Q32 Bio (QTTB) S-4 15 Dec 23 Registration of securities issued in business combination transactions Financial data

Cover Page

Cover Page	9 Months Ended
	Sep. 30, 2023
Document Information [Line Items]
Document Type	S-4
Amendment Flag	false
Entity Registrant Name	Homology Medicines, Inc.
Entity Central Index Key	0001661998
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-3468154
Entity Address, Address Line One	One Patriots Park
Entity Address, City or Town	Bedford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01730
City Area Code	781
Local Phone Number	327-2633
Entity Primary SIC Number	2834
Business Contact [Member]
Document Information [Line Items]
Entity Address, Address Line One	One Patriots Park
Entity Address, City or Town	Bedford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01730
City Area Code	781
Local Phone Number	327-2633
Contact Personnel Name	Paul Alloway, Ph.D.

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 29,111	$ 33,986	$ 108,382
Short-term investments	74,187	141,040	47,491
Assets held for sale	314	0	28,907
Prepaid expenses and other current assets	3,023	5,989	7,129
Total current assets	106,635	181,015	191,909
Equity method investment	13,957	25,814	0
Property and equipment, net	0	1,078	2,252
Right-of-use assets	19,471	20,563	15,607
Restricted cash	0	0	1,953
Total assets	140,063	228,470	211,721
Current liabilities:
Accounts payable	7,803	1,144	2,366
Accrued expenses and other liabilities	15,711	18,715	11,406
Operating lease liabilities	1,778	1,561	246
Deferred revenue	0	1,156	3,208
Total current liabilities	25,292	22,576	17,226
Non-current liabilities:
Operating lease liabilities, net of current portion	26,560	27,916	23,688
Deferred revenue, net of current portion		0	1,156
Total liabilities	51,852	50,492	42,070
Commitments and contingencies (Note 8)		0
Stockholders' equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized; no shares issued and outstanding at September 30, 2023 and December 31, 2022	0	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized; 57,902,210 and 57,483,910 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	6	6	6
Additional paid-in capital	614,220	607,513	593,784
Accumulated other comprehensive loss	(36)	(404)	(7)
Accumulated deficit	(525,979)	(429,137)	(424,132)
Total stockholders' equity	88,211	177,978	169,651
Total liabilities and stockholders' equity	$ 140,063	$ 228,470	$ 211,721

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Common stock, shares issued	57,902,210	57,483,910	57,150,274
Common stock, shares outstanding	57,902,210	57,483,910	57,150,274

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Collaboration revenue	$ 0	$ 802	$ 1,156	$ 2,406	$ 3,208	$ 33,971
Operating expenses:
Research and development	17,519	25,854	60,489	71,202	98,351	93,085
General and administrative	6,842	7,810	23,355	29,991	38,138	36,835
Restructuring and other charges	6,640	0	6,640	0
Total operating expenses	31,001	33,664	90,484	101,193	136,489	129,920
Loss from operations	(31,001)	(32,862)	(89,328)	(98,787)	(133,281)	(95,949)
Other income
Gain on sale of business	0	0	0	131,249	131,249	0
Interest income	1,423	1,269	4,403	1,775	3,230	185
Total other income	1,423	1,269	4,403	133,024	134,479	185
Income (loss) before income taxes	(29,578)	(31,593)	(84,925)	34,237	1,198	(95,764)
Benefit from (provision for) income taxes	0	46	0	(816)	(715)	0
Loss from equity method investment	(3,376)	(2,179)	(11,917)	(4,131)	(5,488)	0
Net income (loss)	$ (32,954)	$ (33,726)	$ (96,842)	$ 29,290	$ (5,005)	$ (95,764)
Net income (loss) per share-basic	$ (0.57)	$ (0.59)	$ (1.68)	$ 0.51	$ (0.09)	$ (1.73)
Net income (loss) per share-diluted	$ (0.57)	$ (0.59)	$ (1.68)	$ 0.51	$ (0.09)	$ (1.73)
Weighted-average common shares outstanding-basic	57,853,132	57,447,192	57,788,755	57,372,399	57,399,762	55,283,318
Weighted-average common shares outstanding-diluted	57,853,132	57,447,192	57,788,755	57,901,298	57,399,762	55,283,318

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (32,954)	$ (33,726)	$ (96,842)	$ 29,290	$ (5,005)	$ (95,764)
Other comprehensive gain (loss):
Change in unrealized gain (loss) on available for sale securities, net	52	(416)	368	(450)	(397)	(7)
Total other comprehensive gain	52	(416)	368	(450)	(397)	(7)
Comprehensive income (loss)	$ (32,902)	$ (34,142)	$ (96,474)	$ 28,840	$ (5,402)	$ (95,771)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Equity Method Investee	ATM	Follow On Offering	Common Stock	Common Stock ATM	Common Stock Follow On Offering	Additional Paid-in Capital	Additional Paid-in Capital Equity Method Investee	Additional Paid-in Capital ATM	Additional Paid-in Capital Follow On Offering	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2020	$ 195,995				$ 5			$ 524,358					$ (328,368)
Beginning balance, Shares at Dec. 31, 2020					50,265,575
Issuance of common stock, net of discounts and issuance costs			$ 1,454	$ 49,744			$ 1			$ 1,454	$ 49,743
Issuance of common stock, net of discounts and issuance costs, Shares						114,914	6,596,306
Vesting of common stock from option exercises	13							13
Vesting of common stock from option exercises, Shares					3,091
Issuance of common stock from option exercises	145							145
Issuance of common stock from option exercises, Shares					59,465
Issuance of common stock pursuant to employee stock purchase plan	826							826
Issuance of common stock pursuant to employee stock purchase plan, Shares					110,923
Stock-based compensation	17,245							17,245
Other comprehensive gain (loss)	(7)											$ (7)
Net income (loss)	(95,764)												(95,764)
Ending balance at Dec. 31, 2021	169,651				$ 6			593,784				(7)	(424,132)
Ending balance, Shares at Dec. 31, 2021					57,150,274
Issuance of common stock from option exercises	1							1
Issuance of common stock from option exercises, Shares					293
Issuance of common stock pursuant to employee stock purchase plan	439							439
Issuance of common stock pursuant to employee stock purchase plan, Shares					147,871
Issuance of common stock from RSU vesting					87,140
Stock-based compensation	4,051							4,051
Other comprehensive gain (loss)	7											7
Net income (loss)	92,105												92,105
Ending balance at Mar. 31, 2022	266,254				$ 6			598,275					(332,027)
Ending balance, Shares at Mar. 31, 2022					57,385,578
Beginning balance at Dec. 31, 2021	169,651				$ 6			593,784				(7)	(424,132)
Beginning balance, Shares at Dec. 31, 2021					57,150,274
Other comprehensive gain (loss)	(450)
Net income (loss)	29,290
Ending balance at Sep. 30, 2022	209,061				$ 6			604,354				(457)	(394,842)
Ending balance, Shares at Sep. 30, 2022					57,480,610
Beginning balance at Dec. 31, 2021	169,651				$ 6			593,784				(7)	(424,132)
Beginning balance, Shares at Dec. 31, 2021					57,150,274
Issuance of common stock, net of discounts and issuance costs, Shares			0
Issuance of common stock from option exercises	1							1
Issuance of common stock from option exercises, Shares					293
Issuance of common stock pursuant to employee stock purchase plan	595							595
Issuance of common stock pursuant to employee stock purchase plan, Shares					226,453
Issuance of common stock from RSU vesting					106,890
Stock-based compensation	13,054	$ 79						13,054
Other comprehensive gain (loss)	(397)											(397)
Net income (loss)	(5,005)												(5,005)
Ending balance at Dec. 31, 2022	177,978				$ 6			607,513				(404)	(429,137)
Ending balance, Shares at Dec. 31, 2022					57,483,910
Beginning balance at Mar. 31, 2022	266,254				$ 6			598,275					(332,027)
Beginning balance, Shares at Mar. 31, 2022					57,385,578
Stock-based compensation	3,143	21						3,143	$ 21
Other comprehensive gain (loss)	(41)											(41)
Net income (loss)	(29,089)												(29,089)
Ending balance at Jun. 30, 2022	240,288							601,439				(41)	(361,116)
Ending balance, Shares at Jun. 30, 2022					57,385,578
Issuance of common stock pursuant to employee stock purchase plan	124							124
Issuance of common stock pursuant to employee stock purchase plan, Shares					78,582
Issuance of common stock from RSU vesting					16,450
Stock-based compensation	2,771	20						2,771	20
Other comprehensive gain (loss)	(416)											(416)
Net income (loss)	(33,726)												(33,726)
Ending balance at Sep. 30, 2022	209,061				$ 6			604,354				(457)	(394,842)
Ending balance, Shares at Sep. 30, 2022					57,480,610
Beginning balance at Dec. 31, 2022	177,978				$ 6			607,513				(404)	(429,137)
Beginning balance, Shares at Dec. 31, 2022					57,483,910
Issuance of common stock pursuant to employee stock purchase plan	150							150
Issuance of common stock pursuant to employee stock purchase plan, Shares					116,332
Issuance of common stock from RSU vesting					194,525
Stock-based compensation	2,369	24						2,369	24
Other comprehensive gain (loss)	222											222
Net income (loss)	(28,844)												(28,844)
Ending balance at Mar. 31, 2023	151,899				$ 6			610,056				(182)	(457,981)
Ending balance, Shares at Mar. 31, 2023					57,794,767
Beginning balance at Dec. 31, 2022	177,978				$ 6			607,513				(404)	(429,137)
Beginning balance, Shares at Dec. 31, 2022					57,483,910
Issuance of common stock, net of discounts and issuance costs, Shares			0
Other comprehensive gain (loss)	368
Net income (loss)	(96,842)
Ending balance at Sep. 30, 2023	88,211				$ 6			614,220				(36)	(525,979)
Ending balance, Shares at Sep. 30, 2023					57,902,210
Beginning balance at Mar. 31, 2023	151,899				$ 6			610,056				(182)	(457,981)
Beginning balance, Shares at Mar. 31, 2023					57,794,767
Issuance of common stock from option exercises	2							2
Issuance of common stock from option exercises, Shares					3,366
Stock-based compensation	2,402	22						2,402	22
Other comprehensive gain (loss)	94											94
Net income (loss)	(35,044)												(35,044)
Ending balance at Jun. 30, 2023	119,375				$ 6			612,482				(88)	(493,025)
Ending balance, Shares at Jun. 30, 2023					57,798,133
Issuance of common stock pursuant to employee stock purchase plan	18							18
Issuance of common stock pursuant to employee stock purchase plan, Shares					17,485
Issuance of common stock from RSU vesting					86,592
Stock-based compensation	1,706	$ 14						1,706	$ 14
Other comprehensive gain (loss)	52											52
Net income (loss)	(32,954)												(32,954)
Ending balance at Sep. 30, 2023	$ 88,211				$ 6			$ 614,220				$ (36)	$ (525,979)
Ending balance, Shares at Sep. 30, 2023					57,902,210

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income (loss)	$ (96,842)	$ 29,290	$ (5,005)	$ (95,764)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	578	997	1,293	8,353
Noncash lease expense	1,091	969	1,306	1,191
Loss from equity method investment	(11,917)	(4,131)	(5,488)	0
Stock-based compensation expense	6,477	9,965	13,054	17,245
Accretion of discount on short-term investments	(2,279)	(872)	(1,947)	894
Loss on disposal of property and equipment	68	0	49	133
Gain on sale of business	0	(131,249)	(131,249)	0
Loss from equity method investment	11,917	4,131
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	2,966	(5,301)	840	(4,996)
Accounts payable	6,659	2,711	(981)	(2,487)
Accrued expenses and other liabilities	(2,996)	5,672	7,418	1,500
Deferred revenue	(1,156)	(2,406)	(3,208)	(33,411)
Operating lease liabilities	(1,138)	(369)	(719)	(2,409)
Net cash used in operating activities	(74,655)	(86,462)	(113,661)	(109,751)
Cash flows from investing activities:
Purchases of short-term investments	(73,240)	(157,460)	(157,460)	(97,392)
Maturities of short-term investments	142,740	47,461	65,461	49,000
Proceeds from sale of business	0	130,000	130,000	0
Purchases of property and equipment	(228)	(1,276)	(1,285)	(2,396)
Proceeds from sale of property and equipment	338	0		28,900
Net cash provided by investing activities	69,610	18,725	36,716	(50,788)
Cash flows from financing activities:
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs			0	49,744
Proceeds from issuance of common stock pursuant to ATM financing, net of discounts and issuance costs			0	1,454
Proceeds from issuance of common stock pursuant to employee stock purchase plan	168	563	595	826
Proceeds from issuance of common stock from option exercises	2	1	1	145
Net cash provided by financing activities	170	564	596	52,169
Net change in cash, cash equivalents and restricted cash	(4,875)	(67,173)	(76,349)	(108,370)
Cash, cash equivalents and restricted cash, beginning of period	33,986	110,335	110,335	218,705
Cash, cash equivalents and restricted cash, end of period	29,111	43,162	33,986	110,335
Supplemental disclosures of noncash investing and financing activities:
Cash paid for income taxes			720	0
Reclassification of liability for common stock vested			0	13
Property and equipment additions included in accounts payable			0	241
Property and equipment additions included in accrued expenses and other liabilities	0	8	8	116
Unrealized loss on available for sale securities, net	$ 368	$ (450)	$ (397)	$ (7)

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS AND BASIS OF PRESENTATION	1. NATURE OF BUSINESS AND BASIS OF PRESENTATION Nature of Business one-time On July 27, 2023, the Company announced that it had completed a review of its business and the Company’s Board of Directors had approved a plan to explore, review and evaluate a range of potential strategic options available to the Company, including, without limitation, an acquisition, merger, reverse merger, sale of assets, strategic partnerships or other transactions. Based on the current financing environment and the Company’s anticipated clinical development timeline for its lead program, HMI-103, On March 9, 2023, the Company filed a Registration Statement on Form S-3 No. 333-270414) million of its common stock, preferred stock, debt securities, warrants and/or units of any combination thereof for a period up to three years from the date of the filing. The Shelf became effective on March 17, 2023. The Company also simultaneously entered into a sales agreement with TD Cowen, as sales agent, providing for the offering, issuance and sale by the Company of up to an aggregate of $ “at-the-market” On March 10, 2022, the Company closed a transaction with Oxford Biomedica plc (“Oxford”), to establish a new adeno-associated virus (“AAV”) vector manufacturing company, Oxford Biomedica Solutions (“OXB Solutions”) that provides AAV vector process development and manufacturing services to biotechnology companies. Under the terms of the agreement, the Company contributed its manufacturing team of 125 employees, manufacturing facility and equipment, manufacturing-related intellectual property and know-how Since its inception and until recently, the Company devoted substantially all of its resources to recruiting personnel, developing its technology platform and advancing its pipeline of product candidates through discovery, preclinical and clinical trials, developing and implementing manufacturing processes, building out manufacturing and research and development space, and maintaining and building its intellectual property portfolio. The Company is subject to a number of risks similar to those of other companies conducting high-risk, early-stage research and development of product candidates. Principal among these risks are dependency on key individuals and intellectual property, competition from other products and companies, and the technical and regulatory risks associated with the successful research, development and manufacturing of its product candidates. To date, the Company has not generated any revenue from product sales and does not expect to generate any revenue from the sale of product in the foreseeable future. Through September 30, 2023, the Company has financed its operations primarily through public offerings of its common stock, the issuance of convertible preferred stock, and with proceeds from its transaction with Oxford (see Note 5), its collaboration and license agreement with a former collaboration partner and its private placement with Pfizer (see Note 12). During the nine months ended September 30, 2023, the Company incurred a loss from operations of $96.8 million and as of September 30, 2023, the Company had $526.0 million in accumulated deficit. The Company has incurred and expects to continue to incur costs and expenditures in connection with the process of evaluating strategic alternatives. There can be no assurance, however, that the Company will be able to successfully consummate any particular strategic transaction. The process of evaluating strategic options has been and may continue to be costly, time-consuming and complex and the Company may incur significant costs related to this continued evaluation, such as legal, accounting and advisory fees and expenses and other related charges. Based on current projections, management believes that the Company’s existing cash and cash equivalents and short-term investments as of September 30, 2023 will enable the Company to continue its operations for at least one year from the date of this filing. However, due to the consideration of certain qualitative factors, including the discontinuation of all clinical trials and research activities, as well as the Company’s workforce reduction of all but a few custodial employees, management has concluded there is substantial doubt regarding the Company’s ability to continue as a going concern for more than twelve months from the issuance date of the unaudited condensed consolidated financial statements for the period ended September 30, 2023. These financial statements do not include any adjustments that might result from the outcome of this uncertainty. Should the Company resume the development of product candidates, it would need to obtain substantial additional funding in connection with continuing operations, particularly as the Company resumes its preclinical activities and clinical trials for its product candidates. There can be no assurance that the Company will be able to o Basis of Presentation audited consolidated financial statements and the notes thereto for the year ended December 31, 2022, included elsewhere in this proxy/registration statement. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position as of September 30, 2023, and consolidated results of operations for the three and nine months ended September 30, 2023 and 2022, and cash flows for the nine months ended September 30, 2023 and 2022. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023.	1. NATURE OF BUSINESS AND BASIS OF PRESENTATION Nature of Business one-time Since its inception, the Company has devoted substantially all of its resources to recruiting personnel, developing its technology platform and advancing its pipeline of product candidates through discovery, preclinical and clinical trials, developing and implementing manufacturing processes, building out manufacturing and research and development space, and maintaining and building its intellectual property portfolio. The Company is subject to a number of risks similar to those of other companies conducting high-risk, early-stage research and development of product candidates. Principal among these risks are dependency on key individuals and intellectual property, competition from other products and companies, and the technical and regulatory risks associated with the successful research, development and manufacturing of its product candidates. The Company’s success is dependent upon its ability to continue to raise additional capital in order to fund ongoing research and development, conduct clinical trials, obtain regulatory approval of its products, further expand access to manufacturing capacity, successfully commercialize its products, generate revenue, meet its obligations, and, ultimately, attain sustainable profitable operations. On March 10, 2022, the Company closed a transaction with Oxford Biomedica plc (“Oxford”), to establish a new adeno-associated virus (“AAV”) vector manufacturing company, Oxford Biomedica Solutions (“OXB Solutions”) that provides AAV vector process development and manufacturing services to biotechnology companies. Under the terms of the agreement, the Company contributed its manufacturing team of 125 employees, manufacturing facility and equipment, manufacturing-related intellectual property and know-how On April 6, 2021, the Company completed a follow-on S-3, On March 12, 2020, the Company filed a Registration Statement on Form S-3 No. 333-237131) “at-the-market” shares of common stock under the Sales Agreement during the during the year ended December 31, 2022. As of December 31, 2022, there remained $148.4 million of common stock available for sale under the ATM. The Shelf will expire and no longer be effective, and accordingly will not be available for use for ATM offerings under the Sales Agreement, after March 12, 2023. To date, the Company has not generated any revenue from product sales and does not expect to generate any revenue from the sale of product in the foreseeable future. Through December 31, 2022, the Company has financed its operations primarily through public offerings of its common stock, the issuance of convertible preferred stock, and with proceeds from its from its transaction with Oxford (see Note 6), its collaboration and license agreement with Novartis Institutes of BioMedical Research, Inc. (“Novartis”) (see Note 10) and its private placement with Pfizer (see Note 15). During the year ended December 31, 2022, the Company incurred a loss from operations of $133.3 million and as of December 31, 2022, had $429.1 million in accumulated deficit. The Company expects to incur additional operating losses and negative operating cash flows for the foreseeable future. Based on current projections, management believes that cash and cash equivalents and short-term investments as of December 31, 2022 will enable the Company to continue its operations for at least one year from the date of this filing. In the absence of a significant source of recurring revenue, the continued viability of the Company beyond that point is dependent on its ability to continue to raise additional capital to finance its operations. There can be no assurance that the Company will be able to obtain sufficient capital to cover its costs on acceptable terms, if at all. Basis of Presentation

