HLA-DPB1 and graft versus host disease: The complex regulation and different HLA-DP expression levels on various cell types is also underlined by an interesting study published by Petersdorf et al. Theses authors showed that a higher expression level of HLA-DP determined by a genetic variant in the regulatory region of HLA-DPB1 increases the risk for GvHD after alloHSCT [6].