The first gene therapy has been approved by the US Food and Drug Administration for the treatment of haemophilia B, but the product – etranacogene dezaparvovec – comes with a price tag of US$3.5 million (AU$5.2 million) per dose.
CSL, which has licensed the product under the brand name Hemgenix, says it reduces the rate of annual bleeds, reduces or eliminates the need for prophylactic therapy and generates elevated and sustained factor IX levels for years after a one-time infusion.
The gene therapy won FDA approval for the treatment of adults with haemophilia B who currently use factor IX prophylaxis therapy, or have current or historical life-threatening haemorrhage or have repeated, serious spontaneous bleeding episodes.
According to a recent review, etranacogene dezaparvovec is a gene transfer therapy that uses an adeno-associated virus (AAV) vector to introduce a working copy of the Factor IX clotting factor gene to the liver.
By restoring endogenous Factor IX production, the one off treatment aims to restore Factor IX levels so that prophylactic replacement may be discontinued, and factor replacement is not needed for high-intensity activities, surgery, trauma, or bleeding
The FDA said approval was based on results from the ongoing HOPE-B trial, involving 54 patients with haemophilia B. This showed that etranacogene dezaparvovec allowed patients to produce mean factor IX activity of 39% at six months and 36.7% at 24 months post infusion.
Seven to 18 months post-infusion, the mean adjusted annualized bleeding rate (ABR) for all bleeds was reduced by 54% compared to the six-month lead-in period on factor IX prophylactic replacement therapy. In addition, 94% of patients discontinued use of prophylaxis and remained free of previous continuous routine prophylaxis therapy.
The most common side effects were liver enzyme elevations, headache, elevated levels of a certain blood enzyme, flu-like symptoms, infusion-related reactions, fatigue, nausea and feeling unwell.
“Gene therapy for haemophilia has been on the horizon for more than two decades,” said Dr Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research.
“Today’s approval provides a new treatment option for patients with haemophilia B and represents important progress in the development of innovative therapies for those experiencing a high burden of disease associated with this form of haemophilia.”
CSL licensed the product from uniQure, and said that despite the high cost of the treatment it would achieve cost savings because a single dose would reduce or eliminate the need for regular infusions of prophylactic therapy with clotting factor for many years.
The approval was welcomed by the US National Hemophilia Foundation.
“It’s an exciting time for the bleeding disorders community as new and ground breaking treatment options become available,” said CEO Dr Len Valentino.
“It is great to see this innovation for people living with haemophilia B, and we will continue our work to ensure all people with inherited bleeding and blood disorders have full access to Hemgenix and like products as they come to market.