FDA Approves Second Gene Therapy for Hemophilia B

The US Food and Drug Administration (FDA) has approved the gene therapy fidanacogene elaparvovec (Beqvez) for adults with hemophilia B, a rare bleeding disorder that affects almost 4 in 100,000 US men.

Patients are eligible for a one-time infusion of Pfizer's gene therapy if they are currently using clotting factor IX prophylaxis therapy; have current or historical life-threatening hemorrhages; or have repeated, serious spontaneous bleeding episodes. 

Beqvez is the second gene therapy the agency has approved for hemophilia B, a deficiency in clotting factor IX because of a faulty gene that occurs mostly in males. The FDA approved the first gene therapy, etranacogene dezaparvovec (Hemgenix), in November 2022. 

Both therapies deliver a functional copy of the factor IX gene to liver cells via a viral vector. 

Pfizer said the list price of Beqvez will be $3.5 million — the same price as Hemgenix. The argument for this hefty price tag is that these gene therapies offer the possibility of a cure whereas ongoing factor IX infusions can cost more than $20 million over a patient's lifetime. Uptake of Hemgenix, however, has been slow, given the cost and concerns about the therapy's durability and safety.

Beqvez was approved on the basis of the phase 3 BENEGENE-2 trial in 45 men with moderate to severe hemophilia B. These men had been on factor IX prophylaxis for at least 6 months and had tested negative for antibodies against the viral delivery vector. 

The annualized bleeding rate fell from a mean of 4.5 events during the pretreatment period of at least 6 months to a mean of 2.5 events between week 12 and data cutoff (median, 1.8 years of follow-up), according to Pfizer's press release. Overall, bleeding events were eliminated in 60% of patients who received the one-time infusion vs 29% of patients on factor IX prophylaxis therapy.

Overall, Pfizer reported that the gene therapy was "generally well-tolerated," with an increase in transaminases reported as the most common adverse event. No deaths, serious infusion reactions, thrombotic events, or development of factor IX antibodies occurred. 

Pfizer has said it will continue to monitor patients to assess the therapy's long-term durability and safety over a 15-year period.