FDA approves first hemophilia B gene therapy

Nov. 23, 2022

The U.S. FDA announced yesterday that it had approved the first gene therapy for adults with Hemophilia B, branded as Hemgenix.

The approval — granted to Australian drugmaker CSL Behring — quickly made the drug the most expensive one in the world, priced at $3.5 million per dose.

CSL bought the rights to the drug from UniQure in 2020 for $450 million, while the drug was still in phase 3 trials. 

Hemgenix is a one-time gene therapy that is given as a single dose by IV fusion. The drug works by carrying a gene for clotting Factor IX and expressing it in the liver to produce the protein, and increase levels of the clotting factors to limit bleeding episodes. 

Patients with Hemophilia are normally treated with Factor IX prophylaxis therapy which some patients may need as often as every other day or 2-3 times per week in order to ensure protection from spontaneous and breakthrough bleeds.

The historic approval was supported by results from the ongoing HOPE-B trial, which is the largest gene therapy trial in hemophilia B to date. Trial results showed that 94% (51 out of 54) of patients treated with Hemgenix were able to discontinue the use of prophylaxis and remained free of previous continuous routine prophylaxis therapy.  

The drug, which received Priority Review, Orphan and Breakthrough Therapy designations by the FDA, is now being assessed by other regulatory agencies.