Tumor-infiltrating NK cells significantly downregulated activating receptors such as NKG2D, DNAM-1, NKp30, CD16, and 2B4, while over-expressing their inhibitory receptors (e.g., NKG2A and PD-1) compared with matched blood NK cells and thereby could not kill target cells and produce cytokines (61, 399, 441). Here, KLRC1 is linked to neoplasm.