Abstract
Pompe disease (glycogen storage disease type II; acid maltase deficiency) is a devastating myopathy resulting from acid α-glucosidase (GAA) deficiency in striated and smooth muscle. Despite the availability of enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA), the limitations of ERT have prompted the preclinical development of gene therapy. Gene therapy has the advantage of continuously producing GAA, in contrast to ERT, which requires frequent injections of rhGAA. An adeno-associated viral (AAV) vector containing a muscle-specific promoter, AAV-MHCK7hGAApA, achieved high GAA expression in heart and skeletal muscle in mice with Pompe disease. However, elevated GAA activity was not sufficient to completely clear accumulated glycogen in skeletal muscle. The process of glycogen clearance from lysosomes might require improved trafficking of GAA to the lysosomes in skeletal muscle, previously achieved with the β(2)-agonist clenbuterol that enhanced glycogen clearance in skeletal muscle without increasing GAA activity. Glycogen clearance was clearly enhanced by treatment with a nondepleting anti-CD4 monoclonal antibody (anti-CD4 mAb) along with muscle-specific GAA expression in cardiac muscle, but that treatment was not effective in skeletal muscle. Furthermore, anti-CD4 mAb treatment along with clenbuterol achieved synergistic therapeutic efficacy in both cardiac and skeletal muscle. This triple therapy increased both muscle strength and weight gain. Overall, triple therapy to enhance GAA trafficking and to suppress immune responses significantly improved the efficacy of muscle-targeted gene therapy in murine Pompe disease.