Prime Medicine (PRME) 10-Q3 Nov 232023 Q3 Quarterly reportFinancial data

Company Profile

Cover

Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2023	Oct. 31, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-41536
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	Yes
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		97,324,301
Entity Central Index Key	0001894562
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023		Dec. 31, 2022
Current assets:
Total cash, and cash equivalents	$ 43,959		$ 187,620
Prepaid expenses and other current assets	19,214		2,697
Total current assets	184,531		296,618
Property and equipment, net	22,032		19,009
Operating lease right-of-use assets	17,270		29,545
Restricted cash	13,496		13,496
Other assets	1,816		1,646
Total assets	239,145		360,314
Current liabilities:
Accounts payable	14,124	[1]	4,332
Accrued expenses and other current liabilities	14,023		10,688	[2]
Operating lease liability	11,219		11,694
Total current liabilities	39,366		26,714
Operating lease liability, net of current	5,822		17,051
Non current deferred tax liability	0		279
Total liabilities	45,188		44,044
Commitments and contingencies
Stockholders’ equity
Common stock, par value of $0.00001 per share; 775,000,000 shares authorized; 97,324,301 and 97,209,213 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	2		2
Additional paid-in capital	619,791		609,849
Accumulated other comprehensive loss	(149)		(384)
Accumulated deficit	(425,687)		(293,197)
Total stockholders’ equity	193,957		316,270
Total liabilities and stockholders’ equity	239,145		360,314
Nonrelated Party
Current assets:
Short-term investments	116,541		98,467
Current liabilities:
Accrued expenses and other current liabilities	14,023		10,688
Related Party
Current assets:
Short-term investments	4,817		7,834
Current liabilities:
Accounts payable	$ 100
Accrued expenses and other current liabilities			$ 300

[1](1) Includes related party amount of $0.1 million as of September 30, 2023.[2](2) Includes related party amount of $0.3 million as of December 31, 2022

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023		Dec. 31, 2022
Common stock, par or stated value (in dollars per share)	$ 0.00001		$ 0.00001
Common stock, shares authorized (in shares)	775,000,000		775,000,000
Common stock, shares issued (in shares)	97,324,301		97,209,213
Common stock, shares outstanding (in shares)	97,324,301		97,209,213
Accounts payable	$ 14,124	[1]	$ 4,332
Accrued expenses and other current liabilities	14,023		10,688	[2]
Related Party
Accounts payable	$ 100
Accrued expenses and other current liabilities			$ 300

[1](1) Includes related party amount of $0.1 million as of September 30, 2023.[2](2) Includes related party amount of $0.3 million as of December 31, 2022

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2023		Sep. 30, 2022	Sep. 30, 2023		Sep. 30, 2022
Operating expenses:
General and administrative	$ 10,492		$ 6,608	$ 30,303		$ 20,194
Total operating expenses	51,459		31,655	136,749		77,858
Loss from operations	(51,459)		(31,655)	(136,749)		(77,858)
Other income (expense):
Change in fair value of short-term investment — related party	(1,579)		1,789	(3,017)		(6,419)
Other income, net	2,222		728	6,997		977
Total other income (expense), net	643		2,517	3,980		(5,442)
Net loss before income taxes	(50,816)		(29,138)	(132,769)		(83,300)
(Provision for) benefit from income taxes	108		(212)	279		762
Net loss	(50,708)		(29,350)	(132,490)		(82,538)
Cumulative dividend on preferred stock	0		(6,362)	0		(18,879)
Net loss attributable to common stockholders	(50,708)		(35,712)	(132,490)		(101,417)
Net loss attributable to common stockholders, diluted	$ (50,708)		$ (35,712)	$ (132,490)		$ (101,417)
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (0.55)		$ (1.61)	$ (1.46)		$ (4.91)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (0.55)		$ (1.61)	$ (1.46)		$ (4.91)
Weighted-average common shares outstanding, diluted (in shares)	91,846,835		22,226,301	90,469,866		20,665,225
Weighted-average common shares outstanding, basic (in shares)	91,846,835		22,226,301	90,469,866		20,665,225
Comprehensive loss:
Net loss	$ (50,708)		$ (29,350)	$ (132,490)		$ (82,538)
Change in unrealized loss on investments, net of tax	119		(304)	235		(427)
Comprehensive loss	(50,589)		(29,654)	(132,255)		(82,965)
Nonrelated Party
Operating expenses:
Research and development	$ 40,967	[1]	$ 25,047	$ 106,446	[1]	$ 57,664

[1](1) Includes related party amount of $0.1 million and $0.8 million for the three and nine months ended September 30, 2023, respectively.

