Omega Therapeutics (OMGA) 10-Q 9 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
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		55,141,838
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, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 81,768	$ 70,615
Marketable securities	7,532	54,063
Accounts receivable, due from related party	397	618
Prepaid expenses and other current assets	12,201	12,294
Total current assets	101,898	137,590
Property and equipment, net	5,356	4,195
Operating lease right-of-use assets, net	110,094	3,668
Restricted cash	341	341
Other assets	119	204
Total assets	217,808	145,998
Current liabilities:
Accounts payable	2,403	3,107
Accrued expenses	7,518	13,841
Other current liabilities	300	159
Lease liabilities, current	12,595	1,524
Long-term debt, current portion	4,000	3,333
Total current liabilities	26,816	21,964
Lease liabilities, non-current	98,745	1,120
Long-term debt, net	15,864	16,603
Other liabilities	340	340
Total liabilities	141,765	40,027
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of September 30, 2023 and December 31, 2022; no shares issued and outstanding as of September 30, 2023 and December 31, 2022	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized as of September 30, 2023 and December 31, 2022; 55,141,838 and 48,072,517 issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	55	48
Additional paid-in capital	390,494	343,608
Accumulated other comprehensive loss	(86)	(479)
Accumulated deficit	(314,420)	(237,206)
Total stockholders' equity	76,043	105,971
Total liabilities and stockholders' equity	$ 217,808	$ 145,998

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
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	55,141,838	48,072,517
Common stock, shares outstanding	55,141,838	48,072,517

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Collaboration revenue from related party	$ 831	$ 595	$ 2,105	$ 1,338
Operating expenses:
Research and development	16,475	20,670	61,454	54,329
General and administrative	7,869	5,198	20,030	16,466
Related party expense, net	(610)	712	183	2,342
Total operating expenses	23,734	26,580	81,667	73,137
Loss from operations	(22,903)	(25,985)	(79,562)	(71,799)
Other Income (expense), net:
Interest income (expense), net	684	184	2,323	(26)
Other income (expense), net	(29)	2	25	(50)
Total other income (expense), net	655	186	2,348	(76)
Net loss	$ (22,248)	$ (25,799)	$ (77,214)	$ (71,875)
Net loss per common stock attributable to common stockholders, basic	$ (0.4)	$ (0.54)	$ (1.44)	$ (1.5)
Net loss per common stock attributable to common stockholders, diluted	$ (0.4)	$ (0.54)	$ (1.44)	$ (1.5)
Weighted-average common stock used in net loss per share attributable to common stockholders, basic	55,140,058	47,854,965	53,629,468	47,837,490
Weighted-average common stock used in net loss per share attributable to common stockholders, diluted	55,140,058	47,854,965	53,629,468	47,837,490
Comprehensive loss:
Net loss	$ (22,248)	$ (25,799)	$ (77,214)	$ (71,875)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	85	89	393	(855)
Comprehensive loss	$ (22,163)	$ (25,710)	$ (76,821)	$ (72,730)

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, 2021	$ 200,628	$ 48	$ 335,147	$ (62)	$ (134,505)
Balance (in shares) at Dec. 31, 2021		47,793,469
Issuance of common stock for options exercised	83		83
Issuance of common stock for options exercised, shares		46,576
Other comprehensive gain (loss)	(797)			(797)
Stock-based compensation	1,604		1,604
Net loss	(20,164)				(20,164)
Balance at Mar. 31, 2022	181,354	$ 48	336,834	(859)	(154,669)
Balance (in shares) at Mar. 31, 2022		47,840,045
Balance at Dec. 31, 2021	200,628	$ 48	335,147	(62)	(134,505)
Balance (in shares) at Dec. 31, 2021		47,793,469
Other comprehensive gain (loss)	(855)
Net loss	(71,875)
Balance at Sep. 30, 2022	133,651	$ 48	340,900	(917)	(206,380)
Balance (in shares) at Sep. 30, 2022		47,856,561
Balance at Mar. 31, 2022	181,354	$ 48	336,834	(859)	(154,669)
Balance (in shares) at Mar. 31, 2022		47,840,045
Issuance of common stock for options exercised	35		35
Issuance of common stock for options exercised, shares		12,463
Other comprehensive gain (loss)	(147)			(147)
Stock-based compensation	2,054		2,054
Net loss	(25,912)				(25,912)
Balance at Jun. 30, 2022	157,384	$ 48	338,923	(1,006)	(180,581)
Balance (in shares) at Jun. 30, 2022		47,852,508
Issuance of common stock for options exercised	4		4
Issuance of common stock for options exercised, shares		4,053
Other comprehensive gain (loss)	89			89
Stock-based compensation	1,973		1,973
Net loss	(25,799)				(25,799)
Balance at Sep. 30, 2022	133,651	$ 48	340,900	(917)	(206,380)
Balance (in shares) at Sep. 30, 2022		47,856,561
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 (loss)	251			251
Stock-based compensation	2,222		2,222
Net 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 (loss)	393			85
Net 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 (loss)	57			57
Stock-based compensation	2,178		2,178
Net 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 (loss)	85
Stock-based compensation	2,280		2,280
Net 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

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Operating activities
Net loss	$ (77,214)	$ (71,875)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,146	1,180
Amortization of debt issuance costs and debt discount	33	33
Amortization of operating lease right-of-use assets	3,844	2,695
Accretion of discounts on marketable securities	(209)	881
Change in fair value of success fee obligation	92	13
Gain on disposal of fixed assets	(232)	(3)
Stock-based compensation expense	6,680	5,631
Changes in operating assets and liabilities:
Accounts receivable due from related party	221	(372)
Prepaid expenses and other current assets	(664)	(8,361)
Other assets	86	(2,997)
Accounts payable	(704)	453
Accrued expenses and other current liabilities	(5,688)	(528)
Other liabilities	(1,811)	(1,028)
Net cash used in operating activities	(74,420)	(74,278)
Investing activities
Purchases of property and equipment	(1,758)	(1,088)
Purchases of marketable securities	(19,768)	(57,415)
Proceeds from maturities of marketable securities	66,901	22,791
Net cash provided by (used in) investing activities	45,375	(35,712)
Financing activities
Proceeds from equity offering	40,000
Payments of equity offering costs	(273)
Payments of financing fees	(15)
Proceeds from issuance of common stock under equity incentive plans	486	122
Net cash provided by financing activities	40,198	122
Net change in cash, cash equivalents and restricted cash	11,153	(109,868)
Cash, cash equivalents and restricted cash—beginning of period	70,956	186,823
Cash, cash equivalents and restricted cash—end of period	82,109	76,955
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	81,768	76,614
Restricted cash	341	341
Cash, cash equivalents and restricted cash—end of period	82,109	76,955
Supplemental disclosures of cash flow information
Cash paid for interest	1,279	814
Supplemental disclosure of noncash investing and financing activities
Purchases of property and equipment included in accounts payable and accrued expenses	$ 318	$ 368

