The efficacy and the risk of immunogenicity of FIX Padua (R338L) in hemophilia B dogs treated by AAV muscle gene therapy

Jonathan D. Finn, Timothy C. Nichols, Nikolaos Svoronos, Elizabeth P. Merricks, Dwight A. Bellenger, Zhangshen Zhou, Paolo Simioni, Katherine A. High and Valder R. Arruda


Studies on gene therapy for hemophilia B (HB) using adeno-associated viral (AAV) vectors showed that the safety of a given strategy is directly related to the vector dose. To overcome this limitation, we sought to test the efficacy and the risk of immunogenicity of a novel factor IX (FIX) R338L associated with ~8-fold increased specific activity. Muscle-directed expression of canine FIX-R338L by AAV vectors was carried out in HB dogs. Therapeutic levels of circulating canine FIX activity (3.5-8%) showed 8-9 fold increased specific activity, similar to humans with FIX-R338L. Phenotypic improvement was documented by the lack of bleeding episodes for a cumulative 5-year observation. No antibody formation and T cell responses to FIX-R338L were observed even upon challenges with FIX-wild type protein. Moreover, no adverse vascular thrombotic complications were noted. Thus, FIX-R338L provides an attractive strategy to safely enhance the efficacy of gene therapy for HB.

  • Submitted June 28, 2012.
  • Accepted August 10, 2012.