NK and cells with NK-like activities in cancer immunotherapy-clinical perspectives

Natural killer (NK) cells are lymphoid cells of innate immunity that take important roles in immune surveillance. NK cells are considered as a bridge between innate and adaptive immunity, and their infiltration into tumor area is related positively with prolonged patient survival. They are defined as CD16+ CD56+ CD3− cells in clinic. NK cells promote cytolytic effects on target cells and induce their apoptosis. Loss of NK cell cytotoxic activity and reduction in the number of activating receptors are the current issues for application of such cells in cellular immunotherapy, which resulted in the diminished long-term effects. The focus of this review is to discuss about the activity of NK cells and cells with NK-like activity including natural killer T (NKT), cytokine-induced killer (CIK) and lymphokine-activated killer (LAK) cells in immunotherapy of human solid cancers.