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2023
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 clinical-stage 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 August 2021, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 8,300,976 shares of its common stock, including 900,976 shares pursuant to the partial exercise of the underwriters’ option to purchase additional shares, at a public offering price of $ 17.00 per share, for aggregate gross proceeds of $ 141.1 million. The Company received approximately $ 128.1 million in net proceeds after deducting underwriting discounts and commissions and other offering expenses payable by the Company. 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. The Company expects that its cash, cash equivalents and marketable securities of $ 89.3 million at September 30, 2023 will enable it to fund its operating expenses and capital expenditure requirements into the third quarter of 2024. The Company has had recurring losses since inception and incurred a loss of $ 77.2 million during the nine months ended September 30, 2023. Net cash used in operations for the nine months ended September 30, 2023 was $ 74.4 million. 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 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 pandemics or 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, 2023
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. 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, 2022 filed with the SEC on March 1, 2023 (the “2022 10-K”). The results for the nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. 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 fair values of certain financial instruments issued prior to the IPO (common stock, redeemable convertible preferred stock, and warrants), the fair value of the success fee obligation, the incremental borrowing rate used in the calculation of lease liabilities, research and development accruals, 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 2022 10-K. There was no significant change of accounting policy during the nine months ended September 30, 2023. Recently Issued Accounting Pronouncements On January 1, 2023, the Company adopted Accounting Standards Update No. 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments . The guidance is effective for fiscal years beginning after December 15, 2022. The adoption of the standard was immaterial to the accompanying condensed consolidated financial statements.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	3. Marketable Securities The following table summarizes the Company’s marketable securities (in thousands): September 30, 2023 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 7,618 $ ( 86 ) $ 7,532 December 31, 2022 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 54,542 $ ( 479 ) $ 54,063 The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity. At September 30, 2023 , the balance in accumulated other comprehensive loss was comprised solely of activity related to marketable securities. There were no realized gains or losses recognized on the sale or maturity of marketable securities for the nine months ended September 30, 2023 and, as a result, the Company did no t reclassify any amounts out of accumulated other comprehensive loss during the year. As of September 30, 2023 , the Company did not intend to sell, and was more than likely not required to sell, the marketable securities in a loss position before recovery of their amortized cost bases. As a result, the Company determined it did no t hold any investments with any other-than-temporary impairment at September 30, 2023 .

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 Clinical development $ 5,135 $ 5,232 Research and development 2,435 2,072 Rent 2,192 1,857 Other receivables 1,036 1,180 Insurance 857 1,020 Software 281 157 Other 265 776 Prepaid expenses and other current assets $ 12,201 $ 12,294

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 Lab equipment $ 6,734 $ 6,121 Furniture and fixtures 1,636 1,093 Leasehold improvements 1,464 1,378 Computer equipment 1,278 190 Construction in process 318 827 Total property and equipment 11,430 9,609 Less accumulated depreciation ( 6,074 ) ( 5,414 ) Property and equipment, net $ 5,356 $ 4,195 Depreciation expense was $ 0.4 million for each of the three months ended September 30, 2023 and 2022. Depreciation expense for the nine months ended September 30, 2023 and 2022 was $ 1.1 million and $ 1.2 million, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2023
Accrued Liabilities, Current [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consist of the following (in thousands): September 30, December 31, 2023 2022 Employee related expenses $ 3,776 $ 4,368 Research costs 1,138 3,876 Professional and consulting fees 1,270 743 Manufacturing costs 401 4,303 Interest 105 122 Other 828 429 Total $ 7,518 $ 13,841

Term Loan

Term Loan	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Term Loan	7. Term Loan On March 9, 2018 (“Closing Date”), the Company entered into the Loan Agreement with Pacific Western Bank (“PWB”) to initially borrow $ 8.0 million. On September 30, 2019, the Company entered into an amendment to the Loan Agreement (the “First Amendment”), in which PWB made an additional term loan to the Company in an aggregate principal amount of $ 12.0 million. On January 22, 2020, the Loan Agreement was further amended (the “Second Amendment”) to extend the principal repayment start date. The Loan Agreement was further amended on December 30, 2020 (the “Third Amendment”) to extend the principal repayment date. The maturity date of the term loan was extended to June 30, 2023 , and it was to be repaid beginning on June 30, 2021 in twenty-four equal installments, including interest at a floating annual rate equal to the greater of (i) 0.75 % above the prime rate then in effect and (ii) 6.00 %, due monthly starting the first month after December 30, 2020. On December 20, 2021, the Company entered into an amendment to the Loan Agreement (the "Fourth Amendment"), in which PWB made an additional term loan in an aggregate principal amount of $ 20.0 million. The proceeds of the term loan pursuant to the Fourth Amendment were first applied to the repayment in full of all outstanding principal and accrued interest on the then outstanding term loan of $ 12.0 million; the remaining cash proceeds of $ 8.0 million was used for general working capital and for capital expenditures purposes. On September 22, 2023, the Company entered into an amendment to the Loan Agreement (the "Fifth Amendment"), in which PWB 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. Under the terms of the Fifth Amendment, 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 PWB, 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, 2023, $ 3.9 million of the net carrying amount of the term loan was classified as short-term and $ 15.9 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, 2023 2022 Principal $ 20,000 $ 20,000 Unamortized debt discount ( 136 ) ( 64 ) Net carrying amount $ 19,864 $ 19,936 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 the date of issuance through September 30, 2023 . 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, 2023 2022 2023 2022 Contractual interest expense $ 469 $ 299 $ 1,336 $ 853 Amortization of debt issuance costs and debt discount 13 9 33 32 Total interest expense $ 482 $ 308 $ 1,369 $ 885 At September 30, 2023 and December 31, 2022, accrued interest on the term loan was $ 105 thous and and $ 121 thousand, respectively. The Company is required to repay the following principal amounts in connection with its term loan (in thousands): 2023 (remaining 3 months) $ 1,000 2024 4,000 2025 4,000 Thereafter 11,000 Total $ 20,000

