Hemophilia B Gene Therapy Is Effective Despite Immune Reactions

In a PhaseI/II study of nine patients with hemophilia B who underwent Spark Therapeutics’ SPK-9001 gene therapy, two patients experienced adverse autoimmune reactions, necessitating treatment with steroids and resulting in the production of lower levels of the blood-clotting protein factor IX (FIX). However, neither patient has suffered from bleeds or required rescue treatment with FIX infusions, and the company says temporary steroid treatment can arrest the immune response before it causes FIX levels to fall to a point where bleeding risk becomes a problem.

The ongoing study has yielded an average FIX level of 28 percent of normal, measured 12 weeks after the one-time infusion. The company’s first treated patient has now been followed for one year and has a FIX level of 33 percent of normal. Another three patients followed for more than seven months have FIX levels ranging from 36 percent to 46 percent. All patients enrolled in the study had FIX levels of approximately 1 percent of normal. According to the company, a minimum FIX level of 12 percent of normal is considered necessary to prevent chronic bleeding in joints; higher FIX levels are better.