Announced Today Encouraging Initial Clinical Data from First Dose Level of pheEDIT Trial Evaluating HMI-103 BEDFORD, Mass., July 27, 2023 (GLOBE NEWSWIRE) — Homology Medicines, Inc. (Nasdaq: FIXX), a genetic medicines company, announced today that it has completed a review of its business, and the Board of Directors has approved a plan to evaluate strategic alternatives to maximize shareholder value. Earlier today, Homology reported encouraging initial data from the first dose level in the Phase 1, dose-escalation trial evaluating gene editing candidate HMI-103 in adults with classical phenylketonuria (PKU), which showed it was generally well-tolerated in all three participants and resulted in a meaningful reduction in plasma phenylalanine (Phe) in two participants as of the data cut-off date of July 26, 2023. Despite these encouraging data, based on the current financing environment and Homology’s anticipated clinical development timelines, Homology will not be further developing its programs and will be instituting a related reduction in force while it explores options for the Company and its assets, including HMI-103. Homology has retained TD Cowen as its strategic financial advisor. “We are pleased with the initial data from the first dose level in our PKU gene editing trial, which support dose-escalation; however, given today’s tough financing conditions and the expected clinical development timeline for HMI-103, we believe the best path forward for our shareholders is to evaluate all strategic options for the Company and our pipeline,” said Albert Seymour, Ph.D., President and Chief Executive Officer. “Unfortunately, this decision impacts our dedicated employees, and I would like to extend my sincere gratitude to our affected colleagues who have been instrumental in building Homology’s platform and programs, and we are committed to supporting them as best as we can during this transition.” Homology has gene editing and gene therapy clinical-stage programs in PKU and Hunter syndrome (MPS II), a preclinical pipeline that includes a gene therapy candidate for metachromatic leukodystrophy and a GTx-mAb (vectorized antibody) candidate for paroxysmal nocturnal hemoglobinuria, as well as intellectual property on its family of 15 adeno-associated viruses (AAVHSCs). Additionally, the Company has a 20 percent stake in Oxford Biomedica Solutions, an AAV manufacturing company based on Homology’s internal process development and manufacturing. Homology is reducing its workforce by 87% and stopping further program development efforts outside of required actions, including continued collection of data from and monitoring of participants in its clinical trials, to significantly reduce the Company’s ongoing operating costs. These measures are expected to extend Homology’s cash runway into 2026. As of March 31, 2023, Homology had approximately $150.0 million in cash, cash equivalents and short-term investments, and the Company will provide an update in its second quarter 2023 financial results. Strategic options may include but are not limited to, an acquisition, merger, reverse merger, sale of assets, strategic partnerships, or other transactions. There can be no assurance of completion of any particular course of action or a defined timeline for completion. For more information, visit www.homologymedicines.com. Forward-Looking Statements This press release contains forward-looking statements. We intend such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation statements regarding: our plans to evaluate strategic options; our anticipated clinical development timelines; the expected financial and operational impacts of our restructuring initiatives; our expectations surrounding the potential, safety, efficacy, and regulatory and clinical progress of our product candidates, including HMI-103 for the treatment of PKU; the potential of our gene therapy and gene editing platforms, including our GTx-mAb platform; our plans and timing for the release of additional preclinical and clinical data; our plans to progress our pipeline of genetic medicine candidates and the anticipated timing for these milestones; and our position as a leader in the development of genetic medicines. The words “believe,” “may,” “will,” “estimate,” “potential,” “continue,” “anticipate,” “intend,” “expect,” “could,” “would,” “project,” “plan,” “target,” and similar expressions are intended to identify forward-looking statements, though not all forward-looking statements use these words or expressions. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: we have and expect to continue to incur significant losses; our need for additional funding, which may not be available; failure to identify additional product candidates and develop or commercialize marketable products; the early stage of our development efforts; potential unforeseen events during clinical trials could cause delays or other adverse consequences; risks relating to the regulatory approval process; interim, topline and preliminary data may change as more patient data become available, and are subject to audit and verification procedures that could result in material changes in the final data; our product candidates may cause serious adverse side effects; inability to maintain our collaborations, or the failure of these collaborations; our reliance on third parties, including for the manufacture of materials for our research programs, preclinical and clinical studies; failure to obtain U.S. or international marketing approval; ongoing regulatory obligations; effects of significant competition; unfavorable pricing regulations, third-party reimbursement practices or healthcare reform initiatives; product liability lawsuits; securities class action litigation; the impact of the COVID-19 pandemic and general economic conditions on our business and operations, including our preclinical studies and clinical trials; failure to attract, retain and motivate qualified personnel; the possibility of system failures or security breaches; risks relating to intellectual property; and significant costs incurred as a result of operating as a public company. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2023 and our other filings with the Securities and Exchange Commission could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change. Company Contact:Brad SmithChief Financial and Business Officer781-691-3519bsmith@homologymedicines.com