Epitope analysis of HLA class I donor specific antibodies in sensitized renal transplant recipients

Objective. The goal of this study was to evaluate the epitope specificity o f donor-specific HLA class I antibodies detected in the serum of alloimmuni zed from a previous renal graft patients. Method. A total of 410 serum samples from 87 patients who had lost a previo us graft, were collected every 4 months during a S-year follow-up period. A ll recipients and donors were typed for class I HLA-antigens by a standard lymphocytotoxicity technique. To define the specificities of the HLA class I antibodies, two techniques were used in parallel: the antihuman globulin augmented CDC (AHG-CDC) technique and an ELISA technique, The mismatched HL A-antigens and the detected HLA class I antibodies were categorized as intr a-cross-reactive group mismatches (intra-CREGs-MMs) and other-CREG-MMs. For each sensitized patient actual and at risk epitope specificities were defi ned. Results. Thirty-eight patients (43.7%) had developed IBG HLA class I-specif ic antibodies with stable specificities against mismatched alloantigens fro m the previous graft. A total of 60 antibody reactivity patterns and 82 spe cificities against private and public epitope were recognized, Patients wit h only intra-CREGs-MMs produced HLA class I-specific antibodies less freque ntly than patients with only other-CREG-MMs, although the difference was ne arly statistically significant (P=0.053). All HLA class I donor-specific an tibodies were considered to have specificities against the private epitopes of the mismatched graft HLA-antigens, In the cases where HLA class I allor eactivity was spreading to more than one donor antigens, we considered that the detected antibodies had specificities against the private and the shar ed between the alloantigens epitope(s). No epitope-specific antibodies were detected against shared epitopes between the mismatched alloantigens and t he HLA-antigens of the patients. In 11/38 cases (28.9%) HLA class I allorea ctivity spreading to non-graft antigens was detected. These antibodies were directed against HLA-antigens that share epitope(s) and have strong serolo gical reactivity with the immunogenic alloantigens. Conclusion. Our data show that a small number of private and public alloepi topes seem to be responsible for antibody production in patients sensitized from a previous graft. A detailed description of these HLA-epitopes, in th e context of clinical graft complications, may lead to an improved organ al location strategy.