NK Cells in Cancer Immunotherapy

Natural killer (NK) cells are crucial components of the innate immune system and play critical roles in host immunity against viral infections and cancer. NK cells’ activity is controlled by the interaction of a wide range of receptors expressed on their surfaces with cell surface ligands. Opposite signals delivered by inhibitory and activating receptors tightly regulate NK cells’ cytotoxicity. Natural killer cells can discriminate between normal and cancer cells. NK cells are known to directly recognize and kill malignant cells or induce apoptosis. However, tumor cells have the ability to evade those attacks. The main mechanisms involve the lack of expression or downregulation of the expression of major histocompatibility complex (MHC) class I molecules and secretion of soluble NKG2D ligands by tumor cells. Furthermore, tumors harbor a population of cancer stem cells (CSCs), which can drive tumor progression and therapeutical resistance. This chapter highlights the roles of NK cells in tumor immunosurveillance and their applications for cancer immunotherapy. NK cell biology and function as well as the role of their receptor interactions will be described. We will discuss the therapeutic applications of NK cells in cancer and NK cells targeting CSCs as a promising strategy for cancer therapy.