Figure 2.

The suppression of antitumor immunity activated by the PD-1/PD-L1 pathway in the tumor microenvironment (TME) of lung cancers. The core of this network is tumor-specific T cells. The PD-1 protein is expressed both on activated T cells by the combination of major histocompatibility (MHC) complex with T cell receptor (TCR), and also exhausted CD8⁺ T cells (Tex). PD-L1 is expressed on various immune cells and stromal cells in TME. The engagement of the PD-1/PD-L1 pathway facilitates the transformation of Texs and the differentiation of regulatory T cells (Treg). Meanwhile, the secretion of IFN-γ by infiltrating immune cells mentioned in the figure upgrades the expression of the PD-L1 protein.