Transplantation of iris pigment epithelium into the choroid slows down thedegeneration of photoreceptors in the RCS rat

Background: Trophic factors [e.g. basic fibroblast growth factor (bFGF)] re leased by transplanted retinal pigment epithelial (RPE) cells are able to s low down the hereditary degeneration of the retina in the Royal College of Surgeons rat in sites distant from the site of transplantation where rod ou ter segment (ROS) phagocytic activity is not reconstituted by the transplan ts. Methods: To investigate whether iris pigmented epithelial (IPE) cells a re also able to generate this rescue by trophic factors, we transplanted IP E cells from Long-Evans rats into the choroid and subretinal space of 17 yo ung RCS rats. The eyes were enucleated after 6 months and prepared for ligh t microscopy. Six age-matched RCS rats served as controls. Light microscope sections from the whole choroid, healthy choriocapillaris, transplanted ce lls and the maximum thickness of the choroid, and outer nuclear layer param eters were analyzed by computer-assisted morphometry. Results: In transplan ted animals photoreceptor cells were rescued from degeneration although the majority of the transplanted IPE cells were located in the choroid. In the non-transplanted group photoreceptors were absent. Conclusions: Transplant ation of IPE cells slows down degeneration of the photoreceptors in the RCS rat. This photoreceptor-sparing effect by the IPE cells was observed even when the transplants were predominantly located within the choroid. The ben eficial effect observed may be related to trophic factors possibly secreted by the transplanted IPE cells.