IMPACT OF POST-TRANSPLANT ANTI-HLA ANTIBODY DEVELOPMENT ON KIDNEY GRAFT OUTCOME MAY BE MODULATED BY SPECIFIC IMMUNOSUPPRESSION

Some recent studies correlated both acute and chronic rejection with post- transplant production of antibodies to donor HLA antigens in renal transplantation. As concerns the assay methodology to reveal anti-HLA antibodies, the new flow cytometry based techniques showed a higher sensitivity and specificity than classical complement-dependent cytotoxicity. Aims of this study were to evaluate incidence, HLA- specificity and trend of donor-directed alloantibodies produced after kidney transplant and to investigate the ability of different immunosuppressants to limit alloantibody synthesis. We analysed sequentially collected serum samples (0 to 106 post-transplant months) from 257 renal transplanted patients for production of circulating HLA antibodies using flow cytometry crossmatch technique. HLA antibody specificity was studied using FlowPRA Screening and Specific tests (micro- beds coated with different HLA class I or II antigens; One Lambda, Inc, CA). Mean follow up was 3.6±2.2 years. Immunosuppressive therapy consisted of cyclosporine/steroid/azathioprine (Aza) or mycophenolate mofetil (MMF). Thirty-nine of 257 patients (15.2%) produced donor-directed alloantibodies. All but two of these 39 patients produced IgG alloantibodies, while in the remaining two patients only IgM antibodies were detectable. HLA specificity analysis of IgG antibodies evidenced anti- HLA class I antibodies in 19 patients (51.4%), anti-HLA class II in 8 patients (21.6%) and anti-HLA class I and II in 10 (27%). According to the length of alloantibody positivity, patients were divided in two groups: Ab-Pos = 24 (61.5%) patients showing a persistent positivity throughout our observation; Ab-Pos/Neg = 15 (38.5%) patients presenting disappearance of alloantibodies over a period of time ranging from 1 to 16 months. Interestingly, Ab-Pos patients showed a significantly higher incidence of anti-HLA class II alloantibodies than Ab-Pos/Neg (66.7% vs. 15.4%, P=0.003). Comparing the trend of alloantibody-positivity and graft outcome, a significantly higher incidence of graft failure and higher serum creatinine levels was evident in Ab-Pos patients than in the Ab- Pos/Neg ones (graft failure: 45.8% vs. 6.7, P=0.01; mean serum creatinine: 2.0±0.4 mg/dL vs. 1.6±0.5 mg/dL, P=0.03). As regards immunosuppressive therapy, we highlighted a significantly higher incidence of MMF-treated patients in the Ab-Pos/Neg group of patients than in the Ab-Pos ones (60% vs. 25%, P=0.03). Moreover Ab-Pos/Neg treated with MMF had lower mean creatinine levels than Ab-Pos/Neg treated with Aza (1.4±0.5 mg/dL vs. 1.9±0.6 mg/dL). In conclusion our findings define the clinical importance of post-transplant monitoring of donor-directed alloantibodies and underline the need to identify HLA antibody specificity. Our data furthermore indicate that MMF, a selective inhibitor of T and B lymphocytes proliferation, is able to limit post-transplant alloantibody synthesis and may consequently improve renal allograft survival preventing chronic rejection.