Survival of allogeneic porcine retinal pigment epithelial sheets after subretinal transplantation.

PURPOSE To examine morphology after transplantation of organized primary porcine RPE sheets into the porcine subretinal space. METHODS Primary RPE sheets were harvested from freshly enucleated female porcine eyes and embedded in a thin slice of 50% gelatin and 300 mM sucrose before subretinal transplantation into male pigs by using vitrectomy techniques. Thirty-eight animals that underwent surgery were observed for up to 3 months without immune suppression. RESULTS Four days after surgery, the subretinal space contained a multilayer of heavily pigmented RPE that was predominantly Barr body positive. One month after transplantation, there was marked shortening of the outer segments with an intact external limiting membrane. The transplant bed contained a pigmented monolayer in some regions, whereas in other regions the graft was folded into multilayers with degenerated inner layers of transplanted cells despite synthesis of basement membrane. The choroidal vessels and choriocapillaris remained patent in the transplant bed. Barr body positive cells were still present 3 months after surgery. There was no infiltration of the graft site with inflammatory cells. CONCLUSIONS Allogeneic RPE grafts survive in the subretinal space up to 3 months after surgery, and the choriocapillaris remains patent in the transplant bed, although there are many heavily pigmented cells within the transplant bed that are Barr body negative by 3 months. Further work is needed to produce uniform repopulation of a sizable portion of Bruch's membrane with a monolayer of transplanted RPE.