Survival of full-thickness retinal xenotransplants without immunosuppression

Background: A study was carried out to explore the survival of xenogeneic f ull-thickness retinal transplants in the subretinal space of hosts without immunosuppression. Methods: Nine adult rabbits received a complete immature rat neuroretina in the subretinal space. No immunosuppression was given, a nd the animals were followed up for 15 or 34 days. The eyes were then exami ned histologically with hematoxylin and eosin staining as well as with anti bodies against major histocompatibility complex (MHC) classes I and II, and the retinal pigment antigen RPE-65. Results. Surviving grafts were found i n 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, subreti nal space and host neuroretina. Conclusions: Full-thickness xenogeneic neur oretinal grafts can survive for at least 34 days in an adult host without i mmunosuppression. 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 devel op if the integrity of the donor tissue is intact and if damage to the RPE is minimal.