268. Optogenetic Engineering of Retinal Ganglion Cells with AAV2.7m8-ChrimsonR-tdTomato (GS030-DP) Is Well Tolerated and Induces Functional Responses to Light in Non-Human Primates

Abstract

Introduction: Expression of a light-sensitive opsin in retinal ganglion cells (RGCs) is an attractive strategy to restore vision. We evaluated the ability of ChrimsonR-tdTomato (ChrR-tdT), derived from the algal light-gated cation channel ChrimsonR (Ed Boyden, MIT), to convert light insensitive RGCs into photoactivatable cells in normal macaques. A photostimulation device (GS030-MD) is developed in parallel to complement the biologics. This GS030 combination treatment is intended to treat blindness caused by retinal degenerative diseases such as retinitis pigmentosa. Methods: Cynomolgus macaques were injected intravitreally with the AAV2.7m8 vector encoding ChrR-tdT under the control of the CAG promoter (GS030-DP; 5×1011 vg/eye). Electrophysiological measurements by microelectrode array (MEA) and patch clamp as well as expression of the ChrR-tdT protein by immunofluorescence were assessed on explanted retinas 2 months after injection. Local tolerance was evaluated by ophthalmic examination and histology at 2 and 6 months post administration. Results: ChR-tdT was essentially expressed in RGCs and its expression restricted to the perifoveal area. MEA recordings showed light responses in all treated retinas, with 3 out of 4 retinas displaying high amplitudes of electrical responses to light stimulation (up to 360 Hz). One retina was less responsive (50 Hz). In patch clamp experiments, conducted by targeting tdT-expressing RGCs, large photocurrents were recorded in 3 out of 4 retinas in response to illumination, and according to the expected action spectrum for ChR-tdT. An exploratory study was conducted in parallel in monkeys, which received a single bilateral intravitreal administration of GS030-DP (5×1011 vg/eye) to assess local tolerance, systemic toxicity and immunogenicity at 2 and 6 months. No clinical signs indicative of systemic toxicity or local intolerance were observed. No adverse effects were seen by ophthalmic or histological examinations, especially no retinal structural modifications, inflammation or necrosis. Anti-AAV2 neutralizing antibodies (NAbs) measured in serum at 2, 3 and 6 months slightly increased at month 2 (≤ 1:100) and then returned to baseline levels at month 6. No NAbs were detected in aqueous humor at necropsy (at 2 or 6 months). In parallel, in preparation of a first-in-man clinical trial, a complete prototype of the photostimulation device (“goggles”) was developed with a full functional optical chain, an electronic subsystem, and firmware and software architecture. These goggles (GS030-MD) capture external scenes through an event-based camera and deliver visual stimuli onto the transduced retina at irradiances shown to activate ChrR-tdT expressing RGCs in monkey retinas. Conclusion: GS030 vector (GS030-DP) transduced efficiently and safely RGCs in vivo after intravitreal administration and induced light responses in normal monkey retinas under pharmacological block of endogenous phototransducion. The GS030 treatment combining the AAV2.7m8-ChrR-tdT vector and the photo stimulation goggles represents a valuable treatment for vision restoration in retinitis pigmentosa.