.59	$	—
Options exercisable as of March 31, 2024		9,026,731		$	10.16		5.68	$	—

Summary of Restricted and Performance Stock Unit Activity

The following table summarizes the Company’s RSU and PSU activity since December 31, 2023:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2023		3,377,804		$	4.26
Granted		1,282,941		$	1.09
Vested		(329,981	)	$	6.24
Forfeited		(178,039	)	$	3.35
Unvested restricted stock units as of March 31, 2024		4,152,725		$	3.16

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 March 31,
	2024		2023
Research and development expenses	$	3,610	$	3,731
General and administrative expenses		2,879		3,119
	$	6,489	$	6,850

Condensed Consolidated Statements of Stockholders' (Deficit) Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Market Equity Offering [Member]
Issuance costs	$ 548	$ 225

Fair Value Measurements - Schedule of Level 3 Inputs to Warrant Liabilities (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Option, Quantitative Disclosures [Line Items]
Volatility	100.20%	101.00%
Warrant [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Term (in years)	1 year 3 months 18 days	1 year 3 months 18 days

Net Loss per Share

3 Months Ended

Mar. 31, 2024

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 March 31,
	2024			2023
Numerator:
Net loss attributable to common stockholders	$	(40,133	)	$	(71,174	)
Denominator:
Weighted-average shares outstanding, basic and diluted		146,101,581			125,862,975
Net loss per share attributable to common stockholders, basic and diluted	$	(0.27	)	$	(0.57	)

Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:
Stock options to purchase common stock		19,158,617			16,826,144
Unvested restricted stock units		4,152,725			4,215,834
Shares issuable under employee stock purchase plan		75,488			68,594
Warrants to purchase common stock		1,177,433			—

The Company’s potential dilutive securities, which include stock options, unvested restricted common stock and shares issuable under the 2015 Employee Stock Purchase Plan, 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 months ended March 31, 2024, 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 (Tables)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Cash, Cash Equivalents and Restricted Cash

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


	March 31,		December 31,
	2024		2023
Cash and cash equivalents	$	111,184	$	127,965
Restricted cash, non-current		8,430		8,185
Total cash, cash equivalents and restricted cash	$	119,614	$	136,150

Restructuring - Additional Information (Detail) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 02, 2023 Employee	Oct. 29, 2023 Employee	Nov. 30, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Workforce reduction rate	41.00%
Number of positions eliminated \| Employee	160	160
Restructuring Charges						$ 5,606
Stock-based compensation expense				$ 6,489	$ 6,850
Restricted Stock Units [Member]
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense			$ 1,255
Severance and other employee costs
Restructuring Cost and Reserve [Line Items]
Restructuring Charges						5,345
Acceleration of unvested equity awards
Restructuring Cost and Reserve [Line Items]
Restructuring Charges						$ 261

- 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 + Details

Notes Payable

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Notes Payable

9. Notes Payable

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 year ended December 31, 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 required 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 March 31, 2024, there were 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 March 31, 2024, the Company was 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 $66, $64, $276, and $270 as of March 31, 2024 and December 31, 2023, respectively.

Changes in the fair values of the Additional Warrants are recorded as other income (expense) in the condensed 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 March 31, 2024 was 15.9%. As of March 31, 2024 and December 31, 2023, the carrying value of the Term Loan was $102,009 and 101,544, 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
2024 (remaining 9 months)	$	—
2025		—
2026		24,750
2027		33,000
2028		33,000
Thereafter		19,250
Total	$	110,000

During the three months ended March 31, 2024, the Company recognized $4,046 of interest expense related to the Term Loan, which is reflected in interest expense on the condensed consolidated statements of operations and comprehensive loss. During the three months ended March 31, 2023, the Company recognized $1,948 of interest expense related to the Loan and Security Agreement with Hercules.

On May 1, 2024, the Company received a Notice of Default and Reservation of Rights (the “Notice”) from the Agent under the Oaktree Credit Agreement. The Notice specified that in the Agent’s view, one or more events of default have occurred under the Oaktree Credit Agreement due to (a) the Company’s non-payment of a milestone payment to Bacthera under the Bacthera Agreement which the Agent characterized as “Indebtedness” that would not be permitted under the Oaktree Credit Agreement and (b) the Company’s failure to deliver written notice to the Agent regarding such non-payment.

The Company has responded by letter to the Notice, advising the Agent that no default or event of default under the Oaktree Credit Agreement has occurred or is continuing, because the payment under the Bacthera Agreement is not due, and, as a result, no notice of non-payment was required. Moreover, even if the payment were due, the Company does not believe such payment would constitute Indebtedness (as defined in the Oaktree Credit Agreement).

Based on the above, the Company believes that it is not in default under the Oaktree Credit Agreement, and that the Agent does not have the right to accelerate the indebtedness or otherwise pursue remedies thereunder. As a result, the Company continues to classify the carrying value of the Term Loan as non-current on its condensed consolidated balance sheet as of March 31, 2024. If the Agent were to pursue any such actions, the Company intends to vigorously defend itself against them and to pursue any counterclaims available to it. The Company is attempting to resolve this matter with the Agent consensually.

