Long-Term Survival of Skin Allografts in Rats Treated with Topical Cyclosporine

The study investigated the effects of topical cyclosporine (CsA) on the survival of skin allografts in rats. Untreated allografts were rejected in approximately 7.4 days, while those treated with CsA survived significantly longer, depending on the dosage and duration of treatment. Continuous CsA treatment at 10 mg/rat/day resulted in long-term graft survival of over 100 days. The therapeutic blood level of CsA was maintained between 250 to 500 ng/ml, with most grafts being rejected when levels fell below 200 ng/ml. Direct application of CsA onto the allografts led to longer survival compared to application on normal skin. The study highlighted that high local concentrations of CsA in allografts were crucial for prolonging graft survival, with minimal cell infiltration and loss of hair follicles observed in long-surviving grafts.