Nonclinical Safety Evaluation of scAAV8- RLBP1 for Treatment of RLBP1 Retinitis Pigmentosa

Retinitis pigmentosa is a form of retinal degeneration usually caused by genetic mutations affecting key functional proteins. We have previously demonstrated efficacy in a mouse model of RLBP1 deficiency with a self-complementary AAV8 vector carrying the gene for human RLBP1 under control of a short RLBP1 promoter (CPK850).¹ In this article, we describe the nonclinical safety profile of this construct as well as updated efficacy data in the intended clinical formulation. In Rlbp1^-/- mice dosed at a range of CPK850 levels, a minimum efficacious dose of 3 × 10⁷ vg in a volume of 1 μL was observed. For safety assessment in these and Rlbp1^+/+ mice, optical coherence tomography (OCT) and histopathological analysis indicated retinal thinning that appeared to be dose-dependent for both Rlbp1 genotypes, with no qualitative difference noted between Rlbp1^+/+ and Rlbp1^-/- mice. In a non-human primate study, RLBP1 mRNA expression was detected and dose dependent intraocular inflammation and retinal thinning were observed. Inflammation resolved slowly over time and did not appear to be exacerbated in the presence of anti-AAV8 antibodies. Biodistribution was evaluated in rats and satellite animals in the non-human primate study. The vector was largely detected in ocular tissues and low levels in the optic nerve, superior colliculus, and lateral geniculate nucleus, with limited distribution outside of these tissues. These data suggest that an initial subretinal dose of ∼3 × 10⁷ vg/μL CPK850 can safely be used in clinical trials.