Dendritic cells (DCs) display an extraordinary capacity to induce T-cell responses providing the opportunity of DC-based cancer vaccination strategies. Additional findings indicate that DCs may also play a crucial role for the activation of natural killer (NK) cells, which are important effectors in innate antitumor immunity. However, studies investigating the interaction between native human DCs and NK cells are limited. Recently, we defined 6-sulfo LacNAc (slan) DCs as a major subpopulation of myeloid human blood DCs, which represent principal producers of the proinflammatory cytokines tumor necrosis factor-α and interleukin (IL)-12. Functional data revealed that slanDCs efficiently induce neoanti- gen-specific CD4⁺ T cells and activate tumor-reactive cytotoxic T cells. When evaluating the crosstalk between slanDCs and NK cells in this study, we found that lipopolysaccharide (LPS)-activated slanDCs efficiently enhance NK cell CD69 expression and interferon (IFN)-γ secretion. NK cell-mediated tumor-directed cytotoxicity was significantly improved by slanDCs. NK cell activation induced by slanDCs was critically dependent on IL-12. When investigating the impact of NK cells on the immunostimulatory capacity of slanDCs, we observed that they promote DC maturation. In addition, NK cells strongly enhanced the secretion of immunomodulatory IL-12 and reduced the release of immunosup- pressive IL-10 by slanDCs. IFN-γ and cell-to-cell contact contributed to these effects. Furthermore, data revealed that DC-NK cell crosstalk improves slanDC-mediated differentiation of naive CD4⁺ T lymphocytes into IFN-γ- producing Th1 cells. In conclusion, we demonstrate a reciprocal activating interaction between slanDCs and NK cells, which may play a pivotal role in the regulation of antitumor immunity.