FIGURE 1.

Variable interactions among immune checkpoints in the TME. There are many immune checkpoints in the TME. Some of them are expressed mainly on T cells including PD‐1, CTLA‐4, and LAG‐3, which could suppress the function of CTLs. The others are mainly expressed on myeloid cells, such as c‐Rel and MerTK, which could enhance the inhibitory function of MDSCs to tumor cells. Abbreviations: TME: tumor microenvironment; CTLs: cytotoxic T lymphocytes; IL: interleukin; CD: cluster of differentiation; MHC: major histocompatibility complex; PD‐1: programmed cell death‐1; PD‐L1: programmed cell death‐Ligand 1; PD‐L2: programmed cell death‐Ligand 2; CTLA‐4: cytotoxic T lymphocyte‐associated antigen 4; VISTA: V‐domain immunoglobulin suppressor of T cell activation; TIGIT: T cell immunoglobulin and ITIM domain; TIM‐3: T cell immunoglobulin and mucin domain‐containing protein 3; LAG‐3: lymphocyte activation gene‐3; ATP: adenosine triphosphate; AMP: adenosine monophosphate; GPI: glycosylphosphatidylinositol; SIRPα: signal regulatory protein α; SIGLEC‐15: sialic acid binding Ig‐like lectin 15; GM‐CSF: granulocyte‐macrophage colony stimulating factor; IL‐RAcP: interleukin‐1 receptor accessory protein; ST2: suppression of tumorigenicity 2; MERTK: c‐mer proto‐oncogene tyrosine kinase; GAS6: growth arrest specific 6; PtdSer: phosphatidylserine; TCR: T cell receptor; SIGLEC‐10: sialic acid binding Ig‐like lectin 10; VSIG‐3: V‐set and immunoglobulin domain‐containing protein 3; LGALS9: galectin‐9; DAP12: DNAX‐activation protein 12; sTn: sialyl‐Tn; PI3K: phosphoinositide 3‐kinase; ARG1: arginase‐1; NOS2: nitric oxide synthase 2