Achievement of normal circulating factor VIII activity following BMN 270 AAV5-FVIII gene transfer: interim, long-term efficacy and safety results from a phase-I/II-study in patients with severe hemophilia A.
Patients with hemophilia A who received a single infusion of an investigational gene therapy showed improved levels of the essential blood clotting protein FVIII, with 11 of 13 achieving normal or near-normal FVIII levels, according to the latest data from a trial that followed patients for up to 19 months. Researchers state that this represents the first successful gene therapy trial for people with hemophilia A.
The therapy uses a viral vector to transfer a functional copy of the gene responsible for producing FVIII, which is mutated in people with hemophilia A, into the patient’s body.
Data were reported on two dosing levels. After several weeks, all patients began producing FVIII. By 20 weeks after the infusion, median FVIII levels in those receiving the higher dose plateaued and remained within the normal range. Those receiving the lower dose had FVIII levels that increased steadily to a median of 34IU/dL by 20 weeks and, in the three patients who had been followed for 32 weeks, a median of 51IU/dL — a level that is within the normal range and represents a dramatic increase over their pre-treatment FVIII levels of less than 1IU/dL.
In contrast to standard care, which requires multiple intravenous therapy infusions per week, this gene therapy appears to have long-lasting effects after a single infusion.
Prior to this study, participants received up to 185 FVIII infusions per year to prevent bleeds, resulting in up to 41 breakthrough bleeding episodes per year despite prophylactic treatment. After receiving the gene therapy, all patients from both dose cohorts were able to completely discontinue prophylactic FVIII infusions, and 10 had no bleeding episodes requiring FVIII treatment from four weeks after infusion through the last follow-up visit. No patients showed evidence of an adverse response by the immune system, a side effect that has posed concern in trials for other gene therapies.
While several gene therapies have shown success for the rarer form, hemophilia B, gene therapy for hemophilia A has been considered more challenging because it is associated with a complex and much larger gene, making successful gene therapy considerably more difficult.
„The clinical data to date for this investigational gene therapy exceeded our expectations, in terms of increasing factor VIII levels and reducing the annualized bleed rate,“ said lead researcher K. John Pasi, MD, professor of hemostasis and thrombosis at Barts and the London School of Medicine and Dentistry and haemophilia clinical director at Barts Health NHS Trust. „Many clinical trial participants have seen factor VIII levels at or close to normal. This clinical result has the potential to improve the lives of patients who now must infuse themselves with factor VIII as often as every other day. With this experimental treatment, we are researching whether it may be possible for hemophilia A patients to reduce or eliminate factor VIII treatment over an extended timeline.“
ASH Annual Meeting 2017, abstract #603