Endothelial cell chimerism after renal transplantation and vascular rejection

Background: The blood vessels of a transplanted organ are the interface between donor and recipient. The endothelium in the blood vessels is thought to be the major target for graft rejection. Endothelial cells of a transplanted organ are believed to remain of donor origin after transplantation. We aimed to verify this concept. Methods: We studied biopsy samples from 12 renal transplants for the presence of endothelial cells of recipient origin. We used three different techniques: immunohistochemistry for MHC class-I antigens, immunohistochemistry for ABO-blood-group antigens, and insitu hybridisation for X and Y chromosomes. After we had confirmed that these techniques did identify endothelial cells of recipient origin, tests were done in a second group of 26 patients to find out whether endothelial chimerism correlated with graft rejection. Findings: We found a strong correlation between the percentage of recipient endothelial cells in the peritubular capillaries and the type of graft rejection (r=0.71, p<0.0001). These cells were found mainly in grafts of patients who had had rejection, especially among patients with vascular rejection. In grafts of patients without rejection only sporadically recipient endothelial cells were detectable. Interpretation: Our data show that endothelial cells of the recipient can replace those of the donor. This replacement is associated with graft rejection. We postulate that endothelium that is damaged by vascular rejection is repaired by endothelial cells of the recipient.