Clinical significance of C4d deposition in stable renal allografts in the early post‐transplantation period

Abstract: The clinical significance of C4d positivity in patients with stable graft function is undetermined. This study evaluated the clinical outcome of protocol biopsy‐proven C4d‐positive renal transplants with stable graft function in the early post‐transplantation period. Protocol biopsies (n = 79) were performed on stable allografts on the 14th post‐transplant day, and indication biopsies (n = 74) were performed on dysfunctioning allografts within one yr after transplantation. Clinical and histological findings, graft function and graft survival rates were compared between C4d‐positive and C4d‐negative grafts in each group. The incidence of C4d positivity was 5.1% in protocol biopsies and 9.5% in indication biopsies. In protocol biopsies, C4d‐positive allografts showed minimal tubulointerstitial inflammation, and the graft function and graft survival rate did not differ from C4d‐negative allografts. All C4d‐positive allografts maintained stable graft function without anti‐rejection therapy, and follow‐up biopsies of two patients showed no C4d deposition or evidence of rejection. On the other hand, C4d‐positive allografts in indication biopsies showed severe tissue injury, and the graft survival rate was significantly lower than C4d‐negative allografts. In conclusion, C4d‐positive allografts with stable graft function in the early post‐transplantation period take an indolent course.