Role of the mixed lymphocyte culture (MLC) reaction in marrow donor selection: Matching for transplants from related haploidentical donors

Abstract

The utility of the MLC assay as a test of HLA-D region matching and predictor of acute graft-versus-host disease (GvHD) was evaluated in 157 patients receiving marrow grafts from HLA-A, B identical related haploidentical donors. All donors and recipients were tested by HLA-DR serology, by Dw phenotyping with homozygous typing cells (HTC) and by standard MLC. Ninety-nine of the donor-recipient pairs were mismatched for a serologically defined HLA-DR antigen while 109 pairs were mismatched for the HLA-DR region by HTC typing. Donor antirecipient relative responses (RR) in MLC, corresponding to the GvHD vector in marrow transplantation, ranged from -4% to 100%, with a median of 25%. A comparison of reactivity in MLC with presence or absence of matching by Dw phenotyping, however, showed a significant overlap in the distribution of RRs from HLA-Dw matched versus Dw mismatched pairs, suggesting that the MLC was not a reliable predictor of HLA-Dw matching. Using an optimally-defined cutoff of 3% RR, the MLC was correlated with risk of developing clinically significant grades II-IV acute GvHD (p = 0.03) but not with risk of developing severe grades III-IV GvHD (p = 0.18). In contrast, matching by Dw phenotype was a significant predictor of GvHD, with Dw-compatible transplant recipients less likely to develop either grades II-IV (p = 0.004) or III-IV (p = 0.036) GvHD than Dw-incompatible transplant recipients. Overall, these results underscore the difficulty in using the MLC to measure HLA-D region compatibility and predict the risk of severe graft-versus-host disease among patients receiving related haploidentical marrow grafts. HLA-D (HTC) typing results correlate primarily with DRB compatibility, and with the advent of DRB1 allele matching by sequence-specific oligonucleotide probes (SSOP) or by direct sequencing, the precision in donor matching achievable with these methods is far greater than with either HLA-D typing or direct MLC testing.