This week in the  New England Journal of Medicine, Lindsey George, MD and colleagues report on their Phase 1/2 study assessing the safety and efficacy of gene therapy to treat patients with hemophilia B. And the results are very impressive. With a cumulative follow-up of 492 weeks, the mean steady-state factor IX activity was 34% of normal and the annualized bleeding rate (ABR) was reduced 97%, from a mean of 11.1 events per year before gene therapy to 0.4 events per year afterwards. Further, the need for using Factor IX infusions was reduced by 99% which is essentially curing the patient of the condition.

The therapy is being developed by Pfizer and Spark Therapeutics. In a news release, Katherine A. High, M.D., president and head of Research and Development at Spark Therapeutics and co-author of the paper said, “The data suggest a one-time infusion of SPK-9001 has the potential to safely sustain factor IX coagulant activity level that may result in the termination of baseline prophylaxis factor infusions, significantly reduce bleeding, and nearly eliminate the need for exogenous factor IX concentrate infusions.” People with hemophilia B have a deficiency in clotting factor IX, which leads to excessive bleeding and bruising in people with this rare disease. Hemophilia B also is called congenital factor IX deficiency or Christmas disease. The current standard of care is recurrent intravenous infusions of either plasma-derived or recombinant factor IX to control and prevent bleeding episodes.