IL15 and neoplasm: To further characterize the role of cytokines in NK cell response to tumor cells, we pre-conditioned primary NK cells overnight with three different sets of cytokines, including IL-2/IL-15, which were important for maintenance and expansion of NK cells in vitro, IFN-α, a pro-inflammatory cytokine involved in both innate and adaptive immune responses [33,34,39], and IL-12/IL-18, reported to enhance anti-tumor function and induce “memory” properties [40].