A single adeno-associated virus (AAV)-murine factor VIII vector partially corrects the hemophilia A phenotype

A major obstacle for delivery of factor (F)VIII using adeno-associated virus (AAV) vectors is the large size of FVIII cDNA, which is well above the 5 kb packaging limit for AAV. Here we construct a < 5 kb FVIII-AAV vector using murine FVIII cDNA and a strong liver-specific albumin promoter. We assessed the efficacy of this vector using three different routes of administration, intraportal, intrasplenic and tail vein injection, in FVIII knockout (FVIII KO) mice. The peak level of FVIII observed was about 8% of normal mouse FVIII activity. Even at 9 months, post vector injection, 14 of 19 mice receiving FVIII-AAV demonstrated phenotypic correction and roughly 2% FVIII activity. The transgene copy number ranged from 0.001 to 0.1 copies per cell, depending upon the somatic tissue. The potential for germline transmission of AAV was assayed in 34 pups obtained from five pairs of treated, phenotypically corrected adult hemophilic mice. Although the parents harbored the transgene in liver, spleen, and gonads, none of the 34 offspring was positive for the transgene, suggesting that the risk of inadvertent germline transmission is low.