Impact of donor-specific antibodies on chronic rejection occurrence and graft loss in renal transplantation: Posttransplant analysis using flow cytometric techniques

Background. Improvements in immunosuppressive therapy have greatly reduced acute rejection (ARj) episodes, ensuring better short-term graft outcome, b ut have not modified long-term survival in renal transplantation. It is now well accepted that chronic rejection (CRj) can be determined by both immun e and/or nonimmune mechanisms. The aim of this study was to evaluate the im portance of the posttransplant humoral immune response towards mismatched H LA graft antigens in CRj occurrence and graft outcome. Methods. Serum samples from 120 nonpresensitized renal transplant recipient s were prospectively screened for 1 year after surgery by means of flow cyt ometry cross-match (FCXM) and FlowPRA beads (microbeads coated with purifie d HLA class I and class II antigens) assays. All transplants were followed- up for 2 years or until graft removal. Results. FCXM monitoring identified donor-specific antibodies (DS-Abs) in 2 9 (24.2%) of 120 transplanted patients. Correlation with clinical data high lighted a higher incidence of ARj in DS-Abs-positive patients compared to n egative patients (62% vs. 13%, P<0.00001). Furthermore, graft failure occur red more frequently among FCXM-positive patients than among negative patien ts (34% vs. 1%, P<0.00001). The deleterious effect of DS-Abs on graft funct ion was confirmed by serum creatinine levels 2 years after transplantation. These were in fact higher in subjects producing DS-Abs than in subjects wi th only ARj (mean creatinine: 2.5 +/-1.3 mg/dL vs.1.7 +/-0.5 mg/dL, P=0.04) . FlowPRA analysis of DS-Ab HLA specificity highlighted the presence of ant i-HLA class I antibodies in 85% of FCXM-positive patients, who also present ed with a higher incidence of HLA-B mismatches than FCXM-negative patients (1.23 +/-0.66 vs. 0.92 +/-0.59, P=0.02). Conclusions. Flow cytometric techniques are precious tools for investigatin g the activation of the humoral response against HLA antigens of the graft in renal transplantation. DS-Abs production has a worse impact on organ fun ction and survival than ARj episodes. These findings represent further proo f of the threat posed by DS-Abs on long-term graft function and draw attent ion to the need for a specific immunosuppressive therapy aimed at counterac ting the different kinds of immune activation toward graft.