DEVELOPMENT OF SAFE AND EFFECTIVE APPROACHES FOR HEMOPHILIA B GENE THERAPY USING HELPER-DEPENDENT ADENOVIRAL VECTORS

Hemophilia B is caused by alterations in the gene encoding for factor IX, which is a blood component produced by the liver and important for the proper functioning of coagulation. Different gene therapy vectors have been studied with the goal of delivering the correct version of the gene to the liver cells, however each of them present some limitations. Helper-dependent adenoviral vectors derive from adenoviruses which have been highly modified so that all the viral genes have been eliminated. The gene of interest, factor IX in our case, can be inserted into the genome of these vectors. These vectors have advantages over other gene transfer systems as they are very efficient in delivering genes to the liver after an intravenous administration. However, in order to achieve efficient gene transfer, high doses of vector are necessary, which are acutely toxic. We propose three different strategies to overcome this toxicity. Since the acute toxicity is clearly dose-dependent, in specific aim 1 we hypothesize that by injecting vector expressing higher levels of factor IX we could reduce the dose necessary for achieving a therapeutic effect and we will reduce the toxic effects. We will test this hypothesis in hemophilia B dogs. In specific aim 2 we hypothesize that by injecting the vector directly into the liver we could overcome the acute response and achieve levels of FIX in the blood which could correct the disease. We will test this hypothesis in hemophilia B dogs as well. In specific aim 3 we hypothesize that using factor IX molecules with modifications increasing their potency will increase the likelihood of correcting the disease and will allow a further reduction in the dose. This latter study has the potential to generate important results for hemophilia B therapy because they will be applicable to other gene transfer systems as well as to recombinant protein replacement therapy.