Homology Medicines Appoints Mary Thistle to Board of Directors

BEDFORD, Mass., March 15, 2018 – Homology Medicines, Inc., a genetic medicines company, announced today the appointment of Mary Thistle, Chief of Staff of the Bill & Melinda Gates Medical Research Institute, to Homology’s Board of Directors. Ms. Thistle
 has more than 25 years of experience in finance, strategy and business
 development functions across different therapeutic areas, including gene

“Mary has extensive strategic operations, business
 development and finance experience that we can leverage to advance our
 nuclease-free gene editing and gene therapy platform,” said Arthur Tzianabos, Ph.D., President and Chief Executive Officer of Homology Medicines. “We believe
the recent addition of two independent and experienced members to our Board
 strengthens our ability to deliver on our mission to cure patients with genetic

Prior to joining the Bill & Melinda Gates Medical
 Research Institute, Ms. Thistle was Chief Operating Officer of Dimension
 Therapeutics Inc. At Dimension, she oversaw the company’s Series B financing
 and initial public offering, expanded the pipeline through strategic business
development transactions, and led the sale of the company to Ultragenyx Pharmaceutical
Inc. Prior, Ms. Thistle was the Senior Vice President, Business Development at 
Cubist Pharmaceuticals, where she was responsible for multiple acquisitions and
 assisted in the sale to Merck. Ms. Thistle held senior level positions at
 ViaCell Inc. in finance, operations and business development, and then served
 as Senior Vice President, Business Development at Perkin Elmer after ViaCell was
 acquired. Ms. Thistle began her career in finance as a Certified Public Accountant.
 Ms. Thistle also serves on the Board of Directors of Enterome SA and is a
graduate of the Women in Bio Boardroom Ready program.

“Homology is pursuing scientific and business
 strategies to advance the Company’s gene therapy and gene editing platform
toward the clinic,” said Ms. Thistle. “Patients with rare diseases need more
 options that have the potential to address the underlying genetic cause of
 disease, and I am excited to join the Board and work with the Homology team
 with the goal of bringing new treatments forward.”

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 a robust intellectual property portfolio
 with issued composition of matter patents in the United States for 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.

Cara Mayfield
Director, Corporate Communications
781-301-7277, ext. 141