Identification of Non-Permissive HLA Allele Mismatch Combinations and Amino Acid Substitution Responsible for Acute Graft-Versus-Host Disease in Unrelated Allogeneic Bone Marrow Transplantation.

Background: In the allogenic hematopoietic stem cell transplantation from unrelated donors (UR-HSCT), an effect of HLA locus mismatch in allele level on clinical outcome has been clarified. However, the effect of each HLA allele mismatch combinations is little known, and its molecular mechanism to induce acute graft versus host disease (aGVHD) remained to be elucidated.

Methods: Consecutive 4866 patients transplanted with T cell replete marrow from a serologically HLA-A, -B and -DR antigen-matched donor through Japan Marrow Donor Program were registered in this cohort study. All HLA-A, -B, -C, -DRB1, -DQB1 and -DPB1 alleles were retrospectively typed in 2171 pairs, and partly in the other pairs. The impact of the HLA allele mismatch combinations in HLA six loci and amino acid substitution positions in HLA-C and HLA-DPB1 locus on aGVHD and survival was analyzed using a multivariable Cox regression model.

Results: Significant high-risk HLA allele mismatch combinations compared with match for severe aGVHD were identified; four in HLA-A allele (donor A*0206- patient A*0201 (n=108) hazard ratio (HR): 1.77, A*0206-A*0207 (n=20) : 3.24, A*2601-A*2603 (n=32): 1.96, A*2602-A*2601 (n=24): 2.18), six in HLA-B (B*1507-B*1501 (n=14): 2.95, B*4002-B*4003 (n=14): 2.44, B*4002-B*4006 (n=85): 1.69, B*4003-B*4006 (n=7): 3.85, B*4006-B*4002 (n=60): 1.62, B*4403-B*4402 (n=4) : 5.78), 11 in HLA-C, six in HLA-DRB1, zero in HLA-DQB1 and two in HLA-DPB1. Amino acid substitutions of position 80 of HLA-C at which donor had Asp80 and patient Lys80 (Asp80-Lys80) and Ser77-Asp77 were first elucidated as significant risk factors for severe aGVHD. These two amino acid substitutions were completely linked, and HR for severe aGVHD was 1.49 (1.01–2.21). As position 80 is ligand for NK cell receptor KIR2DL as a result, further analysis was performed in the KIR2DL ligand match in the GVH vector population. Notably, particular amino acid substitution at positions 95, 156 and 163 of HLA-C was a significant risk factor for severe aGVHD. HR of Leu95-Ile95, Arg156-Leu156, Leu156-Trp156, Trp156-Leu156 and Thr163-Leu163 substitutions were 1.74 (95%CI: 1.06–2.86), 2.10 (1.16–3.81), 5.22 (1.65–16.4), 4.64 (1.04–20.7) and 1.82 (1.11–2.99), respectively. The amplitude of hydropathy scales were 0.7, 8.3, 4.7, 4.7 and 4.7, respectively. Amino acid substitutions of any other positions of HLA-C were not significant risk factors. When analyzing the location of amino acid substitution in HLA-C, residues located in the T-cell receptor contact have marginal impact on severe aGVHD (HR: 1.45 trend P=0.096), and no other locations were significant. In HLA-DPB1 mismatch combinations, there was no obvious tendency to associate the positons of amino acid substitutions with severe aGVHD and grades 2–4 aGVHD.

Conclusion: These findings provide evidences to elucidate the mechanism of aGVHD on the base of HLA molecule. Furthermore, the identification of non-permissive and possible permissive mismatch would be beneficial for the selection of suitable donor and international donor exchange for UR-HSCT.