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation behalf. All intercompany balances and transactions have been eliminated in the condensed consolidated financial statements. Use of Estimates Comprehensive Income (Loss) non-owner available-for-sale Cash and Cash Equivalents and Restricted Cash Short-Term Investments available-for-sale Assets Held for Sale . Equity Method Investment Under the equity method of accounting, the Company’s investment is initially recorded at fair value on the condensed consolidated balance sheets. Upon initial investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that a decline in value has occurred that is other than temporary. Evidence considered in this evaluation includes, but would not necessarily be limited to, the financial condition and near-term prospects of the investee, recent operating trends and forecasted performance of the investee, market conditions in the geographic area or industry in which the investee operates and the Company’s strategic plans for holding the investment in relation to the period of time expected for an anticipated recovery of its carrying value. If the investment is determined to have a decline in value deemed to be other than temporary it is written down to estimated fair value. At September 30, 2023, the Company accounted for its investment in OXB Solutions using the equity method of accounting (see Note 5). Offering Costs paid-in Leases At the commencement date, operating lease liabilities and their corresponding right-of-use right-of-use Right-of-use The Company acts as sublessor related to a sublease of a substantial portion of the Company’s headquarters that is now occupied by OXB Solutions. Fixed sublease payments received are recorded as a reduction to lease cost. Although Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions, the Company remained jointly and severally liable for the payment of rent under this lease as of and for the three and nine months ended September 30, 2023. Therefore, the related right-of-use Research and Development Costs Costs for certain development activities are recognized based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid expense or accrued research and development expense. Income Taxes— more-likely-than-not The Company recorded an income tax benefit of less than $0.1 million and an income tax provision of $0.8 million for the three and nine months ended September 30, 2022, respectively. The year-to-date Revenue Recognition— Revenue from Contracts with Customers Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in the Company’s arrangements would likely consist of a license, rights to the Company’s intellectual property or research, development and manufacturing services. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of consideration to which the Company expects to be entitled to. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts may include development and regulatory milestone payments that are assessed under the most likely amount method and constrained until it is probable that a significant revenue reversal would not occur. Milestone payments that are not within the Company’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from the Company’s collaboration arrangement. The Company allocates the transaction price based on the estimated standalone selling price of each performance obligation. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress for its over-time arrangements at each reporting period and, if necessary, updates the measure of progress and revenue recognized. Net Income (Loss) per Share— Common stock equivalent shares are excluded from the computation of diluted net income (loss) per share if their effect is antidilutive. In periods in which the Company reports a net (loss) attributable to common stockholders, diluted net (loss) per share attributable to common stockholders is generally the same as basic net (loss) per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments 2016-13”) 2016-13 2016-13 2016-13 2016-13	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation Use of Estimates Comprehensive Income (Loss) — non-owner available-for-sale Cash and Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash to amounts shown in the consolidated statements of cash flows: December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 33,986 $ 108,382 Restricted cash — 1,953 Total cash, cash equivalents and restricted cash $ 33,986 $ 110,335 Short-Term Investments available-for-sale one-year Concentrations of Credit Risk Equity Method Investment— Under the equity method of accounting, the Company’s investment is initially recorded at fair value on the consolidated balance sheets. Upon initial investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process share of income or loss of the other entity within other income/expense, which results in an increase or decrease to the carrying value of the investment. If the share of losses exceeds the carrying value of the Company’s investment, the Company will suspend recognizing additional losses and will continue to do so unless it commits to providing additional funding; however, if there are intra-entity profits this can cause the investment balance to go negative. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that a decline in value has occurred that is other than temporary. Evidence considered in this evaluation includes, but would not necessarily be limited to, the financial condition and near-term prospects of the investee, recent operating trends and forecasted performance of the investee, market conditions in the geographic area or industry in which the investee operates and the Company’s strategic plans for holding the investment in relation to the period of time expected for an anticipated recovery of its carrying value. If the investment is determined to have a decline in value deemed to be other than temporary it is written down to estimated fair value. At December 31, 2022, the Company accounted for its investment in OXB Solutions using the equity method of accounting (see Note 6). Offering Costs paid-in Leases At the commencement date, operating lease liabilities and their corresponding right-of-use right-of-use Right-of-use The Company acts as sublessor related to a sublease of a substantial portion of the Company’s headquarters that is now occupied by OXB Solutions (see Note 16). Fixed sublease payments received are recorded as a reduction to lease cost. Although Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions, the Company remains jointly and severally liable for the payment of rent under this lease and was not released from being the primary obligor under such lease. Therefore, the related right-of-use Guarantees and Indemnifications Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that Property and Equipment Computer equipment and software 3 years Laboratory equipment and office furniture 5 years Manufacturing equipment 5 - 7 years Leasehold improvements Shorter of the lease term Assets Held for Sale Impairment of Long-Lived Assets right-of-use Research and Development Costs Costs for certain development activities are recognized based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid expense or accrued research and development expense. Income Taxes than-not the Segment Information Revenue Recognition— Revenue from Contracts with Customers The promised goods or services in the Company’s arrangements would likely consist of a license, rights to the Company’s intellectual property or research, development and manufacturing services. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of consideration to which the Company expects to be entitled to. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts may include development and regulatory milestone payments that are assessed under the most likely amount method and constrained until it is probable that a significant revenue reversal would not occur. Milestone payments that are not within the Company’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from the Company’s collaboration arrangement. The Company allocates the transaction price based on the estimated standalone selling price of each performance obligation. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress for its over-time arrangements at each reporting period and, if necessary, updates the measure of progress and revenue recognized. Stock-based Compensation non-employees The purchase price of common stock under the Company’s employee stock purchase plan (“ESPP”) is equal to 85% of the lesser of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date. The fair value of the look-back provision under the ESPP is calculated using the Black-Scholes option pricing model. The fair value of the look-back provision plus the 15% discount is recognized as compensation expense over the 180-day Fair Value Measurements • Level 1—Quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. Net Loss per Share Common stock equivalent shares are excluded from the computation of diluted net loss per share if their effect is antidilutive. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, 2016-13”) 2016-13 2016-13 2016-13 2016-13

Cash and Cash Equivalents

Cash and Cash Equivalents	12 Months Ended
	Dec. 31, 2022
Cash and Cash Equivalents [Abstract]
CASH AND CASH EQUIVALENTS	3. CASH AND CASH EQUIVALENTS From time to time, the Company may have cash balances in financial institutions in excess of federal deposit insurance limits. The Company has never experienced any losses related to these balances. The Company considers only those investments that are highly liquid, readily convertible to cash, and that mature within three months from date of purchase to be cash equivalents. The following table summarizes the Company’s cash and cash equivalents: December 31, 2022 2021 (in thousands) Cash $ 19 $ 59 Money market funds 33,967 108,323 Total cash and cash equivalents $ 33,986 $ 108,382

Short-Term Investments

Short-Term Investments	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Investments Disclosure [Abstract]
SHORT-TERM INVESTMENTS	3. SHORT-TERM INVESTMENTS The Company may invest its excess cash in fixed income instruments denominated and payable in U.S. dollars, including U.S. treasury securities, commercial paper, corporate debt securities and asset-backed securities in accordance with the Company’s investment policy that primarily seeks to maintain adequate liquidity and preserve capital. The following table summarizes the Company’s short-term investments as of September 30, 2023 and December 31, 2022: As of September 30, 2023 Amortized Unrealized Unrealized Fair (in thousands) Commercial paper $ 3,965 $ — $ (2 ) $ 3,963 US Treasury securities 55,268 6 (7 ) 55,267 Corporate debt securities 14,990 — (33 ) 14,957 Total $ 74,223 $ 6 $ (42 ) $ 74,187 As of December 31, 2022 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 57,138 $ — $ — $ 57,138 US Treasury securities 65,160 — (335 ) 64,825 Corporate debt securities 19,146 — (69 ) 19,077 Total $ 141,444 $ — $ (404 ) $ 141,040 The Company utilizes the specific identification method in computing realized gains and losses. The Company had no realized gains and losses on its available-for-sale	4. SHORT-TERM INVESTMENTS The Company may invest its excess cash in fixed income instruments denominated and payable in U.S. dollars including U.S. treasury securities, commercial paper, corporate debt securities and asset-backed securities in accordance with the Company’s investment policy that primarily seeks to maintain adequate liquidity and preserve capital. The following table summarizes the Company’s short-term investments as of December 31, 2022 and December 31, 2021: As of December 31, 2022 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 57,138 $ — $ — $ 57,138 US Treasury securities 65,160 — (335 ) 64,825 Corporate debt securities 19,146 — (69 ) 19,077 Total $ 141,444 $ — $ (404 ) $ 141,040 As of December 31, 2021 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 27,992 $ — $ — $ 27,992 Corporate debt securities 19,506 — (7 ) 19,499 Total $ 47,498 $ — $ (7 ) $ 47,491 The Company utilizes the specific identification method in computing realized gains and losses. The Company had no realized gains and losses on its available-for-sale

Fair Value Measurements

Fair Value Measurements	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	4. FAIR VALUE MEASUREMENTS The Company’s financial instruments consist of cash and cash equivalents, short-term investments, restricted cash and accounts payable. The carrying amount of cash, restricted cash and accounts payable are each considered a reasonable estimate of fair value due to the short-term maturity. Assets measured at fair value on a recurring basis were as follows: Description September 30, Quoted Prices Significant Other Significant (in thousands) Cash equivalents: Money market mutual funds $ 28,375 $ 28,375 $ — $ — Total cash equivalents $ 28,375 $ 28,375 $ — $ — Short-term investments: Commercial paper $ 3,963 $ — $ 3,963 $ — US Treasury securities 55,267 — 55,267 — Corporate debt securities 14,957 — 14,957 — Total short-term $ 74,187 $ — $ 74,187 $ — Total financial assets $ 102,562 $ 28,375 $ 74,187 $ — Description December 31, Quoted Prices Significant Other Significant (in thousands) Cash equivalents: Money market mutual funds $ 33,967 $ 33,967 $ — $ — Total cash equivalents $ 33,967 $ 33,967 $ — $ — Short-term investments: Commercial paper $ 57,138 $ — $ 57,138 $ — US Treasury securities 64,825 — 64,825 — Corporate debt securities 19,077 — 19,077 — Total short-term investments $ 141,040 $ — $ 141,040 $ — Total financial assets $ 175,007 $ 33,967 $ 141,040 $ — Short-term securities are valued using models or other valuation methodologies that use Level 2 inputs. These models are primarily industry-standard models that consider various assumptions, including time value, yield curve, volatility factors, default rates, current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace. There were no transfers between fair value measurement levels during the three and nine months ended September 30, 2023 and 2022.	5. FAIR VALUE MEASUREMENTS The Company’s financial instruments consist of cash and cash equivalents, short-term investments, restricted cash and accounts payable. The carrying amount of cash, restricted cash and accounts payable are each considered a reasonable estimate of fair value due to the short-term maturity. Assets measured at fair value on a recurring basis were as follows: Description December 31, Quoted Prices Significant Significant (in thousands) Cash equivalents: Money market mutual funds $ 33,967 $ 33,967 $ — $ — Total cash equivalents $ 33,967 $ 33,967 $ — $ — Short-term investments: Commercial paper $ 57,138 $ — $ 57,138 $ — US Treasury securities 64,825 — 64,825 — Corporate debt securities 19,077 — 19,077 — Total short-term investments $ 141,040 $ — $ 141,040 $ — Total financial assets $ 175,007 $ 33,967 $ 141,040 $ — Description December 31, Quoted Prices Significant Significant (in thousands) Cash equivalents: Money market mutual funds $ 108,323 $ 108,323 $ — $ — Total cash equivalents $ 108,323 $ 108,323 $ — $ — Short-term investments: Commercial paper $ 27,992 $ — $ 27,992 $ — Corporate debt securities 19,499 — 19,499 — Total short-term investments $ 47,491 $ — $ 47,491 $ — Total financial assets $ 155,814 $ 108,323 $ 47,491 $ — Short-term securities are valued using models or other valuation methodologies that use Level 2 inputs. These models are primarily industry-standard models that consider various assumptions, including time value, yield curve, volatility factors, default rates, current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace. There were no transfers between fair value measurement levels during the years ended December 31, 2022 and 2021.

