OR5 Can you predict accurate crossmatch results with HLA-DP DSA?

Abstract

Aim The new kidney allocation system has increased transplant rates for highly sensitized candidates in which HLA-DP antibodies are more commonly identified. Accurate crossmatch correlations with HLA-DP donor specific antibodies (DSA) can be difficult given the low and variable expression of HLA-DP antigens and the presence of additional DSAs. Our aim was to optimize a strategy for predicting positive flow cytometric crossmatches (FCXM) in the presence of HLA-DP DSA. Methods Hypotonic dialyzed sera from 22 patients containing antibodies to HLA-DP (MFI range 1217–22,270) in the presence or absence of additional DSA were analyzed using One Lambda Single Antigen Beads. FCXMs were performed on a BD FACS Canto and a ratio >2.5 (test serum to negative control serum) was used as a positive FCXM threshold. Surface HLA expression was measured using class I and II specific monoclonal antibodies. Correlation coefficients were calculated. Results All T-FCXMs were negative. Thirteen of 23 B-FCXM were positive and 7 of 13 positive B-FCXM had HLA-DP DSA MFI >10,000 (++7; +−6; −+3; −−7; r = 0.24). Six of 13 positive B-FCXM had HLA-DP DSA MFI values 1 HLA-A; B; DR or >3 total # DSA) were detected reconciling the positive B-FCXM results. Three B-FCXM were negative despite high HLA-DP DSA levels (>10,000MFI); however, HLA class II expression on donor cells was low in 2 of 3 FCXMs. Seven B-FCXMs were negative with MFI Conclusions The breadth of HLA sensitization in patients that develop antibody to DP antigens complicates accurate crossmatch correlations when HLA-DP DSA is present(r = 0.24). High MFI values in bead based assays serve as a tool in crossmatch prediction, but the added complexity of multiple DSAs and variable expression of antigen on cells impact virtual crossmatch accuracy. There is potential for improved correlations (r = 0.60) using this multifactorial approach, but these data must be further validated using a larger dataset.