Nature of Business and Basis of Presentation	12 Months Ended
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—Homology Medicines, Inc. (the “Company”) is a clinical-stage genetic medicines company dedicated to transforming the lives of patients suffering from rare diseases by addressing the underlying cause of the disease with one-time gene therapy and gene editing treatments. The Company was founded in March 2015 as a Delaware corporation. Its principal offices are in Bedford, Massachusetts. 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 and certain other assets. Oxford paid the Company $130.0 million of upfront cash and invested $50.0 million of cash to fund OXB Solutions in exchange for an 80 percent ownership interest, while Homology retained a 20 percent ownership interest in the new company and received a put option on this ownership position (see Note 6). On April 6, 2021, the Company completed a follow-on public offering of its common stock. The Company sold 6,596,306 shares of its common stock at a price of $7.58 per share and received net proceeds of $49.7 million, after deducting offering expenses of $0.3 million. Under the terms of the underwriting agreement, the Company also granted the underwriter an option exercisable for 30 days to purchase up to an additional 989,445 shares of its common stock at a price of $7.58 per share. The underwriters did not exercise this option. The offering closed on April 9, 2021. The shares were sold pursuant to the Company’s effective shelf registration statement on Form S-3, as amended, and a related prospectus supplement filed with the Securities and Exchange Commission (“SEC”) on April 8, 2021. On March 12, 2020, the Company filed a Registration Statement on Form S-3 (File No. 333-237131) (as amended, the “Shelf”) with the SEC in relation to the registration of 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 12, 2020. The Company also simultaneously entered into a sales agreement with Cowen and Company, LLC (“Cowen”), as sales agent, providing for the offering, issuance and sale by the Company of up to an aggregate of $150.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf (the “ATM”). In connection with the filing of certain post-effective amendments to the Shelf, the sales agreement prospectus supplement now covers the offering, issuance and sale by the Company of up to an aggregate of $148.4 million of its common stock. The Company did not sell any 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—The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business.

Nature of Business and Basis of Presentation

12 Months Ended

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—Homology Medicines, Inc. (the “Company”) is a clinical-stage genetic medicines company dedicated to transforming the lives of patients suffering from rare diseases by addressing the underlying cause of the disease with one-time gene therapy and gene editing treatments. The Company was founded in March 2015 as a Delaware corporation. Its principal offices are in Bedford, Massachusetts.

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 and certain other assets. Oxford paid the Company $130.0 million of upfront cash and invested $50.0 million of cash to fund OXB Solutions in exchange for an 80 percent ownership interest, while Homology retained a 20 percent ownership interest in the new company and received a put option on this ownership position (see Note 6).

On April 6, 2021, the Company completed a follow-on public offering of its common stock. The Company sold 6,596,306 shares of its common stock at a price of $7.58 per share and received net proceeds of $49.7 million, after deducting offering expenses of $0.3 million. Under the terms of the underwriting agreement, the Company also granted the underwriter an option exercisable for 30 days to purchase up to an additional 989,445 shares of its common stock at a price of $7.58 per share. The underwriters did not exercise this option. The offering closed on April 9, 2021. The shares were sold pursuant to the Company’s effective shelf registration statement on Form S-3, as amended, and a related prospectus supplement filed with the Securities and Exchange Commission (“SEC”) on April 8, 2021.

On March 12, 2020, the Company filed a Registration Statement on Form S-3 (File No. 333-237131) (as amended, the “Shelf”) with the SEC in relation to the registration of 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 12, 2020. The Company also simultaneously entered into a sales agreement with Cowen and Company, LLC (“Cowen”), as sales agent, providing for the offering, issuance and sale by the Company of up to an aggregate of $150.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf (the “ATM”). In connection with the filing of certain post-effective amendments to the Shelf, the sales agreement prospectus supplement now covers the offering, issuance and sale by the Company of up to an aggregate of $148.4 million of its common stock. The Company did not sell any 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—The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business.