Figure 1.

Immune checkpoint proteins impair proliferation and multi-functionality of T cells. Interaction between immune checkpoint markers and their ligands transmits inhibitory signals to CD4⁺ and CD8⁺ T cells. These inhibitory signals limit TCR- and CD28-mediated co-stimulatory pathway, including the NF-κB, NFAT, and AP-1 signaling pathways, which suppress proliferation, cytokine production, and cytotoxic response. IC blockers are able to cause ligand dissociation from the ICs and restore T cell activation.