Effect of immunosuppression on outcome measures in a model of rat limbal transplantation

PURPOSE. To examine the effect of immunosuppression with intramuscularly injected cyclosporine and topical corticosteroid on limbal allograft survival in a new model in the inbred rat. METHODS. Orthotopic limbal tissue harvested from male Fischer 344 (isografts) or male Wistar-Firth donors (allografts) was sutured into superior and inferior lamellar excision sites in female recipient Fischer 344 rats. Grafts were examined clinically for at least 55 days. Superficial epithelial cells were sampled weekly, and the DNA extracted and probed for the malespecific gene Sry by polymerase chain reaction. Recipients were killed at established intervals for immunohistochemistry. Graft-recipient animals were randomly assigned to receive either intramuscular cyclosporine plus topical prednisolone phosphate or vehicle for 4 weeks from the time of transplantation. RESULTS. Isografts survived for a median of more than 55 days. Atlografts underwent clinical rejection at a median of 6 to 7 days after grafting. Acutely rejecting allografts showed a dense mononuclear infiltrate consisting of activated CD4⁺ and CD8⁺ T cells with some macrophages. Genomic Sry was usually detectable in cells sampled from the ocular surface for more than 55 days in isografts, but not beyond 7 days in allografts. Immunosuppression prolonged allograft survival significantly, as assessed clinically, but did not prolong donor cell survival on the ocular surface, as assessed by detection of genomic Sry. CONCLUSIONS. A robust model of limbal transplantation was developed in the rat. Isografts survived for the long term, whereas allografts underwent rapid rejection. Although clinical allograft survival was prolonged to a modest extent by immunosuppression, donor cell survival on the ocular surface was not improved.