Equity Method Investment

Equity Method Investment	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Equity Method Investment, Summarized Financial Information [Abstract]
EQUITY METHOD INVESTMENT	5. EQUITY METHOD INVESTMENT Summary of Transaction On March 10, 2022, the Company closed a transaction with OXB Solutions, Oxford Biomedica (US), Inc., (“OXB”), and Oxford, pursuant to the Equity Securities Purchase Agreement (the “Purchase Agreement”), dated as of January 28, 2022, by and among Homology, OXB Solutions and Oxford, whereby, among other things, Homology and Oxford agreed to collaborate to operate OXB Solutions, which provides AAV vector process development and manufacturing services to pharmaceutical and biotechnology companies (the “OXB Solutions Transaction”). Pursuant to the terms of the Purchase Agreement and a contribution agreement (the “Contribution Agreement”) entered into between Homology and OXB Solutions prior to the closing of the OXB Solutions Transaction (the “Closing”), Homology contributed its manufacturing team of 125 employees and assigned and transferred to OXB Solutions all of its assets that are primarily used in the manufacturing of AAV vectors for use in gene therapy and gene editing products, including its manufacturing facility and equipment and manufacturing-related intellectual property and know-how, Effective as of the Closing, Homology sold to OXB, and OXB purchased from Homology, 130,000 Units, (the “Transferred Units”) in exchange for $130.0 million of cash consideration. In connection with the Closing, OXB contributed $50.0 million in cash to OXB Solutions in exchange for an additional, newly issued 50,000 Units. Immediately following the Closing, (i) OXB owned 180,000 Units, representing 80 percent (80%) of the fully diluted equity interests in OXB Solutions, and (ii) Homology owned 45,000 Units, representing 20 percent (20%) of the fully diluted equity interests in OXB Solutions. Pursuant to the Amended and Restated Limited Liability Company Agreement of OXB Solutions (the “OXB Solutions Operating Agreement”) which was executed in connection with the Closing, at any time following the three-year anniversary of the Closing, (i) OXB will have an option to cause Homology to sell and transfer to OXB, and (ii) Homology will have an option to cause OXB to purchase from Homology, in each case all of Homology’s equity ownership interest in OXB Solutions at a price equal to 5.5 times the revenue for the immediately preceding 12-month Pursuant to the OXB Solutions Transaction, the Company also assigned all of its right, title and interest in, to and under its facility lease to OXB Solutions. However, as the Company remained jointly and severally liable for the payment of rent under the facility lease, the Company had not been released from being the primary obligor under such lease as of September 30, 2023 and therefore the related right-of-use Equity Method of Accounting The Company has significant influence over, but does not control, OXB Solutions through its noncontrolling representation on OXB’s board of directors and the Company’s equity interest in OXB Solutions. In addition, the Company and OXB Solutions have intra-entity transactions through a series of agreements entered into in conjunction with the OXB Solutions Transaction, OXB Solutions granted certain licenses to the Company, and the Company has representation on the joint steering committee which oversees the activities governed by the Supply Agreement. Accordingly, the Company does not consolidate the financial statements of OXB Solutions and accounts for its investment using the equity method of accounting. The Company recorded its equity method investment in OXB Solutions at fair value upon deconsolidation of OXB Solutions as of the Closing. The fair value of the equity method investment was determined based on the market approach. This approach estimated the fair value of OXB Solutions based on the implied value for the entity using the consideration paid, including the Options, for a controlling interest in OXB Solutions at the entity’s formation. As part of its fair value analysis, the Company determined that the Options are embedded in the common equity units because the Options are not legally detachable or separately exercisable. Accordingly, the equity method investment and the Options represent one unit of account and the fair value recorded reflects the value of the equity interest and the Options. The valuation included certain subjective assumptions including discounts for lack of control and marketability given the consideration paid for OXB Solutions was for a controlling interest in the entity and the Company owns a noncontrolling interest. As of March 10, 2022, the Closing, the fair value of the Company’s investment in OXB Solutions was $31.2 million and the Company recorded a gain of $131.2 million on the sale of its manufacturing business in other income in the Company’s condensed consolidated statements of operations. The gain was computed as follows: (in thousands) March 10, 2022 Cash received $ 130,000 Plus: Fair value of equity method investment 31,223 Less: Carrying value of transferred assets (29,974 ) Gain on sale of business $ 131,249 During the nine months ended September 30, 2023, the Company determined that the fair value of its investment in OXB Solutions was negatively impacted due to a change in OXB Solutions’ forecasted performance relative to expected performance when the Company initially invested in OXB Solutions. The Company determined that the decline in value was deemed to be other than temporary and recorded an impairment charge of $3.8 million to reduce its equity method investment to fair value. The impairment charge is included in the loss on equity method investment in the Company’s condensed consolidated statements of operations. In addition, the Company records its share of income or losses from OXB Solutions on a quarterly basis. For the nine months ended September 30, 2023, the Company recorded $8.1 million representing its share of OXB Solution’s net loss for the period. As of September 30, 2023, the carrying value of the equity method investment was $14.0 million.	6. EQUITY METHOD INVESTMENT Summary of Transaction On March 10, 2022, the Company closed a transaction with OXB Solutions, Oxford Biomedica (US), Inc., (“OXB”), and Oxford, pursuant to the Equity Securities Purchase Agreement (the “Purchase Agreement”), dated as of January 28, 2022, by and among Homology, OXB Solutions and Oxford, whereby, among other things, Homology and Oxford agreed to collaborate to operate OXB Solutions, which provides AAV vector process development and manufacturing services to pharmaceutical and biotechnology companies (the “OXB Solutions Transaction”). Pursuant to the terms of the Purchase Agreement and a contribution agreement (the “Contribution Agreement”) entered into between Homology and OXB Solutions prior to the closing of the OXB Solutions Transaction (the “Closing”), Homology contributed its manufacturing team of 125 employees and assigned and transferred to OXB Solutions all of its assets that are primarily used in the manufacturing of AAV vectors for use in gene therapy and gene editing products, including its manufacturing facility and equipment and manufacturing-related intellectual property and know-how, Effective as of the Closing, Homology sold to OXB, and OXB purchased from Homology, 130,000 Units, (the “Transferred Units”) in exchange for $130.0 million of cash consideration. In connection with the Closing, OXB contributed $50.0 million in cash to OXB Solutions in exchange for an additional, newly issued 50,000 Units. Immediately following the Closing, (i) OXB owned 180,000 Units, representing 80 percent (80%) of the fully diluted equity interests in OXB Solutions, and (ii) Homology owned 45,000 Units, representing 20 percent (20%) of the fully diluted equity interests in OXB Solutions. Pursuant to the Amended and Restated Limited Liability Company Agreement of OXB Solutions (the “OXB Solutions Operating Agreement”) which was executed in connection with the Closing, at any time following the three-year anniversary of the Closing, (i) OXB will have an option to cause Homology to sell and transfer to OXB, and (ii) Homology will have an option to cause OXB to purchase from Homology, in each case all of Homology’s equity ownership interest in OXB Solutions at a price equal to 5.5 times the revenue for the immediately preceding 12-month The fixed assets transferred to the new company as part of this transaction met the assets held for sale criteria and were reclassified to assets held for sale as of December 31, 2021. The Company determined that the carrying value of the assets held for sale did not exceed fair value less costs to sell, which resulted in no impairment charge for the year ended December 31, 2021. As of December 31, 2021, the Company presented $28.9 million of fixed assets transferred to OXB Solutions as a current asset under the caption of “assets held for sale” in its consolidated balance sheet. Pursuant to the OXB Solutions Transaction, the Company also assigned all of its right, title and interest in, to and under its facility lease to the new company. However, as the Company remains jointly and severally liable for the payment of rent under the facility lease, the Company has not been released from being the primary obligor under such lease and therefore the related right-of-use Equity Method of Accounting The Company has significant influence over, but does not control, OXB Solutions through its noncontrolling representation on OXB’s board of directors and the Company’s equity interest in OXB Solutions. In addition, the Company and OXB Solutions have intra-entity transactions through a series of agreements entered into in conjunction with the OXB Solutions Transaction, OXB Solutions granted certain licenses to the Company, and the Company has representation on the joint steering committee which oversees the activities governed by the Supply Agreement. Accordingly, the Company does not consolidate the financial statements of OXB Solutions and accounts for its investment using the equity method of accounting. The Company recorded its equity method investment in OXB Solutions at fair value upon deconsolidation of OXB Solutions as of the Closing. The fair value of the equity method investment was determined based on the market approach. This approach estimated the fair value of OXB Solutions based on the implied value for the entity using the consideration paid, including the Options, for a controlling interest in OXB Solutions at the entity’s formation. As part of its fair value analysis, the Company determined that the Options are embedded in the common equity units because the Options are not legally detachable or separately exercisable. Accordingly, the equity method investment and the Options represent one unit of account and the fair value recorded reflects the value of the equity interest and the Options. The valuation included certain subjective assumptions including discounts for lack of control and marketability given the consideration paid for OXB Solutions was for a controlling interest in the entity and the Company owns a noncontrolling interest. As of March 10, 2022, the Closing, the fair value of the Company’s investment in OXB Solutions was $31.2 million and the Company recorded a gain of $131.2 million on the sale of its manufacturing business in other income in the Company’s consolidated statements of operations. The gain was computed as follows: (in thousands) March 10, 2022 Cash received $ 130,000 Plus: Fair value of equity method investment 31,223 Less: Carrying value of transferred assets (29,974 ) Gain on sale of business $ 131,249 In addition, the Company records its share of income or losses from OXB Solutions on a quarterly basis. For the year ended December 31, 2022, the Company recorded $5.5 million representing its share of OXB Solution’s net loss. As of December 31, 2022, the carrying value of the equity method investment was $25.8 million. Summarized Financial Information Summarized financial information for OXB Solutions is as follows: December 31, Balance Sheet Data (in thousands) Current assets $ 39,237 Noncurrent assets $ 228,745 Current liabilities $ 12,352 Noncurrent liabilities $ 37,718 December 31, Statement of Operations Data (in thousands) Revenues $ 29,380 Net loss $ 29,036 See Note 16 for information regarding the Company’s related party transactions with OXB Solutions.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	6. PROPERTY AND EQUIPMENT, NET Property and equipment, net consists of the following: As of September 30, 2023 December 31, 2022 (in thousands) Laboratory equipment $ — $ 6,025 Computers and purchased software — 644 Furniture and fixtures — 645 Property and equipment, at cost — 7,314 Less: accumulated depreciation and amortization — (6,236 ) Property and equipment, net $ — $ 1,078 In August 2023, consistent with its decision to stop further development of its programs and explore, review and evaluate a range of potential strategic options available to the Company, the Company committed to a plan to sell its remaining property and equipment and therefore has classified the amount as assets held for sale on the consolidated balance sheet as of September 30, 2023. The assets held for sale were reported at the lower of the carrying amount or fair value with no depreciation expense taken after August 2023. Depreciation expense for the three and nine months ended September 30, 2023 was approximately $0.1 million and $0.6 million, respectively, compared to $0.3 million and $1.0 million, respectively for the three and nine months ended September 30, 2022. The Company had approximately $0.4 million of disposals of property and equipment during the three and nine months ended September 30, 2023. The Company had no disposals of property and equipment during the three and nine months ended September 30, 2022.	7. PROPERTY AND EQUIPMENT Property and equipment, net consists of the following: December 31, 2022 2021 (in thousands) Laboratory equipment $ 6,025 $ 5,857 Computers and purchased software 644 1,596 Furniture and fixtures 645 645 Property and equipment, at cost 7,314 8,098 Less accumulated depreciation and amortization (6,236 ) (5,846 ) Property and equipment, net $ 1,078 $ 2,252 Depreciation expense for the years ended December 31, 2022 and 2021 was approximately $1.3 million and $8.4 million, respectively. The Company disposed of approximately $0.1 million of property and equipment, net during each of the years ended December 31, 2022 and 2021. As of December 31, 2021, the Company has classified an additional $28.9 million of property and equipment, net in assets held for sale (see Note 6).

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER LIABILITIES	7. ACCRUED EXPENSES AND OTHER LIABILITIES Accrued expenses and other liabilities consist of the following: As of September 30, 2023 December 31, 2022 (in thousands) Accrued research and development expenses $ 8,198 $ 9,447 Accrued compensation and benefits 6,660 5,953 Accrued professional fees 648 1,052 Accrued other 205 2,263 Total accrued expenses and other liabilities $ 15,711 $ 18,715	8. ACCRUED EXPENSES AND OTHER LIABILITIES Accrued expenses and other liabilities consist of the following: December 31, 2022 2021 (in thousands) Accrued research and development expenses $ 9,447 $ 2,193 Accrued compensation and benefits 5,953 7,805 Accrued professional fees 1,052 1,371 Accrued other 2,263 37 Total accrued expenses and other liabilities $ 18,715 $ 11,406

Restructuring and Other Charges

Restructuring and Other Charges	9 Months Ended
	Sep. 30, 2023
Restructuring and Related Activities [Abstract]
RESTRUCTURING AND OTHER CHARGES	8. RESTRUCTURING AND OTHER CHARGES On July 25, 2023, the Company’s Board of Directors approved a process to explore, review and evaluate a range of potential strategic options available to the Company, including, without limitation, an acquisition, merger, reverse merger, sale of assets, strategic partnerships or other transactions. Therefore, based on cost-reduction initiatives intended to reduce the Company’s ongoing operating expenses and maximize shareholder value as the Company plans to pursue strategic options, the Company’s Board of Directors also approved a reduction in the Company’s workforce by approximately 80 employees, or 86% of the Company’s workforce as of July 2023. In connection with this corporate restructuring, the Company recorded a restructuring charge for severance and related costs of $6.9 million in the Company’s condensed consolidated statements of operations during the three months ended September 30, 2023. The Company’s restructuring liability, which was included in accrued compensation and benefits, consisted of the following: (in thousands) Employee-Related Accrued restructuring balance at January 1, 2023 $ — Expenses incurred 6,895 Payments (2,154 ) Accrued restructuring balance at September 30, 2023 $ 4,741 The Company had previously granted certain of the terminated employees restricted stock units (“RSUs”) that vest in annual installments based on continued service to the Company, as well as options to purchase shares of the Company’s common stock that typically vest over a period of four years. In connection with the reduction in workforce, the Company agreed to accelerate the vesting of a portion of the RSUs that were unvested as of the employees’ termination dates, and also modify the stock options for terminated employees such that subject to the satisfaction of severance conditions, the terminated employees’ vested options will remain outstanding and exercisable until the first anniversary of each employee’s termination date. These equity modifications, described in detail in Note 10, resulted in a net reduction to stock based compensation expense of $0.3 million reflected within restructuring and other charges in the Company’s condensed consolidated statements of operations during the three months ended September 30, 2023.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	9. COMMITMENTS AND CONTINGENCIES Operating Leases three pro-rata right-of-use In November 2021, the Company entered into an amendment of its December 2017 lease agreement (the “Lease Amendment”) for its corporate headquarters in Bedford, Massachusetts. The Lease Amendment increases the space under lease by approximately 23,011 square feet (the “Expansion Premises”) and extended the expiration date of the existing premises under the lease from February 2027 to June 2030. The payment term with respect to the Expansion Premises commenced on May 1, 2022 and continues for a period of ten years and five months. The term of the Expansion Premises and the existing premises are not coterminous. Annual base rent for the existing premise under the Lease Amendment is approximately $4.7 million beginning on March 1, 2027, and increases by three three right-of-use right-of-use lease liabilities. In February 2022, the Company revised its assumption for when it expects to utilize the tenant improvement allowances. This change in assumption was accounted for as a lease modification and the right-of-use right-of-use In March 2022, in accordance with its transaction with OXB Solutions, the Company assigned all of its right, title and interest in, to and under its corporate headquarters lease to OXB Solutions and entered into a sublease agreement whereby OXB Solutions subleased certain premises in its facility to Homology. The Company was not released from being the primary obligor under such lease as of September 30, 2023 and therefore the related right-of-use In September 2022, the Company concluded that 100% of the tenant improvement allowances would be utilized by OXB Solutions. This change in assumption was accounted for as a lease modification and the right-of-use right-of-use The following table summarizes operating lease costs and variable lease costs, as well as sublease income: Nine months ended September 30, 2023 2022 (in thousands) Operating lease costs $ 3,263 $ 2,826 Variable lease costs 1,551 1,698 Sublease income (2,312 ) (1,210 ) Net lease cost $ 2,502 $ 3,314 The maturities of the Company’s operating lease liabilities and minimum lease payments as of September 30, 2023 were as follows: For the Years Ending December 31, Amount 2023 1,134 2024 4,578 2025 4,715 2026 4,857 Thereafter 26,265 Total undiscounted lease payments $ 41,549 Less: imputed interest (13,211 ) Present value of operating lease liabilities $ 28,338 The following table summarizes the lease term and discount rate as of September 30, 2023: September 30, 2023 Weighted-average remaining lease term (years) Operating leases 7.5 Weighted-average discount rate Operating leases 10.6 % The following table summarizes the supplemental cash flow information related to the Company’s operating lease: Nine months ended September 30, 2023 2022 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 3,310 $ 2,226 Increase in lease liabilities and right-of-use $ — $ 6,262 Legal Proceedings Pizzuto v. Homology Medicines, Inc. HMI-102 1:23-cv-10858-AK	9. COMMITMENTS AND CONTINGENCIES Operating Leases In December 2017, the Company entered into a noncancelable operating lease for approximately 67,000 square feet of research and development, manufacturing and general office space in Bedford, Massachusetts. Prior to a subsequent amendment described below, the lease was set to expire in February 2027 with an option for an additional five-year term. Rent became due under the lease in two phases; rent on the first 46,000 square feet started in September 2018 and rent on the remaining 21,000 square feet started in March 2019. The initial annual base rent was $39.50 per square foot and increases by three pro-rata right-of-use In November 2021, the Company entered into an amendment of its December 2017 lease agreement (the “Lease Amendment”) for its corporate headquarters in Bedford, Massachusetts. The Lease Amendment increases the space under lease by approximately 23,011 square feet (the “Expansion Premises”) and extended the expiration date of the existing premises under the lease from February 2027 to June 2030. The payment term with respect to the Expansion Premises commences on the earlier of (i) the date of the Substantial Completion of the Tenant’s Work (as both terms are defined in the Lease Amendment), (ii) the Company’s occupancy of any portion of the Expansion Premises, and (iii) May 1, 2022, and continues for a period of ten years and five months. The term of the Expansion Premises and the existing premises are not coterminous. Annual base rent for the existing premise under the Lease Amendment is approximately $4.7 million beginning on March 1, 2027, and increases by three three right-of-use right-of-use improvement allowances. This change in assumption was accounted for as a lease modification and the right-of-use right-of-use In March 2022, in accordance with its transaction with OXB Solutions, the Company assigned all of its right, title and interest in, to and under its corporate headquarters lease to OXB Solutions and entered into a sublease agreement whereby OXB Solutions subleased certain premises in its facility to Homology. However, as the Company has not been released from being the primary obligor under such lease, the related right-of-use In September 2022, the Company concluded that 100% of the tenant improvement allowances would be utilized by OXB Solutions. This change in assumption was accounted for as a lease modification and the right-of-use right-of-use The Company maintained letters of credit, secured by restricted cash, for security deposits totaling $2.0 million as of December 31, 2021 in conjunction with its leases. The Company had no security deposit or restricted cash as of December 31, 2022. The following table summarizes operating lease costs and variable lease costs, as well as sublease income for the year ended December 31, 2022: Years ended December 31, 2022 2021 (in thousands) Operating lease costs $ 3,913 $ 2,592 Variable lease costs 2,142 2,127 Sublease income (1,979 ) (861 ) Net lease cost $ 4,076 $ 3,858 The maturities of our operating lease liabilities as of December 31, 2022 were as follows: For the Years Ending December 31, Amount 2023 4,444 2024 4,578 2025 4,715 2026 4,857 Thereafter 26,266 Total undiscounted lease payments $ 44,860 Less: imputed interest (15,383 ) Present value of operating lease liabilities $ 29,477 The following table summarizes the lease term and discount rate as of December 31, 2022: As of Weighted-average remaining lease term (years) Operating leases 8.2 Weighted-average discount rate Operating leases 10.6 % The following table summarizes the supplemental cash flow information related to the Company’s operating leases for the year ended December 31, 2022. Years ended December 31, 2022 2021 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 3,326 $ 3,810 Increase in lease liabilities and right-of-use $ 6,262 $ 10,901 Legal Proceedings HMI-102

