Ocular Safety and Toxicology of Subretinal Gene Therapy With rAAV.hPDE6A in Nonhuman Primates.

Purpose: Reports of gene therapy-associated retinal atrophies and inflammation have highlighted the importance of preclinical safety assessments of adeno-associated virus (AAV) vector systems. We evaluated in nonhuman primates (NHPs) the ocular safety and toxicology of a novel AAV gene therapy targeting retinitis pigmentosa caused by mutations in PDE6A, which has since been used in a phase I/II clinical trial (NCT04611503). Methods: A total of 34 healthy cynomolgus animals (Macaca fascicularis) were treated with subretinal injections of rAAV.hPDE6A and followed over 13 weeks. Three dose levels (low: 1 × 1011, intermediate: 5 × 1011, and high: 1 × 1012 vector genomes [vg]) were compared to sham-injected controls. Safety and toxicity were determined using ophthalmic examinations, electroretinography, ocular histology, and retinal imaging. Results: At the low and intermediate doses, inflammation was mild, electroretinography response was unimpeded, and histology results were in line with surgically induced changes. In contrast, three high-dose animals displayed atrophic changes of the retina and abnormalities in electroretinography, which were considered test article related and adverse. Conclusions: A single subretinal injection of up to 5 × 1011 vg was well tolerated, and a 10-fold lower dose of 5 × 1010 vg was chosen as the starting dose for the ongoing phase I/II clinical trial. Atrophic retinal changes and abnormalities in electroretinography emerged as dose-limiting findings in the high-dose cohort. Translational Relevance: This study demonstrates that treatment candidate rAAV.PDE6A was well tolerated in NHPs. Occurrence of retinal atrophy as a dose-limiting finding highlights the importance of further study into the mechanisms of atrophy induction after retinal gene therapy.