- 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

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	$ (8,158)	$ (9,812)

Inventories

3 Months Ended

Mar. 31, 2024

Inventory Disclosure [Abstract]

Inventories

5. Inventories

Capitalized inventories consist of the following (in thousands):


	March 31, 2024		December 31, 2023
Raw materials	$	4,224	$	4,426
Work in process		37,265		25,221
Finished goods		484		—
Total	$	41,973	$	29,647

Prior to the FDA’s approval for VOWST on April 26, 2023, 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 $15,613 for the three months ended March 31, 2024 and 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 months ended March 31, 2024.

Restructuring

3 Months Ended

Mar. 31, 2024

Restructuring and Related Activities [Abstract]

Restructuring

12. Restructuring

On November 2, 2023, the Company announced 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 included (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.

During the year ended December 31, 2023, the Company recognized a restructuring charge of $5,606, which was incurred entirely in the fourth quarter of 2023, and which represents all restructuring charges expected to be incurred. Restructuring charges included approximately $5,345 of employee related termination costs in the form of salary continuation and cash severance payments, and $261 related to the acceleration of vesting of certain previously granted RSUs and PSUs.

The unpaid restructuring charges are included in accrued expenses and other current liabilities in the Company’s consolidated balance sheets. The following table presents changes in the restructuring liability for the three months ended March 31, 2024 (in thousands):


	As of March 31, 2024
Restructuring expenses	$	5,606
Less: stock-based compensation		(261	)
Cash payments made through March 31, 2024		(4,781	)
Remaining liability included in accrued expenses and other current liabilities	$	564

The Company expects the remaining accrued restructuring charges to be paid in cash by March 31, 2025.

Retention Awards

In November 2023, upon recommendation of the Company's Compensation Committee, the board of directors approved retention awards for employees of the Company in the form of RSUs which vest in two tranches on August 15, 2024, and May 15, 2025, subject to remaining actively employed with the Company through such date. The $1,255 in compensation expense associated with these awards will be recognized ratably over the vesting period.

Accrued Expenses and Other Current Liabilities - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued Expenses and Other Current Liabilities [Member]
Outstanding restructuring liabilities	$ 564	$ 5,080
Bacthera [Member]
Accrued expense	$ 28,046

Common Stock and Stock-Based Awards - Restricted Stock Units - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Oct. 31, 2024	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 6,489	$ 6,850
Retention Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 185
Service Based Restricted Stock Units (RSUs)[Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted		1,282,941	1,692,095
Stock option granted vesting period		4 years
Service Based Restricted Stock Units (RSUs)[Member] \| Share-Based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period		1 year
Vesting rights percentage		25.00%
Service Based Restricted Stock Units (RSUs)[Member] \| Share-Based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period		3 years
Vesting rights percentage		75.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 45	$ 0
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			$ 5.5
Stock-based compensation expense		$ 260	$ 0
Number of shares granted		0	1,322,715
Scenario Forecast [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 725

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Feb. 29, 2016
Related Party Transaction [Line Items]
Deferred income - related party	$ 8,109		$ 7,730
Nestle Health Science [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party	0	$ (1,644)
Deferred revenue	95,364		95,364	$ 120,000
Due from related party	0		0
Nestle Health Science [Member] \| 2021 License Agreement [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party	0	1,122
Deferred revenue	0		0
Payment for collaboration receivable	8,674	0
Payments under agreements with related party	0	$ 13,419
Due from related party	7,418		8,674
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	$ 36,211		$ 28,053

Nature of the Business and Basis of Presentation

3 Months Ended

Mar. 31, 2024

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, 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 gastrointestinal (“GI”)-derived infections and resulting bloodstream 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”). Study cohort 1, which included 13 participants, was designed to assess safety and drug pharmacology, including the gastrointestinal microbiome data from the first 100 days, which showed the successful engraftment of SER-155 bacterial strains in all nine subjects with evaluable microbiome samples, and a substantial reduction in the cumulative incidence of pathogen domination (a biomarker associated with the risk of serious GI infections and enteric-derived bloodstream infections, as well as GvHD) as compared to a reference cohort of patients. The tolerability profile observed was favorable, with no serious adverse events attributed to SER-155 administration. Enrollment in study cohort 2, which includes 45 participants, was completed in April 2024. Study cohort 2 incorporates a randomized, double-blinded placebo-controlled 1:1 design to further evaluate safety and engraftment as well as clinical outcomes, and data readout is anticipated late in the third quarter of 2024.

The Company has built and deploys a reverse translational platform and knowledge base 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 included (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 12, Restructuring.

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to potential commercialization. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.

The 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 March 31, 2024, the Company had an accumulated deficit of $1,018,368 and cash and cash equivalents of $111,184.

The Company’s primary focus in recent months has been and will continue to be supporting commercialization, including the manufacture of VOWST, and the completion of the SER-155 Phase 1b study, which requires capital and resources. 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.

Primarily as a result of the costs associated with commercializing VOWST and continuing the research and development efforts for other product candidates and preclinical programs, the Company incurred a net loss of $40,133 and had net operating cash outflows of $35,236 for the three months ended March 31, 2024. 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 will require additional funding to supply product and support commercialization of VOWST, continue to progress the SER-155 Phase 1b study, 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.

