PDCD1 and graft versus host disease: Recently, PD-1 and its ligand PD-L1 are reported to alleviate GVHD in preclinical studies in mice possibly through suppression of Th1 and CD8+ T cells.40–42 In addition, G-CSF primed donor graft alleviates GVHD in some clinical recipients in previous research,36–38 and our recent mechanism study demonstrated that G-CSF directly restrained T cell activation through G-CSFR.30 Consistently, we also revealed here that G-CSF induced G-CSFR expression in CD8+CD45RA+CCR7+ T cells of donor peripheral blood.