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2023
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, 2023 and December 31, 2022, 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, 2023 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 7,661 $ — $ — $ 7,661 Corporate Debt Securities — 7,532 — 7,532 Total $ 7,661 $ 7,532 $ — $ 15,193 Financial Liabilities Success fee obligations $ — $ — $ 300 $ 300 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 25,776 $ — $ — $ 25,776 Corporate Debt Securities — 54,063 — 54,063 Total $ 25,776 $ 54,063 $ — $ 79,839 Financial Liabilities Success fee obligation $ — $ — $ 118 $ 118 In accordance with the Fourth and Fifth Amendments of the Loan Agreement with PWB, 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 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, 2023 , the Company determined it was 100 % probable of achieving the specified liquidity events and therefore accrued the full amount of the success fee obligations. The following reflects the significant quantitative inputs used to determine the valuation of the success fee obligation as of September 30, 2023 and December 31, 2022: September 30, 2023 December 31, 2022 Discount rate 9.0 % 8.0 % Expected timing of achieving liquidity events (years) 1.3 0.3 - 1.3 Probability of achieving liquidity events 100 % 75 % - 25 % The following table provides a roll-forward of the fair values of the Company’s success fee obligation for which fair value is determined by Level 3 inputs (in thousands): Success fee Success fee Fair value at January 1, 2023 $ 118 $ — Initial fair value of success fee obligation — 90 Change in fair value 82 10 Fair value at September 30, 2023 $ 200 $ 100

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and contingencies 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, which will expire in September 2024 . 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. During 2018, the Company received $ 1.1 million of landlord-funded leasehold improvements related to the leased office space. In February 2016, the FASB issued Accounting Standards Update ASU No. 2016-02, Leases (Topic 842), (“ASU 2016-02”). Under ASU 2016-02, the Company is required to recognize right-of-use assets and liabilities for leases. Upon adoption of ASU 2016-02 on January 1, 2022, the Company's operating lease right-of-use assets were adjusted for accumulated deferred rent, and no additional deferred rent was subsequently recorded. In 2019 and 2020, the Company entered into sublease agreements with two related parties to sublease this office and laboratory space. Refer to Note 16, 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, and was set to expire on July 31, 2022 with 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. In connection with the modifications in 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. 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 $ 0.42 million, and the Company recognized a gain on this disposal of $ 0.23 million in June 2023 since the assets are no longer in service. 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, 02142. The lease includes two phases. Phase 1 includes approximately 78,380 rentable square feet. Phase 2 includes 10,866 rentable square feet in a separate suite. 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 for the fifth floor premises commenced on May 1, 2023 for accounting purposes, and has a term of fifteen years , 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 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. (“FL Labs” 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, 02141 (the “Premises”). The Company leases an aggregate of approximately 89,246 rentable square feet of office and laboratory space located at the Premises pursuant to its lease with ARE-MA Region No. 94, LLC. Metaphore, Apriori and FL Labs are affiliates of Flagship Pioneering, a significant stockholder of the Company. The term of the Sublease with Metaphore and FL Labs has commenced in August, 2023 and will end in August, 2025, and the term of the Sublease with Apriori began in September, 2023 and will end in September, 2025. The Subleases provide that the Subtenants will pay to the Company a monthly license 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 will be 12.0 %, 8.4 % and 8.4 % for Metaphore, Apriori and Labs, respectively. The Company may terminate each Sublease and require the applicable Subtenant to immediately vacate the Premises if such 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 Subleases contain customary covenants, obligations and indemnities in favor of either party. Under the agreements, the Company has received rental income of $ 0.5 million for the nine months ended September 30, 2023, which was recorded within related party expense, net in the condensed consolidated statements of operations and comprehensive loss. Disclosures under Topic 842 As of September 30, 2023, operating lease right-of-use assets, net were $ 110.1 million, which were recorded separately on the Company’s condensed consolidated balance sheet. The corresponding operating lease liabilities were $ 111.3 million as of September 30, 2023, of which $ 12.6 million were recorded in current liabilities and $ 98.7 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, 2023 and 2022 (in thousands). Three Months Ended Three Months Ended Nine Months Ended Nine Months Ended September 30, 2023 September 30, 2022 September 30, 2023 September 30, 2022 Operating lease expense $ 3,866 $ 969 $ 7,854 $ 2,851 Variable lease expense 945 268 1,844 1,169 Total lease expense $ 4,811 $ 1,237 $ 9,698 $ 4,020 V ariable lease expense generally includes common area maintenance, utilities and property taxes. 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 million and $ 1.9 million, respectively was recorded withi n general and administrative expenses in the condensed consolidated statement of operations and comprehensive loss. For the three and nine months ended September 30, 2022 , $ 1.1 million and $ 3.1 million of lease expense, respectively was recorded within research and development expenses and $ 0.2 million and $ 0.9 million, respectively was recorded within 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 As of September 30, 2023 December 31, 2022 Weighted average remaining lease term (years) 14.8 1.8 Weighted average discount rate 8.9 % 5.5 % Supplemental cash flow information relating to the Company's leases for the nine months ended September 30, 2023 and September 30, 2022 were as follows (in thousands): Nine Months Ended Nine Months Ended September 30, 2023 September 30, 2022 Cash paid for amounts included in the measurement of lease liabilities $ 4,473 $ 2,255 Operating lease assets obtained in exchange for lease liabilities $ 110,424 $ 4,393 As of September 30, 2023, the estimated minimum lease payments for 140 First Street, 325 Vassar and 20 Acorn Park for each of the years ending December 31 were as follows (in thousands): 2023 (remaining 3 months) $ 3,237 2024 12,775 Thereafter 189,047 Total minimum lease payments 205,059 Less: Imputed interest ( 93,720 ) Present value of operating lease liabilities $ 111,339

