In addition, myeloid-derived suppressor cells (MDSCs), which are formed under chronic inflammation or infection and stimulated by signals including macrophage (M-)/granulocyte (G-)/granulocyte–macrophage (GM-) colony-stimulating factors (CSFs) and proinflammatory cytokines such as IFN-γ, IL-4, IL-6, and IL-23 [18,19], play a significant role in the treatment of GvHD with their immunosuppressive function, shielding grafted cells from alloreactivity. Here, IL4 is linked to graft versus host disease.