Natural killer (NK) cells exhibit dual functionality: they can protect against GVHD by eliminating activated T cells while secreting anti-inflammatory cytokines like IL-10 and transforming growth factor (TGF)-β; conversely, they may promote GVHD progression through the release of IFN-γ and TNF-α [14,15]. Here, TGFB1 is linked to graft versus host disease.