Omega Therapeutics (OMGA) 10-Q 14 Nov 24 2024 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Nov. 08, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Registrant Name	Omega Therapeutics, Inc.
Entity Central Index Key	0001850838
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		55,366,213
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common stock, par value $0.001 per share
Trading Symbol	OMGA
Security Exchange Name	NASDAQ
Entity File Number	001-40657
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-3247585
Entity Address, Address Line One	140 First StreetSuite 501
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02141
City Area Code	617
Local Phone Number	949-4360
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 30,377	$ 68,443
Marketable securities		4,986
Accounts receivable, due from related party	486	1,006
Accounts receivable		5,125
Prepaid expenses and other current assets	8,090	10,324
Total current assets	38,953	89,884
Property and equipment, net	4,498	5,311
Operating lease right-of-use assets, net	109,245	108,736
Restricted cash		341
Other assets	31	94
Total assets	152,727	204,366
Current liabilities:
Accounts payable	1,434	1,620
Accrued expenses	4,650	7,914
Other current liabilities	2,170	1,972
Lease liabilities, current	11,919	11,300
Long-term debt, current portion	4,000	4,000
Total current liabilities	24,173	26,806
Lease liabilities, non-current	100,627	98,243
Long-term debt, net	11,587	14,885
Other liabilities	4,797	6,416
Total liabilities	141,184	146,350
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of September 30, 2024 and December 31, 2023; no shares issued and outstanding as of September 30, 2024 and December 31, 2023	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized as of September 30, 2024 and December 31, 2023; 55,159,219 and 55,144,982 issued and outstanding as of September 30, 2024 and December 31, 2023, respectively	55	55
Additional paid-in capital	399,000	392,609
Accumulated other comprehensive loss		(14)
Accumulated deficit	(387,512)	(334,634)
Total stockholders' equity	11,543	58,016
Total liabilities and stockholders' equity	$ 152,727	$ 204,366

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	55,159,219	55,144,982
Common stock, shares outstanding	55,159,219	55,144,982

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Collaboration revenue	$ 2,612	$ 831	$ 7,106	$ 2,105
Operating expenses:
Research and development	12,807	16,506	41,162	61,638
General and administrative	6,225	7,228	19,395	20,029
Total operating expenses	19,032	23,734	60,557	81,667
Loss from operations	(16,420)	(22,903)	(53,451)	(79,562)
Other Income (expense), net:
Interest income, net	14	684	644	2,323
Other income (expense), net	(38)	(29)	(71)	25
Total other income (expense), net	(24)	655	573	2,348
Net loss	$ (16,444)	$ (22,248)	$ (52,878)	$ (77,214)
Net loss per common stock attributable to common stockholders, basic	$ (0.3)	$ (0.4)	$ (0.96)	$ (1.44)
Net loss per common stock attributable to common stockholders, diluted	$ (0.3)	$ (0.4)	$ (0.96)	$ (1.44)
Weighted-average common stock used in net loss per share attributable to common stockholders, basic	55,155,583	55,140,058	55,153,699	53,629,468
Weighted-average common stock used in net loss per share attributable to common stockholders, diluted	55,155,583	55,140,058	55,153,699	53,629,468
Comprehensive loss:
Net Income (Loss)	$ (16,444)	$ (22,248)	$ (52,878)	$ (77,214)
Other comprehensive income (loss):
Unrealized gain on marketable securities		85	14	393
Comprehensive loss	$ (16,444)	$ (22,163)	$ (52,864)	$ (76,821)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance at Dec. 31, 2022	$ 105,971	$ 48	$ 343,608	$ (479)	$ (237,206)
Balance (in shares) at Dec. 31, 2022		48,072,517
Issuance of common stock for registered direct offering, net of issuance costs	39,727	$ 7	39,720
Issuance of common stock for registered direct offering, net of issuance costs, shares		6,920,415
Issuance of common stock for options exercised	108		108
Issuance of common stock for options exercised, shares		30,157
Other comprehensive gain	251			251
Stock-based compensation	2,222		2,222
Net Income (Loss)	(25,279)				(25,279)
Balance at Mar. 31, 2023	123,000	$ 55	385,658	(228)	(262,485)
Balance (in shares) at Mar. 31, 2023		55,023,089
Balance at Dec. 31, 2022	105,971	$ 48	343,608	(479)	(237,206)
Balance (in shares) at Dec. 31, 2022		48,072,517
Other comprehensive gain	393
Net Income (Loss)	(77,214)
Balance at Sep. 30, 2023	76,043	$ 55	390,494	(86)	(314,420)
Balance (in shares) at Sep. 30, 2023		55,141,838
Balance at Mar. 31, 2023	123,000	$ 55	385,658	(228)	(262,485)
Balance (in shares) at Mar. 31, 2023		55,023,089
Issuance of common stock for options exercised	371		371
Issuance of common stock for options exercised, shares		113,819
Other comprehensive gain	57			57
Stock-based compensation	2,178		2,178
Net Income (Loss)	(29,687)				(29,687)
Balance at Jun. 30, 2023	95,919	$ 55	388,207	(171)	(292,172)
Balance (in shares) at Jun. 30, 2023		55,136,908
Issuance of common stock for options exercised	7		7
Issuance of common stock for options exercised, shares		4,930
Other comprehensive gain	85			85
Stock-based compensation	2,280		2,280
Net Income (Loss)	(22,248)				(22,248)
Balance at Sep. 30, 2023	76,043	$ 55	390,494	(86)	(314,420)
Balance (in shares) at Sep. 30, 2023		55,141,838
Balance at Dec. 31, 2023	58,016	$ 55	392,609	(14)	(334,634)
Balance (in shares) at Dec. 31, 2023		55,144,982
Issuance of common stock for options exercised	22		22
Issuance of common stock for options exercised, shares		10,003
Other comprehensive gain	14			14
Stock-based compensation	3,431		3,431
Net Income (Loss)	(20,129)				(20,129)
Balance at Mar. 31, 2024	41,354	$ 55	396,062		(354,763)
Balance (in shares) at Mar. 31, 2024		55,154,985
Balance at Dec. 31, 2023	58,016	$ 55	392,609	$ (14)	(334,634)
Balance (in shares) at Dec. 31, 2023		55,144,982
Other comprehensive gain	14
Net Income (Loss)	(52,878)
Balance at Sep. 30, 2024	11,543	$ 55	399,000		(387,512)
Balance (in shares) at Sep. 30, 2024		55,159,219
Balance at Mar. 31, 2024	41,354	$ 55	396,062		(354,763)
Balance (in shares) at Mar. 31, 2024		55,154,985
Stock-based compensation	1,213		1,213
Net Income (Loss)	(16,305)				(16,305)
Balance at Jun. 30, 2024	26,262	$ 55	397,275		(371,068)
Balance (in shares) at Jun. 30, 2024		55,154,985
Issuance of common stock for options exercised	2		2
Issuance of common stock for options exercised, shares		4,234
Stock-based compensation	1,723		1,723
Net Income (Loss)	(16,444)				(16,444)
Balance at Sep. 30, 2024	$ 11,543	$ 55	$ 399,000		$ (387,512)
Balance (in shares) at Sep. 30, 2024		55,159,219

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating activities
Net loss	$ (52,878)	$ (77,214)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,320	1,146
Amortization of debt issuance costs and debt discount	35	33
Amortization of operating lease right-of-use assets	4,208	3,844
Accretion of discounts on marketable securities		(209)
Change in fair value of success fee obligation		92
Loss (gain) on disposal of fixed assets	2	(232)
Stock-based compensation expense	6,367	6,680
Changes in operating assets and liabilities:
Accounts receivable due from related party	520	221
Accounts receivable	5,125
Prepaid expenses and other current assets	2,575	(664)
Other assets	63	86
Accounts payable	(186)	(704)
Accrued expenses and other current liabilities	(3,906)	(5,688)
Other liabilities	(1,737)	(1,811)
Net cash used in operating activities	(38,492)	(74,420)
Investing activities
Purchases of property and equipment	(947)	(1,758)
Purchases of marketable securities		(19,768)
Proceeds from maturities of marketable securities	5,000	66,901
Net cash provided by investing activities	4,053	45,375
Financing activities
Proceeds from equity offering		40,000
Payments of equity offering costs		(273)
Payments of financing fees		(15)
Repayment of debt	(3,333)
Repayment of lease financing	(318)
Proceeds from issuance of common stock under equity incentive plans	24	486
Net cash (used in) provided by financing activities	(3,627)	40,198
Net change in cash, cash equivalents and restricted cash	(38,066)	11,153
Cash, cash equivalents and restricted cash—beginning of period	68,784	70,956
Cash, cash equivalents and restricted cash—end of period	30,718	82,109
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	30,377	81,768
Restricted cash	341	341
Cash, cash equivalents and restricted cash—end of period	30,718	82,109
Supplemental disclosures of cash flow information
Cash paid for interest	$ 1,208	1,279
Supplemental disclosure of noncash investing and financing activities
Purchases of property and equipment included in accounts payable and accrued expenses		$ 318

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (16,444)	$ (16,305)	$ (20,129)	$ (22,248)	$ (29,687)	$ (25,279)	$ (52,878)	$ (77,214)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2024
Nature Of Business And Basis Of Presentation [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Ba sis of Presentation Organization Omega Therapeutics, Inc. (the “Company” or “Omega”) is a biotechnology company pioneering the development of a new class of programmable epigenomic mRNA medicines by leveraging its OMEGA platform. The OMEGA platform harnesses the power of epigenetics, the mechanism that controls gene expression and every aspect of an organism’s life from cell genesis, growth and differentiation to cell death. The OMEGA platform enables control of fundamental epigenetic processes to correct the root cause of disease by restoring aberrant gene expression to a normal range without altering native nucleic acid sequences. The Company was incorporated in July 2016 (“inception”) as a Delaware corporation and its offices are in Cambridge, Massachusetts. Liquidity and Going Concern Since its inception, the Company has devoted substantially all of its resources to building its platform and advancing development of its portfolio of programs, establishing and protecting its intellectual property, conducting research and development activities, organizing and staffing the 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 clinical-stage companies in the biotechnology industry including, but not limited to, technical risks associated with the successful research, development and manufacturing of product candidates, risks related to clinical development of product candidates, developments 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 February 2023, the Company completed a registered direct offering of common stock pursuant to which it issued and sold 6,920,415 shares of its common stock at a purchase price of $ 5.78 per share and secured approximately $ 39.7 million in net proceeds after deducting estimated offering expenses. In August 2023, the Company entered into an Open Market Sale Agreement (the “Sales Agreement”), with Jefferies LLC (“Jefferies”), as sales agent, pursuant to which the Company may, from time to time, issue and sell common stock with an aggregate value of up to $ 60.0 million in “at-the-market,” or ATM, offerings under our Registration Statement on Form S-3 (File No. 333-268254) filed with the SEC on November 8, 2022, which was declared effective on November 18, 2022. During the nine months ended September 30, 2024, the Company did not sell any shares of common stock under the Sales Agreement. The Company has had recurring losses since inception and incurred a loss of $ 52.9 million during the nine months ended September 30, 2024. Net cash used in operations for the nine months ended September 30, 2024 was $ 38.5 million. In order to ensure sufficient resources to advance its lead program and maximize near- and long-term value creation opportunities from its platform, the Company announced a strategic prioritization in March 2024. As part of this initiative, the Company streamlined the organization and optimized its research and development efforts and, as a result, the Company expects that its cash and cash equivalents of $ 30.4 million at September 30, 2024 will enable it to fund its operating expenses and capital expenditure requirements into the second quarter of 2025. The Company expects to continue to generate operating losses and use cash in operations for the foreseeable future. Additional funding will be necessary to fund future preclinical and clinical activities and to develop new product candidates. The Company expects to finance its future cash needs through a combination of equity offerings, debt financings, marketing and distribution arrangements and other collaborations, strategic alliances and licensing arrangements, or other sources. Volatility in the capital markets and general economic conditions in the United States may be a significant obstacle to raising the required funds and, as a result, the Company may be unable to secure the necessary funding on acceptable terms. This raises substantial doubt about the Company's ability to continue as a going concern. The accompanying unaudited condensed financial statements do not include any adjustments that might result from the outcome of these uncertainties. Accordingly, the unaudited condensed financial statements have been prepared on a basis that assumes the Company will continue as a going concern which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Significant Risks and Uncertainties Related to Macroeconomic Conditions The global economy, including credit and financial markets, has recently experienced extreme volatility and disruptions, including, for example, severely diminished liquidity and credit availability, rising interest and inflation rates, crises involving banking and financial institutions, declines in consumer confidence, declines in economic growth, and uncertainty about economic stability. In addition, unstable market and economic conditions and further disruption created by international political unrest, war and terrorism may have serious adverse consequences on our business, financial condition and results of operations. Basis of Presentation The accompanying condensed consolidated unaudited financial statements have been prepared in accordance with accounting principles generally accepted 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 Update (“ASU”), of the Financial Accounting Standards Board (“FASB”). All amounts herein are expressed in U.S. dollars (“USD”) unless otherwise noted.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Principles of Consolidation The accompanying condensed consolidated unaudited financial statements include the accounts of Omega Therapeutics, Inc. and its wholly owned subsidiary, Omega Therapeutics Security Corporation, which is a Massachusetts subsidiary . All intercompany transactions and balances have been eliminated in consolidation. Reclassification The Company reclassified the related party expenses in the prior year to research and development and general and administrative expenses in the condensed consolidated statements of operations and comprehensive loss to conform to the current year's presentation. Unaudited Interim Financial Information The accompanying condensed consolidated unaudited financial statements included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited financial statements have been prepared on the same basis as audited financial statements, except certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been consolidated or omitted from this report, as is permitted by such rules and regulations. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair representation of the results for the reported periods. These condensed consolidated unaudited financial statements should be read in conjunction with the audited financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC on March 28, 2024 (the “2023 10-K”). The results for the nine months ended September 30, 2024 are not necessarily indicative of results to be expected for the year ending December 31, 2024, any other interim periods, or any future year or period. Use of Estimates The preparation of the condensed consolidated unaudited financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses, and the disclosure of contingent assets and liabilities as of and during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates and assumptions reflected in these condensed consolidated unaudited financial statements include, but are not limited to, the selection of useful lives of property and equipment, the incremental borrowing rate used in the calculation of lease liabilities, research and development accruals, and certain judgments regarding revenue recognition and stock-based compensation. Actual results could differ from these estimates. Changes in estimates are reflected in reported results in the period in which they become known. Summary of Significant Accounting Policies The Company’s significant accounting policies are described in Note 2, “Summary of significant accounting policies,” to the Company’s audited financial statements included in the 2023 10-K. There was no significant change of accounting policy during the nine months ended September 30, 2024. Recent accounting pronouncements not yet adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280) , Improvements to Reportable Segment Disclosures . The new standard requires enhanced disclosures about segment information and significant segment expenses. It does not change how a public entity identifies its operating segments. ASU 2023-07 is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. The new standard should be applied retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact on its consolidated financial statements. In December 2023, the FASB issued 2023-09, Income Taxes (Topic 740), Improvements to Income Tax Disclosures . The new standard requires public business entities to disclose information about income taxes paid, specific categories in the rate reconciliation, and additional information for reconciling items that meet a quantitative threshold. The guidance should be applied on a prospective basis. For public business entities, ASU 2023-08 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. For all other entities, the standard is effective for annual periods beginning after December 15, 2025. The Company is currently evaluating the impact on its consolidated financial statements.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	3. Marketable Securities As of September 30, 2024 , the Company did no t hold any marketable securities. All of the Company's previous marketable securities matured during the nine months ended September 30, 2024. The following table summarizes the Company’s marketable securities at December 31, 2023 (in thousands): December 31, 2023 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 5,000 $ ( 14 ) $ 4,986

