Supplement to Accelerating photoreceptor replacement therapy with in-vivo cellular imaging of retinal function

To restore high quality, usable vision in patients, it is important to develop regenerative therapies in an animal model that shares key features of the human visual system. The non-human primate has a virtually identical retinal anatomy and physiology to the human and, uniquely amongst mammalian models, shares a fovea,

the retinal area specialized for high acuity vision. Whilst the non-human primate is the gold standard animal model for research on human vision, its utility for pre-clinical testing has been limited due to both the absence of models of vision loss and the difficulty of demonstrating restored function. Under previous AGI funding, the

Advanced Retinal Imaging Alliance at the University of Rochester has recently overcome these challenges to create a pre-clinical testing platform leveraging adaptive optics technology to: 1.) Create localized regions of photoreceptor ablation in primate that are axially confined, and 2.) Optically read out restored retinal

ganglion cell function by performing cellular scale calcium imaging in the living eye. This system was developed to meet the needs of photoreceptor replacement therapy which requires photoreceptor loss with preserved host retinal circuitry. Furthermore, a high-resolution in vivo imaging approach is well suited for pre-

clinical evaluation of regenerative therapies where the timescales of restored connectivity are unknown and functional integration occurs on the cellular scale. In this proposal, we will use our platform to generate pre- clinical data that will inform future clinical trials of photoreceptor replacement therapy in patients. Functional

integration of transplanted photoreceptors with the host retina requires both high density delivery of high- quality donor photoreceptors and a host retina with the capacity for synaptogenesis. We have assembled a consortium that can explore and optimize both sides of this interaction. In continued collaboration with a team

at the University of Wisconsin led by David Gamm, a clinician and expert in the development of human pluripotent stem cell (hPSC) derived photoreceptor replacement therapy, we will evaluate survival and functional integration of transplanted photoreceptor precursors in primate fovea delivered to the sub-retinal

space as aggregates or following incorporation into custom biodegradable scaffolds. In collaboration with a team at University of California, Berkeley led by Teresa Puthussery, an expert in retinal remodelling in retinal degeneration models and primate histology, we will examine the impact of the loss of photoreceptor signalling

on primate inner retina. We will explore whether deafferented cone bipolar cells can remodel and functionally integrate with donor photoreceptors and whether retinal hyperactivity develops in primate as it does in rodent. To make meaningful progress toward restoring vision in patients who have lived with vision loss for many

years, we will examine how these phenomena develop in the primate fovea over time and whether the regenerative potential of the host can be improved by therapeutic interventions such as retinoic acid blockers. These studies will allow us to fully characterize our primate photoreceptor ablation model and deploy it with

photoreceptor replacement therapies to advance the field toward clinical trials.