The Company’s ability to continue as a going concern is dependent upon its ability to obtain the necessary financing to meet its obligations and repay its liabilities arising from normal business operations when they come due, and to generate profitable operations in the future. Management plans to provide for the Company’s capital requirements through financing or other strategic transactions, including potential business development transactions, and selling shares under the Company’s at the market equity offering. There can be no assurance that the Company will generate significant profit from the transfer of VOWST to Nestlé or its share of collaboration profits resulting from net sales of VOWST, or that it will be able to raise additional capital to fund operations with terms acceptable to the Company, or at all. Because certain elements of management’s plans to mitigate the conditions that raised substantial doubt about the Company’s ability to continue as a going concern are outside of the Company’s control, including the ability to raise capital through an equity or other financing, those elements cannot be considered probable according to Accounting Standards Codification (“ASC”) 205-40, Going Concern (“ASC 205-40”), and therefore cannot be considered in the evaluation of mitigating factors. As a result, management has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for 12 months from the date these condensed consolidated financial statements are issued.

Unaudited Interim Financial Information

The accompanying unaudited condensed consolidated financial statements as of March 31, 2024 and for the three months ended March 31, 2024 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, 2023 included in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2023, which was filed with the SEC on March 5, 2024 (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, 2023 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 months ended March 31, 2024 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2024.

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 111,184	$ 127,965
Restricted cash, non-current	8,430	8,185
Total cash, cash equivalents and restricted cash	$ 119,614	$ 136,150	$ 103,026	$ 171,215

Leases - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Jun. 30, 2023	Apr. 30, 2022	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Jun. 01, 2023	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			$ 105,669		$ 109,793
Present value of operating lease liabilities			112,174		112,392
Impairment loss of leasehold improvements			1,536
Lease payment over sublease term			10,400
Leases Payments			$ 3,596	$ 3,413
Weighted average remaining lease term			7 years 8 months 12 days	8 years 8 months 4 days
Weighted average incremental borrowing rate			13.00%	13.00%
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					1,830
Present value of operating lease liabilities					768
Leasehold Improvements					$ 1,062
Cambridge Massachusetts [Member]
Operating Leased Assets [Line Items]
Impairment loss of leasehold improvements			$ 1,536
Impairment loss			1,731
Impairment loss			3,267
General and Administrative Expenses [Member] \| Cambridge Massachusetts [Member]
Operating Leased Assets [Line Items]
Impairment loss			540
Research and Development Expenses [Member] \| Cambridge Massachusetts [Member]
Operating Leased Assets [Line Items]
Impairment loss			$ 2,727
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease, remaining term			9 years
Lease renewal term (in years)			10 years
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease, remaining term			1 year
Lease renewal term (in years)			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	$ 1,079

Common Stock and Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,489	$ 6,850
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	3,610	3,731
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,879	$ 3,119

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2024

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 March 31,
	2024			2023
Numerator:
Net loss attributable to common stockholders	$	(40,133	)	$	(71,174	)
Denominator:
Weighted-average shares outstanding, basic and diluted		146,101,581			125,862,975
Net loss per share attributable to common stockholders, basic and diluted	$	(0.27	)	$	(0.57	)

Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share:
Stock options to purchase common stock		19,158,617			16,826,144
Unvested restricted stock units		4,152,725			4,215,834
Shares issuable under employee stock purchase plan		75,488			68,594
Warrants to purchase common stock		1,177,433			—

Fair Value Measurements - Additional Information (Detail) - USD ($)	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
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		0
Fair value, assets transfers from Level 2 to Level 1 measurement	0		0
Fair value, assets transfers from Level 1 to Level 3 measurement	0		0
Fair value, assets transfers from Level 3 to Level 1 measurement	0		$ 0
Restricted investments	$ 1,401,000	$ 1,401,000

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

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 $8,430 as of March 31, 2024 and $8,185 as of December 31, 2023, 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):


	March 31,		December 31,
	2024		2023
Cash and cash equivalents	$	111,184	$	127,965
Restricted cash, non-current		8,430		8,185
Total cash, cash equivalents and restricted cash	$	119,614	$	136,150

Recently Issued Accounting Pronouncements

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires public entities to disclose information about their reportable segments’ significant expenses and other segment items on an interim and annual basis. Public entities with a single reportable segment are required to apply the disclosure requirements in ASU 2023-07, as well as all existing segment disclosures and reconciliation requirements in ASC 280, on an interim and annual basis. ASU 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the impact that the adoption of ASU 2023-07 may have on its consolidated financial statements.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures which requires public entities to disclose specific categories in the effective tax rate reconciliation, as well as additional information for reconciling items that exceed a quantitative threshold. ASU 2023-09 also requires all entities to disclose income taxes paid disaggregated by federal, state and foreign taxes, and further disaggregated for specific jurisdictions that exceed 5% of total income taxes paid, among other expanded disclosures. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the impact that the adoption of ASU 2023-09 may have on its consolidated financial statements.

Revenue from Contracts with Customers

3 Months Ended

Mar. 31, 2024

Revenue from Contract with Customer [Abstract]

Revenue from Contracts with Customers

13. 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 14, 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 14, 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 months ended March 31, 2024 and 2023, the Company recognized $0 and $1,122 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 year ended December 31, 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 March 31, 2024, the aggregate amount of the transaction price allocated to the performance obligation of the 2016 License Agreement was approximately $200,000.