License Agreements

License Agreements	12 Months Ended
	Dec. 31, 2022
License Agreement [Abstract]
LICENSE AGREEMENTS	10. LICENSE AGREEMENTS Novartis In November 2017, the Company entered into a collaboration and license agreement with Novartis (as amended, the “Collaboration Agreement”) for the research, development, manufacturing and commercialization of products using the Company’s gene-editing technology for the treatment of certain ophthalmic targets and sickle cell disease. On February 26, 2021, Homology received notice from Novartis that they had elected to terminate the Collaboration Agreement with the Company with respect to the remaining ophthalmic target under the Collaboration Agreement and as a result, the Company regained worldwide exclusive rights to this target. Accordingly, the notice served as notice of Novartis’ termination of the Collaboration Agreement in its entirety, which became effective on August 26, 2021. The Company recognized revenue under the Collaboration Agreement over time using a cost-to-cost As the Collaboration Agreement terminated in 2021, there was no revenue recorded in the year ended December 31, 2022. During the year ended December 31, 2021, the Company recognized revenue under the Collaboration Agreement of $30.8 million, of which $30.2 million was included in deferred revenue at the beginning of 2021. As of December 31, 2022 and 2021, there was no deferred revenue related to the Collaboration Agreement. There was no accounts receivable or deferred revenue on the Company’s consolidated balance sheets related to the Collaboration Agreement in either period presented. City of Hope In April 2016, the Company entered into an exclusive license agreement with City of Hope, or COH, an academic research and medical center. COH granted the Company an exclusive, sublicensable, worldwide license, or the COH License, to certain AAV vector-related patents and know-how know-how The Company is required to pay an annual license fee of $25,000, reimburse COH for patent costs incurred, pay amounts up to $3.2 million upon the achievement of certain development and commercialization milestones for each product under the license, pay royalties on future sales in the low single-digits and royalties on sublicense revenue in the low double-digits, if any. Other than the annual license fee, there were no payments to COH in 2021 or 2022. In January 2023, the Company paid $50,000 to COH upon dosing the first patient in the pheEDIT Phase 1 clinical trial. On August 6, 2021, the Company received notice from COH that it did not accomplish at least one of the partnering milestones by the applicable deadline, as set forth in the COH License. This notice does not affect the Company’s exclusive license in the field of mammalian therapeutics, including all human therapeutics, associated diagnostics, and target validation, or the Mammalian Therapeutic Field, where the Company retains exclusive rights. Instead, the notice served as written notice that the exclusive license granted pursuant to the COH License in all fields except the Mammalian Therapeutic Field converted from exclusive to non-exclusive HMI-102, HMI-103, HMI-203, HMI-204 HMI-104, California Institute of Technology In September 2016, the Company entered into a co-exclusive AAV-related

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
INCOME TAXES	11. INCOME TAXES Provision for income taxes consists of the following: For the Year Ended December 31, 2022 2021 (in thousands) Federal tax provision: Current $ 698 $ — Deferred — — Total federal tax provision 698 — State tax provision: Current 17 — Deferred — — Total state tax provision 17 — Total tax provision $ 715 $ — A reconciliation between the U.S. federal statutory tax and the Company’s tax provision is summarized below. The Company has changed the presentation of its rate reconciliation from percentages to dollar amounts in the current year. For the Year Ended December 31, 2022 2021 (in thousands) Federal statutory tax $ (901 ) $ (20,111 ) Tax credits (13,955 ) (8,940 ) State taxes, net of federal tax benefit (2,994 ) (8,240 ) Non-deductible 875 1,331 Other 1,410 (2,401 ) Change in valuation allowance 16,280 38,361 Tax provision $ 715 $ — The principal components of the Company’s deferred tax assets and liabilities consist of the following: December 31, 2022 2021 (in thousands) Deferred tax assets: Net operating losses $ 76,735 $ 100,417 R&D credits 66,761 51,705 Equity compensation 7,888 6,919 Operating lease liabilities 8,003 6,520 Accrued expense and other 1,479 2,072 Deferred revenue 314 1,189 Capitalized R&D costs 24,477 868 Total deferred tax assets 185,657 169,690 December 31, 2022 2021 (in thousands) Deferred tax liabilities: Right-of-use (5,583 ) (4,252 ) Depreciation (171 ) (1,541 ) Other (251 ) (503 ) Total deferred tax liabilities (6,005 ) (6,296 ) Valuation allowance (179,652 ) (163,394 ) Net deferred taxes $ — $ — The Company recorded an income tax provision of $0.7 million for the year ended December 31, 2022. The year-to-date At December 31, 2022, the Company had $283.5 million and $272.1 million of federal and state net operating loss carryforwards, respectively. Federal net operating loss carryforwards of $0.4 million, generated before 2018, will begin expiring in varying amounts through 2035 unless utilized. The remaining federal net operating loss carryforwards of $283.1 million, generated after 2017, will be carried forward indefinitely. The state net operating losses will begin expiring in varying amounts through 2041 unless utilized. At December 31, 2022, the Company had $55.1 million and $14.8 million of federal and state research and development credit carryforwards, respectively, that expire at various dates through 2041. Included in the $55.1 million of federal research and development credit carryforwards is $45.2 million of orphan drug credit carryforwards. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. A roll forward of the valuation allowance is as follows: Valuation (in thousands) Balance at December 31, 2021 $ (163,394 ) Utilization of net operating losses against taxable income 23,654 Increase in net deferred taxes (39,912 ) Balance at December 31, 2022 $ (179,652 ) For all years through December 31, 2022, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards. Since a full valuation allowance has been provided against the Company’s research and development credits, any reduction in the gross deferred tax asset established for the research and development credit carryforwards would not result in any net impact to the Company’s consolidated financial statements. Realization of the future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. Under the provisions of the Internal Revenue Code, certain substantial changes in the Company’s ownership, including a sale of the Company or significant changes in ownership due to sales of equity, may have limited, or may limit in the future, the amount of net operating loss carryforwards that could be used annually to offset future taxable income. The Company completed a study to assess ownership changes through December 31, 2022. Based on this analysis, the net operating losses are limited but the Company does not believe that any of its net operating losses or research and development credit carryforwards will expire unutilized due to Section 382 limitations. The Company files tax returns in the United States, Massachusetts and several other states. All tax years since inception remain open to examination by the major taxing jurisdictions to which the Company is subject, as carryforward attributes generated in years past may still be adjusted upon examination by the Internal Revenue Service (“IRS”) or other authorities if they have or will be used in a future period. The Company is not currently under examination by the IRS or any other jurisdictions for any tax years. As of December 31, 2022, the Company had no uncertain tax positions. The Company has elected to recognize interest and penalties related to income tax matters as a component of income tax expense, of which no interest or penalties were recorded for the years ended December 31, 2022 and 2021.

Stockholder's Equity

Stockholder's Equity	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
STOCKHOLDERS' EQUITY	12. STOCKHOLDERS’ EQUITY Common Stock Voting Dividends Liquidation Rights winding-up There were 57,483,910 and 57,150,274 shares of common stock outstanding at December 31, 2022 and 2021, respectively. Preferred Stock

Stock Incentive Plans

Stock Incentive Plans	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
STOCK INCENTIVE PLANS	10. STOCK INCENTIVE PLANS 2015 Stock Incentive Plan In December 2015, the Company’s Board of Directors adopted the 2015 Stock Incentive Plan (the “2015 Plan”), which provided for the grant of incentive stock options, nonqualified stock options and restricted stock awards to the Company’s employees, officers, directors, advisors, and outside consultants. Stock options granted under the 2015 Plan generally vest over a four-year period and expire ten years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the 2015 Plan. At September 30, 2023, there were no additional shares available for future grant under the 2015 Plan. 2018 Incentive Award Plan In March 2018, the Company’s Board of Directors adopted and the Company’s stockholders approved the Homology Medicines, Inc. 2018 Incentive Award Plan (the “2018 Plan” and, together with the 2015 Plan, the “Plans”), which became effective on the day prior to the first public trading date of the Company’s common stock. Upon effectiveness of the 2018 Plan, the Company ceased granting new awards under the 2015 Plan. The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock or cash-based awards to employees and consultants of the Company and certain affiliates and directors of the Company. The number of shares of common stock initially available for issuance under the 2018 Plan was 3,186,205 shares of common stock plus the number of shares subject to awards outstanding under the 2015 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company on or after the effective date of the 2018 Plan. In addition, the number of shares of common stock available for issuance under the 2018 Plan is subject to an annual increase on the first day of each calendar year beginning on January 1, 2019, and ending on and including January 1, 2028, equal to the lesser of (i) 4% of the Company’s outstanding shares of common stock on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the Company’s Board of Directors, provided that not more than 20,887,347 shares of common stock may be issued under the 2018 Plan upon the exercise of incentive stock options. Therefore, on January 1, 2023, an additional 2,299,356 shares were added to the 2018 Plan, representing 4% of total common shares outstanding at December 31, 2022. As of September 30, 2023, there were 1,978,793 shares available for future grant under the 2018 Plan. 2018 Employee Stock Purchase Plan In March 2018, the Company’s Board of Directors adopted and the Company’s stockholders approved the Homology Medicines, Inc. 2018 Employee Stock Purchase Plan (the “2018 ESPP”). The 2018 ESPP allows employees to buy Company stock through after-tax Under the 2018 ESPP, employees may purchase common stock through after-tax During the nine months ended September 30, 2023, 133,817 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of approximately $0.2 million. During the nine months ended September 30, 2022, 226,453 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of approximately $0.6 million. Pursuant to the 2018 ESPP, the Company recorded stock-based compensation of less than $0.1 million during the three and nine months ended September 30, 2023 and 2022, respectively. Stock Options The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model, with the assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer group of publicly traded companies that are similar to the Company. The expected term of options was calculated using the simplified method, which represents the average of the contractual term of the option and the weighted-average vesting period of the option. The Company uses the simplified method because it does not have sufficient historical option exercise data to provide a reasonable basis upon which to estimate expected term. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant for periods commensurate with the expected term of the award. The Company recognizes forfeitures as they occur. The assumptions used in the Black-Scholes option pricing model are as follows (note that there were no options granted during the three months ended September 30, 2023): Three months ended Nine months ended September 30, September 30, 2022 2023 2022 Expected volatility 70.1 % 69.2%-69.7% 68.7%-70.1% Weighted-average risk-free interest rate 3.20%-3.66% 3.45%-4.22% 1.46%-3.66% Expected dividend yield — % — % — % Expected term (in years) 6.25 5.5-6.25 5.5-6.25 Underlying common stock fair value $ 1.82-$2.82 $ 0.92-$1.60 $ 1.78-$4.17 The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Weighted- Weighted- Aggregate (in thousands) Outstanding at January 1, 2023 9,865,734 $ 10.96 7.2 $ 493 Granted 3,188,150 $ 1.53 Exercised (3,366 ) $ 0.47 Cancelled/Forfeited (623,776 ) $ 11.11 Outstanding at September 30, 2023 12,426,742 $ 8.55 4.9 $ 488 Vested and expected to vest at September 30, 2023 12,426,742 $ 8.55 4.9 $ 488 Exercisable at September 30, 2023 7,566,304 $ 11.80 4.5 $ 421 The total intrinsic value of options exercised during the nine months ended September 30, 2023 and 2022 was insignificant for each period. The weighted-average grant date fair value per share of options granted during the nine months ended September 30, 2023 and 2022 was $1.01 and $1.72, respectively. Stock Awards Modifications - Corporate Restructuring In connection with the Company’s corporate restructuring (see Note 8), the Company terminated approximately 80 employees and modified approximately 3.3 million existing stock options and approximately 0.4 million existing restricted stock units (“RSUs”) granted to these terminated employees in prior periods. The modification of the vested stock options to permit terminated employees up to one year following their termination date to exercise their options, rather than the 90-day Compensation—Stock Compensation The terminated employees’ RSUs were modified to accelerate the vesting of a portion of the RSUs that were unvested as of the employees’ termination dates. The accelerated vesting of certain RSUs is accounted for as a Type III (improbable to probable) modification under ASC 718. Accordingly, the Company reversed all compensation cost previously recorded on the awards that are not expected to vest under the original terms. Total compensation cost reversed in the three months ended September 30, 2023 was approximately $0.2 million. Total compensation cost of less than $0.1 million, equal to the modification date fair value, was recognized over the remaining service period, beginning on the modification date and ending on each employee’s termination date. Stock Awards Modifications - OXB Solutions Transaction As part of the transaction with OXB Solutions (see Note 5), the Company transferred employees to OXB Solutions and modified approximately 1.6 million existing stock options and approximately 0.1 million existing restricted stock units granted to these transferred employees in prior periods in order to permit such individuals to continue vesting in their awards and exercise their vested options as long as they are employed by and provide services to OXB Solutions. The modification of the unvested stock awards to continue vesting was accounted for as a Type III (improbable to probable) modification under ASC 718. Accordingly, the Company reversed all compensation cost previously recorded on the awards that were not expected to vest under the original terms. Total compensation cost reversed in the three months ended March 31, 2022 was less than $0.1 million. Total compensation cost of $0.8 million, equal to the modification date fair value, will be recognized over the remaining service period. A portion of this total compensation cost will be included as a component of the loss from equity method investment. The modification of the vested stock awards to permit transferred employees to exercise their options over the remaining life of the award, rather than the 90-day 90-day Restricted Stock Units The fair value of RSUs is based on the fair market value of the Company’s common stock on the date of grant. Each RSU represents a contingent right to receive one share of the Company’s common stock upon vesting. In general, RSUs vest annually in two or three equal installments on January 1st of each year after the grant date. The following table summarizes the Company’s RSU activity for the nine months ended September 30, 2023: Number of Weighted- Outstanding at January 1, 2023 543,179 $ 6.12 Granted 483,850 $ 1.60 Vested (281,117 ) $ 5.31 Forfeited (258,184 ) $ 2.54 Outstanding at September 30, 2023 487,728 $ 3.04 Stock-based Compensation Expense The Company recognizes compensation expense for awards to employees based on the grant date fair value of stock-based awards on a straight-line basis over the period during which an award holder provides service in exchange for the award, which is generally the vesting period. The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP, restricted stock units and stock award modifications as follows: Three months ended Nine months ended 2023 2022 2023 2022 (in thousands) Research and development $ 230 $ 889 $ 1,507 $ 4,143 General and administrative 1,477 1,882 4,970 5,822 $1,707 $2,771 $6,477 $9,965 As of September 30, 2023, there was $10.5 million of unrecognized compensation expense related to unvested employee and non-employee	13. STOCK INCENTIVE PLANS 2015 Stock Incentive Plan In December 2015, the Company’s Board of Directors adopted the 2015 Stock Incentive Plan (the “2015 Plan”), which provided for the grant of incentive stock options, nonqualified stock options and restricted stock awards to the Company’s employees, officers, directors, advisors, and outside consultants. Stock options granted under the 2015 Plan generally vest over a four-year period and expire ten years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the 2015 Plan. At December 31, 2022, there were no additional shares available for future grant under the 2015 Plan. 2018 Incentive Award Plan In March 2018, the Company’s Board of Directors adopted and the Company’s stockholders approved the Homology Medicines, Inc. 2018 Incentive Award Plan (the “2018 Plan” and, together with the 2015 Plan, the “Plans”), which became effective on the day prior to the first public trading date of the Company’s common stock. Upon effectiveness of the 2018 Plan, the Company ceased granting new awards under the 2015 Plan. The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock or cash-based awards to employees and consultants of the Company and certain affiliates and directors of the Company. The number of shares of common stock initially available for issuance under the 2018 Plan was 3,186,205 shares of common stock plus the number of shares subject to awards outstanding under the 2015 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company on or after the effective date of the 2018 Plan. In addition, the number of shares of common stock available for issuance under the 2018 Plan is subject to an annual increase on the first day of each calendar year beginning on January 1, 2019 and ending on and including January 1, 2028 equal to the lesser of (i) 4% of the Company’s outstanding shares of common stock on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the Company’s Board of Directors, provided that not more than 20,887,347 shares of common stock may be issued under the 2018 Plan upon the exercise of incentive stock options. As of December 31, 2022, there were 2,188,360 shares available for future grant under the 2018 Plan. On January 1, 2023, an additional 2,299,356 shares were added to the 2018 Plan, representing 4% of total common shares outstanding at December 31, 2022. 2018 Employee Stock Purchase Plan In March 2018, the Company’s Board of Directors adopted, and the Company’s stockholders approved, the Homology Medicines, Inc. 2018 Employee Stock Purchase Plan (the “2018 ESPP”). The 2018 ESPP allows employees to buy Company stock through after-tax Under the 2018 ESPP, employees may purchase common stock through after-tax Code, no employee will be permitted to accrue the right to purchase stock under the 2018 ESPP at a rate in excess of $25,000 worth of shares during any calendar year during which such a purchase right is outstanding (based on the fair market value per share of the Company’s common stock as of the first day of the offering period). During the year ended December 31, 2022, 226,453 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of $0.6 million. During the year ended December 31, 2021, 110,923 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of $0.8 million. Pursuant to the 2018 ESPP, the Company recorded stock-based compensation of less than $0.1 million and $0.1 million for the years ended December 31, 2022 and 2021, respectively. Stock Options The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model, with the assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer group of publicly traded companies that are similar to the Company. The expected term of options was calculated using the simplified method, which represents the average of the contractual term of the option and the weighted-average vesting period of the option. The Company uses the simplified method because it does not have sufficient historical option exercise data to provide a reasonable basis upon which to estimate expected term. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant for periods commensurate with the expected term of the award. The Company recognizes forfeitures as they occur. The assumptions used in the Black-Scholes option pricing model are as follows: For the Year Ended December 31, 2022 2021 Expected volatility 68.7% - 70.1% 64.6% - 71.7% Weighted-average risk-free interest rate 1.46% - 4.16% 0.50% - 1.33% Expected dividend yield — % — % Expected term (in years) 5.5 - 6.25 5.5 - 6.25 Underlying common stock fair value $1.40 - $4.17 $4.85 - $13.91 A summary of option activity under the Plans during the year ended December 31, 2022 is as follows: Number of Weighted- Weighted- Aggregate (in thousands) Outstanding at January 1, 2022 7,624,306 $ 14.25 7.5 $ 2,069 Granted 3,089,655 $ 2.64 Exercised (293 ) $ 2.71 Cancelled/Forfeited (847,934 ) $ 10.25 Outstanding at December 31, 2022 9,865,734 $ 10.96 7.2 $ 493 Vested and expected to vest at 9,865,734 $ 10.96 7.2 $ 493 Exercisable at December 31, 2022 6,111,596 $ 13.19 6.3 $ 493 The total intrinsic value of options exercised during the year ended December 31, 2022 and 2021 was immaterial and $0.6 million, respectively. The weighted-average grant date fair value of options granted during the years ended December 31, 2022 and 2021 was $1.68 and $7.26, respectively. Stock Awards Modifications As part of the transaction with OXB Solutions (see Note 6), the Company transferred employees to OXB Solutions and modified approximately 1.6 million existing stock options and approximately 0.1 million existing restricted stock units granted to these transferred employees in prior periods in order to permit such individuals to continue vesting in their awards and exercise their vested options as long as they are employed by and provide services to OXB Solutions. The modification of the unvested stock awards to continue vesting was accounted for as a Type III (improbable to probable) modification under FASB ASC Topic 718, Compensation—Stock Compensation . The modification of the vested stock awards to permit transferred employees to exercise their options over the remaining life of the award, rather than the 90-day 90-day Restricted Stock Units The fair value of restricted stock units (“RSUs”) is based on the fair market value of the Company’s common stock on the date of grant. Each RSU represents a contingent right to receive one share of the Company’s common stock upon vesting. In general, RSUs vest annually in two or three equal installments on January 1st of each year after the grant date. The following table summarizes the Company’s RSU activity for the year ended December 31, 2022: Number of Weighted- Outstanding at January 1, 2022 307,600 $ 12.75 Granted 400,495 $ 2.70 Vested (106,890 ) $ 12.42 Forfeited (58,026 ) $ 6.05 Outstanding at December 31, 2022 543,179 $ 6.12 Stock-based Compensation Expense The Company recognizes compensation expense for awards to employees based on the grant date fair value of stock-based awards on a straight-line basis over the period during which an award holder provides service in exchange for the award, which is generally the vesting period. The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP and restricted stock units as follows: For the Year Ended December 31, 2022 2021 (in thousands) General and administrative $ 7,867 $ 8,450 Research and development 5,187 8,795 $ 13,054 $ 17,245 As of December 31, 2022, there was $14.6 million of unrecognized compensation expense related to unvested employee and non-employee

