0001193125-23-287451 | S-1/A | XBRL Viewer

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SVB Agreement - Schedule of Determine the Fair Value of the Warrant Upon Issuance (Detail) - Silicon Valley Bank [Member]	Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term (in years)	10 years
Risk-free interest rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding	1,100
Expected dividend yield [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding	0
Expected volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding	72.9

Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. Commitments and Contingencies

790 Memorial Drive Lease

In May 2020, the Company entered into an operating lease agreement (“the 790 Memorial Drive Lease”) to occupy 3,407 square feet of laboratory and office space at 790 Memorial Drive in Cambridge, Massachusetts. The 790 Memorial Drive Lease term commenced on June 15, 2020 and subsequently expired on June 30, 2021. Pursuant to ASC 840, the Company recorded total rent expense of $0.1 million for the year ended December 31, 2021 related to the 790 Memorial Drive Lease.

OKS Building 600/700 Lease

In August 2020, the Company entered into an operating lease agreement (the “OKS Building 600/700 Lease”) to occupy 12,165 square feet of laboratory and office space at One Kendall Square in Cambridge, Massachusetts (the “OKS Facility”). The OKS Building 600/700 Lease term commenced on January 21, 2021 and was originally set to expire on January 31, 2024. The Company provided the landlord with a security deposit in the form of a $0.3 million letter of credit, which was originally recorded as restricted cash and included within “Other

non-current

assets” as of December 31, 2021.

The OKS Building 600/700 Lease also provided the Company with a tenant improvement allowance of $2.4 million, the entirety of which was utilized as of December 31, 2021. Leasehold improvements related to the OKS Building 600/700 Lease were originally being amortized over the lease term, commencing with the date that the leasehold improvements were placed into service.

OKS Sublease

In October 2021, the Company entered into an operating sublease agreement (the “OKS Sublease”) with an unrelated biotechnology company to occupy an additional 5,094 square feet of laboratory and office space in the

OKS Facility. The OKS Sublease term commenced on October 25, 2021 and was originally set to expire on March 31, 2023, unless the sublessor notified the Company in writing by July 1, 2022 that it wished to extend the sublease term through December 31, 2024. The Company provided the sublessor with a security deposit in the form of a $0.2 million letter of credit, which was originally recorded as restricted cash and included within “Other

non-current

assets” as of

December 31, 2021

OKS Sublease Extension and OKS Combined Facility Lease

In May 2022, the sublessor of the OKS Sublease provided the lease extension notification to the Company. As a result of this election, commencing on June 1, 2022, the Company was required to take control over an additional 5,302 square feet for a total occupancy of 10,396 square feet.

In August 2022, however, the Company entered into an amended lease agreement (the “OKS Combined Facility Lease”) with the landlord of the OKS Facility, the primary effects of which were the following:

•

Effective September 1, 2022, the space originally leased from the unrelated biotechnology company would now be leased directly from the OKS Facility landlord.

•

The monthly lease payment amounts owed by the Company were not modified from the original One Kendall Square Sublease, however the Company is now obligated to make an additional payment of $0.3 million at the conclusion of the OKS Combined Facility Lease term.

•

The lease term for the entirety of the Company’s leased space at the One Kendall Square Facility was amended to expire on December 31, 2023.

•

The Company provided the landlord of the OKS Facility with an additional security deposit in the form of a $0.3 million letter of credit. The $0.3 million letter of credit previously issued to the sublessor of the OKS Sublease was subsequently cancelled.

Accounting under ASC 840

As the Company obtained access to the OKS Building 600/700 Lease space in August 2020, it concluded that this represented the lease commencement date for accounting purposes. Prior to the adoption of ASC 842, and pursuant to the legacy guidance within ASC 840, the Company recorded rent expense on a straight-line basis from this date through the end of the lease term and also recorded deferred rent on the consolidated balance sheets. The Company recorded the tenant improvement allowance as a deferred lease incentive and was amortizing the deferred lease incentive as a reduction of rent expense ratably over the lease term.

For the OKS Sublease, the Company similarly recorded rent expense on a straight-line basis through the full potential lease term that would expire on December 31, 2024. The full potential lease term was utilized as the lease extension provision was at the sole discretion of the sublessor. In addition, this straight-line rent expense calculation assumed that, as of April 1, 2023, the Company would occupy the entire

10,396

square feet premises contemplated by the OKS Sublease.

As of December 31, 2021, the future minimum lease payments due under the OKS Building 600/700 Lease and the OKS Sublease were as follows (in thousands):


	Future Minimum Lease Payments
2022	$	1,779
2023		2,315
2024		1,067

Total future minimum lease payments	$	5,161

Pursuant to ASC 840, the Company recorded total rent expense of $0.6 million for the year ended December 31, 2021 related to the OKS Building 600/700 Lease and the OKS Sublease.

Accounting under ASC 842

As a result of the adoption of ASC 842 on January 1, 2022, the Company initially recorded

right-of-use

assets and corresponding lease liabilities for the OKS Building 600/700 Lease and the OKS Sublease. As there was no rate implicit in either lease, the Company estimated its incremental borrowing rate based upon a synthetic credit rating and yield curve analysis. Based upon this analysis, the Company calculated a discount rate of 5.09% for both the OKS Building 600/700 Lease and the OKS Sublease as of January 1, 2022.

The Company then assessed the OKS Combined Facility Lease as a lease modification, concluding that the modification did not result in a separate contract pursuant to ASC

842-10-25-8.

Based upon this assessment, and in accordance with ASC

842-10-25-15,

the Company has accounted for the modification as a termination of the existing leases and the creation of a new operating lease. As there was no rate implicit in the OKS Combined Facility Lease, the Company again estimated its incremental borrowing rate based upon a synthetic credit rating and yield curve analysis. Based upon this analysis, the Company calculated a discount rate of 7.87% as of August 31, 2022, the effective date of the modification.

As the OKS Combined Facility Lease term ends on December 31, 2023, the Company is now amortizing the leasehold improvements originally related to the OKS Building 600/700 Lease through December 31, 2023. Additionally, the combined $0.6 million letters of credit issued to the OKS Facility landlord are classified as restricted cash and included within “Prepaid expenses and other current assets” as of December 31, 2022.

As of December 31, 2022, the future minimum lease payments due under the OKS Combined Facility Lease were as follows (in thousands):


	Amount
2023	$	2,621
Less: effect of discounting		(92	)

Total lease liability	$	2,529

Pursuant to ASC 842, the Company recorded operating lease expense of $1.4 million and variable lease expense of $0.7 million for the year ended December 31, 2022 related to the OKS Building 600/700 Lease, OKS Sublease and OKS Combined Facility Lease. As of December 31, 2022, the remaining lease term of the OKS Combined Facility Lease was 1.0 year.

Cummings Park Sublease

In February 2022, the Company entered into an operating sublease agreement (the “Cummings Park Sublease”) to occupy 18,148 square feet of laboratory and office space at Cummings Park in Woburn, Massachusetts. The Cummings Park Sublease term commenced on February 23, 2022 and will expire on July 31, 2024. Contemporaneously with the execution of the Cummings Park Sublease, the Company provided the landlord with a cash security deposit in the amount of $0.1 million.

Pursuant to the terms of the Cummings Park Sublease, the Company was not obligated to make rental payments until 91 days after the Cummings Park Sublease commencement date (the “Cummings Park Rent Commencement Date”). Rental payments will escalate on each successive anniversary of the Cummings Park Rent Commencement Date.

As of December 31, 2022, the future minimum lease payments due under the Cummings Park Sublease were as follows (in thousands):


	Amount
2023	$	411
2024		212

Total remaining minimum lease payments		623
Less: effect of discounting		(22	)

Total lease liability	$	601

Pursuant to ASC 842, the Company recorded operating lease expense of $0.3 million and variable lease expense of less than $0.1 million for the year ended December 31, 2022 related to the Cummings Park Sublease. As of December 31, 2022, the remaining lease term of the Cummings Park Sublease was 1.6 years.

60 First Street Lease

In April 2022, the Company entered into an operating lease agreement (the “60 First Street Lease”) to occupy 50,453 square feet of laboratory and office space in Cambridge, Massachusetts (the “60 First Street Facility”). The 60 First Street Lease term will commence on the later of i) the substantial completion of the landlord’s base building improvements or ii) October 31, 2022 (such date the “60 First Street Lease Commencement Date”). Rental payments will commence 12 months following the 60 First Street Lease Commencement Date (such date the “60 First Street Rent Commencement Date”), and the 60 First Street Lease will expire on the last day of the 120

full calendar month following the 60 First Street Rent Commencement Date. Rental payments will escalate on each successive anniversary of the 60 First Street Rent Commencement Date, and the total rental payments over the term of the 60 First Street Lease are expected to be $76.7 million. In addition, the 60 First Street Lease also provides the Company with a tenant improvement allowance of $13.1 million.

The Company provided the landlord with a security deposit in the form of a $4.5 million letter of credit, which has been recorded as restricted cash and included within “Other

non-current

assets” as of December 31, 2022. This letter of credit will be reduced to $3.4 million upon substantial completion of the Company’s tenant improvements and then to $2.3 million upon the third anniversary of the 60 First Street Lease Commencement Date.

As of December 31, 2022, the landlord had not yet delivered the 60 First Street Facility to the Company. Accordingly, the Company concluded that the lease commencement date had not occurred and no

right-of-use

asset, lease liability or operating lease expense related to the 60 First Street Lease was recorded as of or for the year ended December 31, 2022. Additionally, the Company did not utilize any portion of the $13.1 million tenant improvement allowance as of December 31, 2022.

Litigation

The Company is not a party to any litigation, nor had it established any reserves for litigation liabilities as of December 31, 2022 or 2021.

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property plant and equipment gross			$ 14,121	$ 8,190
Depreciation expense	$ 2,645	$ 1,760	2,511	1,595
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross			$ 2,049	$ 631

Related Party Transactions - Additional Information (Detail) - Affiliate Of Atlas [Member] - Consulting Services [Member] - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Other sundry liabilities current	$ 0	$ 100,000
Maximum [Member]
Related Party Transaction [Line Items]
Professional fees		$ 100,000
Minimum [Member]
Related Party Transaction [Line Items]
Professional fees	$ 100,000

Preferred Stock - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended								2 Months Ended		12 Months Ended
	Mar. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Nov. 30, 2021 $ / shares shares	Jul. 31, 2021 USD ($) $ / shares shares	Jul. 31, 2020 shares	Jun. 30, 2020 USD ($) shares	Aug. 31, 2019 shares	May 31, 2019 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Jul. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2021 $ / shares shares	Dec. 31, 2021 Member $ / shares shares	Dec. 31, 2021 Directors $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 01, 2021 $ / shares	Jul. 01, 2021	Jun. 01, 2020 $ / shares
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares					2,232,143
Temporary equity issue price per share		$ 2.78						$ 1	$ 2.78		$ 2.78	$ 2.78	$ 2.78	$ 2.78				$ 2.24
Proceeds from redeemable convertible preferred stock \| $						$ 45.5
Minimum issue price per share for convesion of temporary preferred equity into permanent equity		$ 5.56							$ 5.56		$ 5.56	$ 5.56	$ 5.56	$ 5.56
Minimum gross proceeds as per underwriting for conversion of temporary equity into permanent equity \| $											$ 75.0
Percentage Of Temporary Equity Holding Approval Required For Conversion Into Permanent Equity	66.00%	66.00%							66.00%		66.00%	66.00%	66.00%	66.00%
Milestone Based Series B One And Series BTwo Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Class of warrants or rights number of securities covered by warrants or rights \| shares			16,232,013
Class of warrants or rights exercise price per share			$ 2.78
Warrants To Subscribe For Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Class of warrants or rights number of securities covered by warrants or rights \| shares															20,424,108
Class of warrants or rights exercise price per share															$ 2.24
Fair value of liabilities issued during the period measured based on unobservable inputs \| $															$ 11.1
Series Seed 1 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity into permanent equity exchange ratio	0.049688
Series C-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity into permanent equity exchange ratio	0.049688
Series C-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity into permanent equity exchange ratio	0.049688
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares					2,232,143	18,191,965
Temporary equity issue price per share		$ 2.24							$ 2.24		$ 2.24	$ 2.24	$ 2.24	$ 2.24				$ 2.24
Proceeds from redeemable convertible preferred stock \| $										$ 45.5
Embedded derivative value per share																	2.12%
Embedded derivative gain loss on embedded derivative net \| $											$ 13.5
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity conversion price per share		$ 2.24							$ 2.24		$ 2.24	$ 2.24	$ 2.24	$ 2.24
Temporary equity into permanent equity exchange ratio	0.049688
Series B-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares		4,932,950	17,289,273
Temporary equity issue price per share		$ 2.61							$ 2.61		$ 2.61	$ 2.61	$ 2.61	$ 2.61		$ 2.61
Proceeds from redeemable convertible preferred stock \| $									$ 57.7
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity conversion price per share		$ 2.61							$ 2.61		$ 2.61	$ 2.61	$ 2.61	$ 2.61
Temporary equity into permanent equity exchange ratio	0.049688
Series B-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity issue price per share		$ 2.78							$ 2.78		$ 2.78	$ 2.78	$ 2.78	$ 2.78
Proceeds from redeemable convertible preferred stock \| $		$ 12.5
Temporary equity dividend rate percentage		8.00%							8.00%		8.00%	8.00%	8.00%	8.00%
Number of directors entitled to be elected on an as converted basis into common stock													2	2
Temporary equity conversion price per share		$ 2.78							$ 2.78		$ 2.78	$ 2.78	$ 2.78	$ 2.78
Temporary equity into permanent equity exchange ratio	0.049688
Series Seed 3 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity issue price per share		1.3							1.3		1.3	1.3	1.3	1.3
Temporary equity conversion price per share		1.3							1.3		1.3	1.3	1.3	1.3
Series Seed One And Series Two Redeemable Convertibe Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity conversion price per share		1							1		1	1	1	1
Series B One And B Two Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares			17,289,273
Temporary equity issue price per share																$ 2.61
Series Seed Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares							7,780,769
Temporary equity issue price per share								1.3
Series 3 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares							7,780,769
Temporary equity issue price per share								$ 1.3
Series Seed 1 and Series Seed 2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares								4,000,000
Temporary equity issue price per share		1						$ 1	1		1	1	1	1
Proceeds from redeemable convertible preferred stock \| $								$ 13.9
Minimum [Member] \| Series Seed 1 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		1							1		1	1	1	1
Minimum [Member] \| Series C-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		1							1		1	1	1	1
Minimum [Member] \| Series C-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		1.3							1.3		1.3	1.3	1.3	1.3
Minimum [Member] \| Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		2.24							2.24		2.24	2.24	2.24	2.24
Minimum [Member] \| Series B-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		2.61							2.61		2.61	2.61	2.61	2.61
Minimum [Member] \| Series B-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share		$ 2.78							$ 2.78		$ 2.78	$ 2.78	$ 2.78	$ 2.78
One Investors Having Agreed To Subscribe Milestone Based B Two Redeemable Convertible Preferred Stock [Member] \| Milestone Based Series B One And Series BTwo Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Class of warrants or rights number of securities covered by warrants or rights \| shares		134,892							134,892		134,892	134,892	134,892	134,892
Waiver of Milestone Requirements and Exercise of Rights Relating to Subscribe for Temporary Equity [Member] \| Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares				20,424,108								20,424,108
Temporary equity issue price per share				$ 2.24
Proceeds from redeemable convertible preferred stock \| $				$ 45.7							$ 45.7
Waiver Of Milestone Based Conditions And Subscription Of Temporary Equity By he Investor [Member] \| Series B-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares	16,366,905	4,496,403
Temporary equity issue price per share	$ 2.78
Proceeds from redeemable convertible preferred stock \| $	$ 45.5
Atlas Venture Fund XI, L.P. [Member] \| Series Seed 1 and Series Seed 2 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity stock issued during the period shares new issues \| shares								2,000,000
Proceeds from exercise of options linked to issuers equity \| $								$ 2.0

Accrued Expenses and Other Current Liabilities

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Disclosure Of Accrued Expenses And Other Current Liabilities [Abstract]

Accrued Expenses and Other Current Liabilities

6. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities as of September 30, 2023 and December 31, 2022 were comprised as follows (in thousands):


	September 30, 2023		December 31, 2022
Annual bonus	$	2,356	$	2,198
External research and development services		1,910		274
Other employee compensation and benefits		146		426
Financing costs		808		—
Other operating expenses		491		277

Total accrued expenses and other current liabilities	$	5,711	$	3,175

7. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities as of December 31, 2022 and 2021 were comprised as follows (in thousands):


	December 31,
	2022		2021
Annual bonus	$	2,198	$	1,883
Other employee compensation and benefits		426		401
External research and development services		274		440
Other operating expenses		277		497

Total accrued expenses and other current liabilities	$	3,175	$	3,221

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Summary of Provision

The provision for income taxes for the years ended December 31, 2022 and 2021 was comprised as follows (in thousands):


	Year Ended December 31,
	2022		2021
Current taxes:
Federal	$	—	$	—
State		10		2

Total current taxes		10		2
Deferred taxes:
Federal		—		—
State		—		—

Total deferred taxes		—		—

Total provision for income taxes	$	10	$	2

Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate

A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows:


	December 31,
	2022			2021
Income tax computed at federal statutory rate		21.0	%		21.0	%
State taxes, net of federal benefit		6.1	%		9.9	%
Tax credit carryforwards		6.2	%		6.2	%
Permanent items		(0.2	)%		12.5	%
Change in valuation allowance		(32.7	%)		(49.4	%)
Other		(0.4	%)		(0.2	)%

Effective tax rate		—	%		—	%

Summary of Deferred Tax Assets

The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2022 and 2021 were comprised as follows (in thousands):