During the three months ended March 31, 2024 and 2023, using the cost-to-cost method, which best depicts the transfer of control to the customer, the Company recognized $0 and ($1,644), of collaboration revenue – related party, respectively.

As of March 31, 2024 and December 31, 2023, there was $95,364 and $95,364, respectively, of deferred revenue related to the unsatisfied portion of the performance obligation under the Nestlé agreements. As of March 31, 2024 and December 31, 2023, 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 tables present changes in the Company’s contract liabilities during the three months ended March 31, 2024 and 2023 (in thousands):


	Balance as of December 31, 2023		Additions		Deductions		Balance as of March 31, 2024
Three Months Ended March 31, 2024
Contract liabilities:
Deferred revenue - related party	$	95,364		—		—	$	95,364


	Balance as of December 31, 2022		Additions		Deductions			Balance as of March 31, 2023
Three Months Ended March 31, 2023
Contract liabilities:
Deferred revenue - related party	$	96,689		1,644		(1,122	)	$	97,211

During the three months ended March 31, 2024 and 2023 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 March 31,
	2024		2023
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$	—	$	(522	)

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

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Common Stock and Stock-Based Awards

10. Common Stock and Stock-Based Awards

On February 22, 2024, 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 240,000,000 shares to 360,000,000 shares, (the “Share Increase Amendment”). At the Company’s annual meeting of stockholders held on April 4, 2024, the Company’s stockholders approved the Share Increase Amendment. On April 5, 2024, 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 three months ended March 31, 2024 and 2023, the Company sold 15,366,630 and 787,170 shares of common stock under the Sales Agreement, at an average price of approximately $1.23 and $5.67 per share, raising aggregate net proceeds of approximately $18,409 and $4,238, after deducting an aggregate commission of approximately 3% and other issuance costs.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2023:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2023		14,844,112		$	9.64		5.71	$	-
Granted		6,743,362		$	1.07
Exercised		—		$	—
Forfeited		(2,428,857	)	$	8.93
Outstanding as of March 31, 2024		19,158,617		$	6.72		7.59	$	—
Vested or expected to vest as of March 31, 2024		19,158,617		$	6.72		7.59	$	—
Options exercisable as of March 31, 2024		9,026,731		$	10.16		5.68	$	—

The weighted average grant date fair value of stock options granted during the three months ended March 31, 2024 and 2023 was $0.95 and $4.56 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 $45 and $0 of compensation expense during the three months ended March 31, 2024 and 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.

During the three months ended March 31, 2024, the Company granted stock options to certain executives for the purchase of an aggregate of 2,550,010 shares of common stock. These awards will vest only to the extent that the 30-day trailing simple average public market closing price of the Company's common stock reaches certain price thresholds. These awards have an exercise price of $1.10 and vest and become exercisable when the market conditions are satisfied or, if later, on the first anniversary of the grant date. These awards expire 10 years from the date of grant. The fair value of these market-based stock options was estimated using a Monte Carlo valuation method. During the three months ended March 31, 2024, the Company recognized $142 of compensation expense related to these awards.

Restricted Stock Units

The Company has granted restricted stock units with service-based vesting conditions (“RSUs”) and restricted stock units with performance-based vesting conditions (“PSUs”). RSUs and PSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Restricted stock units may not be sold or transferred by the holder and vest according to the vesting conditions of each award. The following table summarizes the Company’s RSU and PSU activity since December 31, 2023:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2023		3,377,804		$	4.26
Granted		1,282,941		$	1.09
Vested		(329,981	)	$	6.24
Forfeited		(178,039	)	$	3.35
Unvested restricted stock units as of March 31, 2024		4,152,725		$	3.16

During the three months ended March 31, 2024 and 2023, the Company granted 1,282,941and 1,692,095 RSUs, respectively. During the three months ended March 31, 2024 and 2023, the Company granted 0 and 1,322,715 PSUs, respectively. RSUs generally vest over four years, with 25% vesting after one year, and the remaining 75% vesting quarterly over the next 3 years, subject to continued service to the Company through the applicable vesting date. PSUs vest according to the performance requirements of the awards, generally when the Company has determined that the specified performance targets have been achieved.

In November 2023, as part of the corporate restructuring described in Note 12, Restructuring, the Company issued retention awards to employees of the Company in the form of RSUs which vest in two tranches on August 15, 2024, and May 15, 2025, subject to remaining actively employed with the Company through such date. The compensation expense associated with these awards will be recognized ratably over the vesting period. For the three months ended March 31, 2024, the Company recognized $185 in compensation expense with respect to the retention awards.

