Hypoxia regulates the differentiation and anti-tumor effector functions of γδT cells in oral cancer

Hypoxia within the tumor microenvironment (TME) is a key factor contributing to immunosuppression in tumors, co-relating with poor treatment outcome and decreased overall survival in advanced oral cancer (OC) patients. V delta 2 is a dominant subset of gamma delta T cells (gamma delta T cells) present in the peripheral blood which exhibits potent anti-tumor cytotoxicity and is evolving as a key player of anti-cancer cellular therapy. However, the fate of gamma delta T cells in hypoxic oral tumors remains elusive. In the present study, we compared the effect of hypoxia (1% O-2) and normoxia (21% O-2) on the expansion, proliferation, activation status, cytokine secretion and cytotoxicity of gamma delta T cells isolated from OC patients and healthy individuals. Hypoxia-exposed gamma delta T cells exhibited reduced cytotoxicity against oral tumor cells. Our data demonstrated that hypoxia reduces the calcium efflux and the expression of degranulation marker CD107a in gamma delta T cells, which explains the decreased anti-tumor cytotoxicity of gamma delta T cells observed under hypoxia. Hypoxia-exposed gamma delta T cells differentiated to gamma delta T17 [gamma delta T cells that produce interleukin (IL)-17] cells, which corroborated our observations of increased gamma delta T17 cells observed in the oral tumors. Co-culture of gamma delta T cells with CD8 T cells in the presence of hypoxia showed that programmed cell death ligand 1 (PD-L1)(high) gamma delta T cells brought about apoptosis of programmed cell death 1 (PD-1)(high) CD8 T cells which could be significantly reversed upon blocking PD-1. Thus, future immunotherapeutic treatment modality for oral cancer may use a combined approach of blocking the PD-1/PD-L1 signaling and targeting hypoxia-inducible factor 1 alpha, which may help in reversing hypoxia-induced immunosuppression.