Potassium channels mediate the inhibitory effect of exosomes on anti-tumor immunity in head and neck cancer

Head and neck squamous cell carcinomas (HNSCC) are aggressive cancers with a relatively low response rate to immunotherapy. Anti-tumor immune responses rely on cytotoxic T and NK cells infiltrating the tumor microenvironment to eliminate cancer cells. However, tumors activate multiple mechanisms to evade these responses. Tumor-derived small extracellular vesicles, also known as exosomes, reshape the tumor microenvironment by impairing cytotoxic T and NK cell function, promoting immune escape and metastasis. Transcriptomic analysis of healthy donor peripheral blood mononuclear cells (PBMCs) exposed to exosomes from HPV-negative HNSCC patient primary cancer cells revealed reduced cytotoxic cells and suppressed immune responses including cytotoxicity, chemokine production, and NK and T cell functions. Bead-based multiplex immunoassay showed that HNSCC-derived exosomes inhibited the release of effector cytokines (IL-2, TNF-, IFN-{gamma}) and cytotoxic molecules from activated CD8 T cells. While ion channels regulate Ca{superscript 2}-dependent cytotoxicity and cytokine production and release, their role in exosome-mediated immune suppression is unexplored. We found that tumor-derived exosomes selectively inhibit KCa3.1 channel activity in CD8 T cells by downregulating calmodulin, ultimately impairing Ca{superscript 2} signaling and IFN-{gamma} release. This study identifies a novel mechanism of exosome-mediated immunosuppression, positioning KCa3.1 as a promising therapeutic target to enhance immune surveillance and immunotherapy response in HNSCC.