High-potency MyoAAV capsids enhanced skeletal muscle correction in a mouse model of GSD IIIa.

Glycogen storage disease type IIIa (GSD IIIa) affects multiple tissues, including liver, heart, and skeletal muscles. We recently reported that an adeno-associated virus serotype 9 vector expressing pullulanase, a bacterial glycogen debranching enzyme, driven by an immunotolerizing dual promoter (AAV9-Dual-Pull), effectively decreased pullulanase-induced cytotoxic T lymphocyte response and corrected disease abnormalities in all major affected tissues in GSD IIIa mice. To reduce effective vector dosages for transgene delivery to skeletal muscles, we packaged the AAV-Dual-Pull vector into two muscle-tropic MyoAAV capsids, MyoAAV4A and MyoAAV4E. Six weeks after administration of the same dose vector (1 × 10¹³ vg/kg), both the MyoAAV vectors demonstrated remarkably greater transduction efficiency and glycogen clearance efficacy in the cardiac and skeletal muscles than the AAV9 vector, accompanied by the improvement of muscle function, reversal of liver abnormalities, and normalization of the disease biomarker, Glc4 in the urine. Furthermore, treatment with the MyoAAV4A-Dual-Pull vector at a 10-fold lower dose (1×10¹² vg/kg) achieved significantly better therapeutic outcomes in the skeletal muscles than the AAV9-Dual-Pull vector at a high dose (1×10¹³ vg/kg). Validation in human liver chimeric mice revealed that the MyoAAV vectors and the AAV9 vectors had a similar efficiency in transducing human hepatocytes, indicating increased translatability for clinical applications.