HLA-DPB1 and graft versus host disease: Patient-donor mismatching for amino acid residues that define the hypervariable regions of DPβ is associated with GVHD risk and can be used to define combinations of patient-donor HLA-DPB1 mismatches that are associated with higher risks (“HLA-DPB1 non-permissive mismatches”) and those associated with GVHD rates not dissimilar to those observed among HLA-DPB1-matched transplants (“HLA-DPB1 permissive mismatches”)44,45.