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 $260 and $0 in compensation expense during the three months ended March 31, 2024 and 2023, respectively, with respect to these PSUs. The remaining $725 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 March 31,
	2024		2023
Research and development expenses	$	3,610	$	3,731
General and administrative expenses		2,879		3,119
	$	6,489	$	6,850

Common Stock and Stock-Based Awards - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Equity [Abstract]
Number of Shares, Beginning Balance	14,844,112
Number of Shares, Granted	6,743,362
Number of Shares, Exercised	0
Number of Shares, Forfeited	(2,428,857)
Number of Shares, Ending Balance	19,158,617	14,844,112
Number of Shares, Vested or expected to vest	19,158,617
Number of Shares, Options exercisable	9,026,731
Weighted Average Exercise Price, Beginning Balance	$ 9.64
Weighted Average Exercise Price, Granted	1.07
Weighted Average Exercise Price, Exercised	0
Weighted Average Exercise Price, Forfeited	8.93
Weighted Average Exercise Price, Ending Balance	6.72	$ 9.64
Weighted Average Exercise Price, Vested or expected to vest	6.72
Weighted Average Exercise Price, Options exercisable	$ 10.16
Weighted Average Remaining Contractual Term, Outstanding	7 years 7 months 2 days	5 years 8 months 15 days
Weighted Average Remaining Contractual Term, Vested or expected to vest	7 years 7 months 2 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 8 months 4 days
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0
Aggregate Intrinsic Value, Vested or expected to vest	0
Aggregate Intrinsic Value, Options exercisable	$ 0

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2024

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, 2023, 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 three months ended March 31, 2024.

Use of Estimates

Restricted Cash

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


	March 31,		December 31,
	2024		2023
Cash and cash equivalents	$	111,184	$	127,965
Restricted cash, non-current		8,430		8,185
Total cash, cash equivalents and restricted cash	$	119,614	$	136,150

Recently Issued Accounting Pronouncements

Collaboration Profit and Loss - Additional Information (Detail) - USD ($)
$ in Thousands

3 Months Ended

Mar. 31, 2024

Mar. 31, 2023

Dec. 31, 2023

Jul. 21, 2021

Jul. 01, 2021

Business Acquisition [Line Items]

Collaboration (profit)/loss related to pre-launch activities

^[1]

$ 0

$ 3,607

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

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

10,064

$ 10,064

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

801

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

$ 2,703

[1]	Includes non-cash collaboration profits and losses related to pre-launch activities; subsequent to the approval of VOWST in April 2023, collaboration (profit) loss sharing - related party is included within changes in operating assets and liabilities

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
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net loss attributable to common stockholders	$ (40,133)	$ (71,174)
Denominator:
Weighted-average shares outstanding - basic	146,101,581	125,862,975
Weighted-average shares outstanding - diluted	146,101,581	125,862,975
Net loss per share attributable to common stockholders - basic	$ (0.27)	$ (0.57)
Net loss per share attributable to common stockholders - diluted	$ (0.27)	$ (0.57)
Anti-dilutive potential common stock equivalents excluded from the calculation of net loss per share
Investment, Type [Extensible Enumeration]	Warrant [Member]
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:	19,158,617	16,826,144
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:	4,152,725	4,215,834
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:	75,488	68,594
Common Stock [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	0

Revenue from Contracts with Customers - Additional Information (Detail) - USD ($)				1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 21, 2021	Jul. 01, 2021	Jan. 31, 2016	May 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2018	Feb. 29, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
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					$ 95,364,000		95,364,000							$ 120,000,000
Maximum development milestone payments to be received					285,000,000
Maximum regulatory payments to be received					375,000,000
Maximum amount to be received on achievement of certain commercial milestones					1,125,000,000
Proceeds on achievement of development milestone									$ 10,000,000	$ 40,000,000	$ 20,000,000	$ 10,000,000
Transaction price allocated to remaining performance obligations					200,000,000
Collaboration revenue - related party					0	$ (1,644,000)
Deferred revenue					95,364,000		$ 95,364,000
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	$ 1,122,000
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	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

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ in Thousands			3 Months Ended
	Nov. 02, 2023 Employee	Oct. 29, 2023 Employee	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporated month and year			2010-10
Entity incorporation, state or country code			DE
Reduction in workforce, percentage		41.00%
Number of positions eliminated \| Employee	160	160
Accumulated deficit			$ (1,018,368)		$ (978,235)
Cash and cash equivalents			111,184		$ 127,965
Net operating cash outflows			(35,236)	$ (76,584)
Net Income (Loss)			$ (40,133)	$ (71,174)

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
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-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1B
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-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-Publisher FASB
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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Reference 29: http://www.xbrl.org/2003/role/disclosureRef
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Reference 30: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
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Reference 32: http://www.xbrl.org/2003/role/exampleRef
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Reference 33: http://www.xbrl.org/2003/role/disclosureRef
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Reference 34: http://www.xbrl.org/2003/role/disclosureRef
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Reference 36: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
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-Section 45
-Paragraph 1A
-Subparagraph (a)
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Reference 37: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 38: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 39: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2024

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

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


	March 31, 2024			December 31, 2023
Laboratory equipment	$	29,003		$	29,081
Computer equipment		4,142			4,142
Furniture and office equipment		5,188			5,430
Leasehold improvements		32,039			33,549
Construction in progress		1,139			1,393
		71,511			73,595
Less: Accumulated depreciation and amortization		(52,396	)		(51,138	)
	$	19,115		$	22,457

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0

- Definition

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

+ References + Details

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

3 Months Ended

Mar. 31, 2024

Mar. 31, 2023

Cash flows from operating activities:

Net Income (Loss)