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
Related Party \| General and administrative
Research and development	$ 100	$ 800

CONDENSED CONSOLIDATED STATEM_3

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, 2021		115,761,842	45,658,957
Beginning balance at Dec. 31, 2021		$ 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
Beginning balance at Dec. 31, 2021	$ (156,241,000)			$ 0	$ 15,162,000	$ (27,000)	$ (171,376,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of forward contract — related party	12,020,000			$ 1,101,525	12,020,000
Stock-based compensation expense	1,123,000				1,123,000
Change in unrealized loss on investments, net of tax	(5,000)					(5,000)
Net loss	(23,840,000)						(23,840,000)
Ending balance (in shares) at Mar. 31, 2022				33,515,385
Ending balance at Mar. 31, 2022	(166,943,000)			$ 0	28,305,000	(32,000)	(195,216,000)
Beginning balance (in shares) at Dec. 31, 2021		115,761,842	45,658,957
Beginning balance at Dec. 31, 2021		$ 196,157,000	$ 199,643,000
Ending balance (in shares) at Sep. 30, 2022		115,761,842	45,658,957
Ending balance at Sep. 30, 2022		$ 196,157,000	$ 199,643,000
Beginning balance (in shares) at Dec. 31, 2021				32,413,860
Beginning balance at Dec. 31, 2021	(156,241,000)			$ 0	15,162,000	(27,000)	(171,376,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized loss on investments, net of tax	(427,000)
Net loss	(82,538,000)
Ending balance (in shares) at Sep. 30, 2022				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	(166,943,000)			$ 0	28,305,000	(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	1,346,000				1,346,000
Change in unrealized loss on investments, net of tax	(118,000)					(118,000)
Net loss	(29,348,000)						(29,348,000)
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		115,761,842	45,658,957
Ending balance at Sep. 30, 2022		$ 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
Change in unrealized loss on investments, net of tax	(304,000)					(304,000)
Net loss	(29,350,000)						(29,350,000)
Ending balance (in shares) at Sep. 30, 2022				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 Dec. 31, 2022	97,209,213			97,209,213
Beginning balance at Dec. 31, 2022	$ 316,270,000			$ 2,000	609,849,000	(384,000)	(293,197,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				18,596
Issuance of common stock upon exercise of stock options	68,000				68,000
Stock-based compensation expense	1,681,000				1,681,000
Change in unrealized loss on investments, net of tax	179,000					179,000
Net loss	(39,397,000)						(39,397,000)
Ending balance (in shares) at Mar. 31, 2023				97,227,809
Ending balance at Mar. 31, 2023	$ 278,801,000			$ 2,000	611,598,000	(205,000)	(332,594,000)
Beginning balance (in shares) at Dec. 31, 2022	97,209,213			97,209,213
Beginning balance at Dec. 31, 2022	$ 316,270,000			$ 2,000	609,849,000	(384,000)	(293,197,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	115,088
Change in unrealized loss on investments, net of tax	$ 235,000
Net loss	$ (132,490,000)
Ending balance (in shares) at Sep. 30, 2023	97,324,301			97,324,301
Ending balance at Sep. 30, 2023	$ 193,957,000			$ 2,000	619,791,000	(149,000)	(425,687,000)
Beginning balance (in shares) at Mar. 31, 2023				97,227,809
Beginning balance at Mar. 31, 2023	278,801,000			$ 2,000	611,598,000	(205,000)	(332,594,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				42,106
Issuance of common stock upon exercise of stock options	166,000				166,000
Stock-based compensation expense	3,583,000				3,583,000
Change in unrealized loss on investments, net of tax	(63,000)					(63,000)
Net loss	(42,385,000)						(42,385,000)
Ending balance (in shares) at Jun. 30, 2023				97,269,915
Ending balance at Jun. 30, 2023	240,102,000			$ 2,000	615,347,000	(268,000)	(374,979,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				54,386
Issuance of common stock upon exercise of stock options	227,000				227,000
Stock-based compensation expense	4,217,000				4,217,000
Change in unrealized loss on investments, net of tax	119,000					119,000
Net loss	$ (50,708,000)						(50,708,000)
Ending balance (in shares) at Sep. 30, 2023	97,324,301			97,324,301
Ending balance at Sep. 30, 2023	$ 193,957,000			$ 2,000	$ 619,791,000	$ (149,000)	$ (425,687,000)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows used in operating activities:
Net loss	$ (132,490)	$ (82,538)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	9,481	3,885
Non cash lease expense	9,440	6,992
Depreciation expense	3,406	1,354
Change in fair value of short-term investment — related party	3,017	6,419
Amortization of premiums and discount on short-term investments	(2,320)	100
Deferred income taxes	(279)	(762)
Loss on disposal of property and equipment	0	8
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(9,040)	(1,080)
Accounts payable	6,861	2,027
Accrued expenses and other current liabilities	(755)	(29,961)
Lease liabilities	(8,869)	(7,558)
Net cash used in operating activities	(121,548)	(101,114)
Cash flows used in investing activities:
Maturities of investments	85,021	68,000
Purchases of investments	(100,541)	(89,464)
Purchases of property and equipment	(6,884)	(11,281)
Payments of security deposits	(170)	(664)
Net cash used in investing activities	(22,574)	(33,409)
Cash flows provided by (used in) financing activities:
Net proceeds from stock option exercises	461	63
Payments of deferred offering costs	0	(2,642)
Net cash provided by (used in) financing activities	461	(2,579)
Net change in cash, cash equivalents, and restricted cash	(143,661)	(137,102)
Cash, cash equivalents, and restricted cash at beginning of period	201,116	198,545
Cash, cash equivalents, and restricted cash at end of period	57,455	61,443
Reconciliation of cash, cash equivalents and restricted cash:
Cash, cash equivalents, and restricted cash at end of period	57,455	61,443
Less: restricted cash	13,496	13,496
Total cash, and cash equivalents	43,959	47,947
Supplemental cash flow information:
Right-of-use assets obtained in exchange for new operating lease liabilities	3,265	28,590
Decrease in right-of-use assets due to lease termination	6,100	0
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses	513	870
Settlement of forward contract — related party	0	12,020
Deferred offering costs included in accounts payable and accrued expenses	$ 0	$ 239

