Adenovirus-Mediated Expression of Human Coagulation Factor IX in the Rhesus Macaque Is Associated With Dose-Limiting Toxicity

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Abstract
We used a first-generation adenovirus vector (AVC3FIX5) to assess whether human factor IX could be expressed and detected in the rhesus macaque, which we have shown does not make high-titer antibodies to human factor IX protein. Three animals received 1 × 1010to 1 × 1011 plaque-forming units per kilogram by intravenous injection. Human factor IX was present within 24 hours of vector administration and peaked 4 days later at 4,000 ng/mL in the high-dose recipient, and lower levels were seen in the intermediate-dose recipient. No human factor IX was detected in the low-dose recipient's plasma. Serum cytokine analysis and early hypoferremia suggested a dose-dependent acute-phase response to the vector. Human factor IX was detectable in rhesus plasma for 2 to 3 weeks for the high- and intermediate-dose recipients, but disappeared concomitant with high-titer antihuman factor IX antibody development. There was substantial, dose-dependent, dose-limiting liver toxicity that was manifest as elevated serum transaminase levels, hyperbilirubinemia, hypoalbuminemia, and prolongation of clotting times. Of particular interest was prolongation of the thrombin clotting time, an indicator of decreased fibrinogen or fibrinogen dysfunction. All evidence of liver toxicity resolved except for persistent hypofibrinogenemia in the high-dose recipient, indicating possible permanent liver damage. Our data suggest a narrow therapeutic window for first-generation adenovirus-mediated gene transfer. The development of antihuman factor IX antibodies and abnormalities of fibrinogen in the rhesus macaque is of concern for application of adenovirus (or other viral) vectors to hemophilia gene therapy.