Transplantation of retinal pigment epithelial cells

Disease of the outer retina may result from malfunction of the retinal pigment epithelium (RPE) or photoreceptors. A primary RPE defect occurs in the retinal dystrophy of the RCS rat, and has been implicated in the pathogenesis of aged-related macular degeneration, Best's disease and choroideremia. Replacement of abnormal by healthy RPE may modify disease progression. Techniques of site preparation and RPE cell transplantation were investigated in the miniature pig, which had similiar retinal morphology to the human. The surgical and microscopic anatomy of young and aged miniature pigs was examined. Feasibility studies were performed to determine the optimal volume for sub-retinal injection in vitro. A recipient site was prepared at the posterior pole of a miniature pig eye by subretinal injection of buffered saline to detach the neuroretina. There was significant, though variable recovery of overlying photoreceptors following retinal reattachment. A discrete area of Bruch's membrane under detached retina was mechanically cleared of RPE cells. Transmission and scanning electron microscopy showed separation at the junction of the RPE basal membrane and the RPE basement membrane. Porcine RPE cells were isolated from eyecups and the effect of the method of removal and culture medium were evaluated. Cells were labelled with tritiated thymidine, fluorescent-coated microspheres of carbon particles. In vitro studies showed that transplanted RPE cells would attach to Bruch's membrane. Injection into the subretinal space using a needle, rather than a blunt tipped endomanipulator, achieved sufficient subretinal concentrations of cells. Autologous cells for transplanation were obtained using open chorioretinal biopsy. Labelled autologous or heterologous RPE cells were later injected onto a prepared site at the posterior pole of the recipient eye. Sufficient numbers of subretinal cells were only obtained with injections of at least 7 x 104 cells, due to cell loss through the retinotomy. This factor and haemorrhage accounted for a very low donor cell concentration on Bruch's membrane. RPE cell viability and long term survival was not demonstrated.