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2023
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. 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 its 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 connection with its IPO, completed in October 2022, 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 $180.2 million in net proceeds, after deducting underwriting discounts, commissions and offering costs of $19.1 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. Risks and Uncertainties 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, 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, 2023, the Company had an accumulated deficit of $425.7 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 investments as of September 30, 2023 of $165.3 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 (“U.S. 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, 2023, the results of its operations for the three and nine months ended September 30, 2023 and 2022, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022, and its cash flows for the nine months ended September 30, 2023 and 2022. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2023 and 2022 are also unaudited. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. The condensed consolidated balance sheet data as of December 31, 2022 was derived from our audited financial statements, but does not include all disclosures required by 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, 2022, and notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the Securities and Exchange Commission (the “SEC”) on March 9, 2023.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The 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, 2022, and notes thereto, included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 9, 2023. 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 U.S. 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 the valuation of the Company’s common stock and stock-based awards, 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. Recently Issued Accounting Pronouncements Not Yet Adopted Accounting standards that have been issued by the FASB 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.

Fair Value Measurements and Inv

Fair Value Measurements and Investments	9 Months Ended
Fair Value Measurements and Investments	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements and Investments	Fair Value Measurements and Investments The following tables present the Company’s fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair value: As of September 30, 2023: (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 20,204 $ — $ 20,204 U.S. Treasury and government securities — 15,980 — 15,980 Short-term investments: U.S. Treasury and government securities — 116,541 — 116,541 Related party short-term investment: Beam equity securities 4,817 — — 4,817 Total cash equivalents and investments $ 4,817 $ 152,725 $ — $ 157,542 As of December 31, 2022: (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 120,511 $ — $ 120,511 Short-term investment: U.S. Treasury securities — 98,467 — 98,467 Related party short-term investment: Beam equity securities 7,834 — — 7,834 Total cash equivalents and short-term investments $ 7,834 $ 218,978 $ — $ 226,812 The Company classifies its U.S. Treasury securities 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. Investments in Debt Securities Unrealized gains and losses of investments in debt securities consisted of the following: As of September 30, 2023: (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 116,692 $ — $ (151) $ 116,541 Total short-term investments in debt securities $ 116,692 $ — $ (151) $ 116,541 As of December 31, 2022: (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments: U.S. Treasury and government securities $ 98,851 $ — $ (384) $ 98,467 Total short-term investments in debt securities $ 98,851 $ — $ (384) $ 98,467 The contractual maturities of the Company’s investments in debt securities held were as follows: (in thousands) September 30, December 31, Due within one year $ 116,541 $ 98,467 Marketable securities in unrealized loss positions consisted of the following: As of September 30, 2023: (in thousands, except number of securities) Number of Securities Fair Value Gross Unrealized Losses Investments in continuous loss position for less than 12 months: U.S. Treasury and government securities 46 $ 111,506 $ (151) Based on factors such as historical experience, market data, issuer-specific factors, and current economic conditions, the Company did not record an allowance for credit losses as of September 30, 2023 related to these investments. Further, given the lack of significant change in the credit risk, the Company does not consider these investments to be impaired.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
Property and Equipment, Net	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following: (in thousands) September 30, December 31, Property and equipment: Laboratory equipment $ 23,663 $ 19,422 Leasehold improvement 579 564 Furniture and Fixture 278 235 Computer hardware and software 11 11 Construction in progress 3,738 1,608 Total property and equipment 28,269 21,840 Less: Accumulated depreciation (6,237) (2,831) Total property and equipment, net $ 22,032 $ 19,009 Depreciation expense related to property and equipment is as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2023 2022 2023 2022 Depreciation Expense $ 1,236 $ 631 $ 3,406 $ 1,354

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
Accrued Expenses and Other Current Liabilities	Sep. 30, 2023
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: (in thousands) September 30, December 31, Accrued expenses and other current liabilities Accrued employee compensation and benefits $ 5,634 $ 6,529 Accrued professional fees 4,963 2,162 Lab-related supplies and services 2,579 1,219 Accrued license fee – related party — 329 Other 847 449 Total accrued expenses and other current liabilities $ 14,023 $ 10,688

