Helper-dependent adenoviral gene therapy mediates long-term correction of the clotting defect in the canine hemophilia A model

Abstract

Background: Adenoviral vector-mediated gene therapy might have potential for long-term correction of the monogenic disease hemophilia A. Objecti ve: In this study, we tested the efficacy of administering a helper-dependent adenoviral vector (HDV) designed formaximal liver-restricted canine factor VIII (cFVIII) expression on three out-bred hemophiliaA dogs. Methods: Three FVIII-deficient animals from the University of North Carolina colony were injected with 1 × 1012 (Dog A), and 3 × 1012 (DogBand C) vp kg-1 helper-dependent adenoviral vector, and we performed systematic analysis of toxicity, persistence of therapeutic gene expression, and molecular analysis of gene transfer. Results: We observed acute dose-dependent elevation in liver enzymes and thrombocytopenia after injection, although both were transient and resolved within 2 weeks. The whole blood clotting time (WBCT), plasma FVIII concentration, FVIII activity, and activated partial thromboplastin time in all animals improved significantly after treatment, and two animals receiving a higher dose reached near normal WBCT with low-level FVIII activity until terminal sacrifice at 3 months, and 2 years. Importantly, the treated dogs suffered no bleeding events after injection. Moreover, we observed persistent vector-specific DNA and RNAin liver tissue collected from one high-dose animal at days 18 and 79, and could not detect the formation of inhibitory antibodies. Conclusion: Although Vector-associated toxicity remains an obstacle, a single injection of HDV led to longterm transgene expression and vector persistence in two FVIIIdeficient animals with conversion of their severe phenotype to a moderate one. © 2006 International Society on Thrombosis and Haemostasis.