	December 31,
	2022			2021
Deferred tax assets:
Net operating loss carryforwards	$	19,580		$	14,481
Tax credit carryforwards		5,477			1,871
Capitalized research and development		10,279			—
Stock-based compensation		319			148
Deferred rent		—			521
Operating lease liability		855			—
Accrued expenses and other temporary differences		707			650

Total deferred tax assets		37,217			17,671
Less: valuation allowance		(36,094	)		(17,091	)

Net deferred tax assets		1,123			580
Deferred tax liabilities:
Operating right-of-use asset		(552	)
Depreciation		(571	)		(580	)

Total deferred tax liabilities		(1,123	)		(580	)

Net deferred taxes	$	—		$	—

Common Stock - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Common stock shares authorized	117,138,030	115,838,000	115,838,000
Common stock dividends declared	$ 0	$ 0

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Jan. 31, 2019
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, capital shares reserved for future issuance	111,134,000	111,134,000		110,432,000	111,047,000
Aggregate Intrinsic value of stock options exercised	$ 2,306	$ 2,306		$ 1,881
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, capital shares reserved for future issuance	4,000	4,000		58,000	488,000
Aggregate Fair value of awards vested		$ 100	$ 400	$ 500	$ 300
Employee Stock Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, capital shares reserved for future issuance	12,304,000	12,304,000		9,280,000	8,322,000
Weighted average grant date fair value of options granted		$ 0.69	$ 0.74	$ 0.73	$ 0.41
Aggregate Intrinsic value of stock options exercised	$ 200	$ 200	$ 100	$ 100	$ 200
Unrecognized stock based compensation cost	$ 3,900	$ 3,900		$ 2,500
Unrecognized stock based compensation cost, weighted average period of recognition		2 years 8 months 12 days		2 years 8 months 12 days
Two Thousand Nineteen Stock Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock shares issuance						2,219,565
Common stock shares under 2019 plan	15,048,960			13,748,930
Common stock, capital shares reserved for future issuance	949,921	949,921		3,217,888

Property and Equipment, Net

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

6. Property and Equipment, Net

Property and equipment, net, as of December 31, 2022 and 2021 was comprised as follows (in thousands):


	Estimated Useful Life	December 31,
	(in Years)	2022			2021
Laboratory equipment	5	$	8,441		$	4,364
Furniture and office equipment	4		477			262
Computer equipment	3		213			50
Leasehold improvements	Shorter of useful life or remaining lease term		2,941			2,883
Construction in progress			2,049			631

Total property and equipment, gross			14,121			8,190
Less: accumulated depreciation			(4,255	)		(1,744	)

Total property and equipment, net		$	9,866		$	6,446

As of December 31, 2022, the Company had construction in progress of $2.0 million, predominately related to laboratory equipment received but not yet installed and capitalizable costs related to the Company’s future corporate headquarters.

Depreciation expense for the years ended December 31, 2022 and 2021 was $2.5 million and $1.6 million, respectively.

Stock-based Compensation - Summary of Components of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,154	$ 905	$ 1,140	$ 807
Research and development [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	402	182	243	137
General and administrative [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 752	$ 723	$ 897	$ 670

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Operating Activities:
Net loss	$ (55,746)	$ (41,998)	$ (58,032)	$ (21,959)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of preferred stock tranche liability				(13,505)
Non-cash lease expense	2,376	977	1,396
Stock-based compensation expense	1,154	905	1,140	807
Depreciation expense	2,645	1,760	2,511	1,595
Non-cash interest expense		30	118	36
Net amortization of premiums and discounts on investments	(80)	42	(145)	20
Loss on disposal of property and equipment				8
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(14)	(616)	(28)	(398)
Accounts payable	309	2,186	1,755	56
Accrued expenses	1,730	(264)	(39)	1,961
Operating lease liabilities	1,313	(1,525)	(2,198)
Deferred rent				(686)
Other non-current assets and liabilities	137	(109)
Other non-current assets			(123)	(29)
Net cash used in operating activities	(46,176)	(38,612)	(53,645)	(32,094)
Investing Activities:
Purchases of investments		(37,213)	(37,213)	(35,067)
Proceeds from maturities of investments	19,000	48,985	53,485
Purchases of property and equipment	(5,830)	(3,725)	(5,136)	(3,752)
Advance payments for property and equipment not yet received	(351)	(76)	(76)	(695)
Proceeds from sale of property and equipment				13
Net cash provided by investing activities	12,819	7,971	11,060	(39,501)
Financing Activities:
Proceeds from exercises of stock options	349	48	62	28
Other financing activities, net	(2,634)	(44)	(44)	(30)
Net cash provided by financing activities	43,173	4	18	115,945
Net increase (decrease) in cash, cash equivalents and restricted cash	9,816	(30,637)	(42,567)	44,350
Cash, cash equivalents and restricted cash, beginning of period	41,477	84,044	84,044	39,694
Cash, cash equivalents and restricted cash, end of period	51,293	53,407	41,477	84,044
Non-cash investing and financing activities:
Property and equipment capitalized under tenant improvement allowance				522
Purchases of property and equipment in accounts payable and accrued expenses	167	183	402	301
Financing costs in accounts payable and accrued expenses	965			44
Operating lease liabilities arising from right-of-use assets	26,777	5,287	5,629
Stock option exercise receivables in prepaid expenses and other current assets	12	1
Supplemental cash flow information:
Cash paid for income taxes			11
Cash paid for operating lease liabilities	2,244	$ 1,600	$ 2,335
Series A Convertible Preferred Stock [Member]
Financing Activities:
Convertible preferred stock, net of issuance costs				45,708
Series B-1 Convertible Preferred Stock [Member]
Financing Activities:
Convertible preferred stock, net of issuance costs				57,739
Series B-2 Convertible Preferred Stock [Member]
Financing Activities:
Convertible preferred stock, net of issuance costs	$ 45,458			$ 12,500

Preferred Stock	9 Months Ended	12 Months Ended
Preferred Stock	Sep. 30, 2023	Dec. 31, 2022
Temporary Equity Disclosure [Abstract]
Preferred Stock	8. Preferred Stock Series Seed Preferred Stock In May 2019, the Company entered into a Series Seed Stock Purchase Agreement (the “Series Seed 1 and 2 Agreement”). Under this Series Seed 1 and 2 Agreement, the Company sold an aggregate of 4,000,000 shares of Series Seed Preferred Stock at a price of $1.00 per share. In addition, the Company was previously party to a Simple Agreement for Future Equity (the “SAFE”) with Atlas Venture Fund XI, L.P. (“Atlas”) whereby the Company received $2.0 million in exchange for granting Atlas the right to participate in a future equity financing. In conjunction with the execution of the Series Seed 1 and 2 Agreement, the SAFE converted into 2,000,000 additional shares of Series Seed Preferred Stock. Subsequently, the Company entered into a Series Seed 3 Preferred Stock Purchase Agreement (the “Series Seed 3 Agreement”) in August 2019 under which it sold 7,780,769 additional shares of Series Seed Preferred Stock at a price of $1.30 per share. Under the Series Seed 1 and 2 Agreement and the Series Seed 3 Agreement, the Company received aggregate net cash proceeds of $13.9 million, after deducting offering expenses paid by the Company. The Company assessed the terms and features of the Series Seed Preferred Stock and concluded that it should be classified outside of permanent equity in the condensed consolidated balance sheets, as the Series Seed Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series Seed Preferred Stock within temporary equity in the condensed consolidated balance sheets. As of September 30, 2023, the Series Seed Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series Seed Preferred Stock is outlined below. Series A Preferred Stock In June 2020, the Company entered into the Series A Preferred Stock Purchase Agreement (the “Series A Agreement”). Under the Series A Agreement, the Company sold 18,191,965 shares at an initial closing in June 2020 and 2,232,143 shares at an additional closing in July 2020, both at a price of $2.24 per share. The Company received aggregate net cash proceeds of $45.5 million from these sales, after deducting offering expenses paid by the Company. The Series A Agreement also included a right (the “Series A Tranche Right”) whereby investors would be obligated to purchase, and the Company obligated to sell, an additional 20,424,108 shares of Series A Preferred Stock at $2.24 per share upon the achievement of certain research and development milestones prior to December 31, 2021 (the “Series A Milestone Closing”). Investors could also elect to waive the conditions of the Series A Milestone Closing and purchase their allotment of additional shares at any time prior to the Series A Milestone Closing. The Company assessed the terms and features of the Series A Preferred Stock and concluded that it should be classified outside of permanent equity in the condensed consolidated balance sheets, as the Series A Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series A Preferred Stock within temporary equity in the condensed consolidated balance sheets. As of September 30, 2023, the Series A Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series A Preferred Stock is outlined below. The Company also assessed the Series A Tranche Right and concluded that it met the definition of a freestanding financial instrument as it was both legally detachable and separately exercisable from the Series A Preferred Stock. In accordance with ASC Topic 480, Distinguishing Liabilities from Equity , the Series A Tranche Right was initially classified as a liability in the consolidated balance sheet since the underlying Series A Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. The Company first allocated the Series A Preferred Stock proceeds to the Series A Tranche Right based upon its fair value at the date of issuance, and the remaining proceeds were allocated to the Series A Preferred Stock. The fair value of the Series A Tranche Right on the date of issuance was determined to be $11.1 million. As the Series A Tranche Right was classified as a liability, it was subsequently re-measured at fair value at each reporting period. In July 2021, the holders of the Series A Preferred Stock elected to waive the conditions of the Series A Milestone Closing and exercise the Series A Tranche Right. Accordingly, the holders purchased 20,424,108 additional shares of Series A Preferred Stock at a price of $2.24 per share. The Company received aggregate net cash proceeds of $45.7 million from this sale, after deducting offering expenses paid by the Company. The Company recognized a $13.5 million gain from the settlement of the Series A Tranche Right and subsequently extinguished the preferred stock tranche asset in conjunction with the issuance of the related Series A Preferred Stock. Series B Preferred Stock In November 2021, the Company entered into the Series B Preferred Stock Purchase Agreement (the “Series B Agreement”). Under the Series B Agreement, the Company initially sold 17,289,273 shares of Series B-1 Preferred Stock at a price of $2.61 per share. The Series B Agreement also contemplated the issuance of Series B-2 Preferred Stock, as outlined further below. The Series B-1 Preferred Stock and the Series B-2 Preferred Stock are collectively referred to as the “Series B Preferred Stock” unless specifically noted. The Series B Agreement also included a right (the “Series B Tranche Right”) whereby investors would be obligated to purchase, and the Company obligated to sell, 16,232,013 shares of Series B-2 Preferred Stock at $2.78 per share upon the achievement of a certain research and development milestone (the “Series B Milestone Closing”). Investors could also elect to waive the conditions of the Series B Milestone Closing and purchase their allotment of Series B-2 Preferred Stock at any time prior to the Series B Milestone Closing. In December 2021, the Company subsequently amended the Series B Agreement (the “Series B Agreement Amendment”) to include two additional investors. Under the Series B Agreement Amendment, the Company sold an additional 4,932,950 shares of Series B-1 Preferred Stock at a price of $2.61 per share. Additionally, one investor elected to waive the conditions of the Series B Milestone Closing and purchase 4,496,403 shares of Series B-2 Preferred Stock at a price of $2.78 per share. The other investor included in the Series B Agreement Amendment maintained the Series B Tranche Right to purchase 134,892 shares of Series B-2 Preferred Stock. In total during November and December 2021, the Company received aggregate net cash proceeds of $57.7 million from the sale of Series B-1 Preferred Stock and $12.5 million from the sale of Series B-2 Preferred Stock, after deducting offering expenses paid by the Company. The Company also assessed the Series B Tranche Right and concluded that, while separately exercisable, it was not legally detachable from the Series B Preferred Stock. Accordingly, the Company concluded that the Series B Tranche Right did not meet the definition of a freestanding financial instrument and was instead an embedded feature of the Series B Preferred Stock. In March 2023, the holders of the Series B Preferred Stock elected to waive the conditions of the Series B Milestone Closing and exercise the Series B Tranche Right. Accordingly, the holders purchased 16,366,905 shares of Series B-2 Preferred Stock at a price of $2.78 per share. The Company received aggregate net cash proceeds of $45.5 million from this sale, after deducting offering expenses paid by the Company. The Company assessed the terms and features of the Series B Preferred Stock and concluded that it should be classified outside of permanent equity in the condensed consolidated balance sheets, as the Series B Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series B Preferred Stock within temporary equity in the condensed consolidated balance sheets. As of September 30, 2023, the Series B Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series B Preferred Stock is outlined below. Rights, Preferences and Privileges of Preferred Stock The rights, preferences and privileges of the Series Seed Preferred Stock, the Series A Preferred Stock, the Series B-1 Preferred Stock and the Series B-2 Preferred Stock are as follows. In the discussion below, the Series Seed Preferred Stock and the Series A Preferred Stock, Series B-1 Preferred Stock and the Series B-2 Preferred Stock are collectively referred to as the “Preferred Stock” unless specifically noted. Conversion Each share of Preferred Stock shall be convertible, at the option of the holder thereof, at any time and from time to time, and without the payment of additional consideration by the holder thereof, into such number of fully paid and non-assessable shares of common stock as is determined by dividing the original issuance price by the conversion price in effect at the time of conversion. The original conversion price of the Series Seed 1 Preferred Stock and Series Seed 2 Preferred Stock is $1.00, the original conversion price of the Series Seed 3 Preferred Stock is $1.30, the original conversion price of the Series A Preferred Stock is $2.24, the original conversion price of the Series B-1 Preferred Stock is $2.61 and the original conversion price of the Series B-2 Preferred Stock is $2.78. Shares of preferred stock are subject to adjustments to reflect the issuance of common stock, options, warrants, or other rights to subscribe for or to purchase common stock for a consideration per share, less than the conversion price then in effect and subsequent stock dividends, stock splits, combinations, or recapitalizations. The Preferred Stock is subject to mandatory conversion upon the closing of a sale of common stock to the public at a price of at least $5.56 per share (subject to appropriate adjustment in the event of a stock dividend, stock split, combination or other similar recapitalization) in a firm-commitment underwritten public offering resulting in at least $75.0 million of gross proceeds to the Company. The Preferred Stock is also subject to mandatory conversion upon the vote or written consent of the holders of at least 66% of the then-outstanding shares of Preferred Stock, voting as a single class on an as-converted to common stock basis. Dividends The holders of Preferred Stock, in preference to common stockholders, are entitled to receive, when, as and if declared by the Company’s Board of Directors, dividends at a rate of 8% annually. Dividends on Preferred Stock are non-cumulative and are payable only when and if declared by the Company’s Board of Directors. The holders of Preferred Stock are entitled to participate in dividends on common stock on an as-converted basis when and if declared by the Company’s Board of Directors. Since the Company’s inception, no dividends have been declared. Liquidation Preference In the event of any voluntary or involuntary liquidation, dissolution, winding up or deemed liquidation event of the Company, the holders of shares of Preferred Stock then outstanding shall be entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock, an amount equal to the original issue price per share plus any dividends declared but unpaid thereon. For clarity, the original issue price of the Series Seed 1 Preferred Stock and Series Seed 2 Preferred Stock was $1.00 per share, the original issue price of the Series Seed 3 Preferred Stock was $1.30 per share, the original issue price of the Series A Preferred Stock was $2.24 per share, the original issue price of the Series B-1 Preferred Stock was $2.61 per share and the original issue price of the Series B-2 Preferred Stock was $2.78 per share. If upon any voluntary or involuntary liquidation, dissolution, winding up or deemed liquidation event of the Company, the assets of the Company available for distribution are insufficient to pay the holders of Preferred Stock the full amount to which they are entitled, the holders of shares of Preferred Stock shall share ratably in any distribution of the assets available for distribution in proportion to the respective amounts which would otherwise be payable in respect of the shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full. Redemption The Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event, which includes a merger or a sale of substantially all of the assets of the Company. As of September 30, 2023, a deemed liquidation event is not considered to be probable. Voting Rights The holders of Preferred Stock are entitled to vote based on the number of common shares that their preferred shares convert into on as-converted basis at the time of such vote. Except in specific circumstances, holders of Preferred Stock shall vote as a single class with the common stockholders. The holders of record of the shares of the Series Seed Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors. The holders of record of the shares of the Series A Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors. The holders of record of the shares of the Series B Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors. Conversion of Preferred Stock Pursuant to the terms of the Merger Agreement, immediately prior to closing of the Merger, each share of Preferred Stock issued and outstanding immediately prior to the Closing of the Merger was converted into shares of the Company’s common stock, and then exchanged in the Merger for shares of Frequency common stock using an exchange ratio of 0.049688 . The conversion was approved by greater than 66% of the then-outstanding shares of Preferred Stock, voting as a single class on an as-converted to common stock basis.	10. Preferred Stock Series Seed Preferred Stock In May 2019, the Company entered into a Series Seed Stock Purchase Agreement (the “Series Seed 1 and 2 Agreement”). Under this Series Seed 1 and 2 Agreement, the Company sold an aggregate of 4,000,000 shares of Series Seed Preferred Stock at a price of $1.00 per share. In addition, the Company was previously party to a Simple Agreement for Future Equity (the “SAFE”) with Atlas Venture Fund XI, L.P. (“Atlas”) whereby the Company received $2.0 million in exchange for granting Atlas the right to participate in a future equity financing. In conjunction with the execution of the Series Seed 1 and 2 Agreement, the SAFE converted into 2,000,000 additional shares of Series Seed Preferred Stock. Subsequently, the Company entered into a Series Seed 3 Preferred Stock Purchase Agreement (the “Series Seed 3 Agreement”) in August 2019 under which it sold 7,780,769 additional shares of Series Seed Preferred Stock at a price of $1.30 per share. Under the Series Seed 1 and 2 Agreement and the Series Seed 3 Agreement, the Company received aggregate net cash proceeds of $13.9 million, after deducting offering expenses paid by the Company. The Company assessed the terms and features of the Series Seed Preferred Stock and concluded that it should be classified outside of permanent equity in the consolidated balance sheets, as the Series Seed Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series Seed Preferred Stock within temporary equity in the consolidated balance sheets. As of December 31, 2022, the Series Seed Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series Seed Preferred Stock is outlined below. Series A Preferred Stock In June 2020, the Company entered into the Series A Agreement. Under the Series A Agreement, the Company sold 18,191,965 shares at an initial closing in June 2020 and 2,232,143 shares at an additional closing in July 2020, both at a price of $2.24 per share. The Company received aggregate net cash proceeds of $45.5 million from these sales, after deducting offering expenses paid by the Company. As outlined within Note 3, “Fair Value Measurements”, the Series A Agreement also included the Series A Tranche Right whereby investors would be obligated to purchase, and the Company obligated to sell, an additional 20,424,108 shares of Series A Preferred Stock at $2.24 per share upon the achievement of certain research and development milestones prior to December 31, 2021 (the “Series A Milestone Closing”). Investors could also elect to waive the conditions of the Series A Milestone Closing and purchase their allotment of additional shares at any time prior to the Series A Milestone Closing. The Company assessed the terms and features of the Series A Preferred Stock and concluded that it should be classified outside of permanent equity in the consolidated balance sheets, as the Series A Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series A Preferred Stock within temporary equity in the consolidated balance sheets. As of December 31, 2022, the Series A Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series A Preferred Stock is outlined below. The Company also assessed the Series A Tranche Right and concluded that it met the definition of a freestanding financial instrument as it was both legally detachable and separately exercisable from the Series A Preferred Stock. In accordance with ASC 480, the Series A Tranche Right was initially classified as a liability in the consolidated balance sheet because the underlying Series A Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. The Company first allocated the Series A Preferred Stock proceeds to the Series A Tranche Right based upon its fair value at the date of issuance, and the remaining proceeds were allocated to the Series A Preferred Stock. The fair value of the Series A Tranche Right on the date of issuance was determined to be $11.1 million using a probability-weighted present value model that considered the probability of triggering the Series A Tranche Right through the achievement of the certain research and development milestones outlined in the Series A Agreement. The Company converted the future values to their present values using a discount rate it considered to be appropriate for probability-adjusted cash flows. As the Series A Tranche Right was classified as a liability, it was subsequently re-measured at fair value at each reporting period. In July 2021, the holders of the Series A Preferred Stock elected to waive the conditions of the Series A Milestone Closing and exercise the Series A Tranche Right. Accordingly, the holders purchased 20,424,108 additional shares of Series A Preferred Stock at a price of $2.24 per share. The Company received aggregate net cash proceeds of $45.7 million from this sale, after deducting offering expenses paid by the Company. As detailed further within Note 3, “Fair Value Measurements”, the preferred stock tranche liability was measured at fair value contemporaneously with the exercise of the Series A Tranche Right. Based upon this valuation, the Company determined that a preferred stock tranche asset existed due to the fair value of the Series A Preferred Stock being $2.12, an amount less than the contractual purchase price. As a result of the change in the fair value of the preferred stock tranche asset, the Company recognized a $13.5 million gain in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2021. The preferred stock tranche asset was then extinguished in conjunction with the issuance of the related Series A Preferred Stock. Series B Preferred Stock In November 2021, the Company entered into the Series B Preferred Stock Purchase Agreement (the “Series B Agreement”). Under the Series B Agreement, the Company initially sold 17,289,273 shares of Series B-1 Preferred Stock at a price of $2.61 per share. The Series B Agreement also contemplates the issuance of Series B-2 Preferred Stock, as outlined further below. The Series B-1 Preferred Stock and the Series B-2 Preferred Stock are collectively referred to as the “Series B Preferred Stock” unless specifically noted. The Series B Agreement also includes a right (the “Series B Tranche Right”) whereby investors would be obligated to purchase, and the Company obligated to sell, 16,232,013 shares of Series B-2 Preferred Stock at $2.78 per share upon the achievement of a certain research and development milestone (the “Series B Milestone Closing”). Investors can also elect to waive the conditions of the Series B Milestone Closing and purchase their allotment of Series B-2 Preferred Stock at any time prior to the Series B Milestone Closing. In December 2021, the Company subsequently amended the Series B Agreement (the “Series B Agreement Amendment”) to include two additional investors. Under the Series B Agreement Amendment, the Company sold an additional 4,932,950 shares of Series B-1 Preferred Stock at a price of $2.61 per share. Additionally, one investor elected to waive the conditions of the Series B Milestone Closing and purchase 4,496,403 shares of Series B-2 Preferred Stock at a price of $2.78 per share. The other investor included in the Series B Agreement Amendment maintains the Series B Tranche Right to purchase 134,892 shares of Series B-2 Preferred Stock. In total, the Company received aggregate net cash proceeds of $57.7 million from the sale of Series B-1 Preferred Stock and $12.5 million from the sale of Series B-2 Preferred Stock, after deducting offering expenses paid by the Company. The Company assessed the terms and features of the Series B Preferred Stock and concluded that it should be classified outside of permanent equity in the consolidated balance sheets, as the Series B Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event that is outside of the Company’s control. Accordingly, the Company has classified the Series B Preferred Stock within temporary equity in the consolidated balance sheets. As of December 31, 2022, the Series B Preferred Stock is not being accreted to redemption as a deemed liquidation event is not considered to be probable. Further information on the rights, preferences and privileges of the Series B Preferred Stock is outlined below. The Company also assessed the Series B Tranche Right and concluded that, while separately exercisable, it is not legally detachable from the Series B Preferred Stock. Accordingly, the Company concluded that the Series B Tranche Right does not meet the definition of a freestanding financial instrument and is instead an embedded feature of the Series B Preferred Stock. Rights, Preferences and Privileges of Preferred Stock The rights, preferences and privileges of the Series Seed Preferred Stock, the Series A Preferred Stock, the Series B-1 Preferred Stock and the Series B-2 Preferred Stock are as follows. In the discussion below, the Series Seed Preferred Stock and the Series A Preferred Stock, Series B-1 Preferred Stock and the Series B-2 Preferred Stock are collectively referred to as the “Preferred Stock” unless specifically noted. Conversion Each share of Preferred Stock shall be convertible, at the option of the holder thereof, at any time and from time to time, and without the payment of additional consideration by the holder thereof, into such number of fully paid and non-assessable shares of common stock as is determined by dividing the original issuance price by the conversion price in effect at the time of conversion. The original conversion price of the Series Seed 1 Preferred Stock and Series Seed 2 Preferred Stock is $1.00, the original conversion price of the Series Seed 3 Preferred Stock is $1.30, the original conversion price of the Series A Preferred Stock is $2.24, the original conversion price of the Series B-1 Preferred Stock is $2.61 and the original conversion price of the Series B-2 Preferred Stock is $2.78. Shares of preferred stock are subject to adjustments to reflect the issuance of common stock, options, warrants, or other rights to subscribe for or to purchase common stock for a consideration per share, less than the conversion price then in effect and subsequent stock dividends, stock splits, combinations, or recapitalizations. The Preferred Stock is subject to mandatory conversion upon the closing of a sale of common stock to the public at a price of at least $5.56 per share (subject to appropriate adjustment in the event of a stock dividend, stock split, combination or other similar recapitalization) in a firm-commitment underwritten public offering resulting in at least $75.0 million of gross proceeds to the Company. The Preferred Stock is also subject to mandatory conversion upon the vote or written consent of the holders of at least 66% of the then-outstanding shares of Preferred Stock, voting as a single class on an as-converted to common stock basis. Dividends The holders of Preferred Stock, in preference to common stockholders, are entitled to receive, when, as and if declared by the Company’s Board of Directors, dividends at a rate of 8% annually. Dividends on Preferred Stock are non-cumulative and are payable only when and if declared by the Company’s Board of Directors. The holders of Preferred Stock are entitled to participate in dividends on common stock on an as-converted basis when and if declared by the Company’s Board of Directors. Since the Company’s inception, no dividends have been declared. Liquidation Preference In the event of any voluntary or involuntary liquidation, dissolution, winding up or deemed liquidation event of the Company, the holders of shares of Preferred Stock then outstanding shall be entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock, an amount equal to the original issue price per share plus any dividends declared but unpaid thereon. For clarity, the original issue price of the Series Seed 1 Preferred Stock and Series Seed 2 Preferred Stock was $1.00 per share, the original issue price of the Series Seed 3 Preferred Stock was $1.30 per share, the original issue price of the Series A Preferred Stock was $2.24 per share, the original issue price of the Series B-1 Preferred Stock was $2.61 per share and the original issue price of the Series B-2 Preferred Stock was $2.78 per share. If upon any voluntary or involuntary liquidation, dissolution, winding up or deemed liquidation event of the Company, the assets of the Company available for distribution are insufficient to pay the holders of Preferred Stock the full amount to which they are entitled, the holders of shares of Preferred Stock shall share ratably in any distribution of the assets available for distribution in proportion to the respective amounts that would otherwise be payable in respect of the shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full. Redemption The Preferred Stock is contingently redeemable upon the occurrence of a deemed liquidation event, which includes a merger or a sale of substantially all of the assets of the Company. As of December 31, 2022, a deemed liquidation event is not considered to be probable. Voting Rights The holders of Preferred Stock are entitled to vote based on the number of common shares that their preferred shares convert into on as-converted basis at the time of such vote. Except in specific circumstances, holders of Preferred Stock shall vote as a single class with the common stockholders. The holders of record of the shares of the Series Seed Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors. The holders of record of the shares of the Series A Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors. The holders of record of the shares of the Series B Preferred Stock, voting exclusively and as a separate class on an as-converted to common stock basis, are entitled to elect two members to the Company’s Board of Directors.