License Agreements

License Agreements	9 Months Ended
	Sep. 30, 2023
License Agreements [Abstract]
License Agreements	10. 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 sub 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 nine months ended September 30, 2023 and 2022, the Company recognized expenses of $ 0.3 million, and less than $ 0.1 million, respectively for the license maintenance fees and milestone payments. There was no outstanding payment due to WIBR as of September 30, 2023 and December 31, 2022. 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 $ 0.1 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. 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 the nine months ended September 30, 2023 and 2022, the Company recorded an aggregate o f $ 0.1 mi llion and $ 1.6 million of research and development expenses, respectively, 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 Acuitas for the nine months ended September 30, 2023, and 2022. 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 has made an upfront cash payment of $ 1.0 million, and developmental milestone payments of $ 1.0 million to Nitto in 2022. Both payments have been recorded as research and development expenses. The Company is also 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 expense was recorded related to Nitto for the nine months ended September 30, 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. During the nine months ended September 30, 2023, the Company recorded an aggregate of $ 0.9 millio n 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, 2023
Collaboration Agreement [Abstract]
Collaboration Agreements	11. Collaboration Agreements 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 Company expects to receive approximately $ 2.8 million in cost reimbursement through 2023 to fund the related research and development activities. 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, 2023 was determined to be $ 7.8 mil lion based 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, and an increase of $ 2.4 million in the third quarter of 2023, both of which were agreed upon with PMCo. As of September 30, 2023, the remaining transaction price was estimated to be $ 3.5 m illion, which is expected to be recognized as revenue through 2024. The Company recognized funded research and collaboration revenue of $ 0.8 million and $ 2.1 million in the condensed consolidated statement of operations and comprehensive loss during three and nine months ended September 30, 2023, respectively. 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, 2023, the Company determined that the proceeds from such transaction was not probable of recognition. Nitto Denko Corporation On October 12, 2022, the Company entered into a Collaboration and License Agreement with 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. See further discussion in Note 10, License Agreements .

Preferred and Common Stock

Preferred and Common Stock	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Preferred and Common Stock	12. Preferred and Common Stock The Company’s board of directors and stockholders approved an amendment to the Company’s certificate of incorporation, which became effective on July 23, 2021. The amendment, among other things, effected a 1-for-3.777776 reverse stock split of the Company’s issued and outstanding common stock, a proportional adjustment to the conversion price for Series A, B and C Preferred Stock and to the exercise prices and number of shares of common stock underlying the outstanding stock options. All share, per share and additional paid in capital amounts for all periods presented in the accompanying unaudited financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect the reverse stock split. In August 2021, the Company completed its IPO pursuant to which it issued and sold 8,300,976 shares of its common stock, including 900,976 shares pursuant to the partial exercise of the underwriters’ option to purchase additional shares, at a public offering price of $ 17.00 per share, for aggregate gross proceeds of $ 141.1 million. The Company received approximately $ 128.1 million in net proceeds after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In connection with the completion of the IPO, 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, 2023, the Company has reserved an aggregate of 6,126,108 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 3,929,691 shares of common stock subject to outstanding stock options issued under the 2017 Plan may become available for future issuance under the 2021 Plan to the extent such stock options are forfeited.

Equity Incentive Plan

Equity Incentive Plan	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Equity Incentive Plan	13. Equity Incentive Plan 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, 2023 , there were no shares available for future grants under the 2017 Plan and a total of 3,929,691 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, 2023, there were 2,196,417 shares available for future grants under the 2021 Plan, and a total of 5,238,811 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, 2023 2022 2023 2022 Research and development $ 1,093 $ 1,110 $ 3,358 $ 2,913 General and administrative 1,187 863 3,322 2,718 Total stock-based compensation expense $ 2,280 $ 1,973 $ 6,680 $ 5,631 Stock Options A summary of option activity under the Company’s equity incentive plans during the nine months ended September 30, 2023 was as follows: Weighted Weighted Aggregate Number average contractual value (1) (in thousands) Outstanding as of January 1, 2023 8,438,573 $ 6.00 8.40 $ 12,976 Granted 1,577,002 5.77 Exercised ( 148,906 ) 3.26 Forfeited ( 601,156 ) 8.38 Expired ( 97,011 ) 15.00 Outstanding as of September 30, 2023 9,168,502 5.75 7.92 2,884 Vested and expected to vest as of September 30, 2023 9,168,502 5.75 7.92 2,884 Exercisable as of September 30, 2023 4,339,081 $ 4.58 7.03 $ 2,836 (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, 2023 . The weighted-average grant date fair value per share of stock options granted during the nine months ended September 30, 2023 and 2022 was $ 3.99 and $ 5.52 , respectively. The aggregate intrinsic value of stock options exercised during the nine months ended September 30, 2023 was $ 0.7 million. As of September 30, 2023, there was $ 20.4 million of unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of approximately 2.2 years.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	14. 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, 2023 2022 2023 2022 Numerator: Net loss attributable to common stockholders $ ( 22,248 ) $ ( 25,799 ) $ ( 77,214 ) $ ( 71,875 ) Denominator: Weighted average number of common stock, basic and diluted 55,140,058 47,854,965 53,629,468 47,837,490 Net loss per common stock attributable to common stockholders, basic and diluted $ ( 0.40 ) $ ( 0.54 ) $ ( 1.44 ) $ ( 1.50 ) 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, 2023 2022 Outstanding options to purchase common stock 9,168,502 7,855,182

