Preclinical biodistribution and toxicology assessment of an AAV5-based subretinal modifier gene therapy for retinitis pigmentosa

Retinitis pigmentosa (RP) is a multifactorial disease caused by mutations in over 100 genes, affecting ~1 in 4,000 people worldwide, and is characterized by abnormalities in the rod and cone photoreceptors. Gene therapy approaches are promising and have been established to provide an unprecedented treatment option for genetic diseases caused by mutation(s) in a single gene. However, traditional gene therapy approaches are not pragmatic for RP due to its heterogeneous genetic background. To this end, modifier gene therapy is a unique approach in which a transgene can correct or rescue the detrimental effects caused by mutations in unrelated gene(s). Nuclear receptor subfamily 2 group E member 3 (NR2E3) is a nuclear hormone receptor that exhibits the characteristics of a modifier gene. In preclinical studies, subretinal delivery of NR2E3 rescued the RP phenotype by resetting the molecular pathways to restore normal ocular structure and function in multiple models of RP disease. For clinical studies, AAV5<i>-hNR2E3</i> was designed for the subretinal delivery of the <i>hNR2E3</i> gene through the AAV5 vector in RP patients. In this study, we evaluated the safety and biodistribution (delivery and expression) of a gene therapy candidate, OCU400 (AAV5<i>-hNR2E3</i>), in Göttingen minipigs delivered via the subretinal route. Administration of the product at all dose levels was well tolerated, resulting in ocular changes that were minor and mostly related to the dosing procedure, with no significant signs of systemic or ocular toxicity. AAV5<i>-hNR2E3</i> vector was preferentially localized to the target retinal tissues with minimal to no exposure to systemic organs and tissues after subretinal administration. This localized delivery efficiently transduced retinal cells, where the delivered transgene produced the NR2E3 protein.