HIGH-LEVEL TISSUE-SPECIFIC EXPRESSION OF FUNCTIONAL HUMAN FACTOR-VIIIIN MICE

Hemophilia A results from subnormal levels of blood coagulation factor VIII (FVIII) and is an attractive target for gene therapy. However, p rogress has been impeded by features of FVIII biology such as low mRNA accumulation and the instability of the protein. We have shown previo usly that a FVIII adenoviral vector, Av1ALH81, allowed high-level expr ession of human FVIII in mice sustained for several weeks. Here, we ha ve generated a second FVIII adenoviral vector, Av1ALAPH81, in which an intron was introduced into the FVIII expression cassette. Administrat ion of Av1ALAPH81 to mice resulted in significantly increased FVIII pl asma levels, 1,046 +/- 163 ng/ml compared to 307 +/- 93 ng/ml of FVIII detected in mice that received Av1ALH81. Normal FVIII levels in human s are 100-200 ng/ml and therapeutic levels are as low as 10 ng/ml. The rapeutic levels are defined as the amount of FVIII necessary to conver t severe hemophilia to a moderate or mild hemophiliac condition. The i ncreased potency of the second FVIII adenoviral vector allowed the adm inistration of significantly lower, less toxic vector doses, while ret aining the potential for high FVIII expression. Furthermore, we demons trate that adenoviral-mediated expression of human FVIII can be limite d to the liver by inclusion of a liver-specific promoter, thereby achi eving the first step in regulated expression of human FVIII in vivo.