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Summary of Property Plant and Equipment Net

Property and equipment, net, as of December 31, 2022 and 2021 was comprised as follows (in thousands):


	Estimated Useful Life	December 31,
	(in Years)	2022			2021
Laboratory equipment	5	$	8,441		$	4,364
Furniture and office equipment	4		477			262
Computer equipment	3		213			50
Leasehold improvements	Shorter of useful life or remaining lease term		2,941			2,883
Construction in progress			2,049			631

Total property and equipment, gross			14,121			8,190
Less: accumulated depreciation			(4,255	)		(1,744	)

Total property and equipment, net		$	9,866		$	6,446

Investments

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Investments

4. Investments

The Company did not have short-term investments as of September 30, 2023.

Short-term investments as of December 31, 2022 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper	$	14,935	$	—	$	—		$	14,935
Government securities		3,985		—		(5	)		3,980

Total	$	18,920	$	—	$	(5	)	$	18,915

As of September 30, 2023, the Company held no securities that were in an unrealized loss position. As of December 31, 2022, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $4.0 million. The Company did not record any charges for credit-related impairments during the nine months ended September 30, 2023.

4. Investments

Cash equivalents and short-term investments as of December 31, 2022 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds, included in cash and cash equivalents	$	14,904	$	—	$	—		$	14,904
Short-term investments:
Commercial paper		14,935		—		—			14,935
Government securities		3,985		—		(5	)		3,980

Total	$	33,824	$	—	$	(5	)	$	33,819

Cash equivalents and short-term investments as of December 31, 2021 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds, included in cash and cash equivalents	$	71,579	$	—	$	—		$	71,579
Short-term investments:
Corporate debt securities		12,085		—		(7	)		12,078
Commercial paper		22,962		—		—			22,962

Total	$	106,626	$	—	$	(7	)	$	106,619

As of December 31, 2022 and 2021, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $4.0 million and $12.1 million, respectively. As of December 31, 2022 and 2021 the Company held no securities that were in an unrealized loss position for more than twelve months. As of December 31, 2022, the Company did not intend to sell, and would not be more likely than not required to sell,

the securities in an unrealized loss position before recovery of their amortized cost bases. Furthermore, the Company determined that there was no material change in the credit risk of these securities. As a result, the Company determined it did not hold any securities with any o

the

r-than-temporary impairment as of December 31, 2022.

Stock-based Compensation - Summary of Fair Value Assumptions on Stock Options Granted (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement [Abstract]
Risk-free interest rate	3.60%	1.90%	2.50%	1.00%
Expected dividend yield
Expected term (in years)	6 years	6 years 1 month 6 days	6 years	6 years
Expected volatility	69.50%	73.40%	72.90%	71.90%

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2021
Series A Convertible Preferred Stock [Member]
Temporary equity stock isssuance costs		$ 42
Series B-1 Convertible Preferred Stock [Member]
Temporary equity stock isssuance costs		297
Series B-2 Convertible Preferred Stock [Member]
Temporary equity stock isssuance costs	$ 42	$ 0

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	15. Related Party Transactions As a result of Atlas’ ownership of the Company’s Series Seed Preferred Stock, Series A Preferred Stock and Series B Preferred Stock, Atlas represents an affiliate of the Company. During the years ended December 31, 2022 and 2021, the Company incurred expenses of less than $0.1 million and $0.1 million, respectively, related to consulting services provided by an affiliate of Atlas. As of December 31, 2021, the Company had amounts due to this affiliate of $0.1 million. No such amounts were due to this affiliate as of December 31, 2022.

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

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

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

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

+ Details

Fair Value Measurements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			9 Months Ended	12 Months Ended
	Jul. 31, 2021	Jul. 31, 2020	Jun. 30, 2020	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Jun. 01, 2020	May 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Temporary equity stock issued during the period shares new issues		2,232,143
Temporary equity issue price per share						$ 2.78	$ 2.24	$ 1
Fair Value measurement gain loss						$ 13,500
Fair value, measurement recurring basis, liability, transfers, net				$ 0	$ 0	0
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure				$ 0	$ 0	$ 0
Series A Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure	$ 2,500
Temporary equity stock issued during the period shares new issues	20,424,108	20,424,108	20,424,108
Temporary equity issue price per share	$ 2.24
Share price	$ 2.12

The Company and Liquidity	9 Months Ended	12 Months Ended
The Company and Liquidity	Sep. 30, 2023	Dec. 31, 2022
Disclosure Of The Company And Liquidity [Abstract]
The Company and Liquidity	1. The Company and Liquidity Nature of Business Korro Bio, Inc. (the “Company”) is an RNA editing company focused on the discovery and development of novel genetic medicines. The Company was incorporated in September 2018 as RNABIO, Inc. and subsequently renamed in November 2018. Risks and Uncertainties 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 pre-clinical and clinical testing and regulatory approval, prior to commercialization. These efforts will require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. Merger Agreement & Pre-Closing Financing On July 14, 2023, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Frequency Therapeutics, Inc., a Delaware corporation (“Frequency”) and Frequency Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Frequency (“Merger Sub”). Upon the terms and subject to the satisfaction of the conditions described in the Merger Agreement, Merger Sub will be merged with and into Korro Bio, Inc., with Korro Bio, Inc. surviving as a wholly owned subsidiary of Frequency (the “Merger”). In contemplation of the Merger, the Company also entered into a subscription agreement with certain parties to purchase shares of the Company’s common stock for an aggregate purchase price of approximately $117.3 million (the “Pre-Closing Financing”). On November 3, 2023 (the “Closing Date”), following approval by the stockholders of the Company and Frequency, the Pre-Closing Financing closed immediately prior to consummation of the Merger. Subject to the terms and conditions of the Merger Agreement, immediately prior to the Closing Date, each then outstanding share of the Company’s common stock (including common stock issued upon the conversion of the Company’s preferred stock but excluding the common stock issued in the Pre-Closing Financing) converted into the right to receive 5,161,114 shares of Frequency’s common stock calculated in accordance with the Merger Agreement. The Company’s Pre-Closing Financing was contingent on and occurred prior to the closing of the Merger, subject to customary closing conditions. Shares of the Company’s common stock issued pursuant to the Pre-Closing Financing were converted into the right to receive 2,077,864 shares of Frequency common stock calculated in accordance with Merger Agreement immediately prior to closing. The Merger will be accounted for as a reverse recapitalization with the Company being the accounting acquirer and Frequency as the acquired company for accounting purposes. Going Concern Pursuant to Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 205-40, Presentation of Financial Statements—Going Concern , an entity is required to assess whether there are conditions and events, considered in the aggregate, that raise substantial doubt about an entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. As of September 30, 2023, the Company had cash, cash equivalents and short-term investments of $46.1 million. On November 3, 2023, the Company issued additional shares of common stock in the Pre-Closing Financing for aggregate proceeds of $117.3 million and the Company received $26.9 million from the Merger. The Company expects that its cash and cash equivalents outstanding as of September 30, 2023, together with the proceeds from the sale of shares of common stock issued in the Pre-Closing Financing and the Merger on November 3, 2023, will be sufficient to fund its obligations for at least 12 months from the date of issuance of these condensed consolidated financial statements.	1. The Company and Liquidity Nature of Business Korro Bio, Inc. (the “Company”) is an RNA editing company focused on the discovery and development of novel genetic medicines. The Company was incorporated in September 2018 as RNABIO, Inc. and subsequently renamed in November 2018. Risks and Uncertainties 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 pre-clinical and clinical testing and regulatory approval, prior to commercialization. These efforts will require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. Going Concern Pursuant to Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 205-40, Presentation of Financial Statements-Going Concern , an entity is required to assess whether there are conditions and events, considered in the aggregate, that raise substantial doubt about an entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company has been financed from its inception through December 31, 2022 primarily through $15.9 million of net cash proceeds received from the sale of Series Seed convertible preferred stock (the “Series Seed Preferred Stock”), $91.2 million of net cash proceeds received from the sale of Series A convertible preferred stock (the “Series A Preferred Stock”), $57.7 million of net cash proceeds received from the sale of Series B-1 convertible preferred stock (the “Series B-1 Preferred Stock”) and $12.5 million of net cash proceeds received from the sale of Series B-2 convertible preferred stock (the “Series B-2 Preferred Stock”). As outlined further within Note 16, “Subsequent Events”, the Company also received $45.5 million of net cash proceeds in March 2023 from the sale of additional shares of Series B-2 Preferred Stock. The Company is not currently generating revenue, expects to continue incurring significant operating losses and negative operating cash flows for the foreseeable future and has no currently available sources of financing. As such, the Company will require additional financing. However, if the Company is unable to obtain additional financing, the Company would be forced to delay, reduce or eliminate its research and development programs and/or relinquish valuable rights to its technology and product candidates. There is no assurance that the Company will be successful in obtaining sufficient financing on acceptable terms to continue funding its operations. Based upon the above considerations, the Company has concluded that there is substantial doubt about its ability to continue as a going concern within one year from July 27, 2023, the date these consolidated financial statements were issued.

