Using a proinflammatory cytokine cocktail composed of tumor necrosis factor -a, IL-1b, IL-6 and prostaglandin E2. Over the years, it has become apparent that these “gold-standard” DCs, commonly referred to as ‘IL-4 DCs’, are suboptimal in terms of antigen presentation function and T cell stimulatory capacity. This explains the impetus behind the many efforts that are currently being made to optimize the culture conditions for ex vivo monocyte-derived DC generation. Within this context, we and others have shown that the immunostimulatory properties of monocyte-derived DCs can be significantly enhanced by replacing IL-4 with IL-15 for DC differentiation and by using Toll-like receptor stimuli to trigger DC maturation. In addition, we have found that these so-called ‘IL-15 DCs’ display a rather unconventional DC phenotype, with a subset of these cells being positive for the cell surface marker CD56. Since CD56 is the archetypal phenotypic marker of NK cells, we here aimed to investigate whether IL-15 DCs also bear functional resemblance with NK cells in terms of cytotoxic activity. In this study, IL-15 DCs are shown to possess potent tumor antigen presentation function in combination with lytic potential against the classical NK cell target cell line K562, thus confirming the hypothesis that IL-15 DCs qualify for the designation of killer DCs. To further address the possibility that the observed lytic activity against K562 cells might have resulted from this low-level contamination with NK cells, we additionally performed a cytotoxicity assay against the U937 cell line, another known NK cellsensitive target cell line. As shown in Figure S2, both CD56 + and CD562 IL-15 DC preparations failed to affect the viability of U937 cells, even at the high 50:1 E:T ratio used, indicating that the presence of these few NK cell contaminants was not a major concern in our experimental design. Dendritic cells, the quintessential antigen-presenting cells of the human immune system, have attracted much interest for active, specific Butenafine hydrochloride 
immunotherapy of cancer over the years. Despite some clinical successes, there is a general consensus that DC-based anti-tumor immunotherapy has not yet fulfilled its full therapeutic potential and that there remains considerable room for improvement, especially when it comes to optimizing the immunostimulatory activity of the DCs used for clinical application. Due to their potent immunostimulatory properties, monocyte-derived DCs generated in the presence of GM-CSF and IL-15 have been advocated as promising new vehicles for DC-based immunotherapy. In this study, we reveal for the first time that IL-15 DCs, in addition to a robust capacity for tumor antigen presentation, possess tumor cell killing potential. Our findings thus establish a previously unrecognized ‘killer DC’ function for IL-15 DCs, providing further support to their application in DC-based cancer immunotherapy Orbifloxacin protocols. Although a subset of IL-15 DCs expresses the archetypal NK cell marker CD56, we found no evidence for a further phenotypic overlap between IL-15 DCs and NK cells, nor could these cells be identified as the human homologue of murine NKDCs. Our phenotypic data unequivocally establish that IL-15 DCs are genuine monocyte-derived DCs despite the rather unconventional expression of CD56. Perhaps the most compelling evidence for this comes from our cell sorting experiment in which CD14 + monocytes were flow sorted to ultra-high purity and then subjected to IL-15 DC differentiation. In this experiment, we showed that CD56 + IL-15 DCs can also be differentiated.