0001628280-22-029889 | 10-Q | XBRL Viewer

Stock-Based Compensation - Narrative (Details)					1 Months Ended						3 Months Ended		9 Months Ended		12 Months Ended
Stock-Based Compensation - Narrative (Details)	Aug. 04, 2022 USD ($) shares	Jun. 03, 2022 shares	Feb. 09, 2022 shares	Oct. 27, 2021 vestingCondition shares	Aug. 31, 2022 USD ($) installment grant $ / shares shares	Jun. 30, 2022 installment grant shares	May 31, 2022 $ / shares shares	Aug. 31, 2021 $ / shares shares	Sep. 30, 2019 shares	Feb. 28, 2019 shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) installment shares	Dec. 31, 2020 installment shares	Dec. 31, 2019 shares	Apr. 30, 2021 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options outstanding (in shares)											3,971,557		3,971,557		3,002,803
Shares reserved of future issuance (in shares)											57,287,852		57,287,852
Share-based compensation expense \| $											$ 1,417,000	$ 339,000	$ 3,885,000	$ 639,000
Granted (in shares)													1,160,074
Granted (in dollars per share) \| $ / shares													$ 8.40
Time-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost \| $											16,100,000		$ 16,100,000
Unrecognized compensation costs, period of recognition (in years)													3 years 2 months 12 days
Performance-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost \| $											$ 2,600,000		$ 2,600,000		$ 1,400,000
Granted (in shares)					90,066	32,166									241,248
Vesting, number of installments (in shares) \| installment						3									3
Number of vesting conditions \| vestingCondition				2
Number of grants \| grant					2	3
Granted (in dollars per share) \| $ / shares					$ 7.96
Aggregate grant date fair value \| $	$ 500,000
Performance-Based Stock Options \| Share-Based Payment Arrangement, Tranche One And Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Granted (in shares)				160,833
Performance-Based Stock Options \| Share-Based Payment Arrangement, Tranche One
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Granted (in shares)		10,722			57,900
Vesting, number of installments (in shares) \| installment					3
Cash generated from business development deals \| $					$ 100,000,000
Performance-Based Stock Options \| Share-Based Compensation Arrangement, Tranche Two And Three
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Granted (in shares)	21,444
Performance-Based Stock Options \| Share-Based Payment Arrangement, Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Granted (in shares)					32,166
Vesting, number of installments (in shares) \| installment					3
Performance-Based Stock Options \| Chief Technology Officer
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Granted (in shares)				80,416
Unvested restricted common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issued (in dollars per share) \| $ / shares							$ 0.00004	$ 0.00004			$ 0.00004		$ 0.00004
Repurchased stock (in shares)							3,116	18,227
Unvested restricted common stock \| Co-Founder
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Grants (in shares)									20,835,277
Restricted Stock, Performance-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense \| $													$ 0
Grants (in shares)													0
Remaining shares subject to service conditions (in shares)											4,192,997		4,192,997		4,553,223
Unrecognized compensation expense \| $											$ 300,000		$ 300,000
Compensation expense, milestones achieved \| $													$ 100,000
Restricted Stock, Performance-Based \| Co-Founder
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting, number of installments (in shares) \| installment															3	3
Grants (in shares)									3,472,545						385,998	694,679	3,472,545
Restricted Stock, Time-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period (in years)													4 years
Unrecognized compensation costs, period of recognition (in years)													1 year 3 months 18 days
Grants (in shares)													0
Remaining shares subject to service conditions (in shares)											6,404,723		6,404,723		10,801,361
Aggregate fair value or restricted common stock \| $													$ 400,000
Unrecognized compensation expense \| $											$ 400,000		$ 400,000
Restricted Stock, Time-Based \| Co-Founder
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Grants (in shares)									17,362,732
Restricted Stock, Time-Based \| Co-Founder B
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period (in years)										4 years
Grants (in shares)										694,679
2019 Equity Incentive Plan \| Stock Options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issuable under plan (in shares)																	6,171,635	11,561,815
Shares remaining available for grant (in shares)											1,392,540		1,392,540
Percent of fair market value of common stock (in percent)													110.00%
Voting power (in percent)											10.00%		10.00%
Expiration period (in years)													10 years
Award vesting period (in years)													4 years
2019 Equity Incentive Plan \| Stock Options to purchase common stock \| Share-Based Payment Arrangement, Tranche One
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting rights (in percent)													25.00%
2019 Equity Incentive Plan \| Stock Options to purchase common stock \| Share-Based Payment Arrangement, Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period (in years)													36 months
2019 Equity Incentive Plan \| Share-Based Payment Arrangement, ISO Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period (in years)													5 years
2022 Stock Option and Incentive Plan and 2019 Equity Incentive Plan \| Stock Options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved of future issuance (in shares)			8,041,688
2022 Stock Option and Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options outstanding (in shares)											0		0
2022 Stock Option and Incentive Plan \| Stock Options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of annual increase in shares reserved for future issuance			5.00%
Options issued (in shares)													0
2022 Employee Stock Purchase Plan \| Employee Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of annual increase in shares reserved for future issuance			1.00%
Shares reserved of future issuance (in shares)			971,350
Additional shares allowable under plan (in shares)			971,350
Share-based compensation expense \| $											$ 0		$ 0

Stock-Based Compensation - Restricted Stock Activity (Details)	9 Months Ended
	Sep. 30, 2022 $ / shares shares
Restricted Stock, Time-Based
Number of Shares
Beginning of period (in shares) \| shares	10,801,361
Issued (in shares) \| shares	0
Vested (in shares) \| shares	(4,385,478)
Repurchased (in shares) \| shares	(11,160)
End of period (in shares) \| shares	6,404,723
Weighted-Average Grant-Date Fair Value
Beginning of period (in dollars per share) \| $ / shares	$ 0.10
Issued (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	0.09
Repurchased (in dollars per share) \| $ / shares	0.35
End of period (in dollars per share) \| $ / shares	$ 0.04
Restricted Stock, Performance-Based
Number of Shares
Beginning of period (in shares) \| shares	4,553,223
Issued (in shares) \| shares	0
Vested (in shares) \| shares	(360,226)
Repurchased (in shares) \| shares	0
End of period (in shares) \| shares	4,192,997
Weighted-Average Grant-Date Fair Value
Beginning of period (in dollars per share) \| $ / shares	$ 0.10
Issued (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	0.19
Repurchased (in dollars per share) \| $ / shares	0
End of period (in dollars per share) \| $ / shares	$ 0.10

License and Collaboration Agreements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development	$ 25,047	$ 7,400	$ 57,664	$ 17,661
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development	$ 1,300	$ 3,800	$ 1,300	$ 3,800	$ 5,000

Common Stock (Details)	Sep. 30, 2022 vote shares
Equity [Abstract]
Number of votes per common share \| vote	1
Common stock reserved for conversion of preferred stock (in shares) \| shares	57,287,852

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Leases - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2022	Nov. 30, 2021
Lessee, Lease, Description [Line Items]
Operating lease, remaining lease term	5 years	5 years
Arsenal Street Sublease
Lessee, Lease, Description [Line Items]
Sublease income	$ 0.1	$ 0.2
Cambridge, Massachusetts Office Space
Lessee, Lease, Description [Line Items]
Commencement of rent payments (in years)			11 months
Expected liability to be paid	$ 208.7	$ 208.7
Term of contract, lease not yet commenced (in years)	10 years	10 years

Leases (Tables)

9 Months Ended

Sep. 30, 2022

Leases [Abstract]

Schedule of Operating Lease Liability

Future annual lease payments under non-cancelable operating leases as of September 30, 2022 were as follows (in thousands):


Remaining 2022	$	2,415
2023	12,610
2024	13,035
2025	3,510
2026	1,683
2027	567
Total future minimum lease payments	33,820
Less: imputed interest	(2,381)
	$	31,439

Convertible Preferred Stock - Narrative (Details)			1 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended
Convertible Preferred Stock - Narrative (Details)	Oct. 12, 2022	Dec. 31, 2020 installment $ / shares	Oct. 31, 2022 shares	Apr. 30, 2021 USD ($) $ / shares shares	Nov. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Sep. 30, 2022 USD ($) director $ / shares	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) installment $ / shares
Class of Stock [Line Items]
Minimum proceeds from future initial public offering issuance								$ 50,000,000
Dividends, preferred stock								$ 0	$ 0
Subsequent Event
Class of Stock [Line Items]
Reverse stock split			0.32167
Series A Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) \| shares				70,761,842	34,999,999	10,000,001
Sale of stock, price per share (in usd per share) \| $ / shares				$ 1.00	$ 1.00	$ 1.00
Sale of stock, consideration received				$ 70,800,000	$ 35,000,000	$ 10,000,000
Stock issuance costs				41,000	46,000	$ 20,000
Obligation to purchase additional stock (in shares) \| shares						104,999,997
Obligation to purchase additional stock (in dollars per share) \| $ / shares						$ 1.00
Preferred stock tranche right liability				$ 91,800,000		$ 6,300,000
Sale of stock, consideration contributed by company					$ 9,500,000
Number of directors allowed to be elected by stockholders \| director								3
Percentage of required stockholders' outstanding shares		65.00%						65.00%		65.00%
Dividend rate (in usd per share) \| $ / shares								$ 0.25
Number of installments \| installment		3								3
Convertible preferred stock, redeemable period		60 days
Increase in carrying amount of redeemable preferred stock							$ 300,000		$ 1,500,000	$ 1,600,000
Preferred stock, convertible, conversion ratio						0.1
Series A Redeemable Convertible Preferred Stock \| Subsequent Event
Class of Stock [Line Items]
Shares converted as part of IPO (in shares) \| shares			37,236,772
Series A Redeemable Convertible Preferred Stock \| Measurement Input, Share Price
Class of Stock [Line Items]
Preferred stock tranche right liability, measurement input, per share (in dollars per share) \| $ / shares		$ 0.76		$ 2.31	$ 0.73					$ 0.76
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) \| shares				45,658,957
Sale of stock, price per share (in usd per share) \| $ / shares				$ 4.3803
Sale of stock, consideration received				$ 200,000,000
Stock issuance costs				$ 400,000
Dividend rate (in usd per share) \| $ / shares								$ 1.09
Series B Convertible Preferred Stock \| Subsequent Event
Class of Stock [Line Items]
Shares converted as part of IPO (in shares) \| shares			14,686,986
Common Stock \| Subsequent Event
Class of Stock [Line Items]
Reverse stock split	0.32167

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	161,420,799	161,420,799
Redeemable convertible and convertible preferred stock, shares issued (in shares)	161,420,799	161,420,799
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	161,420,799	161,420,799
Redeemable convertible and convertible preferred stock, liquidation preference	$ 354,693	$ 335,814
Common stock, par or stated value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)	293,258,790	293,258,790
Common stock, shares issued (in shares)	33,559,912	32,413,860
Common stock, shares outstanding (in shares)	33,559,912	32,413,860
Series A Redeemable Convertible Preferred Stock
Redeemable convertible and convertible preferred stock, par or stated value (in dollars per share)	$ 0.00001	$ 0.00001
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	115,761,842	115,761,842
Redeemable convertible and convertible preferred stock, shares issued (in shares)	115,761,842	115,761,842
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	115,761,842	115,761,842
Redeemable convertible and convertible preferred stock, liquidation preference	$ 131,927	$ 125,000
Series B Convertible Preferred Stock
Redeemable convertible and convertible preferred stock, par or stated value (in dollars per share)	$ 0.00001	$ 0.00001
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	45,658,957	45,658,957
Redeemable convertible and convertible preferred stock, shares issued (in shares)	45,658,957	45,658,957
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	45,658,957	45,658,957
Redeemable convertible and convertible preferred stock, liquidation preference	$ 222,766	$ 210,814

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2022
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Founder Consulting Services For both the three and nine months ended September 30, 2022 and 2021, the Company made payments of $37,500 and $0.1 million, respectively, to one of the Co-founder shareholders for scientific consulting and other expenses. As of September 30, 2022 and December 31, 2021, there were no amounts included within accounts payable. Beam Therapeutics The Company and Beam Therapeutics, (“Beam”), are parties to the Beam Collaboration Agreement and the Beam Mutual Subscription Agreement and have a common founder and one common board member (see Note 10). For the year ended December 31, 2021, the Company made payments of $0.1 million to Beam for general and administrative services pursuant to an agreement to receive certain interim management and startup services (see Note 10). The agreement ended on March 31, 2021 and for the nine months ended September 30, 2021, the Company made payments of $0.1 million for such services. Newpath Partners In connection with the Series A and B Preferred Stock closings (see Note 6), the Company issued and sold 9,999,999 and 5,250,781 shares of Series A and B Preferred Stock, respectively, to Newpath Partners L.P. (“Newpath”), which is an affiliate to one of the Company’s board members, for an aggregate purchase price of $10.0 million and $23.0 million, respectively. Myeloid Therapeutics In December 2021, the Company and Myeloid entered into the Myeloid Collaboration Agreement and Myeloid Subscription Agreement (see Note 10). The Company and Myeloid have one common board member, who is also an affiliate of Newpath, one of the Company’s holders of Series A and B Preferred Stock.

