Optogenetic restoration of retinal ganglion cell activity in the living primate

Abstract

Optogenetic therapies for vision restoration aim to confer intrinsic light sensitivity to retinal ganglion cells when photoreceptors have degenerated and light sensitivity has been irreversibly lost. We combine adaptive optics ophthalmoscopy with calcium imaging to optically record optogenetically restored retinal ganglion cell activity in the fovea of the living primate. Recording from the intact eye of a living animal, we compare the patterns of activity evoked by the optogenetic actuator ChrimsonR with natural photoreceptor mediated stimulation in the same retinal ganglion cells. Optogenetic responses are recorded more than one year following administration of the therapy and two weeks after acute loss of photoreceptor input in the living animal. This in vivo imaging approach could be paired with any therapy to minimize the number of primates required to evaluate restored activity on the retinal level, while maximizing translational benefit by using an appropriate pre-clinical model of the human visual system.

In vivooptogenetic stimulation of the primate retina activates the visual cortex after long-term transduction

“…Using ex vivo live imaging and histology, we show here that expression persists in cells in the perifovea region more than 20 months after the injection, and we demonstrate, with electrophysiological recordings, that these transduced RGCs remain functional, displaying rapid, robust responses. Previous studies based on ex vivo retinal recordings in NHP models have demonstrated efficient optogene expression for up to six months [11,13,14], and studies based on retinal imaging in vivo extended this functional window up to 14 months [17]. This maintenance of activity so long after the injection is consistent with the notion that gene therapy can lead to long-term gene expression.…”

“…We have previously shown that the transduced retina displays high spatiotemporal resolution ex vivo , compatible with the perception of highly dynamic visual scenes at light levels suitable for use in humans. Other studies have provided evidence of retinal activation in vivo [17]. Here, we demonstrate, in non-human primates, sustained functional efficacy ~20 months after delivery of an AAV2.7m8-ChrimsonR-tdTomato vector similar to that currently undergoing clinical evaluation.…”

“…Based on our retinal observations, we can interpret these VEP recordings as reflecting the activation of cortical neurons due to the direct functional optogenetic activation of RGCs, leading to the synaptic transfer of information to cortical neurons. All previous studies on optogenetic RGC activation in the primate retina were performed on RGCs either in vitro [11,13,14] or in vivo [17]. The recorded rates of RGC firing activity and the reported increases in calcium indicator fluorescence were highly suggestive of potential information transfer to the higher visual centers, but no experimental demonstration for the existence of this communication was provided.…”

Optogenetic Gene Therapy for the Degenerate Retina: Recent Advances

“…Several pre-clinical optogenetic studies have used canine and non-human primate models to assess the safety and expression profile of optogenetic vectors (Ivanova et al, 2010;Sengupta et al, 2016;Ameline et al, 2017) as well as the function and characteristics of optogenetic tools in terms of their ability to restore vision (Chaffiol et al, 2017;McGregor et al, 2020). Compared to murine models, limited in vivo (Ivanova et al, 2010;Chaffiol et al, 2017;McGregor et al, 2020) and ex-vivo (Sengupta et al, 2016) transduction of retinal ganglion cells was demonstrated in marmoset and macaque retinae, respectively, following delivery of AAV encoding microbial opsin-based sensors, with intra-ocular inflammatory responses observed in treated eyes (Chaffiol et al, 2017). In addition, despite longterm expression, similar findings of limited expression were observed in a canine model following treatment with a microbial and a human opsin (Ameline et al, 2017).…”

Inflammation in Viral Vector-Mediated Ocular Gene Therapy: A Review and Report From a Workshop Hosted by the Foundation Fighting Blindness, 9/2020

“…Dr. Juliette McGregor and Dr. William Merigan presented data from imaging studies in cynomolgus NHPs ( Macaca fascicularis ) that used adaptive optics to optically record from retinal ganglion cells following intravitreal injection of AAV2 vectors ( Table 1A ) for calcium imaging (GCaMP) optogenetic therapy (ChrimsonR). 15 Because inflammation would greatly limit imaging, macaques were both pre-screened to exclude animals with anti-AAV antibodies and pretreated with subcutaneous cyclosporine A for one to 20 weeks before AAV vector injection ( Table 2A ). Although numbers were small, increasing time of immunosuppressive pretreatment was generally associated with improved lateral extent of foveal gene expression.…”