Prolonged viability of human skin xenografts in rats by cyclosporine

The immunosuppressant cyclosporine (CSA) has shown usefulness in both animal and human transplantation. The present study investigated the effect of CSA in human to rat skin xenografts. Recipient rats received either a fresh split-thickness (0.020 in.) or full-thickness graft obtained from plastic surgery, or frozen cadaver skin. The graft bed of recipient Lewis rats was prepared by full-thickness excision. Animals were maintained on CSA 25 mg/kg/day X 50 days, followed by 12.5 mg/kg 2 X/week. Control animals received an equivalent volume of vehicle. All animals receiving split-thickness grafts and treated with CSA maintained their grafts significantly longer (up to 255 days) than controls. The 2 CSA-treated full-thickness grafts and the 10 vehicle-treated controls showed clinical and microscopic signs of rejection at a mean of 6.4 days. Histologic examination of successful grafts showed areas of viable epidermis with a negligible inflammatory infiltrate. There was some loss of normal polarity and occasional apoptotic pigmented basal cells. The dermis revealed moderate fibrosis, probably secondary to the surgical procedure. Graft viability was confirmed by autoradiography. Immunohistochemical staining for S-100 protein revealed morphologic alteration of suprabasilar dendritic (Langerhans-indeterminate) cells, as well as their existence in xenografts at 12 weeks posttransplantation. Toxicities reflected by weight loss and blood chemistries were felt to be dose-dependent. This in vivo model may provide a means for testing percutaneous drug penetration and pharmacokinetics in human skin, and for observing the immune component of explanted cutaneous neoplasms and dermatoses.