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 600	$ 200	$ 1,354	$ 339

Fair Value Measurements - Hierarchy For Assets and Liabilities Measured At Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	$ 9,543	$ 15,962
Total assets	127,537	133,650
Related party forward contract liability		12,020
Total liabilities		12,020
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	28,819	49,450
U.S. Treasury bills and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	89,175	68,238
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	9,543	15,962
Total assets	9,543	15,962
Related party forward contract liability		0
Total liabilities		0
Level 1 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 1 \| U.S. Treasury bills and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
Total assets	117,994	117,688
Related party forward contract liability		0
Total liabilities		0
Level 2 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	28,819	49,450
Level 2 \| U.S. Treasury bills and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	89,175	68,238
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
Total assets	0	0
Related party forward contract liability		12,020
Total liabilities		12,020
Level 3 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 \| U.S. Treasury bills and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0	$ 0

Stock-Based Compensation

9 Months Ended

Sep. 30, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

2019 Equity Incentive Plan

The Company’s 2019 Stock Option and Grant Plan (the “2019 Plan”) provides for the Company to grant incentive stock options (“ISO”), non-qualified stock options, unrestricted stock awards, restricted stock awards (“RSA”) and other stock-based awards (collectively, the “Awards”) to the officers, employees, consultants and other key persons of the Company. The 2019 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated.

The total number of shares of common stock issuable under the 2019 Plan was 6,171,635. In April 2021, the Company’s board of directors further increased the number of shares of common stock reserved for issuance under the plan from 6,171,635 shares to 11,561,815 shares. As of September 30, 2022 there were 1,392,540 shares remaining available for future grants under the 2019 Plan. Shares of unused common stock underlying any Awards that are forfeited, canceled or reacquired by the Company prior to vesting will again be available for the grant of awards under the 2019 Plan.

The exercise price for stock options granted may not be less than the fair market value of the Company’s common stock on the date of grant, as determined by the board of directors, or at least 110 percent of the fair market value of the Company’s common stock on the date of grant in the case of an ISO granted to an employee who owns stock representing more than 10 percent of the voting power of all classes of stock (“10% Owner”) as determined by the board of directors as of the date of grant. The Company’s board of directors determines the fair market value of the Company’s common stock, taking into consideration its most recently available valuation of common stock performed by third parties as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant. Unless otherwise provided, at the time of grant, the options granted pursuant to the 2019 Plan expire ten years from the date of grant, or five years from the date of grant in the case of an ISO that is granted to a 10% Owner. Awards typically vest over four years, with the first 25 percent vesting on the first anniversary of the vesting commencement date and the remainder vesting in 36 equal monthly installments thereafter, contingent on the recipient’s continued employment, service or relationship with the Company.

In October 2022, the Company completed its IPO, and in connection with the closing the Board determined that no further awards would be granted under the 2019 Plan.

2022 Stock Option and Incentive Plan

On February 9, 2022, the Company’s board of directors adopted, and on October 10, 2022 its stockholders approved, the 2022 Stock Option and Incentive Plan (the “2022 Plan”), which became effective immediately preceding the date on which the registration statement for the Company’s IPO is declared effective by the SEC. The 2022 Plan allows the Company to make equity-based and cash-based incentive awards to its officers, employees, directors, and consultants. The 2022 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2022 Plan is 8,041,688 shares, which includes the number of shares remaining available for grant under the 2019 Plan, as of the effective date, for the issuance of awards under the 2022 Plan. In addition, the number of shares reserved and available for issuance under the 2022 Plan will automatically increase on January 1, 2023 and each January 1 thereafter, by five percent of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the compensation committee.

The shares of common stock underlying any awards under the 2022 Plan and the 2019 Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire, or are otherwise terminated (other than by exercise) will be added back to the shares of common stock available for issuance under the 2022 Plan.

As of September 30, 2022, no options were issued and outstanding under the 2022 Plan.

2022 Employee Stock Purchase Plan

On February 9, 2022, the Company’s board of directors adopted, and on October 10, 2022 its stockholders approved, the 2022 Employee Stock Purchase Plan (the “2022 ESPP”), which became effective immediately preceding the date on which the registration statement for the Company’s IPO is declared effective by the SEC. A total of 971,350 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2022 ESPP shall cumulatively increase beginning on January 1, 2023 and each January 1 thereafter through January 1, 2032, by the least of (i) 971,350 shares of common stock, (ii) one percent of the outstanding number of shares of common stock on the immediately preceding December 31, or (iii) such number of shares of common stock as determined by the administrator of the 2022 ESPP.

No shares of the Company’s common stock were issued and no stock-based compensation expense was recognized during the three and nine months ended September 30, 2022 related to the 2022 ESPP.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2021:


	Number of Shares	Weighted-Average Exercise Price





Balance at December 31, 2021	3,002,803	$	3.96
Granted	1,160,074	8.40
Exercised	(55,687)	3.67
Forfeited	(135,633)	4.66
Balance at September 30, 2022	3,971,557	$	5.24


Options vested and exercisable at September 30, 2022	536,064	$	3.71
Options vested and expected to vest at September 30, 2022	3,971,557	$	5.24

As of September 30, 2022, there was $16.1 million of total unrecognized compensation cost related to time-based unvested stock options the Company expects to recognize such amount over a remaining weighted-average period of 3.2 years.

Performance-Based Stock Options

During the year ended December 31, 2021, the Company granted performance-based stock options to purchase 241,248 shares of common stock. The performance-based options commence vesting upon the achievement of (i) IND acceptance, (ii) consummation of the Company’s IPO and (iii) a research milestone to be mutually agreed upon and vest over three equal installments. On February 9, 2022, the Company’s board of directors established and approved the third performance-based vesting milestone, which requires the building of a chemistry facility, initiation of pegRNA piloting operations, and production of a GLP toxicology lot suitable for in vivo non-human primate studies, for stock options to purchase 80,416 shares of common stock granted on October 27, 2021 to the Company’s CTO. The first two performance-based vesting conditions for stock options to purchase 160,833 shares of common stock granted were established by the board of directors on October 27, 2021. The grant date of these awards for accounting purposes is the date on which the performance conditions of the award were established by the board of directors and all terms of the award were known by the recipient. As a result, the grant-date fair value of each such award for accounting purposes was determined on October 27, 2021 and such awards are reflected in the Company’s total stock options outstanding as of December 31, 2021. The performance-based vesting condition for stock options to purchase 80,416 shares of common stock granted on October 27, 2021 which was not established by the Company’s board of directors until February 9, 2022 and therefore a grant date for accounting purposes had not been established for those stock options as of December 31, 2021 although such stock options are included in the Company’s total stock options outstanding as of December 31, 2021. The accounting grant date was established on February 9, 2022 and as such are outstanding stock options for accounting purposes as of September 30, 2022.

In June 2022, the Company granted three performance-based stock options to purchase a total of 32,166 shares of common stock. The performance-based options commence vesting upon the achievement of (i) IND acceptance, (ii) consummation of the Company’s IPO and (iii) first regulatory designation granted to Prime Medicine and vest over three equal installments. The grant date of these awards for accounting purposes is the date on which the performance conditions of the award are established by the board of directors and all terms of the award are known by the recipient. As a result, the grant-date fair value for accounting purposes for the first performance-based stock options to purchase 10,722 shares of common stock was determined on June 3, 2022, when the performance-based vesting conditions were established by the board of directors and the terms of the awards were communicated to the recipients. The second and third performance-based vesting conditions for stock options to purchase the remaining 21,444 shares of common stock was not established by the Company’s board of directors until August 4, 2022 and therefore a grant date for accounting purposes had not been established for those stock options as of September 30, 2022 although such stock options are included in the Company’s total stock options outstanding for legal purposes as of September 30, 2022.

In August 2022, the Company granted 90,066 shares of performance-based options, at an exercise price of $7.96 per share. This includes two grants, and 57,900 of the performance-based options vest in three equal installments upon the achievement of (i) IND acceptance, (ii) consummation of the Company’s IPO and (iii) business development deals which generate $100.0 million or more in upfront and near-term unrestricted cash. The remaining 32,166 of the performance-based options vest in three equal installments upon the achievement of (i) IND acceptance, (ii) consummation of the Company’s IPO and (iii) maximize the senior leadership team effectiveness by accomplishment of four criteria through year end 2023. The grant date of these awards for accounting purposes is the date on which the performance conditions of the award are established by the board of directors and all terms of the award are known by the recipient. As a result, the grant-date fair value for accounting purposes was determined on August 4, 2022, when the performance-based vesting conditions were established by the board of directors and the terms of the awards were communicated to the recipients. The aggregate grant-date fair value is $0.5 million.

Through September 30, 2022, the Company concluded that the achievement of all of the performance conditions for such awards was not probable or consummated.

As of September 30, 2022 and December 31, 2021, there was $2.6 million and $1.4 million respectively, of total unrecognized compensation cost related to performance-based stock options.

Restricted Common Stock Awards

The Company awards restricted common stock to employees and non-employees under its 2019 Plan. The fair value of each share of restricted common stock is based on the market price of the Company's common stock on the date of grant.

For a period of up to six months from a grantee’s termination, the Company has the right and option to repurchase unvested restricted common stock at the lower of (i) the original purchase price per share ($0.00004) or (ii) the fair market value per share as of the date of the Company elects to exercise its repurchase right. In August 2021, the Company repurchased 18,227 unvested shares of the restricted common stock at a price of $0.00004 per share, the original sale price, and the repurchased common shares were restored to the amount of unissued, authorized shares of common stock as of December 31, 2021. In May 2022, the Company repurchased 3,116 unvested shares of the restricted common stock at a price of $0.00004 per share, the original sale price, and the repurchased common shares were restored to the amount of unissued, authorized shares of common stock as of September 30, 2022.

Shares of restricted common stock granted to employees and directors are not deemed, for accounting purposes, to be outstanding until those shares have vested.

Each award type is discussed below.

Time-Based Restricted Common Stocks

The majority of the restricted common stock have time-based vesting conditions and vest over a four-year period, subject to the employee’s continued employment with, or service to, the Company on such vesting date. Compensation expense is recognized on a straight-line basis over the vesting period.

Time-Based Restricted Common Stock

In September 2019, a co-founder of the Company was granted a total of 20,835,277 shares of restricted common stock, of which 3,472,545 shares are performance-based restricted common stock as described below. The remaining 17,362,732 shares are subject to service conditions. In February 2020, another co-founder of the Company was granted 694,679 shares of restricted common stock that are subject to service conditions. These awards vest over a four-year period and provide for accelerated vesting of a portion of the unvested awards, as determined in the award agreement, upon the initial or subsequent closings of the Series A Preferred Stock. Upon the grant date, the Company determined the initial and subsequent closings of the Series A Preferred Stock were probable to occur and recognized the compensation expense over the expected service period.

The following table summarizes the Company’s time-based restricted common stock activity since December 31, 2021:


	Number of Shares	Weighted-Average Grant-Date Fair Value




Unvested restricted common stock at December 31, 2021	10,801,361	$	0.10
Issued	—	—
Vested	(4,385,478)	0.09
Repurchased	(11,160)	0.35
Unvested restricted common stock at September 30, 2022	6,404,723	$	0.04

The aggregate fair value of restricted common stock that vested during the nine months ended September 30, 2022 was $0.4 million.