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
Stock-Based Compensation	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	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 was 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. In October 2022, in connection with the closing of the Company’s IPO, the Board of Directors 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 was 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 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. The number of shares reserved and available for issuance under the 2022 Plan increased on January 1, 2023 and will increase on each January 1 hereafter, 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. On January 1, 2023, the annual increase resulted in an additional 4,860,461 shares authorized being added to the 2022 Plan. As of September 30, 2023, the Company had 16,734,122 shares reserved under the 2022 Plan and the 2019 Plan, and 8,808,586 shares available for issuance 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 was declared effective by the SEC. The number of shares of common stock that may be issued under the 2022 ESPP cumulatively increased beginning on January 1, 2023 and shall increase on each January 1 hereafter 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. On January 1, 2023, the annual increase resulted in an additional 971,350 shares authorized being added to the 2022 Plan. As of September 30, 2023, the Company had 1,942,700 shares available for issuance under the 2022 Plan. No shares of the Company’s common stock were issued during the nine months ended September 30, 2023 related to the 2022 ESPP. Stock Options The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Shares Weighted-Average Exercise Price Outstanding at December 31, 2022 3,954,265 $ 6.43 Granted 3,950,794 12.87 Exercised (115,088) 4.02 Cancelled or forfeited (276,165) 8.82 Outstanding at September 30, 2023 7,513,806 $ 9.77 Options vested and exercisable at September 30, 2023 1,926,941 $ 6.49 Options vested and expected to vest at September 30, 2023 7,513,806 $ 9.77 As of September 30, 2023, there was $44.0 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 2.9 years. Performance-Based Stock Options The following table summarizes the Company’s performance-based stock option activity for the nine months ended September 30, 2023: Number of Shares Weighted-Average Outstanding at December 31, 2022 411,730 $ 6.65 Granted — — Exercised — — Cancelled or forfeited — — Outstanding at September 30, 2023 411,730 $ 6.65 Vested and exercisable at September 30, 2023 121,160 $ 5.11 As of September 30, 2023, there was $2.3 million of total unrecognized compensation cost related to performance-based stock options. Restricted Common Stock Awards The Company awarded restricted common stock to employees and non-employees under its 2019 Plan. The vesting of these restricted stock awards are time-based or performance-based. Time-Based Restricted Common Stock The following table summarizes the Company’s time-based restricted common stock activity for the nine months ended September 30, 2023 : Number of Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2022 5,015,034 $ 0.10 Issued — — Vested (3,753,034) 0.08 Repurchased — — Outstanding at September 30, 2023 1,262,000 $ 0.16 As of September 30, 2023, there was $0.2 million of total unrecognized compensation cost related to unvested ti me-based restricted common stock which the Company expects to recognize over a weighted-average period of 0.9 years. Performance-Based Restricted Common Stock The following table summarizes the Company’s performance-based restricted common stock activity for the nine months ended September 30, 2023 : Number of Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2022 3,832,769 $ 0.07 Issued — — Vested — — Repurchased — — Outstanding at September 30, 2023 3,832,769 $ 0.07 As of September 30, 2023, 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 condensed consolidated statements of operations and comprehensive loss: Three Months Ended Nine Months Ended (in thousands) 2023 2022 2023 2022 Stock-based compensation expense: Research and development $ 2,224 $ 950 $ 5,558 $ 2,597 General and administrative 1,993 467 3,923 1,288 Total stock-based compensation expense $ 4,217 $ 1,417 $ 9,481 $ 3,885

Leases

Leases	9 Months Ended
Leases	Sep. 30, 2023
Leases [Abstract]
Leases	LeasesIn April 2023, the Company entered into an amendment to its operating lease (the “Amended Lease”) for additional office and laboratory space at 21 Erie Street, Cambridge, Massachusetts. The Amended Lease is subject to fixed-rate rent escalations. The 23-month lease term of the Amended Lease, over which the Company is obligated to pay approximately $3.7 million, commenced in April 2023. Upon the commencement of the Amended Lease, the Company recorded a lease liability and a right-of-use asset of $3.3 million. The table below reconciles the undiscounted future annual lease payments to the total operating lease liabilities recorded in the condensed consolidated balance sheet as of September 30, 2023 : (in thousands) Undiscounted Undiscounted lease payments: Remaining in 2023 $ 3,649 2024 9,669 2025 2,656 2026 1,683 2027 567 Total undiscounted lease payments 18,224 Less: imputed interest (1,183) Total operating lease liability $ 17,041 The Company is party to a lease for office and laboratory space at 60 First Street, Cambridge, Massachusetts, with the rent commencement date expected to occur in the first quarter of 2024, subject to any credits pursuant to the terms of the lease. Also subject to any credits pursuant to the terms of the lease, the Company expects to pay up to approximately $208.7 million over the ten-year lease term . As of September 30, 2023, the lease has not commenced in accordance with ASC 842, Leases ; accordingly, the operating lease liabilities and operating lease right-of-use assets on the condensed consolidated balance sheet through September 30, 2023, and the table above excludes any amounts related to this lease. As of September 30, 2023, the Company determined that it is reasonably certain to exercise its option to terminate one of its leases. This option allows the Company to terminate its lease by providing an advanced notice to the lessor. This determination and the subsequent reassessment of the lease resulted in a $6.1 million deduction of the Company’s operating lease liability and its operating lease right-of-use asset on the condensed consolidated balance sheet as of September 30, 2023. Further, the above table includes the reduction in lease payments resulting from the reasonably certain lease termination.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
License and Collaboration Agreements	Sep. 30, 2023
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 11, License and Collaboration Agreements , in the audited consolidated financial statements for the year ended December 31, 2022, and notes thereto, included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 9, 2023. Since the date of those financial statements, there have been no changes to its license agreements except as otherwise described herein.