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2024
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid Expenses and Other Current Assets	4. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2024 2023 Clinical development $ 4,557 $ 5,168 Research and development 1,168 1,609 Insurance 922 716 Other receivables 477 855 Software 354 303 Restricted cash 341 — Facilities — 1,242 Other 271 431 Prepaid expenses and other current assets $ 8,090 $ 10,324

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consists of the following (in thousands): September 30, December 31, 2024 2023 Lab equipment $ 7,472 $ 6,633 Furniture and fixtures 1,636 1,636 Leasehold improvements 1,431 1,290 Computer equipment 1,226 1,226 Construction in process — 588 Total property and equipment 11,765 11,373 Less accumulated depreciation ( 7,267 ) ( 6,062 ) Property and equipment, net $ 4,498 $ 5,311 Depreciation expense for each of the three months ended September 30, 2024 and 2023 was $ 0.4 million. Depreciation expense for the nine months ended September 30, 2024 and 2023 w as $ 1.3 million and $ 1.1 million, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2024
Accrued Liabilities, Current [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consist of the following (in thousands): September 30, December 31, 2024 2023 Employee related expenses $ 2,664 $ 4,482 Professional and consulting fees 1,130 716 Manufacturing costs 483 547 Research costs 217 1,395 Interest — 147 Other 156 627 Accrued expenses $ 4,650 $ 7,914 In the first quarter of 2024, the Company accrued $ 0.8 million of severance and other costs associated with the Company's cost reduction activities, which was fully paid out in the second quarter of 2024. In the second quarter of 2024, the Company accrued $ 0.7 million of severance and other costs associated with the separation of the Company's former Chief Financial Officer and Chief Medical Officer, which will be paid out in the form of salary continuation in regular installments over the 9-month period following their respective termination dates.

Term Loan

Term Loan	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Term Loan	7. Term Loan On March 9, 2018, the Company entered into the Loan Agreement with Banc of California (“BOC”, formerly known as Pacific Western Bank) to initially borrow $ 8.0 million, which was further amended on September 30, 2019 (the “First Amendment”), January 22, 2020 (the “Second Amendment”), December 30, 2020 (the “Third Amendment”), and December 20, 2021 (the “Fourth Amendment”). On September 22, 2023, the Company entered into another amendment to the Loan Agreement (the “ Fifth Amendment ” ), in which BOC extended the maturity date of the loan to September 30, 2027 , subject to further extension to September 30, 2028 upon receipt by the Company on or before December 31, 2024 of at least $ 50.0 million of cash proceeds from the sale of its equity securities and/or non-refundable upfront strategic partnership proceeds. Repayment of the loan began on September 30, 2023 , with monthly principal payments of $ 0.3 million plus interest, along with a closing payment of $ 4.0 million on September 30, 2027 if the maturity date is not extended to September 30, 2028. Interest will continue to be determined at a floating annual rate equal to the greater of (i) 0.50 % above the prime rate then in effect and (ii) 5.50 %. The Company incurred $ 15 thousand of debt issuance costs, which was recorded as a direct reduction against the additional term loan and will be amortized over the life of the associated term loan as a component of interest expense using the effective interest method. The Company is required to pay a success fee of $ 0.1 million pursuant to the Fifth Amendment, in addition to the $ 0.2 million success fee obligation pursuant to the Fourth Amendment. The success fees are contingent on achieving specified liquidity events. The Company determined that the success fee obligation represented a freestanding financial instrument, and it was classified as a liability on the Company’s condensed consolidated balance sheet and initially recorded at fair value, with changes in fair value for each reporting period recognized in other expense, net in the condensed consolidated statements of operations and comprehensive loss. The fair value of such obligation is remeasured at the end of each reporting period until the liability is settled. In addition, pursuant to the Fifth Amendment, the Company agreed to maintain with BOC, at all times, a balance of at least $ 5.0 million of unrestricted cash, subject to termination upon the Company’s prepayment of outstanding loans in an aggregate amount of at least $ 5.0 million or if the principal balance of the loans is less than $ 10.0 million. Borrowings under the Loan Agreement, as amended, are collateralized by substantially all of the Company’s personal property, other than its intellectual property. There are no financial covenants associated with the Loan Agreement, as amended; however, the Company is subject to certain affirmative and negative covenants to which the Company will remain subject until maturity. As of September 30, 2024, $ 4.0 million of the net carrying amount of the term loan was classified as short-term and $ 11.6 million was classified as long-term based on the repayment start date. The Company’s outstanding term loan balance was comprised of the following (in thousands): September 30, December 31, 2024 2023 Principal $ 15,667 $ 19,000 Unamortized debt discount ( 80 ) ( 115 ) Net carrying amount $ 15,587 $ 18,885 The Company determined that the expected life of the debt was equal to the term on the term loan. The effective interest rate on the liability component ranged from 5.53 % to 9.27 % for the period from t he date of issuance through September 30, 2024 . The following table sets forth total interest expense recognized related to the term loan (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Contractual interest expense $ 373 $ 469 $ 1,185 $ 1,336 Amortization of debt issuance costs and debt discount 11 13 35 33 Total interest expense $ 384 $ 482 $ 1,220 $ 1,369 At September 30, 2024 and December 31, 2023, accrued interest on the term loan was zero an d $ 147 thousand, respectively. The Company is required to repay the following principal amounts in connection with its term loan (in thousands): 2024 (remaining 3 months) $ 1,000 2025 4,000 2026 4,000 2027 6,667 Total $ 15,667

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	8. Fair Value of Financial Instruments The fair value of the Company’s cash and cash equivalents and restricted cash are measured through quoted market prices; the fair value of the Company's marketable securities is determined based on the pricing inputs other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date. Other current assets, accounts payable and accrued liabilities approximate their fair values as of September 30, 2024 and December 31, 2023, due to their short-term nature. The carrying value of the Company’s debt approximates its fair value due to its variable interest rate, which approximates a market interest rate. The success fee obligation associated with the Loan Agreement, as amended, contains unobservable inputs that reflect the Company’s own assumptions in which there is little, if any, market activity at the measurement date, thus the success fee obligation is measured at its fair value on a recurring basis using unobservable inputs. The fair value of the Company’s financial instruments is summarized in the table below (in thousands): September 30, 2024 Level 1 Level 2 Level 3 Total Financial Liabilities Success fee obligation $ — $ — $ 300 $ 300 December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 10,402 $ — $ — $ 10,402 Corporate Debt Securities — 4,986 — 4,986 Total $ 10,402 $ 4,986 $ — $ 15,388 Financial Liabilities Success fee obligation $ — $ — $ 300 $ 300 In accordance with the Fourth and Fifth Amendments of the Loan Agreement with BOC, the Company will be required to pay success fees totaling $ 0.3 million upon the achievement of certain liquidity events; accordingly, the related obligation is recorded as other current liabilities on the condensed consolidated balance sheets as it is deemed more probable than not by the Company to be settled in less than one year. The fair value of the success fee obligation was determined using the probability-weighted expected return method. The key estimates and assumptions impacting the fair value included the probability of achieving a specified liquidity event, the expected timing of achieving a liquidity event and the discount rate. The fair value of the success fee obligation is remeasured at each reporting period, with changes in fair value recognized in the condensed consolidated statements of operations and comprehensive loss, until such liability was settled. As of September 30, 2024 , the Company determined it was 100 % probable of achieving the specified liquidity events and therefore accrued the full amount of the success fee obligation. The following reflects the significant quantitative inputs used to determine the valuation of the success fee obligation as of September 30, 2024 and December 31, 2023: September 30, 2024 December 31, 2023 Discount rate 8.5 % 9.0 % Expected timing of achieving liquidity events (years) 0.3 1.0 Probability of achieving liquidity events 100 % 100 % The change in fair value of the Company's success fee obligation was immaterial in the nine months ended September 30, 2024 .

