KLRK1 and neoplasm: The coat may cause the transference of MHC class I from platelets to tumor cells, resulting in high-level expression of normal MHC class I, and thus protect tumor cells from being attacked by NK cells.[31,32] Moreover, a previous study also found that TGF-β released from platelets can downregulate NKG2D thereby inhibiting NK cells antitumor reactivity, which will further pamper the existence of tumor cells.[33] Apart from NK cells, cytotoxic T lymphocytes (CTLs) also show great importance in tumor immunosurveillance.