Gene therapy is a promising approach to treat hemophilia, caused by blood clotting factor deficiencies. However, viral vectors, even high-capacity gutless adenoviral vectors need to be used in high amounts to result in sufficient levels of the therapeutic protein and cause toxicity to the host. VIB scientists have developed novel recombinant high capacity adenoviral vectors that produce unprecedented, high levels of clotting factors.
A first invention relates to gutless recombinant vectors, comprised of the Ad5 left and right terminus, the clotting Factor VIII (FVIII) cDNA lacking the B-domain and the α-antitrypsin or ApoE-ApoCII promoters. A vector dose of 5x109 infectious units in FVIII-deficient mice resulted in stable FVIII expression levels exceeding 15,000 mU/mL. Even a 50-fold lower dose resulted in physiologic levels of FVIII. Furthermore, vector administration did not result in thrombocytopenia, anemia or elevation of pro-inflammatory cytokines.
A second invention relates to a recombinant adenoviral vector comprising a capsid protein coupled to a Glycine-Alanine Repeat domain (GAR-domain). The GAR-domain inhibits T-cell mediated immune rejection of the proteins produced by the transduced cells. This vector therefore allows for sustained production of clotting factors.
The recombinant adenoviral vectors encoding clotting factors can be administered in sufficient amounts for gene therapy of hemophilia without causing toxicity to the host.