FDA Approves First Gene Therapy for Hemophilia B

Hans-Peter Kiem, MD, PhD - November 22, 2022

The approval of Hemgenix is the first of its kind for hemophilia B patients, who typically control the disease with regular infusions of the clotting factor they lack.

Today the FDA approved the investigational gene therapy etranacogene dezaparvovec, or Hemgenix, to treat adults with hemophilia B, making it the first gene therapy option for people living with the genetic bleeding disorder.

Hemophilia B occurs when genes that are vital to producing clotting factor IX are faulty, resulting in prolonged external or internal bleeding in the body. Without the ability to effectively stop bleeding, a simple cut or bruise can lead to external bleeds, and internal bleeding inside joints and muscles can damage organs including the brain.

The approval of Hemgenix is the first of its kind for hemophilia B patients, who typically control the disease with regular infusions of the clotting factor they lack. Hemgenix works by delivering a functional copy of the faulty gene into a cell, instructing the cell to produce the missing clotting factor IX which helps control bleeding. Developed by CSL Behring and UniQure, it has been shown in clinical trials to significantly reduce the rate of annual bleeds in people with hemophilia B after a single infusion.

CSL’s biologics license application (BLA) was accepted for priority review in May. The BLA was supported by results from the HOPE-B trial, the largest gene therapy trial in hemophilia B to date. Results showed that hemophilia B patients treated with Hemgenix demonstrated a 64 percent reduction in the adjusted annualized bleeding rate. Hemgenix produced mean FIX activity of 39.0 IU/dL at six months and 36.9 IU/dL at 18 months post infusion. Additionally, all FIX-treated bleeds were reduced by 77 percent over months seven to 18, and 98 percent of subjects treated with a full dose of the gene therapy discontinued use of prophylaxis.

Under its deal with UniQure, CSL will commercialize the therapy and holds responsibility for all regulatory interactions.

Dr. Kiem is president of ASGCT. He is also a professor of medicine and pathology and director of the stem cell and gene therapy program at the University of Washington, and the Stephanus Family Endowed Chair for Cell and Gene Therapy at the Fred Hutchinson Cancer Center.