Tumor-associated fibroblasts (TAFs) are the most abundant cell type in the microenvironment of head and neck squamous cell carcinoma (HNSCC). We and others previously reported that secreted factors from TAFs increase the proliferation, migration, and invasion of HNSCC. Further studies revealed that HNSCC-secreted factors induce secretory autophagy in TAFs. However, the contribution of TAF autophagy to immune-evasion in the HNSCC microenvironment is unknown. Natural killer (NK) cells are an essential arm of anti-tumor immunity; thus, our study set out to determine the role of TAF autophagy in suppressing NK cell effector functions against HNSCC. To address this, we treated the NK cell line NK-92MI with conditioned media from primary HNSCC TAFs or normal fibroblasts derived from cancer-free subjects and assessed changes in IFN-γ production and cytotoxicity, measures of NK cell activation. We then assessed the role of TAF autophagy in mediating this effect by repeating the studies using conditioned media from TAFs whose autophagy had either been inhibited by chloroquine treatment or knocked down by siRNA. Finally, we assessed the mechanisms by which autophagy in the TAF affects NK cell function. Our data demonstrate HNSCC tumor cells orchestrate a complex mechanism of NK cell inhibition through the modulation of TAFs in the microenvironment. Treatment with TAF-conditioned media induced IFN-γ mRNA expression in NK-92MI cells. Interestingly, TAF-conditioned media also reduced NK cell-mediated cytotoxicity as compared to conditioned media from normal fibroblasts. Knockdown of key regulators in the secretory autophagy pathway by siRNA abrogated release of TAF-secreted factors, including hepatocyte growth factor (HGF). HGF induced NK-92MI expression of IFN-γ mRNA, which could be abrogated by an inhibitor of the HGF receptor, c-MET. In conclusion, these data describe a previously undefined effect of TAFs on NK cell function in the HNSCC microenvironment.
Citation Format: Jonathan David Enders, Jacob New, Rana Aliani, Sufi Mary Thomas. Secretory autophagy in tumor-associated fibroblasts alter effector function of natural killer cells against HNSCC [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B72.