Abstract

The immune system plays a key role in the protective response against oral squamous cell carcinoma (OSCC); however, the tumour microenvironment (TME) impairs this anti-cancer response by promoting an anti-inflammatory environment. Regulatory T-cells (Tregs) and Th2 effector cells (Teff) are associated with poor prognosis in OSCC. However, the main immunomodulatory mechanisms associated with the enrichment of these subsets in OSCC remain unknown. We characterised Th-like lineages in Tregs and Teff and evaluated immunomodulatory changes induced by the TME in OSCC. Our phenotypic data revealed a higher distribution of tumour-infiltrating CCR8+ and Th2-like Treg in OSCC compared with non-malignant samples, whereas the percentages of Th1 cells were reduced in cancer. We then analysed the direct effect of the TME by exposing T-cell subsets to cancer secretomes and observed the OSCC- secretome induced CCR8 expression and reduced cytokine production. Transcriptomic analysis showed that the co-culture with OSCC-secretome induced several gene changes associated with the vitamin D (VitD) signalling pathway in T-cells. In addition, proteomic analysis identified the presence of several proteins associated with prostaglandin E2 (PGE2) production by rapid membrane VitD signalling and a reduced presence of the VitD-binding-protein. Thus, we analysed the effect of VitD and PGE2 and observed that VitD promotes a regulatory Th2-like response with CCR8 expression whilst PGE2 also modulated CCR8 but inhibited cytokine production in combination with VitD. Overall, our data showed the immunomodulatory changes induced by the TME involving CCR8 expression and regulatory Th2 phenotypes, which are associated with PGE2 mediated VitD signalling pathway in OSCC.