As of September 30, 2022, there was $0.4 million of total unrecognized compensation cost related to unvested time-based restricted common stock which the Company expects to recognize over a weighted-average period of 1.3 years.

Performance-Based Restricted Common Stock

The Company has also granted performance‑based restricted common stock to certain executive officers and key persons of the Company with terms that allow the grantees to vest in a specific number of shares based upon the achievement of performance‑based milestones. The Company granted 3,472,545 shares of performance-based restricted common stock to a co-founder of the Company in 2019, which will vest upon on the dosing of first patient in a Phase II or later-stage clinical trial or FDA approval of compound. The Company granted 694,679 and 385,998 shares of performance-based restricted common stock to certain executive officers in the years ended December 31, 2020 and 2021, respectively. These awards vest in three equal installments upon the achievements of (i) proof of concept in lead indication (which was achieved in May 2022), (ii) IND acceptance and (iii) consummation of the Company’s IPO.

Share‑based compensation expense associated with the performance-based restricted common stock is recognized if the performance condition is considered probable of achievement using the Company’s best estimates of the time to vesting for the achievement of the performance‑based milestones. Each reporting period, the Company updates its assessment of the probability that the performance-based milestones will be achieved. As of December 31, 2020 and 2021, the Company has concluded it was not probable that these performance conditions related to performance-based restricted common stock would be achieved, and as a result no compensation expense related to the performance-based restricted common stock has been recorded. As of September 30, 2022, the Company has concluded that the proof of concept in a lead indication was achieved in May 2022, but it was not probable that the remaining performance conditions related to performance-based restricted common stock would be achieved. As a result, compensation expense of $0.1 million was recorded for the milestone achieved, and no compensation expense related to the remaining performance-based restricted common stock has been recorded. The fair value of the restricted common stock was based on the fair market value of the Company’s common stock on the date of grant.

The following table summarizes the Company’s performance-based restricted common stock activity since December 31, 2021:


	Number of Shares	Weighted-Average Grant-Date Fair Value




Unvested restricted common stock at December 31, 2021	4,553,223	$	0.10
Issued	—	—
Vested	(360,226)	0.19
Repurchased	—	—
Unvested restricted common stock at September 30, 2022	4,192,997	$	0.10

As of September 30, 2022, there was $0.3 million of total unrecognized compensation cost related to unvested performance-based restricted common stock.

Stock-Based Compensation

The following table below summarizes the classification of the Company’s stock-based compensation expense related to stock options and restricted common stock awards in the consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
General and administrative	$	467	$	130	$	1,288	$	172
Research and development	950		209		$	2,597	$	467
	$	1,417	$	339	$	3,885	$	639

CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE AND CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Stock issuance costs		$ 2,642	$ 0
Series A Redeemable Convertible Preferred Stock
Stock issuance costs	$ 41
Series B Convertible Preferred Stock
Stock issuance costs	$ 80

Common Stock

9 Months Ended

Sep. 30, 2022

Equity [Abstract]

Common Stock

Convertible Preferred Stock

The Company has issued Series A Preferred Stock and Series B convertible preferred stock (the “Series B Preferred Stock” and, together with the Series A Preferred Stock, the “Preferred Stock”).

The Series A preferred stock and Series B preferred stock, described in more detail below, converted into 37,236,772 shares and 14,686,986 shares of common stock, respectively, in October 2022 as part of the Company’s IPO.

In September 2019, the Company completed its first closing of its Series A Preferred Stock and issued and sold 10,000,001 shares of Series A Preferred Stock at a price of $1.00 per share for gross proceeds of $10.0 million (the “2019 Preferred Stock Financing”). The Company incurred issuance costs of $20,000 in connection with this transaction.

The purchase agreement for the Series A Preferred Stock obligated the investors of the 2019 Preferred Stock Financing to purchase an additional 104,999,997 Series A Preferred Stock at a price of $1.00 per share in the subsequent closings upon certain conditions (“Series A Subsequent Closings”). The investors’ obligation to purchase shares in the subsequent closing terminated upon occurrence of a Deemed Liquidation Event (as defined below), the Company’s initial public offering, or bankruptcy by the Company. If an investor did not participate in the subsequent closing when obligated to do so, then any existing Series A Preferred Stock held by that investor would be converted into common shares of the Company on a ten-for-one basis.

The Company concluded that these obligations of investors to participate in the subsequent closing of Series A Preferred Stock met the definition of a freestanding financial instrument that was required to be recorded as a liability at fair value as (i) the instruments are legally detachable and separately exercisable from the Series A Preferred Stock and (ii) the rights will require the Company to transfer assets upon future closings of the Series A Preferred Stock. Upon the first closing of the Series A Preferred Stock in September 2019, the Company recorded a preferred stock tranche right liability of $6.3 million and a corresponding reduction to the carrying value of the Series A Preferred Stock (see Note 3).

In November 2020, the Company completed the second closing of its Series A Preferred Stock, in which the Company issued and sold 34,999,999 shares of Series A Preferred Stock, at a price of $1.00 per share, for gross proceeds of $35.0 million and incurred $46,000 of issuance costs. As the fair value of the Series A Preferred Stock was $0.73 at the time of the second closing, the Company recorded a capital contribution of $9.5 million for the difference between the fair value per share and the $1.00 per share paid by the holders of the Series A Preferred Stock participating in the second closing, which included members of the Company’s board of directors.

In April 2021, the Company completed the third and fourth closings of its Series A Preferred Stock, in which the Company issued and sold an aggregate of 70,761,842 shares of Series A Preferred Stock, at a price of $1.00 per

share, for gross proceeds of $70.8 million and incurred $41,000 of issuance costs. As a result of this issuance, the Series A preferred stock tranche right liability with a then fair value of $91.8 million, based on a fair value of $2.31 per share of Series A Preferred Stock immediately prior to the closings, was settled in full and reclassified as an increase to the carrying value of Series A Preferred Stock.

In April 2021, the Company issued and sold 45,658,957 shares of Series B Preferred Stock, at a price of $4.3803 per share, for gross proceeds of $200.0 million and incurred $0.4 million of issuance costs.

Upon issuance of each series of Preferred Stock, the Company assessed the embedded conversion and liquidation features of the securities and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance date of each series of Preferred Stock.

On October 12, 2022, in connection with the Company’s IPO, the Company effected a 1-for-3.10880 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios of each series of the Company’s preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the preferred stock conversion ratios.

As of each balance sheet date, the Preferred Stock consisted of the following (in thousands, except share amounts):


	September 30, 2022
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	131,927	$	3.10880	37,236,772
Series B Preferred Stock	45,658,957	45,658,957	199,643		$	222,766	$	13.6175	14,686,986
	161,420,799	161,420,799	$	395,800	$	354,693			51,923,758


	December 31, 2021
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	125,000	$	3.10880	37,236,776
Series B Preferred Stock	45,658,957	45,658,957	$	199,643	$	210,814	$	13.6175	14,686,988
	161,420,799	161,420,799	$	395,800	$	335,814			51,923,764

The holders of the Preferred Stock have the following rights and preferences:

Voting

The holders of the Preferred Stock are entitled to vote, together with the holders of common stock, as a single class, on all matters submitted to the shareholders for a vote and are entitled to the number of votes equal to the number of common stock into which the Preferred Stock could convert on the record date for determination of shareholders entitled to vote. A majority vote of the holders of Preferred Stock is required to, among others, liquidate or dissolve the Company, amend the certificate of incorporation or bylaws, reclassify common stock or establish another class of capital stock, create shares that would rank senior to or authorize additional shares of Preferred Stock, declare a dividend or make a distribution, or change the authorized number of directors constituting the board of directors.

In addition, the holders of shares of Series A Preferred Stock, voting exclusively and as a separate class, are entitled to elect three directors of the Company. The holders of shares of common stock and any other class or series of voting stock (including the Series B Preferred Stock), exclusively and voting together as a single class, are entitled to elect the balance of the total number of directors of the Company.

Conversion

Each Preferred Stock is convertible into voting common stock, at any time, at the option of the holder, and without the payment of additional consideration, at the applicable conversion ratio then in effect. In addition, each share of Preferred Stock will be automatically converted into shares of common stock at the then-effective applicable conversion ratio upon either (i) the closing of a firm-commitment underwritten public offering of its common stock resulting in at least $50.0 million of gross proceeds, net of underwriting discount and commissions, to the Company, or (ii) the date specified by vote or written consent of the holders of a majority in voting power of the outstanding shares of Preferred Stock, voting as a single class.

The conversion ratio of each class of Preferred Stock is determined by dividing the Original Issue Price of each class of Preferred Stock by the Conversion Price of each class. As of September 30, 2022 and December 31, 2021, the Conversion Price was $3.10880 per share for Series A Preferred Stock and $13.6175 per share for Series B Preferred Stock, each subject to appropriate adjustment in the event of any share dividend, share split, combination or other similar recapitalization with respect to the Preferred Stock.

Upon the closing of the IPO in October 2022, 161,420,799 shares of outstanding convertible preferred stock were automatically converted into 51,923,758 shares of common stock, after the effect of the one-for-3.10880 reverse stock split, with the related carrying value of $395.8 million reclassified to common stock and additional paid-in capital.

There shall be no adjustment in the conversion price of the Series A Preferred Stock as the result of the issuance or deemed issuance of additional shares of Company’s common stock if the Company receives written notice from the holders of at least 65 percent of the then outstanding shares of Series A Preferred Stock agreeing that no such adjustment shall be made as the result of the issuance or deemed issuance of additional shares of the Company’s common stock. There shall be no adjustment in the conversion price of the Series B Preferred Stock as the result of the issuance or deemed issuance of additional shares of the Company’s common stock if the Company receives written notice from the holders of at least a majority of the then outstanding shares of Series B Preferred Stock agreeing that no such adjustment shall be made as the result of the issuance or deemed issuance of such additional shares of the Company’s common stock.

In the event that any holder of shares of Series A Preferred Stock is required to participate in a Series A Subsequent Closing pursuant to the purchase agreement does not purchase the aggregate number of subsequent closing shares, then each share of Series A Preferred Stock held by such holder shall automatically be converted into shares of common stock at a ratio of one share of common stock for every ten shares of Series A Preferred Stock held immediately prior to the consummation of such Series A Subsequent Closing.

Dividends

The holders of the Series A Preferred Stock are entitled to receive cumulative dividends at a rate of $0.25 per share per annum of the Original Issue Price when, as and if declared by the board of directors (the “Series A Preferred Dividend”). The holders of the series B Preferred Stock are entitled to receive cumulative dividends at a rate of $1.09 per share per annum of the Original Issue Price when, as and if declared by the board of directors (the “Series B Preferred Dividend”, and together with Series A Preferred Dividend, the “Preferred Dividend”).

The Company may not declare, pay or set aside any dividends on common shares of the Company unless the holders of Preferred Stock then outstanding first receive, or simultaneously receive, the Preferred Dividend on each outstanding Preferred Stock and a dividend on each outstanding Preferred Stock in an amount at least equal to the greater of (i) the amount of the aggregate Preferred Dividend then accrued on such share of Preferred Stock and not previously paid and (ii) (a) in the case of a dividend on common stock or any class or series that is convertible into common stock, that dividend per share of Preferred Stock as would equal to the product of (1) the dividend payable

on each share of such class or series determined, as if all shares of such class or series had been converted into common stock and (2) the number of shares of common stock issuable upon conversion of a share of such series of Preferred Stock, in each case calculated on the record date for determination of the holders entitle to receive such dividend or the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common shares or (b) in the case of a dividend on any class or series that is not convertible into common stock, at a rate per share of Preferred Stock determined by (1) dividing the amount of dividend payable on each share of such class or series of capital stock by the original issuance price of such class or series of capital stock and (2) multiplying such faction by an amount equal to the Original Issue Price for such series of Preferred Stock. If the Company declares, pays, or sets aside, on the same date, a dividend on shares of more than one class or series of shares in the capital of the Company (other than the Preferred Stock), the dividend payable to the holders of Preferred Stock shall be calculated based upon the dividend on the class or series of shares in the capital of the Company that would result in the highest dividend on the Preferred Stock. Through September 30, 2022 and December 31, 2021 no cash dividends have been declared or paid.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, or upon the occurrence of a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding are entitled, on a pari passu basis, to be paid out of the assets or funds of the Company available for distribution to stockholders before any payment is made to the holders of common stock. The holders of Preferred Stock are entitled to an amount per share equal to (i) in the case of Series A Preferred Stock, the Original Issue Price plus any accruing dividends accrued but unpaid thereon, whether or not declared, together with any other dividends declared but unpaid thereon, and (ii) in the case of Series B Preferred Stock, the greater of (a) the applicable Original Issue Price plus any accruing dividends accrued but unpaid thereon, whether or not declared, together with any other dividends declared, or not declared, but unpaid thereon (the "Series B Preference Amount") or (b) the amount that would have been payable had all shares of each series of Preferred Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or Deemed Liquidation Event (as defined below). After the payment in full of the Series A Preferred Stock preference amount and if applicable, the Series B Preference Amount, the remaining assets of the Company available for distribution to stockholders shall be distributed among the holders of Series A Preferred Stock and common stock on a pro rata basis provided that such distribution includes holders of Series B Preferred Stock if such distribution is greater than the Series B Preference Amount.