Leases

Leases	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Leases	9. Leases The Company has the following operating leases for its corporate offices and lab space located in Cambridge, Massachusetts . 325 Vassar Street In 2017, the Company entered a noncancelable operating lease agreement to lease its office space at 325 Vassar Street, Cambridge, Massachusetts. The Company is required to pay property taxes, insurance, and normal maintenance costs. The operating lease contains predetermined fixed escalations of minimum rentals during the lease term. In 2019 and 2020, the Company entered into sublease agreements with two related parties to sublease this office and laboratory space. The lease and subleases expired in September 2024 . Refer to Note 17, Related Party Transactions , for further details. 20 Acorn Park Drive On July 13, 2020, the Company entered into a Shared Space Arrangement (the "Arrangement") with Sail Biomedicines, Inc., (“Sail Bio”, also formerly known as Senda Biosciences, Inc. and Kintai Therapeutics, Inc. prior to its merger with LARONDE, Inc.) to share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts . Sail Bio is a related party as it is an affiliate of Flagship Pioneering (“Flagship”). The Arrangement commenced on August 1, 2020, with an expiration date of July 31, 2022 and two options to extend the term of the Arrangement for a period of 24 months each. The operating lease contains predetermined fixed escalations of minimum rentals during the lease term, and the Company is required to pay property taxes, insurance, and normal maintenance costs. In January 2022, the Company entered into an amendment to the Arrangement with Sail Bio to exercise the option to renew the lease through July 2023 . The Company also modified certain provisions related to the extension term. The Company did not subsequently renew the lease, and the lease expired at the end of July 2023 . Refer to Note 17, Related Party Transactions , for further details. 140 First Street (formerly known as One Charles Park) On November 4, 2021, the Company entered into a lease with ARE-MA Region No. 94, LLC to lease an aggregate of approximately 89,246 rentable square feet of office and laboratory space located at 140 First Street, Cambridge, Massachusetts. The lease includes two phases. Phase 1 includes approximately 78,380 rentable square feet for the fifth floor. Phase 2 includes 10,866 rentable square feet in a separate suite on the first floor. In accordance with the lease agreement, the Company paid $ 0.8 million upon the execution of the lease, which has offset the first month's rent. Phase 1 of the lease commenced in May 2023, and Phase 2 commenced in August 2023. On May 3, 2023, the Company entered into a first amendment to the lease to, among other things, delay the delivery date of part of the premises, increase the initial base rent by $ 1.00 per rentable square foot per year, and change the address. The operating lease commenced on May 1, 2023 for the fifth floor premises and August 1, 2023 for the first floor premises for accounting purposes. The lease term for each of the floor premises is fifteen years from the respective commencement date, subject to certain extension rights. The base rent for the leased space is $ 116.00 per square foot, subject to an annual upward adjustment of 3 % of the then current rental rate, starting on the first anniversary of the first full payment of rent under the lease. The operating lease includes a tenant improvement allowance of $ 300 per rentable square foot that is incorporated into the base rent payments, as well as an additional improvement allowance that is required to be repaid to the landlord as additional monthly rent over the lease term at an interest rate of 8 %. On June 24, 2024, the Company entered into a second amendment to the lease to no longer require landlord consent to enter into Shared Space Arrangements. On July 31, 2024, the Company entered into a third amendment to the lease for 1 40 First Street, Cambridge, Massachusetts , pursuant to which the Landlord made available $ 3.3 million from the Second Additional Improvement Allowance (as defined in the Lease), which was not previously used by the Company, for the design and construction of a portion of the Premises. On July 11, 2023, the Company entered into a Shared Space Arrangement with Apriori Bio, Inc. (“Apriori”), and on July 12, 2023, the Company entered into two Shared Space Arrangements with Metaphore Biotechnologies, Inc. (“Metaphore”) and Flagship Labs 89, Inc., now known as Prologue Medicines, Inc., ("Prologue" and, together with Metaphore and Apriori, the “Subtenants”), pursuant to which the Company agreed to sublease an aggregate of approximately 22,500 rentable square feet of office and laboratory space located at 140 First Street, Cambridge, Massachusetts (the “Premises”). Metaphore, Apriori and Prologue are affiliates of Flagship. The term of the Shared Space Arrangement with Metaphore and Prologue commenced in August, 2023 and was scheduled to end in August, 2025, and the term of the Shared Space Arrangement with Apriori began in September, 2023 and was scheduled to end in September, 2025. The Shared Space Arrangements provide that the Subtenants will pay to the Company a monthly fee that is a proportionate share of the actual base rent, operating expenses and other costs for the use and occupancy of the subleased portion of the Premises charged by the Landlord under the Lease and paid by the Company. Such proportionate share was 12.0 %, 8.4 % and 8.4 % for Metaphore, Apriori and Prologue, respectively. In June 2024, the Company entered into amendments to the Shared Space Arrangements with the Subtenants, which increased the proportionate share to 16.2 %, 11.3 % and 11.3 % for Metaphore, Apriori and Prologue, respectively, effective July 1, 2024. On August 27, 2024, the Company entered into an Amended and Restated Shared Space Arrangement with each of the Subtenants, effective September 1, 2024 (the "Effective Date"), which further increased their proportionate share. Such proportionate share for each of Apriori and Prologue is 12.6 % from the Effective Date until November 1, 2024 (the "November Effective Date"), 13.9 % thereafter until April 1, 2025 (the "April Effective Date") and 14.3 % thereafter until August 31, 2026 (the "Termination Date"). Such proportionate share for Metaphore is 17.5 % from the Effective Date until the November Effective Date, 18.7 % thereafter until the April Effective Date and 19.2 % thereafter until the Termination Date. On August 1, 2024, the Company entered into a Shared Space Arrangement with Flagship Labs 97, Inc. ( “ FL 97 ” ), pursuant to which the Company agreed to sublease approximately 12.2 % of its aggregate rentable square footage, for laboratory space located on the first floor at 140 First Street, Cambridge, Massachusetts commencing August 2024 and ending July 2027, with two options to extend for a period of 24 months each. On August 27, 2024, the Company also entered into Shared Space Arrangements with Flagship Labs 101, Inc. ( “ FL 101 ” ) and Flagship Labs 104, Inc. ("FL 104"), and together with FL 101 and the other Subtenants, the "SSA Subtenants"), pursuant to which the Company agreed to sublease a portion of its rentable square footage located at 140 First Street, Cambridge, Massachusetts commencing on the Effective Date. Such proportionate share for FL 101 is 3.6 % from January 1, 2025 until the April Effective Date and 6.4 % thereafter until the Termination Date, and for FL101 is 1.0 % from January 1, 2025 through the Termination Date for FL 104. Each of FL 97, FL 101, and FL 104 are affiliates of Flagship. The total commitment for the SSA Subtenants' share of the base rent over the term of the six Shared Space Arrangements described above is $ 14.2 mill ion. The Company may terminate each Shared Space Arrangement and require the applicable SSA Subtenant to immediately vacate the Premises if such SSA Subtenant causes a default under the Lease, is in default of any provision in the applicable Sublease or acts in a manner deemed by the Company, in its sole discretion, as dangerous or threatening. The Shared Space Arrangements contain customary covenants, obligations and indemnities in favor of either party. For the three and nine months ended September 30, 2024, the Company received rental income of $ 1.8 million and $ 3.9 million, respectively, under the Shared Space Arrangements, which was recorded as a reduction of research and development expense and general and administrative expense in the accompanying condensed consolidated statements of operations and comprehensive loss. As of September 30, 2024, operating lease right-of-use assets, net were $ 109.2 million, which were recorded separately on the Company’s condensed consolidated balance sheet. The corresponding operating lease liabilities were $ 112.5 million as of September 30, 2024, of which $ 11.9 million were recorded in current liabilities and $ 100.6 million were recorded in long-term liabilities on the Company’s condensed consolidated balance sheet. The right-of-use assets represent the Company’s right to use an underlying asset during the lease term and the related lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Both the right-of-use assets and the corresponding liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. As the Company’s leases do not provide an implicit rate, the Company estimated the incremental borrowing rate based on the interest rate from the amended Term Loan, which was fully collateralized, as well as a term matched secured market rate. The following table summarizes the components of lease expense for the three and nine months ended September 30, 2024 and 2023 (in thousands). Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Operating lease expense $ 3,871 $ 3,866 $ 11,496 $ 7,854 Variable lease expense 1,088 945 3,225 1,844 Total lease expense $ 4,959 $ 4,811 $ 14,721 $ 9,698 Variable lease expense generally includes common area maintenance, utilities and property taxes. For the three and nine months ended September 30, 2024, $ 3.5 million and $ 10.6 million, respectively of lease expense was recorded within research and development expenses and $ 1.5 million and $ 4.1 million, respectively was recorded within general and administrative expenses in the condensed consolidated statement of operations and comprehensive loss. For the three and nine months ended September 30, 2023, $ 4.0 million and $ 7.8 million, respectively of lease expense was recorded within research and development expenses and $ 0.8 mill ion and $ 1.9 million, respectively was recorded withi n general and administrative expenses in the condensed consolidated statement of operations and comprehensive loss. The weighted average remaining lease term and discount rate related to the Company's leases were as follows: As of September 30, 2024 December 31, 2023 Weighted average remaining lease term (years) 13.9 14.5 Weighted average discount rate 8.9 % 8.9 % Supplemental cash flow information relating to the Company's leases for the nine months ended September 30, 2024 and 2023 were as follows (in thousands): Nine Months Ended September 30, 2024 2023 Cash paid for amounts included in the measurement of lease liabilities $ 9,144 $ 4,473 Operating lease assets obtained in exchange for lease liabilities $ — $ 110,424 As of September 30, 2024, the estimated minimum lease payments for 140 First Street for each of the years ending December 31 were as follows (in thousands): 2024 (remaining 3 months) $ 3,070 2025 12,492 2026 12,819 2027 13,155 2028 13,501 Thereafter 144,664 Total minimum lease payments 199,701 Less: Imputed interest ( 87,155 ) Present value of operating lease liabilities $ 112,546 Thermo Furniture Sale-Leaseback In December 2023 , the Company entered into a sale-leaseback arrangement with Thermo Fisher Financial Services, Inc. to provide $ 2.6 million in cash proceeds for previously acquired furniture and equipment. The term of the leaseback is 5 years, with an option to purchase the assets for $1 at the end of the term. The Company concluded the leaseback would be classified as a financing lease. Therefore, the transaction was deemed a failed sale-leaseback and was accounted for as a financing arrangement. T he Company will make monthly payments of $ 53 thousand over the term of the lease. As of September 30, 2024, $ 0.5 million of the financing obligation is included in current liabilities and $ 1.8 million is included in long-term liabilities on the Company’s condensed consolidated b alance sheet. The assets continue to be depreciated over their useful lives, and payments are allocated between interest expense and repayment of the financing liability.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Legal Matters From time to time, the Company may be a party to litigation, arbitration or other legal proceedings in the course of our business, including the matters described below. The claims and legal proceedings in which the Company could be involved include challenges to the scope, validity or enforceability of patents relating to its products or product candidates, and challenges by the Company to the scope, validity or enforceability of the patents held by others. These include claims by third parties that the Company infringes their patents or breaches its license or other agreements with such third parties. The outcome of any such legal proceedings, regardless of the merits, is inherently uncertain. In addition, litigation and related matters are costly and may divert the attention of the Company's management and other resources that would otherwise be engaged in other activities. If the Company was unable to prevail in any such legal proceedings, its business, results of operations, liquidity and financial condition could be adversely affected. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company's accounting policy for accrual of legal costs is to recognize such expenses as incurred. On June 11, 2024, a shareholder derivative suit captioned Joel Newman v. Flagship Pioneering, Inc., et al., was filed in the Court of Chancery of the State of Delaware (the “Complaint”), alleging breaches of fiduciary duty and unjust enrichment in connection with the Company’s decision to enter into a Research Collaboration Agreement with Novo Nordisk A/S ("Novo Nordisk") and Pioneering Medicines 08, Inc. The Complaint names the Company as nominal defendant, and names certain of the Company’s officers and directors, among others, as defendants. The Complaint seeks damages, rescissory relief, attorneys’ fees and costs, and any other and further relief the court deems just and proper. The defendants filed a motion to dismiss on September 10, 2024. Thereafter, plaintiff gave notice that he intends to file an amended complaint, which is due by December 11, 2024. The Company is unable to reasonably estimate the potential loss or range of loss associated with this matter and intends to defend itself vigorously. Refer also to contractual commitments as described in Note 7, Term Loan , Note 9, Leases , and Note 11, License agreements .