Net Loss per Share

Net Loss per Share	9 Months Ended
Net Loss per Share	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic and diluted net loss per common share attributable to common stockholders was calculated as follows: Three Months Ended Nine Months Ended (in thousands, except share and per share amounts) 2023 2022 2023 2022 Numerator: Net loss $ (50,708) $ (29,350) $ (132,490) $ (82,538) Cumulative dividend on preferred stock — (6,362) — (18,879) Net loss attributable to common stockholders $ (50,708) $ (35,712) $ (132,490) $ (101,417) Denominator: Weighted-average common shares outstanding, basic and diluted 91,846,835 22,226,301 90,469,866 20,665,225 Net loss per share attributable to common stockholders, basic and diluted $ (0.55) $ (1.61) $ (1.46) $ (4.91) Diluted net loss per share available to common stockholders 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 stockholders as their effect was anti-dilutive. In periods in which the Company reports a net loss available to common stockholders, diluted net loss per share available to common stockholders is the same as basic net loss per share available to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. 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, 2023 2022 Anti-dilutive common stock equivalents: Options to purchase common stock 7,634,966 3,971,557 Unvested restricted common stock 5,094,769 10,597,726 Convertible preferred stock (as converted to common stock) — 51,923,758 Total anti-dilutive common stock equivalents: 12,729,735 66,493,041

Related Party Transactions

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Founder Consulting Services For both the three months ended September 30, 2023 and 2022, the Company made payments of $37,500 in each period, and for the nine months ended September 30, 2023 and 2022, the Company made payments of $112,500 in each period to one of the co-founder stockholders for scientific consulting and other expenses. As of September 30, 2023, $12,500 was included within accounts payable, and, as of December 31, 2022, there were no amounts included within accounts payable. Myeloid Therapeutics In December 2021, the Company and Myeloid Therapeutics, Inc. (“Myeloid”) entered into the Myeloid Collaboration Agreement and Myeloid Subscription Agreement. The Company and Myeloid have one common board member, who is also an affiliate of Newpath, one of the Company’s holders of its common stock. The Company provided notice to Myeloid of its intent to terminate the Myeloid Collaboration Agreement during the second quarter of 2023, which termination is now effective. As of September 30, 2023, there was $0.1 million in

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2023
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 (“U.S. 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, 2023, the results of its operations for the three and nine months ended September 30, 2023 and 2022, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022, and its cash flows for the nine months ended September 30, 2023 and 2022. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2023 and 2022 are also unaudited. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. The condensed consolidated balance sheet data as of December 31, 2022 was derived from our audited financial statements, but does not include all disclosures required by 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, 2022, and notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the Securities and Exchange Commission (the “SEC”) on March 9, 2023.
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. 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
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet AdoptedAccounting standards that have been issued by the FASB 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

Fair Value Measurements and I_2

Fair Value Measurements and Investments (Tables)	9 Months Ended
Fair Value Measurements and Investments (Tables)	Sep. 30, 2023
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 that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair value: As of September 30, 2023: (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 20,204 $ — $ 20,204 U.S. Treasury and government securities — 15,980 — 15,980 Short-term investments: U.S. Treasury and government securities — 116,541 — 116,541 Related party short-term investment: Beam equity securities 4,817 — — 4,817 Total cash equivalents and investments $ 4,817 $ 152,725 $ — $ 157,542 As of December 31, 2022: (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 120,511 $ — $ 120,511 Short-term investment: U.S. Treasury securities — 98,467 — 98,467 Related party short-term investment: Beam equity securities 7,834 — — 7,834 Total cash equivalents and short-term investments $ 7,834 $ 218,978 $ — $ 226,812
Schedule of Debt Securities, Available-for-Sale	Unrealized gains and losses of investments in debt securities consisted of the following: As of September 30, 2023: (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 116,692 $ — $ (151) $ 116,541 Total short-term investments in debt securities $ 116,692 $ — $ (151) $ 116,541 As of December 31, 2022: (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments: U.S. Treasury and government securities $ 98,851 $ — $ (384) $ 98,467 Total short-term investments in debt securities $ 98,851 $ — $ (384) $ 98,467 Marketable securities in unrealized loss positions consisted of the following: As of September 30, 2023: (in thousands, except number of securities) Number of Securities Fair Value Gross Unrealized Losses Investments in continuous loss position for less than 12 months: U.S. Treasury and government securities 46 $ 111,506 $ (151)
Schedule of Investments Classified by Contractual Maturity Date	The contractual maturities of the Company’s investments in debt securities held were as follows: (in thousands) September 30, December 31, Due within one year $ 116,541 $ 98,467

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
Property and Equipment, Net (Tables)	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net and Depreciation Expense	Property and equipment, net consisted of the following: (in thousands) September 30, December 31, Property and equipment: Laboratory equipment $ 23,663 $ 19,422 Leasehold improvement 579 564 Furniture and Fixture 278 235 Computer hardware and software 11 11 Construction in progress 3,738 1,608 Total property and equipment 28,269 21,840 Less: Accumulated depreciation (6,237) (2,831) Total property and equipment, net $ 22,032 $ 19,009 Depreciation expense related to property and equipment is as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2023 2022 2023 2022 Depreciation Expense $ 1,236 $ 631 $ 3,406 $ 1,354