Unless at least the holders of a majority in voting power of the outstanding shares of Preferred Stock, elect otherwise, a Deemed Liquidation Event shall include a merger, consolidation, or share exchange (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation) or a sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company.

Redemption

As of December 31, 2020, at the written election of at least 65 percent of the holders of the outstanding shares of Series A Preferred Stock, voting together as a single class and on an as-converted to common stock basis, the shares of Series A Preferred Stock outstanding were redeemable, at any time on or after the fifth anniversary of issuance, in three equal annual installments commencing 60 days after receipt of the required vote. Shares of Series A Preferred Stock were redeemable in an amount equal to the Original Issue Price per share plus any accruing dividends accrued but unpaid thereon, whether or not declared.

In April 2021, in connection with the Series B Preferred Stock closing, the Company adopted an amended and restated certificate of incorporation, which removed the redemptions rights of the holders of Series A Preferred Stock. As a result of this amendment, Series A Preferred Stock was no longer redeemable at the option of the holders. The Company determined that the changes to the rights underlying the Series A Preferred Stock was not substantive and did not materially modify the rights and preferences of the holders of Series A Preferred Stock.

Prior to the amendment, the Company recognized changes in the redemption values of its Series A Preferred Stock over the period from the date of issuance to the earliest redemption date and adjusted the carrying value of the instrument to equal the redemption value at the redemption date. During the period from September 19, 2019 (inception) to December 31, 2019, the years ended December 31, 2020 and 2021, the Company recorded adjustments to increase the carrying values of the Series A Preferred Stock by an aggregate of $0.3 million, $1.6 million, and $1.5 million, respectively, which resulted in an increase in redeemable convertible preferred stock by those amounts, offset by charges against additional paid-in-capital, if any, and then in the absence of additional paid-in capital the accretion is charged to the accumulated deficit.

The Company’s articles of the corporation, as amended and restated, does not provide redemption rights to the holders of Series B Preferred Stock.

Common Stock

The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preferences of the holders of the Preferred Stock set forth above. Each share of common stock entitles the holder to one vote, together with the holders of the Preferred Stock, on all matters submitted to the stockholders for a vote. The holders of common stock are entitled to receive dividends, if any, as declared by the Company’s board of directors, subject to the preferential dividend rights of Preferred Stock.

As of September 30, 2022 the Company had reserved 57,287,852 shares, respectively, of common stock for the potential conversion of shares of Preferred Stock into common stock, the exercise of outstanding stock options for common stock, and the issuance of common stock options and restricted stock awards remaining available for grant under the 2019 Equity Incentive Plan.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI https://asc.fasb.org/topic&trid=2208762

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (g)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (h)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 16
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496180-112644

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126731327&loc=SL126733271-114008

+ Details

Convertible Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2022

Temporary Equity Disclosure [Abstract]

Temporary Equity

As of each balance sheet date, the Preferred Stock consisted of the following (in thousands, except share amounts):


	September 30, 2022
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	131,927	$	3.10880	37,236,772
Series B Preferred Stock	45,658,957	45,658,957	199,643		$	222,766	$	13.6175	14,686,986
	161,420,799	161,420,799	$	395,800	$	354,693			51,923,758


	December 31, 2021
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	125,000	$	3.10880	37,236,776
Series B Preferred Stock	45,658,957	45,658,957	$	199,643	$	210,814	$	13.6175	14,686,988
	161,420,799	161,420,799	$	395,800	$	335,814			51,923,764

Nature of the Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 31, 2022 USD ($) $ / shares shares	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Subsequent Event [Line Items]
Stock issuance costs		$ 2,642	$ 0
Accumulated deficit		253,914		$ 171,376
Cash, cash equivalents, and short-term investments		$ 146,700
Subsequent Event
Subsequent Event [Line Items]
Reverse stock split	0.32167
Subsequent Event \| IPO
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares) \| shares	11,721,456
Sale of stock, price per share (in usd per share) \| $ / shares	$ 17.00
Proceeds from IPO	$ 180,300
Stock issuance costs	$ 19,000
Subsequent Event \| Over-Allotment Option
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares) \| shares	1,427,338

Leases - Schedule of Maturity (Details) $ in Thousands	Sep. 30, 2022 USD ($)
Leases [Abstract]
Remaining 2022	$ 2,415
2023	12,610
2024	13,035
2025	3,510
2026	1,683
2027	567
Total future minimum lease payments	33,820
Less: imputed interest	(2,381)
Total operating lease liability	$ 31,439

Net Loss per Share - Schedule of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net loss	$ (29,350)	$ (29,348)	$ (23,840)	$ (16,412)	$ 616	$ (86,660)	$ (82,538)	$ (102,456)
Accretion of preferred stock to redemption value	0			0			0	(1,468)
Cumulative dividend on preferred stock	(6,362)			(6,363)			(18,879)	(10,922)
Net loss attributable to common stockholders, basic	(35,712)			(22,775)			(101,417)	(114,846)
Net loss attributable to common stockholders, diluted	$ (35,712)			$ (22,775)			$ (101,417)	$ (114,846)
Denominator:
Weighted-average common shares outstanding, diluted (in shares)	22,226,301			14,965,186			20,665,225	11,795,738
Weighted-average common shares outstanding, basic (in shares)	22,226,301			14,965,186			20,665,225	11,795,738
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (1.61)			$ (1.52)			$ (4.91)	$ (9.74)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (1.61)			$ (1.52)			$ (4.91)	$ (9.74)

Net Loss per Share - Schedule of Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	66,493,041	69,985,777
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	51,923,758	51,923,764
Stock Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	3,971,557	1,311,101
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	10,597,726	16,750,912

Fair Value Measurements - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Apr. 30, 2021	Nov. 30, 2020	Sep. 30, 2019	Dec. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Anti-dilution obligation, achievement threshold				$ 100.0
Broad Institute
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sale of stock, number of shares issued (in shares)				2,498,850
Convertible preferred stock, shares issued, value				$ 7.5
Series A Redeemable Convertible Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sale of stock, number of shares issued (in shares)	70,761,842	34,999,999	10,000,001
Series A Redeemable Convertible Preferred Stock \| Measurement Input, Share Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche right liability, measurement input, per share (in dollars per share)	$ 2.31	$ 0.73			$ 0.76
Common Stock \| Measurement Input, Share Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Anti-dilution obligation, measurement input, per share (in dollars per share)				$ 3.02	$ 0.35

Stock-Based Compensation - Stock Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2022
Number of Shares
Beginning of period (in shares)	3,002,803
Granted (in shares)	1,160,074
Exercised (in shares)	(55,687)
Forfeited (in shares)	(135,633)
Options vested and exercisable, end of period (in shares)	536,064
Options vested and expected to vest, end of period (in shares)	3,971,557
End of period (in shares)	3,971,557
Weighted-Average Exercise Price
Beginning of the period (in dollars per share)	$ 3.96
Granted (in dollars per share)	8.40
Exercised (in dollars per share)	3.67
Forfeited (in dollars per share)	4.66
Options vested and exercisable, end of period (in dollars per share)	3.71
Options vested and expected to vest, end of period (in dollars per share)	5.24
End of period (in dollars per share)	$ 5.24

Convertible Preferred Stock - Preferred Stock at Balance Sheet Date (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)	161,420,799			161,420,799
Preferred Stock Issued and Outstanding (in shares)	161,420,799			161,420,799
Carrying Value	$ 395,800			$ 395,800
Liquidation Preference	$ 354,693			$ 335,814
Common Stock Issuable Upon Conversion (in shares)	51,923,758			51,923,764
Redeemable convertible and convertible preferred stock, shares issued (in shares)	161,420,799			161,420,799
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)	115,761,842			115,761,842
Preferred Stock Issued and Outstanding (in shares)	115,761,842	115,761,842	115,761,842	115,761,842	115,761,842	115,761,842	45,000,000	45,000,000
Carrying Value	$ 196,157	$ 196,157	$ 196,157	$ 196,157	$ 196,157	$ 196,157	$ 32,330	$ 31,136
Liquidation Preference	$ 131,927			$ 125,000
Conversion price per share (in dollars per share)	$ 3.10880			$ 3.10880
Common Stock Issuable Upon Conversion (in shares)	37,236,772			37,236,776
Redeemable convertible and convertible preferred stock, shares issued (in shares)	115,761,842			115,761,842
Series B Preferred Stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)	45,658,957			45,658,957
Preferred Stock Issued and Outstanding (in shares)	45,658,957	45,658,957	45,658,957	45,658,957	45,658,957	45,658,957	0	0
Carrying Value	$ 199,643	$ 199,643	$ 199,643	$ 199,643	$ 199,643	$ 199,643	$ 0	$ 0
Liquidation Preference	$ 222,766			$ 210,814
Conversion price per share (in dollars per share)	$ 13.6175			$ 13.6175
Common Stock Issuable Upon Conversion (in shares)	14,686,986			14,686,988
Redeemable convertible and convertible preferred stock, shares issued (in shares)	45,658,957			45,658,957

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2022

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

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


	September 30,		December 31,
	2022		2021
Laboratory equipment	$	16,227	$	5,274
Leasehold improvement	475		125
Furniture and Fixture	215		144
Computer hardware and software	11		—
Total property and equipment	16,928		5,543
Less: Accumulated depreciation and amortization	(1,961)		(611)
Property and equipment, net	$	14,967	$	4,932

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2022

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Numerator:
Net loss	$	(29,350)	$	(16,412)	$	(82,538)	$	(102,456)
Accretion of preferred stock to redemption value	—		—		—		(1,468)
Cumulative dividend on preferred stock	(6,362)		(6,363)		(18,879)		(10,922)
Net loss attributable to common stockholders	$	(35,712)	$	(22,775)	$	(101,417)	$	(114,846)
Denominator:
Weighted-average common shares outstanding, basic and diluted	22,226,301		14,965,186		20,665,225		11,795,738
Net loss per share attributable to common stockholders, basic and diluted	$	(1.61)	$	(1.52)	$	(4.91)	$	(9.74)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	As of September 30, 2022
		2022	2021
Convertible preferred stock (as converted to common stock)		51,923,758	51,923,764
Stock Options to purchase common stock		3,971,557	1,311,101
Unvested restricted common stock		10,597,726	16,750,912
		66,493,041	69,985,777

Net Loss per Share

9 Months Ended

Sep. 30, 2022

Earnings Per Share [Abstract]

Net Loss per Share

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Numerator:
Net loss	$	(29,350)	$	(16,412)	$	(82,538)	$	(102,456)
Accretion of preferred stock to redemption value	—		—		—		(1,468)
Cumulative dividend on preferred stock	(6,362)		(6,363)		(18,879)		(10,922)
Net loss attributable to common stockholders	$	(35,712)	$	(22,775)	$	(101,417)	$	(114,846)
Denominator:
Weighted-average common shares outstanding, basic and diluted	22,226,301		14,965,186		20,665,225		11,795,738
Net loss per share attributable to common stockholders, basic and diluted	$	(1.61)	$	(1.52)	$	(4.91)	$	(9.74)

Diluted net loss per share available to common shareholders was computed by giving effect to all potentially dilutive common stock equivalents outstanding for the period. For purposes of this calculation, preferred stock, unvested restricted stock and stock options to purchase common stock were considered common stock equivalents but had been excluded from the calculation of diluted net loss per share available to common shareholders as their effect was anti-dilutive. In periods in which the Company reports a net loss available to common shareholders, diluted net loss per share available to common shareholders is the same as basic net loss per share available to common shareholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.


