KLRK1 and neoplasm: Tumor cells and immunosuppressive cells express or secrete podocalyxin-like protein 1 (PCLP1), activin-a, indoleamine-pyrrole 2,3-dioxygenase (IDO), PGE2, TGF-β, and macrophage migration inhibitory factor (MIF) in the TME to mediate NKG2D downregulation.