SAN DIEGO – Patients with hemophilia B who received a single infusion of the gene transfer therapy SPK-9001 achieved steady-state factor IX activity levels averaging 28% and persisting over 1,650 cumulative days of observation, according to updated results from a phase I/II trial.
All nine patients treated to date have exceeded the steady-state factor IX activity level typically needed to prevent breakthrough bleeds, Katherine A. High, MD, reported at the American Society of Hematology. There have been no confirmed bleeds, all patients remain off prophylactic factor IX, none have developed factor IX inhibitory antibodies, and Enzyme-Linked ImmunoSpot testing has uncovered no evidence of emergent reactivity to the gene product. Two patients developed an immune response to the viral capsid in the product, with a corresponding drop in factor IX activity levels. Tapering doses of corticosteroids halted the immune response and patients maintained sufficient levels of factor IX activity to prevent breakthrough bleeds or the need for replacement factor.
Spark Therapeutics Inc. and Pfizer sponsored the work. Dr. High is president and chief scientific officer of Spark. She discussed the trial in.