Stem Cell Based Treatment Strategies for Degenerative Diseases of the Retina

Background: The main cause of progressive vision impairment in retinal degenerative diseases is the dysfunction of photoreceptors and the underlying retinal pigment epithelial cells. The inadequate regenerative capacity of the neural retina and lack of established therapeutic options demand the development of clinical grade protocols to halt degenerative process in the eye or to replace the damaged cells by using stem cell derived products. Recently, stem cell-based regenerative therapies are at the forefront of clinical investigations for retinal dystrophies. Objective: This article will review different stem cell-based therapies currently employed for retinal degenerative diseases, recent clinical trials, and major challenges in the translation of these therapies from bench to bedside. Methodology: A systematic literature review was carried out to identify potentially relevant articles published in MEDLINE/PubMed, Embase, ClinicalTrials.gov, Drugs@FDA, European Medicines Agency, World Health Organization International Clinical Trials Registry Platform and CENTRAL Result: Transplantation of healthy cells to replace the damaged cells in the outer retina is a clinically relevant concept because the inner retina that communicates with the visual areas of the brain remains functional even after the photoreceptors are completely lost. Different methods have been established for the differentiation of pluripotent stem cells into different retinal cell types that can be used for therapies. Factors released from transplanted somatic stem cells showed trophic support and photoreceptor rescue during early stages of the disease. Several preclinical and phase I/II clinical studies using terminally differentiated photoreceptor/ retinal pigment epithelial cells derived from pluripotent stem cells have shown proof of concept for visual restoration in Age-related macular degeneration (AMD), Stargardt disease and Retinitis pigmentosa (RP). Conclusion: Cell replacement therapy has great potential for vision restoration. The results obtained from the initial clinical trials are encouraging and indicates its therapeutic benefits. The current status of the therapies suggests that there is a long way to go before these results can be applied to routine clinical practice. Input from the ongoing multicentre clinical trials will give a more refined idea for the future design of clinical- grade protocols to transplant GMP level HLA matched cells.