In recent years, the effects of cancer chemotherapy and radiotherapy (CT/RT) regimens as they apply to the immune system have been explored. NK cells represent the main cytotoxic arm of the innate immune system, and their functionality is vital to establishing an effective anti tumor immune response. This review examines current CT/RT interventions in light of their effects on NK cell functionality. The effects of CT/RT on the expression of the various ligands for activating and inhibitory NK cell receptors are discussed. Expression of ligands for the activating NKG2D receptor is enhanced by cell stress; accordingly there are numerous reports of their higher expression in cells exposed to various CT/RT agents. In contrast, some agents have been reported to cause ligand shedding, which can serve to inhibit NK cell activity. Reported effects of CT/RT on tumor expression of ligands for the activating Natural Cytotoxicity Receptors, and of HLA class I ligands for NK cell inhibitory receptors are also noted. Additionally, we describe reports concerning the direct effects of CT/RT on NK cell function. Many treatments adversely affect NK cell function directly, but observations made through in vitro systems may differ from those obtained utilizing clinical samples. The effects of CT/RT on both direct NK cell cytotoxicity and on NK cell-mediated Antibody Dependent Cellular Cytotoxicity are explored. Taken together, CT/RT affects NK cell anti-tumor immunity from multiple angles. The interplay is complex, and future work is needed to achieve the optimal synergy between CT/RT and innate as well as adaptive immunity in the treatment of cancer.
Keywords: Chemotherapy, Radiotherapy, Cancer, Natural Killer (NK) cells, Receptors, Ligands, Natural cytotoxicity receptors (NCRs)