867. Correction of Glycogen Storage Disease Type II by Intramuscular Administration of an Adeno-Associated Virus 6 (AAV2/6) Vector Containing a Muscle-Specific Promoter

Abstract

Severe glycogen storage disease type II (GSD II; Pompe disease; MIM 232300) typically causes death in childhood from cardiomyopathy and cardiorespiratory failure. The underlying deficiency of acid a-glucosidase (GAA) in heart and skeletal muscle has been corrected by enzyme replacement in clinical trials. An AAV2/2 vector containing the hybrid CMV enhancer/chicken beta-actin promoter (CB promoter) to drive hGAA expression was administered by intramuscular injection in GAA-knockout (GAA-KO) mice, and GAA activity increased to normal levels at 6 weeks following vector administration. However, an AAV2/6 vector produced high-level hGAA at 10 days following intramuscular injection in GAA-KO mice that disappeared by 6 weeks. In contrast, an AAV2/6 vector persistently elevated hGAA to approximately 10-fold above normal in the injected gastrocnemius in immunodeficient, GAA-KO/SCID mice 6-weeks following vector administration, and reduced glycogen content to normal levels. AAV2/6 vectors have elicited an immune response in other mouse models for muscular dystrophy, and a CD4+ lympocytic infiltrate was observed in response to the AAV2/6 vector in immunocompetent GAA-KO mice. Therefore, a muscle-specific muscle creatine kinase (MCK) promoter was substituted for the CB promoter in an AAV vector encoding hGAA (AAV-MCKGAApA). The AAV2/6 vector containing the MCK promoter produced high levels of hGAA for longer than 6 weeks in immunocompetent hGAA mice, up to approximately 100-fold greater than GAA levels observed in skeletal muscle for normal mice. Glycogen content was reduced to normal in the injected muscle with AAV-MCKGAApA. However, no secretion of hGAA and uptake in distal tissues was observed, since GAA activity was not elevated in the contralateral gastrocnemius muscle, heart or diaphragm of GAA-KO mice following intramuscular injection of AAV-MCKGAApA. Thus, the threshold for GAA secretion from transduced skeletal muscle exceeds the normal GAA level by > 100-fold (> 4000 nmole/hr/mg). In summary, we demonstrated persistent correction of glycogen storage with an AAV2/6 vector containing a muscle-specific promoter in GSD II mice, and this approach should be considered for muscle-targeted gene therapy in Pompe disease.