AAV-Mediated Exon Skipping Therapy for Usher Syndrome, Type 2A.

Usher syndrome can cause loss of vision, hearing and balance. There are four clinical subtypes, USH1 through 4, which are associated with mutations in genes important for structure, function and survival of photoreceptor cells in the retina and sensory hair cells in the inner ear. Genetic mutations in the USH2A gene, which encodes usherin protein, are the most common cause of Usher syndrome worldwide, with c.2299delG (p.Glu767Serfs*21) being the most frequent pathogenic variant. An investigational antisense oligonucleotide (ASO) for USH2A c.2299delG, QR-421a, designed to bypass the mutation, has already shown promise in Phase 1/2 clinical trials (Dulla et al., 2021). While recently developed chemistry provides longer ASO half-lives, repeated injection of ASOs may be required to provide long-term efficiency. To overcome this limitation, we screened novel USH2A exon 13 skippers and 20 AAV capsids with the goal of developing a vectorized ASO exon skipping strategy. Optimized vectors and skippers were evaluated in inner ear and retinal organoids derived from human stem cell lines bearing the USH2A c.2299delG mutation. The data revealed enhanced skipping of the pathogenic exon, offering an alternative strategy for treatment of USH2A patients using a single local injection which may prevent progression of vision and hearing loss.