AAV8-Factor IX Hepatic Gene Transfer with Transient Immunosuppression Is Safe but Is Abrogated by Low Titers of Neutralizing Antibody in Rhesus Macaques.

AAV8 vectors have potential in human gene transfer due to improved transduction efficiencies as demonstrated in small animal models, and are also reported to show less cross-reactivity to AAV2 neutralizing antibodies prevalent in humans. To assess this hypothesis, the efficacy and safety of AAV8-human Factor IX (hFIX) was evaluated in rhesus macaques. At doses of 5–20x10¹² vg/kg, AAV8-hFIX achieved therapeutic to supraphysiological levels of circulating human FIX via intra-hepatic artery delivery in AAV8-naïve macaques. However, transduction was abrogated in macaques with pre-existing AAV8 neutralizing antibodies at titers as low as 1:5. Intrahepatic delivery of AAV8-hFIX resulted in gene transfer primarily in liver, and was well distributed among individual hepatic lobes. Two macaques that experienced traumatic catheterization developed immediate and delayed (week 4–6) transient transaminitis post surgery. Nevertheless, a significant percentage of AAV8-hFIX transduced hepatocytes persisted despite the liver damage and partial loss of hFIX expression. Transduction was well tolerated in all other macaques. Transient immunosuppression with tacrolimus and mycophenolate mofetil did not impair AAV8-hFIX transduction. The results [1] support AAV8-mediated gene transfer in humans but indicate that both the efficacy achieved and the resistance to pre-existing neutralizing antibodies of AAV8-hFIX are unlikely to be significantly enhanced over AAV2 vector, [2] suggest that a peri-operative insult and likely triggering of innate immunity may result in a later inflammatory response that results in a decrease in transgene protein production, and [3] provide evidence that a short course of immunosuppression does not alter liver transduction by AAV vectors.