	As of September 30, 2022
		2022	2021
Convertible preferred stock (as converted to common stock)		51,923,758	51,923,764
Stock Options to purchase common stock		3,971,557	1,311,101
Unvested restricted common stock		10,597,726	16,750,912
		66,493,041	69,985,777

Property and Equipment, Net

9 Months Ended

Sep. 30, 2022

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

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


	September 30,		December 31,
	2022		2021
Laboratory equipment	$	16,227	$	5,274
Leasehold improvement	475		125
Furniture and Fixture	215		144
Computer hardware and software	11		—
Total property and equipment	16,928		5,543
Less: Accumulated depreciation and amortization	(1,961)		(611)
Property and equipment, net	$	14,967	$	4,932

Depreciation and amortization expense of property and equipment for the three and nine months ended September 30, 2022 was $0.6 million and $1.4 million, respectively. Depreciation and amortization expense of

property and equipment for the three and nine months ended September 30, 2021 was $0.2 million and $0.3 million, respectively.

Fair Value Measurements - Schedule of Short-Term Investments (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Equity Securities, FV-NI [Abstract]
Amortized Cost	$ 5,486	$ 5,486
Unrealized Gains	4,057	10,476
Unrealized Losses	0	0
Fair Value	9,543	15,962
Securities, amortized costs	95,115	73,751
Securities, unrealized gains	4,057	10,476
Securities, unrealized losses	(454)	(27)
Securities, fair value	98,718	84,200
U.S. Treasury bills and government securities
Debt Securities, Available-for-Sale [Abstract]
Amortized Cost	89,629	68,265
Unrealized Gains		0
Unrealized Losses	(454)	(27)
Fair Value	$ 89,175	$ 68,238

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2022

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value (in thousands):


	Fair Value Measurements at September 30, 2022:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	28,819	$	—	$	28,819
Short-term investment:
U.S. Treasury bills and government securities	—		89,175		—		89,175
Related party short-term investment:
Beam equity securities	9,543		—		—		9,543
	$	9,543	$	117,994	$	—	$	127,537


	Fair Value Measurements at December 31, 2021
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	49,450	$	—	$	49,450
Short-term investment:
U.S. Treasury bills and government securities	—		68,238		—		68,238
Related party short-term investment:
Beam equity securities	15,962		—		—		15,962
	$	15,962	$	117,688	$	—	$	133,650
Liabilities:
Related party forward contract liability	—		—		12,020		12,020
	$	—	$	—	$	12,020	$	12,020

Debt and Equity Securities

Short-term investments consisted of the following (in thousands):


	Fair Value Measurements at September 30, 2022
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Short-term investments:
U.S. Treasury bills and government securities	$	89,629			$	(454)	$	89,175
Related party short-term investment:
Beam equity securities	5,486		4,057		—		9,543
	$	95,115	$	4,057	$	(454)	$	98,718


	December 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Short-term investments:
U.S. Treasury bills and government securities	$	68,265	$	—	$	(27)	$	68,238
Related party short-term investment:
Beam equity securities	$	5,486	$	10,476	$	—	$	15,962
	$	73,751	$	10,476	$	(27)	$	84,200

Investments Classified by Contractual Maturity Date

The contractual maturities of the Company’s short-term investments in available-for-sale debt securities held were as follows:


	September 30, 2022		December 31, 2021
Due within one year	$	89,175	$	68,238
	$	89,175	$	68,238

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

The following table provides a roll-forward of the aggregate fair value of the Company’s preferred stock tranche right liability, for which fair value is determined using Level 3 inputs (in thousands):


	Preferred Stock Tranche Right





Balance as of December 31, 2020	$	17,515
Change in fair value of Series A preferred stock tranche right liability	74,319
Reclassification of Series A preferred stock tranche right liability upon settlement	(91,834)
Balance as of December 31, 2021	$	—

The following table provides a roll-forward of the aggregate fair value of the Company’s anti-dilution obligation, for which fair value was determined using Level 3 inputs (in thousands):


	Anti-dilution Obligation




Balance as of December 31, 2020	$	855
Change in fair value of anti-dilution obligation	6,681
Reclassification of anti-dilution obligation upon settlement	(7,536)
Balance as of December 31, 2021	$	—

A reconciliation of the related party forward contract liability measured and recorded at fair value on a recurring basis is as follows (in thousands):


	Forward Contract


Balance as of December 31, 2021	$	12,020
Reclassification of related party forward contract liability upon settlement	(12,020)
Balance as of September 30, 2022	$	—

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2022

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities

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


	September 30,		December 31,
	2022		2021
Accrued Myeloid license fee–related party	$	—	$	30,000
Accrued employee compensation and benefits	4,111		2,364
Accrued professional fees	1,070		3,830

Lab-related supplies and services	1,167		719
Other	182		279
Total	$	6,530	$	37,192

Subsequent Events (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 12, 2022	Oct. 31, 2022 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($)	Oct. 24, 2022 shares	Dec. 31, 2021 shares
Subsequent Event [Line Items]
Stock issuance costs \| $					$ 2,642	$ 0
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)			161,420,799		161,420,799			161,420,799
Share-based compensation expense \| $			$ 1,417	$ 339	$ 3,885	$ 639
Common stock, shares authorized (in shares)			293,258,790		293,258,790			293,258,790
Subsequent Event
Subsequent Event [Line Items]
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)		161,420,799
Reverse stock split		0.32167
Carrying value of convertible stock reclassified \| $		$ 395,800
Number of shares vested (in shares)		121,160
Share-based compensation expense \| $		$ 1,000
Common stock, shares authorized (in shares)							775,000,000
Subsequent Event \| Unvested restricted common stock
Subsequent Event [Line Items]
Number of shares vested (in shares)		360,225
Subsequent Event \| Common Stock
Subsequent Event [Line Items]
Convertible preferred stock, number of shares converted into common stock (in shares)		51,923,758
Reverse stock split	0.32167
Subsequent Event \| IPO
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares)		11,721,456
Sale of stock, price per share (in usd per share) \| $ / shares		$ 17.00
Proceeds from IPO \| $		$ 180,300
Stock issuance costs \| $		$ 19,000
Subsequent Event \| Over-Allotment Option
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares)		1,427,338

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. Intercompany balances and transactions have been eliminated in consolidation. The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). The accompanying condensed consolidated financial statements of Prime Medicine, Inc. are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2022 and the results of its operations for the three and nine months ended September 30, 2022 and 2021, and its cash flows for the nine months ended September 30, 2022 and 2021. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2022 and 2021 are also unaudited. The results for the nine months ended September 30, 2022 are not necessarily indicative of results to be expected for the year ending December 31, 2022, any other interim periods, or any future year or period. The condensed consolidated balance sheet data as of December 31, 2021 was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2021, and notes thereto, which are included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act with the Securities and Exchange Commission (the “SEC”) on October 21, 2022.
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected within these condensed consolidated financial statements include, but are not limited to, revenue recognition, the valuation of the Company’s common stock and stock-based awards, the valuation of preferred stock tranche right liability, the valuation of the anti-dilution obligation and the valuation of the related party forward contract liability. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ materially from those estimates or assumptions.
Cash and Cash Equivalents	Cash and Cash EquivalentsThe Company considers all highly liquid investments with an original maturity of three months or less at the time of initial purchase to be cash equivalents
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In August 2020, the FASB issued ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40). This standard eliminates the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. In addition, the new guidance modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted earnings per share (“EPS”) computation. Additionally, the amended guidance requires the application of the if-converted method for calculating diluted EPS and the treasury stock method will no longer be available. For public business entities, it is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years using the fully retrospective or modified retrospective method. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years. Early adoption is permitted but no earlier than fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company is currently evaluating the potential impact that ASU 2020-06 will have on its condensed consolidated financial statements and related disclosures but does not currently expect that the adoption of ASU 2020-06 will have a material impact. Other accounting standards that have been issued by the Financial Accounting Standards Board or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption

Commitment and Contingencies	9 Months Ended
Commitment and Contingencies	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company’s commitments under its operating leases are described in Note 9. Additionally, as part of the lease agreement the Company entered into in May 2022 for 480 Arsenal Street, the Company signed a participation rights agreement for up to $2.0 million, which allows the landlord or an affiliate or designee of the landlord to participate in any future issuance of equity at the same terms and pricing as other investors. Since the right to participate is on the same terms and pricing afforded to other investors, the participation right is deemed to be at fair value with no separate accounting required. With the completion of our IPO in October 2022, this agreement terminated. License and Collaboration Agreements The Company entered into various license and collaboration agreements under which it is obligated to make fixed and contingent payments (see Note 10). 401(k) Plan The Company maintains a defined-contribution plan under Section 401(k) of the Internal Revenue Code of 1986 (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 on a pre-tax basis. Matching contributions to the 401(k) Plan may be made at the discretion of management. The Company is not required to make any matching contributions to the 401(k) Plan. In July 2022, the Company announced a new company match for the 401(k) retirement plan beginning on July 1, 2022. For the three and nine months ended September 30, 2022, the Company has contributed $0.1 million. As of September 30, 2022, $0.3 million is included within accrued expenses. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with all board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any indemnification arrangements that could have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of September 30, 2022 and December 31, 2021. Legal Proceedings From time to time, the Company may become involved in legal proceedings or other litigation relating to claims arising in the ordinary course of business. The Company accrues a liability for such matters when it is probable that future expenditures will be made and that such expenditures can be reasonably estimated. Significant judgment is required to determine both probability and estimated exposure amount. Legal fees and other costs associated with such proceedings are expensed as incurred. As of September 30, 2022 and December 31, 2021, the Company was not a party to any material legal proceedings or claims.

Commitment and Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2022	Sep. 30, 2022	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Participation rights agreement, amount	$ 2.0
Employer contribution amount		$ 0.1	$ 0.1
Accrued employee benefits		$ 0.3	$ 0.3

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 47,947	$ 185,420
Short-term investments	89,175	68,238
Related party short-term investment	9,543	15,962
Prepaid expenses and other current assets	2,180	959
Total current assets	148,845	270,579
Property and equipment, net	14,967	4,932
Operating lease right-of-use lease assets	32,344	10,746
Restricted cash	13,496	13,125
Other assets	5,613	2,474
Total assets	215,265	301,856
Current liabilities:
Accounts payable	4,111	1,435
Accrued expenses and other current liabilities	6,530	37,192
Related party forward contract liability	0	12,020
Operating lease liability	11,577	7,336
Total current liabilities	22,218	57,983
Operating lease liability, net of current	19,862	3,070
Non current deferred tax liability	481	1,243
Total liabilities	42,561	62,296
Commitments and contingencies (Note 11)
Redeemable convertible and convertible preferred stock, carrying amount	395,800	395,800
Stockholders’ equity (deficit):
Common stock, $0.00001 par value; 293,258,790, and 293,258,790 shares authorized at September 30, 2022 and December 31, 2021, respectively; and 33,559,912, and 32,413,860 shares issued and outstanding at September 30, 2022 and December 31, 2021, respectively	0	0
Additional paid-in capital	31,272	15,163
Accumulated other comprehensive loss	(454)	(27)
Accumulated deficit	(253,914)	(171,376)
Total stockholders’ (deficit)	(223,096)	(156,240)
Total liabilities, redeemable convertible and convertible preferred stock and stockholders’ (deficit)	$ 215,265	$ 301,856
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	161,420,799	161,420,799
Redeemable convertible and convertible preferred stock, shares issued (in shares)	161,420,799	161,420,799
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	161,420,799	161,420,799
Series A Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible and convertible preferred stock, carrying amount	$ 196,157	$ 196,157
Stockholders’ equity (deficit):
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	115,761,842	115,761,842
Redeemable convertible and convertible preferred stock, shares issued (in shares)	115,761,842	115,761,842
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	115,761,842	115,761,842
Series B Convertible Preferred Stock
Current liabilities:
Redeemable convertible and convertible preferred stock, carrying amount	$ 199,643	$ 199,643
Stockholders’ equity (deficit):
Redeemable convertible and convertible preferred stock, shares authorized (in shares)	45,658,957	45,658,957
Redeemable convertible and convertible preferred stock, shares issued (in shares)	45,658,957	45,658,957
Redeemable convertible and convertible preferred stock, shares outstanding (in shares)	45,658,957	45,658,957

Convertible Preferred Stock

9 Months Ended

Sep. 30, 2022

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

As of each balance sheet date, the Preferred Stock consisted of the following (in thousands, except share amounts):


	September 30, 2022
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	131,927	$	3.10880	37,236,772
Series B Preferred Stock	45,658,957	45,658,957	199,643		$	222,766	$	13.6175	14,686,986
	161,420,799	161,420,799	$	395,800	$	354,693			51,923,758


	December 31, 2021
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Conversion price per share		Common Stock Issuable Upon Conversion
Series A Preferred Stock	115,761,842	115,761,842	$	196,157	$	125,000	$	3.10880	37,236,776
Series B Preferred Stock	45,658,957	45,658,957	$	199,643	$	210,814	$	13.6175	14,686,988
	161,420,799	161,420,799	$	395,800	$	335,814			51,923,764

The holders of the Preferred Stock have the following rights and preferences:

Voting

Conversion

Dividends

Liquidation

Redemption

The Company’s articles of the corporation, as amended and restated, does not provide redemption rights to the holders of Series B Preferred Stock.

