Helper Activity of Natural Killer Cells During the Dendritic Cell-mediated Induction of Melanoma-specific Cytotoxic T Cells

Natural killer (NK) cells have been shown to mediate important immunoregulatory helper functions in addition to their cytolytic activity. In particular, NK cells are capable of preventing maturation-related dendritic cell (DC) exhaustion, inducing the development of type-1 polarized mature DCs (DC1) with an enhanced ability to produce interleukin (IL)-12p70, a factor essential for type-1 immunity and effective anticancer responses. Here we show that the NK cell-mediated type-1 polarization of DCs can be applied in the context of patients with advanced cancer to enhance the efficacy of DCs in inducing tumor-specific cytotoxic T lymphocytes. NK cells isolated from patients with late-stage (stage III and IV) melanoma responded with high interferon-g production and the induction of type-1-polarized DCs on exposure to defined combinations of stimulatory agents, including interferon-alpha and IL-18. The resulting DCs showed strongly-enhanced IL-12p70 production on subsequent T-cell interaction compared with immature DCs (average of 19-fold enhancement) and nonpolarized IL-1b/TNF-alpha/IL-6/PGE2-matured standard DCs (average of 215-fold enhancement). Additional inclusion of polyinosinic: polycytidylic acid during NK-DC cocultures optimized the expression of CD80, CD86, CD40, and HLA-DR on the resulting (NK)DC1, increased their CCR7-mediated migratory responsiveness to the lymph node-associated chemokine CCL21, and further enhanced their IL-12-producing capacity. When compared in vitro with immature DCs and nonpolarized standard DCs, NKDC1 were superior in inducing functional melanoma-specific cytotoxic T lymphocytes capable of recognizing multiple melanoma-associated antigens and killing melanoma cells. These results indicate that the helper function of NK cells can be used in clinical settings to improve the effectiveness of DC-based cancer vaccines.