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Sep. 30, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses and other current liabilities consisted of the following: (in thousands) September 30, December 31, Accrued expenses and other current liabilities Accrued employee compensation and benefits $ 5,634 $ 6,529 Accrued professional fees 4,963 2,162 Lab-related supplies and services 2,579 1,219 Accrued license fee – related party — 329 Other 847 449 Total accrued expenses and other current liabilities $ 14,023 $ 10,688

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
Stock-Based Compensation (Tables)	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Share-Based Payment Arrangement, Option, Activity	The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Shares Weighted-Average Exercise Price Outstanding at December 31, 2022 3,954,265 $ 6.43 Granted 3,950,794 12.87 Exercised (115,088) 4.02 Cancelled or forfeited (276,165) 8.82 Outstanding at September 30, 2023 7,513,806 $ 9.77 Options vested and exercisable at September 30, 2023 1,926,941 $ 6.49 Options vested and expected to vest at September 30, 2023 7,513,806 $ 9.77 The following table summarizes the Company’s performance-based stock option activity for the nine months ended September 30, 2023: Number of Shares Weighted-Average Outstanding at December 31, 2022 411,730 $ 6.65 Granted — — Exercised — — Cancelled or forfeited — — Outstanding at September 30, 2023 411,730 $ 6.65 Vested and exercisable at September 30, 2023 121,160 $ 5.11
Schedule of Share-Based Payment Arrangement, Outstanding Award, Activity, Excluding Option	The following table summarizes the Company’s time-based restricted common stock activity for the nine months ended September 30, 2023 : Number of Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2022 5,015,034 $ 0.10 Issued — — Vested (3,753,034) 0.08 Repurchased — — Outstanding at September 30, 2023 1,262,000 $ 0.16 The following table summarizes the Company’s performance-based restricted common stock activity for the nine months ended September 30, 2023 : Number of Shares Weighted-Average Grant-Date Fair Value Outstanding at December 31, 2022 3,832,769 $ 0.07 Issued — — Vested — — Repurchased — — Outstanding at September 30, 2023 3,832,769 $ 0.07
Schedule of Share-Based Payment Arrangement, Expensed and Capitalized, Amount	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 condensed consolidated statements of operations and comprehensive loss: Three Months Ended Nine Months Ended (in thousands) 2023 2022 2023 2022 Stock-based compensation expense: Research and development $ 2,224 $ 950 $ 5,558 $ 2,597 General and administrative 1,993 467 3,923 1,288 Total stock-based compensation expense $ 4,217 $ 1,417 $ 9,481 $ 3,885

Leases (Tables)

Leases (Tables)	9 Months Ended
Leases (Tables)	Sep. 30, 2023
Leases [Abstract]
Schedule of Operating Lease Liability	as of September 30, 2023 : (in thousands) Undiscounted Undiscounted lease payments: Remaining in 2023 $ 3,649 2024 9,669 2025 2,656 2026 1,683 2027 567 Total undiscounted lease payments 18,224 Less: imputed interest (1,183) Total operating lease liability $ 17,041

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
Net Loss per Share (Tables)	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Net Loss Per Share, Basic and Diluted	Basic and diluted net loss per common share attributable to common stockholders was calculated as follows: Three Months Ended Nine Months Ended (in thousands, except share and per share amounts) 2023 2022 2023 2022 Numerator: Net loss $ (50,708) $ (29,350) $ (132,490) $ (82,538) Cumulative dividend on preferred stock — (6,362) — (18,879) Net loss attributable to common stockholders $ (50,708) $ (35,712) $ (132,490) $ (101,417) Denominator: Weighted-average common shares outstanding, basic and diluted 91,846,835 22,226,301 90,469,866 20,665,225 Net loss per share attributable to common stockholders, basic and diluted $ (0.55) $ (1.61) $ (1.46) $ (4.91)
Schedule of Antidilutive Securities Excluded from Computation of Net Loss 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, 2023 2022 Anti-dilutive common stock equivalents: Options to purchase common stock 7,634,966 3,971,557 Unvested restricted common stock 5,094,769 10,597,726 Convertible preferred stock (as converted to common stock) — 51,923,758 Total anti-dilutive common stock equivalents: 12,729,735 66,493,041

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	Oct. 12, 2022	Oct. 31, 2022 USD ($) $ / shares shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Reverse stock split	0.32167
Stock issuance costs			$ 0	$ 2,642
Accumulated deficit			425,687		$ 293,197
Cash, cash equivalents, and investments			$ 165,300
Common Stock
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Convertible preferred stock, number of shares converted into common stock (in shares) \| shares		51,923,758
IPO
Organization, Consolidation and Presentation of Financial Statements [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
Proceeds from IPO		$ 180,200
Stock issuance costs		$ 19,100
Over-Allotment Option
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Sale of stock, number of shares issued (in shares) \| shares		1,427,338

Fair Value Measurements and I_3

Fair Value Measurements and Investments - Schedule of Hierarchy For Assets and Liabilities Measured At Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 116,541	$ 98,467
Total assets	157,542	226,812
Related Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	4,817	7,834
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	20,204	120,511
U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	15,980
Short-term investments	116,541	98,467
U.S. Treasury and government securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	116,541
U.S. Treasury securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		98,467
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	4,817	7,834
Level 1 \| Related Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	4,817	7,834
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 and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Level 1 \| U.S. Treasury and government securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Level 1 \| U.S. Treasury securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	152,725	218,978
Level 2 \| Related Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
Level 2 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	20,204	120,511
Level 2 \| U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	15,980
Level 2 \| U.S. Treasury and government securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	116,541
Level 2 \| U.S. Treasury securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		98,467
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Level 3 \| Related Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
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 and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Level 3 \| U.S. Treasury and government securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0
Level 3 \| U.S. Treasury securities \| Nonrelated Party
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		$ 0

