Sustained and complete phenotype correction of hemophilia B mice followingintramuscular injection of AAV1 serotype vectors

We previously reported that direct intramuscular injection of non-serotype- 2 AAV vectors, especially AAV serotype 1 (AAV1), resulted in expression of supranormal levels of canine F9 in immunodeficient mice. Here we test the a bility of the AAV1-F9 vector to deliver sustained expression and correction of factor IX (FIX) deficiency in genetically engineered hemophilic mice. I ntramuscular injection of AAV1-F9 resulted in 100-1000 times more canine F9 in plasma of recombinant AAV1-F9 mice compared with injection of AAV2-F9. Assessment of clotting activity by activated partial thromboplastin time co nfirmed that circulating canine FIX was indeed functional. Moreover, phenot ypic correction assayed by tail clip challenge resulted in survival of all AAV1-F9 treated animals, in contrast to naive mice and 50 % of AAV2-treated hemophilia B mice, which failed to survive. Administration of cyclophospha mide (CTX) was required to suppress formation of anti-canine FIX antibodies for AAV2-treated animals, whereas it was dispensable for those treated wit h AAV1-F9. This difference in immunogenicity further emphasizes the usefuln ess of serotype-specific vectors. Finally, we report that correction of the hemophilia phenotype using AAV1-F9 was complete and persistent (over 8 mon ths), a result that underscores the value of continued exploration of alter native AAV serotype vectors.