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	15. Income Taxes During the three and nine months ended September 30, 2023 and 2022, 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, 2023
Related Party Transactions [Abstract]
Related Party Transactions	16. Related Party Transactions For the nine months ended September 30, 2023, related party expense, net 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 % o f the Company’s outstanding voting stock as of September 30, 2023. 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, 2023 and 2022, the Company incurred $ 0.1 million and $ 0.4 million, respectively, primarily for reimbursable expenses. For the nine months ended September 30, 2023 and 2022, the Company incurred $ 0.4 million and $ 1.2 million, respectively, primarily for reimbursable expenses. These expenses are recorded as related party expense in the accompanying condensed consolidated statements of operations and comprehensive loss. As of September 30, 2023 and December 31, 2022, there was an immaterial amount of outstanding payments due to Flagship. 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 sublease term will expire at the end of the Company’s lease agreement with the landlord in September 2024. 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”), approximating $ 1.3 million per year. 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. Under the sublease agreement, the Company received rental income of $ 1.9 million and $ 1.7 million during the nine months ended September 30, 2023 and 2022, respectively, which was recorded within related party expense, net in the condensed consolidated statements of operations and comprehensive loss. There was no outstanding receivable due from Sail Bio as of September 30, 2023 and December 31, 2022. In July 2023 the Company entered into three Shared Space Agreements with related parties Metaphore Biotechnologies, Inc., Apriori Bio, Inc., and Flagship Labs 89, Inc. These companies are affiliates of Flagship Pioneering, a significant 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. Under the agreements, the Company has received rental income of $ 0.5 million for the nine months ended September 30, 2023. Such rental income was reflected as a reduction of related party expense in the accompanying condensed consolidated statements of operations and comprehensive loss. There was no outstanding receivables due from the Subtenants as of September 30, 2023. Refer to other related party transactions as described in Note 9, Commitments and contingencies , Note 10, License agreements and Note 11, Collaboration agreement .

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2023
Retirement Benefits [Abstract]
Employee Benefits	17. 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, 2023 and 2022, the Company made matching contributions totaling $ 0.5 million and $ 0.2 million, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
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.
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 fair values of certain financial instruments issued prior to the IPO (common stock, redeemable convertible preferred stock, and warrants), the fair value of the success fee obligation, the incremental borrowing rate used in the calculation of lease liabilities, research and development accruals, 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.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements On January 1, 2023, the Company adopted Accounting Standards Update No. 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments . The guidance is effective for fiscal years beginning after December 15, 2022. The adoption of the standard was immaterial to the accompanying condensed consolidated financial statements.

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Securities	The following table summarizes the Company’s marketable securities (in thousands): September 30, 2023 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 7,618 $ ( 86 ) $ 7,532 December 31, 2022 Amortized cost Gross unrealized losses Fair value Corporate debt securities $ 54,542 $ ( 479 ) $ 54,063

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 Clinical development $ 5,135 $ 5,232 Research and development 2,435 2,072 Rent 2,192 1,857 Other receivables 1,036 1,180 Insurance 857 1,020 Software 281 157 Other 265 776 Prepaid expenses and other current assets $ 12,201 $ 12,294

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 Lab equipment $ 6,734 $ 6,121 Furniture and fixtures 1,636 1,093 Leasehold improvements 1,464 1,378 Computer equipment 1,278 190 Construction in process 318 827 Total property and equipment 11,430 9,609 Less accumulated depreciation ( 6,074 ) ( 5,414 ) Property and equipment, net $ 5,356 $ 4,195

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2023
Accrued Liabilities, Current [Abstract]
Summary of Accrued Expenses	Accrued expenses consist of the following (in thousands): September 30, December 31, 2023 2022 Employee related expenses $ 3,776 $ 4,368 Research costs 1,138 3,876 Professional and consulting fees 1,270 743 Manufacturing costs 401 4,303 Interest 105 122 Other 828 429 Total $ 7,518 $ 13,841

Term Loan (Tables)

Term Loan (Tables)	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Summary of Outstanding Term Loan Balance	As of September 30, 2023, $ 3.9 million of the net carrying amount of the term loan was classified as short-term and $ 15.9 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, 2023 2022 Principal $ 20,000 $ 20,000 Unamortized debt discount ( 136 ) ( 64 ) Net carrying amount $ 19,864 $ 19,936
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, 2023 2022 2023 2022 Contractual interest expense $ 469 $ 299 $ 1,336 $ 853 Amortization of debt issuance costs and debt discount 13 9 33 32 Total interest expense $ 482 $ 308 $ 1,369 $ 885
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): 2023 (remaining 3 months) $ 1,000 2024 4,000 2025 4,000 Thereafter 11,000 Total $ 20,000

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 7,661 $ — $ — $ 7,661 Corporate Debt Securities — 7,532 — 7,532 Total $ 7,661 $ 7,532 $ — $ 15,193 Financial Liabilities Success fee obligations $ — $ — $ 300 $ 300 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets Money market funds $ 25,776 $ — $ — $ 25,776 Corporate Debt Securities — 54,063 — 54,063 Total $ 25,776 $ 54,063 $ — $ 79,839 Financial Liabilities Success fee obligation $ — $ — $ 118 $ 118
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, 2023 and December 31, 2022: September 30, 2023 December 31, 2022 Discount rate 9.0 % 8.0 % Expected timing of achieving liquidity events (years) 1.3 0.3 - 1.3 Probability of achieving liquidity events 100 % 75 % - 25 %
Summary of Fair Values of Success Fee Obligation	The following table provides a roll-forward of the fair values of the Company’s success fee obligation for which fair value is determined by Level 3 inputs (in thousands): Success fee Success fee Fair value at January 1, 2023 $ 118 $ — Initial fair value of success fee obligation — 90 Change in fair value 82 10 Fair value at September 30, 2023 $ 200 $ 100

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [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, 2023 and 2022 (in thousands). Three Months Ended Three Months Ended Nine Months Ended Nine Months Ended September 30, 2023 September 30, 2022 September 30, 2023 September 30, 2022 Operating lease expense $ 3,866 $ 969 $ 7,854 $ 2,851 Variable lease expense 945 268 1,844 1,169 Total lease expense $ 4,811 $ 1,237 $ 9,698 $ 4,020 V
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 As of September 30, 2023 December 31, 2022 Weighted average remaining lease term (years) 14.8 1.8 Weighted average discount rate 8.9 % 5.5 %
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, 2023 and September 30, 2022 were as follows (in thousands): Nine Months Ended Nine Months Ended September 30, 2023 September 30, 2022 Cash paid for amounts included in the measurement of lease liabilities $ 4,473 $ 2,255 Operating lease assets obtained in exchange for lease liabilities $ 110,424 $ 4,393
Summary of Estimated Minimum Lease Payments	As of September 30, 2023, the estimated minimum lease payments for 140 First Street, 325 Vassar and 20 Acorn Park for each of the years ending December 31 were as follows (in thousands): 2023 (remaining 3 months) $ 3,237 2024 12,775 Thereafter 189,047 Total minimum lease payments 205,059 Less: Imputed interest ( 93,720 ) Present value of operating lease liabilities $ 111,339

