A Study to Evaluate Safety, Tolerability, and Efficacy of AB-1009 Gene Therapy (GAA Gene) in Adult Participants With Late Onset Pompe Disease (PROGRESS-GT LOPD)

Inclusion criteria

• Participant must be ≥18 years of age at the time of signing the informed consent form.
• Confirmed GAA enzyme deficiency from any tissue source and/or confirmed biallelic GAA gene mutations.
• Undergone enzyme replacement treatment (ERT) (either alglucosidase alfa (Lumizyme®) or avalglucosidase alfa-ngpt (Nexviazyme®)), for at least 6 months (at least 10 infusions) before signing the initial informed consent form. During the screening process, participants need to remain on their current ERT until close to dosing;
• FVC in the upright position ≥30% and ≤80% of predicted;
• Capable of walking at least 100 meters in the 6MWT (use of a cane, quad cane, or standard walker is permitted);
• Contraceptive/barrier use by men and women requirements as per protocol.
• Capable of giving informed consent and able to understand and comply with all study procedures.

Exclusion criteria

• Severe cardiomyopathy, defined as left ventricular ejection fraction (LVEF) \<40% or New York Heart Association (NYHA) functional class 3 or above;
• Require invasive mechanical ventilation, or rely on noninvasive ventilation during the day;
• Intolerance to ERT or investigator-assessed intolerance to ERT, prior experience of serious ERT-related infusion-associated reactions (IARs);
• Have known intrinsic liver diseases, including hepatitis, HIV-related liver disease, prior diagnosis of portal hypertension, splenomegaly, hepatic encephalopathy, severe fatty liver, cirrhosis or liver fibrosis ≥stage 2, ultrasound-identified liver neoplasms, or laboratory tests suggesting elevated alpha-fetoprotein. Patients with liver function tests including ALT or AST \>3× upper limit of normal (ULN) or any total bilirubin above ULN during screening will also be excluded;
• Prior or ongoing medical condition(s), physical finding(s), assessment findings, or laboratory abnormality that, in the investigator's opinion, would impact participant's safety and compliance with the study procedures.
• Have received gene therapy prior to screening;
• Have received any systemic immunosuppressants (except inhalation or topical use) other than glucocorticoids or investigator-recommended immunosuppressants 30 days prior to screening through completion of screening, and/or known intolerance to immunosuppressants such as glucocorticoids;
• Use of investigational drugs or drugs that could affect this study as evaluated by the investigator within 30 days prior to screening through completion of Week 52 or within 5 half-lives of the investigational drug (whichever is longer);
• Have received any vaccine within 30 days prior to dosing;
• Other conditions that make the participant not eligible for the study according to the investigator.