[Natural killer cells: from basic discovery toward translational insights]

Natural killer (NK) cells are cytotoxic lymphocytes that play an essential role in controlling viral infections and cancer. Although tumor cells and virus-infected cells with reduced expression of major histocompatibility complex (MHC) class I molecules can escape from T cell-mediated immune responses, NK cells use a variety of receptors to recognize and efficiently eradicate these targets through cytotoxic activity. NK cells are also an attractive tool for the development of therapies for incurable viral infections and cancer. However, effective strategies to enhance NK cell-mediated immune responses have not yet been established. This article provides an overview of the mechanisms underlying target recognition by NK cells. It also explains the adaptive immune features, including antigen-specific proliferation and differentiation into memory NK cells, as an emerging aspect of NK cell biology. Furthermore, it outlines chimeric antigen receptor (CAR) NK cell therapy as a therapeutic approach for invigorating the anti-tumor activity of NK cells, and reviews recent research trends, including the current status and challenges of CAR-NK cells.