Natural killer cell

Natural killer (NK) cells are lymphocytes of the innate immune system that function as key effector cells in cancer surveillance and anti-tumor immunity. Distinct from T lymphocytes and other adaptive immune cells, NK cells are activated in response to transformed cells and can adopt multiple functional states, including enhanced "trained" states induced by microbial exposure that have been associated with protection against cancer metastasis in experimental contexts. These cells mediate their cytotoxic functions through direct cell killing and through antibody-dependent cellular cytotoxicity via FcγRIIIa receptor engagement, and their activity can be modulated through diverse mechanisms including physical exercise, immunomodulatory compounds, and engineered therapeutics.

NK cell function is regulated by underlying metabolic and mitochondrial processes, and their dysfunction—induced by radiation exposure, environmental factors, or lipid metabolism reprogramming in the tumor microenvironment—can significantly impair anti-tumor immune responses. Therapeutic strategies to enhance NK cell-mediated immunity include engineered chimeric antigen receptor (CAR)-NK cell approaches and immunomodulatory interventions targeting regulatory pathways such as PD-1/PD-L1. In clinical applications including allogeneic hematopoietic stem cell transplantation for hematologic malignancies, NK cells function synergistically with T cells to provide durable anti-tumor immunity and support immune reconstitution.