Regulation of Natural Killer Cell Responses By Dendritic Cells Via Lymphotoxin-Alpha, Interleukin-12, and Tumor Growth Factor-Beta

Dendritic cells (DC) induce T-cell responses in cancer patients. However, less is known about the role of DC-vaccines in shaping natural killer (NK) cell responses. In this study, we sought to investigate the activity of NK cells following vaccination with DC. Patients with chronic lymphocytic leukemia (CLL) and melanoma were vaccinated with tumor-antigen loaded monocytes-derived DC and NK cell activity was analyzed before and two weeks after vaccination. Compared with pre-vaccination samples, NK cells expressed reduced levels of several activation markers and produced less IFNγ (p=0.03). To further explore the mechanism of the reduced NK cell responses, DC were differentiated from monocytes in GM-CSF, IL-4 and LPS and thereafter co-cultured with autologous NK cells in vitro. In these experiments, DC-mediated inhibition of NK cells was independent of cell-contact but dependent on the phosphorylation status of STAT3 in DC. Compared with untreated DC, STAT3-inhibited-DC produced higher amounts of lymphotoxin-alpha (LTα, 5.5±5.0 vs. 38.1±25.9 pg/ml; p=0.005) and IL-12 (29.6±39.0 vs. 176.8±96.8 pg/ml; p=0.005) and reduced amounts of tumor growth factor-beta (TGFβ, 495.0±138.7 vs. 300.4±141.8 pg/ml; p=0.03) and did not suppress NK cell proliferation (p=0.03), cytotoxicity (p=0.0003), and IFNγ production (p=0.02). Neutralization of TGFβ resulted in elevated production of LTα (2.25±4.5 vs. 251.5±12.0 pg/ml; p=0.03) and IL-12 (0.25±0.5 vs. 15.0±1.82 pg/ml; p=0.02) by DC and addition of recombinant LTα or IL-12 in co-cultures of DC and NK cells was indispensable to maintain NK cell activity. Compared with LPS, DC matured with a cocktail of R848, poly I:C, and IFNγ showed reduced levels of pSTAT3 and produced higher levels of LTα and IL-12 and did not inhibit NK cell activity. These results show that LTα, IL-12 and TGFβ are involved in the cross-talk between NK cells and DC. Our findings have important implications for the development of DC-based vaccination strategies to potentiate NK-cell responses in patients with cancer.