Photoreceptor Transplantation and Regeneration

A recent study showed that an electronic chip implanted under the human retina restored some extent of vision to a blind patient. Because the device was implanted where the light sensitive cells, the photoreceptors, should have been, this study demonstrated that it is possible to take advantage of the internal circuitry of the retina even in the absence of photoreceptors and in the presence of extensive glial and neuronal reorganization. This result strongly supports the development of cell replacement therapies for the cure of photoreceptor degeneration, provided that the cells are implanted in the same anatomical location. Similarly to other sensory neurons but differently from neurons lost in most degenerative diseases, photoreceptors are the first neurons of the circuit and only have to make efferent connections. Secondly, photoreceptors are histologically located in a restricted region of the organ. These features make them the most immediately transplantable type of neuron and interesting candidates for clinical trials involving cell transplantation. In cell replacement therapies the identification of the source of cells able to integrate and connect to the host tissue needs to be defined. For the retina, cells showing the best survival and integration rates are post-mitotic rod precursors, rather than immature retinal progenitors. Given the difficulty of obtaining human fetal cells, many studies are undergoing to differentiate cells with such features starting from stem cells. Three main classes of stem cells are under investigation to be sources for in vitro photoreceptor generation. They are embryonic stem cells, induced pluripotent stem cells and adult retinal stem cells. This chapter will describe the current preclincal studies for in vitro generation and subsequent transplantation of photoreceptor precursors

Montmorillonite clay based polyurethane nanocomposite as substrate for retinal pigment epithelial cell growth.

The subretinal transplantation of retinal pigment epithelial cells (RPE cells) grown on polymeric supports may have interest in retinal diseases affecting RPE cells. In this study, montmorillonite based polyurethane nanocomposite (PU-NC) was investigated as substrate for human RPE cell growth (ARPE-19 cells). The ARPE-19 cells were seeded on the PU-NC, and cell viability, proliferation and differentiation were investigated. The results indicated that ARPE-19 cells attached, proliferated onto the PU-NC, and expressed occludin. The in vivo ocular biocompatibility of the PU-NC was assessed by using the HET-CAM; and through its implantation under the retina. The direct application of the nanocomposite onto the CAM did not compromise the vascular tissue in the CAM surface, suggesting no ocular irritancy of the PU-NC film. The nanocomposite did not elicit any inflammatory response when implanted into the eye of rats. The PU-NC may have potential application as a substrate for RPE cell transplantation