Severe acute graft‐vs‐host disease in a patient with acute monocytic leukemia having a recombination event between HLA‐A/B loci from a multiple recombinant family

Human leukocyte antigen (HLA) recombination, particularly multiple recombinations can produce novel haplotypes, thereby complicating donor–recipient selection and possibly inducing severe graft-vs-host disease (GVHD) after nonfully matched allogeneic hematopoietic stem cell transplantation. Here, we report for the first time that a 30-year-old female acute monocytic leukemia patient with an HLA-A/B recombinant haplotype, who has three unmatched and one HLA-B/DRB1 recombinant haplotype siblings, presented grade IV acute GVHD (aGVHD) after transplantation from a sibling with a single allele only mismatch at the classical HLA-A locus. Furthermore, using a new three-dimensional structure modeling application, we inferred that the structural differences in peptide-binding and T-cell receptor interaction sites can significantly change the immunogenicity of mismatched HLA molecules, potentially one of the main causes of aGVHD.