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
NET INCOME (LOSS) PER SHARE	11. NET INCOME (LOSS) PER SHARE Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares outstanding during the applicable period. Diluted net income (loss) per share incorporates the additional shares issuable upon assumed exercise of stock options and the vesting of restricted stock units, except in such case when their inclusion would be anti-dilutive. Three months ended Nine months ended (in thousands, except per share amounts) 2023 2022 2023 2022 Numerator: Net income (loss) $ (32,954 ) $ (33,726 ) $ (96,842 ) $ 29,290 Denominator: Weighted-average common shares outstanding-basic 57,853,132 57,447,192 57,788,755 57,372,399 Dilutive securities — — — 528,899 Weighted-average common shares outstanding-diluted 57,853,132 57,447,192 57,788,755 57,901,298 Net income (loss) per share-basic $ (0.57 ) $ (0.59 ) $ (1.68 ) $ 0.51 Net income (loss) per share-diluted $ (0.57 ) $ (0.59 ) $ (1.68 ) $ 0.51 For the three and nine months ended September 30, 2023, as well as for the three months end September 30, 2022, the effect of dilutive securities including stock options, restricted stock units and unvested common stock from early exercise of options, was excluded from the denominator for the calculation of diluted net loss per share because the Company recognized a net loss for the periods and their inclusion would be anti-dilutive. Anti-dilutive securities excluded for the three months ended September 30, 2023 and 2022 were 12,993,266 and 9,933,508, respectively, and for the nine months ended September 30, 2023 and 2022 were 12,507,026 and 9,048,927, respectively.

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
DEFINED CONTRIBUTION PLAN	14. DEFINED CONTRIBUTION PLAN The Company has a 401(k) defined contribution plan (the “401(k) Plan”) for all of its employees. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits, while the Company contributes to the plan at the discretion of the Board of Directors. The Company’s discretionary match made under the 401(k) Plan for the years ended December 31, 2022 and 2021 was $0.6 million and $0.8 million, respectively.

Pfizer Stock Purchase Agreement

Pfizer Stock Purchase Agreement	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Pfizer Inc.
PFIZER STOCK PURCHASE AGREEMENT	12. PFIZER STOCK PURCHASE AGREEMENT On November 9, 2020, the Company entered into a common stock purchase agreement (the “Stock Purchase Agreement”) with Pfizer Inc. (“Pfizer”), pursuant to which the Company agreed to issue and sell to Pfizer 5,000,000 shares of the Company’s common stock through a private placement transaction (the “Private Placement”) at a purchase price of $12.00 per share, for an aggregate purchase price of $60.0 million. The shares of common stock sold to Pfizer were subject to a one-year lock-up Under the Stock Purchase Agreement, Pfizer was granted an exclusive right of first refusal (the “ROFR”) for a 30-month HMI-102 HMI-103. HMI-102 HMI-103 The Company recorded the issuance of common stock at its estimated fair value of $52.0 million, which reflected a discount for the lack of marketability of the shares. The remaining $8.0 million of aggregate purchase price was allocated to the other elements of the Stock Purchase Agreement, which represented a contract with a customer. The Company concluded that the Information Committee represented the only performance obligation under the contract. The ROFR did not provide Pfizer with a material right and was therefore not a performance obligation. As such, the Company allocated the $8.0 million to the Information Committee obligation. The Company recognizes revenue over time as the measure of progress, which it believes best depicts the transfer of control to Pfizer. The Information Committee met regularly over the ROFR Period to share information which resulted in recognition of the transaction price over the 30-month During the nine months ended September 30, 2023, the Company recognized collaboration revenue of $1.2 million, compared to $0.8 million and $2.4 million, respectively for the three and nine months ended September 30, 2022. As the ROFR Period expired in May 2023, there was no	15. PFIZER STOCK PURCHASE AGREEMENT On November 9, 2020, the Company entered into a common stock purchase agreement (the “Stock Purchase Agreement”) with Pfizer Inc. (“Pfizer”), pursuant to which the Company agreed to issue and sell to Pfizer 5,000,000 shares of the Company’s common stock through a private placement transaction (the “Private Placement”) at a purchase price of $12.00 per share, for an aggregate purchase price of $60.0 million. The shares of common stock sold to Pfizer were subject to a one-year lock-up Under the Stock Purchase Agreement, Pfizer was granted an exclusive right of first refusal (the “ROFR”) for a 30-month HMI-102 HMI-103. HMI-102 HMI-103 HMI-102 HMI-103 The Company recorded the issuance of common stock at its estimated fair value of $52.0 million, which reflects a discount for the lack of marketability of the shares. The remaining $8.0 million of aggregate purchase price was allocated to the other elements of the Stock Purchase Agreement, which represent a contract with a customer. The Company concluded that the Information Committee represents the only performance obligation under the contract. The ROFR does not provide Pfizer with a material right and is therefore not a performance obligation. As such, the Company allocated the $8.0 million to the Information Committee obligation. The Company recognizes revenue over time as the measure of progress which it believes best depicts the transfer of control to Pfizer. The Information Committee will meet regularly over the ROFR Period to share information which results in recognition of the transaction price over the 30-month The Company recognized collaboration revenue of $3.2 million during each of the years ended December 31, 2022

Related Party Transactions

Related Party Transactions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	13. RELATED PARTY TRANSACTIONS Oxford Biomedica Solutions LLC As described in Note 5, the Company has significant influence over, but does not control, OXB Solutions through its noncontrolling representation on OXB Solution’s board of directors and the Company’s equity interest in OXB Solutions. In March 2022, concurrently with the closing of the transaction with OXB Solutions, the Company entered into certain ancillary agreements with OXB Solutions including a supply agreement, a lease assignment and assumption agreement, a sublease agreement and a transitional services agreement. Supply Agreement Pursuant to the terms of the Manufacturing and Supply Agreement with OXB Solutions entered into in March 2022 (the “Supply Agreement”), the Company agreed to purchase from OXB Solutions at least 50% of its clinical supply requirements of AAV-based one-year fiscal year ending December 31, 2023. As of September 30, 2023, the Company had approximately $1.4 million in remaining purchase obligations to OXB Solutions pursuant to the Supply Agreement. There are no minimum purchase commitments in 2024 (year three) of the Supply Agreement. After the initial term, the Company will have the right to terminate the Supply Agreement for convenience or other reasons specified in the Supply Agreement upon prior written notice. Either party may terminate the Supply Agreement upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party. During the three and nine months ended September 30, 2023, the Company recorded purchases of drug substance from OXB Solutions related to the Supply Agreement of $8.4 million and $21.7 million, respectively, as well as purchases of process development services of approximately $3.1 million and $5.8 million, respectively, and stability services and other support services of approximately $0.4 million and $1.2 million, respectively. During the three and nine months ended September 30, 2022, the Company recorded purchases of drug substance from OXB Solutions related to the Supply Agreement of $6.0 million and $7.5 million, respectively, as well as purchases of process development services of approximately $2.2 million and $10.2 million, respectively. These amounts are included within research and development expenses on the Company’s condensed consolidated statements of operations. The amounts due to OXB Solutions under the Supply Agreement were $12.6 million and $5.2 million as of September 30, 2023 and December 31, 2022, respectively, and were included in accounts payable and accrued expenses and other liabilities on the Company’s condensed consolidated balance sheets. Lease Assignment and Sublease Agreement As described in Note 9, the Company leases space for research and development, manufacturing and general office space in Bedford, Massachusetts. In March 2022, the Company and OXB Solutions entered into a lease assignment and assumption agreement pursuant to which Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions and a sublease agreement whereby OXB Solutions subleased certain premises in its facility to Homology. However, as of and for the three and nine months ended September 30, 2023, the Company remained jointly and severally liable for the payment of rent under this lease and had not been released from being the primary obligor under such lease and therefore the related right-of-use During the three and nine months ended September 30, 2023, the Company recorded sublease income of $0.8 million and $2.3 million, respectively, related to the sublease agreement with OXB Solutions. During the three and nine months ended September 30, 2022, the Company recorded sublease income of $0.5 million and $1.2 million, respectively, related to the sublease agreement with OXB Solutions. This amount was recognized as a reduction to lease expense in the Company’s condensed consolidated statements of operations. During 2023, OXB Solutions assumed responsibility for paying the landlord for invoices related to the leased property and, as such, the Company began making direct payments to OXB Solutions for amounts due to OXB Solutions under the sublease. Therefore, as of September 30, 2023, the amount of sublease income payable to OXB Solutions was $0.1 million and was included in accrued expenses on the Company’s condensed consolidated balance sheets. As of December 31, 2022, the amount of sublease income receivable from OXB Solutions was $0.5 million and was included in prepaid expenses and other current assets on the Company’s condensed consolidated balance sheets. Transitional Services Agreement Under the transitional services agreement with OXB Solutions (the “Services Agreement”), the Company is performing certain services for the benefit of OXB Solutions and OXB Solutions is performing certain services for the benefit of the Company. The term of the Services Agreement will not exceed eighteen months and lasts until the earlier of termination for convenience, termination for cause in the event of an uncured material breach, termination as a result of bankruptcy of either party, and expiration or termination of the only remaining outstanding service as set forth in the Services Agreement. Each company is fully reimbursing the other for these services. The Services Agreement was substantially complete as of September 30, 2023. Expenses incurred by the Company for services provided by OXB Solutions recognized under the Services Agreement totaled $0.3 million for the nine months ended September 30, 2023, and $0.2 million and $0.5 million for the three and nine months ended September 30, 2022, respectively, and are presented within research and development expenses in the condensed consolidated statements of operations as the services related to facilities support within the Company’s research and development labs. As of September 30, 2023 and December 31, 2022, the amount due to OXB Solutions under the Services Agreement was $0.1 million at each balance sheet date, and was included in accrued expenses and other liabilities on the Company’s condensed consolidated balance sheets. The Company provided finance, human resources, IT and legal services to OXB Solutions under the Services Agreement and recognized $0.5 million for the nine months ended September 30, 2023, and $0.8 million and $1.7 million for the three and nine months ended September 30, 2022, respectively, for amounts reimbursed by OXB Solutions as a reduction to general and administrative expense in the Company’s condensed consolidated statements of operations. The Company did not provide reimbursable services to OXB Solutions under the Services Agreement during the three months ended September 30, 2023. As of December 31, 2022, the Company had a receivable balance of $0.3 million from OXB Solutions which was recorded as a component of prepaid expenses and other current assets in the Company’s condensed consolidated balance sheets. Pursuant to the Services Agreement, the Company has been paying vendors on OXB Solutions’ behalf; this process will be fully transitioned to OXB Solutions in 2023. As of December 31, 2022, the amount receivable from OXB Solutions for amounts paid to vendors on their behalf was $1.1 million and was included in prepaid expenses and other current assets on the Company’s condensed consolidated balance sheets.	16. RELATED PARTY TRANSACTIONS Oxford Biomedica Solutions LLC As described in Note 6, the Company has significant influence over, but does not control, OXB Solutions through its noncontrolling representation on OXB Solution’s board of directors and the Company’s equity interest in OXB Solutions. In March 2022, concurrently with the closing of the transaction with OXB Solutions, the Company entered into certain ancillary agreements with OXB Solutions including a supply agreement, a lease assignment and assumption agreement, a sublease agreement and a transitional services agreement. Supply Agreement Pursuant to the terms of the Manufacturing and Supply Agreement with OXB Solutions entered into in March 2022 (the “Supply Agreement”), the Company has agreed to purchase from OXB Solutions at least 50% of its clinical supply requirements of AAV-based one-year During the year ended December 31, 2022, the Company recorded purchases of drug substance from OXB Solutions related to the Supply Agreement of approximately $13.9 million, purchases of process development services of approximately $12.5 million and stability and other support of approximately $1.8 million. These amounts are included within research and development expenses on the Company’s consolidated statements of operations. As of December 31, 2022, the amount due to OXB Solutions under the Supply Agreement was $5.2 million and was included in accrued expenses and other liabilities on the Company’s consolidated balance sheets. Lease Assignment and Sublease Agreement As described in Note 9, the Company leases space for research and development, manufacturing and general office space in Bedford, Massachusetts. The Company and OXB Solutions entered into a lease assignment and assumption agreement pursuant to which Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions and a sublease agreement whereby OXB Solutions subleased certain premises in its facility to Homology. However, as the Company remains jointly and severally liable for the payment of rent under this lease, the Company has not been released from being the primary obligor under such lease and therefore the related right-of-use During the year ended December 31, 2022, the Company recorded sublease income of $2.0 million related to the sublease agreement with OXB Solutions. This amount was recognized as a reduction to lease expense in the Company’s consolidated statements of operations. As of December 31, 2022, the amount of sublease income receivable from OXB Solutions was $0.5 million and was included in accrued expenses and other liabilities on the Company’s condensed consolidated balance sheets. Transitional Services Agreement Under the transitional services agreement with OXB Solutions (the “Services Agreement”), the Company is performing certain services for the benefit of OXB Solutions and OXB Solutions is performing certain services for the benefit of the Company. The term of the Services Agreement will not exceed eighteen months and lasts until the earlier of termination for convenience, termination for cause in the event of an uncured material breach, termination as a result of bankruptcy of either party, and expiration or termination of the only remaining outstanding service as set forth in the Services Agreement. Each company is fully reimbursing the other for these services. Expenses incurred by the Company for services provided by OXB Solutions recognized under the Services Agreement totaled approximately $0.7 million for the year ended December 31, 2022, and is presented within research and development expenses in the consolidated statements of operations as the services related to facilities support within the Company’s research and development labs. As of December 31, 2022, the amount due to OXB Solutions under the Services Agreement was $0.1 million and was included in accrued expenses and other liabilities on the Company’s condensed consolidated balance sheets. The Company provided finance, human resources, IT and legal services to OXB Solutions under the Services Agreement and recognized $1.7 million for the year ended December 31, 2022, for amounts reimbursed by OXB Solutions as a reduction to general and administrative expense in the Company’s consolidated statements of operations. As of December 31, 2022, the Company had a receivable balance of $0.3 million from OXB Solutions which was recorded as a component of prepaid expenses and other current assets in the Company’s condensed consolidated balance sheets. Pursuant to the Services Agreement, the Company has been paying vendors on OXB Solutions’ behalf; this process will be fully transitioned to OXB Solutions in 2023. As of December 31, 2022, the amount receivable from OXB Solutions for amounts paid to vendors on their behalf was $1.1 million and was included in prepaid expenses and other current assets on the Company’s consolidated balance sheets. In addition, the Company had an amount due to OXB Solutions of $2.0 million as a result of a year-end

