Abstract
The formation of inhibitory anti-factor IX (anti-FIX) antibodies is a major complication of FIX protein replacement-based treatment for hemophilia B. It is difficult to treat patients with anti-FIX antibodies. Gene therapy is emerging as a potentially effective treatment for hemophilia. Direct i.m. injection of adeno-associated virus (AAV) is a safe and efficient procedure for hemophilia B gene therapy. However, the development of anti-FIX antibodies following i.m. of AAV may impede its application to patients. We aimed to investigate induction of immune tolerance to human FIX (hFIX) by i.m. of AAV1, further validating i.m. of AAV1 for hemophilia B gene therapy. Cohorts of hemostatically normal and hemophilia B mice with diverse genetic and MHC backgrounds received i.m. of AAV-hFIX. Human FIX antigen and anti-hFIX antibodies were examined. I.m. of 1 x 10(11) vector genomes (VG) of AAV2 elicits formation of anti-hFIX antibodies comparable to those by hFIX protein replacement. I.m. of 1 x 10(11) VG of AAV1 results in expression of therapeutic levels of hFIX (up to 950 ng mL(-1), mean = 772 ng mL(-1), SEM +/- 35.7) and hFIX-specific immune tolerance in C57BL/6 mice. A single i.m. of AAV1 can result in efficient expression of therapeutic levels of hFIX and induction of hFIX tolerance in hemostatically normal and hemophilic B mice. Our results substantiate the prospect of i.m. of AAV1 for hemophilia B gene therapy and FIX tolerance induction.
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