License Agreements

License Agreements	9 Months Ended
	Sep. 30, 2024
License Agreements [Abstract]
License Agreements	11. License Agreements Flagship Pioneering Innovations V, Inc. In March 2019, the Company entered into an exclusive license agreement with Flagship Pioneering Innovations V, Inc., an affiliate of Flagship, under which the Company was granted an exclusive, worldwide, royalty-bearing, sublicensable, transferable license under specified patent rights to develop, manufacture and commercialize licensed products (the “Flagship License”). Under the terms of the Flagship License, the Company is obligated to pay low single digit percentage royalties on net sales of licensed products by the Company. Royalties shall be paid by the Company on a country-by-country basis until expiration or abandonment of the last valid patent claim covering such licensed product in such country. The Company is also obligated to reimburse Flagship for patent prosecution costs. The royalty payment is contingent upon sales of licensed products under the Flagship License. As such, when such expense is considered probable and estimable at the commencement of sales, the Company will account for the royalty expense as cost of sales for the amount it is obligated. Whitehead Institute for Biomedical Research In May 2019, the Company entered into an exclusive license agreement with the Whitehead Institute for Biomedical Research (“WIBR”), an affiliate of one of the Company’s board members, under which the Company was granted an exclusive, worldwide, royalty-bearing, sublicensable license under specified patent rights to research, make, have made, use, sell, offer to sell, lease and import products and to perform and have performed licensed processes (the “WIBR Exclusive License”). Under the terms of the WIBR Exclusive License, the Company paid a nonrefundable upfront fee of less than $ 0.1 million upon the commencement of the exclusive license agreement. The Company is obligated to pay WIBR annual license maintenance fees of less than $ 0.1 million and low single digit percentage royalties on net sales of licensed products by the Company and its affiliates and sublicensees. Additionally, the Company is required to make milestone payments of up to $ 1.7 million in the aggregate for each of the first three licensed products (excluding backup products) upon the achievement of specified clinical and regulatory milestones. In addition, the Company is required to pay to WIBR a percentage of the non-royalty payments that it receives from sublicensees of the WIBR Exclusive License. This percentage ranges from zero to low double-digits and will be based upon the stage of development of the licensed product at the time such sublicense is executed. In May 2019, the Company also entered into a co-exclusive license agreement with WIBR under which the Company was granted a co-exclusive, worldwide, royalty-bearing, sublicensable license under specified patent rights to research, make, have made, use, sell, offer to sell, lease and import products and to perform and have performed licensed processes (the “WIBR Co-Exclusive License”). Under the terms of the WIBR Co-Exclusive License, the Company paid a nonrefundable upfront fee of less than $ 0.1 million upon the commencement of the co-exclusive license agreement. The Company is obligated to pay WIBR annual license maintenance fees of less than $ 0.1 million and low single digit percentage royalties on net sales of licensed products by the Company and its affiliates and sublicensees as well as low single digit percentage royalties on licensed service income received by the Company and its affiliates. Additionally, the Company is required to make milestone payments of up to $ 1.9 million in the aggregate for each of the first three licensed products (excluding backup products) upon the achievement of specified clinical and regulatory milestones. In addition, the Company is required to pay to WIBR annual fees of less than $ 0.1 million for each sublicense agreement. For the three months ended September 30, 2024 and 2023 , the Company recognized an immaterial amount and $ 0.1 million, respectively, of expenses for the license maintenance fees and milestone payments. For the nine months ended September 30, 2024 and 2023, the Company recognized expenses o f $ 0.2 million and $ 0.3 milli on, respectively for the license maintenance fees and milestone payments. There were no outstanding payments due to WIBR as of September 30, 2024 and December 31, 2023. The annual maintenance fees will be recorded as an expense on an annual basis based on the stated amount for the applicable year. Upon determination that a milestone payment is probable to occur, the amount due will be recorded as research and development expense. Lastly, the royalty payments and the sublicense non-royalty payments are contingent upon sales of licensed products or execution of a sublicense agreement under the WIBR Exclusive and Co-Exclusive Licenses. As such, when such expenses are considered probable and estimable at the commencement of sales or execution of a sublicense agreement, the Company will accrue royalty expense and sublicense non-royalty payments, as applicable, for the amount the Company is obligated. Acuitas Therapeutics, Inc. In October 2020, the Company entered into a development and option agreement (the “Development and Option Agreement”) with Acuitas Therapeutics, Inc. (“Acuitas”). Under the terms of the Development and Option Agreement, the parties agreed to jointly develop certain products combining the Company’s gene modulating therapeutics with Acuitas' lipid nanoparticles. Additionally, in accordance with the Development and Option Agreement, the Company has options to obtain non-exclusive, worldwide, sublicensable licenses under Acuitas’ patents and know-how related to lipid nanoparticle technology (“Acuitas LNP Technology”) with respect to two specified targets (e.g., EC constructs) (“Reserved Targets”) to develop and commercialize one or more therapeutic products relating to such targets. For each option and Reserved Target, the Company is obligated to pay an annual technology access fee and target reservation and maintenance fees collectively in the low-mid six figures until such Reserved Target is removed from the Reserved Target list or until the Company exercises an option with respect to such Reserved Target. In the event that the Company exercises the options, the Company will pay $ 1.5 million for the first non-exclusive license and $ 1.75 million for the second non-exclusive license. Under the terms of the Development and Option Agreement, the Company is also responsible for the full-time equivalent ("FTE") funding obligations, which is expected to be approximately $ 0.4 million per year, and reimbursements to Acuitas for certain development and material costs incurred by them. In March 2021, the Company exercised the first option under the Development and Option Agreement and entered into a non-exclusive license agreement with Acuitas (the “Acuitas License Agreement”) under which the Company was granted a non-exclusive, worldwide, sublicensable license under the Acuitas LNP Technology to research, develop, manufacture, and commercially exploit products consisting of the Company’s gene modulating therapeutics and Acuitas’ lipid nanoparticles. In connection with the option exercise, the Company incurred an expense for the option exercise fee of $ 1.5 million. Under the Acuitas License Agreement, the Company is required to pay Acuitas an annual license maintenance fee in the high six figures until the Company achieves a certain development milestone. Acuitas is entitled to receive potential clinical and regulatory milestone payments of up to $ 18.0 million in the aggregate if the milestones are achieved. With respect to the sale of each licensed products, the Company is also obligated to pay Acuitas low single digit percentage royalties on net sales of the licensed products by the Company and its affiliates and sublicensees in a given country until the last to occur, in such country, of (i) the expiration or abandonment of all licensed patent rights covering the licensed product, (ii) expiration of any regulatory exclusivity for the licensed product, or (iii) ten years from the first commercial sale of the licensed product. For each of the three months ended September 30, 2024 and 2023 , the Company recorded less than $ 0.1 million of research and development expenses consisting of technology access fees, target reservation and maintenance fees, the costs of services performed by Acuitas, material costs and reimbursable costs. For each of the nine months ended September 30, 2024 and 2023 , the Company recorded $ 0.1 million of research and development expenses consisting of technology access fees, target reservation and maintenance fees, the costs of services performed by Acuitas, material costs and reimbursable costs. The option exercise fee under the Development and Option Agreement was recorded as research and development expense upon the Company’s exercise of the first option. Additionally, the technology access fees, target reservation and maintenance fees, expenses associated with the FTE funding obligations and reimbursements for development and material costs incurred by Acuitas are recorded as research and development expense when incurred. The annual maintenance fee will be recorded as an expense on an annual basis based on the stated amount for the applicable year. Upon determination that a milestone payment is probable to occur, the amount due will be recorded as research and development expense. There were no milestones triggered, and no milestone expense was recorded related to the Acuitas agreements for the nine months ended September 30, 2024 and 2023. Lastly, the royalty payment is contingent upon sales of licensed products under the Acuitas License Agreement. As such, when such expenses are considered probable and estimable at the commencement of sales, the Company will accrue royalty expense for the amount the Company is obligated. Nitto Denko Corporation On October 12, 2022, the Company entered into a Collaboration and License Agreement (the "Nitto Agreement”) with Nitto Denko Corporation (“Nitto”), pursuant to which, among other things, Nitto granted the Company an exclusive, worldwide, royalty-bearing, fully transferable and fully sublicensable license under all intellectual property owned or controlled by Nitto relating to its lipid nanoparticle delivery technology. Under the terms of the Nitto Agreement, the Company made an upfront cash payment of $ 1.0 million, and developmental milestone payments of $ 1.0 million to Nitto in 2022. Both payments were recorded as research and development expenses. The Company may be required to make up to $ 83.0 million in future payments to Nitto based upon the achievement of specified development, regulatory and sales milestones. There were no milestones triggered, and no milestone expense was recorded related to the Nitto Agreement for the nine months ended September 30, 2024 and 2023. The Company is also obligated to pay to Nitto tiered, single-digit percentage royalties on a country-by-country basis based on net sales of the licensed product, subject to reduction in specified circumstances. As such, when these expenses are considered probable and estimable, the Company will accrue expense for the amount the Company is obligated. On May 2, 2024, the Company provided notice to terminate its Collaboration and License Agreement with Nitto Denko Corporation pursuant to Section 10.3(b) of the agreement, with an effective date of June 1, 2024 or thirty (30) days from notification. There was no penalty or fee associated with the termination. During the three and nine months ended September 30, 2024 , the Company recorded no research and development expenses related to the Nitto Agreement. During the three and nine months ended September 30, 2023, the Company recorded $ 0.4 million an d $ 0.9 million, respectively, of research and development expenses consisting of material costs, costs of services performed by Nitto, and reimbursable costs.

Collaboration Agreement

Collaboration Agreement	9 Months Ended
	Sep. 30, 2024
Collaboration Agreement [Abstract]
Collaboration Agreements	12. Collaboration Agreements PMCo In November 2021, the Company entered into a five-year collaboration agreement with PMCo, an affiliate of Flagship, under which PMCo was granted an exclusive license covering specified patent rights of the Company’s lipid nanoparticle technology to develop one or more therapeutic products to treat diseases related to the cystic fibrosis transmembrane conductance regulator gene, like cystic fibrosis. Under the terms of the agreement, the Company will perform certain research activities in accordance with the research plan, and PMCo will be solely responsible for, at its sole cost and expense, and will have sole discretion with respect to, developing, manufacturing, seeking regulatory approval for and commercializing licensed products. The research plan funding may be adjusted upon mutual written agreement from both parties. Additionally, in the event PMCo is acquired or sold, the Company is entitled to receive a portion of the proceeds of such transaction, subject to various reductions and other amounts payable in accordance with the agreement . The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, PMCo, is a customer. The Company determined that the research activities and the exclusive license granted under the collaboration agreement is considered as a single performance obligation, and therefore, the transaction price was allocated entirely to the single performance obligation. The Company recognizes revenue related to the single performance obligation over time as the underlying services are performed and/or external costs are incurred. The total transaction price at September 30, 2024 was determined to be $ 7.0 million base d on the current estimated required efforts to fulfill the performance obligation. This total includes an increase of $ 1.9 million in the fourth quarter of 2022, an increase of $ 2.4 million in the third quarter of 2023, an increase of $ 0.1 million in the fourth quarter of 2023, and a decrease of $ 0.9 million in the third quarter of 2024, all of which were agreed upon with PMCo, to the original transaction price as of the inception of the contract of $ 3.5 million. As of September 30, 2024 , the transaction price had been fully recognized as revenue and no further research and development activities are expected to be performed. The Company recognized funded research and collaboration reve nue of $ 0.3 million and $ 1.9 million during the three and nine months ended September 30, 2024 , respectively, and $ 0.8 million and $ 2.1 million during the three and nine months ended September 30, 2023, respectively in the condensed consolidated statement of operations and comprehensive loss. Costs incurred associated with this collaboration agreement were recorded as research and development expenses. Pursuant to the agreement, the Company is entitled to receive a portion of the sales proceeds in the event PMCo is acquired or sold. At the end of each reporting period, the Company evaluates the probability of occurrence of such transaction. As of September 30, 2024, the Company determined that the proceeds from such transaction was not probable of recognition. Novo Nordisk On December 31, 2023, the Company entered into a Research Collaboration Agreement with Novo Nordisk A/S ("Novo Nordisk") and Pioneering Medicines 08, Inc., an affiliate of Flagship (and with respect to certain provisions set forth in the agreement, Pioneering Medicines (NN), LLC and PM (NN) Explorations, Inc.). Under the terms of the agreement, the Company granted to Novo Nordisk an exclusive, royalty-bearing, transferable license, with the right to grant sublicenses through multiple tiers, for certain of its intellectual property to conduct research and development activities under an agreed-upon research and development plan relating to a product candidate, or program target, for the prevention, treatment or control of a cardiometabolic disease, including diabetes. In January 2024, the Company received an upfront nonrefundable payment of $ 5.1 million from Novo Nordisk and expects to receive approximate ly $ 21.6 million in cost reimburse ment through 2027 to fund the related research and development activities. The research plan funding may be adjusted upon mutual written agreement from all the parties. The Company is also eligible to receive development and commercial milestone payments, as well as tiered royalties on annual net sales of a licensed product. The term of the agreement expires at the end of the royalty term, which is the later of the 10 th anniversary of the first commercial sale, the expiration of the last-to-expire payment claim, or expiration of regulatory exclusivity. Upon the expiration of the royalty term for a given licensed product in a given country in the territory, the licenses granted to Novo Nordisk pursuant to the agreement under the Omega licensed intellectual property survive and become perpetual, irrevocable, fully paid-up and royalty free with respect to such licensed product in such country. The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Novo Nordisk, is a customer. The Company determined that the research activities and the exclusive license granted under the collaboration agreement is considered as a single combined performance obligation as they are incapable of being distinct. The Company recognizes revenue related to the single performance obligation over time using the input method. Under the input method, the extent of progress towards completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation, which the Company believes best measures its progress towards satisfying the combined performance obligation. A cost-based input method of revenue recognition requires management to make estimates of costs to complete performance obligation. In making such estimates, judgment is required to evaluate assumptions related to cost estimates. As of September 30, 2024, the total transaction price was determined to be $ 26.7 million bas ed on the upfront nonrefundable payment and estimated required research and development efforts. As of September 30, 2024, the remaining transaction price was estimated t o be $ 21.5 million, which is e xpected to be recognized as revenue through 2027. The Company recognized funded research and collaboration revenue of $ 2.3 million and $ 5.2 million in the condensed consolidated statement of operations and comprehensive loss during the three and nine months ended September 30, 2024, respectively. Additionally, the Company had $ 1.1 million of current deferred revenue and $ 3.0 million of noncurrent deferred revenue as of September 30, 2024 based on the period the services are expected to be performed and/or related costs to be incurred. Costs incurred associated with this collaboration agreement were recorded as research and development expenses. The Company will assess the probability of achieving the milestones and include them in the transaction price when they are deemed probable. Royalties will be recognized when the subsequent sales occur based on the sales or usage-based royalty exception. ASC 606 Disclosures To-date, the Company has only generated revenues from its collaboration agreements with PMCo and Novo Nordisk. During the three and nine months ended September 30, 2024, the Company recognized total collaboration revenue of $ 2.6 million and $ 7.1 million, respectively. During the three and nine months ended September 30, 2023, the Company recognized total collaboration revenue of $ 0.8 millio n and $ 2.1 million, respectively. The following table summarizes the Company's contract assets and liabilities (in thousands): September 30, December 31, 2024 2023 Contract assets: Accounts receivable $ 333 $ 6,131 Unbilled revenue — 89 Contract liabilities: Deferred revenue- current 1,054 — Deferred revenue- noncurrent 2,968 — The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled revenue (contract assets) and deferred revenue (contract liabilities) on the condensed consolidated balance sheets. Deferred revenue is included in Other current liabilities and Other liabilities on the condensed consolidated balance sheets. During the nine months ended September 30, 2024 and 2023, the Company recogniz ed $ 1.0 million and less than $ 0.1 million of revenue, respectively, which were included in the deferred revenue balances as of December 31, 2023 and 2022, respectively.

