The purpose of this study is to evaluate the safety, tolerability, and efficacy of a single intravenous infusion of SPK-3006 in adults with clinically moderate, late-onset Pompe disease receiving enzyme replacement therapy (ERT). Participants will be treated in sequential, dose-level cohorts.

Inclusion Criteria:

• Provide written informed consent;
• Males and Females ≥18 years of age with late-onset Pompe disease;
• Received ERT for at least the previous 24 months
• Have clinically moderate, late-onset Pompe disease characteristics;
• Agree to use reliable contraception.

Exclusion Criteria:

• Active hepatitis B and/or C;
• Significant underlying liver disease;
• Human immunodeficiency virus (HIV) infection;
• Prior hypersensitivity to rhGAA;
• Pre-existing anti-AAV neutralizing antibody titers;
• High titer antibody responses to rhGAA;
• Requires any invasive ventilation or requires noninvasive ventilation while awake and upright;
• Received any prior vector or gene transfer agent;
• Active malignancy (except non-melanoma skin cancer);
• History of liver cancer;
• Pregnant or nursing women;
• Any evidence of active infection at the time of SPK-3006 infusion.