Long nerve allografts in sheep with cyclosporin A immunosuppression

Rodent studies of nerve allografts are limited by a relatively short length of graft segment. The authors attempted to establish an outbred sheep mode l that would allow the study of longer, more clinically relevant nerve gaps . Using outbred ewes, two 8-cm long radial sensory nerves were grafted into gaps (5 cm) in the median nerve. Sheep received an autograft and an allogr aft. Four sheep were immunosuppressed with Cyclosporin A (CsA) and four wer e controls. Blood CsA levels greater than 1000 mu g/L were obtained. System ic immunosuppression resulted in severe opportunistic infections, and the s heep were sacrificed between 35 and 47 days following surgery. Histological ly, in the autografts and CsA-treated allografts, evidence of nerve regener ation was seen. Non-immunosuppressed allografts were clearly rejected. Whil e clear differences in the histology of experimental and control grafted ne rve tissues were seen, the sheep allograft model presents considerable chal lenges due to immunosuppression-related infectious complications.