ENHANCED DETECTION AND CHARACTERIZATION OF HLA-SENSITIZATION IN RENAL TRANSPLANT RECIPIENTS

Dealing with sera from prospective transplant recipients, we need a sensitive and specific technique for proper determination of these patients’ allosensitization status. A new flow-cytometry based assay (FlowPRATM) proved to be more sensitive in revealing the existence of HLA- specific IgG antibodies (Abs) than conventional citotoxicity (CDC) based assay. Using FlowPRATM Screening and Specific tests we investigated humoral sensitization to HLA due to different immunizing events in 230 transplant candidates exposed to a single kind of immunizing event. Patient population was thus divided in three groups: Ts-group (110 transfused pts); Tx-group (41 previously transplanted pts); Pg-group (79 pts who had pregnancies and/or abortions). FlowPRA Screening highlighted a significantly higher incidence of sensitized subjects in both the Tx-group (36.6%, P<0.00001) and the Pg-group (27.8%, P<0.00001) than in the Ts- group (3.6%). Comparison of CDCPRA and FlowPRATM screening results showed a higher incidence of “false negative” CDC results in the Tx-group and particularly in the Pg-group (p=0.02) compared to the Ts-group of patients. Analysis of HLA class I Abs specificity evidenced a high incidence of CREG Abs (mainly against CREG 1C) in the Tx-group (80%) and in the Pg-group (95.4%). Remarkably 11 of the 21 (52.4%) CREG-specific Abs evidenced in the sera of the Pg pts and 6 of the 15 (40%) found in the Tx pts were INTRA-CREG Abs. As regards HLA class II specificity, our study evidenced DR and/or DQ specific Abs in 61.5% of Pg pts and in 63.6% of Tx pts; Abs directed towards a public antigen (DR51, DR52, DR53) were present in 30.8% of Pg pts and 18.2% of Tx pts. In conclusion we demonstrated, by means of the sensitive and specific FlowPRATM technique, that pregnancy had a strong immunogenicity, similar to that of transplants, but often underestimated by CDC assay and confirmed that pre-sensitization status must thus be attentively investigated before transplantation lowering risk of rejection and poor graft survival.