Stock-based Compensation (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Components of Stock-Based Compensation Expense Recognized

Total stock-based compensation expense recognized in the condensed consolidated statements of operations and comprehensive loss for the nine months ended September 30, 2023 and 2022 was as follows (in thousands):


	Nine Months Ended September 30,
	2023		2022
Research and development	$	402	$	182
General and administrative		752		723

Total stock-based compensation expense	$	1,154	$	905

Total stock-based compensation expense recognized in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2022 and 2021 was as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	243	$	137
General and administrative		897		670

Total stock-based compensation expense	$	1,140	$	807

Summary of Activity Under RSU Plans

The following table summarizes restricted common stock activity during the nine months ended September 30, 2023 (in thousands, except per share amounts):


	Shares			Weighted-Average Grant Date Fair Value per Share
Unvested as of December 31, 2022		58		$	0.03
Granted		—		$	—
Vested		(54	)	$	0.01
Repurchased		—		$	—

Unvested as of September 30, 2023		4		$	0.04

The following table summarizes restricted common stock activity during the year ended December 31, 2022 (in thousands, except per share amounts):


	Shares			Weighted-Average Grant Date Fair Value per Share
Unvested as of December 31, 2021		488		$	0.02
Granted		—		$	—
Vested		(430	)	$	0.01
Repurchased		—		$	—

Unvested as of December 31, 2022		58		$	0.03

Summary of Fair Value Assumptions on Stock Options Granted

The fair value of stock options granted during the nine months ended September 30, 2023 and 2022 was calculated on the date of grant using the following weighted-average assumptions:


	Nine Months Ended September 30,
	2023			2022
Risk-free interest rate		3.6	%		1.9	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			6.1
Expected volatility		69.5	%		73.4	%

The fair value of stock options granted during the years ended December 31, 2022 and 2021 was calculated on the date of grant using the following weighted-average assumptions:


	Year Ended December 31,
	2022			2021
Risk-free interest rate		2.5	%		1.0	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			6.0
Expected volatility		72.9	%		71.9	%

Summary of Activity Under Stock Option Plans

The following table summarizes changes in stock option activity during the nine months ended September 30, 2023 (in thousands, except per share amounts):


	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		9,280		$	0.74		8.0	$	2,953
Granted		4,050		$	1.06
Exercised		(533	)	$	0.66
Cancelled		(488	)	$	1.00

Outstanding as of September 30, 2023		12,309		$	0.84		8.1	$	3,135

Exercisable at September 30, 2023		5,480		$	0.67		7.3	$	2,306

The following table summarizes changes in stock option activity during the year ended December 31, 2022 (in thousands, except per share amounts):


	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2021		8,322		$	0.59		8.9	$	4,478
Granted		3,156		$	1.11
Exercised		(176	)	$	0.36
Cancelled		(2,022	)	$	0.73

Outstanding as of December 31, 2022		9,280		$	0.74		8.0	$	2,953

Exercisable at December 31, 2022		4,203		$	0.60		7.1	$	1,881

Net Loss Per Share (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Earnings Per Share [Abstract]

Summary of Computation of Diluted Net Loss Per Share

For purposes of the diluted net loss per share calculation, convertible preferred stock, outstanding stock options, outstanding warrants and unvested restricted common stock are considered to be potentially dilutive securities, however the following common stock equivalents were excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands):


	September 30, 2023		December 31, 2022
Series Seed Preferred Stock		13,781		13,781
Series A Preferred Stock		40,848		40,848
Series B-1 Preferred Stock		22,222		22,222
Series B-2 Preferred Stock		20,863		4,496
Unvested restricted common stock		4		58
Outstanding stock options		12,304		9,280
Outstanding warrant		162		162

Total		110,184		90,847

The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands):


	Year Ended December 31,
	2022		2021
Series Seed Preferred Stock		13,781		13,781
Series A Preferred Stock		40,848		40,848
Series B-1 Preferred Stock		22,222		22,222
Series B-2 Preferred Stock		4,496		4,496
Unvested restricted common stock		58		488
Outstanding stock options		9,280		8,322
Outstanding warrant		162		162

Total		90,847		90,319

Common Stock

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Stockholders' Equity Note [Abstract]

Common Stock

7. Common Stock

As of September 30, 2023, the Company was authorized to issue 117,138,030 shares of common stock. Holders of common stock are entitled to one vote per share. In addition, holders of common stock are entitled to receive dividends, if and when declared by the Company’s Board of Directors. As of September 30, 2023, no dividends had been declared.

As of September 30, 2023 and December 31, 2022, the Company had reserved for future issuance the following number of shares of common stock (in thousands):


	September 30, 2023		December 31, 2022
Conversion of outstanding Series Seed Preferred Stock		13,781		13,781
Conversion of outstanding Series A Preferred Stock		40,848		40,848
Conversion of outstanding Series B-1 Preferred Stock		22,222		22,222
Conversion of outstanding Series B-2 Preferred Stock		20,863		4,496
Future issuances of Series B-2 Preferred Stock		—		16,367
Vesting of restricted common stock		4		58
Exercises of outstanding stock options		12,304		9,280
Exercise of outstanding warrant		162		162
Future issuances under 2019 Stock Incentive Plan		950		3,218

Total reserved for future issuance		111,134		110,432

9. Common Stock

As of December 31, 2022, the Company was authorized to issue 115,838,000 shares of common stock. Holders of common stock are entitled to one vote per share. In addition, holders of common stock are entitled to receive dividends, if and when declared by the Company’s Board of Directors. As of December 31, 2022, no dividends had been declared.

As of December 31, 2022 and 2021, the Company had reserved for future issuance the following number of shares of common stock (in thousands):


	December 31,
	2022		2021
Conversion of outstanding Series Seed Preferred Stock		13,781		13,781
Conversion of outstanding Series A Preferred Stock		40,848		40,848
Conversion of outstanding Series B-1 Preferred Stock		22,222		22,222
Conversion of outstanding Series B-2 Preferred Stock		4,496		4,496
Future issuances of Series B-2 Preferred Stock		16,367		16,367
Vesting of restricted common stock		58		488
Exercises of outstanding stock options		9,280		8,322
Exercise of outstanding warrant		162		162
Future issuances under 2019 Stock Incentive Plan		3,218		4,361

Total reserved for future issuance		110,432		111,047

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

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

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

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (i)
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 505
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-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Commitments and Contingencies - Summary of Future Minimum Operating Lease Liabilities (Detail) $ in Thousands	Dec. 31, 2021 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2022	$ 1,779
2023	2,315
2024	1,067
Total future minimum lease payments	$ 5,161

Property and Equipment, Net - Summary of Property Plant and Equipment Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 14,121	$ 8,190
Less: accumulated depreciation	(4,255)	(1,744)
Total property and equipment, net	$ 9,866	$ 6,446	$ 12,892
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	5 years	5 years
Property plant and equipment gross	$ 8,441	$ 4,364
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	4 years	4 years
Property plant and equipment gross	$ 477	$ 262
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years	3 years
Property plant and equipment gross	$ 213	$ 50
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life description	Shorter of useful life or remaining lease term	Shorter of useful life or remaining lease term
Property plant and equipment gross	$ 2,941	$ 2,883
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 2,049	$ 631

Fair Value Measurements - Summary of Reconciliation of the Preferred Stock Tranche Liability (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value upon exercise of Series A Tranche Right	$ 13,500
Preferred Stock Tranche Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2020	(11,054)
Change in fair value upon exercise of Series A Tranche Right	13,505
Reclassification to Series A Preferred Stock upon extinguishment	(2,451)
Balance at December 31, 2021	$ 0

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended	5 Months Ended
	Mar. 31, 2023	Dec. 31, 2021	Jul. 31, 2020	Jun. 30, 2020	Mar. 31, 2023	Jul. 27, 2023	Mar. 01, 2023	Jun. 01, 2020	May 31, 2019
Subsequent Event [Line Items]
Temporary equity stock issued during the period shares new issues			2,232,143
Temporary equity issue price per share		$ 2.78						$ 2.24	$ 1
Proceeds from redeemable convertible preferred stock				$ 45.5
Series B-2 Preferred Stock [Member]
Subsequent Event [Line Items]
Temporary equity issue price per share		$ 2.78
Proceeds from redeemable convertible preferred stock		$ 12.5
Collaboration And License Agreement [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Payment upon execution of the agreement	$ 2.5
Collaboration And License Agreement [Member] \| Commercial Milestone [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Milestone payment receivable							$ 57.0
Subsequent Event [Member] \| Series B-2 Preferred Stock [Member]
Subsequent Event [Line Items]
Temporary equity stock issued during the period shares new issues					16,366,905
Temporary equity issue price per share							$ 2.78
Proceeds from redeemable convertible preferred stock					$ 45.5
Subsequent Event [Member] \| Merger Agreement And Preclosing Financing [Member]
Subsequent Event [Line Items]
Common stock subscribed but not issued value							$ 117.3
Subsequent Event [Member] \| Collaboration And License Agreement [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Payment upon execution of the agreement	$ 2.5
Aggregate payment made						$ 2.8
Subsequent Event [Member] \| Collaboration And License Agreement [Member] \| Research and Development Expense [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Expenses incurred in connection with agreement					$ 2.5
Subsequent Event [Member] \| Collaboration And License Agreement [Member] \| Product Milestone [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Milestone payment receivable							40.5
Subsequent Event [Member] \| Collaboration And License Agreement [Member] \| Commercial Milestone [Member] \| Genevant [Member]
Subsequent Event [Line Items]
Milestone payment receivable							$ 57.0

Income Taxes - Summary of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred Tax Assets, Tax Deferred Expense [Abstract]
Net operating loss carryforwards	$ 19,580	$ 14,481
Tax credit carryforwards	5,477	1,871
Capitalized research and development	10,279
Stock-based compensation	319	148
Deferred rent		521
Operating lease liability	855
Accrued expenses and other temporary differences	707	650
Total deferred tax assets	37,217	17,671
Valuation allowance	(36,094)	(17,091)
Net deferred tax assets	1,123	580
Deferred tax liabilities:
Operating right-of-use asset	(552)
Depreciation	(571)	(580)
Total deferred tax liabilities	(1,123)	(580)
Net deferred taxes

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Basis of Presentation and Significant Accounting Policies [Abstract]

Summary of Financial Statement Line Item Affected by the Adoption of ASC 842

The following table presents a summary of the amount by which each financial statement line item was affected by the adoption of ASC 842 (in thousands):


	January 1, 2022
	Prior to the Adoption of ASC 842		Effect of Adoption			Subsequent to the Adoption of ASC 842
Operating lease right-of-use asset	$	—	$	2,922		$	2,922
Operating lease liabilities, current portion	$	—	$	1,577		$	1,577
Deferred rent, current portion	$	939	$	(939	)	$	—
Operating lease liabilities, net of current portion	$	—	$	3,253		$	3,253
Deferred rent, net of current portion	$	969	$	(969	)	$	—

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) shares in Thousands, $ in Thousands	Total	Series Seed Convertible Preferred Stock [Member]	Series A Convertible Preferred Stock [Member]	Series B-1 Convertible Preferred Stock [Member]	Series B-2 Convertible Preferred Stock [Member]	Preferred Stock [Member] Series Seed Convertible Preferred Stock [Member]	Preferred Stock [Member] Series A Convertible Preferred Stock [Member]	Preferred Stock [Member] Series B-1 Convertible Preferred Stock [Member]	Preferred Stock [Member] Series B-2 Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance, shares at Dec. 31, 2020						13,781	20,424	0	0
Beginning balance at Dec. 31, 2020						$ 15,924	$ 34,479	$ 0	$ 0
Beginning balance, shares at Dec. 31, 2020										4,072
Beginning balance at Dec. 31, 2020	$ (21,156)									$ 4	$ 682	$ 0	$ (21,842)
Convertible preferred stock, net of issuance costs, share							20,424	22,222	4,496
Convertible preferred stock, net of issuance costs							$ 45,708	$ 57,703	$ 12,500
Reclassification of preferred stock tranche asset upon issuance of Series A convertible preferred stock							$ (2,451)
Exercises of stock options, share										246
Exercises of stock options	28										28
Vesting of restricted common stock, share										470
Vesting of restricted common stock	7									$ 1	6
Issuance of warrant to purchase common stock	72										72
Stock-based compensation expense	807										807
Other comprehensive income	(7)											(7)
Net loss	(21,959)												(21,959)
Ending balance, shares at Dec. 31, 2021		13,781	40,848	22,222	4,496	13,781	40,848	22,222	4,496
Ending balance at Dec. 31, 2021		$ 15,924	$ 77,736	$ 57,703	$ 12,500	$ 15,924	$ 77,736	$ 57,703	$ 12,500
Ending balance, shares at Dec. 31, 2021										4,788
Ending balance at Dec. 31, 2021	$ (42,208)									$ 5	1,595	(7)	(43,801)
Issuance of common stock for services rendered, share	10
Issuance of common stock for services rendered	$ 11										11
Exercises of stock options, share	144
Exercises of stock options	$ 49										49
Vesting of restricted common stock, share	381
Vesting of restricted common stock	$ 5										5
Stock-based compensation expense	894										894
Other comprehensive income	(3)											(3)
Net loss	(41,998)												(41,998)
Ending balance, shares at Sep. 30, 2022						13,781	40,848	22,222	4,496
Ending balance at Sep. 30, 2022						$ 15,924	$ 77,736	$ 57,703	$ 12,500
Ending balance, shares at Sep. 30, 2022										5,323
Ending balance at Sep. 30, 2022	(83,250)									$ 5	2,554	(10)	(85,799)
Beginning balance, shares at Dec. 31, 2021		13,781	40,848	22,222	4,496	13,781	40,848	22,222	4,496
Beginning balance at Dec. 31, 2021		$ 15,924	$ 77,736	$ 57,703	$ 12,500	$ 15,924	$ 77,736	$ 57,703	$ 12,500
Beginning balance, shares at Dec. 31, 2021										4,788
Beginning balance at Dec. 31, 2021	(42,208)									$ 5	1,595	(7)	(43,801)
Issuance of common stock for services rendered, share										10
Issuance of common stock for services rendered	11										11
Exercises of stock options, share										176
Exercises of stock options	62										62
Vesting of restricted common stock, share										430
Vesting of restricted common stock	5										5
Stock-based compensation expense	1,129										1,129
Other comprehensive income	2											2
Net loss	(58,032)												(58,032)
Ending balance, shares at Dec. 31, 2022		13,781	40,848	22,222	4,496	13,781	40,848	22,222	4,496
Ending balance at Dec. 31, 2022		$ 15,924	$ 77,736	$ 57,703	$ 12,500	$ 15,924	$ 77,736	$ 57,703	$ 12,500
Ending balance, shares at Dec. 31, 2022										5,404
Ending balance at Dec. 31, 2022	$ (99,031)									$ 5	2,802	(5)	(101,833)
Convertible preferred stock, net of issuance costs, share	16,367
Convertible preferred stock, net of issuance costs									$ 45,458
Issuance of common stock for services rendered, share	6
Issuance of common stock for services rendered	$ 6										6
Exercises of stock options, share	538
Exercises of stock options	$ 361									$ 2	359
Vesting of restricted common stock, share	54
Stock-based compensation expense	$ 1,148										1,148
Other comprehensive income	5											5
Net loss	(55,746)												(55,746)
Ending balance, shares at Sep. 30, 2023			40,848	22,222	20,863	13,781	40,848	22,222	20,863
Ending balance at Sep. 30, 2023		$ 15,924	$ 77,736	$ 57,703	$ 57,958	$ 15,924	$ 77,736	$ 57,703	$ 57,958
Ending balance, shares at Sep. 30, 2023										6,002
Ending balance at Sep. 30, 2023	$ (153,257)									$ 7	$ 4,315	$ 0	$ (157,579)

Investments - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Short-term investments	$ 0	$ 18,915	$ 35,040
Debt securities, available-for-sale, unrealized loss position	0
Debt securities, available-for-sale, continuous unrealized loss position		$ 4,000	$ 12,100
Impairment on short-term investments	$ 0

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 46,119	$ 36,333	$ 83,492
Short-term investments	0	18,915	35,040
Prepaid expenses and other current assets	3,026	1,835	1,243
Total current assets	49,145	57,083	119,775
Property and equipment, net	12,892	9,866	6,446
Advance payments for property and equipment	351	76	695
Operating lease right-of-use assets	26,425	2,024
Other non-current assets	7,018	4,693	659
Total assets	95,831	73,742	127,575
Current liabilities:
Accounts payable	2,836	2,605	789
Accrued expenses and other current liabilities	5,711	3,175	3,221
Deferred rent, current portion			939
Operating lease liabilities, current portion	992	2,921
Total current liabilities	9,539	8,701	4,949
Deferred rent, net of current portion			969
Operating lease liabilities, net of current portion	30,228	209
Other non-current liabilities			2
Total liabilities	39,767	8,910	5,920
Commitments and contingencies
Stockholders' deficit
Common stock	7	5	5
Additional paid-in capital	4,315	2,802	1,595
Accumulated other comprehensive loss		(5)	(7)
Accumulated deficit	(157,579)	(101,833)	(43,801)
Total stockholders' deficit	(153,257)	(99,031)	(42,208)
Total liabilities, convertible preferred stock and stockholders' deficit	95,831	73,742	127,575
Series Seed Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock	15,924	15,924	15,924
Series A Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock	77,736	77,736	77,736
Series B1 Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock	57,703	57,703	57,703
Series B2 Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock	$ 57,958	$ 12,500	$ 12,500

