PDCD1 and cancer: Moreover, the activation of adenosine/A2AR signalling promoted Treg cell proliferation and the secretions of immune-suppressive factors (including TGFβ and IL-10) and upregulated the expression of immune-checkpoint receptors (such as PD-1, CTLA4 and LAG3), which mediated immunosuppression TME in tumor tissue and immune escape of cancer cells [74–76].