Donor cell repopulation of whole-limb allografts in the rat: detection with green fluorescent protein

Although cell traffic between donor and recipient has previously been observed during allogeneic organ transplantation, little is known about cell traffic following whole-limb allografting. Whole-limb grafts are composed of composite tissues, and thus cell repopulations of recipients may be different for each component. This study was conducted using green fluorescent protein (GFP) transgenic rats to define cell repopulation of whole-limb allografts.

Twenty-four hind-limb allotransplants were performed across GFP-positive (Wistar background) and GFP-negative (Lewis) rats. Eighteen recipient animals were treated with continuous FK506 immunosuppression at a dose of 0.5 mg/kg/day up to 6 months after transplantation and assessed until 18 months posttransplantation. The expression of the GFP gene was examined under 489-nm excitation light and semiquantitatively assessed by polymerase chain reaction.

Allografted limbs showed acute rejection in nontreated recipients, but no rejection episodes occurred in FK506-treated recipients until 18 months posttransplantation. Intense GFP expression was noted in allotransplanted GFP-negative limbs at 18 months posttransplant. GFP expression was especially marked at the interfollicular epidermis in the skin component and the endothelial cells. Polymerase chain reaction using GFP-specific primers confirmed the presence of the GFP gene in these tissues. Allotransplanted GFP-positive limbs retained marked GFP expression at the muscle fiber.

The authors' results demonstrate that recipient-derived cells gradually migrate into grafted skin, endothelial cells, muscle, and bone marrow cells. Recipient-derived stem cells may contribute to this cell renewal within the graft. Repopulation of antigenic skin components in the graft with recipient cells may also help in avoiding rejection.