PROJECT SUMMARY The incidence rates of head and neck squamous cell carcinoma (HNSCC) in the United States have quadrupled in the past several decades. The current standard treatment regimen is associated with significant co-morbidities such as dysphagia and osteoradionecrosis. The mechanisms underlying poor immunological host responses are multifactorial, and the most significant challenge is that HNSCC contains few tumor- specific cytotoxic T lymphocytes in the tumor microenvironment (TME), despite abundant mutations. Data from our group suggests that type I interferon (IFN-I) signaling in HNSCC patients is critically associated with a Tc1/TH1-skewed TME and superior patient prognosis. Indeed, stimulator of interferon inducible genes (STING)-mediated IFN-I signaling has proven a central mechanism in facilitating CD8+ T-cell expansion. However, the STING pathway is frequently suppressed in cancers, and the mechanisms underlying type I interferon signaling remain insufficiently characterized. Preliminary data from our lab has shown that the regulatory nucleotide-binding domain and leucine rich repeat (NLR) protein NLRC3, which has been previously characterized as a negative regulator of type I interferon signaling in myeloid cells, is upregulated in human HNSCC cells resistant to cell-mediated cytotoxicity, indicating its potential role in mediating cancer immunosuppression. Therefore, the first aim of this project is to elucidate how NLRC3 modulates tumor and host-intrinsic type I interferon signaling in head and neck cancer pathology. The second aim of this project will investigate the immunological mechanisms which influence cytotoxic T cell infiltration into tumors post-treatment with activators of STING-dependent type I interferon signaling. Given the central role of M1-like macrophages and CD8a+ dendritic cells in promoting CD8+ T-cell maturation, the experiments proposed will likely provide a critical link in combating oral cancer immunosuppression. This proposal will be conducted under the guidance of Dr. Lei and Dr. Chen, whose combined expertise in immunology, cancer biology, and oral health will provide crucial leadership for the execution the proposed experiments.