Development of an Optimized rAAV2/6 Human Factor 8 cDNA Vector Cassette for Hemophilia a Gene Therapy

Hemophilia A, which is caused by a mutation in the Factor 8 (F8) gene resulting in a deficiency or lack of the Factor VIII (FVIII) protein, is the most common inherited bleeding disorder in humans with an estimated worldwide incidence of half a million people. The disorder is X-linked and occurs in approximately 1 in 5,000 males; however there is also a growing appreciation of the impact on carrier females having a single mutant allele, with at least 10% of hemophilia A female carriers having less than normal clotting activity. Even modest increases in Factor V III activity (>1% of normal) can have a positive impact on patient lives, thus making the disease an ideal candidate for liver-directed gene therapy. Recombinant AAV (rAAV) has been used extensively for nearly 20 years as a gene therapy vector in preclinical and clinical studies where rAAV delivery to non-dividing tissues such as liver, brain and muscle affords stable, long-term transgene expression. However, there has been a lag in the clinical translation of a rAAV gene therapy approach for Hemophilia A/human F8 (hF8) compared to Hemophilia B/human Factor 9 due to poor yields of rAAV encoding a F8 transgene at clinical scale, and a requirement for large doses of rAAV F8 vector to achieve therapeutically relevant levels of circulating human FVIII (hFVIII), with the attendant risk of inducing an AAV-directed immune response requiring transient immunosuppression. To address these issues we optimized a rAAV F8 cDNA vector cassette to improve both virus yields and liver-specific hFVIII expression. The rAAV F8 cDNA vector cassette optimization required multi-factorial modifications to the liver-specific promoter module, hF8 transgene, synthetic polyadenylation signal and vector backbone sequence. This iterative process resulted in improved vector yields at research scale and greater than five-fold improvement in vector yields at clinical scale using our proven manufacturing process. Administration of the optimized rAAV hF8 cDNA packaged in serotype AAV2/6 at a dose of ~7.2E+12 vg/kg to both wild type and Hemophilia A mice resulted in robust circulating hFVIII levels and activity (levels in wild type mice were 241.6% of normal, and activity in Hemophilia A mice were 330.9% of normal). An analysis of hF8 mRNA levels in different tissues following dosage with our optimized vector demonstrated that hF8 expression from the modified promoter module was restricted to the liver. Notably there was a striking impact on hemostasis in the Hemophilia A mice treated with the optimized rAAV hF8 cDNA, with a reduction in bleeding time from 38.3 minutes to 2.5 minutes in treated mice (n = 12, p-value Disclosures Riley: Sangamo BioSciences Inc: Employment. Boonsripisal: Sangamo BioSciences Inc: Employment. Goodwin: Sangamo BioSciences Inc: Employment. Garces: Sangamo BioSciences Inc: Employment. Ballaron: Sangamo BioSciences Inc: Employment. Tran: Sangamo BioSciences Inc: Employment. Kang: Sangamo BioSciences Inc: Employment. Zhang: Sangamo BioSciences Inc: Employment. Meyer: Sangamo BioSciences Inc: Employment. Greengard: Sangamo BioSciences Inc: Employment. Surosky: Sangamo BioSciences Inc: Employment. Ando: Sangamo BioSciences Inc: Employment. Lillicrap: bayer: Research Funding; biogen: Research Funding; CSL: Research Funding; Octapharma: Research Funding; Sangamo Biosciences Inc: Research Funding. Nichol: Sangamo BioSciences Inc: Employment. Holmes: Sangamo BioSciences Inc: Employment.