Stem cells in the retina: Regeneration and cell therapy

The retina is a laminated neural tissue composed of seven different cell types. Like other parts of the central nervous system (CNS), the retina can undergo degeneration due to genetic mutations or following damage. In the context of the CNS, the retina stands out for its ability in some non-mammalian vertebrates to fully or partially regenerate during development and sometimes in the adult. Various sources of cells have been reported to support regeneration and some of them have been described in mammals. This feature contributes to the idea that i) the mammalian retina is not fully devoid of endogenous potential for repair and ii) more extensively the retina could represent a model to develop and test new strategies for CNS regeneration. Although these approaches are still far from becoming clinically applicable, huge progress has been made concerning the ability to produce retinal cells from embryonic stem (ES) cells or induced pluripotent stem (iPS) cells. ES and iPS cells have the capacity for self-renewal, proliferation and differentiation into all specialized cell types of the adult organism. Different protocols have been established allowing the generation of various retinal cell types, such as photoreceptors or retinal pigmented epithelial cells from ES or iPS cells. Integration and functional recovery have been reported after cell transplantation in different animal models of visual defects, thus holding great promise for restoring vision by means of cell therapy.