Correlation between virtual crossmatch, flow cytometric crossmatch and donor-specific alloantibodies in pretransplant evaluation for hematopoietic stem cell transplantation

Introduction: Donor-specific HLA antibodies (DSAs) have an adverse effect on engraftment after HLA- mismatched hematopoietic stem cell transplantation (HSCT). The presence of DSAs and flow cytometric crossmatch (FCXM) play an increasingly important role in donor selection. Aim: The aim of this study was to evaluate the correlation between virtual crossmatch (VXM), physical FCXM (PXM) and DSAs for assessing alloimmune reactivity before HSCT. Materials and methods: Forward (donor lymphocytes with recipient serum), reverse (patient lymphocytes with donor serum) and autologous FCXM were performed. HLA antibodies specificities were determined using Luminex technology (Single Antigen Beads Assay–SAB) and accepted as positive at mean fluorescence intensity (MFI) ≥1500. VXM was determined based on the donor HLA and recipient DSAs. Results: Of the 129 candidates for allogeneic HSCT, anti-HLA antibodies were detected in 43 (33.3%) of them. DSAs were present in 25 patients. Out of 340 FCXM performed 73 were positive. Best VXM prediction (90.6%) was observed for the negative samples. Positive virtual T-cell crossmatches correspond to the PXM in 87.5% (28/32). The lowest (29/45, 64.4%) was the correlation in the B-cell crossmatches. The MFI values predictive for a positive FCXM are highest for HLA-DR and -DQ antibodies (MFI ≥5000).  Conclusion: The correlation between VXM and FCXM depends on both the MFI value and the locus specificity of the DSAs. VXM could be taken into consideration in the process of donor search. The decision to transplant should be based on DSAs and a physical FCXM.