Preferred and Common Stock

Preferred and Common Stock	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Preferred and Common Stock	13. Preferred and Common Stock In 2021, the Company’s board of directors and stockholders approved the Company’s Amended and Restated Certificate of Incorporation to, among other things, provide for 200,000,000 authorized shares of common stock with a par value of $ 0.001 per share and 10,000,000 authorized shares of preferred stock with a par value of $ 0.001 per share. In February 2023, the Company completed a registered direct offering of common stock pursuant to which it issued and sold 6,920,415 shares of its common stock at a purchase price of $ 5.78 per share and secured approximately $ 39.7 million in net proceeds after deducting estimated offering expenses of $ 0.3 million. The holders of common stock are entitled to one vote for each share of common stock. Subject to the payment in full of all preferential dividends to which the holders of the preferred stock are entitled, the holders of common stock shall be entitled to receive dividends out of funds legally available. In the event of any voluntary or involuntary liquidation, dissolution, or winding up of the Company, after the payment or provision for payment of all debts and liabilities of the Company and all preferential amounts to which the holders of preferred stock are entitled with respect to the distribution of assets in liquidation, the holders of common stock shall be entitled to share ratably in the remaining assets of the Company available for distribution. As of September 30, 2024, the Company has reserved an aggregate of 9,666,626 shares of common stock for the potential exercise of outstanding stock options under its equity incentive plans. Upon the effectiveness of the 2021 Incentive Award Plan (“2021 Plan”), the Company ceased granting awards under the 2017 Equity Incentive Plan (“2017 Plan”), and the 3,709,118 shares of common stock subject to outstanding stock options i ssued under the 2017 Plan may become available for future issuance under the 2021 Plan to the extent such stock options are forfeited.

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Equity Incentive Plans	14. Equity Incentive Plans 2017 Equity Incentive Plan In June 2017, the Company’s board of directors adopted the 2017 Plan, which provided for the grant of qualified incentive stock options and nonqualified stock options, restricted stock or other awards to the Company’s employees and non-employees for the issuance or purchase of shares of the Company’s common stock. As of September 30, 2024 , there were no shares available for future grants under the 2017 Plan and a total of 3,709,118 shares of the Company’s common stock were subject to outstanding stock options issued under the 2017 Plan. The 2017 Plan is administered by the Company’s board of directors or a committee thereof to the extent the Company’s board of directors has delegated its power or authority under the 2017 Plan. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, except that the exercise price per share of stock options may not be less than 100 % of the fair market value of the common stock on the date of grant. Stock options awarded under the 2017 Plan expire 10 years after the grant date unless the board of directors sets a shorter term. Incentive stock options and nonqualified stock options granted to employees and non-employees typically vest over four years . Certain stock options provide for accelerated vesting if there is a change in control, as defined in the 2017 Plan. 2021 Incentive Award Plan The Company's board of directors adopted, and the Company’s stockholders approved, the 2021 Plan in July 2021. The 2021 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards, and subsequent to the IPO, all equity-based awards are granted under the 2021 Plan. The Company initially reserved 2,960,000 shares of its common stock for future issuance under the 2021 Plan, and such number of shares of common stock is subject to an annual increase on the first day of each calendar year, beginning on January 1, 2022 and ending on and including January 1, 2031, equal to the lesser of (i) 4 % of the aggregate number of shares of common stock outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as is determined by the board of directors. As of September 30, 2024, there were 3,886,711 shares available for future grants under the 2021 Plan, and a total of 5,957,508 shares of the Company’s common stock were subject to outstanding stock options issued under the 2021 Plan. The Company recorded stock-based compensation expense as research and development and general and administrative expenses in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Research and development $ 515 $ 1,093 $ 2,341 $ 3,358 General and administrative 1,208 1,187 4,026 3,322 Total stock-based compensation expense $ 1,723 $ 2,280 $ 6,367 $ 6,680 Stock Options A summary of option activity under the Company’s equity incentive plans during the nine months ended September 30, 2024 was as follows: Weighted Weighted Aggregate Number average contractual value (1) (in thousands) Outstanding as of January 1, 2024 8,780,737 $ 5.69 7.52 $ 5,033 Granted 3,974,475 3.23 Exercised ( 14,237 ) 1.75 Forfeited ( 2,272,471 ) 5.60 Expired ( 801,878 ) 8.80 Outstanding as of September 30, 2024 9,666,626 4.45 6.85 1,187 Vested and expected to vest as of September 30, 2024 9,666,626 4.45 6.85 1,187 Exercisable as of September 30, 2024 5,497,704 $ 4.66 5.22 $ 1,187 (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money as of September 30, 2024 . Included in the stock options granted during the nine months ended September 30, 2024 , the Company granted the Chief Executive Officer an option to purchase 314,326 shares of the Company’s common stock. The option vests as to 25 % of the underlying shares on February 7, 2025 and as to the remainder in twelve equal quarterly installments thereafter, such that the option will be fully vested and exercisable on February 7, 2028 . In the event the Board determines that the consummation of a transaction for business development purposes satisfies the corporate goals for business development collaborations, any outstanding, unvested portion of the option will fully vest on the first anniversary of the consummation of such transaction. The potential acceleration of vesting due to the transaction is a performance condition and as of September 30, 2024, the performance condition has not been achieved. Therefore, the Company recognizes the stock-based compensation expense for the stock option over the explicit service period. The assumptions used in the Black-Scholes option-pricing model for all the stock options granted were as follows : Nine months ended September 30, 2024 Expected volatility 75.00 % - 87.29 % Weighted-average risk-free interest rate 4.16 % Expected dividend yield 0.00 % Weighted-average expected term (in years) 5.89 The weighted-average grant date fair value per share of stock options granted during the nine months ended September 30, 2024 was $ 2.21 . The aggregate intrinsic value of stock options exercised during the nine months ended September 30, 2024 was $ 0.03 million. As of September 30, 2024, there was $ 10.4 million of unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of approximately 1.9 years. 2021 Employee Stock Purchase Plan The Company's board of directors adopted, and the Company’s stockholders approved, the Employee Stock Purchase Plan (the “2021 ESPP”) in July 2021. The purpose of the 2021 ESPP is to provide eligible employees with an opportunity to purchase shares of the Company's common stock through accumulated contributions. The 2021 ESPP permits participants to purchase shares of common stock through contributions (generally in the form of payroll deductions) of up to an amount of their eligible compensation determined by the administrator. Subject to certain other limitations or unless otherwise determined by the administrator, a participant may purchase a maximum of 100,000 shares of common stock during an offering period. The offering periods under the 2021 ESPP will begin on such date as determined by the administrator and not exceed 27 months. Amounts deducted and accumulated by the participant are used to purchase shares of common stock on each exercise date. The purchase price of the shares will be determined by the administrator but in no event will be less than 85 % of the lower of the fair market value of common stock on the enrollment date or on the exercise date. Participants may end their participation at any time during an offering period and will be paid their accrued contributions that have not yet been used to purchase shares of common stock, provided that they give notice of such withdrawal within the time period required by the administrator. Participation ends automatically upon termination of employment with the Company. The 2021 ESPP provides for an annual increase to the number of shares available for issuance thereunder on the first day of each calendar year beginning on January 1, 2022 and ending on and including January 1, 2031, by an amount equal to the lesser of (i) 1 % of the aggregate number of shares of common stock outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as is determined by our board of directors, provided that no more than 6,450,000 shares of our common stock may be issued under the 2021 ESPP. As of September 30, 2024, the Company had not consummated an offering period under the 2021 ESPP. As of September 30, 2024, the Company had 1,990,108 shares of common s tock available for issuance under the 2021 ESPP.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	15. Net Loss per Share Attributable to Common Stockholders For periods in which the Company reports a net loss attributable to common stockholders, potentially dilutive securities have been excluded from the computation of diluted net loss per share as their effects would be anti-dilutive. Therefore, the weighted average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders $ ( 16,444 ) $ ( 22,248 ) $ ( 52,878 ) $ ( 77,214 ) Denominator: Weighted average number of common stock, basic and diluted 55,155,583 55,140,058 55,153,699 53,629,468 Net loss per common stock attributable to common stockholders, basic and diluted $ ( 0.30 ) $ ( 0.40 ) $ ( 0.96 ) $ ( 1.44 ) The Company excluded the following potential common stock, presented based on amounts outstanding at period end, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect: As of September 30, 2024 2023 Outstanding options to purchase common stock 9,666,626 9,168,502

