Efficacy, pharmacokinetics, and safety in the mouse and primate retina of dual AAV vectors for Usher syndrome type 1B

Gene therapy of Usher syndrome type 1B (USH1B) due to mutations in the large <i>Myosin VIIA</i> (<i>MYO7A</i>) gene is limited by the packaging capacity of adeno-associated viral (AAV) vectors. To overcome this, we have previously developed dual AAV8 vectors which encode human <i>MYO7A</i> (dual AAV8.<i>MYO7A</i>). Here we show that subretinal administration of 1.37E+9 to 1.37E+10 genome copies of a good-manufacturing-practice-like lot of dual AAV8.<i>MYO7A</i> improves the retinal defects of a mouse model of USH1B. The same lot was used in non-human primates at doses 1.6× and 4.3× the highest dose proposed for the clinical trial which was based on mouse efficacy data. Long-lasting alterations in retinal function and morphology were observed following subretinal administration of dual AAV8.<i>MYO7A</i> at the high dose. These findings were modest and improved over time in the low-dose group, as also observed in other studies involving the use of AAV8 in non-human primates and humans. Biodistribution and shedding studies confirmed the presence of vector DNA mainly in the visual pathway. Accordingly, we detected human MYO7A mRNA expression predominantly in the retina. Overall, these studies pave the way for the clinical translation of subretinal administration of dual AAV vectors in USH1B subjects.