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
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, 2023 2022 2023 2022 Research and development $ 1,093 $ 1,110 $ 3,358 $ 2,913 General and administrative 1,187 863 3,322 2,718 Total stock-based compensation expense $ 2,280 $ 1,973 $ 6,680 $ 5,631
Summary of Option Activity	A summary of option activity under the Company’s equity incentive plans during the nine months ended September 30, 2023 was as follows: Weighted Weighted Aggregate Number average contractual value (1) (in thousands) Outstanding as of January 1, 2023 8,438,573 $ 6.00 8.40 $ 12,976 Granted 1,577,002 5.77 Exercised ( 148,906 ) 3.26 Forfeited ( 601,156 ) 8.38 Expired ( 97,011 ) 15.00 Outstanding as of September 30, 2023 9,168,502 5.75 7.92 2,884 Vested and expected to vest as of September 30, 2023 9,168,502 5.75 7.92 2,884 Exercisable as of September 30, 2023 4,339,081 $ 4.58 7.03 $ 2,836 (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, 2023 .

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 2023 2022 Numerator: Net loss attributable to common stockholders $ ( 22,248 ) $ ( 25,799 ) $ ( 77,214 ) $ ( 71,875 ) Denominator: Weighted average number of common stock, basic and diluted 55,140,058 47,854,965 53,629,468 47,837,490 Net loss per common stock attributable to common stockholders, basic and diluted $ ( 0.40 ) $ ( 0.54 ) $ ( 1.44 ) $ ( 1.50 )
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, 2023 2022 Outstanding options to purchase common stock 9,168,502 7,855,182

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	Feb. 28, 2023	Aug. 31, 2021	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, shares issued			55,141,838		48,072,517
Cash, cash equivalents and marketable securities			$ 89,300
Recurring losses			77,200
Net cash used in operations			$ (74,420)	$ (74,278)
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
IPO
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, shares issued		8,300,976
Offering price per share		$ 17
Gross proceeds from IPO		$ 141,100
Net proceeds		$ 128,100
Underwriters’ Option to Purchase Additional Shares
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, shares issued		900,976

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Details) - Marketable Securities - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Marketable Securities, Amortized cost	$ 7,618	$ 54,542
Marketable Securities, Gross unrealized losses	(86)	(479)
Marketable Securities, Fair value	$ 7,532	$ 54,063

Marketable Securities - Additio

Marketable Securities - Additional Information (Details)	9 Months Ended
	Sep. 30, 2023 USD ($)
Investments, Debt and Equity Securities [Abstract]
Realized losses recognized on the sale or maturity of marketable securities	$ 0
Realized gains recognized on the sale or maturity of marketable securities	0
Investments with other-than-temporary impairment	0
Debt securities reclassified to accumulated other comprehensive loss	$ 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, 2023	Dec. 31, 2022
Prepaid Expense and Other Assets, Current [Abstract]
Clinical development	$ 5,135	$ 5,232
Research and development	2,435	2,072
Rent	2,192	1,857
Other receivables	1,036	1,180
Insurance	857	1,020
Software	281	157
Other	265	776
Prepaid expenses and other current assets	$ 12,201	$ 12,294

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Total property and equipment	$ 11,430	$ 9,609
Less accumulated depreciation	(6,074)	(5,414)
Property and equipment, net	5,356	4,195
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	6,734	6,121
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	1,636	1,093
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	1,464	1,378
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	1,278	190
Construction in Process
Property Plant And Equipment [Line Items]
Total property and equipment	$ 318	$ 827

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation	$ 400	$ 400	$ 1,146	$ 1,180

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued Liabilities, Current [Abstract]
Employee related expenses	$ 3,776	$ 4,368
Research costs	1,138	3,876
Professional and consulting fees	1,270	743
Manufacturing costs	401	4,303
Interest	105	122
Other	828	429
Total	$ 7,518	$ 13,841

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - USD ($)					9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 22, 2023	Dec. 20, 2021	Dec. 30, 2020	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2019	Mar. 09, 2018
Debt [Line Items]
Aggregate principal amount	$ 20,000,000				$ 20,000,000	$ 20,000,000
Unamortized debt discount	136,000				136,000	64,000
Net carrying amount of term loan classified as short-term	3,900,000				3,900,000
Net carrying amount of term loan classified as long-term	$ 15,864,000				15,864,000	16,603,000
Accrued interest on term loan					$ 105,000	$ 121,000
Maximum
Debt [Line Items]
Effective interest rate on the liability component	9.27%				9.27%
Minimum
Debt [Line Items]
Effective interest rate on the liability component	5.53%				5.53%
Loan Agreement | Pacific Western Bank
Debt [Line Items]
Maximum borrowing capacity								$ 8,000,000
First Amendment | Pacific Western Bank
Debt [Line Items]
Aggregate principal amount							$ 12,000,000
Third Amendment | Pacific Western Bank
Debt [Line Items]
Line of credit facility, Interest rate during period				6%
Maturity date				Jun. 30, 2023
Third Amendment | Pacific Western Bank | Prime Rate
Debt [Line Items]
Addition percent to variable rate				0.75%
Fourth Amendment | Pacific Western Bank
Debt [Line Items]
Aggregate principal amount			$ 20,000,000
Debt extinguished			12,000,000
Proceeds from bank			$ 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, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Principal	$ 20,000	$ 20,000
Unamortized debt discount	(136)	(64)
Net carrying amount	$ 19,864	$ 19,936

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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Disclosure [Abstract]
Contractual interest expense	$ 469	$ 299	$ 1,336	$ 853
Amortization of debt issuance costs and debt discount	13	9	33	32
Total interest expense	$ 482	$ 308	$ 1,369	$ 885

