KLRK1 and neoplasm: During immune evasion of tumor cells, a large number of bioactive molecules contained in tumor cell-derived exosomes, such as transforming growth factor-β (TGF-β), programmed death ligand (PD-L1), ligand for natural killer cell activated receptor NKG2D (MICA/B), apoptosis-associated protein Fas-L, etc., will recognize the cognate receptor on NK cells and abolish the anti-tumor activity.