Common Stock

- Definition

+ References

+ Details

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2022
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In October 2022, the Company completed its IPO of its common stock. In connection with its IPO, the Company issued and sold 11,721,456 shares of its common stock, including 1,427,338 shares pursuant to the exercise of the underwriters’ option to purchase additional shares, at a price to the public of $17.00 per share. As a result of the IPO, the Company received $180.3 million in net proceeds, after deducting underwriting discounts, commissions and offering costs of $19.0 million. Upon the closing of the IPO, 161,420,799 shares of outstanding convertible preferred stock were automatically converted into 51,923,758 shares of common stock, after the effect of the one-for-3.10880 reverse stock split, with the related carrying value of $395.8 million reclassified to common stock and additional paid-in capital. Additionally, the performance vesting condition for 360,225 restricted stock units and 121,160 stock options issued under the 2019 Plan was deemed satisfied upon the effective date of the Company's registration statement on Form S-1 filed with the SEC in connection with the IPO. The related compensation expense for these awards was approximately $1.0 million. On February 9, 2022, the Company’s board of directors approved the third amended and restated certificate of incorporation, which was filed upon the closing of the IPO, on October 24, 2022, and which, among other things, increases the number of shares of common stock authorized for issuance from 293,258,790 to 775,000,000 shares of common stock.

Related Party Transactions (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
Related Party Transactions (Details) - USD ($)	Apr. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Series A Preferred Stock \| Newpath Partners
Related Party Transaction [Line Items]
Sale of stock, number of shares issued (in shares)	9,999,999
Sale of stock, consideration received	$ 10,000,000
Series B Preferred Stock \| Newpath Partners
Related Party Transaction [Line Items]
Sale of stock, number of shares issued (in shares)	5,250,781
Sale of stock, consideration received	$ 23,000,000
Scientific Consulting \| Co-Founder Shareholder
Related Party Transaction [Line Items]
Amounts of transaction		$ 37,500	$ 100,000	$ 37,500	$ 100,000
Interim Management And Startup Services \| Beam Therapeutics
Related Party Transaction [Line Items]
SG&A expense with related party					$ 100,000	$ 100,000

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2022

Share-Based Payment Arrangement [Abstract]

Share-Based Payment Arrangement, Option, Activity

The following table summarizes the Company’s stock option activity since December 31, 2021:


	Number of Shares	Weighted-Average Exercise Price





Balance at December 31, 2021	3,002,803	$	3.96
Granted	1,160,074	8.40
Exercised	(55,687)	3.67
Forfeited	(135,633)	4.66
Balance at September 30, 2022	3,971,557	$	5.24


Options vested and exercisable at September 30, 2022	536,064	$	3.71
Options vested and expected to vest at September 30, 2022	3,971,557	$	5.24

Share-Based Payment Arrangement, Outstanding Award, Activity, Excluding Option

The following table summarizes the Company’s time-based restricted common stock activity since December 31, 2021:


	Number of Shares	Weighted-Average Grant-Date Fair Value




Unvested restricted common stock at December 31, 2021	10,801,361	$	0.10
Issued	—	—
Vested	(4,385,478)	0.09
Repurchased	(11,160)	0.35
Unvested restricted common stock at September 30, 2022	6,404,723	$	0.04

The following table summarizes the Company’s performance-based restricted common stock activity since December 31, 2021:


	Number of Shares	Weighted-Average Grant-Date Fair Value




Unvested restricted common stock at December 31, 2021	4,553,223	$	0.10
Issued	—	—
Vested	(360,226)	0.19
Repurchased	—	—
Unvested restricted common stock at September 30, 2022	4,192,997	$	0.10

Share-Based Payment Arrangement, Expensed and Capitalized, Amount


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
General and administrative	$	467	$	130	$	1,288	$	172
Research and development	950		209		$	2,597	$	467
	$	1,417	$	339	$	3,885	$	639

Fair Value Measurements - Roll Forward (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Preferred Stock Tranche Right
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 0	$ 17,515
Change in fair value		74,319
Reclassification upon settlement		(91,834)
Ending balance		0
Anti-dilution Obligation
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	0	855
Change in fair value		6,681
Reclassification upon settlement		(7,536)
Ending balance		0
Forward Contract
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	12,020
Reclassification upon settlement	(12,020)
Ending balance	$ 0	$ 12,020

Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2022	Nov. 08, 2022
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2022
Document Transition Report	false
Entity File Number	001-04321
Entity Registrant Name	Prime Medicine, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-3097762
Entity Address, Address Line One	21 Erie Street
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	564-0013
Title of 12(b) Security	Common stock, par value $0.00001 per share
Trading Symbol	PRME
Security Exchange Name	NASDAQ
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		97,208,342
Entity Central Index Key	0001894562
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

Sep. 30, 2022

Sep. 30, 2021

Sep. 30, 2022

Sep. 30, 2021

Operating expenses:

Research and development

$ 25,047

$ 7,400

$ 57,664

$ 17,661

General and administrative

6,608

3,027

20,194

6,737

Total operating expenses

31,655

10,427

77,858

24,398

Loss from operations

(31,655)

(10,427)

(77,858)

(24,398)

Other income (expense):

Change in fair value of preferred stock tranche right liability

(74,319)

Change in fair value of anti-dilution obligation

(6,681)

Change in fair value of related party short-term investment

1,789

(8,354)

(6,419)

1,075

Other income (expense), net

^[1]

728

(1)

977

Total other expense, net

2,517

(8,355)

(5,442)

(79,925)

Net loss before income taxes

(29,138)

(18,782)

(83,300)

(104,323)

Provision for (benefit from) income taxes

212

(2,370)

(762)

(1,867)

Net loss

(29,350)

(16,412)

(82,538)

(102,456)

Accretion of preferred stock to redemption value

(1,468)

Cumulative dividend on preferred stock

(6,362)

(6,363)

(18,879)

(10,922)

Net loss attributable to common stockholders, basic

(35,712)

(22,775)

(101,417)

(114,846)

Net loss attributable to common stockholders, diluted

$ (35,712)

$ (22,775)

$ (101,417)

$ (114,846)

Net loss per share attributable to common stockholders, basic (in dollars per share)

$ (1.61)

$ (1.52)

$ (4.91)

$ (9.74)

Net loss per share attributable to common stockholders, diluted (in dollars per share)

$ (1.61)

$ (1.52)

$ (4.91)

$ (9.74)

Weighted-average common shares outstanding, diluted (in shares)

22,226,301

14,965,186

20,665,225

11,795,738

Weighted-average common shares outstanding, basic (in shares)

22,226,301

14,965,186

20,665,225

11,795,738

Comprehensive loss:

Net loss

$ (29,350)

$ (16,412)

$ (82,538)

$ (102,456)

Change in unrealized (losses) gains on investments, net of tax

(304)

(427)

(9)

Total other comprehensive loss

(304)

(427)

(9)

Comprehensive loss

$ (29,654)

$ (16,387)

$ (82,965)

$ (102,465)

[1]	Includes no related party amounts for the three months ended September 30, 2022 and 2021, and zero and $(429) for the nine months ended September 30, 2022 and 2021, respectively (see Note 13).

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 16,928	$ 5,543
Less: Accumulated depreciation and amortization	(1,961)	(611)
Property and equipment, net	14,967	4,932
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	16,227	5,274
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property and equipment	475	125
Furniture and Fixture
Property, Plant and Equipment [Line Items]
Total property and equipment	215	144
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 11	$ 0

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2022
Accounting Policies [Abstract]
Significant Accounting Policies	Summary of Significant Accounting PoliciesThe Company's significant accounting policies are disclosed in Note 2, "Summary of significant accounting policies," in the audited consolidated financial statements for the year ended December 31, 2021, and notes thereto, included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act with the SEC on October 21, 2022. Since the date of those financial statements, there have been no material changes to its significant accounting policies. Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected within these condensed consolidated financial statements include, but are not limited to, revenue recognition, the valuation of the Company’s common stock and stock-based awards, the valuation of preferred stock tranche right liability, the valuation of the anti-dilution obligation and the valuation of the related party forward contract liability. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ materially from those estimates or assumptions. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the time of initial purchase to be cash equivalents. As of September 30, 2022 and December 31, 2021, the amount of cash equivalents included in cash and cash equivalents totaled $28.8 million and $49.5 million, respectively. Restricted Cash Restricted cash consisted of letters of credit totaling $13.5 million and $13.1 million as of September 30, 2022 and December 31, 2021, respectively, that are required to be maintained in connection with the Company’s lease arrangements. Both letters of credit are in the name of the Company’s landlords and are required to fulfill lease requirements in the event the Company should default on its lease obligations. As of both September 30, 2022 and December 31, 2021, the Company classified its restricted cash as non-current on the consolidated balance sheets based on the release dates of the restrictions. Recently Issued Accounting Pronouncements Not Yet Adopted In August 2020, the FASB issued ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40). This standard eliminates the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. In addition, the new guidance modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted earnings per share (“EPS”) computation. Additionally, the amended guidance requires the application of the if-converted method for calculating diluted EPS and the treasury stock method will no longer be available. For public business entities, it is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years using the fully retrospective or modified retrospective method. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years. Early adoption is permitted but no earlier than fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company is currently evaluating the potential impact that ASU 2020-06 will have on its condensed consolidated financial statements and related disclosures but does not currently expect that the adoption of ASU 2020-06 will have a material impact. Other accounting standards that have been issued by the Financial Accounting Standards Board or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption.