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	16. Income Taxes During the three and nine months ended September 30, 2024 and 2023, the Company recorded a full valuation allowance on federal and state deferred tax assets since management does not forecast the Company to be in a taxable position in the near future. The rules dealing with U.S. federal, state and local income taxation are constantly under review by persons involved in the legislative process and by the IRS and the U.S. Treasury Department. Changes to tax laws (which changes may have retroactive application) could adversely affect our stockholders or us. The Company assesses the impact of various tax reform proposals and modifications to existing tax treaties in all jurisdictions where it has operations to determine the potential effect on its business and any assumptions it has made about its future taxable income. The Company cannot predict whether any specific proposals will be enacted, the terms of any such proposals or what effect, if any, such proposals would have on its business if they were to be enacted.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2024
Related Party Transactions [Abstract]
Related Party Transactions	17. Related Party Transactions For the three and nine months ended September 30, 2024 and 2023, related party transactions consisted primarily of rent payments and reimbursable expenses, offset by sublease income received from related parties. The majority ownership of the Company is held by Flagship, in which it holds shares representing approximately 53 % of th e Company’s outstanding voting stock as of September 30, 2024. Flagship historically provided management services to the Company, and the Company reimburses Flagship for certain expenses, including insurance and benefits, and related fees, and software licenses incurred on the Company’s behalf. For the three months ended September 30, 2024 and 2023, the Company inc urred zero and $ 0.1 million, respectively, p rimarily for reimbursable expenses. For the nine months ended September 30, 2024 and 2023, the Company incurred an immaterial amount and $ 0.4 million, respectively, primarily for reimbursable expenses. These expenses are recorded as general and administrative expense in the accompanying condensed consolidated statements of operations and comprehensive loss. As of September 30, 2024 and December 31, 2023, there was zero and an immaterial amount of outstanding pa yments due to Flagship, respectively. In July 2023 the Company entered into three Shared Space Agreements with related parties Metaphore, Apriori, and Prologue. These companies are affiliates of Flagship, a controlling stockholder of the Company. P ursuant to the agreements, the Company agreed to sublease an aggregate of approximately 22,500 rentable square feet of office and laboratory space at 140 First Street. In June 2024, the Company entered into amendments to the Shared Space Arrangements with the Subtenants, which increased the total sublease to 30,447 rentable square feet effective July 1, 2024. On August 27, 2024, the Company entered into an Amended and Restated Shared Space Arrangement with each of the Subtenants, which increased the total sublease to 33,447 rentable square feet effective September 1, 2024, with further increases in the future as defined in the arrangements. On August 1, 2024, the Company entered into a Shared Space Arrangement with FL 97, pursuant to which the Company agreed to sublease approximately 10,866 rentable square feet, for laboratory space located on the first floor at 140 First Street, Cambridge, Massachusetts. On August 27, 2024, the Company entered into Shared Space Arrangements with FL 101 and FL 104, pursuant to which the Company agreed to sublease 3,550 rentable square feet, for laboratory space located at 140 First Street, effective September 1, 2024, with increases in the future as defined in the agreement. Under the Shared Space Arrangements, the Company has received aggregate rental income of $ 1.8 million and $ 3.9 million for the three and nine months ended September 30, 2024 , respectively. Such rental income was reflected as a reduction of research and development expense and general and administrative expense in the accompanying condensed consolidated statements of operations and comprehensive loss. There were $ 0.2 million and zero of outstanding receivables due from the subtenants as of September 30, 2024 and December 31, 2023, respectively. In September 2020, the Company sublet the entire space of its 325 Vassar Street facility, approximately 19,404 square feet, to Sail Bio (formerly known as LARONDE, Inc. and VL50, Inc.), which is an affiliate of Flagship. The rental rate for the sublease arrangement is equal to the Company’s rental obligation per the agreement with BMR-325 Vassar Street LLC, reduced by the sublease income received from Cygnal Therapeutics, Inc. (“Cygnal”). The sublessee is obligated to pay all real estate taxes and costs related to the subleased premises, including cost of operations, maintenance, repair, replacement and property management. The sublease expired at the end of the Company's lease agreement with the landlord in September 2024 with no extension. During each of the three months ended September 30, 2024 and 2023, the Company received rental income and reimbursement of related expenses of $ 0.6 million. Du ring each of the nine months ended September 30, 2024 and 2023, the Company received rental income and reimbursement of related expenses of $ 1.8 million and $ 1.9 million , respectively, which was recorded within research and development expense and general and administrative expense in the condensed consolidated statements of operations and comprehensive loss. There were no outstanding receivables due from Sail Bio as of September 30, 2024 and December 31, 2023. In July 2020, the Company entered into a Shared Space Arrangement (the Arrangement) with Sail Bio to share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts. In January 2022, the Company entered into an amendment to the Arrangement with Sail Bio to exercise the option to renew the lease through July 2023 . In connection with the amendment, the Company made an upfront payment of $ 2.9 million in January 2022, to cover the rent payments for the extended lease term. The Company did not subsequently renew the lease, and the lease expired at the end of July 2023. Additionally, upon the expiration of the extended lease term, the Company received $ 0.65 million from Sail Bio for all furniture, fixtures and equipment owned by the Company that will remain at the lease property. The net book value of these assets was determined to be $ 0.4 million, and the Company recognized a gain on this disposal of $ 0.2 million in June 2023. Refer to other related party transactions as described in Note 9, Leases , Note 11, License Agreements and Note 12, Collaboration Agreements .

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
Employee Benefits	18. Employee Benefits In 2018, the Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code, or 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. On May 1, 2022, the Company began matching 50 % of employee contributions of up to 6 % of eligible compensation contributed on a pre-tax and/or Roth after-tax basis to the 401(k) Plan. During the nine months ended September 30, 2024 and 2023, the Company made matching contributions totaling $ 0.4 million and $ 0.5 million, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying condensed consolidated unaudited financial statements include the accounts of Omega Therapeutics, Inc. and its wholly owned subsidiary, Omega Therapeutics Security Corporation, which is a Massachusetts subsidiary . All intercompany transactions and balances have been eliminated in consolidation.
Reclassification	Reclassification The Company reclassified the related party expenses in the prior year to research and development and general and administrative expenses in the condensed consolidated statements of operations and comprehensive loss to conform to the current year's presentation.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated unaudited financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses, and the disclosure of contingent assets and liabilities as of and during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates and assumptions reflected in these condensed consolidated unaudited financial statements include, but are not limited to, the selection of useful lives of property and equipment, the incremental borrowing rate used in the calculation of lease liabilities, research and development accruals, and certain judgments regarding revenue recognition and stock-based compensation. Actual results could differ from these estimates. Changes in estimates are reflected in reported results in the period in which they become known.
Recent accounting pronouncements not yet adopted	Recent accounting pronouncements not yet adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280) , Improvements to Reportable Segment Disclosures . The new standard requires enhanced disclosures about segment information and significant segment expenses. It does not change how a public entity identifies its operating segments. ASU 2023-07 is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. The new standard should be applied retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact on its consolidated financial statements. In December 2023, the FASB issued 2023-09, Income Taxes (Topic 740), Improvements to Income Tax Disclosures . The new standard requires public business entities to disclose information about income taxes paid, specific categories in the rate reconciliation, and additional information for reconciling items that meet a quantitative threshold. The guidance should be applied on a prospective basis. For public business entities, ASU 2023-08 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. For all other entities, the standard is effective for annual periods beginning after December 15, 2025. The Company is currently evaluating the impact on its consolidated financial statements.

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Securities	The following table summarizes the Company’s marketable securities at December 31, 2023 (in thousands): December 31, 2023 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 5,000 $ ( 14 ) $ 4,986

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2024
Prepaid Expense and Other Assets, Current [Abstract]
Summary of Prepaid Expenses and other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2024 2023 Clinical development $ 4,557 $ 5,168 Research and development 1,168 1,609 Insurance 922 716 Other receivables 477 855 Software 354 303 Restricted cash 341 — Facilities — 1,242 Other 271 431 Prepaid expenses and other current assets $ 8,090 $ 10,324

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2024
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consists of the following (in thousands): September 30, December 31, 2024 2023 Lab equipment $ 7,472 $ 6,633 Furniture and fixtures 1,636 1,636 Leasehold improvements 1,431 1,290 Computer equipment 1,226 1,226 Construction in process — 588 Total property and equipment 11,765 11,373 Less accumulated depreciation ( 7,267 ) ( 6,062 ) Property and equipment, net $ 4,498 $ 5,311

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2024
Accrued Liabilities, Current [Abstract]
Summary of Accrued Expenses	Accrued expenses consist of the following (in thousands): September 30, December 31, 2024 2023 Employee related expenses $ 2,664 $ 4,482 Professional and consulting fees 1,130 716 Manufacturing costs 483 547 Research costs 217 1,395 Interest — 147 Other 156 627 Accrued expenses $ 4,650 $ 7,914

Term Loan (Tables)

Term Loan (Tables)	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Summary of Outstanding Term Loan Balance	As of September 30, 2024, $ 4.0 million of the net carrying amount of the term loan was classified as short-term and $ 11.6 million was classified as long-term based on the repayment start date. The Company’s outstanding term loan balance was comprised of the following (in thousands): September 30, December 31, 2024 2023 Principal $ 15,667 $ 19,000 Unamortized debt discount ( 80 ) ( 115 ) Net carrying amount $ 15,587 $ 18,885
Summary of Interest Expense Recognized Related to Term loan	The following table sets forth total interest expense recognized related to the term loan (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Contractual interest expense $ 373 $ 469 $ 1,185 $ 1,336 Amortization of debt issuance costs and debt discount 11 13 35 33 Total interest expense $ 384 $ 482 $ 1,220 $ 1,369
Schedule of Principal Amount in Connection With Term Loan	The Company is required to repay the following principal amounts in connection with its term loan (in thousands): 2024 (remaining 3 months) $ 1,000 2025 4,000 2026 4,000 2027 6,667 Total $ 15,667

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Summary of Fair Value of Financial Instruments	The fair value of the Company’s financial instruments is summarized in the table below (in thousands): September 30, 2024 Level 1 Level 2 Level 3 Total Financial Liabilities Success fee obligation $ — $ — $ 300 $ 300 December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 10,402 $ — $ — $ 10,402 Corporate Debt Securities — 4,986 — 4,986 Total $ 10,402 $ 4,986 $ — $ 15,388 Financial Liabilities Success fee obligation $ — $ — $ 300 $ 300
Summary of Significant Quantitative Inputs Used to Determine Valuation of Success Fee Obligation	The following reflects the significant quantitative inputs used to determine the valuation of the success fee obligation as of September 30, 2024 and December 31, 2023: September 30, 2024 December 31, 2023 Discount rate 8.5 % 9.0 % Expected timing of achieving liquidity events (years) 0.3 1.0 Probability of achieving liquidity events 100 % 100 %

Collaboration Agreements (Table

Collaboration Agreements (Tables)	9 Months Ended
	Sep. 30, 2024
Collaboration Agreement [Abstract]
Summary of Contract Assets and Liabilities	The following table summarizes the Company's contract assets and liabilities (in thousands): September 30, December 31, 2024 2023 Contract assets: Accounts receivable $ 333 $ 6,131 Unbilled revenue — 89 Contract liabilities: Deferred revenue- current 1,054 — Deferred revenue- noncurrent 2,968 —

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Summary of Components of Lease Expense	The following table summarizes the components of lease expense for the three and nine months ended September 30, 2024 and 2023 (in thousands). Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Operating lease expense $ 3,871 $ 3,866 $ 11,496 $ 7,854 Variable lease expense 1,088 945 3,225 1,844 Total lease expense $ 4,959 $ 4,811 $ 14,721 $ 9,698
Summary of Weighted Average Remaining Lease Term And Discount Rate Related to Leases	The weighted average remaining lease term and discount rate related to the Company's leases were as follows: As of September 30, 2024 December 31, 2023 Weighted average remaining lease term (years) 13.9 14.5 Weighted average discount rate 8.9 % 8.9 %
Summary of Supplemental Cash Flow Information Relating to Leases	Supplemental cash flow information relating to the Company's leases for the nine months ended September 30, 2024 and 2023 were as follows (in thousands): Nine Months Ended September 30, 2024 2023 Cash paid for amounts included in the measurement of lease liabilities $ 9,144 $ 4,473 Operating lease assets obtained in exchange for lease liabilities $ — $ 110,424
Summary of Estimated Minimum Lease Payments	As of September 30, 2024, the estimated minimum lease payments for 140 First Street for each of the years ending December 31 were as follows (in thousands): 2024 (remaining 3 months) $ 3,070 2025 12,492 2026 12,819 2027 13,155 2028 13,501 Thereafter 144,664 Total minimum lease payments 199,701 Less: Imputed interest ( 87,155 ) Present value of operating lease liabilities $ 112,546

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Summary of Stock-based Compensation Expense	The Company recorded stock-based compensation expense as research and development and general and administrative expenses in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Research and development $ 515 $ 1,093 $ 2,341 $ 3,358 General and administrative 1,208 1,187 4,026 3,322 Total stock-based compensation expense $ 1,723 $ 2,280 $ 6,367 $ 6,680
Summary of Option Activity	A summary of option activity under the Company’s equity incentive plans during the nine months ended September 30, 2024 was as follows: Weighted Weighted Aggregate Number average contractual value (1) (in thousands) Outstanding as of January 1, 2024 8,780,737 $ 5.69 7.52 $ 5,033 Granted 3,974,475 3.23 Exercised ( 14,237 ) 1.75 Forfeited ( 2,272,471 ) 5.60 Expired ( 801,878 ) 8.80 Outstanding as of September 30, 2024 9,666,626 4.45 6.85 1,187 Vested and expected to vest as of September 30, 2024 9,666,626 4.45 6.85 1,187 Exercisable as of September 30, 2024 5,497,704 $ 4.66 5.22 $ 1,187 (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money as of September 30, 2024 .
Summary of Assumptions Used in Black Scholes Option Pricing Model for All Stock Options	The assumptions used in the Black-Scholes option-pricing model for all the stock options granted were as follows : Nine months ended September 30, 2024 Expected volatility 75.00 % - 87.29 % Weighted-average risk-free interest rate 4.16 % Expected dividend yield 0.00 % Weighted-average expected term (in years) 5.89

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Summary of the Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders $ ( 16,444 ) $ ( 22,248 ) $ ( 52,878 ) $ ( 77,214 ) Denominator: Weighted average number of common stock, basic and diluted 55,155,583 55,140,058 55,153,699 53,629,468 Net loss per common stock attributable to common stockholders, basic and diluted $ ( 0.30 ) $ ( 0.40 ) $ ( 0.96 ) $ ( 1.44 )
Schedule of Anti-Dilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential common stock, presented based on amounts outstanding at period end, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect: As of September 30, 2024 2023 Outstanding options to purchase common stock 9,666,626 9,168,502

