A GLP-compliant toxicology and biodistribution study: systemic delivery of a rAAV9 vector for the treatment of mucopolysaccharidosis IIIB.

No treatment is currently available for mucopolysaccharidosis (MPS) IIIB, a neuropathic lysosomal storage disease due to defect in α-N-acetylglucosaminidase (NAGLU). In preparation for a clinical trial, we performed an IND-enabling GLP-toxicology study to assess systemic rAAV9-CMV-hNAGLU gene delivery in WT C57BL/6 mice at 1x1014vg/kg and 2x1014vg/kg (n=30/group, M:F=1:1), and non-GLP testing in MPS IIIB mice at 2x1014vg/kg. Importantly, no adverse clinical signs or chronic toxicity were observed through the 6 month study duration. The rAAV9-mediated rNAGLU expression was rapid and persistent in virtually all tested CNS and somatic tissues. However, acute liver toxicity occurred in 33% (5/15) WT males in the 2x1014vg/kg cohort, which was dose-dependent, sex-associated and genotype-specific, likely due to hepatic rNAGLU over-expression. Interestingly, a significant dose response was observed only in the brain and spinal cord, whereas in the liver at 24-wk pi, NAGLU activity was reduced to endogenous levels in the high dose cohort but remained at supranormal levels in the low dose group. The possibility of rAAV9 germline transmission appears to be minimal. The vector delivery resulted in transient T-cell responses and characteristic acute antibody responses to both AAV9 and rNAGLU in all rAAV9-treated animals, with no detectable impacts on tissue transgene expression. This study demonstrates a generally safe and effective profile, and may have identified the upper dosing limit of rAAV9-CMV-hNAGLU via systemic delivery for the treatment of MPS IIIB.