Nature of the Business and Basis of Presentation	9 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	Nature of the Business and Basis of Presentation Prime Medicine, Inc., together with its consolidated subsidiary (the “Company”) is a biotechnology company committed to deliver genetic therapies to address diseases by deploying gene editing technology, Prime Editing. The company is deploying Prime Editing technology, a versatile, precise, efficient and broad gene editing technology, which is designed to make only the right edit at the right position within a gene. With the theoretical potential to repair approximately 90 percent of known disease-causing genetic mutations across many organs and cell types, medicines based on Prime Editing, if approved, could offer a one-time curative genetic therapeutic option to a broad set of patients. The Company was incorporated in the State of Delaware in September 2019. Reverse Stock Split On October 12, 2022, in connection with the Company’s initial public offering (“IPO”), the Company effected a 1-for-3.10880 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios of each series of the Company’s preferred stock (see Note 6). Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the preferred stock conversion ratios. Liquidity and capital resources Since its inception, the Company has devoted substantially all of our resources to building our Prime editing platform and advancing development of our portfolio of programs, establishing and protecting our intellectual property, conducting research and development activities, organizing and staffing our company, business planning, raising capital and providing general and administrative support for these operations. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, technical risks associated with the successful research, development and manufacturing of product candidates, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Current and future programs will require significant research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. In October 2022, the Company completed its IPO of its common stock. In connection with its IPO, the Company issued and sold 11,721,456 shares of its common stock, including 1,427,338 shares pursuant to the exercise of the underwriters’ option to purchase additional shares, at a price to the public of $17.00 per share. As a result of the IPO, the Company received $180.3 million in net proceeds, after deducting underwriting discounts, commissions and offering costs of $19.0 million. In connection with the IPO, all outstanding shares of redeemable convertible preferred stock converted into 51,923,758 shares of the Company’s common stock. The Company is subject to risks and uncertainties common to early stage companies in the biotechnology industry, including, but not limited to, completing preclinical studies and clinical trials, obtaining regulatory approval for product candidates, market acceptance of products, development by competitors of new technological innovations, dependence on key personnel, the ability to attract and retain qualified employees, reliance on third-party organizations, protection of proprietary technology, compliance with government regulations, the impact of the COVID-19 pandemic, and the ability to raise additional capital to fund operations. The Company’s product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure, and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Since its inception, the Company has incurred substantial losses and as of September 30, 2022, the Company had an accumulated deficit of $253.9 million. The Company expects to generate operating losses and negative operating cash flows for the foreseeable future. The Company expects that its cash, cash equivalents, and short term investments as of September 30, 2022 of $146.7 million will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these financial statements. The Company will need additional financing to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. The Company may be unable to raise additional funds or enter into such other agreements when needed on favorable terms or at all. The inability to raise capital as and when needed would have a negative impact on the Company’s financial condition and its ability to pursue its business strategy. The Company will need to generate significant revenue to achieve profitability, and it may never do so. Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. Intercompany balances and transactions have been eliminated in consolidation. The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). The accompanying condensed consolidated financial statements of Prime Medicine, Inc. are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2022 and the results of its operations for the three and nine months ended September 30, 2022 and 2021, and its cash flows for the nine months ended September 30, 2022 and 2021. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2022 and 2021 are also unaudited. The results for the nine months ended September 30, 2022 are not necessarily indicative of results to be expected for the year ending December 31, 2022, any other interim periods, or any future year or period. The condensed consolidated balance sheet data as of December 31, 2021 was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2021, and notes thereto, which are included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act with the Securities and Exchange Commission (the “SEC”) on October 21, 2022. Impact of the COVID-19 Pandemic The Company is subject to a number of risks associated with the COVID-19 global pandemic, including potential delays associated with the Company’s ongoing preclinical studies and anticipated clinical trials. COVID-19 may have an adverse impact on the Company’s operations, supply chains and distribution systems or those of its third-party vendors and collaborators, and increase expenses, including as a result of impacts associated with preventive and precautionary measures that are being taken, such as restrictions on travel and border crossings, quarantine policies and social distancing. The Company and its third-party vendors and collaborators may experience disruptions in supply of items that are essential for its research and development activities. The Company cannot predict the scope and severity of any economic recovery after the COVID-19 pandemic abates, including following any additional “waves” or other intensifying of the pandemic will have on its financial condition, operations, and business plans.

Stock-Based Compensation - Stock-Based Compensation Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 1,417	$ 339	$ 3,885	$ 639
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	467	130	1,288	172
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 950	$ 209	$ 2,597	$ 467

License and Collaboration Agreements	9 Months Ended
License and Collaboration Agreements	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements The Company's significant license agreements are disclosed in Note 10, "License and Collaboration Agreements," in the audited consolidated financial statements for the year ended December 31, 2021, and notes thereto, included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act with the SEC on October 21, 2022. Since the date of those financial statements, there have been no changes to its license agreements, except as noted below. Broad Pledge The Company accounts for this Pledge as research and development expenses as it has access to certain data generated as a result of the Pledge. For the year ended December 31, 2021, the Company recognized $5.0 million of research and development expense in connection with the Pledge. For both the three and nine months ended September 30, 2022 and 2021, the Company recognized $1.3 million and $3.8 million, respectively, of research and development expense in connection with the Pledge.

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued Myeloid license fee–related party	$ 0	$ 30,000
Accrued employee compensation and benefits	4,111	2,364
Accrued professional fees	1,070	3,830
Lab-related supplies and services	1,167	719
Other	182	279
Accrued expenses and other current liabilities	$ 6,530	$ 37,192

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2022

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

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


	September 30,		December 31,
	2022		2021
Accrued Myeloid license fee–related party	$	—	$	30,000
Accrued employee compensation and benefits	4,111		2,364
Accrued professional fees	1,070		3,830

Lab-related supplies and services	1,167		719
Other	182		279
Total	$	6,530	$	37,192

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities:
Net loss	$ (82,538)	$ (102,456)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	1,354	339
Amortization of premiums and discount on short-term investments	100	0
Stock-based compensation expense	3,885	639
Non cash lease expense	6,992	2,910
Deferred income taxes	(762)	(1,867)
Loss on disposal of property and equipment	8	0
Change in fair value of preferred stock tranche right liability	0	74,319
Change in fair value of anti-dilution obligation	0	6,681
Change in fair value of related party short-term investment	6,419	(1,075)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,080)	(642)
Accounts payable	2,027	1,105
Accrued expenses and other current liabilities	(29,961)	1,896
Lease liabilities	(7,558)	(2,744)
Net cash used in operating activities	(101,114)	(20,895)
Cash flows from investing activities:
Purchases of property and equipment	(11,281)	(3,768)
Purchase of short-term investments	(89,464)	(81,841)
Matured short-term investments	68,000	0
Payments of security deposits	(664)	(171)
Net cash used in investing activities	(33,409)	(85,780)
Cash flows from financing activities:
Payments of deferred offering costs	(2,642)	0
Net proceeds from stock option exercises	63	0
Net cash (used in) provided by financing activities	(2,579)	270,364
Net (decrease) increase in cash, cash equivalents and restricted cash	(137,102)	163,689
Cash and cash equivalents at beginning of period	198,545	36,975
Cash and cash equivalents at end of period	61,443	200,664
Supplemental cash flow information:
Right-of-use assets obtained in exchange for new operating lease liabilities	28,590	10,103
Supplemental disclosure of non-cash investing and financing activities:
Settlement of anti-dilution obligation	0	7,536
Settlement of related party forward contract	12,020	0
Deferred offering costs included in accounts payable and accrued expenses at period end	239	0
Purchases of property and equipment included in accounts payable and accrued expenses at period end	870	0
Accretion of preferred stock to redemption value	0	1,468
Unrealized loss on short-term investments	454	9
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	47,947	200,664
Restricted cash	13,496	0
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	61,443	200,664
Series A Redeemable Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from the issuance of convertible preferred stock	0	70,721
Supplemental disclosure of non-cash investing and financing activities:
Settlement of Series A preferred stock tranche obligation	0	91,834
Issuance of Series A preferred stock at a price below fair value	0	998
Series B Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from the issuance of convertible preferred stock	$ 0	$ 199,643

CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE AND CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($)	Total	Series A Redeemable Convertible Preferred Stock	Series B Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Losses	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020		45,000,000	0
Beginning balance at Dec. 31, 2020		$ 31,136,000	$ 0
Temporary Equity [Abstract]
Accretion of preferred stock to redemption value		$ 1,194,000
Ending balance (in shares) at Mar. 31, 2021		45,000,000	0
Ending balance at Mar. 31, 2021		$ 32,330,000	$ 0
Beginning balance (in shares) at Dec. 31, 2020				28,489,599
Beginning balance at Dec. 31, 2020	$ 2,338,000			$ 0	$ 8,347,000	$ 0	$ (6,009,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock to redemption value	(1,194,000)				(1,194,000)
Issuance of common stock and settlement of the anti-dilution obligation (in shares)				1,443,638
Stock-based compensation expense	206,000				206,000
Net loss	(86,660,000)						(86,660,000)
Ending balance (in shares) at Mar. 31, 2021				29,933,237
Ending balance at Mar. 31, 2021	(85,310,000)			$ 0	7,358,000	0	(92,669,000)
Beginning balance (in shares) at Dec. 31, 2020		45,000,000	0
Beginning balance at Dec. 31, 2020		$ 31,136,000	$ 0
Temporary Equity [Abstract]
Accretion of preferred stock to redemption value	1,468,000
Ending balance (in shares) at Sep. 30, 2021		115,761,842	45,658,957
Ending balance at Sep. 30, 2021		$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Dec. 31, 2020				28,489,599
Beginning balance at Dec. 31, 2020	2,338,000			$ 0	8,347,000	0	(6,009,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(102,456,000)
Change in unrealized gain on investments, net of tax	(9,000)
Ending balance (in shares) at Sep. 30, 2021				32,413,860
Ending balance at Sep. 30, 2021	(94,418,000)			$ 0	14,055,000	(9,000)	(108,465,000)
Beginning balance (in shares) at Mar. 31, 2021		45,000,000	0
Beginning balance at Mar. 31, 2021		$ 32,330,000	$ 0
Temporary Equity [Abstract]
Accretion of preferred stock to redemption value		$ 274,000
Issuance of redeemable convertible preferred stock including settlement of the third and fourth tranche right liability and issuance of convertible stock, net of issuance costs (in shares)		70,761,842	45,658,957
Issuance of redeemable convertible preferred stock including settlement of the third and fourth tranche right liability and issuance of convertible stock, net of issuance costs (in shares)		$ 71,719,000	$ 199,643,000
Reclassification of preferred stock tranche liability upon settlement		$ 91,834,000
Ending balance (in shares) at Jun. 30, 2021		115,761,842	45,658,957
Ending balance at Jun. 30, 2021		$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Mar. 31, 2021				29,933,237
Beginning balance at Mar. 31, 2021	(85,310,000)			$ 0	7,358,000	0	(92,669,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Series A redeemable convertible preferred stock, including the settlement of the third and fourth tranche right liability, net of issuance costs of $41	(998,000)				(998,000)
Accretion of redeemable convertible preferred stock to redemption value	(274,000)				(274,000)
Issuance of common stock and settlement of the anti-dilution obligation	7,536,000				7,536,000
Issuance of common stock and settlement of the anti-dilution obligation (in shares)				2,498,850
Stock-based compensation expense	94,000				94,000
Net loss	616,000						616,000
Change in unrealized gain on investments, net of tax	(34,000)					(34,000)
Ending balance (in shares) at Jun. 30, 2021				32,432,087
Ending balance at Jun. 30, 2021	(78,370,000)			$ 0	13,716,000	(34,000)	(92,053,000)
Ending balance (in shares) at Sep. 30, 2021		115,761,842	45,658,957
Ending balance at Sep. 30, 2021		$ 196,157,000	$ 199,643,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of unvested restricted common stock (in shares)				(18,227)
Stock-based compensation expense	339,000				339,000
Net loss	(16,412,000)						(16,412,000)
Change in unrealized gain on investments, net of tax	25,000					25,000
Ending balance (in shares) at Sep. 30, 2021				32,413,860
Ending balance at Sep. 30, 2021	$ (94,418,000)			$ 0	14,055,000	(9,000)	(108,465,000)
Beginning balance (in shares) at Dec. 31, 2021	161,420,799	115,761,842	45,658,957
Beginning balance at Dec. 31, 2021	$ 395,800,000	$ 196,157,000	$ 199,643,000
Ending balance (in shares) at Mar. 31, 2022		115,761,842	45,658,957
Ending balance at Mar. 31, 2022		$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Dec. 31, 2021	32,413,860			32,413,860
Beginning balance at Dec. 31, 2021	$ (156,240,000)			$ 0	15,163,000	(27,000)	(171,376,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of related party forward contract	12,020,000			$ 1,101,525	12,020,000
Stock-based compensation expense	1,123,000				1,123,000
Net loss	(23,840,000)						(23,840,000)
Change in unrealized gain on investments, net of tax	(5,000)					(5,000)
Ending balance (in shares) at Mar. 31, 2022				33,515,385
Ending balance at Mar. 31, 2022	$ (166,942,000)			$ 0	28,306,000	(32,000)	(195,216,000)
Beginning balance (in shares) at Dec. 31, 2021	161,420,799	115,761,842	45,658,957
Beginning balance at Dec. 31, 2021	$ 395,800,000	$ 196,157,000	$ 199,643,000
Temporary Equity [Abstract]
Accretion of preferred stock to redemption value	$ 0
Ending balance (in shares) at Sep. 30, 2022	161,420,799	115,761,842	45,658,957
Ending balance at Sep. 30, 2022	$ 395,800,000	$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Dec. 31, 2021	32,413,860			32,413,860
Beginning balance at Dec. 31, 2021	$ (156,240,000)			$ 0	15,163,000	(27,000)	(171,376,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	55,687
Net loss	$ (82,538,000)
Change in unrealized gain on investments, net of tax	$ (427,000)
Ending balance (in shares) at Sep. 30, 2022	33,559,912			33,559,912
Ending balance at Sep. 30, 2022	$ (223,096,000)			$ 0	31,272,000	(454,000)	(253,914,000)
Beginning balance (in shares) at Mar. 31, 2022		115,761,842	45,658,957
Beginning balance at Mar. 31, 2022		$ 196,157,000	$ 199,643,000
Ending balance (in shares) at Jun. 30, 2022		115,761,842	45,658,957
Ending balance at Jun. 30, 2022		$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Mar. 31, 2022				33,515,385
Beginning balance at Mar. 31, 2022	(166,942,000)			$ 0	28,306,000	(32,000)	(195,216,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of unvested restricted common stock (in shares)				(3,116)
Stock-based compensation expense	1,345,000				1,345,000
Net loss	(29,348,000)						(29,348,000)
Change in unrealized gain on investments, net of tax	(118,000)					(118,000)
Ending balance (in shares) at Jun. 30, 2022				33,512,269
Ending balance at Jun. 30, 2022	$ (195,063,000)			$ 0	29,651,000	(150,000)	(224,564,000)
Ending balance (in shares) at Sep. 30, 2022	161,420,799	115,761,842	45,658,957
Ending balance at Sep. 30, 2022	$ 395,800,000	$ 196,157,000	$ 199,643,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				55,687
Issuance of common stock upon exercise of stock options	204,000				204,000
Repurchase of unvested restricted common stock (in shares)				(8,044)
Stock-based compensation expense	1,417,000				1,417,000
Net loss	(29,350,000)						(29,350,000)
Change in unrealized gain on investments, net of tax	$ (304,000)					(304,000)
Ending balance (in shares) at Sep. 30, 2022	33,559,912			33,559,912
Ending balance at Sep. 30, 2022	$ (223,096,000)			$ 0	$ 31,272,000	$ (454,000)	$ (253,914,000)

