Different combinations of cytokines and activating receptor stimuli are required for human natural killer cell functional diversity.

Although cytokine induced NK cell activation protocols are commonly used in many laboratories worldwide, a systematic study of the effect of different cytokines either alone or in combination on NK cell function is lacking. In this study we performed a comparative evaluation of several cytokines potentially important for NK cell stimulation, focusing particularly on IL21 because of its promising role in anti-tumor therapy. To simulate in vivo physiological condition, we evaluated cytokine stimulation in total peripheral blood mononuclear cells (PBMCs), as accessory cells are responsible for the secretion of many soluble factors and can simultaneously trigger multiple activation signals through engagement of NK cell activating receptors. We show here that NK cell responses are finely regulated by several incoming stimuli and that combinations of IL21+IL2 or IL21+IL15 strongly induced NK cell function. Cytokine stimulation combined with NK receptor engagement can be helpful in the dissection of NK cell responses in health and disease.