FIGURE 1.

Tumor recognition by natural killer cells, cytokine‐induced killer cells, and invariant natural killer T cells. A, NK cell antitumor activity is determined by the balance of signals from inhibitory and activating receptors expressed at the cell surface to trigger cytokine secretion or direct tumor cell lysis, with the collective engagement of several activation receptors such as the combination of LFA‐1, NKG2D, and 2B4 on NK cells inducing NK cell natural cytotoxicity against tumor targets. B, CIK cell cytokine secretion and tumor lysis are mainly mediated through NKG2D‐signaling and the engagement of MHC‐related ligands MICA/B and the ULBP family of ligands. C, iNKT cells express an invariant T‐cell receptor that is specifically activated by α‐GalCer loaded on CD1d molecules expressed by antigen‐presenting cells to exert direct cytotoxicity against tumor targets or secrete large amounts of cytokines like IFN‐ γ or IL‐4. α‐GalCer; alpha‐galactosylceramide, APC; antigen‐presenting cell, GM‐CSF; granulocyte‐macrophage colony‐stimulating factor, ICAM‐1; intracellular adhesion molecule 1, IFN‐ γ; interferon‐gamma, IL‐2; interleukin‐2, LFA‐1; lymphocyte function‐associated antigen 1 MICA/B; MHC class I chain‐related protein A and B, NK; natural killer, iNKT; invariant natural killer T cell, TCR; T‐cell receptor, TNF‐α; tumor necrosis factor‐alpha, ULBP; UL16 binding protein