Safety, efficacy, and distal nerve Schwann cell biodistribution in mice and NHPs to support translation of AAV9 RNAi therapy for CMT1A

Charcot-Marie-Tooth (CMT) type 1A, the most common inherited demyelinating peripheral neuropathy, is caused by PMP22 gene duplication, leading to overproduction of PMP22 protein in Schwann cells. To treat CMT1A, we developed a PMP22 gene silencing therapy using adeno-associated viral vectors (AAV9) to deliver a therapeutic miRNA expression cassette (U6.miR871) via lumbar intrathecal administration. A single injection produced long-term miR871 expression, triggered selective RNA interference against the PMP22 mRNA, and subsequently lowered protein levels and improved disease manifestations in a humanized CMT1A model. To support clinical translation, we confirmed on-target specificity of miR871 for PMP22 in vitro, identified a safe and effective dosing range in mice, demonstrated absence of significant toxicity in rodents and non-human primates (NHPs), and performed a detailed AAV biodistribution study in a large animal model. We found vector biodistribution and miR871 expression in distal peripheral nerves, PMP22 target engagement in mice and NHPs, and silencing to levels expected to support normal myelination in humans. We identified the minimally efficacious to maximum tolerated dose range of AAV9.U6.miR871 in mice and confirmed safety range in NHPs for extrapolation to anticipated clinical trials. Our study supports the scale-up potential of gene therapy to treat CMT1A and other demyelinating peripheral neuropathies.