Abstract 2043: The role of CCL20 in response to radiation in head and neck squamous cell carcinomas

Abstract

Abstract Background: Radioresistance is responsible for most cases of tumor progression and recurrence in head and neck squamous cell carcinomas (HNSCC). Combined radiotherapy (RT) and immunotherapy (IT) treatment has improved survival for a minority of patients with inflamed tumors or tumors susceptible to RT-induced inflammation. To enhance the response of radioresistant tumors to radiation, an understanding of the factors that suppress anti-tumor immunity is necessary. In this regard, regulatory T cells (Tregs) are critical mediators of immune suppression in HNSCCs and their depletion improves tumor response to RT. In this study, we investigated how radiation modulates Treg infiltration through the chemokine CCL20. We hypothesized that radiation induces CCL20 secretion resulting in Treg infiltration and suppression of anti-tumor immunity and that blocking CCL20 could lead to improved response to RT. Methods: Human (Cal27, SCC9) and mouse (MOC1, MOC2) cell lines with different immune phenotypes were irradiated at doses of 2Gy or 10Gy. Conditioned media (CM), RNA and protein were collected for the assessment of CCL20. qPCR was used to determine CCL20 gene expression. In vivo, MOC2 cell were were implanted into the right buccal cavity of mice and the effect of neutralizing CCL20 antibody was determined alone and in combination with RT. Blood samples were collected before and after RT for the analysis of serum levels of CCL20. Tumor samples were analyzed by flow cytometry to determine immune infiltrates, including CD8 T cells and Tregs. Results: Cal27 and MOC2 tumors had a gene signature associated with immunosuppression and Treg infiltration whereas SCC9 and MOC1 tumors displayed a gene signature associated with an inflamed microenvironment. In vitro, high-dose radiation significantly induced CCL20 in Cal27 and MOC2 cells relative to control. Multiplex analysis of chemokines from conditioned media samples showed that induction of CCL20 was associated with increased secretion of GM-CSF by MOC2 and Cal27 cells. In vivo, inhibition of CCL20 alone resulted in a significant decrease in tumor growth compared to control in MOC2 tumors. The combination of RT and anti-CCL20 showed a significant decrease in tumor volume compared to RT alone. Conclusion: Our data suggests that high-dose radiation promotes the induction of CCL20 secretion by tumor cells which is responsible for attraction of Tregs. Inhibition of CCL20 secretion using anti-CCL20 antibodies can slow down tumor growth and enhance the response to radiation. Citation Format: Cleopatra Rutihinda, Ayman J. Oweida, Patrick Delage, Léanie Moreau, Safia Chelighem, Nour Elhouda Saidi. The role of CCL20 in response to radiation in head and neck squamous cell carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2043.