Survival of full-thickness retinal xenotransplants without immunosuppression.

Abstract

A study was carried out to explore the survival of xenogeneic full-thickness retinal transplants in the subretinal space of hosts without immunosuppression. Nine adult rabbits received a complete immature rat neuroretina in the subretinal space. No immunosuppression was given, and the animals were followed up for 15 or 34 days. The eyes were then examined histologically with hematoxylin and eosin staining as well as with antibodies against major histocompatibility complex (MHC) classes I and II, and the retinal pigment antigen RPE-65. Surviving grafts were found in five out of nine eyes. Three grafts displayed the laminated appearance of a normal retina, and two had developed into rosettes. In four of the five specimens with surviving grafts, the host retinal pigment epithelium (RPE) was continuous, and MHC labeling showed no or minimal upregulation. In four specimens, no graft was found. Three of these displayed RPE defects and an increase in MHC class I- and II-labeled cells in the host choroid, subretinal space and host neuroretina. Full-thickness xenogeneic neuroretinal grafts can survive for at least 34 days in an adult host without immunosuppression. Immature grafts can develop the laminated appearance of a normal retina. The integrity of the host RPE seems to correlate with graft survival. We conclude that xenogeneic retinal grafts can survive and develop if the integrity of the donor tissue is intact and if damage to the RPE is minimal.