What is the true incidence of acute rejection (AR) in renal transplant recipients receiving calcineurin inhibitors?

The incidence of AR has fallen by 50% since the introduction of calcineurin inhibitors, but the incidence of chronic graft nephropathy has remained unaltered. One explanation could be a significant incidence of unsuspected acute rejection injury (USAR) that escapes current anti-rejection therapy. The aim of this study was to investigate, in a longitudinal manner, the histological incidence of acute rejection on protocol biopsies. Patients were randomised to receive either Neoral (NTT) or Prograf (PTT) based triple therapy. Each AR was confirmed histologically. Patients also underwent protocol biopsies at 3, 6, and 12 months post-transplant regardless of renal function. No patient received anti-rejection therapy on the basis of scheduled biopsy alone. This interim analysis of 87 patients consists of 122 clinically indicated and 123 scheduled biopsies. The incidence of AR + USAR was 63% in the NTT group and 41% in PTT group (p<0.05). The difference between the two groups was more significant for the incidence of AR (42%vs.23%; p