The objective is to determine whether early exposure to F. VIII in the fetus or neonate abrogates antibody development in mouse hemophiliacs. B-domain-deleted F. VIII has been expressed in our laboratory in several vectors: adenovirus, adeno-associated virus and as DNA plasmids. All three have been shown to express functional F. VIII in vitro. In vivo experiments are underway to see if expression can be detected in serum of treated mice. Preliminary data show that the constructs can correct clotting times in hemophiliac mice. Future experiments will determine whether these constructs induce antibody responses in adult mice as expected. If antibodies are induced the constructs will be introduced earlier in the life of these mice to see whether they can be tolerized rather than immunized. First neonatal treatment will be tried and if this fails fetal treatment will be attempted to induce tolerance. In addition, this project will help decide which constructs are more effective in replacement therapy both in regard to levels of expression of F. VIII and in the ability of each construct to be immunogenic. Immune responses aginst F. VIII and against the vector will be assessed in terms of antibody and cellular responses. Antibodies and cytotoxic T cell responses against the vector can be expected to limit the usefulness of the particular vector.
