PD-1 and TIGIT blockade differentially affect tumour cell survival under hypoxia and glucose deprived conditions in oesophageal adenocarcinoma; implications for overcoming resistance to PD-1 blockade in hypoxic tumours

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PD-1 and TIGIT expression are highly expressed on the surface of oesophageal epithelial cells during the early stages of metaplasia.

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Glucose deprivation and hypoxia upregulate PD-1 and TIGIT on the surface of oesophageal adenocarcinoma (OAC) cells in vitro.

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PD-1 and TIGIT blockade decrease Bcl-2 and Bcl-xL expression in OAC cells.

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PD-1 blockade in OAC cells enhances basal respiration and glycolytic reserve and upregulates GLUT1 on the surface of a subpopulation of OAC cells.

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PD-1 inhibition confers a survival advantage to OAC cells under glucose deprivation and hypoxia.

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TIGIT blockade decreases OAC cell proliferation and induces OAC cell death under normoxia, hypoxia and nutrient deprivation.

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TIGIT blockade increases ECAR yet decreases a range of metabolic parameters in OAC cells.

Recent studies have demontrated that immune checkpoint receptors are expressed on the surface of oesophageal adenocarcinoma (OAC) cells and might confer a survival advantage. This study explores the role of PD-1 and TIGIT signalling in OAC cells in either promoting or inhibiting the survival of OAC cells under characteristic features of the tumour microenvironment including nutrient-deprivation and hypoxia. PD-1 and TIGIT are expressed in normal and pre-malignant oesophageal epithelial cells and this expression significantly decreases along the normal- Barrett's Oesophagus- OAC disease sequence. However, glucose-deprivation and hypoxia significantly upregulated PD-1 and TIGIT on the surface of OAC cells in vitro. PD-1 blockade decreased OAC cell proliferation under normoxia but enhanced proliferation and decreased cell death in OAC cells under hypoxia and glucose-deprivation. TIGIT blockade decreased proliferation and induced OAC cell death, an effect that was maintained under nutrient-deprivation and hypoxia. Basal respiration and glycolytic reserve were enhanced and GLUT1 was upregulated on the surface of a subpopulation of OAC cells following PD-1 blockade. In contrast, TIGIT blockade enhanced a glycolytic phenotype in OAC cells, yet decreased other metabolic parameters including oxidative phosphorylation and basal respiration. Interestingly, inhibition of oxidative phosphorylation significantly upregulated TIGIT expression and inhibition of oxidative phosphorylation and glycolysis significantly decreased PD-1 on the surface of a subpopulation of OAC cells in vitro. These findings suggest an immune-independent mechanism for PD-1 inhibitor resistance in hypoxic tumours and suggest that TIGIT might be a more effective therapeutic target in OAC compared with PD-1 for treating hypoxic tumours.