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	14. SUBSEQUENT EVENTS Release Letter On September 25, 2023, the Company signed and executed a release letter with its lessor related to its headquarters in Bedford, MA. The lessor agreed to release the Company of all obligations under the lease effective October 1, 2023 (the “Release Date”) in exchange for a $0.1 million cash payment. For accounting purposes, the release letter is not considered a modification of the lease until the Release Date as the Company is not released from its obligations under the lease until such date. As of September 30, 2023, the lease had a remaining right-of-use right-of-use right-of-use right-of-use Agreement and Plan of Merger On November 16, 2023, the Company, Kenobi Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Company (“Merger Sub”), and Q32 Bio Inc., a Delaware corporation (“Q32”), entered into an Agreement and Plan The Merger Agreement contains customary representations, warranties and covenants made by the Company and Q32, including covenants relating to obtaining the requisite approvals of the stockholders of the Company and Q32, indemnification of directors and officers, and the Company’s and Q32’s conduct of their respective businesses between the date of signing the Merger Agreement and the closing of the Merger. The Merger Agreement also contains certain customary termination rights. The Merger Agreement further provides that, upon termination of the Merger Agreement under specified circumstances, Q32 may be required to pay the Company a termination fee of $5.9 million, or the Company may be required to pay Q32 a termination fee of $2.4 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation audited consolidated financial statements and the notes thereto for the year ended December 31, 2022, included elsewhere in this proxy/registration statement. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position as of September 30, 2023, and consolidated results of operations for the three and nine months ended September 30, 2023 and 2022, and cash flows for the nine months ended September 30, 2023 and 2022. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023.
Principles of Consolidation	Principles of Consolidation behalf. All intercompany balances and transactions have been eliminated in the condensed consolidated financial statements.	Principles of Consolidation
Use of Estimates	Use of Estimates	Use of Estimates
Comprehensive Income (Loss)	Comprehensive Income (Loss) non-owner available-for-sale	Comprehensive Income (Loss) — non-owner available-for-sale
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash to amounts shown in the consolidated statements of cash flows: December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 33,986 $ 108,382 Restricted cash — 1,953 Total cash, cash equivalents and restricted cash $ 33,986 $ 110,335
Short-Term Investments	Short-Term Investments available-for-sale	Short-Term Investments available-for-sale one-year
Concentration of Credit Risk		Concentrations of Credit Risk
Assets Held for Sale	Assets Held for Sale .	Assets Held for Sale
Equity Method Investment	Equity Method Investment Under the equity method of accounting, the Company’s investment is initially recorded at fair value on the condensed consolidated balance sheets. Upon initial investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that a decline in value has occurred that is other than temporary. Evidence considered in this evaluation includes, but would not necessarily be limited to, the financial condition and near-term prospects of the investee, recent operating trends and forecasted performance of the investee, market conditions in the geographic area or industry in which the investee operates and the Company’s strategic plans for holding the investment in relation to the period of time expected for an anticipated recovery of its carrying value. If the investment is determined to have a decline in value deemed to be other than temporary it is written down to estimated fair value. At September 30, 2023, the Company accounted for its investment in OXB Solutions using the equity method of accounting (see Note 5).	Equity Method Investment— Under the equity method of accounting, the Company’s investment is initially recorded at fair value on the consolidated balance sheets. Upon initial investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process share of income or loss of the other entity within other income/expense, which results in an increase or decrease to the carrying value of the investment. If the share of losses exceeds the carrying value of the Company’s investment, the Company will suspend recognizing additional losses and will continue to do so unless it commits to providing additional funding; however, if there are intra-entity profits this can cause the investment balance to go negative. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that a decline in value has occurred that is other than temporary. Evidence considered in this evaluation includes, but would not necessarily be limited to, the financial condition and near-term prospects of the investee, recent operating trends and forecasted performance of the investee, market conditions in the geographic area or industry in which the investee operates and the Company’s strategic plans for holding the investment in relation to the period of time expected for an anticipated recovery of its carrying value. If the investment is determined to have a decline in value deemed to be other than temporary it is written down to estimated fair value. At December 31, 2022, the Company accounted for its investment in OXB Solutions using the equity method of accounting (see Note 6).
Offering Costs	Offering Costs paid-in	Offering Costs paid-in
Leases	Leases At the commencement date, operating lease liabilities and their corresponding right-of-use right-of-use Right-of-use The Company acts as sublessor related to a sublease of a substantial portion of the Company’s headquarters that is now occupied by OXB Solutions. Fixed sublease payments received are recorded as a reduction to lease cost. Although Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions, the Company remained jointly and severally liable for the payment of rent under this lease as of and for the three and nine months ended September 30, 2023. Therefore, the related right-of-use	Leases At the commencement date, operating lease liabilities and their corresponding right-of-use right-of-use Right-of-use The Company acts as sublessor related to a sublease of a substantial portion of the Company’s headquarters that is now occupied by OXB Solutions (see Note 16). Fixed sublease payments received are recorded as a reduction to lease cost. Although Homology assigned all of its right, title and interest in, to and under this lease to OXB Solutions, the Company remains jointly and severally liable for the payment of rent under this lease and was not released from being the primary obligor under such lease. Therefore, the related right-of-use
Guarantees and Indemnifications		Guarantees and Indemnifications Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that
Property and Equipment		Property and Equipment Computer equipment and software 3 years Laboratory equipment and office furniture 5 years Manufacturing equipment 5 - 7 years Leasehold improvements Shorter of the lease term
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets right-of-use
Research and Development Costs	Research and Development Costs Costs for certain development activities are recognized based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid expense or accrued research and development expense.	Research and Development Costs Costs for certain development activities are recognized based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid expense or accrued research and development expense.
Income Taxes	Income Taxes— more-likely-than-not The Company recorded an income tax benefit of less than $0.1 million and an income tax provision of $0.8 million for the three and nine months ended September 30, 2022, respectively. The year-to-date	Income Taxes than-not the
Segment Information		Segment Information
Revenue Recognition	Revenue Recognition— Revenue from Contracts with Customers Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in the Company’s arrangements would likely consist of a license, rights to the Company’s intellectual property or research, development and manufacturing services. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of consideration to which the Company expects to be entitled to. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts may include development and regulatory milestone payments that are assessed under the most likely amount method and constrained until it is probable that a significant revenue reversal would not occur. Milestone payments that are not within the Company’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from the Company’s collaboration arrangement. The Company allocates the transaction price based on the estimated standalone selling price of each performance obligation. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress for its over-time arrangements at each reporting period and, if necessary, updates the measure of progress and revenue recognized.	Revenue Recognition— Revenue from Contracts with Customers The promised goods or services in the Company’s arrangements would likely consist of a license, rights to the Company’s intellectual property or research, development and manufacturing services. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of consideration to which the Company expects to be entitled to. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts may include development and regulatory milestone payments that are assessed under the most likely amount method and constrained until it is probable that a significant revenue reversal would not occur. Milestone payments that are not within the Company’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from the Company’s collaboration arrangement. The Company allocates the transaction price based on the estimated standalone selling price of each performance obligation. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress for its over-time arrangements at each reporting period and, if necessary, updates the measure of progress and revenue recognized.
Stock-based Compensation		Stock-based Compensation non-employees The purchase price of common stock under the Company’s employee stock purchase plan (“ESPP”) is equal to 85% of the lesser of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date. The fair value of the look-back provision under the ESPP is calculated using the Black-Scholes option pricing model. The fair value of the look-back provision plus the 15% discount is recognized as compensation expense over the 180-day
Fair Value Measurements		Fair Value Measurements • Level 1—Quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Net Income (Loss) per Share	Net Income (Loss) per Share— Common stock equivalent shares are excluded from the computation of diluted net income (loss) per share if their effect is antidilutive. In periods in which the Company reports a net (loss) attributable to common stockholders, diluted net (loss) per share attributable to common stockholders is generally the same as basic net (loss) per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.	Net Loss per Share Common stock equivalent shares are excluded from the computation of diluted net loss per share if their effect is antidilutive. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments 2016-13”) 2016-13 2016-13 2016-13 2016-13	Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, 2016-13”) 2016-13 2016-13 2016-13 2016-13

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash to amounts shown in the consolidated statements of cash flows: December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 33,986 $ 108,382 Restricted cash — 1,953 Total cash, cash equivalents and restricted cash $ 33,986 $ 110,335
Schedule of Estimated Useful Life of Asset	Computer equipment and software 3 years Laboratory equipment and office furniture 5 years Manufacturing equipment 5 - 7 years Leasehold improvements Shorter of the lease term

Cash and Cash Equivalents (Tabl

Cash and Cash Equivalents (Tables)	12 Months Ended
	Dec. 31, 2022
Cash and Cash Equivalents [Abstract]
Summary of Cash and Cash Equivalents	The following table summarizes the Company’s cash and cash equivalents: December 31, 2022 2021 (in thousands) Cash $ 19 $ 59 Money market funds 33,967 108,323 Total cash and cash equivalents $ 33,986 $ 108,382

Short-Term Investments (Tables)

Short-Term Investments (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Investments Disclosure [Abstract]
Summary of Short Term Investments	The following table summarizes the Company’s short-term investments as of September 30, 2023 and December 31, 2022: As of September 30, 2023 Amortized Unrealized Unrealized Fair (in thousands) Commercial paper $ 3,965 $ — $ (2 ) $ 3,963 US Treasury securities 55,268 6 (7 ) 55,267 Corporate debt securities 14,990 — (33 ) 14,957 Total $ 74,223 $ 6 $ (42 ) $ 74,187 As of December 31, 2022 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 57,138 $ — $ — $ 57,138 US Treasury securities 65,160 — (335 ) 64,825 Corporate debt securities 19,146 — (69 ) 19,077 Total $ 141,444 $ — $ (404 ) $ 141,040	The following table summarizes the Company’s short-term investments as of December 31, 2022 and December 31, 2021: As of December 31, 2022 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 57,138 $ — $ — $ 57,138 US Treasury securities 65,160 — (335 ) 64,825 Corporate debt securities 19,146 — (69 ) 19,077 Total $ 141,444 $ — $ (404 ) $ 141,040 As of December 31, 2021 Amortized Unrealized Unrealized Fair Value (in thousands) Commercial paper $ 27,992 $ — $ — $ 27,992 Corporate debt securities 19,506 — (7 ) 19,499 Total $ 47,498 $ — $ (7 ) $ 47,491

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value on Recurring Basis	Assets measured at fair value on a recurring basis were as follows: Description September 30, Quoted Prices Significant Other Significant (in thousands) Cash equivalents: Money market mutual funds $ 28,375 $ 28,375 $ — $ — Total cash equivalents $ 28,375 $ 28,375 $ — $ — Short-term investments: Commercial paper $ 3,963 $ — $ 3,963 $ — US Treasury securities 55,267 — 55,267 — Corporate debt securities 14,957 — 14,957 — Total short-term $ 74,187 $ — $ 74,187 $ — Total financial assets $ 102,562 $ 28,375 $ 74,187 $ — Description December 31, Quoted Prices Significant Other Significant (in thousands) Cash equivalents: Money market mutual funds $ 33,967 $ 33,967 $ — $ — Total cash equivalents $ 33,967 $ 33,967 $ — $ — Short-term investments: Commercial paper $ 57,138 $ — $ 57,138 $ — US Treasury securities 64,825 — 64,825 — Corporate debt securities 19,077 — 19,077 — Total short-term investments $ 141,040 $ — $ 141,040 $ — Total financial assets $ 175,007 $ 33,967 $ 141,040 $ —	Assets measured at fair value on a recurring basis were as follows: Description December 31, Quoted Prices Significant Significant (in thousands) Cash equivalents: Money market mutual funds $ 33,967 $ 33,967 $ — $ — Total cash equivalents $ 33,967 $ 33,967 $ — $ — Short-term investments: Commercial paper $ 57,138 $ — $ 57,138 $ — US Treasury securities 64,825 — 64,825 — Corporate debt securities 19,077 — 19,077 — Total short-term investments $ 141,040 $ — $ 141,040 $ — Total financial assets $ 175,007 $ 33,967 $ 141,040 $ — Description December 31, Quoted Prices Significant Significant (in thousands) Cash equivalents: Money market mutual funds $ 108,323 $ 108,323 $ — $ — Total cash equivalents $ 108,323 $ 108,323 $ — $ — Short-term investments: Commercial paper $ 27,992 $ — $ 27,992 $ — Corporate debt securities 19,499 — 19,499 — Total short-term investments $ 47,491 $ — $ 47,491 $ — Total financial assets $ 155,814 $ 108,323 $ 47,491 $ —

Equity Method Investment (Table

Equity Method Investment (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Equity Method Investment, Summarized Financial Information [Abstract]
Gain on sale of equity method investment	The gain was computed as follows: (in thousands) March 10, 2022 Cash received $ 130,000 Plus: Fair value of equity method investment 31,223 Less: Carrying value of transferred assets (29,974 ) Gain on sale of business $ 131,249	The gain was computed as follows: (in thousands) March 10, 2022 Cash received $ 130,000 Plus: Fair value of equity method investment 31,223 Less: Carrying value of transferred assets (29,974 ) Gain on sale of business $ 131,249
Schedule of Summarized Financial Information		Summarized financial information for OXB Solutions is as follows: December 31, Balance Sheet Data (in thousands) Current assets $ 39,237 Noncurrent assets $ 228,745 Current liabilities $ 12,352 Noncurrent liabilities $ 37,718 December 31, Statement of Operations Data (in thousands) Revenues $ 29,380 Net loss $ 29,036 See Note 16 for information regarding the Company’s related party transactions with OXB Solutions.

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: As of September 30, 2023 December 31, 2022 (in thousands) Laboratory equipment $ — $ 6,025 Computers and purchased software — 644 Furniture and fixtures — 645 Property and equipment, at cost — 7,314 Less: accumulated depreciation and amortization — (6,236 ) Property and equipment, net $ — $ 1,078	Property and equipment, net consists of the following: December 31, 2022 2021 (in thousands) Laboratory equipment $ 6,025 $ 5,857 Computers and purchased software 644 1,596 Furniture and fixtures 645 645 Property and equipment, at cost 7,314 8,098 Less accumulated depreciation and amortization (6,236 ) (5,846 ) Property and equipment, net $ 1,078 $ 2,252

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consist of the following: As of September 30, 2023 December 31, 2022 (in thousands) Accrued research and development expenses $ 8,198 $ 9,447 Accrued compensation and benefits 6,660 5,953 Accrued professional fees 648 1,052 Accrued other 205 2,263 Total accrued expenses and other liabilities $ 15,711 $ 18,715

Restructuring and Other Charg_2

Restructuring and Other Charges (Tables)	9 Months Ended
	Sep. 30, 2023
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Liability in Accrued Compensation and Benefits	The Company’s restructuring liability, which was included in accrued compensation and benefits, consisted of the following: (in thousands) Employee-Related Accrued restructuring balance at January 1, 2023 $ — Expenses incurred 6,895 Payments (2,154 ) Accrued restructuring balance at September 30, 2023 $ 4,741

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Schedule of Operating Lease Costs, Variable Lease Costs and Sub Lease Income	The following table summarizes operating lease costs and variable lease costs, as well as sublease income: Nine months ended September 30, 2023 2022 (in thousands) Operating lease costs $ 3,263 $ 2,826 Variable lease costs 1,551 1,698 Sublease income (2,312 ) (1,210 ) Net lease cost $ 2,502 $ 3,314	The following table summarizes operating lease costs and variable lease costs, as well as sublease income for the year ended December 31, 2022: Years ended December 31, 2022 2021 (in thousands) Operating lease costs $ 3,913 $ 2,592 Variable lease costs 2,142 2,127 Sublease income (1,979 ) (861 ) Net lease cost $ 4,076 $ 3,858
Schedule of Operating Lease Liabilities and Minimum Lease Payments	The maturities of the Company’s operating lease liabilities and minimum lease payments as of September 30, 2023 were as follows: For the Years Ending December 31, Amount 2023 1,134 2024 4,578 2025 4,715 2026 4,857 Thereafter 26,265 Total undiscounted lease payments $ 41,549 Less: imputed interest (13,211 ) Present value of operating lease liabilities $ 28,338	The maturities of our operating lease liabilities as of December 31, 2022 were as follows: For the Years Ending December 31, Amount 2023 4,444 2024 4,578 2025 4,715 2026 4,857 Thereafter 26,266 Total undiscounted lease payments $ 44,860 Less: imputed interest (15,383 ) Present value of operating lease liabilities $ 29,477
Schedule of Lease Term and Discount Rate	The following table summarizes the lease term and discount rate as of September 30, 2023: September 30, 2023 Weighted-average remaining lease term (years) Operating leases 7.5 Weighted-average discount rate Operating leases 10.6 %	The following table summarizes the lease term and discount rate as of December 31, 2022: As of Weighted-average remaining lease term (years) Operating leases 8.2 Weighted-average discount rate Operating leases 10.6 %
Schedule of Operating Lease Liabilities	The following table summarizes the supplemental cash flow information related to the Company’s operating lease: Nine months ended September 30, 2023 2022 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 3,310 $ 2,226 Increase in lease liabilities and right-of-use $ — $ 6,262	The following table summarizes the supplemental cash flow information related to the Company’s operating leases for the year ended December 31, 2022. Years ended December 31, 2022 2021 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 3,326 $ 3,810 Increase in lease liabilities and right-of-use $ 6,262 $ 10,901