$ (40,133)

$ (71,174)

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

Stock-based compensation expense

6,489

6,850

Depreciation and amortization expense

1,559

1,400

Non-cash operating lease cost

2,393

2,070

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

(187)

Amortization of debt issuance costs

465

187

Loss on disposal of fixed assets

293

Impairment of long-lived assets

3,267

Change in fair value of warrant liabilities

(416)

Collaboration (profit) loss sharing - related party (3)

^[1]

3,607

Changes in operating assets and liabilities:

Prepaid expenses and other current and other non-current assets

4,406

3,044

Collaboration receivable - related party

1,256

Inventories

(12,326)

Deferred income - related party

379

Deferred revenue - related party

522

Accounts payable

1,594

(3,806)

Operating lease liabilities

(218)

(67)

Accrued expenses and other current and long-term liabilities (4)

^[2]

(4,244)

(19,030)

Net cash used in operating activities

(35,236)

(76,584)

Cash flows from investing activities:

Purchases of property and equipment

(62)

(4,068)

Purchases of investments

(4,426)

Sales and maturities of investments

11,233

Net cash (used in) provided by investing activities

(62)

2,739

Cash flows from financing activities:

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

18,409

4,239

Proceeds from exercise of stock options

188

Issuance of common stock under ESPP

353

1,229

Net cash provided by financing activities

18,762

5,656

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

(16,536)

(68,189)

Cash, cash equivalents and restricted cash at beginning of period

136,150

171,215

Cash, cash equivalents and restricted cash at end of period

119,614

103,026

Supplemental disclosure of cash flow information:

Cash paid for interest

3,580

1,737

Supplemental disclosure of non-cash investing and financing activities:

Property and equipment purchases included in accounts payable and accrued expenses

$ 0

$ 928

[1]	Includes non-cash collaboration profits and losses related to pre-launch activities; subsequent to the approval of VOWST in April 2023, collaboration (profit) loss sharing - related party is included within changes in operating assets and liabilities
[2]	Includes related party amounts of $8,158 and $(9,812) at March 31, 2024 and 2023, respectively (see Note 17)

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
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

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, 2022	$ 10,783	$ 125	$ 875,181	$ (864,511)	$ (12)
Beginning balance, shares at Dec. 31, 2022		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	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, 2023	$ (44,856)	$ 135	933,244	(978,235)	0
Beginning balance, shares at Dec. 31, 2023	135,041,467	135,041,467
Issuance of common stock upon exercise of stock options, value	$ 0
Issuance of common stock upon exercise of stock options, shares	0
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	$ 0	$ 1	(1)
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		609,962
Issuance of common stock under ESPP, value	353		353
Issuance of common stock under ESPP, shares		423,975
Issuance of common stock from at the market equity offering, value	18,409	$ 15	18,394
Issuance of common stock from at the market equity offering, shares		15,366,630
Stock-based compensation expense	6,489		6,489
Other comprehensive income	0
Net Income (Loss)	(40,133)			(40,133)
Ending balance at Mar. 31, 2024	$ (59,738)	$ 151	$ 958,479	$ (1,018,368)	$ 0
Ending balance, shares at Mar. 31, 2024	151,442,034	151,442,034

Commitments and Contingencies

3 Months Ended

Mar. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

15. 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 March 31, 2024 or December 31, 2023.

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 March 31, 2024 or December 31, 2023.

Income Taxes

3 Months Ended

Mar. 31, 2024

Income Tax Disclosure [Abstract]

Income Taxes

16. Income taxes

The Company did not provide for any income taxes in its condensed consolidated statement of operations and comprehensive loss for the three months ended March 31, 2024 and 2023. 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 ending December 31, 2024. 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 March 31, 2024 and December 31, 2023, and has not recorded any income taxes for the three months ended March 31, 2024 and 2023. 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
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-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
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-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

Notes Payable (Tables)

3 Months Ended

Mar. 31, 2024

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
2024 (remaining 9 months)	$	—
2025		—
2026		24,750
2027		33,000
2028		33,000
Thereafter		19,250
Total	$	110,000

Restructuring (Tables)

3 Months Ended

Mar. 31, 2024

Restructuring and Related Activities [Abstract]

Schedule of Changes in Restructuring Liability

The following table presents changes in the restructuring liability for the three months ended March 31, 2024 (in thousands):


	As of March 31, 2024
Restructuring expenses	$	5,606
Less: stock-based compensation		(261	)
Cash payments made through March 31, 2024		(4,781	)
Remaining liability included in accrued expenses and other current liabilities	$	564

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Unrealized (loss) gain on investments, net of tax	$ 0	$ 0

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

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 March 31, 2024 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	82	$	—	$	—	$	82
Total assets	$	82	$	—	$	—	$	82

Warrant liabilities	$	—	$	—	$	130	$	130
Total liabilities	$	—	$	—	$	130	$	130


	Fair Value Measurements as of December 31, 2023 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	81	$	—	$	—	$	81
Total assets	$	81	$	—	$	—	$	81

Warrant liabilities	$	—	$	—	$	546	$	546
Total liabilities	$	—	$	—	$	546	$	546

Schedule Of Level 3 Inputs to Warrant Liabilities

As of March 31, 2024 and December 31, 2023, the Level 3 inputs to the warrant liabilities are as follows:



	March 31, 2024			December 31, 2023
Volatility		100.2	%		101.0	%
Term (in years)		1.3			1.3

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


	Warrant Liabilities

Balance as of December 31, 2023	$	546
Issuance of warrants		—
Adjustment to fair value		(416	)
Balance as of March 31, 2024		130

Property and Equipment, Net

3 Months Ended

Mar. 31, 2024

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

6. Property and Equipment, Net

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


	March 31, 2024			December 31, 2023
Laboratory equipment	$	29,003		$	29,081
Computer equipment		4,142			4,142
Furniture and office equipment		5,188			5,430
Leasehold improvements		32,039			33,549
Construction in progress		1,139			1,393
		71,511			73,595
Less: Accumulated depreciation and amortization		(52,396	)		(51,138	)
	$	19,115		$	22,457

Depreciation and amortization expense was $1,559 and 1,400 for the three months ended March 31, 2024 and 2023, respectively. During the three months ended March 31, 2024 and 2023, the Company disposed of certain assets with a cost basis of $594 and $9, respectively. In addition, the Company recorded an impairment loss of $1,536 related to leasehold improvements at one of the Company’s locations for which impairment indicators were determined to exist as of March 31, 2024. See Note 8, Leases, for further details.

Notes Payable - Summary of Future Principal Payments Due Under the Oaktree Credit Arrangement, Excluding Interest and End of Term Charge (Detail) $ in Thousands	Mar. 31, 2024 USD ($)
Debt Disclosure [Abstract]
2024 (remaining 9 months)	$ 0
2025	0
2026	24,750
2027	33,000
2028	33,000
Thereafter	19,250
Total	$ 110,000

- Definition

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

+ References + Details

Notes Payable - Additional Information (Detail) $ / shares in Units, $ in Thousands			3 Months Ended
	Jun. 30, 2026	Apr. 27, 2023 USD ($) TradingDays $ / shares shares	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Debt Instrument [Line Items]
Net proceeds received from credit facility		$ 50,446
Trading days prior to the funding date \| TradingDays		30
Interest expense			$ 4,663	$ 1,948
Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate		7.875%
Line of credit facility exit fee percentage		1.50%
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%
Loan and Security Agreement [Member] \| Hercules Credit Facility [Member]
Debt Instrument [Line Items]
Interest expense				$ 1,948
Oaktree Credit Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Interest expense			$ 4,046
Oaktree Credit Agreement [Member] \| Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate effective percentage			15.90%
Oaktree Credit Agreement [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Carrying value of debt			$ 102,009		$ 101,544
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
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 [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		50,000
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 [Member] \| Oaktree Fund Administration, LLC [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount		$ 30,000
Interest Rate Floor [Member] \| Term Loan Facility [Member] \| Secured Overnight Financing Rate Sofr [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate		2.50%
Interest rate cap [Member] \| Term Loan Facility [Member] \| Secured Overnight Financing Rate 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			66		276
Tranche C Warrant [Member]
Debt Instrument [Line Items]
Derivative liabilities			$ 64		$ 270

Collaboration Profit and Loss - Schedule of Collaboration Profit (Loss) (Detail) - USD ($)
$ in Thousands

3 Months Ended

Mar. 31, 2024

Mar. 31, 2023

Business Combinations [Abstract]

Share of VOWST net loss

$ 7,128

$ 0

Profit on transfer of VOWST inventory to Nestle

(4,710)

Collaboration (profit)/loss related to pre-launch activities

^[1]

3,607

Collaboration (profit) loss sharing - related party

$ 2,418

$ 3,607

[1]	Includes non-cash collaboration profits and losses related to pre-launch activities; subsequent to the approval of VOWST in April 2023, collaboration (profit) loss sharing - related party is included within changes in operating assets and liabilities

Revenue from Contracts with Customers - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 0	$ (522)

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Restricted cash	$ 8,430	$ 8,185

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (40,133)	$ (71,174)

- Definition

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

+ References

+ Details

Collaboration Profit and Loss

3 Months Ended

Mar. 31, 2024

Nestle Health Science [Member]

Business Combinations [Abstract]

Collaboration profit and loss

14. 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 13, 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 both March 31, 2024 and December 31, 2023, there was $10,064 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 months ended March 31, 2024 and 2023, the Company recognized $0, and $801 respectively, in research and development expenses and $0 and $2,703 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.

