Fig. 1

Immunoregulatory checkpoints in the tumor microenvironment. Illustration of immunoregulatory checkpoints in the tumor microenvironment, detailing cell interactions. T cells, with receptors like PD-1 and CTLA-4, mainly receive inhibitory signals from APC and tumor cell ligands such as PD-L1. Conversely, receptors like CD28 on T cells interact with ligands like CD80/86 on APCs, initiating activation. NK cells are controlled by activating receptors such as 4-1BB and inhibitory receptors like NKG 2A, which interact with HLA-E on tumor cells. Tumor cells themselves express ligands like PD-L1 to inhibit T-cell function and CD47 to evade immune clearance. Naive T cells show CD27 as a primary activation marker. Arrows indicate the direction of interaction between ligands and their corresponding receptors: solid for stimulation and dashed for inhibition