Dual AAV-mediated gene therapy restores hearing in a DFNB9 mouse model

Significance In humans, inner ear development is completed in utero, with hearing onset at ∼20 weeks of gestation. However, genetic forms of congenital deafness are typically diagnosed during the neonatal period. Gene therapy approaches in animal models should therefore be tested after the period of hearing onset, to determine whether they can reverse an existing deafness phenotype. Here, we used a mouse model of DFNB9, a human deafness form accounting for 2–8% of all cases of congenital genetic deafness. We show that local gene therapy in the mutant mice not only prevents deafness when administered to immature hearing organs, but also durably restores hearing when administered at a mature stage, raising hopes for future gene therapy trials in DFNB9 patients.
Autosomal recessive genetic forms (DFNB) account for most cases of profound congenital deafness. Adeno-associated virus (AAV)-based gene therapy is a promising therapeutic option, but is limited by a potentially short therapeutic window and the constrained packaging capacity of the vector. We focus here on the otoferlin gene underlying DFNB9, one of the most frequent genetic forms of congenital deafness. We adopted a dual AAV approach using two different recombinant vectors, one containing the 5′ and the other the 3′ portions of otoferlin cDNA, which exceed the packaging capacity of the AAV when combined. A single delivery of the vector pair into the mature cochlea of Otof−/− mutant mice reconstituted the otoferlin cDNA coding sequence through recombination of the 5′ and 3′ cDNAs, leading to the durable restoration of otoferlin expression in transduced cells and a reversal of the deafness phenotype, raising hopes for future gene therapy trials in DFNB9 patients.