In vivo evaluation of gene editing and prosthetic strategies to restore vision in small and large animal models of retinal degeneration

Inherited retinal diseases (IRDs) form a group of diverse disorders that lead to the degeneration of the light-sensing cells of the retina: the photoreceptors. IRDs are among the leading causes of blindness in working-age adults living in industrialized countries and their treatment has been a long-term challenge in medicine. Given the heterogeneity of IRDs in terms of causative genes and symptoms, finding a common therapy is not a real possibility. Conversely, it is important to research as many different approaches as possible so as to have the opportunity to decide which one to use for a specific patient. The outcome of clinical interventions depends in large part on the preclinical research conducted on animal models. As an example of this, this thesis illustrates two preclinical approaches to the treatment of retinal degenerations that lie at the opposite ends of the spectrum of available therapies. The first approach discussed is gene editing. This strategy is most effective during the development of the retina and can be used to correct genetic mutations causing the degeneration of photoreceptors on the progenitor cells. Here, we used a tailored gene editing system based on clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to prevent photoreceptor death in the retinal degeneration 10 (Rd10) mouse model of retinitis pigmentosa. The construct was delivered in the photoreceptor cells by electroporation and targets the mutated gene, editing its sequence with the help of a DNA repair template. This technique for gene editing has shown promising results in terms of visual function preservation in mice, inspiring further research into viral-free gene editing approaches. On the opposite side of the range of therapeutic options, prosthetic devices are generally used for late-stage retinal degeneration since they bypass the photoreceptor layer and rely on the retinal internal circuits to perform visual stimulation. In this work, I describe a series of experiments performed to test the POLYRETINA photovoltaic epiretinal visual prosthesis, previously developed by our laboratory, in a minipig model of chemically induced retinal degeneration. First, the visual responses were carefully characterized in the animal model before and after the injection of the toxin. Then, preliminary results were obtained using the prosthesis to stimulate the blind retina. Although the experiments are still ongoing, the results are encouraging and demonstrate that we could indeed use a completely photovoltaic prosthesis to restore visual perception in blind patients. In conclusion, this thesis displays preclinical research concerning two ways to restore vision, each adapted to a different stage of retinal degeneration. The overarching goal is to improve as much as possible the outcome of the therapy for the benefit of blind patients. To this end, we need to continue to test all the approaches that have so far shown promising results, such as the ones presented herein, while continuing to develop new ones. This outlook, implemented at the preclinical level, can lead to the best chances of a successful clinical intervention. At the same time, the diagnostic tools need to be perfected and precisely utilized to determine which therapeutic option is best suited for a specific patient.