Fair Value Measurements and I_4

Fair Value Measurements and Investments - Schedule of Short-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 116,692	$ 98,851
Unrealized Gains	0	0
Unrealized Losses	(151)	(384)
Fair Value	116,541	98,467
U.S. Treasury and government securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	116,692	98,851
Unrealized Gains	0	0
Unrealized Losses	(151)	(384)
Fair Value	$ 116,541	$ 98,467

Fair Value Measurements and I_5

Fair Value Measurements and Investments - Schedule of Contractual Maturities of Short-Term Investments in Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Due within one year	$ 116,541	$ 98,467

Fair Value Measurements and I_6

Fair Value Measurements and Investments - Schedule of Marketable Securities In Unrealized Loss Position (Details) - U.S. Treasury and government securities $ in Thousands	Sep. 30, 2023 USD ($) security
Investments in continuous loss position for less than 12 months:
Number of Securities \| security	46
Fair Value	$ 111,506
Gross Unrealized Losses	$ (151)

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 28,269	$ 21,840
Less: Accumulated depreciation	(6,237)	(2,831)
Total property and equipment, net	22,032	19,009
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	23,663	19,422
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property and equipment	579	564
Furniture and Fixture
Property, Plant and Equipment [Line Items]
Total property and equipment	278	235
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total property and equipment	11	11
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,738	$ 1,608

Property and Equipment, Net -_2

Property and Equipment, Net - Schedule of Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1,236	$ 631	$ 3,406	$ 1,354

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Line Items]
Total accrued expenses and other current liabilities	$ 14,023	$ 10,688	[1]
Nonrelated Party
Payables and Accruals [Line Items]
Accrued employee compensation and benefits	5,634	6,529
Accrued professional fees	4,963	2,162
Lab-related supplies and services	2,579	1,219
Accrued license fee–related party	0	329
Other	847	449
Total accrued expenses and other current liabilities	$ 14,023	$ 10,688

[1](2) Includes related party amount of $0.3 million as of December 31, 2022

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions		9 Months Ended
	Feb. 09, 2022	Sep. 30, 2023	Jan. 01, 2023
Options to purchase common stock \| 2022 Stock Option and Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of annual increase in shares reserved for future issuance (as a percent)	5%
Shares issuable under plan (in shares)			4,860,461
Shares available for grant (in shares)		8,808,586
Options to purchase common stock \| 2022 Stock Option and Incentive Plan and 2019 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issuable under plan (in shares)		16,734,122
Employee Stock \| 2022 Employee Stock Purchase Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of annual increase in shares reserved for future issuance (as a percent)	1%
Shares issuable under plan (in shares)			971,350
Shares available for grant (in shares)		1,942,700
Additional shares allowable under plan (in shares)	971,350
Options issued (in shares)		0
Time-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost		$ 44
Unrecognized compensation costs, period of recognition (in years)		2 years 10 months 24 days
Performance-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost		$ 2.3
Restricted Stock, Time-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation expense		$ 0.2
Unrecognized compensation costs, period of recognition (in years)		10 months 24 days
Restricted Stock, Performance-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation expense		$ 0.3

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2023
Number of Shares
Beginning of period (in shares)	3,954,265
Granted (in shares)	3,950,794
Exercised (in shares)	(115,088)
Cancelled or forfeited (in shares)	(276,165)
End of period (in shares)	7,513,806
Options vested and exercisable, end of period (in shares)	1,926,941
Options vested and expected to vest, end of period (in shares)	7,513,806
Weighted-Average Exercise Price
Beginning of period (in dollars per share)	$ 6.43
Granted (in dollars per share)	12.87
Exercised (in dollars per share)	4.02
Cancelled or forfeited (in dollars per share)	8.82
End of period (in dollars per share)	9.77
Options vested and exercisable, end of period (in dollars per share)	6.49
Options vested and expected to vest, end of period (in dollars per share)	$ 9.77
Performance-Based Stock Options
Number of Shares
Beginning of period (in shares)	411,730
Granted (in shares)	0
Exercised (in shares)	0
Cancelled or forfeited (in shares)	0
End of period (in shares)	411,730
Options vested and exercisable, end of period (in shares)	121,160
Weighted-Average Grant Date Fair Value
Beginning of period (in dollars per share)	$ 6.65
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Cancelled or forfeited (in dollars per share)	0
End of period (in dollars per share)	6.65
Vested and exercisable, end of period (in dollars per share)	$ 5.11

