Preparation for a Gene Augmentation Trial for RDH12-Associated Retinal Degenerations

Abstract

Purpose : Mutations in RDH12, which encodes a retinol dehydrogenase localizing to photoreceptor inner segments, cause early onset retinal degeneration. We defined changes in retinal structure and function in pediatric patients with Leber congenital amaurosis (LCA) due to RDH12 mutations. We also initiated safety evaluations of AAV8 delivering a photoreceptor-driven human codon optimized (hco) RDH12 cDNA in non-human primates (NHPs).

Methods : Twenty-six patients (ages 2-21 years) with RDH12-LCA underwent a complete ophthalmic exam and imaging with SD-OCT and 20 of these individuals were evaluated longitudinally over 3 years. In animal studies, 4 macaques already enrolled in an AAV vaccine study received bilateral subretinal i(SR) injections of AAV8.RK1.hcoRDH12 in a dose-ranging study (3E10 – 3E11vg). One additional animal was injected with a similar vector that incorporated eGFP. Follow-up was performed with protocols that matched those used in patients. Animals were evaluated for transgene expression and histopathology 4 weeks post-injection.

Results : In the patients, visual acuity ranged from 20/40 to 20/800 and remained stable in most patients. SD-OCT showed early foveal thinning in all patients but detectable outer nuclear layer (ONL) at greater eccentricities from the fovea. ONL extent and thickness declined over the course of the study. FST sensitivities were rod-mediated and reduced on average by ~2.5 log units and declined by about 5 dB over 3 years. In NHPs, retinas developed pigmentary changes outlining the area of subretinal injection similar to that seen in other SR injection studies. SD-OCT imaging revealed injection-related alterations in retinal structure. Histologic analyses revealed minimal inflammation at 3E10 or 1E11 vg and rare monocytic peri-vascular infiltrate at 3E11vg. RDH12 immuno-staining was specific to photoreceptors, as was GFP in retinas treated with AAV.RK1.eGFP

Conclusions : Detectable but dysfunctional photoreceptors in the pericentral and peripapillary retina of patients with RDH12-LCA suggest these regions may be targets for gene augmentation. Subretinal delivery of AAV8.RK1.hcoRDH12 in NHP was safe at 1E11vg with only mild inflammation at 3E11vg. The RK1 promoter limited expression to photoreceptors. The data support plans for a formal GLP preclinical toxicity study prerequisite to a human clinical trial.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.