Homology Medicines Initiates Phase 1/2 Study for HMI-102 Gene Therapy Candidate for Adults with PKU and Expects Initial Clinical Results by Year End 2019

- Enrollment in the pheNIX Study Marks First Gene Therapy Clinical Trial for PKU -

BEDFORD, Mass., June 10, 2019 (GLOBE NEWSWIRE) -- Homology Medicines, Inc. (Nasdaq: FIXX), a genetic medicines company, announced today that it has commenced enrollment of the Phase 1/2 pheNIX trial for HMI-102, a one-time gene therapy development candidate for the treatment of adults with phenylketonuria (PKU). The pheNIX study is designed to evaluate the safety and efficacy of the investigational gene therapy in a randomized, concurrently-controlled, dose-escalation study. PKU is an inborn error of metabolism caused by a mutation in the PAH gene that results in a potentially toxic buildup of phenylalanine (Phe), an essential amino acid derived primarily from dietary protein.

"Our early work with the clinical sites has enabled us to move expeditiously from receiving IND clearance to enrolling patients," said Arthur Tzianabos, Ph.D., President and Chief Executive Officer of Homology Medicines. "We now have both external and internal operational GMP capabilities utilizing our proprietary process development and commercial manufacturing platform that can supply HMI-102 for the pheNIX trial all the way through to commercial scale. Our early investment in manufacturing is a key strategic advantage for Homology that has allowed us to progress this program rapidly to the clinic." 

The pheNIX trial is expected to enroll up to 21 patients ages 18-55 years old who have been diagnosed with classic PKU and will receive a single dose of HMI-102. 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. Homology expects to report initial clinical data from the pheNIX trial by the end of 2019. Additional information about the pheNIX trial can be found at www.clinicaltrials.gov.

Albert Seymour, Ph.D., Chief Scientific Officer of Homology Medicines, commented, "Now that enrollment in the Phase 1/2 pheNIX study is underway, HMI-102 becomes the first gene therapy candidate for PKU to enter the clinic, which is a major advancement for patients living with this disease. This achievement also reflects the dedication and expertise of our team, a remarkable group that has brought this novel AAVHSC vector from early research to a human development candidate in just three years. We look forward to continuing our work with patient advocacy organizations and the broader PKU community as we strive to bring clinically meaningful and potentially curative therapies to patients."

In April 2019, Homology announced that the U.S. Food and Drug Administration (FDA) cleared the Investigational New Drug (IND) application for HMI-102 for the treatment of PKU, and in May 2019, the FDA granted Fast Track Designation. Previously, 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.

About HMI-102
HMI-102 is designed to use one of Homology's proprietary suite of human hematopoietic stem cell-derived adeno-associated virus vectors (AAVHSCs) to deliver a functional copy of the phenylalanine hydroxylase (PAH) gene to the liver cells, where there is a missing or mutated PAH gene. This in vivo gene therapy approach is intended to enable the production of the PAH enzyme responsible for metabolizing Phe. People with PKU are not able to metabolize Phe properly, resulting in significantly elevated levels of Phe, and if left untreated, can lead to severe neurological impairment. Phe reduction is an established clinical endpoint for PKU registrational trials.

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; and the potential, safety, efficacy, and regulatory and clinical progress of our product candidates; advancing our novel platform and pipeline; our goal of delivering potential cures to patients; 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: 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 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; effects of significant competition; failure to attract, retain and motivate qualified personnel; the possibility of system failures or security breaches; and risks relating to intellectual property. 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.

Contact
Theresa McNeely
SVP, Corporate Communications & Patient Advocacy
tmcneely@homologymedicines.com
781-301-7277

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