Public epitope specificity of HLA class I antibodies induced by a failed kidney transplant: alloantibody characterization by flow cytometric techniques.

BACKGROUND: Patients whose kidney grafts fail develop alloantibodies that react with many HLA molecules. We analyzed the epitope specificity of HLA class I alloantibodies in the sera of 55 patients who had been sensitized by kidney grafts, and investigated the immunogenicity of various polymorphic epitopes. METHODS: HLA class I alloantibodies were detected and characterized by flow cytometry (FlowPRA beads). Potential "immunizing epitopes" were identified by comparing the amino acid sequences of HLA class I antigens/alleles of the donor, recipient and the antibody-reactivity pattern. RESULTS: In the 55 anti-HLA class I-positive patients, 82 different antibody reactivity patterns were identified; all but 5 (94%) were determined by a "public epitope" of donor HLA-A and/or -B molecules. Forty-five of 50 patients who showed HLA-A Res-MMs with their donors produced HLA-A antibodies, but only 31 of 51 subjects with HLA-B Res-MMs produced HLA-B antibodies (P=0.001; O.R.=5.81). The antibody patterns were specific for a "single" epitope of the mismatched donor molecules in 91% of patients. Forty-three of the 120 (36%) mismatched HLA-A and/or -B epitopes were positively correlated with antibody production. The polymorphic determinants of higher immunogenic capacity were b80N (Bw6-associated) and ab82-83LR (Bw4-associated) public epitopes. CONCLUSIONS: The humoral immune response against a kidney graft mainly produces HLA class I antibodies specific for "public epitopes" of mismatched donor molecules. A "single" donor-epitope may determine the production of a spread antibody pattern. In renal transplantation, epitope matching is better than HLA antigen matching for avoiding or minimizing development of HLA antibodies.

Post-transplant donor-specific antibody production and graft outcome in kidney transplantation: results of sixteen-year monitoring by flow cytometry.

Our data show that monitoring by sensitive flow cytometric techniques of the de novo production of anti-HLA antibodies in patients receiving kidney transplantation is a useful and noninvasive tool to identify the onset of an immune response towards the graft before any clinical manifestation of antibody-mediated graft injury. Consequently prospective posttransplant monitoring of anti-HLA donor-directed antibodies may offer the chance to realize an effective clinical intervention in order to prevent graft dysfunction and to prolong graft survival. The long follow-up period of the study allowed us to demonstrate a very low graft survival rate in patients who developed donor-specific HLA antibodies in comparison with patients who did not have antibodies, thus confirming the "humoral theory of transplantation". The posttransplant production of anti-HLA antibodies can predict not only graft failure but also chronic dysfunction of the graft. Moreover, our findings suggest that graft survival is influenced by the epitope- and locus-specificity of anti-HLA donor-directed antibodies. The interval between antibody appearance and loss of graft function was short in some patients but reached several years in others. Moreover, some patients showed consistent production of antibodies for many years and an uneventful clinical status. These findings suggest a mechanism of graft "accommodation" or the production of "harmless" antibodies. Immunosuppressive drug combinations able to inhibit T and B cell activation are useful tools to prevent the humoral immune response against graft and consequently to prolong graft survival.