Homology Medicines Announces FDA Fast Track Designation for HMI-102 Gene Therapy Development Candidate for Adults with PKU

- Company Provides Details of pheNIX, the First Gene Therapy Trial for PKU, and Remains on Track to Report Initial Clinical Results from the Phase 1/2 Study in 2019 -

BEDFORD, Mass., May 14, 2019
– Homology Medicines, Inc. (Nasdaq: FIXX), a genetic medicines company, announced today that the U.S. Food and Drug Administration (FDA) has granted Fast Track designation for HMI-102, Homology’s one-time gene therapy development candidate for the treatment of adults with phenylketonuria (PKU). PKU is an inborn error of metabolism primarily caused by mutations in the PAH gene that lead to phenylalanine hydroxylase (PAH) deficiency resulting in the inability to breakdown phenylalanine (Phe), an essential amino acid found in natural protein.

“We believe FDA’s decision to grant Fast Track designation is a positive step forward for the development of HMI-102, which is designed to treat the underlying cause of this disease and allow freedom from a restrictive diet, the current standard of care,” said Arthur Tzianabos, Ph.D., President and Chief Executive Officer of Homology Medicines. “The Homology team has been on its own fast track for the past three years working hard to advance its dual gene therapy and gene editing platform from initial concept to the clinic, with the goal of delivering potential cures to patients living with PKU as well as other rare diseases.”

FDA’s Fast Track process is intended to facilitate the development process and expedite review of drugs that are designed to treat serious conditions and fill an unmet medical need to get them to patients earlier. A drug with Fast Track designation can be eligible for more frequent meetings with and written communications from FDA and rolling review of a marketing application, which can lead to earlier drug approval and access by patients.1

In April 2019, Homology announced that FDA cleared the Investigational New Drug (IND) application for HMI-102 for the treatment of PKU. Previously, the FDA and the European Medicines Agency (EMA) granted orphan drug designation for HMI-102 in the United States and European Union for the use of human hematopoietic stem cell-derived adeno-associated virus AAVHSC15 to treat PAH deficiency, the primary cause of PKU. The Company is currently working with treatment centers to begin the Phase 1/2 pheNIX trial for adult patients with PKU, and expects to report initial clinical data in 2019.

pheNIX, the first gene therapy clinical trial in PKU, is an open-label, randomized, concurrently controlled, dose-escalation study designed to evaluate the safety and efficacy of HMI-102 in adults, aged 18-55 with classic PKU. HMI-102 is designed to deliver a functional copy of the PAH gene to liver cells. In addition to safety measures, the trial will also evaluate reduction in serum Phe levels. The study design allows for expansion of the number of patients in any dose cohort as long as the dose selected has been deemed safe and effective by the Data Monitoring Committee and the Homology Review Team. A decision to expand a dose cohort would trigger the addition of a concurrent, randomized control arm consisting of classic PKU patients that will be monitored for Phe levels before they crossover into the treatment arm.

About Phenylketonuria (PKU)
PKU is a rare, inherited inborn error of metabolism caused by a mutation in the PAH gene. The current standard of care is a highly restrictive diet, but it is not always effective, and there are currently no treatments available that address the genetic defect in PKU. If left untreated, PKU can result in progressive and severe neurological impairment. PKU affects approximately 16,500 people in the U.S., and an estimated 350 newborns are diagnosed each year.

About Homology Medicines, Inc.
Homology Medicines, Inc. is a genetic medicines company dedicated to transforming the lives of patients suffering from rare genetic diseases with significant unmet medical needs by curing the underlying cause of the disease. Homology’s proprietary platform is designed to utilize its human hematopoietic stem cell-derived adeno-associated virus vectors (AAVHSCs) to precisely and efficiently deliver genetic medicines in vivo either through a gene therapy or nuclease-free gene editing modality across a broad range of genetic disorders. Homology has a management team with a successful track record of discovering, developing and commercializing therapeutics with a particular focus on rare diseases, and intellectual property covering its suite of 15 AAVHSCs. Homology believes that its compelling preclinical data, scientific expertise, product development strategy, manufacturing capabilities and intellectual property position it as a leader in the development of genetic medicines. For more information, please visit www.homologymedicines.com.

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements regarding our expectations surrounding the design, initiation, enrollment and timing of the release of data for the pheNIX clinical trial in PKU; the potential, safety, efficacy, and regulatory and clinical progress of our product candidates, including without limitation HMI-102; advancing our novel gene therapy and gene editing technology platform and pipeline; our goal of delivering potential cures to patients with PKU and other rare genetic diseases; beliefs about preclinical data; and our position as a leader in the development of genetic medicines. 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: the fact that 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 marketable products; the early stage of our development efforts; our failure or the failure of our collaborators to successfully develop and commercialize drug candidates; potential unforeseen events during clinical trials could cause delays or other adverse consequences; risks relating to the capabilities and potential expansion of our manufacturing facility; risks relating to the regulatory approval process; 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; the inability to obtain orphan drug exclusivity; 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; failure to attract, retain and motivate qualified personnel; the possibility of system failures or security breaches; risks relating to intellectual property; the price of our common stock may be volatile; significant costs as a result of operating as a public company; and any securities class action litigation. 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, 2019 and our other filings with the SEC 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.

1 “Fast Track.” U.S. Food and Drug Administration. https://www.fda.gov/ForPatients/Approvals/Fast/ucm405399.htm. Published January 4, 2018. Accessed May 6, 2019.

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