SVB Agreement (Tables)

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Schedule of Determine The Fair Value Of The Warrant Upon Issuance

To determine the fair value of the warrant upon issuance, the Company utilized the Black-Scholes option-pricing model with the following assumptions:


	Assumption
Risk-free interest rate		1.1	%
Expected dividend yield		—	%
Expected term (in years)		10.0
Expected volatility		72.9	%

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Accrued Expenses And Other Current Liabilities [Abstract]
Annual bonus	$ 2,356	$ 2,198	$ 1,883
External research and development services	1,910	274	440
Other employee compensation and benefits	146	426	401
Financing costs	808
Other operating expenses	491	277	497
Total accrued expenses and other current liabilities	$ 5,711	$ 3,175	$ 3,221

Common Stock - Schedule of Reserved for Future Issuance (Detail) - shares shares in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Total reserved for future issuance	111,134	110,432	111,047
Conversion of outstanding Series Seed Preferred Stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	13,781	13,781	13,781
Conversion of outstanding Series A Preferred Stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	40,848	40,848	40,848
Conversion of outstanding Series B-1 Preferred Stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	22,222	22,222	22,222
Conversion of outstanding Series B-2 Preferred Stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	20,863	4,496	4,496
Future issuances of Series B-2 Preferred Stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	0	16,367	16,367
Vesting of restricted common stock [Member]
Class of Stock [Line Items]
Total reserved for future issuance	4	58	488
Exercises of outstanding stock options [Member]
Class of Stock [Line Items]
Total reserved for future issuance	12,304	9,280	8,322
Exercise of outstanding warrant [Member]
Class of Stock [Line Items]
Total reserved for future issuance	162	162	162
Future issuances under 2019 Stock Incentive Plan [Member]
Class of Stock [Line Items]
Total reserved for future issuance	950	3,218	4,361

Genevant Agreement - Additional Information (Detail) - Collaboration and License Agreement [Member] - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2023	Sep. 30, 2023	Mar. 01, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments received		$ 0.0
Reimbursements received		$ 0.8
Genevant [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payment upon execution of the agreement	$ 2.5
Genevant [Member] \| Potential Clinical Milestone Payments [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment receivable			$ 13.5
Genevant [Member] \| Potential Regulatory and Development Milestone Payments [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment receivable			27.0
Genevant [Member] \| Commercial Milestone [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment receivable			$ 57.0

Commitments and Contingencies - Additional Information (Detail) $ in Thousands			5 Months Ended	9 Months Ended		12 Months Ended
	Oct. 01, 2021 ft²	Aug. 01, 2020 ft²	Dec. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) ft²	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Aug. 31, 2022	Aug. 01, 2022 USD ($)	Jun. 30, 2022 ft²	Jun. 01, 2022 ft²	Apr. 01, 2022 ft²	Feb. 01, 2022 ft²	Jan. 01, 2022	May 01, 2020 ft²
Lessee, Lease, Description [Line Items]
Lessee operating lease not yet commenced term of contract												120 months
Total future minimum lease payments							$ 5,161
Tenant improvement allowances unutilized			$ 13,100			$ 13,100
Operating lease fixed costs				$ 4,335	$ 1,648
Operating lease variable lease costs				$ 742	$ 534
Sixty First Street Lease [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²												50,453
Incentive from lessor			13,100			13,100
Total future minimum lease payments			76,700			76,700
Sixty First Street Lease [Member] \| Upon Substantial Completion Of Tenant Improvements [Member]
Lessee, Lease, Description [Line Items]
Estimated amount of security deposits			3,400			3,400
Sixty First Street Lease [Member] \| Three Years After Lease Commencement [Member]
Lessee, Lease, Description [Line Items]
Estimated amount of security deposits			2,300			2,300
Other Noncurrent Assets [Member] \| Sixty First Street Lease [Member]
Lessee, Lease, Description [Line Items]
Security deposits			4,500			$ 4,500
MA [Member] \| Cumming Park Sublease [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²													18,148
Operating lease date of expiry						Jul. 31, 2024
Incentive from lessor			$ 100			$ 100
Operating lease fixed costs						300
Operating lease variable lease costs						$ 100
Operating lease weighted average remaining lease term			1 year 7 months 6 days			1 year 7 months 6 days
MA [Member] \| Sixty First Street Lease [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²				50,453
Incentive from lessor				$ 13,100
Operating lease weighted average discount rate percentage				11.10%
Operating lease weighted average remaining lease term				10 years 4 months 24 days
Seven Hundred And Ninety Memorial Drive [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²															3,407
Operating lease rental expenses							100
OKS Building Six Hundred By Seven Hundred Lease [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²		12,165
Operating lease date of expiry		Jan. 31, 2024
Incentive from lessor							2,400
OKS Building Six Hundred By Seven Hundred Lease [Member] \| MA [Member] \| Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Security deposits							300
Operating Sublease Agreement With OKS [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²	5,094
Operating lease date of expiry	Dec. 31, 2024
Operating Sublease Agreement With OKS [Member] \| MA [Member] \| Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Security deposits							200
OKS Sublease Agreement After Sublease Extension One [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²											5,302
OKS Building Six Hundred By Seven Hundred Lease And OKS Sublease Agreement After Sublease Extension One [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²										10,396
OKS Building Six Hundred By Seven Hundred Lease Agreement After Amendment One [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Operating lease date of expiry		Dec. 31, 2023
OKS Building Six Hundred By Seven Hundred And OKS Sub Lease Agreement After Amendment One [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Security deposits			$ 600			$ 600
Operating lease monthly rental payment required									$ 300
Operating lease additional monthly rent payment required									$ 300
Security deposits cancelled			$ 300
Operating lease weighted average discount rate percentage								7.87%
Operating lease fixed costs						1,400
Operating lease variable lease costs						$ 700
Operating lease weighted average remaining lease term			1 year			1 year
OKS Building Six Hundred By Seven Hundred And OKS Sub Lease Agreement After Amendment One [Member] \| MA [Member] \| Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Security deposits			$ 300			$ 300
OKS Six Hundred By Seven Hundred Lease And OKS Operating Sublease [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Operating lease rental expenses							$ 600
Operating lease weighted average discount rate percentage														5.09%

Investments - Summary of Short Term Investments and Cash Equivalents (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 33,824	$ 106,626
Unrealized Losses	(5)	(7)
Fair Value	33,819	106,619
Corporate debt securities [Member]
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		12,085
Unrealized Losses		(7)
Fair Value		12,078
Commercial paper [Member]
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,935	22,962
Fair Value	14,935	22,962
Government securities [Member]
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,985
Unrealized Losses	(5)
Fair Value	3,980
Short-term investments [Member]
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	18,920
Unrealized Losses	(5)
Fair Value	18,915
Money market funds [Member]
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,904	71,579
Fair Value	$ 14,904	$ 71,579

Basis of Presentation and Summary of Significant Accounting Policies

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Basis of Presentation and Significant Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The condensed consolidated financial statements include the accounts of Korro Bio, Inc. and its wholly-owned subsidiary, Korro Mass Securities, Inc., which was established in December 2020. All intercompany transactions and balances have been eliminated in consolidation.

Summary of Significant Accounting Policies

The Company’s significant accounting policies are disclosed in the audited financial statements for the years ended December 31, 2022 and 2021, included in Exhibit 99.6 of Frequency’s Current Report on Form

8-K

of which this Exhibit 99.5 is part. Since the date of those annual financial statements, there have been no changes to the Company’s significant accounting policies, except as noted below.

Unaudited Interim Financial Information

The accompanying condensed consolidated balance sheet as of September 30, 2023, and the condensed consolidated statements of operations and comprehensive loss, condensed consolidated statements of convertible preferred stock and stockholders’ deficit and condensed consolidated statements of cash flows for the nine months ended September 30, 2023 and 2022 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position as of September 30, 2023 and the results of its operations and its cash flows for the nine months ended September 30, 2023 and 2022. The financial data and other information disclosed in these notes related to the nine months ended September 30, 2023 and 2022 are also unaudited. The results for the nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the full year or for any other subsequent interim period.

Use of Estimates

The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates which include, but are not limited to, accrued expenses and stock-based compensation expense. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

. This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and it establishes additional disclosure requirements related to credit risks. For

available-for-sale

debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. The Company adopted this new standard effective January 1, 2023, and there was no impact to the condensed consolidated financial statements as a result of the adoption of this guidance.

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”). These consolidated financial statements have been prepared on the going concern basis of accounting, which assumes continuity of operations, realization of assets and satisfaction of liabilities in the ordinary course of business.

The consolidated financial statements include the accounts of Korro Bio, Inc. and its wholly-owned subsidiary, Korro Mass Securities, Inc., which was established in December 2020. All intercompany transactions and balances have been eliminated in consolidation.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment. The Company operates only in the United States.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, accrued expenses and stock-based compensation expense. During the year ended December 31, 2021, the Company’s estimates also included the valuation of the preferred stock tranche asset and liability related to the Series A Preferred Stock. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Fair Value of Financial Instruments

ASC Topic 820,

Fair Value Measurement

, (“ASC 820”) establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances.

ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following:

•

Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities.

•

Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.

•

Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.

To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Cash Equivalents

Cash equivalents are highly-liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. These assets include investments in money market funds that invest in U.S. Treasury obligations. Cash equivalents are reflected at fair value based on quoted market prices, as further described in Note 3, “Fair Value Measurements”.

Investments

Investments consist of securities with original maturities greater than three months when purchased. Short-term investments consist of investments that are available for use in current operations. Long-term investments consist of investments with maturities of greater than one year that are not available for use in current operations. The Company did not maintain any long-term investments as of December 31, 2022 or 2021.

The Company classifies all of its investments as

available-for-sale

securities. Accordingly, these investments are recorded at fair value. Realized gains and losses and amortization and accretion of discounts and premiums are included in “Other income, net”. Unrealized gains and losses on

available-for-sale

securities are included in “Accumulated other comprehensive loss” as a component of stockholders’ deficit until realized.

The Company reviews its investment portfolio to identify and evaluate investments that have indicators of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.

Property and Equipment

Property and equipment are recorded at cost and consists of laboratory equipment, furniture and office equipment, computer equipment, leasehold improvements, and construction in progress. The Company capitalizes property and equipment that is acquired for research and development activities and that has alternative future use. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Property and equipment not yet placed into service is capitalized as construction in progress and is depreciated once placed into service. Leasehold improvements are depreciated over the lesser of their useful lives or the term of the lease. Depreciation, including depreciation for assets recorded under capital leases, is calculated over the estimated useful lives of the assets using the straight-line method.

Impairment of Long-lived Assets

The Company reviews long-lived assets when events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. Recoverability is measured by comparing the carrying value of the asset to the future undiscounted cash flows from the use and eventual disposition of the asset. If an asset is considered to be impaired, the impairment loss to be recognized is measured as the amount by which the carrying value of the asset exceeds its fair value.

Research and Development Expenses

Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties, academic and

non-profit

institutions and consultants; salaries and personnel-related costs, including

non-cash

stock-based compensation expense; license fees to acquire

in-process

technology and other expenses, which include direct and allocated expenses for laboratory, facilities and other costs.

Non-refundable

advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.

As part of the process of preparing the consolidated financial statements, the Company is required to estimate its accrued research and development expenses as of each balance sheet date. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. This process involves reviewing open contracts and purchase orders, communicating with internal personnel to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual cost. The Company periodically confirms the accuracy of its estimates with its service providers and makes adjustments if necessary. The majority of the Company’s service providers invoice monthly in arrears for services performed or when contractual milestones are met. The financial terms of agreements with these service providers are subject to negotiation, vary from

contract-to-contract

and may result in uneven payment flows. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.

Intellectual Property Expenses

The Company expenses legal costs related to patent applications as they are incurred. Such costs are classified as general and administrative expenses within the consolidated statements of operations and comprehensive loss.

Stock-based Compensation

The Company accounts for stock-based payments in accordance with ASC Topic 718,

Compensation-Stock Compensation

(“ASC 718”). This guidance requires all stock-based payments, including grants of stock options and restricted common stock, to be recognized as expense in the consolidated statements of operations and comprehensive loss based on their grant date fair values. For stock options granted to employees,

non-employees

and members of the Company’s Board of Directors for their services on the Board of Directors, the Company estimates the grant date fair value of each stock option using the Black-Scholes option-pricing model. For restricted common stock granted to employees and

non-employees,

the Company estimates the grant date fair value of each award using the intrinsic value, which is based on the value of the underlying common stock less any purchase price. For stock-based payments subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of stock-based payment on a straight-line basis over the requisite service period.

The Company estimates the grant date fair value of its common stock using an appropriate valuation methodology, in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid,

Valuation of

Privately-Held

Company

Equity

Securities

Issued

Compensation

. Historically, the Company has utilized a market approach to determine its total equity value and the option pricing method (“OPM”) to allocate this equity value among various classes of securities. The OPM treats common stock and convertible preferred stock as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under the OPM, the common stock has value only if the funds available for distribution to stockholders exceeds the value of the convertible preferred stock liquidation preferences at the time of the liquidity event, such as a strategic sale or a merger. A discount for lack of marketability of the common stock is

then applied to arrive at an indication of value for the common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, guideline public company information, the prices at which the Company sold convertible preferred stock to third parties in arms’ length transactions, the rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event such as an initial public offering or sale. Significant changes to the assumptions used in the valuations could result in different fair values of stock options and restricted stock at each valuation date, as applicable.

In addition to the grant date fair value of the Company’s common stock, the Black-Scholes option pricing model requires the input of certain subjective assumptions, including (i) the calculation of expected term of the stock-based payment, (ii) the risk-free interest rate, (iii) the expected stock price volatility and (iv) the expected dividend yield. The Company uses the simplified method as proscribed by SEC Staff Accounting Bulletin No. 107 to calculate the expected term for stock options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The Company determines the risk-free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. Because there is no public market for the Company’s common stock, there is a lack of Company-specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of publicly-traded companies with similar characteristics to itself, including stage of product development and therapeutic focus within the life sciences industry. Historical volatility is calculated over a period of time commensurate with the expected term of the stock-based payment. The Company uses an assumed dividend yield of zero as the Company has never paid dividends on its common stock, nor does it expect to pay dividends on its common stock in the foreseeable future.

The Company accounts for forfeitures of all stock-based payments when such forfeitures occur.

Income Taxes

Income taxes are recorded in accordance with ASC Topic 740,

Income Taxes

, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions using a

more-likely-than-not

threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors, including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position.

Interest and penalty charges, if any, related to income taxes would be classified as a component of the “Provision for income taxes” in the consolidated statements of operations and comprehensive loss.

Net Loss per Share

Basic net loss per share is calculated by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares

outstanding for the period, including any dilutive effect from convertible preferred stock, outstanding stock options, outstanding warrants or unvested restricted common stock.

The Company follows the

two-class

method when computing net loss per share for periods when issued shares that meet the definition of participating securities are outstanding. The

two-class

method calls for the calculation of net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The

two-class

method requires income available to common stockholders to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Net losses are not allocated to the Company’s preferred stockholders as they do not have an obligation to share in the Company’s net losses.

Concentration of Credit Risk and

Off-Balance

Sheet Risk

Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash, cash equivalents and investments. Cash balances are deposited with federally-insured financial institutions in the United States and may, at times, exceed federally-insured limits. The Company maintains its cash, cash equivalents and investments with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s cash equivalents are comprised of money market funds that are invested in U.S. Treasury and government agency obligations. The Company’s investments are comprised of commercial paper and government securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any single issuer and to only invest in securities of a high credit quality.

The Company has no significant

off-balance

sheet risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (“ASU”)

2016-02,

Leases (Topic 842)

, which requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and changes many key definitions, including the definition of a lease. The new standard includes a short-term lease exception for leases with a term of 12 months or less, as part of which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. In July 2018, the FASB also issued ASU

2018-11,

Leases (Topic 842): Targeted Improvements

, which permits entities to continue applying legacy guidance in ASC Topic 840,

Leases

(“ASC 840”), including its disclosure requirements, in the comparative periods presented in the year that the entity adopts the new leasing standard. Under this transition method, the cumulative effect of initially applying ASC 842 is recognized as an adjustment to the opening balance of retained earnings or accumulated deficit at the beginning of the annual reporting period that includes the date of initial application. Finally, in June 2020, the FASB issued ASU

2020-05,

Revenue from Contracts with Customers (Topic 606) and Leases (Topic 842): Effective Dates for Certain Entities

, whereby the effective date of this standard was deferred to annual reporting periods beginning after December 15, 2021 and interim periods within annual reporting periods beginning after December 15, 2022, and early adoption was still permitted.

Accordingly, the Company adopted ASC 842, as amended, on January 1, 2022 using the modified retrospective approach, which provides a method for recording existing leases at adoption and does not require restating comparative financial information. For the comparative period presented in these consolidated financial statements, lease-related disclosures continue to be presented in accordance with ASC 840. The Company also elected to utilize certain practical expedients under ASC 842, which among other things, permit the Company to i) maintain the lease classification for any existing leases, ii) maintain the Company’s determination as to

whether any expired or existing contracts are or contain leases and iii) not separate nonlease components. Additionally, the Company elected an accounting policy whereby it does not apply the recognition requirements of ASC 842 to short-term leases with a term of 12 months or less.

