Transmigration of donor cells involved in the sciatic nerve graft

Recently, human hand transplantation in Europe has shown that motor function may be recovered in some cases. However, little is known about cell trafficking involved the graft nerve. We have succeeded to use green fluorescent protein transgenic (GFP-Tg) rats with various cells strongly expressing GFP in a model a long-term survival of limb graft. In this model, we found retrograde migration of GFP-positive donor cells through the sclatic nerve anastomosis. It is well known that cellular components in the peripheral nerve graft especially Schwann cells, play an important role in the axonal regeneration promoted by nerve grafting. However, it was difficult to distinguish the cellular component of the nerve graft from recipient cells. The purpose of this study was to evaluate the migration of donor origin cells to the recipient's nerve and to examine the contribution of these cells in axonal regeneration using a simplified model of sciatic grafting.

Nerve defects were created in recipient rats, using three experimental combinations: group 1: wild-type rats from GFP Tg rats; group 2: GFP Tg rats from wild-type rats; group 3: wild-type rats from GFP Tg rats whose nerve grafts had been pretreated by freeze-thawing cycles (representing an acellular graft). The sciatic nerve specimens were examined under excitation light at 1, 2, and 3 weeks after transplantation.

GFP-positive area expanded clearly beyond the anastomosis both proximally and distally in group 1 and infiltrated into the middle of the null graft in group 2. On the contrary, freeze-thawing grafts donated GFP Tg rats lost GFP expression completely. Columns of GFP-positive cells were formed in the degenerated graft migrated into the recipient's nerve both ante- and retrograde. The S100-positive GFP-positive cells were considered to be graft-origin Schwann cells. The regenerating axons were accompanied with these double-positive cells in the recipient nerve. In conclusion, we have visualized the contribution of graft cells to axonal regeneration beyond a peripheral nerve anastomosis.