Today, the U.S. Food and Drug Administration approved Hemgenix (etranacogene dezaparvovec), an adeno-associated virus vector-based gene therapy for the treatment of adults with Hemophilia B (congenital Factor IX deficiency) who currently use Factor IX prophylaxis therapy, or have current or historical life-threatening hemorrhage, or have repeated, serious spontaneous bleeding episodes.

“Gene therapy for hemophilia has been on the horizon for more than two decades. Despite advancements in the treatment of hemophilia, the prevention and treatment of bleeding episodes can adversely impact individuals’ quality of life,” said Peter Marks, M.D., Ph.D., director of the FDA’s Center for Biologics Evaluation and Research. “Today’s approval provides a new treatment option for patients with Hemophilia B and represents important progress in the development of innovative therapies for those experiencing a high burden of disease associated with this form of hemophilia.”

Hemophilia B is a genetic bleeding disorder resulting from missing or insufficient levels of blood clotting Factor IX, a protein needed to produce blood clots to stop bleeding. Symptoms can include prolonged or heavy bleeding after an injury, surgery, or dental procedure; in severe cases, bleeding episodes can occur spontaneously without a clear cause. Prolonged bleeding episodes can lead to serious complications, such as bleeding into joints, muscles or internal organs, including the brain. 

Most individuals who have Hemophilia B and experience symptoms are men. The prevalence of Hemophilia B in the population is about one in 40,000; Hemophilia B represents about 15% of patients with hemophilia. Many women carriers of the disease have no symptoms. However, an estimated 10-25% of women carriers have mild symptoms; in rare cases, women may have moderate or severe symptoms. 

Treatment typically involves replacing the missing or deficient clotting factor to improve the body’s ability to stop bleeding and promote healing. Patients with severe Hemophilia B typically require a routine treatment regimen of intravenous (IV) infusions of Factor IX replacement products to maintain sufficient levels of clotting factor to prevent bleeding episodes.

Hemgenix is a one-time gene therapy product given as a single dose by IV infusion. Hemgenix consists of a viral vector carrying a gene for clotting Factor IX. The gene is expressed in the liver to produce Factor IX protein, to increase blood levels of Factor IX and thereby limit bleeding episodes. 

The safety and effectiveness of Hemgenix were evaluated in two studies of 57 adult men 18 to 75 years of age with severe or moderately severe Hemophilia B. Effectiveness was established based on decreases in the men’s annualized bleeding rate (ABR). In one study, which had 54 participants, the subjects had increases in Factor IX activity levels, a decreased need for routine Factor IX replacement prophylaxis, and a 54% reduction in ABR compared to baseline.

The most common adverse reactions associated with Hemgenix included liver enzyme elevations, headache, mild infusion-related reactions and flu-like symptoms. Patients should be monitored for adverse infusion reactions and liver enzyme elevations (transaminitis) in their blood. 

This application received Priority Review, Orphan and Breakthrough Therapy designations. 

The FDA granted approval of Hemgenix to CSL Behring LLC.