The components of the collaboration profit (loss) sharing for the three months ended March 31, 2024 and 2023 are as follows:


	Three Months Ended March 31,
	2024			2023
Share of VOWST net loss	$	7,128		$	—
Profit on transfer of VOWST inventory to Nestlé		(4,710	)		—
Collaboration (profit)/loss related to pre-launch activities		—			3,607
Total collaboration (profit) loss sharing - related party	$	2,418		$	3,607

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2024	May 06, 2024
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
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	Non-accelerated Filer
Entity Small Business	true
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	101 Cambridgepark Drive
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02140
City Area Code	617
Local Phone Number	945-9626
Entity Common Stock Shares Outstanding		151,447,763
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

Investments - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Investments [Abstract]
Maximum maturity days for cash equivalents	90 days	90 days
Restricted investments	$ 1,401	$ 1,401

Revenue from Contracts with Customers - Changes in Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Deductions	$ 0	$ (522)
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Balance at beginning of period	95,364	96,689
Deferred revenue - related party, Additions	0	1,644
Deferred revenue - related party, Deductions	0	(1,122)
Deferred revenue - related party, Balance at end of period	$ 95,364	$ 97,211

Inventories - Schedule of Capitalized Inventories (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Raw materials	$ 4,224	$ 4,426
Work in process	37,265	25,221
Finished goods	484	0
Total	$ 41,973	$ 29,647

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 1,559	$ 1,400
Impairment loss of leasehold improvements	1,536
Disposal of fully depreciated assets cost basis	$ 594	$ 9

Fair Value Measurements - Schedule of Reconciliation Company's Liabilities Measured at Fair Value on Recurring Basis (Detail) - Warrant [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 546
Issuance of warrants	0
Adjustment to fair value	(416)
Ending Balance	$ 130

Restructuring - Schedule of Changes in Restructuring Liability (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		$ 5,606
Accrued Expenses and Other Current Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 5,606
Less: stock-based compensation	(261)
Cash payments made through March 31, 2024	(4,781)
Remaining liability included in accrued expenses and other current liabilities	$ 564	$ 5,080

- 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 + Details

Fair Value Measurements - Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	$ 130	$ 546
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	130	546
Equity, Fair Value Disclosure [Abstract]
Total liabilities	130	546
Investments:
Total assets	82	81
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents	82	81
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	0
Investments:
Total assets	82	81
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents	82	81
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	0
Equity, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Investments:
Total assets	0	0
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability, Noncurrent	130	546
Equity, Fair Value Disclosure [Abstract]
Total liabilities	$ 130	546
Investments:
Total assets		$ 0

Leases (Tables)

3 Months Ended

Mar. 31, 2024

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):


	March 31, 2024		December 31, 2023
Assets:
Operating lease assets	$	105,669	$	109,793

Liabilities:
Operating lease liabilities	$	8,833	$	6,677
Operating lease liabilities, net of current portion		103,341		105,715
Total operating lease liabilities	$	112,174	$	112,392

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 March 31,
	2024			2023
Operating lease costs	$	5,771		$	5,410
Short-term lease costs		374			368
Variable lease costs		1,967			1,763
Sublease income		(376	)		—
Total lease costs	$	7,736		$	7,541

Schedule of Future Payments of Operating Lease Liabilities

As of March 31, 2024, future payments of operating lease liabilities are as follows (in thousands):


	As of March 31, 2024
2024 (remaining 9 months)	$	16,273
2025	$	22,062
2026	$	22,674
2027	$	23,347
2028	$	23,580
2029 and thereafter	$	65,819
Total future minimum lease payments	$	173,755
Less: interest		(61,581	)
Present value of operating lease liabilities	$	112,174

Inventories - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Inventory Disclosure [Abstract]
Pre-launch inventory expensed as research and development	$ 0	$ 15,613
Inventory Written- down	$ 0

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

Mar. 31, 2024

Dec. 31, 2023

Current assets:

Cash and cash equivalents

$ 111,184

$ 127,965

Collaboration receivable - related party

7,418

8,674

Inventories

41,973

29,647

Prepaid expenses and other current assets

4,606

9,124

Total current assets

165,181

175,410

Property and equipment, net

19,115

22,457

Operating lease assets

105,669

109,793

Restricted cash

8,430

8,185

Restricted investments

1,401

Other non-current assets

^[1]

41,466

41,354

Total assets

341,262

358,600

Current liabilities:

Accounts payable

5,219

3,641

Accrued expenses and other current liabilities

^[2]

76,317

80,611

Operating lease liabilities

8,833

6,677

Deferred income - related party

8,109

7,730

Total current liabilities

98,478

98,659

Long term portion of note payable, net of discount

102,009

101,544

Operating lease liabilities, net of current portion

103,341

105,715

Deferred revenue - related party

95,364

Warrant liabilities

130

546

Other long-term liabilities

1,678

1,628

Total liabilities

401,000

403,456

Commitments and contingencies (Note 15)

Stockholders' deficit:

Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2024 and December 31, 2023; no shares issued and outstanding at March 31, 2024 and December 31, 2023

Common stock, $0.001 par value; 240,000,000 shares authorized at March 31, 2024 and December 31, 2023, respectively; 151,442,034 and 135,041,467 shares issued and outstanding at March 31, 2024 and December 31, 2023, respectively

151

135

Additional paid-in capital

958,479

933,244

Accumulated other comprehensive loss

Accumulated deficit

(1,018,368)

(978,235)

Total stockholders' deficit

(59,738)

(44,856)

Total liabilities and stockholders' deficit

$ 341,262

$ 358,600

[1]	Includes $38,877 as of March 31, 2024 and December 31, 2023, of milestones related to the construction of the Company's dedicated manufacturing suite at BacThera AG, or Bacthera. Such amounts will form part of the right-of-use asset upon lease commencement.
[2]	Includes related party amounts of $36,211 and $28,053 at March 31, 2024 and December 31, 2023, respectively (see Note 17)