A recombinant AAV vector has been generated to carry the codon-optimized acid alpha-glucosidase (coGAA) gene expressed from a human desmin enhancer/promoter (DES). The proposed clinical trial is a within-participant, double-blind, randomized, phase I controlled study evaluating the toxicology, biodistribution and potential activity of re-administration of rAAV9-DES-hGAA injected intramuscularly into the TA. Nine participants (18 to 50-years old) who reside within the United States with Late-Onset Pompe Disease (LOPD) will be included. The goal of the immune modulation strategy is to ablate B-cells (Rituximab and Sirolimus) prior to the initial exposure to the study agent in one leg and the subsequent exposure of the same vector to the contralateral leg after four months. At each study agent dosing, the contralateral leg will receive excipient. Patients will act as their own controls. Repeated measures, at baseline and during the following 3 months after each injection, will assess the safety, biochemical and functional impact of the vector.