Stock-Based Compensation -Sched

Stock-Based Compensation -Schedule of Restricted Stock Activity (Details)	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Restricted Stock, Time-Based
Number of Shares
Beginning of period (in shares) \| shares	5,015,034
Issued (in shares) \| shares	0
Vested (in shares) \| shares	(3,753,034)
Repurchased (in shares) \| shares	0
End of period (in shares) \| shares	1,262,000
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	0.08
Repurchased (in dollars per share) \| $ / shares	0
End of period (in dollars per share) \| $ / shares	$ 0.16
Restricted Stock, Performance-Based
Number of Shares
Beginning of period (in shares) \| shares	3,832,769
Issued (in shares) \| shares	0
Vested (in shares) \| shares	0
Repurchased (in shares) \| shares	0
End of period (in shares) \| shares	3,832,769
Weighted-Average Grant-Date Fair Value
Beginning of period (in dollars per share) \| $ / shares	$ 0.07
Issued (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	0
Repurchased (in dollars per share) \| $ / shares	0
End of period (in dollars per share) \| $ / shares	$ 0.07

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock-Based Compensation Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 4,217	$ 1,417	$ 9,481	$ 3,885
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	2,224	950	5,558	2,597
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 1,993	$ 467	$ 3,923	$ 1,288

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	Sep. 30, 2023 USD ($) lease	Apr. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Total undiscounted lease payments	$ 18,224
Operating lease right-of-use assets	17,270		$ 29,545
Operating lease, liability	$ 17,041	$ 3,300
Number of leases terminated \| lease	1
Deduction in right-of-use assets due to lease termination	$ 6,100
Deduction in right-of-use assets due to lease termination	6,100
21 Erie Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Operating lease, term of contract (in years)		23 months
Total undiscounted lease payments		$ 3,700
Operating lease right-of-use assets		$ 3,300
60 First Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Expected liability to be paid	$ 208,700
Term of contract, lease not yet commenced (in years)	10 years

Leases - Schedule of Maturity (

Leases - Schedule of Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Apr. 30, 2023
Leases [Abstract]
Remaining in 2023	$ 3,649
2024	9,669
2025	2,656
2026	1,683
2027	567
Total undiscounted lease payments	18,224
Less: imputed interest	(1,183)
Total operating lease liability	$ 17,041	$ 3,300

Net Loss per Share - Schedule o

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, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (50,708)	$ (42,385)	$ (39,397)	$ (29,350)	$ (29,348)	$ (23,840)	$ (132,490)	$ (82,538)
Cumulative dividend on preferred stock	0			(6,362)			0	(18,879)
Net loss attributable to common stockholders	(50,708)			(35,712)			(132,490)	(101,417)
Net loss attributable to common stockholders, diluted	$ (50,708)			$ (35,712)			$ (132,490)	$ (101,417)
Denominator:
Weighted-average common shares outstanding, diluted (in shares)	91,846,835			22,226,301			90,469,866	20,665,225
Weighted-average common shares outstanding, basic (in shares)	91,846,835			22,226,301			90,469,866	20,665,225
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (0.55)			$ (1.61)			$ (1.46)	$ (4.91)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (0.55)			$ (1.61)			$ (1.46)	$ (4.91)

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	12,729,735	66,493,041
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	7,634,966	3,971,557
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	5,094,769	10,597,726
Convertible preferred stock (as converted to common stock)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	0	51,923,758

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	3 Months Ended			9 Months Ended
Related Party Transactions (Details) - USD ($)	Sep. 30, 2023		Sep. 30, 2022	Sep. 30, 2023		Sep. 30, 2022	Dec. 31, 2022
Related Party Transaction [Line Items]
Accrued expenses and other current liabilities	$ 14,023,000			$ 14,023,000			$ 10,688,000	[1]
Accounts payable	14,124,000	[2]		14,124,000	[2]		4,332,000
Related Party
Related Party Transaction [Line Items]
Accrued expenses and other current liabilities							300,000
Accounts payable	100,000			100,000
Co-Founder Shareholder \| Scientific Consulting \| Related Party
Related Party Transaction [Line Items]
Amounts of transaction	37,500		$ 37,500	112,500		$ 112,500
Accounts payable	$ 12,500			$ 12,500			0
Myeloid Therapeutics \| Collaborative Arrangement, License Agreement \| Related Party
Related Party Transaction [Line Items]
Accrued expenses and other current liabilities							$ 300,000

[1](2) Includes related party amount of $0.3 million as of December 31, 2022[2](1) Includes related party amount of $0.1 million as of September 30, 2023.

Stock-Based Compensation -Schedule of Restricted Stock Activity (Details)	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Restricted Stock, Time-Based
Number of Shares
Beginning of period (in shares) \| shares	5,015,034
Issued (in shares) \| shares	0
Vested (in shares) \| shares	(3,753,034)
Repurchased (in shares) \| shares	0
End of period (in shares) \| shares	1,262,000
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	0.08
Repurchased (in dollars per share) \| $ / shares	0
End of period (in dollars per share) \| $ / shares	$ 0.16
Restricted Stock, Performance-Based
Number of Shares
Beginning of period (in shares) \| shares	3,832,769
Issued (in shares) \| shares	0
Vested (in shares) \| shares	0
Repurchased (in shares) \| shares	0
End of period (in shares) \| shares	3,832,769
Weighted-Average Grant-Date Fair Value
Beginning of period (in dollars per share) \| $ / shares	$ 0.07
Issued (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	0
Repurchased (in dollars per share) \| $ / shares	0
End of period (in dollars per share) \| $ / shares	$ 0.07