Increasing evidences suggest that G-CSF affects different immune cells [13, 15], which modulate T cell response directly by inducing Th2 differentiation [16, 17] or mobilizing functional regulatory T cells [18], or indirectly through monocytes [19–21], DC [22], and neutrophils [23] to prevent GVHD. Here, CSF3 is linked to graft versus host disease.