Term Loan - Schedule of Princip

Term Loan - Schedule of Principal Amount in Connection With Term Loan (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
2023 (remaining 3 months)	$ 1,000
2024	4,000
2025	4,000
Thereafter	11,000
Total	$ 20,000	$ 20,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial Assets
Total financial assets	$ 15,193	$ 79,839
Success Fee Obligations
Financial Liabilities
Total financial liabilities	300	118
Money Market Funds
Financial Assets
Total financial assets	7,661	25,776
Corporate Debt Securities
Financial Assets
Total financial assets	7,532
Marketable Securities
Financial Assets
Total financial assets		54,063
Level 1
Financial Assets
Total financial assets	7,661	25,776
Level 1 | Money Market Funds
Financial Assets
Total financial assets	7,661	25,776
Level 2
Financial Assets
Total financial assets	7,532	54,063
Level 2 | Corporate Debt Securities
Financial Assets
Total financial assets	7,532
Level 2 | Marketable Securities
Financial Assets
Total financial assets		54,063
Level 3 | Success Fee Obligations
Financial Liabilities
Total financial liabilities	$ 300	$ 118

Fair Value of Financial Instr_4

Fair Value of Financial Instruments Additional Information (Details) $ in Millions	Sep. 30, 2023 USD ($)
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

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, 2023 yr	Dec. 31, 2022 yr
Discount Rate
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	0.09	0.08
Expected Timing of Achieving Liquidity Events (years)
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	1.3
Expected Timing of Achieving Liquidity Events (years) | Minimum
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input		0.3
Expected Timing of Achieving Liquidity Events (years) | Maximum
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input		1.3
Probability of Achieving Liquidity Events
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input	1
Probability of Achieving Liquidity Events | Minimum
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input		0.75
Probability of Achieving Liquidity Events | Maximum
Fair Value Liabilities Measured On Recurring Basis [Line Items]
Success fee, measurement input		0.25

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Summary of Fair Values of Success Fee Obligation (Details) - Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Success Fee Obligation from the Fourth Amendment
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 118
Change in fair value	82
Ending balance	200
Success Fee Obligation from the Fifth Amendment
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Initial fair value of success fee obligation	90
Change in fair value	10
Ending balance	$ 100

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)

1 Months Ended

3 Months Ended

6 Months Ended

9 Months Ended

12 Months Ended

Jul. 12, 2023 Space

Jul. 11, 2023 Space

May 04, 2023 $ / ft²

May 03, 2023 $ / ft²

Nov. 04, 2021 USD ($) ft² Phase

Jul. 31, 2023 ft² Space

Jan. 31, 2022 USD ($)

Sep. 30, 2023 USD ($)

Sep. 30, 2022 USD ($)

Jun. 30, 2023 USD ($)

Sep. 30, 2023 USD ($) ft² Option

Sep. 30, 2022 USD ($)

Dec. 31, 2020 Sublease

Dec. 31, 2019 Sublease

Dec. 31, 2022 USD ($)

Dec. 31, 2018 USD ($)

Leases [Line Items]

Lease expiration date

Sep. 30, 2024

Landlord-funded leasehold improvements

$ 1,100,000

Deferred rent

$ 0

Number of phases | Phase

2

Base rent per square foot | $ / ft²

1

Lease payment

$ 3,866,000

$ 969,000

7,854,000

$ 2,851,000

Net book value of assets

$ 420,000

Gain on disposal of assets

$ 230,000

Right-of-use assets

110,094,000

110,094,000

$ 3,668,000

Lease liabilities

111,339,000

111,339,000

Lease liabilities, current

12,595,000

12,595,000

1,524,000

Lease liabilities, non-current

98,745,000

98,745,000

$ 1,120,000

Lease expense

4,811,000

1,237,000

9,698,000

4,020,000

Number of shared space arrangements | Space

3

Research and Development Expenses

Leases [Line Items]

Lease expense

4,000,000

1,100,000

7,800,000

3,100,000

General and Administrative Expenses

Leases [Line Items]

Lease expense

$ 800,000

$ 200,000

1,900,000

900,000

140 First Street Lease Agreement

Leases [Line Items]

Lessee operating lease, description

The operating lease for the fifth floor premises commenced on May 1, 2023 for accounting purposes, and has a term of fifteen years, subject to certain extension rights.

Rentable square feet of office and laboratory | ft²

89,246

Lease term

15 years

Base rent per square foot | $ / ft²

116

Base rent annual upward adjustment percentage

3%

Tenant improvement allowance per rentable square foot | $ / ft²

300

Lease term interest rate

8%

Lease payment

$ 800,000

Shared Space Arrangement

Leases [Line Items]

Number of shared space arrangements | Space

2

1

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

22,500

Shared Space Arrangement | Related Party Expense

Leases [Line Items]

Sublease rental income received

$ 500,000

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, and was set to expire on July 31, 2022 with two options to extend the term of the Arrangement for a period of 24 months each.

Area of leased space | ft²

69,867

Upfront payment

$ 2,900,000

Reimbursement for office furniture purchases

$ 650,000

Sail Biomedicines, Inc | Related Party Expense

Leases [Line Items]

Sublease rental income received

$ 1,900,000

$ 1,700,000

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

12%

Apriori

Leases [Line Items]

Monthly license fee proportionate share, percentage

8.40%

Labs

Leases [Line Items]

Monthly license fee proportionate share, percentage

8.40%

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

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Lessee Disclosure [Abstract]
Operating lease expense	$ 3,866	$ 969	$ 7,854	$ 2,851
Variable lease expense	945	268	1,844	1,169
Total lease expense	$ 4,811	$ 1,237	$ 9,698	$ 4,020

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Weighted Average Remaining Lease Term And Discount Rate Related to Leases (Details)	Sep. 30, 2023	Dec. 31, 2022
Leases [Line Items]
Weighted average remaining lease term (years)	14 years 9 months 18 days	1 year 9 months 18 days
Weighted average discount rate	8.90%	5.50%

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Supplemental Cash Flow Information Relating to Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Leases [Line Items]
Cash paid for amounts included in the measurement of lease liabilities	$ 4,473	$ 2,255
Operating lease assets obtained in exchange for lease liabilities	$ 110,424	$ 4,393

Commitments and Contingencies_5

Commitments and Contingencies - Summary of Estimated Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Leases [Abstract]
2023 (remaining 6 months)	$ 3,237
2024	12,775
Thereafter	189,047
Total minimum lease payments	205,059
Less: Imputed interest	(93,720)
Present value of operating lease liabilities	$ 111,339