Upon the adoption of ASC 842, the Company removed its legacy deferred rent balances that were previously recorded under ASC 840 and established an operating lease

right-of-use

asset of $2.9 million, an operating lease liability, current of $1.6 million and an operating lease liability, net of current portion of $3.3 million, all relating to the Company’s existing operating lease for its current corporate headquarters. There was no impact to the opening balance of accumulated deficit as a result of the adoption of ASC 842.

The following table presents a summary of the amount by which each financial statement line item was affected by the adoption of ASC 842 (in thousands):


	January 1, 2022
	Prior to the Adoption of ASC 842		Effect of Adoption			Subsequent to the Adoption of ASC 842
Operating lease right-of-use asset	$	—	$	2,922		$	2,922
Operating lease liabilities, current portion	$	—	$	1,577		$	1,577
Deferred rent, current portion	$	939	$	(939	)	$	—
Operating lease liabilities, net of current portion	$	—	$	3,253		$	3,253
Deferred rent, net of current portion	$	969	$	(969	)	$	—

The adoption of ASC 842 did not have a material impact on the consolidated statement of operations and comprehensive loss or the consolidated statement of cash flows for the year ended December 31, 2022.

In December 2019, the FASB issued ASU

2019-12,

Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

, which eliminates certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities when investment ownership changes. In addition, ASU

2019-12

simplifies the accounting for the interim period effects of changes in tax laws or rates and transactions that result in a

step-up

in the tax basis of goodwill. This guidance is effective for annual reporting periods beginning after December 15, 2021 and interim periods within annual reporting periods beginning after December 15, 2022, and early adoption is permitted. The Company adopted this new standard effective January 1, 2022, and there was no impact to the consolidated financial statements as a result of the adoption of this guidance.

Recent Accounting

Pronouncements-Yet

to be Adopted

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

available-for-sale

debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This guidance was originally effective for annual reporting periods beginning after December 15, 2020 and interim periods within fiscal years beginning after December 31, 2021, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU

2019-10,

Financial Instruments-Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates

, whereby the effective date of this standard was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted.

Accordingly, the Company will adopt this new standard effective January 1,

2023

, and it does not expect that the adoption of ASU

2016-13

will have a material impact on the consolidated financial statements.

Commitments and Contingencies - Summary of Future Operating Lease Liability (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
OKS Building Six Hundred By Seven Hundred And OKS Sub Lease Agreement After Amendment One [Member]
Lessee Operating Lease Liability Maturity [Line Items]
2023	$ 2,621
Less: effect of discounting	(92)
Total lease liability	2,529
Cummings Park Sublease [Member]
Lessee Operating Lease Liability Maturity [Line Items]
2023	411
2024	212
Total remaining minimum lease payments	623
Less: effect of discounting	(22)
Total lease liability	$ 601

Restricted Cash - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Current restricted cash	$ 1.8	$ 0.6
Noncurrent restricted cash	$ 3.4	$ 4.5	$ 0.6

Restricted Cash

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Cash and Cash Equivalents [Abstract]

Restricted Cash

5. Restricted Cash

As of September 30, 2023, the Company maintained current restricted cash of $1.8 million and

non-current

restricted cash of $3.4 million. As of December 31, 2022, the Company maintained current restricted cash of $0.6 million and

non-current

restricted cash of $4.5 million. Such current amounts are included within “Prepaid expenses and other current assets” and such

non-current

amounts are included within “Other

non-current

assets” in the condensed consolidated balance sheets. All restricted cash amounts are comprised solely of letters of credit required pursuant to the Company’s facility leases.

The following table provides a reconciliation of cash, cash equivalents and restricted cash as of September 30, 2023 and 2022 that sums to the total of the same amounts shown in the condensed consolidated statements of cash flows (in thousands):


	September 30,
	2023		2022
Cash and cash equivalents	$	46,119	$	48,113
Restricted cash		5,174		5,294

Cash, cash equivalents and restricted cash	$	51,293	$	53,407

5. Restricted Cash

As of December 31, 2022, the Company maintained current restricted cash of $0.6 million and

non-current

restricted cash of $4.5 million. As of December 31, 2021, the Company maintained

non-current

restricted cash of $0.6 million. Such current amounts are included within “Prepaid expenses and other current assets” and such

non-current

amounts are included within “Other

non-current

assets” in the consolidated balance sheets. All restricted cash amounts are comprised solely of letters of credit required pursuant to the Company’s facility leases.

The following table provides a reconciliation of cash, cash equivalents and restricted cash as of December 31, 2022 and 2021 that sums to the total of the same amounts shown in the consolidated statements of cash flows (in thousands):


	December 31,
	2022		2021
Cash and cash equivalents	$	36,333	$	83,492
Restricted cash		5,144		552

Cash, cash equivalents and restricted cash	$	41,477	$	84,044

Investments (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Summary of Short Term Investments and Cash Equivalents

Short-term investments as of December 31, 2022 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper	$	14,935	$	—	$	—		$	14,935
Government securities		3,985		—		(5	)		3,980

Total	$	18,920	$	—	$	(5	)	$	18,915

Cash equivalents and short-term investments as of December 31, 2022 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds, included in cash and cash equivalents	$	14,904	$	—	$	—		$	14,904
Short-term investments:
Commercial paper		14,935		—		—			14,935
Government securities		3,985		—		(5	)		3,980

Total	$	33,824	$	—	$	(5	)	$	33,819

Cash equivalents and short-term investments as of December 31, 2021 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds, included in cash and cash equivalents	$	71,579	$	—	$	—		$	71,579
Short-term investments:
Corporate debt securities		12,085		—		(7	)		12,078
Commercial paper		22,962		—		—			22,962

Total	$	106,626	$	—	$	(7	)	$	106,619

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
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-Section 50
-Paragraph 9
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Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
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+ Details

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Jan. 01, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset	$ 26,425	$ 2,024
Operating lease liabilities, current portion	992	2,921
Operating lease liabilities, net of current portion	$ 30,228	$ 209
Adoption of ASC 842 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset			$ 2,900
Operating lease liabilities, current portion			1,600
Operating lease liabilities, net of current portion			$ 3,300

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
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-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 89: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 90: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481925/310-20-65-2

Reference 91: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481925/310-20-65-2

Reference 92: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480424/946-10-50-3

+ Details

Stock-based Compensation

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

9. Stock-based Compensation

2019 Stock Incentive Plan

In January 2019, the Company’s Board of Directors adopted the 2019 Stock Incentive Plan (the “2019 Plan”). The 2019 Plan provides for the grant of stock options, stock awards and restricted stock units to employees, members of the Company’s Board of Directors and

non-employee

consultants and advisors. The 2019 Plan initially provided for the issuance of up to 2,219,565 shares of common stock. The 2019 Plan was subsequently amended in May 2019, June 2020, October 2020, April 2021, November 2021 and March 2023 to modify the number of shares of common stock issuable under the 2019 Plan. Subsequent to the March 2023 amendment to the 2019 Plan, the Company can now issue up to 15,048,960 shares of common stock under the 2019 Plan. As of September 30, 2023, there were 949,921 shares available for future issuance under the 2019 Plan.

Stock-based Compensation Expense


	Nine Months Ended September 30,
	2023		2022
Research and development	$	402	$	182
General and administrative		752		723

Total stock-based compensation expense	$	1,154	$	905

Restricted Common Stock Activity

Prior to the adoption of the 2019 Plan, the Company issued shares of restricted common stock to its founders as well as to certain employees. The restrictions on the common stock generally lapse over two to four years. In the event that a recipient ceases to provide service to the Company, the Company has the right to repurchase any unvested shares of restricted common stock at their original purchase price. As a result of this repurchase right, the Company recorded the issuance of such restricted common stock as a liability in the condensed consolidated balance sheets. Amounts are reclassified to common stock at par and additional

paid-in

capital as the restricted common stock vests and restrictions lapse.

The following table summarizes restricted common stock activity during the nine months ended September 30, 2023 (in thousands, except per share amounts):


	Shares			Weighted-Average Grant Date Fair Value per Share
Unvested as of December 31, 2022		58		$	0.03
Granted		—		$	—
Vested		(54	)	$	0.01
Repurchased		—		$	—

Unvested as of September 30, 2023		4		$	0.04

The aggregate fair value of restricted common stock that vested during the nine months ended September 30, 2023, based upon the fair value of the underlying restricted common stock on the day of vesting, was less than $0.1 million, and for the nine months ended September 30, 2022 was $0.4 million.

Stock Option Activity

The fair value of stock options granted during the nine months ended September 30, 2023 and 2022 was calculated on the date of grant using the following weighted-average assumptions:


	Nine Months Ended September 30,
	2023			2022
Risk-free interest rate		3.6	%		1.9	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			6.1
Expected volatility		69.5	%		73.4	%

Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the nine months ended September 30, 2023 and 2022 was $0.69 and $0.74 per share, respectively.

The following table summarizes changes in stock option activity during the nine months ended September 30, 2023 (in thousands, except per share amounts):


	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		9,280		$	0.74		8.0	$	2,953
Granted		4,050		$	1.06
Exercised		(533	)	$	0.66
Cancelled		(488	)	$	1.00

Outstanding as of September 30, 2023		12,309		$	0.84		8.1	$	3,135

Exercisable at September 30, 2023		5,480		$	0.67		7.3	$	2,306

The aggregate intrinsic value of stock options exercised during the nine months ended September 30, 2023 and 2022 was $0.2 million and $0.1 million, respectively.

As of September 30, 2023, there was unrecognized stock-based compensation expense related to unvested stock options of $3.9 million, which the Company expects to recognize over a weighted-average period of approximately 2.7 years.

11. Stock-based Compensation

2019 Stock Incentive Plan

non-employee

shares of common stock issuable under the 2019 Plan. Subsequent to the November 2021 amendment to the 2019 Plan, the Company can now issue up to 13,748,930 shares of common stock under the 2019 Plan. As of December 31, 2022, there were 3,217,888 shares available for future issuance under the 2019 Plan.

Stock-based Compensation Expense

Total stock-based compensation expense recognized in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2022 and 2021 was as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	243	$	137
General and administrative		897		670

Total stock-based compensation expense	$	1,140	$	807

Restricted Common Stock Activity

Prior to the adoption of the 2019 Plan, the Company issued shares of restricted common stock to its founders as well as to certain employees. The restrictions on the common stock generally lapse over two to four years. In the event that a recipient ceases to provide service to the Company, the Company has the right to repurchase any unvested shares of restricted common stock at their original purchase price. As a result of this repurchase right, the Company recorded the issuance of such restricted common stock as a liability in the consolidated balance sheets. Amounts are reclassified to common stock at par and additional

paid-in

capital as the restricted common stock vests and restrictions lapse.

The following table summarizes restricted common stock activity during the year ended December 31, 2022 (in thousands, except per share amounts):


	Shares			Weighted-Average Grant Date Fair Value per Share
Unvested as of December 31, 2021		488		$	0.02
Granted		—		$	—
Vested		(430	)	$	0.01
Repurchased		—		$	—

Unvested as of December 31, 2022		58		$	0.03

The aggregate fair value of restricted common stock that vested during the years ended December 31, 2022 and 2021, based upon the fair value of the underlying restricted common stock on the day of vesting, was $0.5 million and $0.3 million, respectively.

Stock Option Activity

The fair value of stock options granted during the years ended December 31, 2022 and 2021 was calculated on the date of grant using the following weighted-average assumptions:


	Year Ended December 31,
	2022			2021
Risk-free interest rate		2.5	%		1.0	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			6.0
Expected volatility		72.9	%		71.9	%

Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the years ended December 31, 2022 and 2021 was $0.73 and $0.41 per share, respectively.

The following table summarizes changes in stock option activity during the year ended December 31, 2022 (in thousands, except per share amounts):


	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2021		8,322		$	0.59		8.9	$	4,478
Granted		3,156		$	1.11
Exercised		(176	)	$	0.36
Cancelled		(2,022	)	$	0.73

Outstanding as of December 31, 2022		9,280		$	0.74		8.0	$	2,953

Exercisable at December 31, 2022		4,203		$	0.60		7.1	$	1,881

The aggregate intrinsic value of stock options exercised during the years ended December 31, 2022 and 2021 was $0.1 million and $0.2 million, respectively.

As of December 31, 2022, there was unrecognized stock-based compensation expense related to unvested stock options of $2.5 million, which the Company expects to recognize over a weighted-average period of approximately 2.7 years.

Restricted Cash (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Cash and Cash Equivalents [Abstract]

Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash


	September 30,
	2023		2022
Cash and cash equivalents	$	46,119	$	48,113
Restricted cash		5,174		5,294

Cash, cash equivalents and restricted cash	$	51,293	$	53,407


	December 31,
	2022		2021
Cash and cash equivalents	$	36,333	$	83,492
Restricted cash		5,144		552

Cash, cash equivalents and restricted cash	$	41,477	$	84,044

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Basis of Presentation and Significant Accounting Policies [Abstract]

Basis of Presentation and Consolidation

Segment Information

Unaudited Interim Financial Information

Use of Estimates

Fair Value of Financial Instruments

ASC Topic 820,

Fair Value Measurement

•

Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities.

•

Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.

•

Cash Equivalents

Investments

The Company classifies all of its investments as

available-for-sale

securities are included in “Accumulated other comprehensive loss” as a component of stockholders’ deficit until realized.

Property and Equipment

Impairment of Long-lived Assets

Research and Development Expenses

Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties, academic and

non-profit

institutions and consultants; salaries and personnel-related costs, including

non-cash

stock-based compensation expense; license fees to acquire

in-process

technology and other expenses, which include direct and allocated expenses for laboratory, facilities and other costs.

Non-refundable

contract-to-contract

and may result in uneven payment flows. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.

Intellectual Property Expenses

Stock-based Compensation

The Company accounts for stock-based payments in accordance with ASC Topic 718,

Compensation-Stock Compensation

non-employees

non-employees,

Valuation of

Privately-Held

Company

Equity

Securities

Issued

Compensation

The Company accounts for forfeitures of all stock-based payments when such forfeitures occur.

Income Taxes

Income taxes are recorded in accordance with ASC Topic 740,

Income Taxes

The Company accounts for uncertain tax positions using a

more-likely-than-not

Net Loss per Share

outstanding for the period, including any dilutive effect from convertible preferred stock, outstanding stock options, outstanding warrants or unvested restricted common stock.

The Company follows the

two-class

method when computing net loss per share for periods when issued shares that meet the definition of participating securities are outstanding. The

two-class

Concentration of Credit Risk and Off-Balance Sheet Risk

Concentration of Credit Risk and

Off-Balance

Sheet Risk

The Company has no significant

off-balance

sheet risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements.

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

available-for-sale

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (“ASU”)

2016-02,

Leases (Topic 842)

2018-11,

Leases (Topic 842): Targeted Improvements

, which permits entities to continue applying legacy guidance in ASC Topic 840,

Leases

2020-05,

Revenue from Contracts with Customers (Topic 606) and Leases (Topic 842): Effective Dates for Certain Entities

Upon the adoption of ASC 842, the Company removed its legacy deferred rent balances that were previously recorded under ASC 840 and established an operating lease

right-of-use

The following table presents a summary of the amount by which each financial statement line item was affected by the adoption of ASC 842 (in thousands):


	January 1, 2022
	Prior to the Adoption of ASC 842		Effect of Adoption			Subsequent to the Adoption of ASC 842
Operating lease right-of-use asset	$	—	$	2,922		$	2,922
Operating lease liabilities, current portion	$	—	$	1,577		$	1,577
Deferred rent, current portion	$	939	$	(939	)	$	—
Operating lease liabilities, net of current portion	$	—	$	3,253		$	3,253
Deferred rent, net of current portion	$	969	$	(969	)	$	—

In December 2019, the FASB issued ASU

2019-12,

Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

2019-12

simplifies the accounting for the interim period effects of changes in tax laws or rates and transactions that result in a

step-up

Recent Accounting Pronouncements-Yet to be Adopted

Recent Accounting

Pronouncements-Yet

to be Adopted

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

available-for-sale

2019-10,

Financial Instruments-Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates

Accordingly, the Company will adopt this new standard effective January 1,

2023

, and it does not expect that the adoption of ASU

2016-13

will have a material impact on the consolidated financial statements.

