KLRK1 and neoplasm: One of the reasons for the anti-tumor immune activity of NK cells is attributed to the binding of its surface-activated receptor natural killer cell group 2D (NKG2D) to MHC class I chain-related protein A/B (MICA/B), an NKG2D ligand on the surface of tumor cells, thus activating NK cell function and enables NK cells to kill tumor cells (232).