KLRK1 and cancer: The downregulation of NKG2D on natural killer (NK) cells and CD8 + T cells resulted in the impairment of their cytotoxic function, thereby promoting immunosuppression and tumor immune evasion.124 Furthermore, exosomes transfer immunosuppressive molecules from cancer cells to immune cells, which promote cancer progression by suppressing the function of immune cells.125 TGF-β is one of the major immunosuppressive cytokines.