Net Loss Per Share - Summary of Computation of Diluted Net Loss Per Share (Detail) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	110,184	90,847	90,319
Series Seed Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	13,781	13,781	13,781
Series A Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	40,848	40,848	40,848
Series B-1 Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	22,222	22,222	22,222
Series B-2 Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	20,863	4,496	4,496
Unvested restricted common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4	58	488
Outstanding stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	12,304	9,280	8,322
Outstanding Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	162	162	162

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Disclosure Of Accrued Expenses And Other Current Liabilities [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities as of September 30, 2023 and December 31, 2022 were comprised as follows (in thousands):


	September 30, 2023		December 31, 2022
Annual bonus	$	2,356	$	2,198
External research and development services		1,910		274
Other employee compensation and benefits		146		426
Financing costs		808		—
Other operating expenses		491		277

Total accrued expenses and other current liabilities	$	5,711	$	3,175

Accrued expenses and other current liabilities as of December 31, 2022 and 2021 were comprised as follows (in thousands):


	December 31,
	2022		2021
Annual bonus	$	2,198	$	1,883
Other employee compensation and benefits		426		401
External research and development services		274		440
Other operating expenses		277		497

Total accrued expenses and other current liabilities	$	3,175	$	3,221

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Common stock par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Common stock shares authorized	117,138,030	115,838,000	115,838,000
Common stock, shares, issued	6,006,000	5,462,000	5,276,000
Common stock, shares, outstanding	6,002,000	5,404,000	4,788,000
Series Seed Convertible Preferred Stock [Member]
Temporary equity, par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized	13,781,000	13,781,000	13,781,000
Temporary equity, shares issued	13,781,000	13,781,000	13,781,000
Temporary equity, shares outstanding		13,781,000	13,781,000
Temporary equity, liquidation preference	$ 16,115	$ 16,115	$ 16,115
Series A Convertible Preferred Stock [Member]
Temporary equity, par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized	40,848,000	40,848,000	40,848,000
Temporary equity, shares issued	40,848,000	40,848,000	40,848,000
Temporary equity, shares outstanding	40,848,000	40,848,000	40,848,000
Temporary equity, liquidation preference	$ 91,500	$ 91,500	$ 91,500
Series B1 Convertible Preferred Stock [Member]
Temporary equity, par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized	22,222,000	22,222,000	22,222,000
Temporary equity, shares issued	22,222,000	22,222,000	22,222,000
Temporary equity, shares outstanding	22,222,000	22,222,000	22,222,000
Temporary equity, liquidation preference	$ 58,000	$ 58,000	$ 58,000
Series B2 Convertible Preferred Stock [Member]
Temporary equity, par or stated value per share	$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized	20,863,000	20,863,000	20,863,000
Temporary equity, shares issued	20,863,000	4,496,000	4,496,000
Temporary equity, shares outstanding	20,863,000	4,496,000	4,496,000
Temporary equity, liquidation preference	$ 58,000	$ 12,500	$ 12,500

Net Loss Per Share

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Earnings Per Share [Abstract]

Net Loss Per Share

12. Net Loss per Share


	September 30, 2023		December 31, 2022
Series Seed Preferred Stock		13,781		13,781
Series A Preferred Stock		40,848		40,848
Series B-1 Preferred Stock		22,222		22,222
Series B-2 Preferred Stock		20,863		4,496
Unvested restricted common stock		4		58
Outstanding stock options		12,304		9,280
Outstanding warrant		162		162

Total		110,184		90,847

16. Net Loss per Share

The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands):


	Year Ended December 31,
	2022		2021
Series Seed Preferred Stock		13,781		13,781
Series A Preferred Stock		40,848		40,848
Series B-1 Preferred Stock		22,222		22,222
Series B-2 Preferred Stock		4,496		4,496
Unvested restricted common stock		58		488
Outstanding stock options		9,280		8,322
Outstanding warrant		162		162

Total		90,847		90,319

Leases - Summary of Lease Cost (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Lessee Disclosure [Abstract]
Operating lease costs	$ 4,335	$ 1,648
Variable lease costs	742	534
Total lease costs	$ 5,077	$ 2,182

Common Stock (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Stockholders' Equity Note [Abstract]

Schedule of Reserved for Future Issuance

As of September 30, 2023 and December 31, 2022, the Company had reserved for future issuance the following number of shares of common stock (in thousands):


	September 30, 2023		December 31, 2022
Conversion of outstanding Series Seed Preferred Stock		13,781		13,781
Conversion of outstanding Series A Preferred Stock		40,848		40,848
Conversion of outstanding Series B-1 Preferred Stock		22,222		22,222
Conversion of outstanding Series B-2 Preferred Stock		20,863		4,496
Future issuances of Series B-2 Preferred Stock		—		16,367
Vesting of restricted common stock		4		58
Exercises of outstanding stock options		12,304		9,280
Exercise of outstanding warrant		162		162
Future issuances under 2019 Stock Incentive Plan		950		3,218

Total reserved for future issuance		111,134		110,432

As of December 31, 2022 and 2021, the Company had reserved for future issuance the following number of shares of common stock (in thousands):


	December 31,
	2022		2021
Conversion of outstanding Series Seed Preferred Stock		13,781		13,781
Conversion of outstanding Series A Preferred Stock		40,848		40,848
Conversion of outstanding Series B-1 Preferred Stock		22,222		22,222
Conversion of outstanding Series B-2 Preferred Stock		4,496		4,496
Future issuances of Series B-2 Preferred Stock		16,367		16,367
Vesting of restricted common stock		58		488
Exercises of outstanding stock options		9,280		8,322
Exercise of outstanding warrant		162		162
Future issuances under 2019 Stock Incentive Plan		3,218		4,361

Total reserved for future issuance		110,432		111,047

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

12. Income Taxes

The provision for income taxes for the years ended December 31, 2022 and 2021 was comprised as follows (in thousands):


	Year Ended December 31,
	2022		2021
Current taxes:
Federal	$	—	$	—
State		10		2

Total current taxes		10		2
Deferred taxes:
Federal		—		—
State		—		—

Total deferred taxes		—		—

Total provision for income taxes	$	10	$	2

A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows:


	December 31,
	2022			2021
Income tax computed at federal statutory rate		21.0	%		21.0	%
State taxes, net of federal benefit		6.1	%		9.9	%
Tax credit carryforwards		6.2	%		6.2	%
Permanent items		(0.2	)%		12.5	%
Change in valuation allowance		(32.7	%)		(49.4	%)
Other		(0.4	%)		(0.2	)%

Effective tax rate		—	%		—	%

The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2022 and 2021 were comprised as follows (in thousands):


	December 31,
	2022			2021
Deferred tax assets:
Net operating loss carryforwards	$	19,580		$	14,481
Tax credit carryforwards		5,477			1,871
Capitalized research and development		10,279			—
Stock-based compensation		319			148
Deferred rent		—			521
Operating lease liability		855			—
Accrued expenses and other temporary differences		707			650

Total deferred tax assets		37,217			17,671
Less: valuation allowance		(36,094	)		(17,091	)

Net deferred tax assets		1,123			580
Deferred tax liabilities:
Operating right-of-use asset		(552	)
Depreciation		(571	)		(580	)

Total deferred tax liabilities		(1,123	)		(580	)

Net deferred taxes	$	—		$	—

As of December 31, 2022, the Company had federal and state net operating loss (“NOL”) carryforwards of $72.1 million and $70.3 million, respectively. Federal NOLs may be carried forward indefinitely. State NOLs expire at various dates from 2038 through 2042. As of December 31, 2022, the Company had federal research and development tax credit carryforwards of $3.5 million that expire at various dates from 2040 through 2042. In addition, as of December 31, 2022, the Company had state research and development tax credit carryforwards of $2.6 million that expire at various dates from 2034 through 2037.

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which primarily pertain to NOL carryforwards, tax credit carryforwards and capitalized research and development. The Company has determined that it is more likely than not that it will not realize the benefits of its deferred tax assets, and as a result, a valuation allowance of $36.1 million has been established at December 31, 2022. The increase in the valuation allowance of $19.0 million during the year ended December 31, 2022 was primarily due to the additional operating loss generated by the Company.

NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50% as defined under Sections 382 and 383 in the Internal Revenue Code (“IRC”). This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the Company’s value immediately prior to the ownership change. As a result of ownership changes in the Company from its inception through December 31, 2022, the Company’s NOL and tax credit carryforwards allocable to the periods preceding each such ownership change could be subject to limitations under IRC Section 382, however the Company has not yet completed an IRC Section 382 study.

The Company had no unrecognized tax benefits as of either December 31, 2022 or 2021. The Company has not conducted a study of its research and development credit carryforwards generated during any year. This study, once completed, may result in an adjustment to the Company’s research and development credit carryforwards.

However, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credit carryforwards, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated statements of operations and comprehensive loss if an adjustment were required.

The Company files income tax returns in the United States federal tax jurisdiction and the Massachusetts state tax jurisdiction. Because the Company is in a loss carryforward position, it is generally subject to examination by federal and state tax authorities for all tax years in which a loss carryforward is available.

As of December 31, 2022, the Company has not incurred any material interest or penalty charges.

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

+ Details

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Defined Contribution Plan [Abstract]
Deinfed contribution employer matching contribution percentage of match	100.00%
Defined contribution employer matching contribution percent	3.00%
Defined contribution plan employer discretionary contribution amount	$ 200	$ 0

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Financial Statement Line Item Affected by the Adoption of ASC 842 (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Jan. 01, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset	$ 26,425	$ 2,024
Operating lease liabilities, current portion	992	2,921
Deferred rent, current portion			$ 939	$ 939
Operating lease liabilities, net of current portion	$ 30,228	$ 209
Deferred rent, net of current portion			969	$ 969
Adoption of ASC 842 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset			2,900
Operating lease liabilities, current portion			1,600
Operating lease liabilities, net of current portion			3,300
Effect of Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset			2,922
Operating lease liabilities, current portion			1,577
Deferred rent, current portion			(939)
Operating lease liabilities, net of current portion			3,253
Deferred rent, net of current portion			(969)
Subsequent to the Adoption of ASC 842 [Member] \| Adoption of ASC 842 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset			2,922
Operating lease liabilities, current portion			1,577
Operating lease liabilities, net of current portion			$ 3,253

- 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

Subsequent Events

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Subsequent Events [Abstract]

Subsequent Events

13. Subsequent Events

The Company has completed an evaluation of all subsequent events after the unaudited condensed consolidated balance sheet date of September 30, 2023 through November 6, 2023, the date these condensed consolidated financial statements were issued, to ensure that these condensed consolidated financial statements include appropriate disclosure of events both recognized in the condensed consolidated financial statements as of September 30, 2023, and events that occurred subsequently but were not recognized in the condensed consolidated financial statements. Except as disclosed elsewhere in Note 1 to the condensed consolidated financial statements, the Company concluded that no events or transactions have occurred that require disclosure in the accompanying condensed consolidated financial statements.

17. Subsequent Events

The Company has evaluated subsequent events for recognition and disclosure purposes through July 27, 2023, the date these consolidated financial statements were issued. Except for the matters described below, the Company has concluded that no other events or transactions have occurred that require disclosure in the consolidated financial statements.

Genevant Agreement

In March 2023, the Company entered into a collaboration and license agreement (the “Genevant Agreement”) with Genevant Sciences GmbH (“Genevant”) to combine the Company’s RNA editing technology with Genevant’s lipid nanoparticle technology to develop and potentially commercialize an RNA therapeutic for

alpha-1

antitrypsin deficiency. Key financial terms under the Genevant Agreement are as follows:

•

The Company made a $2.5 million payment to Genevant in March 2023 upon execution of the Genevant Agreement.

•

The Company will reimburse Genevant for certain

out-of-pocket

and full-time equivalent costs incurred as a result of research and development activities performed under the Genevant Agreement.

•

Genevant is entitled to receive payments from the Company upon the achievement of specified clinical, regulatory and commercial milestones, including potential precommercial milestone payments up to an aggregate total of $40.5 million per product and potential commercial milestone payments up to an aggregate total of $57.0 million.

•

Genevant is eligible to receive royalties at tiered percentage rates beginning in the

mid-single-digits,

based on future annual net sales of licensed products within the scope of the Genevant Agreement.

The Company has paid Genevant $2.8 million through July 27, 2023, the date these consolidated financial statements were issued, and has recorded the $2.5 million nonrefundable, payment within research and development expense in the condensed consolidated statement of operations for the three months ended March 31, 2023.

Sale of Series

B-2

Preferred Stock

In March 2023, the holders of the Series B Preferred Stock elected to waive the conditions of the Series B Milestone Closing and exercise the Series B Tranche Right. Accordingly, the holders purchased 16,366,905 shares of Series

B-2

Preferred Stock at a price of $2.78 per share. The Company received aggregate net cash proceeds of $45.5 million from this sale.

Merger Agreement &

Pre-Closing

Financing

On July 14, 2023, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Frequency Therapeutics, Inc., a Delaware corporation (“Frequency”) and Frequency Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Frequency (“Merger Sub”). Upon the terms and subject to the satisfaction of the conditions described in the Merger Agreement, Merger Sub will be merged with and into Korro Bio, Inc., with Korro Bio, Inc. surviving the Merger as a wholly owned subsidiary of Frequency (the “merger”). In contemplation of the proposed merger, the Company also entered into a subscription agreement with certain parties to purchase shares of the Company’s common stock for an aggregate purchase price of approximately $117.3 million (the

“pre-closing

financing”).

Subject to the terms and conditions of the Merger Agreement, immediately prior to the effective time of the merger (“Effective Time”), each then outstanding share of the Company’s common stock (including common stock issued upon the conversion of the Company’s preferred stock but excluding the common stock issued in the

pre-closing

financing) will be converted into the right to receive a number of shares of Frequency’s common stock calculated in accordance with the Merger Agreement.

The Company’s

pre-closing

financing is contingent on and will occur prior to the closing of the merger, subject to customary closing conditions. Shares of the Company’s common stock issued pursuant to the

pre-closing

financing will be converted into the right to receive a number of shares of Frequency common stock calculated in accordance with Merger Agreement at the Effective Time of the merger.

The merger and the

pre-closing

financing are expected to close in the fourth quarter of 2023. The merger is subject to approval by the stockholders of the Company and Frequency as well as other customary closing conditions, including the effectiveness of a registration statement filed with the SEC in connection with the transaction. If Frequency is unable to satisfy certain closing conditions or if other mutual closing conditions are not satisfied, the Company will not be obligated to complete the merger. The Merger Agreement contains certain termination rights of the Company and Frequency. The merger is expected to be treated as a reverse recapitalization in accordance with U.S. GAAP.

Income Taxes - Summary of Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Current taxes:
Federal
State	10	2
Total current taxes	10	2
Deferred taxes:
Federal
State
Total deferred taxes
Total provision for income taxes	$ 10	$ 2

- Definition

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

+ References + Details

SVB Agreement

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

SVB Agreement

8. SVB Agreement

In January 2021, the Company and Silicon Valley Bank (“SVB”) entered into a Loan and Security Agreement (the “SVB Agreement”). Under the original terms of the SVB Agreement, the Company had the ability to borrow up to $15.0 million at any time prior to December 31, 2021. The SVB Agreement was subsequently amended in December 2021 to extend this borrowing availability period through December 31, 2022. The Company did not borrow any amounts under the SVB Agreement prior to the expiry of the borrowing availability period.

In conjunction with the execution of the SVB Agreement, the Company issued SVB a warrant to purchase 162,000 shares of common stock at an exercise price of $0.58 per share. This warrant was exercisable immediately upon issuance and expires on January 21, 2031. The Company determined that this warrant represents a debt issuance cost associated with the overall credit facility. As such, the warrant was recorded as a deferred financing cost and as a component of additional

paid-in

capital on the consolidated balance sheets. This deferred financing cost, as well as others incurred in conjunction with the execution of the SVB Agreement were amortized from the date of issuance through December 31, 2022, the expiry of the SVB Agreement’s borrowing availability period.

To determine the fair value of the warrant upon issuance, the Company utilized the Black-Scholes option-pricing model with the following assumptions:


	Assumption
Risk-free interest rate		1.1	%
Expected dividend yield		—	%
Expected term (in years)		10.0
Expected volatility		72.9	%

Based upon these assumptions, the fair value of the warrant issued to SVB was determined to be less than $0.1 million. As of December 31, 2022, the warrant had not been exercised by SVB.

- 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

Genevant Agreement

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Genevant Agreement

10. Genevant Agreement

In March 2023, the Company entered into a collaboration and license agreement (the “Genevant Agreement”) with Genevant Sciences GmbH (“Genevant”). Key financial terms under the Genevant Agreement are as follows:

•

The Company made a $2.5 million payment to Genevant in March 2023 upon execution of the Genevant Agreement and recorded the payment within research and development expense in the condensed consolidated statement of operations for the nine months ended September 30, 2023.

•

The Company will reimburse Genevant for certain

out-of-pocket

and full-time equivalent costs incurred as a result of research and development activities performed under the Genevant Agreement.

•

Genevant is entitled to receive payments from the Company upon the achievement of certain milestones, including potential clinical milestone payments of up to $13.5 million, potential regulatory and development milestone payments of up to $27.0 million, and potential commercial milestone payments up to an aggregate total of $57.0 million.

•

Genevant is eligible to receive royalties at percentage rates in the

mid-single-digits,

based on future annual net sales of licensed products within the scope of the Genevant Agreement.

As of September 30, 2023, no milestones have been achieved and the Company has recorded reimbursements of $0.8 million within research and development expense in the condensed consolidated statement of

operations

Stock-based Compensation - Summary of Activity under RSU Plans (Detail) - Restricted Stock [Member] - $ / shares shares in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Opening Balance, Share	58	488
Granted
Vested	(54)	(430)
Repurchased
Closing Balance, Share	4	58
Weighted Average Opening Balance, Per Share	$ 0.03	$ 0.02
Weighted Average,Granted
Weighted Average,Vested	0.01	0.01
Weighted Average,Repurchased
Weighted Average Closing Balance, Per Share	$ 0.04	$ 0.03

Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 43,490	$ 33,819	$ 106,619
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	43,490	14,904	71,579
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		14,935	12,078
Government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		3,980	22,962
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	43,490	14,904	71,579
Level 1 [Member] \| Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	$ 43,490	14,904	71,579
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total		18,915	35,040
Level 2 [Member] \| Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		14,935	12,078
Level 2 [Member] \| Government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		$ 3,980	$ 22,962

Fair Value Measurements

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. Investments also include commercial paper and government securities which are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The carrying amounts reflected in the condensed consolidated balance sheets for cash, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature.

Assets measured at fair value on a recurring basis as of September 30, 2023 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	43,490	$	43,490	$	—	$	—

Total	$	43,490	$	43,490	$	—	$	—

Assets measured at fair value on a recurring basis as of December 31, 2022 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	14,904	$	14,904	$	—	$	—
Short-term investments:
Commercial paper		14,935		—		14,935		—
Government securities		3,980		—		3,980		—

Total	$	33,819	$	14,904	$	18,915	$	—

There were no liabilities measured at fair value on a recurring basis as of September 30, 2023 or December 31, 2022.

There were no changes in valuation techniques, nor were there any transfers among the fair value hierarchy levels during the nine months ended September 30, 2023 or during the year ended December 31, 2022.

