699. Correction of Glycogen Storage Disease Type II (GSD II) with an Adeno-Associated Virus 8 (AAV2/8) Vector

Abstract

Glycogen storage disease type II (GSD II; Pompe disease; MIM 232300) is an autosomal recessive disorder caused by a deficiency in the activity of the lysosomal enzyme alpha-glucosidase (GAA; acid maltase; EC 3.2.1.20). The disease is characterized by massive accumulation of glycogen in the lysosomes and cytoplasm of striated muscle, with a subsequent disruption of cellular functions. Clinically, the disease spectrum varies in severity and age of onset, and the manifestations include muscle weakness, hypotonia, hypertrophic cardiomyopathy and respiratory failure. Intravenous administration of adenovirus vectors encoding GAA previously demonstrated generalized correction of glycogen storage in the GAA-knockout (GAA-KO) mouse model, although GAA secretion stopped and glycogen content increased coincident with appearance of anti-GAA antibodies. Tissue-specific expression of an introduced therapeutic protein has prevented the formation of neutralizing antibodies in other models, but not in GAA-KO mice. Consequently, an AAV2/8 vector containing a liver-specific promoter (LSP) to drive GAA expression (AAV-LSPGAApA) was administered (1 x 10E11 particles intravenously) in 3 month-old immunocompetent GAA-KO mice. A second group of age-matched GAA-KO mice was injected with a similar dose of an AAV2/8 vector containing hGAA under the control of the CMV enhancer/chicken |[beta]|-actin (CB) promoter for comparison (AAV-CBGAApA). High-level hGAA was detectable by Western blot in plasma for longer than 6 weeks with AAV-LSPGAApA in GAA-KO mice, in contrast to AAV-CBGAApA which produced low-level hGAA in the plasma only during the first week. The latter vector has produced sustained, high-level hGAA in plasma in immunodeficient (GAA-KO/SCID) mice, indicating the significance of the immune response to hGAA secretion. ELISA performed at 1, 3, and 6 weeks following vector administration demonstrated no detectable anti-GAA antibodies in response to liver-specific hGAA expression in GAA-KO mice ( 1:800) at the 6 week time point. The level of hGAA activity in plasma with AAV-LSPGAApA (>1000 nmol/hr/ml) has previously corrected glycogen storage in the heart of tolerant GAA-KO mice. This combined approach to liver-targeted gene therapy of GSD II with a liver-directed AAV serotype and a liver-specific promoter provides a substantially greater and more sustained level of hGAA expression in vivo than has previously been reported. Further work will be carried out to determine the implications of this sustained, high-level expression of the enzyme on disease phenotype. Thus, use of a liver-specific promoter prevented neutralizing antibody formation in GSD II mice and will enhance the development of gene therapy in Pompe disease.