Long-term correction of canine hemophilia B by gene transfer of blood coagulation factor IX mediated by adeno-associated viral vector

Hemophilia B is a severe X-linked bleeding diathesis caused by the absence of functional blood coagulation factor TX, and is an excellent candidate fo r treatment of a genetic disease by gene therapy. Using an adeno-associated viral vector, we demonstrate sustained expression (>17 months) of factor I X in a large-animal model at levels that would have a therapeutic effect in humans (up to 70 ng/ml, adequate to achieve phenotypic correction, in an a nimal injected with 8.5 x 10(12) vector particles/kg). The five hemophilia B dogs treated showed stable, vector dose-dependent partial correction of t he whole blood clotting time and, at higher doses, of the activated partial thromboplastin time. In contrast to other viral gene delivery systems, thi s minimally invasive procedure, consisting of a series of percutaneous intr amuscular Injections at a single timepoint, was not associated with local o r systemic toxicity. Efficient gene transfer to muscle was shown by immunof luorescence staining and DNA analysis of biopsied tissue, Immune responses against factor IX were either absent or transient. These data provide stron g support for the feasibility of the approach for therapy of human subjects .