First-In-Human Study to Evaluate Safety, Tolerability, and PK of Intravenous ATB200 Alone and When Co-Administered With Oral AT2221

This is an open-label, fixed-sequence, ascending-dose, first-in-human study to evaluate the effect of a highly targeted rhGAA (ATB200) co-administered with an enzyme stabilizer (AT2221). The study aims to evaluate safety, tolerability, pharmacokinetics (PK), efficacy, pharmacodynamics (PD), and immunogenicity of ATB200 co-administered with AT2221. Stage 1: evaluation of safety, tolerability, and PK following sequential single ascending doses of intravenously infused ATB200 Stage 2: evaluation of safety, tolerability, and PK following single- and multiple-ascending dose combinations of ATB200 and AT2221 Stage 3: evaluation of long term safety, tolerability, and efficacy following 24 month treatment of ATB200 co-administered with AT2221 Stage 4: open-label extension period with functional assessments every 6 months