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Aug. 31, 2023	Feb. 28, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, shares issued			55,159,219		55,144,982
Cash and cash equivalents			$ 30,377	$ 81,768	$ 68,443
Recurring losses			52,900
Net cash used in operations			$ (38,492)	$ (74,420)
Registered Direct Offering
Nature Of Business And Basis Of Presentation [Line Items]
Offering price per share		$ 5.78
Common stock issued and sold		6,920,415
Net proceeds from direct offering		$ 39,700
ATM Offerings
Nature Of Business And Basis Of Presentation [Line Items]
Aggregate value of common stock issue and sell	$ 60,000

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Details) - Marketable Securities $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-Sale [Line Items]
Marketable Securities, Amortized cost	$ 5,000
Marketable Securities, Gross unrealized losses	(14)
Marketable Securities, Fair value	$ 4,986

Marketable Securities - Additio

Marketable Securities - Additional Information (Details)	Sep. 30, 2024 USD ($)
Investments, Debt and Equity Securities [Abstract]
Marketable securities hold	$ 0

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Prepaid Expense and Other Assets, Current [Abstract]
Clinical development	$ 4,557	$ 5,168
Research and development	1,168	1,609
Insurance	922	716
Other receivables	477	855
Software	354	303
Restricted cash	341
Facilities		1,242
Other	271	431
Prepaid expenses and other current assets	$ 8,090	$ 10,324

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Total property and equipment	$ 11,765	$ 11,373
Less accumulated depreciation	(7,267)	(6,062)
Property and equipment, net	4,498	5,311
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	7,472	6,633
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	1,636	1,636
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	1,431	1,290
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,226	1,226
Construction in Process
Property Plant And Equipment [Line Items]
Total property and equipment		$ 588

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Depreciation	$ 400	$ 400	$ 1,320	$ 1,146

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Accrued Liabilities, Current [Abstract]
Employee related expenses	$ 2,664	$ 4,482
Professional and consulting fees	1,130	716
Manufacturing costs	483	547
Research costs	217	1,395
Interest		147
Other	156	627
Accrued expenses	$ 4,650	$ 7,914

Accrued Expenses - Additional I

Accrued Expenses - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2024	Mar. 31, 2024
Accrued Liabilities, Current [Abstract]
Employee related expenses inclusive of severance and other costs	$ 0.7	$ 0.8

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - USD ($)			9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 22, 2023	Sep. 30, 2024	Dec. 31, 2023	Mar. 09, 2018
Debt [Line Items]
Aggregate principal amount			$ 15,667,000	$ 19,000,000
Unamortized debt discount			80,000	115,000
Net carrying amount of term loan classified as short-term			4,000,000
Net carrying amount of term loan classified as long-term			11,587,000	14,885,000
Accrued interest on term loan			$ 0	$ 147,000
Maximum
Debt [Line Items]
Effective interest rate on the liability component			9.27%
Minimum
Debt [Line Items]
Effective interest rate on the liability component			5.53%
Loan Agreement | Pacific Western Bank
Debt [Line Items]
Maximum borrowing capacity					$ 8,000,000
Fourth Amendment | Pacific Western Bank | Maximum
Debt [Line Items]
Success fee payable		$ 200,000
Fifth Amendment | Pacific Western Bank
Debt [Line Items]
Line of credit facility, Floating annual interest rate		0.50%
Line of credit facility, Interest rate during period		5.50%
Proceeds from bank		$ 50,000,000
Monthly principal payments plus interest	$ 300,000
Maturity date		Sep. 30, 2027	Sep. 30, 2028
Debt issuance costs		$ 15,000
Principal repayment start date			Sep. 30, 2023
Minimum unrestricted cash requirement		5,000,000
Minimum prepayment amount for termination of unrestricted cash		5,000,000
Minimum principal balance requirement		10,000,000
Fifth Amendment | Pacific Western Bank | Maximum
Debt [Line Items]
Monthly principal payments plus interest		4,000,000
Fifth Amendment | Pacific Western Bank | Minimum
Debt [Line Items]
Success fee payable		$ 100,000

Term Loan - Summary of Outstand

Term Loan - Summary of Outstanding Term Loan Balance (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Disclosure [Abstract]
Principal	$ 15,667	$ 19,000
Unamortized debt discount	(80)	(115)
Net carrying amount	$ 15,587	$ 18,885

Term Loan - Summary of Interest

Term Loan - Summary of Interest Expense Recognized Related to Term loan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt Disclosure [Abstract]
Contractual interest expense	$ 373	$ 469	$ 1,185	$ 1,336
Amortization of debt issuance costs and debt discount	11	13	35	33
Total interest expense	$ 384	$ 482	$ 1,220	$ 1,369

Term Loan - Schedule of Princip

Term Loan - Schedule of Principal Amount in Connection With Term Loan (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Disclosure [Abstract]
2024 (remaining 3 months)	$ 1,000
2025	4,000
2026	4,000
2027	6,667
Total	$ 15,667	$ 19,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Financial Assets
Total financial assets		$ 15,388
Success Fee Obligation
Financial Liabilities
Total financial liabilities	$ 300	300
Money Market Funds
Financial Assets
Total financial assets		10,402
Corporate Debt Securities
Financial Assets
Total financial assets		4,986
Level 1
Financial Assets
Total financial assets		10,402
Level 1 | Money Market Funds
Financial Assets
Total financial assets		10,402
Level 2
Financial Assets
Total financial assets		4,986
Level 2 | Corporate Debt Securities
Financial Assets
Total financial assets		4,986
Level 3 | Success Fee Obligation
Financial Liabilities
Total financial liabilities	$ 300	$ 300

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Details) $ in Millions	Sep. 30, 2024 USD ($)	Dec. 31, 2023
Fourth and Fifth Amendments | Pacific Western Bank
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee payable	$ 0.3
Measurement Input Probability Of Achieving Liquidity Events [Member]
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	1	1

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Summary of Significant Quantitative Inputs Used to Determine Valuation of Success Fee Obligation (Details)	Sep. 30, 2024 yr	Dec. 31, 2023 yr
Discount Rate
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	0.085	0.09
Expected Timing of Achieving Liquidity Events (years)
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	0.3	1
Probability of Achieving Liquidity Events
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	1	1

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 01, 2024

Aug. 27, 2024

Aug. 01, 2024 Space

Jul. 31, 2024 USD ($)

Jul. 01, 2024

Jul. 12, 2023 Space

Jul. 11, 2023 Space

May 03, 2023 $ / ft²

Nov. 04, 2021 USD ($) ft² Phase

Dec. 31, 2023 USD ($)

Jul. 31, 2023 ft² Space

Jan. 31, 2022

Jul. 31, 2020 ft²

Sep. 30, 2024 USD ($) Space

Sep. 30, 2023 USD ($)

Sep. 30, 2024 USD ($) ft² Option

Sep. 30, 2023 USD ($)

Dec. 31, 2020 Sublease

Dec. 31, 2019 Sublease

Leases [Line Items]

Lease expiration date

Sep. 30, 2024

Lessee operating lease, description

share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts.

Number of phases | Phase

2

Base rent per square foot | $ / ft²

1

Number of shared space arrangements | Space

3

Lease payment

$ 3,871

$ 3,866

$ 11,496

$ 7,854

Right-of-use assets

$ 108,736

109,245

109,245

Lease liabilities

112,546

112,546

Lease liabilities, current

11,300

11,919

11,919

Lease liabilities, non-current

$ 98,243

100,627

100,627

Lease expense

4,959

4,811

14,721

9,698

Thermo Fisher Financial Services, Inc.

Leases [Line Items]

Sale leaseback, date

December 2023

Sale leaseback term

5 years

Sale leaseback, terms

In December 2023, the Company entered into a sale-leaseback arrangement with Thermo Fisher Financial Services, Inc. to provide $2.6 million in cash proceeds for previously acquired furniture and equipment.

Cash proceeds from furniture and equipment

$ 2,600

Option to purchase the assets

option to purchase the assets for $1 at the end of the term.

Monthly payments

$ 53

Finance obligation current

$ 500

$ 500

Finance Obligation, Current, Statement of Financial Position

Liabilities, Current

Liabilities, Current

Finance obligation noncurrent

$ 1,800

$ 1,800

Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]

Liabilities

Liabilities

Research and Development Expenses

Leases [Line Items]

Lease expense

$ 3,500

4,000

$ 10,600

7,800

General and Administrative Expenses

Leases [Line Items]

Lease expense

$ 1,500

$ 800

4,100

$ 1,900

140 First Street Lease Agreement

Leases [Line Items]

Lessee operating lease, description

The operating lease commenced on May 1, 2023 for the fifth floor premises and August 1, 2023 for the first floor premises for accounting purposes. The lease term for each of the floor premises is fifteen years from the respective commencement date, subject to certain extension rights.

Rentable square feet of office and laboratory | ft²

89,246

Base rent per square foot | $ / ft²

116

Tenant improvement allowance per rentable square foot | $ / ft²

300

Lease term interest rate

8%

Landlord second additional improvement allowance

$ 3,300

Base rent annual upward adjustment percentage

3%

Lease payment

$ 800

Shared Space Arrangement

Leases [Line Items]

Lease arrangement description

commencing on the Effective Date.

commencing August 2024 and ending July 2027, with two options to extend for a period of 24 months each.

Percentage of sublease space

12.20%

Sublease, option to extend

two options to extend for a period of 24 months each.

Number of shared space arrangements | Space

1

2

1

6

Rentable area of office and laboratory space agreed to sublease | ft²

22,500

Commitment for subtenants

$ 14,200

Shared Space Arrangement | Research and Development Expense and General and Administrative Expense

Leases [Line Items]

Sublease rental income received

$ 1,800

$ 3,900

Phase I

Leases [Line Items]

Rentable square feet of office and laboratory | ft²

78,380

Phase II

Leases [Line Items]

Rentable square feet of office and laboratory | ft²

10,866

Sail Biomedicines, Inc

Leases [Line Items]

Lease expiration date

Jul. 31, 2023

Lessee operating lease, description

share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts

Number of options to extend terms | Option

2

Term of lease arrangement period

24 months

Lease arrangement description

The Arrangement commenced on August 1, 2020, with an expiration date of July 31, 2022 and two options to extend the term of the Arrangement for a period of 24 months each.

Area of leased space | ft²

69,867

69,867

LARONDE, Inc.

Leases [Line Items]

Number of sublease agreements with related parties | Sublease

2

Cygnal

Leases [Line Items]

Number of sublease agreements with related parties | Sublease

2

Metaphore

Leases [Line Items]

Monthly license fee proportionate share, percentage

16.20%

12%

Metaphore | November Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

17.50%

Metaphore | April Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

18.70%

Metaphore | Termination Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

19.20%

Apriori

Leases [Line Items]

Monthly license fee proportionate share, percentage

11.30%

8.40%

Apriori | November Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

12.60%

Apriori | April Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

13.90%

Apriori | Termination Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

14.30%

Labs

Leases [Line Items]

Monthly license fee proportionate share, percentage

11.30%

8.40%

Labs | November Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

12.60%

Labs | April Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

13.90%

Labs | Termination Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

14.30%

FL 101 | April Effective Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

3.60%

FL 101 | Termination Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

6.40%

FL 101 | FL 104 Termination Date

Leases [Line Items]

Monthly license fee proportionate share, percentage

1%

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Lessee Disclosure [Abstract]
Operating lease expense	$ 3,871	$ 3,866	$ 11,496	$ 7,854
Variable lease expense	1,088	945	3,225	1,844
Total lease expense	$ 4,959	$ 4,811	$ 14,721	$ 9,698

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Term And Discount Rate Related to Leases (Details)	Sep. 30, 2024	Dec. 31, 2023
Leases [Line Items]
Weighted average remaining lease term (years)	13 years 10 months 24 days	14 years 6 months
Weighted average discount rate	8.90%	8.90%

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Relating to Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Leases [Line Items]
Cash paid for amounts included in the measurement of lease liabilities	$ 9,144	$ 4,473
Operating lease assets obtained in exchange for lease liabilities		$ 110,424

Leases - Summary of Estimated M

Leases - Summary of Estimated Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Leases [Abstract]
2024 (remaining 3 months)	$ 3,070
2025	12,492
2026	12,819
2027	13,155
2028	13,501
Thereafter	144,664
Total minimum lease payments	199,701
Less: Imputed interest	(87,155)
Present value of operating lease liabilities	$ 112,546