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of provision for income taxes	Provision for income taxes consists of the following: For the Year Ended December 31, 2022 2021 (in thousands) Federal tax provision: Current $ 698 $ — Deferred — — Total federal tax provision 698 — State tax provision: Current 17 — Deferred — — Total state tax provision 17 — Total tax provision $ 715 $ —
Schedule of Reconciliation between U.S. Federal Statutory Tax Rate and Effective Tax Rate	A reconciliation between the U.S. federal statutory tax and the Company’s tax provision is summarized below. The Company has changed the presentation of its rate reconciliation from percentages to dollar amounts in the current year. For the Year Ended December 31, 2022 2021 (in thousands) Federal statutory tax $ (901 ) $ (20,111 ) Tax credits (13,955 ) (8,940 ) State taxes, net of federal tax benefit (2,994 ) (8,240 ) Non-deductible 875 1,331 Other 1,410 (2,401 ) Change in valuation allowance 16,280 38,361 Tax provision $ 715 $ —
Schedule of Deferred Tax Assets and Liabilities	The principal components of the Company’s deferred tax assets and liabilities consist of the following: December 31, 2022 2021 (in thousands) Deferred tax assets: Net operating losses $ 76,735 $ 100,417 R&D credits 66,761 51,705 Equity compensation 7,888 6,919 Operating lease liabilities 8,003 6,520 Accrued expense and other 1,479 2,072 Deferred revenue 314 1,189 Capitalized R&D costs 24,477 868 Total deferred tax assets 185,657 169,690 December 31, 2022 2021 (in thousands) Deferred tax liabilities: Right-of-use (5,583 ) (4,252 ) Depreciation (171 ) (1,541 ) Other (251 ) (503 ) Total deferred tax liabilities (6,005 ) (6,296 ) Valuation allowance (179,652 ) (163,394 ) Net deferred taxes $ — $ —
Schedule of valuance allowance	A roll forward of the valuation allowance is as follows: Valuation (in thousands) Balance at December 31, 2021 $ (163,394 ) Utilization of net operating losses against taxable income 23,654 Increase in net deferred taxes (39,912 ) Balance at December 31, 2022 $ (179,652 )

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model	The assumptions used in the Black-Scholes option pricing model are as follows (note that there were no options granted during the three months ended September 30, 2023): Three months ended Nine months ended September 30, September 30, 2022 2023 2022 Expected volatility 70.1 % 69.2%-69.7% 68.7%-70.1% Weighted-average risk-free interest rate 3.20%-3.66% 3.45%-4.22% 1.46%-3.66% Expected dividend yield — % — % — % Expected term (in years) 6.25 5.5-6.25 5.5-6.25 Underlying common stock fair value $ 1.82-$2.82 $ 0.92-$1.60 $ 1.78-$4.17	The assumptions used in the Black-Scholes option pricing model are as follows: For the Year Ended December 31, 2022 2021 Expected volatility 68.7% - 70.1% 64.6% - 71.7% Weighted-average risk-free interest rate 1.46% - 4.16% 0.50% - 1.33% Expected dividend yield — % — % Expected term (in years) 5.5 - 6.25 5.5 - 6.25 Underlying common stock fair value $1.40 - $4.17 $4.85 - $13.91
Summary of Option Activity under Plans	The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Weighted- Weighted- Aggregate (in thousands) Outstanding at January 1, 2023 9,865,734 $ 10.96 7.2 $ 493 Granted 3,188,150 $ 1.53 Exercised (3,366 ) $ 0.47 Cancelled/Forfeited (623,776 ) $ 11.11 Outstanding at September 30, 2023 12,426,742 $ 8.55 4.9 $ 488 Vested and expected to vest at September 30, 2023 12,426,742 $ 8.55 4.9 $ 488 Exercisable at September 30, 2023 7,566,304 $ 11.80 4.5 $ 421	A summary of option activity under the Plans during the year ended December 31, 2022 is as follows: Number of Weighted- Weighted- Aggregate (in thousands) Outstanding at January 1, 2022 7,624,306 $ 14.25 7.5 $ 2,069 Granted 3,089,655 $ 2.64 Exercised (293 ) $ 2.71 Cancelled/Forfeited (847,934 ) $ 10.25 Outstanding at December 31, 2022 9,865,734 $ 10.96 7.2 $ 493 Vested and expected to vest at 9,865,734 $ 10.96 7.2 $ 493 Exercisable at December 31, 2022 6,111,596 $ 13.19 6.3 $ 493
Summary of Company's RSU Activity	The following table summarizes the Company’s RSU activity for the nine months ended September 30, 2023: Number of Weighted- Outstanding at January 1, 2023 543,179 $ 6.12 Granted 483,850 $ 1.60 Vested (281,117 ) $ 5.31 Forfeited (258,184 ) $ 2.54 Outstanding at September 30, 2023 487,728 $ 3.04	The following table summarizes the Company’s RSU activity for the year ended December 31, 2022: Number of Weighted- Outstanding at January 1, 2022 307,600 $ 12.75 Granted 400,495 $ 2.70 Vested (106,890 ) $ 12.42 Forfeited (58,026 ) $ 6.05 Outstanding at December 31, 2022 543,179 $ 6.12
Schedule of Stock-Based Compensation Expense	The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP, restricted stock units and stock award modifications as follows: Three months ended Nine months ended 2023 2022 2023 2022 (in thousands) Research and development $ 230 $ 889 $ 1,507 $ 4,143 General and administrative 1,477 1,882 4,970 5,822 $1,707 $2,771 $6,477 $9,965	The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP and restricted stock units as follows: For the Year Ended December 31, 2022 2021 (in thousands) General and administrative $ 7,867 $ 8,450 Research and development 5,187 8,795 $ 13,054 $ 17,245

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Anti-dilutive Effect Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders	Diluted net income (loss) per share incorporates the additional shares issuable upon assumed exercise of stock options and the vesting of restricted stock units, except in such case when their inclusion would be anti-dilutive. Three months ended Nine months ended (in thousands, except per share amounts) 2023 2022 2023 2022 Numerator: Net income (loss) $ (32,954 ) $ (33,726 ) $ (96,842 ) $ 29,290 Denominator: Weighted-average common shares outstanding-basic 57,853,132 57,447,192 57,788,755 57,372,399 Dilutive securities — — — 528,899 Weighted-average common shares outstanding-diluted 57,853,132 57,447,192 57,788,755 57,901,298 Net income (loss) per share-basic $ (0.57 ) $ (0.59 ) $ (1.68 ) $ 0.51 Net income (loss) per share-diluted $ (0.57 ) $ (0.59 ) $ (1.68 ) $ 0.51

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended						9 Months Ended		12 Months Ended
	Mar. 09, 2023	Mar. 10, 2022	Apr. 06, 2021	Mar. 12, 2020	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Jul. 31, 2023
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from Sale of Equity Method Investments		$ 130,000
Net proceed from issuance of common stock													$ 0	$ 49,744
Net income					$ (32,954)	$ (35,044)	$ (28,844)	$ (33,726)	$ (29,089)	$ 92,105	$ (96,842)	$ 29,290	(5,005)	(95,764)
Loss from operations					(31,001)			$ (32,862)			(89,328)	$ (98,787)	(133,281)	(95,949)
Accumulated deficit					$ (525,979)						$ (525,979)		$ (429,137)	$ (424,132)
Reduction in workforce															86%
Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings				$ 148,400
Net proceed from issuance of common stock	$ 250,000
Oxford Biomedica Plc
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from Sale of Equity Method Investments		50,000
Upfront Payment Received		$ 130,000
Follow On Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Share			6,596,306											6,596,306
Shares issued price per share			$ 7.58
Net proceeds after deducting underwriting discounts and commissions and offering expenses			$ 49,700
Common Stock Offering Expenses			$ 300
Underwriters Option | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Share			989,445
Shares issued price per share			$ 7.58
ATM
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Share											0		0
Proceeds through future financings											$ 75,000		$ 148,400
ATM | Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings	$ 75,000			$ 150,000
ATM | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Share														114,914
ATM | Oxford Biomedica Plc
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Sale of Stock, Percentage of Ownership after Transaction		80%
ATM | Homology Member
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Sale of Stock, Percentage of Ownership after Transaction		20%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Cash and cash equivalents	$ 29,111	$ 33,986	$ 108,382
Restricted cash	$ 0	0	1,953
Total cash, cash equivalents and restricted cash		$ 33,986	$ 110,335

Summary of Significant Accoun_5

Summary of Significant Accounting Policies (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Outstanding claim					$ 0
Impairment of long-lived assets					$ 0
Tax positions, description			The Company determines whether it is more likely than not that a tax position will be sustained upon examination. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized.		The Company determines whether it is more likely than not that a tax position will be sustained upon examination. The tax benefit to be recognized for any tax position that meets the more-likely- than-not recognition threshold is calculated as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized.
Provision for income taxes	$ 0	$ 46	$ 0	$ (816)	$ (715)	$ 0
Restricted cash	$ 0		$ 0		$ 0	$ 1,953
Employee Stock Purchase Plan
Purchase of common stock through payroll deductions expressed in percentage of fair market value			85%		85%
Share based compensation, discount from market price					15%
Share based compensation arrangement by share based payment purchase period					180 days
Less Than [Member]
Provision for income taxes		$ (100)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Estimated Useful Life of Asset (Details)	12 Months Ended
	Dec. 31, 2022
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Laboratory Equipment and Office Furniture
Property Plant And Equipment [Line Items]
Estimated useful life of asset	5 years
Manufacturing Equipment | Minimum
Property Plant And Equipment [Line Items]
Estimated useful life of asset	5 years
Manufacturing Equipment | Maximum
Property Plant And Equipment [Line Items]
Estimated useful life of asset	7 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful life of asset, term	Shorter of the lease term or estimated useful life

Summary of Cash and Cash Equiva

Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 29,111	$ 33,986	$ 108,382
Cash
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents		19	59
Money Market Funds
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents		$ 33,967	$ 108,323

Short-Term Investments - Summar

Short-Term Investments - Summary of Short Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	$ 74,223	$ 141,444	$ 47,498
Cash equivalents and short-term investments, Unrealized Gains	6	0	0
Cash equivalents and short-term investments, Unrealized Losses	(42)	(404)	(7)
Cash equivalents and short-term investments, Fair Value	74,187	141,040	47,491
Commercial Paper
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	3,965	57,138	27,992
Cash equivalents and short-term investments, Unrealized Gains	0	0	0
Cash equivalents and short-term investments, Unrealized Losses	(2)	0	0
Cash equivalents and short-term investments, Fair Value	3,963	57,138	27,992
US Treasury Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	55,268	65,160
Cash equivalents and short-term investments, Unrealized Gains	6	0
Cash equivalents and short-term investments, Unrealized Losses	(7)	(335)
Cash equivalents and short-term investments, Fair Value	55,267	64,825
Corporate Debt Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	14,990	19,146	19,506
Cash equivalents and short-term investments, Unrealized Gains	0	0	0
Cash equivalents and short-term investments, Unrealized Losses	(33)	(69)	(7)
Cash equivalents and short-term investments, Fair Value	$ 14,957	$ 19,077	$ 19,499

Short-Term Investments - Additi

Short-Term Investments - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Cash Cash Equivalents And Available For Sale Securities [Abstract]
Realized gains and losses on available-for-sale securities	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Contractual maturity date of investments			less than one year		less than one year	less than one year

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	$ 28,375	$ 33,967
Financial assets, fair value	102,562	175,007
Short-term investments	74,187	141,040
Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	28,375	33,967
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	3,963	57,138
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	14,957	19,077
US Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	55,267	64,825
Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	28,375	33,967
Financial assets, fair value	28,375	33,967
Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1) | Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	28,375	33,967
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, fair value	74,187	141,040
Short-term investments	74,187	141,040
Significant Other Observable Inputs (Level 2) | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	3,963	57,138
Significant Other Observable Inputs (Level 2) | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	14,957	19,077
Significant Other Observable Inputs (Level 2) | US Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 55,267	64,825
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value		33,967	$ 108,323
Financial assets, fair value		175,007	155,814
Short-term investments		141,040	47,491
Fair Value, Measurements, Recurring | Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value		33,967	108,323
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		57,138	27,992
Fair Value, Measurements, Recurring | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		19,077	19,499
Fair Value, Measurements, Recurring | US Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		64,825
Fair Value, Measurements, Recurring | Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value		33,967	108,323
Financial assets, fair value		33,967	108,323
Fair Value, Measurements, Recurring | Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1) | Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value		33,967	108,323
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, fair value		141,040	47,491
Short-term investments		141,040	47,491
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value			0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		57,138	27,992
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		19,077	$ 19,499
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | US Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		$ 64,825

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Transfers between fair value measure levels	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

Equity Method Investment (Addit

Equity Method Investment (Additional Information) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 10, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Mar. 11, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Gain on sale of business	$ 131,249	$ 0	$ 0	$ 0	$ 131,249	$ 131,249	$ 0
Loss from equity method investment		(3,376)	$ (2,179)	(11,917)	$ (4,131)	(5,488)	0
Equity method investment		13,957		13,957		25,814	0
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equity method investment cash consideration		$ 74,100		$ 74,100		$ 74,100
OXB Solutions [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Transferred units	130,000
Equity method investment, description of principal activities	Homology to sell and transfer to OXB, and (ii) Homology will have an option to cause OXB to purchase from Homology, in each case all of Homology’s equity ownership interest in OXB Solutions at a price equal to 5.5 times the revenue for the immediately preceding 12-month period (together, the “Options”), subject to a maximum amount of $74.1 million.
Assets held for sale							$ 28,900
Equity method investments, ownership description				The valuation included certain subjective assumptions including discounts for lack of control and marketability given the consideration paid for OXB Solutions was for a controlling interest in the entity and the Company owns a noncontrolling interest.		The valuation included certain subjective assumptions including discounts for lack of control and marketability given the consideration paid for OXB Solutions was for a controlling interest in the entity and the Company owns a noncontrolling interest.
Fair value of investment	$ 31,200
Gain on sale of business	$ 131,200
Loss from equity method investment				$ 8,100		$ 5,500
Impairment Charge				$ 3,800
OXB Solutions [Member] | Equity Securities Purchase Agreement
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common Unit, Issued	175,000
Equity method investment, ownership percentage	100%
Contributed cash	$ 50,000							$ 50,000
Additional units issued	50,000
Homology | Equity Securities Purchase Agreement
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equity method investment, ownership percentage	20%
Ownership interests, units	45,000
OXB
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Transferred units	130,000
OXB | Equity Securities Purchase Agreement
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equity method investment, ownership percentage	80%
Transferred units, value	$ 130,000
Ownership interests, units	180,000

Equity Method Investment - Sche

Equity Method Investment - Schedule of equity method investment fair value (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 10, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Equity Method Investment, Summarized Financial Information [Abstract]
Cash received	$ 130,000
Plus: Fair value of equity method investment	31,223
Less: Carrying value of transferred assets	(29,974)
Gain on sale of business	$ 131,249	$ 0	$ 0	$ 0	$ 131,249	$ 131,249	$ 0

Equity Method Investment - Sc_2

Equity Method Investment - Schedule of Summarized Financial Information (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Current assets	$ 106,635		$ 181,015	$ 191,909
Current liabilities	25,292		22,576	17,226
Net loss	$ (96,842)	$ 29,290	(5,005)	$ (95,764)
OXB Solutions [Member]
Schedule of Equity Method Investments [Line Items]
Current assets			39,237
Noncurrent assets			228,745
Current liabilities			12,352
Noncurrent liabilities			37,718
Revenues			29,380
Net loss			$ 29,036

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 0	$ 7,314	$ 8,098
Less: accumulated depreciation and amortization	0	(6,236)	(5,846)
Property and equipment, net	0	1,078	2,252
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	0	6,025	5,857
Computers and Purchased Software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	0	644	1,596
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 0	$ 645	$ 645

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Depreciation	$ 100	$ 300	$ 578	$ 997	$ 1,293	$ 8,353
Disposal of property and equipment	$ 400	$ 0	400	0	$ 100	100
Property and equipment, net assets held for sale			338	$ 0		$ 28,900
Depreciation expense on asset held for sale			$ 0

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 8,198	$ 9,447	$ 2,193
Accrued compensation and benefits	6,660	5,953	7,805
Accrued professional fees	648	1,052	1,371
Accrued other	205	2,263	37
Total accrued expenses and other liabilities	$ 15,711	$ 18,715	$ 11,406

Restructuring and Other Charg_3

Restructuring and Other Charges - Accrued Compensation and Benefits (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Restructuring and Related Activities [Abstract]
Accrued restructuring, Beginning Balance	$ 0
Expenses incurred	6,895
Payments	(2,154)
Accrued restructuring, Ending Balance	$ 4,741

Restructuring and Other Charg_4

Restructuring and Other Charges (Additional Information) (Details) $ in Millions		3 Months Ended	9 Months Ended
	Jul. 25, 2023 EMPLOYEE	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Stock based compensation			$ 0.3
Corporate Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Vest over period			4 years
Corporate Restructuring [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance and related Cost		$ 6.9
Reduction in employee | EMPLOYEE	80
Reduction in employee pecentage	86%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended				9 Months Ended		12 Months Ended
	Feb. 28, 2022 USD ($)	Dec. 31, 2017 ft² PHASE $ / ft²	Nov. 30, 2017 USD ($) ft²	Sep. 30, 2016	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Commitment And Contingencies [Line Items]
Sublease aggregate base rent obligation							$ 2,700
Tenant improvement allowance			$ 6,300
Increase (Decrease) in right-of-use asset	$ 200						10,900
Sublease income					$ 2,312	$ 1,210	1,979	$ 861
Security deposit							0	$ 2,000
Increase in Lease Liability					10,900
OXB Solutions [Member]
Commitment And Contingencies [Line Items]
Increase (Decrease) in right-of-use asset					6,100		6,100
Sublease income					$ 2,300		2,000
Tenant improvement allowances percentage					100%	100%
Maximum
Commitment And Contingencies [Line Items]
Tenant improvement allowance					$ 10,900		10,900
Bedford, Massachusetts
Commitment And Contingencies [Line Items]
Operating lease beginning year and month				2016-11
Operating lease expiration year and month		2027-02	2027-02	2021-10
Operating lease agreements additional term				3 years
Sublease aggregate base rent obligation			$ 1,400		$ 4,700		$ 4,700
Office space leased | ft²		67,000	23,011
Lessee, operating lease, lease not yet commenced, renewal term		5 years
Number of phases | PHASE		2
Initial annual base rent per square foot | $ / ft²		39.5
Percentage increase in initial annual base rent per square foot.		3%	3%
Bedford, Massachusetts | Phase One
Commitment And Contingencies [Line Items]
Office space leased | ft²		46,000
Rent due date		2018-09
Bedford, Massachusetts | Phase Two
Commitment And Contingencies [Line Items]
Office space leased | ft²		21,000
Rent due date		2019-03

