Stem cell-based therapies for retinal diseases: focus on clinical trials and future prospects

Stem cell-based therapy has gained importance over the past decades due to huge advances in science and technology behind the generation and directed differentiation of pluripotent cells from embryos and adult cells. Preclinical proof-of-concept studies have been followed by clinical trials showing efficacy and safety of transplantation of stem cell-based therapy, which are beginning to establish this as a modality of treatment. Disease candidates of interest are primarily conditions that may benefit from replacing dead or dying cells, including advanced inherited retinal dystrophies and age-related macular degeneration, and predominantly seek to transplant either RPE or photoreceptors, although neurotrophic approaches have also been trialed. Whilst a consensus has yet to be reached about the best stage/type of cells for transplantation (stem cells, progenitor cells, differentiated RPE and photoreceptors) and the methods of implantation (sheet, suspension), several CTs have shown safety. There remain potential concerns regarding tumorigenicity and immune rejection; however, with ongoing improvements in cell generation, selection, and delivery, these can be minimized. Earlier studies showed efficacy with immunosuppressive drugs to prevent rejection, and recent donor-matched transplants have avoided the need for immunosuppression. Retinal regenerative medicine is a challenging field and is in a nascent stage but holds tremendous promise. This narrative review delves into the current understanding of stem cells and the latest clinical trials of retinal cell transplantation.