Bayer Prioritizes AAV Gene Therapy AB-1009 for Pompe Disease

March 04, 2026 —

Bayer has discontinued development of its early-stage gene therapy candidate ACTUS-101 for late-onset Pompe disease, choosing instead to focus on another AAV-based therapy in its pipeline, AB-1009. Both programs originated from Bayer’s $2 billion acquisition of Asklepios BioPharmaceutical (AskBio) in 2020, which significantly expanded the company’s gene therapy capabilities.

Pompe disease is a rare, autosomal recessive metabolic disorder caused by mutations in the GAA gene, resulting in glycogen accumulation in muscle cells and progressive muscular degeneration. While enzyme replacement therapies (ERTs) are currently available, they do not fully address the underlying genetic defect, prompting ongoing research into gene therapy approaches that could provide long-lasting therapeutic benefit.

ACTUS-101 had already entered a Phase 1 clinical trial at the time of Bayer’s acquisition of AskBio. However, the program’s future became uncertain earlier this year when Bayer announced it would halt further patient enrollment. According to the federal clinical trials database, the study enrolled a total of seven participants before the decision was made to discontinue development.

Instead, Bayer is concentrating its resources on AB-1009, another AAV-based gene therapy designed to treat late-onset Pompe disease. The candidate recently entered a Phase 1/2 clinical trial in the United States and has received both Fast Track and Orphan Drug designations from the U.S. Food and Drug Administration. The therapy aims to address the root cause of the disease by delivering a functional copy of the GAA gene, enabling cells to produce the deficient enzyme responsible for breaking down glycogen.

Researchers involved in the trial believe this approach could potentially restore enzyme production and reduce disease progression. Tahseen Mozaffar, M.D., director of the UCI Health ALS & Neuromuscular Center and principal investigator for the AB-1009 study, noted that the therapy is being evaluated for its ability to correct the underlying genetic defect and increase enzyme production in patients with Pompe disease.

Pompe disease gene therapy development has proven challenging across the industry. In December, the Denali Therapeutics saw the FDA place a clinical hold on its enzyme replacement therapy candidate due to immune reaction concerns observed in preclinical studies. Meanwhile, Roche previously exited its own Pompe gene therapy program in 2024 after evaluating the competitive landscape and the presence of existing enzyme replacement treatments.

Other companies remain active in the field. Astellas Pharma is developing a gene therapy candidate for Pompe disease that experienced a temporary regulatory hold in 2022 following reports of nerve damage in one trial participant. The hold was lifted in early 2023, allowing development to continue.

By discontinuing ACTUS-101 and concentrating on AB-1009, Bayer appears to be streamlining its strategy to focus on a single AAV gene therapy program that it believes holds stronger potential for advancing treatment options for patients with Pompe disease.