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Operating Lease Costs, Variable Lease Costs and Sub Lease Income (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Operating lease costs	$ 3,263	$ 2,826	$ 3,913	$ 2,592
Variable lease costs	1,551	1,698	2,142	2,127
Sublease income	(2,312)	(1,210)	(1,979)	(861)
Net lease cost	$ 2,502	$ 3,314	$ 4,076	$ 3,858

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Operating Lease Liabilities and Minimum Lease Payments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
2023	$ 1,134	$ 4,444
2024	4,578	4,578
2025	4,715	4,715
2026	4,857	4,857
Thereafter	26,265	26,266
Total undiscounted lease payments	41,549	44,860
Less: imputed interest	(13,211)	(15,383)
Present value of operating lease liabilities	$ 28,338	$ 29,477

Commitments and Contingencies_4

Commitments and Contingencies - Schedule of Lease Term and Discount Rate (Details)	Sep. 30, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term (years), Operating leases	7 years 6 months	8 years 2 months 12 days
Weighted-average discount rate, Operating leases	10.60%	10.60%

Commitments and Contingencies_5

Commitments and Contingencies - Summary of Cash Paid for Company's Operating Lease Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 3,310	$ 2,226	$ 3,326	$ 3,810
Increase in lease liabilities and right-of-use assets due to lease remeasurements	$ 0	$ 6,262	$ 6,262	$ 10,901

License Agreements - Additional

License Agreements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
License Agreement [Line Items]
Collaboration agreement revenue recognized		$ 0	$ 802	$ 1,156	$ 2,406	$ 3,208	$ 33,971
City of Hope
License Agreement [Line Items]
Annual license fee						25,000
City of Hope | Maximum
License Agreement [Line Items]
Development and commercialization milestone payment						3,200
City of Hope | January 2023
License Agreement [Line Items]
Amount paid to related party upon dosing the first patient						50,000
California Institute Of Technology | Maximum | Co Exclusive License Agreement
License Agreement [Line Items]
Development and regulatory milestone payments	$ 7,200
California Institute Of Technology | Minimum | Co Exclusive License Agreement
License Agreement [Line Items]
Annual minimal royalty fee	$ 20,000
Novartis
License Agreement [Line Items]
Collaboration agreement revenue recognized							26,900
Novartis | Collaborative Arrangement
License Agreement [Line Items]
Collaboration revenue							0
Collaboration agreement revenue recognized							30,800
Deferred revenue						0	0
Accounts receivable						$ 0	0
Novartis | Collaborative Arrangement | Deferred Revenue
License Agreement [Line Items]
Collaboration agreement revenue recognized							$ 30,200

Income Taxes - Schedule of prov

Income Taxes - Schedule of provision for income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Federal tax provision:
Current					$ 698	$ 0
Deferred					0	0
Total federal tax provision					698	0
State tax provision:
Current					17	0
Deferred					0	0
Total state tax provision					17	0
Tax provision	$ 0	$ (46)	$ 0	$ 816	$ 715	$ 0

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation between U.S. Federal Statutory Tax and Effective Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory tax					$ (901)	$ (20,111)
Tax credits					(13,955)	(8,940)
State taxes, net of federal tax benefit					(2,994)	(8,240)
Non-deductible expenses					875	1,331
Other					1,410	(2,401)
Change in valuation allowance					16,280	38,361
Tax provision	$ 0	$ (46)	$ 0	$ 816	$ 715	$ 0

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating losses	$ 76,735	$ 100,417
R&D credits	66,761	51,705
Equity compensation	7,888	6,919
Operating lease liabilities	8,003	6,520
Accrued expense and other	1,479	2,072
Deferred revenue	314	1,189
Capitalized R&D costs	24,477	868
Total deferred tax assets	185,657	169,690
Deferred tax liabilities:
Right-of-use assets	(5,583)	(4,252)
Depreciation	(171)	1,541
Other	(251)	503
Total deferred tax liabilities	(6,005)	(6,296)
Valuation allowance	(179,652)	(163,394)
Net deferred taxes	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Income tax expense	$ 0	$ (46,000)	$ 0	$ 816,000	$ 715,000	$ 0
Net operating loss carryforwards					400,000
Uncertain tax positions					0
Income tax expense, interest or penalties					0	$ 0
Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards					55,100,000
Orphan Drug
Income Tax Disclosure [Line Items]
Tax credit carryforwards					$ 45,200,000
Tax credit carryforwards expiration year					2041
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards					$ 283,500,000
Net operating loss carryforwards indefinitely					$ 283,100,000
Net operating loss carryforwards expiration year					2035
Federal | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards					$ 55,100,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards					272,100,000
State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards					$ 14,800,000

Income Taxes - Schedule of valu

Income Taxes - Schedule of valuance allowance (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Income Tax Disclosure [Abstract]
Balance at December 31, 2021	$ (163,394)
Utilization of net operating losses against taxable income	23,654
Increase in net deferred taxes	(39,912)
Balance at December 31, 2022	$ (179,652)

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2022	Sep. 30, 2023	Dec. 31, 2021
Equity [Abstract]
Common stock, voting rights	Each holder of outstanding shares of common stock are entitled to one vote in respect of each share.
Common stock, shares outstanding	57,483,910	57,902,210	57,150,274
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 01, 2023 shares	Mar. 31, 2018 shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) EMPLOYEE $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate proceeds from shares issued under the plan						$ 168	$ 563	$ 595	$ 826
Stock-based compensation			$ 1,707	$ 2,771		$ 6,477	$ 9,965	13,054	17,245
Total intrinsic value of options exercised								$ 600	$ 600
Weighted-average grant date fair value per share for options granted | $ / shares						$ 1.01	$ 1.72	$ 1.68	$ 7.26
Total compensation cost reversed			100					$ 100
Compensation cost, Total								800
Share-Based Goods and Nonemployee Services Transaction, Modification of Terms, Incremental Compensation Cost			100			$ 400		$ 400
Number of employees get terminated | EMPLOYEE						80
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost reversed			200
Compensation cost, Total			100			$ 100
Number of stock award and exercise vested option to transferred employees | shares						400,000
Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees | shares						3,300,000
OXB Solutions [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost reversed					$ 100
Compensation cost, Total			$ 800			$ 800
OXB Solutions [Member] | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees | shares						100,000		100,000
OXB Solutions [Member] | Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees | shares						1,600,000		1,600,000
2015 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period						4 years		4 years
Stock options expiration period						10 years		10 years
Number of additional shares available for future grant | shares			0			0		0
2018 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance | shares		3,186,205
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock	4%	4%
Maximum shares of common stock may be issued | shares		20,887,347
Number of shares outstanding available for future grant | shares	2,299,356		1,978,793			1,978,793		2,188,360
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance | shares		353,980
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock	1%	1%
Number of shares outstanding available for future grant | shares	574,839		2,693,911			2,693,911		1,776,431
Maximum shares allowed to be issued under ESPP | shares		4,778,738
Purchase of common stock through payroll deductions expressed in percentage of fair market value						85%		85%
Common stock offering period						6 months		6 months
Number of shares issued to the plan | shares						133,817	226,453	226,453	110,923
Aggregate proceeds from shares issued under the plan						$ 200	$ 600	$ 600	$ 800
Stock-based compensation			$ 100	$ 100		100	$ 100	100	$ 100
Excess of accrued right to purchase stock						25,000		25,000
2015 and 2018 Stock Incentive Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense			$ 10,500			$ 10,500		$ 14,600
Unrecognized compensation expense estimated to be recognized over period						2 years 2 months 12 days		2 years 3 months 18 days

Stock Incentive Plans - Schedul

Stock Incentive Plans - Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model (Details) - $ / shares	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	70.10%
Expected volatility, minimum		69.20%	68.70%	68.70%	64.60%
Expected volatility, maximum		69.70%	70.10%	70.10%	71.70%
Weighted-average risk-free interest rate, minimum	3.20%	3.45%	1.46%	1.46%	0.50%
Weighted-average risk-free interest rate, maximum	3.66%	4.22%	3.66%	4.16%	1.33%
Expected dividend yield	0%	0%	0%	0%	0%
Expected term (in years)	6 years 3 months
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		5 years 6 months	5 years 6 months	5 years 6 months	5 years 6 months
Underlying common stock fair value	$ 1.82	$ 0.92	$ 1.78	$ 1.4	$ 4.85
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		6 years 3 months	6 years 3 months	6 years 3 months	6 years 3 months
Underlying common stock fair value	$ 2.82	$ 1.6	$ 4.17	$ 4.17	$ 13.91

Stock Incentive Plans - Summary

Stock Incentive Plans - Summary of Option Activity under Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding at Beginning Balance	9,865,734	7,624,306
Number of Options, Granted	3,188,150	3,089,655
Number of Options, Exercised	(3,366)	(293)
Number of Options, Cancelled/Forfeited	(623,776)	(847,934)
Number of Options, Outstanding at Ending Balance	12,426,742	9,865,734	7,624,306
Number of Options, Vested and expected to vest	12,426,742	9,865,734
Number of Options, Exercisable	7,566,304	6,111,596
Weighted-Average Exercise Price per Share, Outstanding at Beginning Balance	$ 10.96	$ 14.25
Weighted-Average Exercise Price per Share, Granted	1.53	2.64
Weighted-Average Exercise Price per Share, Exercised	0.47	2.71
Weighted-Average Exercise Price per Share, Cancelled/Forfeited	11.11	10.25
Weighted-Average Exercise Price per Share, Outstanding at Ending Balance	8.55	10.96	$ 14.25
Weighted-Average Exercise Price per Share, Vested and Expected to vest	8.55	10.96
Weighted-Average Exercise Price Per Share, Exercisable	$ 11.8	$ 13.19
Weighted Average Remaining Contractual Term, Outstanding	4 years 10 months 24 days	7 years 2 months 12 days	7 years 6 months
Weighted Average Remaining Contractual Term, Vested and Expected to vest	4 years 10 months 24 days	7 years 2 months 12 days
Weighted Average Remaining Contractual Term, Exercisable	4 years 6 months	6 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance	$ 488	$ 493	$ 2,069
Aggregate Intrinsic Value, Vested and Expected to vest	488	493
Aggregate Intrinsic Value, Exercisable	$ 421	$ 493

Stock Incentive Plans - Summa_2

Stock Incentive Plans - Summary of RSU Activity (Details) - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding at Beginning Balance	9,865,734	7,624,306	7,624,306
Number of Options, Granted	3,188,150		3,089,655
Number of Options, Outstanding at Ending Balance	12,426,742		9,865,734	7,624,306
Weighted-average grant date fair value per share for options granted	$ 1.01	$ 1.72	$ 1.68	$ 7.26
RSU Member
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding at Beginning Balance	543,179	307,600	307,600
Number of Options, Granted	483,850		400,495
RSU Vested	(281,117)		(106,890)
RSU, Forfeited	(258,184)		(58,026)
Number of Options, Outstanding at Ending Balance	487,728		543,179	307,600
Weighted-Average Grant Date Fair Value, Outstanding	$ 6.12	$ 12.75	$ 12.75
Weighted-average grant date fair value per share for options granted	1.6		2.7
Weighted-Average Grant Date Fair Value, Vested	5.31		12.42
Weighted-Average Grant Date Fair Value, Forfeited	2.54		6.05
Weighted-Average Grant Date Fair Value, Outstanding	$ 3.04		$ 6.12	$ 12.75

Stock Incentive Plans - Sched_2

Stock Incentive Plans - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 1,707	$ 2,771	$ 6,477	$ 9,965	$ 13,054	$ 17,245
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	1,477	1,882	4,970	5,822	7,867	8,450
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 230	$ 889	$ 1,507	$ 4,143	$ 5,187	$ 8,795

Net Income (Loss) Per Share - S

Net Income (Loss) Per Share - Schedule of Anti-dilutive Effect Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 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	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net income (loss)	$ (32,954)	$ (35,044)	$ (28,844)	$ (33,726)	$ (29,089)	$ 92,105	$ (96,842)	$ 29,290	$ (5,005)	$ (95,764)
Weighted-average common shares outstanding-basic	57,853,132			57,447,192			57,788,755	57,372,399	57,399,762	55,283,318
Dilutive securities	$ 0			$ 0			$ 0	$ 528,899
Weighted-average common shares outstanding-diluted	57,853,132			57,447,192			57,788,755	57,901,298	57,399,762	55,283,318
Net income (loss) per share-basic	$ (0.57)			$ (0.59)			$ (1.68)	$ 0.51	$ (0.09)	$ (1.73)
Net income (loss) per share-diluted	$ (0.57)			$ (0.59)			$ (1.68)	$ 0.51	$ (0.09)	$ (1.73)

Net Income (Loss) Per Share (Ad

Net Income (Loss) Per Share (Additional Information) (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Anti-dilutive securities	12,993,266	9,933,508	12,507,026	9,048,927

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Discretionary match made under the 401(k) Plan by employer	$ 0.6	$ 0.8

Pfizer Stock Purchase Agreeme_2

Pfizer Stock Purchase Agreement - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 09, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs						$ 0	$ 49,744
Collaboration agreement revenue recognized		$ 0	$ 802	$ 1,156	$ 2,406	3,208	33,971
Pfizer Inc.
Common stock estimated fair value	$ 52,000
Stock purchase agreement remaining allocated value	8,000
Allocated Information Committee obligation	$ 8,000
Pfizer Inc. | Collaborative Arrangement
Collaboration agreement revenue recognized			$ 800	1,200	$ 2,400	3,200	3,200
Deferred revenue		$ 0		$ 0		$ 1,200	$ 4,400
Private Placement
Issuance of common stock, net of discounts and issuance costs, Shares	5,000,000
Shares issued price per share	$ 12
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs	$ 60,000
Common stock purchase agreement condition	The shares of common stock sold to Pfizer were subject to a one-year lock-up from closing, during which time Pfizer was prohibited from selling or otherwise disposing of such shares.

Related Party Transactions (Add

Related Party Transactions (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Sublease income			$ 2,312	$ 1,210			$ 1,979	$ 861
General and administrative	$ 6,842	$ 7,810	23,355	29,991			38,138	36,835
Prepaid expenses and other current assets	3,023		3,023				5,989	$ 7,129
Oxford Biomedica [Member]
Related Party Transaction [Line Items]
Sublease income	800	500	2,300	1,200			2,000
Expenses recognized under the transitional services		(200)	(300)	(500)			(700)
Amount due to OXB Solutions							500
General and administrative		800	500	1,700			1,700
Prepaid expenses and other current assets							300
Amount due to OXB Solutions	100		$ 100				500
Oxford Biomedica [Member] | Vendor [Member]
Related Party Transaction [Line Items]
Due from related party							1,100
Receivables from affiliates							$ 1,100
Oxford Biomedica [Member] | Supply Agreement [Member]
Related Party Transaction [Line Items]
Clinical supply requirements			50%				50%
Purchases of drug substance	8,400	6,000	$ 21,700	7,500			$ 13,900
Amount due to OXB Solutions							5,200
Amount due to OXB Solutions	12,600		12,600				5,200
Remaining purchase obligations	1,400		1,400
Oxford Biomedica [Member] | Supply Agreement [Member] | Process Development Services [Member]
Related Party Transaction [Line Items]
Recorded purchases	3,100	$ 2,200	5,800	$ 10,200			12,500
Oxford Biomedica [Member] | Supply Agreement [Member] | Stability and Other Support [Member]
Related Party Transaction [Line Items]
Recorded purchases	$ 400		$ 1,200				1,800
Oxford Biomedica [Member] | Transitional Services Agreement [Member]
Related Party Transaction [Line Items]
Amount due to OXB Solutions							100
Amount due to OXB Solutions							100
Oxford Biomedica [Member] | Transitional Services Agreement [Member] | Vendor [Member]
Related Party Transaction [Line Items]
Amount due to OXB Solutions							$ 2,000
Oxford Biomedica [Member] | Forecast [Member] | Supply Agreement [Member]
Related Party Transaction [Line Items]
Purchase commitment amount					$ 0	$ 29,700

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) - USD ($) $ in Thousands	Nov. 16, 2023	Oct. 01, 2023	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Right-of-use assets			$ 19,471	$ 20,563	$ 15,607
Operating Lease Liability			$ 28,338	$ 29,477
Q32 Bio Inc [Member]
Subsequent Event [Line Items]
Termination fee to be paid	$ 5,900
Terminatin fee to be receiable	$ 2,400
Subsequent Event [Member]
Subsequent Event [Line Items]
Gain on operating lease liability		$ 8,800
Cash payment for release operating lease		100
Subsequent Event [Member] | OXB Solutions [Member]
Subsequent Event [Line Items]
Right Of Use Asset Obtained In Exchange For Operating Lease Liability		$ 1,600