245. AAV2/8-Mediated Efficacy and Immune Tolerance in a Pompe Disease Mouse Model

Abstract

Pompe disease is an inherited metabolic disorder caused by a deficiency of the lysosomal enzyme acid -glucosidase (GAA). The disease is characterized by accumulation of glycogen in various tissues, including the central and peripheral nervous systems, but the pathology most dramatically affects skeletal and cardiac muscles. Severely affected patients present within the first year of life with hypotonia and cardiomyopathy, resulting in death from cardiopulmonary failure. To assess the utility of gene therapy for Pompe disease, we generated recombinant AAV8-based serotype vectors encoding for GAA under the transcriptional control of a liver-restricted promoter (DC190). Systemic administration of 5X1011 drp of AAV8/DC190-GAA into Pompe mice generated high levels (25-30 g/ml) of GAA in the serum that persisted for 6 months post-administration. GAA activity was also detected in several muscle groups isolated from the AAV8-treated mice, indicating that GAA was efficiently taken up into these tissues from circulation. Glycogen storage was completely corrected in the heart and diaphragm and reduced by 50% in the skeletal muscles as early as 4 weeks post-treatment. All tissues were completely cleared of glycogen storage by 10 weeks, and remained at baseline at the 6-month time point. Histomorphometric analysis of PAS-stained tissues confirmed that glycogen deposits were effectively cleared from the affected tissues. Histopathology observed in the dorsal root ganglia of Pompe mice was also normalized suggesting that treatment may impact the peripheral nerve disease. Consistent with previous studies using the DC190 promoter, no antibodies to the human GAA were detected in the sera of AAV8/DC190-GAA-treated mice. Furthermore, no antibodies were generated following two subsequent challenges with recombinant GAA emulsified in Complete Freund's adjuvant, suggesting the AAV8/DC190-GAA-treated mice were immune tolerized. Immune responses were also assessed at the cellular level by assaying lymphocyte proliferation and IFN secretion using cells harvested from the spleens of the treated mice. Cells from the AAV8/DC190-GAA-treated mice showed an attenuated response to antigenic stimulation compared to controls. These data support the continued evaluation of AAV8-mediated gene therapy as an approach to treat the systemic manifestations of Pompe disease.