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Homology Medicines Announces Peer-Reviewed Publication Describing Molecular Characterization of Precise In Vivo Nuclease-Free Gene Editing with PKU Program

 - Methods Showed Efficient On-Target Gene Integration with No Unintended DNA Modifications -

BEDFORD, Mass., May 26, 2020 – Homology Medicines, Inc. (Nasdaq: FIXX), a genetic medicines company, announced today the peer-reviewed publication of methods used to evaluate the on-target efficiency and precision of Homology’s in vivo phenylketonuria (PKU) gene editing program. These quantitative molecular methods provide a framework to characterize homologous recombination-based, nuclease-free gene integration and evaluate whether any unintended on-target mutations or viral insertions occurred.

“As we continue to develop our AAVHSC-based gene editing technology into new treatment options and potential cures for patients, we believe that it is important to employ quantitative molecular methods to characterize changes to the genome,” stated Albert Seymour, Ph.D., Chief Scientific Officer of Homology Medicines. “We used multiple molecular methods to assess our gene editing technology, which demonstrated precise PAH gene integration into the target location without introducing any unintended mutations or viral components. We believe that the framework described herein represents a major advancement in the field of AAV-based gene editing and, going forward, should now enable the ability to make direct data comparisons across studies.”

In the publication, one of Homology’s family of 15 adeno-associated viral vectors derived from human hematopoietic stem cells (AAVHSC15) was used to deliver the human PAH gene into the murine model with human hepatocytes. This construct is designed to leverage the body’s natural DNA repair process of homologous recombination, without requiring a nuclease to cut the DNA. Key findings in the publication include:

Single I.V. administration of the AAVHSC15-based gene editing construct resulted in seamless integration of the human PAH gene in human hepatocytes in the murine model

To determine whether gene integration occurred at the human PAH locus, the study employed a targeted integration (TI) PCR, and the TI amplicon was then purified and Sanger sequenced. The resulting data matched with reference, confirming PAH gene integration.

Gene integration was precise without de novo mutations

Next-generation sequence analysis spanning the full integration site revealed there were no unintended on-target mutations.

AAVHSC15-mediated gene editing occurs via homologous recombination

Analysis of the target location showed a pattern of DNA strand cross-over that supports homologous recombination as the pathway for gene integration. These findings are consistent with published work demonstrating AAV-mediated gene integration occurs via the homologous recombination pathway.

No inverted terminal repeats (ITRs) integrations

Long-read sequencing was used to determine that there were no ITRs at the integration site, which also supports that AAVHSC15-mediated gene editing is due to homologous recombination.

Gene integration efficiency was characterized at the DNA level

Two independent quantitation assays directly assessed the DNA, including linkage analysis by droplet digital PCR (ddPCR) and 3-primer next-generation sequencing, and each demonstrated approximately 6% gene integration. This level of editing is an improvement over the efficiencies published in others’ nuclease-free gene editing studies. The integration efficiencies in this publication are consistent with efficiencies seen in the PKU Pahenu2 murine model following a single administration of Homology’s nuclease-free gene editing construct, which corrected the disease phenotype.Homology Medicines is currently in IND-enabling studies with a lead gene editing development candidate, HMI-103, for the treatment of pediatric patients with PKU. Since the liver rapidly divides throughout childhood, a gene editing approach, which unlike gene therapy makes a permanent correction to the genome, could offer a potential cure for children with PKU.

The publication, “Molecular Characterization of Precise In Vivo Targeted Gene Integration in Human Cells Using AAVHSC15,” was peer-reviewed and published in the journal PLOS ONE. For more information, please visit or

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

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 without limitation statements regarding our expectations surrounding the potential of our gene editing framework and the ability to make direct data comparisons across studies; the potential, safety, efficacy, and regulatory and clinical progress of our product candidates; 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: the impact of the COVID-19 pandemic on our business and operations, including our preclinical studies and clinical trials, and on general economic conditions; 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 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; 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 and significant costs 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 quarterly period ended March 31, 2020 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.

iEllsworth J, Smith L, St. Martin T, et al. Nuclease-free genome editing by AAVHSC vectors leads to in vivo genome correction and amelioration of disease phenotype in a mouse model of phenylketonuria (PKU). Human Gene Therapy. Nov 2019. A1-A221.

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