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, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
License Agreements [Line Items]
License maintenances fees							$ 300,000
Research and development					$ 16,475,000	$ 20,670,000	61,454,000	$ 54,329,000
Related Party
License Agreements [Line Items]
Other Liabilities					$ 0		0		$ 0
Maximum
License Agreements [Line Items]
License maintenances fees								100
Nitto
License Agreements [Line Items]
Milestone payments							0
Research and development	$ 1,000,000						$ 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
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			$ 100,000
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]
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	$ 1,600,000

Collaboration Agreements (Addit

Collaboration Agreements (Additional Information) (Details) - Collaboration Agreement - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2021	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement period	5 years
Amount of cost reimbursement receivable to fund research and development activities	$ 2.8
Transaction price				$ 7.8
Increase in transaction price		$ 2.4	$ 1.9
Remaining transaction price		3.5		3.5
Research and collaboration revenue		$ 0.8		$ 2.1

Preferred and Common Stock (Add

Preferred and Common Stock (Additional Information) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	9 Months Ended
	Feb. 28, 2023	Aug. 31, 2021	Sep. 30, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Common stock issued and sold			55,141,838	48,072,517
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
IPO
Class of Stock [Line Items]
Common stock issued and sold		8,300,976
Offering price per share		$ 17
Gross proceeds from IPO		$ 141.1
Net proceeds		$ 128.1
Underwriters’ Option to Purchase Additional Shares
Class of Stock [Line Items]
Common stock issued and sold		900,976
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		3,929,691
2017 and 2021 Plans
Class of Stock [Line Items]
Common stock subject to outstanding stock options issued			6,126,108
Amended and Restated Certificate of Incorporation
Class of Stock [Line Items]
Reverse stock split description			1-for-3.777776
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 Plan - Additio

Equity Incentive Plan - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2023	Sep. 30, 2022	Jul. 31, 2021
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		3,929,691
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		2,196,417
Common stock subject to outstanding stock options issued		5,238,811
Common stock reserved for future issuance				2,960,000
Common stock shares reserved for future issuance increased percentage		4%
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		$ 3.99	$ 5.52
Intrinsic value of stock options exercised		$ 0.7
Unrecognized compensation cost related to unvested stock options		$ 20.4
Unrecognized compensation cost, weighted-average period of recognition		2 years 2 months 12 days

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,280	$ 1,973	$ 6,680	$ 5,631
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,093	1,110	3,358	2,913
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,187	$ 863	$ 3,322	$ 2,718

Equity Incentive Plan - Summa_2

Equity Incentive Plan - 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, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options Outstanding, Beginning balance | shares	8,438,573
Number of options, Granted | shares	1,577,002
Number of options, Exercised | shares	(148,906)
Number of options, Forfeited | shares	(601,156)
Number of options, Expired | shares	(97,011)
Number of options Outstanding, Ending balance | shares	9,168,502	8,438,573
Number of options, Vested and expected to vest | shares	9,168,502
Number of options, Exercisable | shares	4,339,081
Weighted average exercise price Outstanding, Beginning balance | $ / shares	$ 6
Weighted average exercise price, Granted | $ / shares	5.77
Weighted average exercise price, Exercised | $ / shares	3.26
Weighted average exercise price, Forfeited | $ / shares	8.38
Weighted average exercise price, Expired | $ / shares	15
Weighted average exercise price Outstanding, Ending balance | $ / shares	5.75	$ 6
Weighted average exercise price, Vested and expected to vest | $ / shares	5.75
Weighted average exercise price, Exercisable | $ / shares	$ 4.58
Weighted average remaining contractual life (years), Outstanding	7 years 11 months 1 day	8 years 4 months 24 days
Weighted average remaining contractual life (years), Vested and expected to vest	7 years 11 months 1 day
Weighted average remaining contractual life (years), Exercisable	7 years 10 days
Aggregate intrinsic value, Outstanding | $	$ 2,884	$ 12,976
Aggregate intrinsic value, Vested and expected to vest | $	2,884
Aggregate intrinsic value, Exercisable | $	$ 2,836

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, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss attributable to common stockholders	$ (22,248)	$ (29,687)	$ (25,279)	$ (25,799)	$ (25,912)	$ (20,164)	$ (77,214)	$ (71,875)
Denominator:
Weighted-average common stock used in net loss per share attributable to common stockholders, basic	55,140,058			47,854,965			53,629,468	47,837,490
Weighted-average common stock used in net loss per share attributable to common stockholders, diluted	55,140,058			47,854,965			53,629,468	47,837,490
Net loss per common stock attributable to common stockholders, basic	$ (0.4)			$ (0.54)			$ (1.44)	$ (1.5)
Net loss per common stock attributable to common stockholders, diluted	$ (0.4)			$ (0.54)			$ (1.44)	$ (1.5)

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, 2023	Sep. 30, 2022
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	9,168,502	7,855,182

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	1 Months Ended		3 Months Ended		9 Months Ended
	Jul. 31, 2023 ft² Space	Sep. 30, 2020 USD ($) ft²	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Related Party Transaction [Line Items]
Number of shared space arrangements | Space	3
Shared Space Agreements
Related Party Transaction [Line Items]
Rentable area of office and laboratory space agreed to sublease | ft²	22,500
Sail Biomedicines, Inc
Related Party Transaction [Line Items]
Area of real estate property | ft²		19,404
Sublease income		$ 1,300,000
Sail Biomedicines, Inc | Related Party
Related Party Transaction [Line Items]
Outstanding receivable			$ 0		$ 0		$ 0
Subtenants
Related Party Transaction [Line Items]
Outstanding receivable			0		0
Related Party Expense | Shared Space Agreements
Related Party Transaction [Line Items]
Sublease rental income received						$ 500,000
Related Party Expense | Sail Biomedicines, Inc
Related Party Transaction [Line Items]
Sublease rental income received					1,900,000	1,700,000
Flagship | Related Party Expense | Reimbursable Expenses | Related Party
Related Party Transaction [Line Items]
Related party expenses for management service			$ 100,000	$ 400,000	$ 400,000	$ 1,200,000
Omega Therapeutics, Inc. | Flagship
Related Party Transaction [Line Items]
Ownership percentage			53%		53%

Employee Benefits (Additional I

Employee Benefits (Additional Information) (Details) - 401(k) Plan - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
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	$ 0.5	$ 0.2