Fair Value Measurements

9 Months Ended

Sep. 30, 2022

Fair Value Disclosures [Abstract]

Fair Value Measurements

We record cash equivalents, short-term investments, preferred stock tranche right liability, anti-dilution obligation and the related party forward contract liability at fair value. ASC 820, Fair Value Measurements and Disclosures, establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our own assumptions (unobservable inputs). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The hierarchy consists of three levels:

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.


	Fair Value Measurements at September 30, 2022:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	28,819	$	—	$	28,819
Short-term investment:
U.S. Treasury bills and government securities	—		89,175		—		89,175
Related party short-term investment:
Beam equity securities	9,543		—		—		9,543
	$	9,543	$	117,994	$	—	$	127,537


	Fair Value Measurements at December 31, 2021
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	49,450	$	—	$	49,450
Short-term investment:
U.S. Treasury bills and government securities	—		68,238		—		68,238
Related party short-term investment:
Beam equity securities	15,962		—		—		15,962
	$	15,962	$	117,688	$	—	$	133,650
Liabilities:
Related party forward contract liability	—		—		12,020		12,020
	$	—	$	—	$	12,020	$	12,020

The Company classifies its U.S. Treasury as short-term based on each instrument’s underlying contractual maturity date. The fair value of the Company’s U.S. Treasury securities and money market funds are classified as Level 2 because they are valued using observable inputs to quoted market prices, benchmark yields, reported trades,

broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency and U.S. Treasury securities.

The underlying securities held in the money market funds held by the Company are all government backed securities.

Short-term investments consisted of the following (in thousands):


	Fair Value Measurements at September 30, 2022
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Short-term investments:
U.S. Treasury bills and government securities	$	89,629			$	(454)	$	89,175
Related party short-term investment:
Beam equity securities	5,486		4,057		—		9,543
	$	95,115	$	4,057	$	(454)	$	98,718


	December 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Short-term investments:
U.S. Treasury bills and government securities	$	68,265	$	—	$	(27)	$	68,238
Related party short-term investment:
Beam equity securities	$	5,486	$	10,476	$	—	$	15,962
	$	73,751	$	10,476	$	(27)	$	84,200

The contractual maturities of the Company’s short-term investments in available-for-sale debt securities held were as follows:


	September 30, 2022		December 31, 2021
Due within one year	$	89,175	$	68,238
	$	89,175	$	68,238

Valuation of Preferred Stock Tranche Right Liability

The preferred stock tranche right liability in the table above is composed of the fair value of rights to purchase Series A Preferred Stock (see Note 6). The fair value of the preferred stock tranche right liability was determined based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The fair value of the preferred stock tranche right liability was determined using a Black-Scholes option pricing model, which considered as inputs the estimated fair value of the preferred stocks as of each valuation date, the risk-free interest rate, volatility and estimated time to each tranche closing.

The most significant assumption in the Black-Scholes option pricing model impacting the fair value of the preferred stock tranche right liability is the fair value of the Company’s convertible preferred stock as of each measurement date. The Company determines the fair value per share of the underlying convertible preferred stock by taking into consideration the most recent sales of its convertible preferred stock, results obtained from third-party valuations and additional factors the Company deems relevant. In November 2020, the second tranche of the Series A Preferred Stock closed. The fair value of each Series A Preferred Stock was $0.73 per share upon the closing of the second tranche. As of December 31, 2020, the fair value of Series A Preferred Stock was $0.76 per share. In April 2021, the third and fourth tranches of the Series A Preferred Stock closed. Upon satisfaction of certain conditions and the closing date of the third and fourth tranches, the associated Series A preferred stock tranche right

liability was settled. The fair value of Series A Preferred Stock was $2.31 per share upon the closing of the third and fourth tranches. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining estimated time to each tranche closing. The volatility is based on the historical volatility of publicly traded peer companies. Changes in the estimated fair value of the Company’s convertible preferred stock can have a significant impact on the fair value of the preferred stock tranche right liability.

The preferred stock tranche right liability was initially recorded at fair value upon the date of issuance of the preferred stock tranche right and is subsequently remeasured to fair value at each reporting date, and immediately prior to the closing dates of Series A preferred stock tranches. Changes in the fair value of the preferred stock tranche right liability are recognized as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss. Changes in the fair value of the preferred stock tranche right liability were recognized until the preferred stock tranche right liability was settled in full upon the satisfaction of certain conditions in April 2021.


	Preferred Stock Tranche Right





Balance as of December 31, 2020	$	17,515
Change in fair value of Series A preferred stock tranche right liability	74,319
Reclassification of Series A preferred stock tranche right liability upon settlement	(91,834)
Balance as of December 31, 2021	$	—

Valuation of Anti-dilution Obligation

The fair value of the anti-dilution obligation recognized in connection with the anti-dilution provisions set forth in the Company's license agreement with Broad Institute (see Note 11) was determined based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy.

The fair value of the anti-dilution obligation was estimated using a probability-weighted scenario which considered as inputs the probability of occurrence of events that would trigger the issuance of shares, including (i) the closing of Series A Preferred Stock, (ii) the Company’s initial public offering, and (iii) no future sale of equity securities. The weighted-average fair value of all scenarios was calculated utilizing the fair value per share of the underlying common stock. Changes in the estimated fair value of common stock and the probability of achieving different financing scenarios can have a significant impact on the fair value of the anti-dilution obligation. The most significant assumption impacting the fair value of the anti-dilution obligation was the fair value of the Company’s common stock as of each measurement date. The Company determined the fair value per share of the underlying common stock by taking into consideration the most recent sales of its convertible preferred stock, results obtained from third-party valuations and additional factors the Company deems relevant. The per share fair value of the Company’s common stock was $0.35 as of December 31, 2020. Immediately prior to the settlement of the anti-dilution obligation, the fair value of the Company’s common stock was $3.02 per share.

The anti-dilution obligation was initially recorded at fair value upon entering into the license agreement with Broad Institute and was subsequently remeasured to fair value at each reporting date. Changes in fair value of the anti-dilution obligation were recognized as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss. Changes in the fair value of the anti-dilution obligation were recognized until achievement of $100.0 million in cumulative equity financing is raised by the Company, which was achieved in connection with the fourth Series A Preferred Stock closing, resulting in the issuance of 2,498,850 shares of common stock to Broad Institute with a fair value of $7.5 million.

The following table provides a roll-forward of the aggregate fair value of the Company’s anti-dilution obligation, for which fair value was determined using Level 3 inputs (in thousands):


	Anti-dilution Obligation




Balance as of December 31, 2020	$	855
Change in fair value of anti-dilution obligation	6,681
Reclassification of anti-dilution obligation upon settlement	(7,536)
Balance as of December 31, 2021	$	—

Valuation of the Related Party Forward Contract Liability

The Company measured its related party forward contract liability, which was established in connection with its obligation to issue shares of its common stock to Myeloid Therapeutics, Inc. (“Myeloid”) under a stock subscription agreement (see Note 11), at fair value based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The initial fair value of the related party forward contract liability was determined based on the number of shares to be issued by the Company and the then per share fair value of the Company’s common stock, which was determined based, in part, on a third-party valuation that utilized methodologies and assumptions consistent with the Company’s most recent common stock valuations, including on a minority, nonmarketable interest basis.

Changes in the fair value of the related party forward contract liability will be recognized as other income (expense), net in the consolidated statements of operations through the settlement date. There was no change in the fair value of the Company’s common stock from the initial date of the related party forward contract liability and December 31, 2021 and the settlement which occurred in January 2022. Upon settlement, the fair value of the related party forward contract liability was reclassified to equity upon issuance of the common stock to Myeloid.

A reconciliation of the related party forward contract liability measured and recorded at fair value on a recurring basis is as follows (in thousands):


	Forward Contract


Balance as of December 31, 2021	$	12,020
Reclassification of related party forward contract liability upon settlement	(12,020)
Balance as of September 30, 2022	$	—

- Definition

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

+ References + Details

Leases

9 Months Ended

Sep. 30, 2022

Leases [Abstract]

Leases

Our building leases are comprised of office and laboratory space under non-cancelable operating leases. These lease agreements have remaining lease terms of five years and contain various clauses for renewal at our option. The renewal options were not included in the calculation of the operating lease assets and the operating lease liabilities as the renewal options are not reasonably certain of being exercised. The lease agreements do not contain residual value guarantees.

Summary of lease costs

The following table contains a summary of the lease costs and other information pertaining to the Company’s operating leases for the three and nine months ended September 30, 2022 and 2021.

In connection with the Arsenal Street Sublease, the Company recorded operating sublease income of $0.1 million and $0.2 million, respectively for the three and nine months ended September 30, 2022 in other income (expense), net in the condensed consolidated statements of operations. The Company was not relieved of its primary obligation under the operating lease as a result of the sublease.

Future annual lease payments under non-cancelable operating leases as of September 30, 2022 were as follows (in thousands):


Remaining 2022	$	2,415
2023	12,610
2024	13,035
2025	3,510
2026	1,683
2027	567
Total future minimum lease payments	33,820
Less: imputed interest	(2,381)
	$	31,439

The lease for office and laboratory space at 60 First Street, Cambridge, Massachusetts has not yet commenced and the expected date for which the Company obtains control of the space is currently uncertain but not expected to occur until the first half of 2023. The Company currently expects rent to commence 11 months after taking possession of the space, with occupancy expected to begin in 2024, for which the Company will pay approximately $208.7 million over the ten-year lease term. As the lease has not commenced as of September 30, 2022, the operating lease liabilities on the consolidated balance sheet through September 30, 2022 and the table above excludes any amounts related to this lease.

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 28,800	$ 49,500
Restricted cash	$ 13,496	$ 13,125

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Related party amounts	$ 0	$ 0	$ 0	$ (429,000)

Fair Value Measurements - Contractual Maturities of Short-Term Investments in Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Due within one year	$ 89,175	$ 68,238
Total available-for-sale securities	$ 89,175	$ 68,238