License Agreements - Additional

License Agreements - Additional Information (Details)		1 Months Ended			3 Months Ended		9 Months Ended
	Oct. 12, 2022 USD ($)	Mar. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)	May 31, 2019 USD ($) Product	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
License Agreements [Line Items]
License maintenances fees					$ 100,000	$ 100,000	$ 200,000	$ 300,000
Research and development					12,807,000	16,506,000	$ 41,162,000	61,638,000
WIBR Exclusive License Agreement
License Agreements [Line Items]
Number of licensed products | Product				3
Percentage of non-royalty payments description							This percentage ranges from zero to low double-digits and will be based upon the stage of development of the licensed product at the time such sublicense is executed.
WIBR Exclusive License Agreement | Maximum
License Agreements [Line Items]
Nonrefundable upfront fee paid.				$ 100,000
Annual license maintenance fees				100,000
Milestone payments				$ 1,700,000
WIBR Co-Exclusive License Agreement
License Agreements [Line Items]
Number of licensed products | Product				3
WIBR Co-Exclusive License Agreement | Maximum
License Agreements [Line Items]
Nonrefundable upfront fee paid.				$ 100,000
Annual license maintenance fees				100,000
Milestone payments				1,900,000
Annual fees for each sublicense agreement				$ 100,000
Development and Option Agreement
License Agreements [Line Items]
Reimbursements for development and material costs incurred by Acuitas			$ 400,000
Development and Option Agreement | First Non-exclusive License
License Agreements [Line Items]
Annual technology access fee			1,500,000
Development and Option Agreement | Second Non-exclusive License
License Agreements [Line Items]
Annual technology access fee			$ 1,750,000
Acuitas License Agreement
License Agreements [Line Items]
Milestone payments							$ 0	0
Option exercise fee		$ 1,500,000
Potential clinical and regulatory milestone payments aggregate amount entitled to receive Acuitas		$ 18,000,000
Research and development							100,000	100,000
Acuitas License Agreement | Maximum
License Agreements [Line Items]
Research and development					100,000	100,000
Nitto
License Agreements [Line Items]
Milestone payments							0	0
Research and development	$ 1,000,000				0	$ 400,000	0	$ 900,000
Upfront payment	1,000,000
Nitto | Maximum
License Agreements [Line Items]
Future payments based upon the achievement of specified development, regulatory and sales milestones	$ 83,000,000
Related Party
License Agreements [Line Items]
Other Liabilities					$ 0		$ 0		$ 0

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended				9 Months Ended
	Jan. 31, 2024	Nov. 30, 2021	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development activities			$ 12,807,000		$ 16,506,000		$ 41,162,000	$ 61,638,000
606 Disclosures
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Current deferred revenue			1,054,000				1,054,000
Non Current deferred revenue			2,968,000				2,968,000
Novo Nordisk
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of cost reimbursement receivable to fund research and development activities	$ 21,600,000
Transaction price							26,700,000
Nonrefundable upfront payment	$ 5,100,000
Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement period		5 years
Transaction price							7,000,000
Increase in transaction price				$ 100,000	2,400,000	$ 1,900,000
Decrease in transaction price			900,000
Original transaction price for inception of contract							3,500,000
Research and development activities							0
Research and collaboration revenue			300,000		800,000		1,900,000	2,100,000
Current deferred revenue			1,000,000				1,000,000
Collaboration Agreement | 606 Disclosures
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total collaboration revenue			2,600,000		800,000		7,100,000	2,100,000
Collaboration Agreement | Novo Nordisk
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price			21,500,000				21,500,000
Research and collaboration revenue			2,300,000				5,200,000
Current deferred revenue			1,100,000				1,100,000
Non Current deferred revenue			$ 3,000,000				$ 3,000,000
Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Current deferred revenue					$ 100,000			$ 100,000

Collaboration Agreements - Summ

Collaboration Agreements - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable	$ 486	$ 1,006
606 Disclosures
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable	333	6,131
Unbilled revenue		$ 89
Deferred revenue- current	1,054
Deferred revenue- noncurrent	$ 2,968

Preferred and Common Stock - Ad

Preferred and Common Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 28, 2023	Sep. 30, 2024	Dec. 31, 2023	Dec. 31, 2021	Aug. 31, 2021
Class of Stock [Line Items]
Common stock issued and sold		55,159,219	55,144,982
Shares of common stock authorized		200,000,000	200,000,000
Common stock, par value		$ 0.001	$ 0.001
Shares of preferred stock authorized		10,000,000	10,000,000
Preferred stock, par value		$ 0.001	$ 0.001
Registered Direct Offering
Class of Stock [Line Items]
Offering price per share	$ 5.78
Common stock issued and sold	6,920,415
Net proceeds from direct offering	$ 39.7
Estimated offering expenses	$ 0.3
2017 Plan
Class of Stock [Line Items]
Common stock subject to outstanding stock options issued					3,709,118
2017 and 2021 Plans
Class of Stock [Line Items]
Common stock subject to outstanding stock options issued		9,666,626
Amended and Restated Certificate of Incorporation
Class of Stock [Line Items]
Shares of common stock authorized				200,000,000
Common stock, par value				$ 0.001
Shares of preferred stock authorized				10,000,000
Preferred stock, par value				$ 0.001

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended
	Jul. 31, 2021 shares	Jun. 30, 2017	Sep. 30, 2024 USD ($) Installments $ / shares shares
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance stock options vesting date			Feb. 07, 2025
Performance stock options exercisable date			Feb. 07, 2028
Number of installments | Installments			12
Common Stock | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted to the Chief Executive Officer			314,326
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant			0
Common stock subject to outstanding stock options issued			3,709,118
2017 Equity Incentive Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period		10 years
Vesting period		4 years
2017 Equity Incentive Plan | Stock Options | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock percentage		100%
2021 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant			3,886,711
Common stock subject to outstanding stock options issued			5,957,508
Common stock reserved for future issuance	2,960,000
Common stock shares reserved for future issuance increased percentage			4%
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for future issuance increased percentage			1%
Maximum shares purchased under employee stock purchase plan during offering period	100,000
Total number of shares of common stock available for issuance			1,990,108
2021 Employee Stock Purchase Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock percentage			85%
2021 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock subject to outstanding stock options issued			6,450,000
Expiration period			27 months
2017 Equity Incentive Plan and 2021 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted to the Chief Executive Officer			3,974,475
2017 Equity Incentive Plan and 2021 Incentive Award Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share of stock options granted | $ / shares			$ 2.21
Intrinsic value of stock options exercised | $			$ 30
Unrecognized compensation cost related to unvested stock options | $			$ 10,400
Unrecognized compensation cost, weighted-average period of recognition			1 year 10 months 24 days
Stock Options Vest on February 7, 2025 | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of performance stock options vest			25%

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,723	$ 2,280	$ 6,367	$ 6,680
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	515	1,093	2,341	3,358
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,208	$ 1,187	$ 4,026	$ 3,322

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Option Activity (Details) - 2017 Equity Incentive Plan and 2021 Incentive Award Plan $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options Outstanding, Beginning balance | shares	8,780,737
Number of options, Granted | shares	3,974,475
Number of options, Exercised | shares	(14,237)
Number of options, Forfeited | shares	(2,272,471)
Number of options, Expired | shares	(801,878)
Number of options Outstanding, Ending balance | shares	9,666,626	8,780,737
Number of options, Vested and expected to vest | shares	9,666,626
Number of options, Exercisable | shares	5,497,704
Weighted average exercise price Outstanding, Beginning balance | $ / shares	$ 5.69
Weighted average exercise price, Granted | $ / shares	3.23
Weighted average exercise price, Exercised | $ / shares	1.75
Weighted average exercise price, Forfeited | $ / shares	5.6
Weighted average exercise price, Expired | $ / shares	8.8
Weighted average exercise price Outstanding, Ending balance | $ / shares	4.45	$ 5.69
Weighted average exercise price, Vested and expected to vest | $ / shares	4.45
Weighted average exercise price, Exercisable | $ / shares	$ 4.66
Weighted average remaining contractual life (years), Outstanding	6 years 10 months 6 days	7 years 6 months 7 days
Weighted average remaining contractual life (years), Vested and expected to vest	6 years 10 months 6 days
Weighted average remaining contractual life (years), Exercisable	5 years 2 months 19 days
Aggregate intrinsic value, Outstanding | $	$ 1,187	$ 5,033
Aggregate intrinsic value, Vested and expected to vest | $	1,187
Aggregate intrinsic value, Exercisable | $	$ 1,187

Equity Incentive Plans - Summ_3

Equity Incentive Plans - Summary of Assumptions Used in Black Scholes Option Pricing Model for All Stock Options (Details)	9 Months Ended
	Sep. 30, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Weighted-average risk-free interest rate	4.16%
Expected dividend yield	0%
Weighted-average expected term (in years)	5 years 10 months 20 days
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility	75%
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility	87.29%

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Summary of the Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net loss attributable to common stockholders	$ (16,444)	$ (16,305)	$ (20,129)	$ (22,248)	$ (29,687)	$ (25,279)	$ (52,878)	$ (77,214)
Denominator:
Weighted-average common stock used in net loss per share attributable to common stockholders, basic	55,155,583			55,140,058			55,153,699	53,629,468
Weighted-average common stock used in net loss per share attributable to common stockholders, diluted	55,155,583			55,140,058			55,153,699	53,629,468
Net loss per common stock attributable to common stockholders, basic	$ (0.3)			$ (0.4)			$ (0.96)	$ (1.44)
Net loss per common stock attributable to common stockholders, diluted	$ (0.3)			$ (0.4)			$ (0.96)	$ (1.44)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Schedule of Anti-Dilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Outstanding Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	9,666,626	9,168,502

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)

1 Months Ended

3 Months Ended

6 Months Ended

9 Months Ended

Jul. 31, 2023 ft² Space

Jan. 31, 2022 USD ($)

Jul. 31, 2020 ft²

Sep. 30, 2024 USD ($)

Sep. 30, 2023 USD ($)

Jun. 30, 2023 USD ($)

Sep. 30, 2024 USD ($) ft²

Sep. 30, 2023 USD ($)

Aug. 27, 2024 ft²

Aug. 01, 2024 ft²

Jul. 01, 2024 ft²

Dec. 31, 2023 USD ($)

Sep. 30, 2020 ft²

Related Party Transaction [Line Items]

Number of shared space arrangements | Space

3

Lessee operating lease, description

share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts.

Net book value of assets

$ 400,000

Gain on disposal of assets

$ 200,000

Lease expiration date

Sep. 30, 2024

Shared Space Agreements

Related Party Transaction [Line Items]

Area of real estate property | ft²

3,550

10,866

30,447

Rentable area of office and laboratory space agreed to sublease | ft²

22,500

Amended and Restated Shared Space Arrangement

Related Party Transaction [Line Items]

Area of real estate property | ft²

33,447

Sail Biomedicines, Inc

Related Party Transaction [Line Items]

Area of real estate property | ft²

19,404

Outstanding receivables

$ 0

$ 0

$ 0

Lessee operating lease, description

share one-third of Sail Bio's 69,867 square feet of leased space at 20 Acorn Park Drive, Cambridge, Massachusetts

Area of leased space | ft²

69,867

69,867

Upfront payment

$ 2,900,000

Reimbursement for office furniture purchases

$ 650,000

Lease expiration date

Jul. 31, 2023

Subtenants

Related Party Transaction [Line Items]

Outstanding receivables

200,000

$ 200,000

0

Related Party

Related Party Transaction [Line Items]

Payments outstanding

0

0

$ 0

Related Party Expense | Shared Space Agreements

Related Party Transaction [Line Items]

Sublease rental income received

1,800,000

3,900,000

Related Party Expense | Sail Biomedicines, Inc

Related Party Transaction [Line Items]

Reimbursement of sublease rental related expense

600,000

$ 600,000

1,800,000

$ 1,900,000

Flagship | Related Party

Related Party Transaction [Line Items]

Payments outstanding

0

0

Flagship | Reimbursable Expenses | Related Party

Related Party Transaction [Line Items]

Related party expenses for management service

$ 0

$ 100,000

$ 400,000

$ 400,000

Omega Therapeutics, Inc. | Flagship

Related Party Transaction [Line Items]

Ownership percentage

53%

53%

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - 401(k) Plan - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Defined Contribution Plan Disclosure [Line Items]
Employee benefits description	the Company began matching 50% of employee contributions of up to 6% of eligible compensation contributed on a pre-tax and/or Roth after-tax basis to the 401(k) Plan.
Employer matching contribution, percentage of match	50%
Percentage of eligible compensation contributed	6%
Total contribution	$ 0.4	$ 0.5