Safety in Nonhuman Primates of Ocular AAV2-RPE65, a Candidate Treatment for Blindness in Leber Congenital Amaurosis

Abstract

Leber congenital amaurosis (LCA) is a molecularly heterogeneous disease group that leads to blindness. LCA caused by RPE65 mutations has been studied in animal models and vision has been restored by subretinal delivery of AAV-RPE65 vector. Human ocular gene transfer trials are being considered. Our safety studies of subretinal AAV-2/2. RPE65 in RPE65 -mutant dogs showed evidence of modest photoreceptor loss in the injection region in some animals at higher vector doses. We now test the hypothesis that there can be vectorrelated toxicity to the normal monkey, with its human-like retina. Good Laboratory Practice safety studies following single intraocular injections of AAV-2/2. RPE65 in normal cynomolgus monkeys were performed for 1-week and 3-month durations. Systemic toxicity was not identified. Ocular-specific studies included clinical examinations, electroretinography, and retinal histopathology. Signs of ocular inflammation postinjection had almost disappeared by 1 week. At 3 months, electroretinography in vector-injected eyes was no different than in vehicle-injected control eyes or compared with presurgical recordings. Healed sites of retinal perforation from subretinal injections were noted clinically and by histopathology. Foveal architecture in subretinally injected eyes, vector or vehicle, could be abnormal. Morphometry of central retina showed no photoreceptor layer thickness abnormalities occurring in a dose-dependent manner. Vector sequences were present in the injected retina, vitreous, and optic nerve at 1 week but not consistently in the brain. At 3 months, there were no vector sequences in optic nerve and brain. The results allow for consideration of an upper range for no observed adverse effect level in future human trials of subretinal AAV-2/2. RPE65. The potential value of foveal treatment for LCA and other retinal degenerations warrants further research into how to achieve gene transfer without retinal injury from surgical detachment of the retina. KeywordsLeber congenital amaurosis, blindness, mutated dogs, retina, injection, dogs and safety data with rAAV-2/2.RPE65. Questions about systemic and retinal toxicity are asked in a nonhuman primate, the only mammal with a foveate retina like that of humans, to determine whether there is sufficient safety to initiate human clinical trials.

Human cone photoreceptor dependence on RPE65 isomerase

“…Large animal studies to date, including primate safety studies, have mainly treated the area centralis or central retinal region (14,(41)(42)(43), so this region is a likely target for subretinal gene therapy. Thus, our finding of early foveal cone loss has strong clinical relevance.…”

A Subretinal Cell Delivery Method via Suprachoroidal Access in Minipigs: Safety and Surgical Outcomes

“…Preclinical studies of these products generally focus on the safety and tolerability of the cells, rather than the procedure 38,39 ; furthermore, preclinical studies of subretinal cell delivery have reported the occurrence of retinal perforations and hemorrhages, though not generally the rates of these complications. [39][40][41] These findings highlight the need for a procedure and device with improved safety outcomes for subretinal delivery of therapeutic products.…”

AAV-Mediated Gene Therapy for Retinal Disorders in Large Animal Models

“…They did not detect vector DNA in a dose escalation study of subretinally injected AAV2/2 in dogs (Jacobson et al 2006a), but temporarily detected it in the optic nerve and brain of primates 1 week after the animals received a subretinal injection of AAV2/2 vector (Jacobson et al 2006b). At 3 months after injection, only one primate had a detectable number of copies in the left geniculate nucleus.…”