Peripheral nerve allografts: survey of present state in an experimental model of the rat

Rejection and regeneration processes in peripheral nerve allografts are analyzed in this review of a series of experiments with special reference to the possible clinical application of peripheral nerve allografting in clinical reconstructive surgery. A long segment of the sciatic nerve (2.5 cm) was grafted between congenic rat strains across a maximal genetic barrier; immunohistologically, donor- and recipient-derived structures can be differentiated. If allografting was performed without immunosuppression, a rejection response with consecutive regeneration of minor quality was observed. Under immunosuppression with cyclosporin A no rejection response was observed and regeneration quality was comparable to control autografts. The persistence of donor-derived Schwann cells in the immunosuppressed allografts can be demonstrated immunohistologically. After discontinuation of immunosuppression a rejection response is exerted. We conclude that Schwann cells are eliminated from peripheral nerves during rejection. Consecutive regeneration of minor quality is possible, which implies the ingrowth of recipient-derived Schwann cells into the rejected allograft. Under immunosuppression, allogenic Schwann cells survive and actively promote regeneration. They are still immunologically competent and can exert rejection when immunosuppression is discontinued. A certain degree of replacement of donor-derived Schwann cells seems possible.