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-α, IFN-γ) and cytotoxic molecules from activated CD8(+) T cells. While ion channels regulate Ca(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(2+) signaling and IFN-γ 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.