Hypothesis: the effectiveness of treatment of Pompe Disease with rhGAA enzyme replacement therapy (ERT) is limited at least in part because patients develop antibodies against the provided rhGAA enzyme. Treatment with immunomodulatory drugs may dampen or eliminate the anti-rhGAA immune response in patients receiving ERT, thereby allowing for greater ERT efficacy. Studying the immune response to rhGAA may provide valuable insight into the role of the immune system in the effectiveness of ERT for Pompe Disease.