3. Fair Value Measurements

The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. Investments also include commercial paper and government securities that are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The carrying amounts reflected in the consolidated balance sheets for cash, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature.

Assets measured at fair value on a recurring basis as of December 31, 2022 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	14,904	$	14,904	$	—	$	—
Short-term investments:
Commercial paper		14,935		—		14,935		—
Government securities		3,980		—		3,980		—

Total	$	33,819	$	14,904	$	18,915	$	—

Assets measured at fair value on a recurring basis as of December 31, 2021 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	71,579	$	71,579	$	—	$	—
Short-term investments:
Corporate debt securities		12,078		—		12,078		—
Commercial paper		22,962		—		22,962		—

Total	$	106,619	$	71,579	$	35,040	$	—

There were no liabilities measured at fair value on a recurring basis as of December 31, 2022 or 2021. However, as outlined further within Note 10, “Preferred Stock”, the Company sold 20,424,108 shares of Series A Preferred Stock in June and July 2020 pursuant to a Series A Preferred Stock Purchase Agreement (the “Series A Agreement”). Included in the terms of the Series A Agreement was a right (the “Series A Tranche Right”) that was initially accounted for as a liability under ASC Topic 480,

Distinguishing Liabilities from Equity

(“ASC 480”) and measured at fair value at each reporting period.

In July 2021, the holders of the Series A Preferred Stock elected to waive the milestone conditions outlined further within Note 10, “Preferred Stock”, and exercise the Series A Tranche Right. Accordingly, the holders purchased 20,424,108 additional shares of Series A Preferred Stock at a price of $2.24 per share. As a result, the preferred stock tranche liability was measured at fair value contemporaneously with the exercise of the Series A Tranche Right. The Company utilized the market-adjusted equity method and the option-pricing method to determine the fair value of the Series A Preferred Stock being purchased under the Series A Tranche Right. Based upon this valuation, the Company determined that a preferred stock tranche asset existed in the amount of $2.5 million due to the fair value of the Series A Preferred Stock being $2.12 per share, an amount less than the

contractual purchase price. As a result of the change in the fair value of the preferred stock tranche asset, the Company recognized a $13.5 million gain in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2021. The preferred stock tranche asset was then extinguished in conjunction with the issuance of the related Series A Preferred Stock.

The following table provides a reconciliation of the preferred stock tranche liability (in thousands):


	Preferred Stock Tranche Liability
Balance at December 31, 2020	$	(11,054	)
Change in fair value upon exercise of Series A Tranche Right		13,505
Reclassification to Series A Preferred Stock upon extinguishment		(2,451	)

Balance at December 31, 2021	$	—

The estimates outlined above were based, in part, on subjective assumptions. Changes to these assumptions could have had a significant impact on the reported fair values of the preferred stock tranche liability and/or the preferred stock tranche asset.

There were no changes in valuation techniques, nor were there any transfers among the fair value hierarchy levels during the years ended December 31, 2022 or 2021.

- 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

Commitments and Contingencies (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Lessee Operating Lease Liability Maturity [Line Items]

Summary of Future Minimum Operating Lease Liabilities

As of December 31, 2021, the future minimum lease payments due under the OKS Building 600/700 Lease and the OKS Sublease were as follows (in thousands):


	Future Minimum Lease Payments
2022	$	1,779
2023		2,315
2024		1,067

Total future minimum lease payments	$	5,161

Summary of Future Operating Lease Liability

Future minimum lease payments for all leases, net of $11.0 million expected to be received and intended to be used related to the remaining tenant improvement allowance and rent credits associated with the 60 First Street Lease, as of September 30, 2023 were as follows (in thousands):


	As of September 30, 2023
Remaining of 2023	$	548
2024		(8,956	)
2025		6,247
2026		7,341
2027		7,557
Thereafter		52,498

Total future minimum lease payments		65,235
Less: interest		(34,015	)

Present value of operating lease liabilities	$	31,220

OKS Building Six Hundred By Seven Hundred And OKS Sub Lease Agreement After Amendment One [Member]

Lessee Operating Lease Liability Maturity [Line Items]

Summary of Future Operating Lease Liability

As of December 31, 2022, the future minimum lease payments due under the OKS Combined Facility Lease were as follows (in thousands):


	Amount
2023	$	2,621
Less: effect of discounting		(92	)

Total lease liability	$	2,529

Cummings Park Sublease [Member]

Lessee Operating Lease Liability Maturity [Line Items]

Summary of Future Operating Lease Liability

As of December 31, 2022, the future minimum lease payments due under the Cummings Park Sublease were as follows (in thousands):


	Amount
2023	$	411
2024		212

Total remaining minimum lease payments		623
Less: effect of discounting		(22	)

Total lease liability	$	601

SVB Agreement - Additional information (Detail) - Silicon Valley Bank [Member] $ / shares in Units, shares in Thousands, $ in Millions	Dec. 31, 2022 USD ($) $ / shares shares
Line of Credit Facility [Line Items]
Maximum borrowing capacity under the credit facility	$ 15.0
Line of credit	$ 0.0
Number of securities into which the class of warrant or right may be converted \| shares	162,000
Exercise price per share or per unit of warrants or rights outstanding \| $ / shares	$ 0.58
Expiration date of outstanding warrant	Jan. 21, 2031
Fair value of warrant	$ 0.1

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Cover Page	9 Months Ended
Cover Page	Sep. 30, 2023
Document Information [Line Items]
Document Type	S-1/A
Amendment Flag	false
Entity Registrant Name	KORRO BIO, INC.
Entity Central Index Key	0001703647
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	One Kendall Square
Entity Address, Address Line Two	Building 600-700
Entity Address, Address Line Three	Suite 6-401
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	468-1999
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Primary SIC Number	2834
Entity Tax Identification Number	47-2324450
Business Contact [Member]
Document Information [Line Items]
Entity Address, Address Line One	One Kendall Square
Entity Address, Address Line Two	Building 600-700
Entity Address, Address Line Three	Suite 6-401
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	468-1999
Contact Personnel Name	Ram Aiyar

Leases - Additional Information (Detail) $ in Thousands	9 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Sep. 30, 2023 USD ($) ft²	May 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Apr. 01, 2022 ft²
Lessee, Lease, Description [Line Items]
Operating lease right of use asset	$ 26,425		$ 2,024
One Kendall Square Cambridge [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²	22,561
Operating lease date of expiry	Dec. 31, 2023
Cummings Park Wobum [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²	18,148
Operating lease date of expiry	Jul. 31, 2024
60 First Street Lease [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²				50,453
Incentive from lessor			$ 13,100
60 First Street Lease [Member] \| MA [Member]
Lessee, Lease, Description [Line Items]
Area of real estate \| ft²	50,453
Operating lease right of use asset		$ 26,800
Operating lease liability	$ 31,220	$ 26,800
Lessee operating lease term	11 years
Lessee operating lease payments due	$ 62,100
Incentive from lessor	13,100
Tenanant improvement allowance utilized	$ 2,100
Lessee operating lease renewal term	5 years
Incentive from lessor net	$ 11,000
Operating lease weighted average remaining lease term	10 years 4 months 24 days
Operating lease weighted average discount rate	11.10%
Minimum [Member]
Lessee, Lease, Description [Line Items]
Operating leases weighted average remaning lease term	3 months
Maximum [Member]
Lessee, Lease, Description [Line Items]
Operating leases weighted average remaning lease term	11 years

Fair Value Measurements (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2023

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of Assets Measured at Fair Value on a Recurring Basis

Assets measured at fair value on a recurring basis as of September 30, 2023 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	43,490	$	43,490	$	—	$	—

Total	$	43,490	$	43,490	$	—	$	—

Assets measured at fair value on a recurring basis as of December 31, 2022 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	14,904	$	14,904	$	—	$	—
Short-term investments:
Commercial paper		14,935		—		14,935		—
Government securities		3,980		—		3,980		—

Total	$	33,819	$	14,904	$	18,915	$	—

Assets measured at fair value on a recurring basis as of December 31, 2022 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	14,904	$	14,904	$	—	$	—
Short-term investments:
Commercial paper		14,935		—		14,935		—
Government securities		3,980		—		3,980		—

Total	$	33,819	$	14,904	$	18,915	$	—

Assets measured at fair value on a recurring basis as of December 31, 2021 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market funds, included in cash and cash equivalents	$	71,579	$	71,579	$	—	$	—
Short-term investments:
Corporate debt securities		12,078		—		12,078		—
Commercial paper		22,962		—		22,962		—

Total	$	106,619	$	71,579	$	35,040	$	—

Summary of Reconciliation of the Preferred Stock Tranche Liability

The following table provides a reconciliation of the preferred stock tranche liability (in thousands):


	Preferred Stock Tranche Liability
Balance at December 31, 2020	$	(11,054	)
Change in fair value upon exercise of Series A Tranche Right		13,505
Reclassification to Series A Preferred Stock upon extinguishment		(2,451	)

Balance at December 31, 2021	$	—

Leases (Tables)

9 Months Ended

Sep. 30, 2023

Lessee Disclosure [Abstract]

Summary of Future Operating Lease Payments Due


	As of September 30, 2023
Remaining of 2023	$	548
2024		(8,956	)
2025		6,247
2026		7,341
2027		7,557
Thereafter		52,498

Total future minimum lease payments		65,235
Less: interest		(34,015	)

Present value of operating lease liabilities	$	31,220

Summary of Lease Cost

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


	Nine Months Ended September 30,
	2023		2022
Operating lease costs	$	4,335	$	1,648
Variable lease costs		742		534

Total lease costs	$	5,077	$	2,182

Leases

9 Months Ended

Sep. 30, 2023

Lessee Disclosure [Abstract]

Leases

11. Leases

The Company’s building leases consist of office and laboratory space under

non-cancelable

leases that have remaining terms from approximately 3 months to 11 years.

The Company is party to an operating lease at One Kendall Square, Cambridge, Massachusetts and occupies 22,561 square feet of laboratory and office space (the “OKS Facility”) which expires on December 31, 2023, and an operating sublease agreement at Cummings Park in Woburn, Massachusetts and occupies 18,148 square feet of laboratory and office space (the “Cummings Park Sublease”) which expires on July 31, 2024.

The Company is party to an operating lease for 50,453 square feet of office and laboratory space at 60 First Street, Cambridge, Massachusetts (the “60 First Street Lease”). In May 2023, the Company obtained control over the space and the Company recognized the operating lease

right-of-use

asset and the operating lease liability of $26.8 million on the commencement date of the lease. The total rental payments over the 11 year lease are expected to be $62.1 million, including rent credits and other lease incentives per the terms of the lease. Specifically, the 60 First Street Lease provides the Company with a tenant improvement allowance of $13.1 million. The Company utilized $2.1 million of the $13.1 million tenant improvement allowance as of September 30, 2023. The Company has an option to extend the lease for an additional period of five years with the rent during the option period being the then fair market rent.


	As of September 30, 2023
Remaining of 2023	$	548
2024		(8,956	)
2025		6,247
2026		7,341
2027		7,557
Thereafter		52,498

Total future minimum lease payments		65,235
Less: interest		(34,015	)

Present value of operating lease liabilities	$	31,220

As of September 30, 2023, the weighted average remaining lease term was 10.4 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 11.1%.

The Company combines the lease and

non-lease

components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities and maintenance costs, are not included in the measurement of

right-of-use

assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs.

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


	Nine Months Ended September 30,
	2023		2022
Operating lease costs	$	4,335	$	1,648
Variable lease costs		742		534

Total lease costs	$	5,077	$	2,182

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 0	$ 0
Valuation allowance	36,094	$ 17,091
Deferred tax assets increase decrease in the valuation allowance	$ 19,000
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Period of cumulative change in ownership	3 years
Internal Revenue Service (IRS) [Member] \| Minimum [Member]
Operating Loss Carryforwards [Line Items]
Cumulative change in ownership percentage	50.00%
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 72,100
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	70,300
Tax Year 2040 to 2042 [Member] \| Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carry forward	3,500
Tax Period 2034 to 2037 [Member] \| State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carry forward	$ 2,600

Income Taxes - Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory rate	21.00%	21.00%
State taxes, net of federal benefit	6.10%	9.90%
Tax credit carryforwards	6.20%	6.20%
Permanent items	(0.20%)	12.50%
Change in valuation allowance	(32.70%)	(49.40%)
Other	(0.40%)	(0.20%)
Effective tax rate

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2022
Defined Contribution Plan [Abstract]
401(k) Savings Plan	14. 401(k) Savings Plan The Company has a defined-contribution savings plan under Section 401(k) of the IRC (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation, subject to statutory limitations. Beginning on April 1, 2022, the Company matches 100% of an employee’s 401(k) contributions up to a maximum of 3% of the participant’s salary, subject to employer match limitations under the IRC. As such, the Company made $0.2 million of matching contributions to the 401(k) Plan during the year ended December 31, 2022. The Company did not make any matching contributions during the year ended December 31, 2021.

The Company and Liquidity - Additional Information (Detail) - USD ($) $ in Thousands			1 Months Ended		9 Months Ended	12 Months Ended	50 Months Ended
	Nov. 03, 2023	Jul. 14, 2023	Mar. 31, 2023	Jun. 30, 2020	Sep. 30, 2023	Dec. 31, 2021	Dec. 31, 2022
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock				$ 45,500
Frequency Therapeutics, Inc [Member]
Disclosure Of The Company And Liquidity [Line Items]
Cash, cash equivalents, and short-term investments					$ 46,100
Merger Agreement [Member] \| Frequency Therapeutics, Inc [Member]
Disclosure Of The Company And Liquidity [Line Items]
Number of shares of equity interests issuable to acquire entity		5,161,114
Subsequent Event [Member] \| Frequency Therapeutics, Inc [Member]
Disclosure Of The Company And Liquidity [Line Items]
Cash acquired from acquisition	$ 26,900
Subsequent Event [Member] \| Pre-Closing Financing [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from issuance of common stock	$ 117,300
Pre-Closing Financing [Member]
Disclosure Of The Company And Liquidity [Line Items]
Common stock subscribed but not issued value		$ 117,300
Pre-Closing Financing [Member] \| Frequency Therapeutics, Inc [Member]
Disclosure Of The Company And Liquidity [Line Items]
Number of shares of equity interests issuable to acquire entity		2,077,864
Series Seed Convertible Preferred Stock [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock							$ 15,900
Series A Convertible Preferred Stock [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock						$ 45,708	91,200
Series B-1 convertible preferred stock [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock						57,739	57,700
Series B-2 convertible preferred stock [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock					$ 45,458	$ 12,500	$ 12,500
Series B-2 convertible preferred stock [Member] \| Subsequent Event [Member]
Disclosure Of The Company And Liquidity [Line Items]
Proceeds from redeemable convertible preferred stock			$ 45,500

Restricted Cash - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 46,119	$ 36,333	$ 48,113	$ 83,492
Restricted cash	5,174	5,144	5,294	552
Cash, cash equivalents and restricted cash	$ 51,293	$ 41,477	$ 53,407	$ 84,044	$ 39,694

Stock-based Compensation - Summary of Activity under Stock Option Plans (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement [Abstract]
Opening Balance, Options	9,280	8,322
Granted, Options	4,050	3,156
Exercised, Options	(533)	(176)
Cancelled, Options	(488)	(2,022)
Closing Balance, Options	12,309	9,280	8,322
Closing Balance, Exercisable	5,480	4,203
Opening Balance, Weighted Average Exercise Price	$ 0.74	$ 0.59
Weighted Average Exercise Price, Granted	1.06	1.11
Weighted Average Exercise Price, Exercised	0.66	0.36
Weighted Average Exercise Price, Cancelled	1	0.73
Closing Balance, Weighted Average Exercise Price	0.84	0.74	$ 0.59
Closing Balance, Weighted Average Exercise Price, Exercisable	$ 0.67	$ 0.6
Weighted Average Remaining Contractual Term	8 years 1 month 6 days	8 years	8 years 10 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 3 months 18 days	7 years 1 month 6 days
Aggregate Intrinsic Value	$ 3,135	$ 2,953	$ 4,478
Aggregate Intrinsic Value, Exercisable	$ 2,306	$ 1,881

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 41,828	$ 30,052	$ 42,201	$ 23,805
General and administrative	15,813	12,485	16,797	11,689
Total operating expenses	57,641	42,537	58,998	35,494
Loss from operations	(57,641)	(42,537)	(58,998)	(35,494)
Other income, net
Change in fair value of preferred stock tranche liability				13,505
Other income, net	1,895	539	976	32
Total other income, net			976	13,537
Loss before provision for income taxes			(58,022)	(21,957)
Provision for income taxes			10	2
Net loss	$ (55,746)	$ (41,998)	$ (58,032)	$ (21,959)
Net loss per share, basic	$ (9.98)	$ (8.3)	$ (11.3)	$ (4.94)
Net loss per share, diluted	$ (9.98)	$ (8.3)	$ (11.3)	$ (4.94)
Weighted-average common shares outstanding, basic	5,583	5,058	5,136	4,447
Weighted-average common shares outstanding, diluted	5,583	5,058	5,136	4,447
Comprehensive loss:
Net loss	$ (55,746)	$ (41,998)	$ (58,032)	$ (21,959)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale investments	5	(3)	2	(7)
Comprehensive loss	$ (55,741)	$ (42,001)	$ (58,030)	$ (21,966)

Leases - Summary of Future Operating Lease Payments Due (Detail) - Massachusetts - 60 First Street Lease [Member] - USD ($) $ in Thousands	Sep. 30, 2023	May 31, 2023
Lessee Operating Lease Liability Maturity [Line Items]
Remaining of 2023	$ 548
2024	(8,956)
2025	6,247
2026	7,341
2027	7,557
Thereafter	52,498
Total future minimum lease payments	65,235
Less: interest	(34,015)
Present value of operating lease liabilities	$ 31,220	$ 26,800