Immune checkpoint proteins are regulators of the immune system that prevent foreign antigens and preferably the host’s immune cells from attacking, thereby regulating self-tolerance, immune homeostasis and prevent autoimmunity.
The checkpoint proteins can send two types of signals to express these immune responses
1. Co-stimulatory checkpoints deliver positive signals to T cells following their binding to ligands and receptors on antigen-presenting cells (APCs). They can stimulate immune responses, including CD27, CD40, OX40, GITR, 4-1BB, CD28, ICOS and many more.
2. Co-inhibitory checkpoints deliver negative signals to T cells upon interaction with their counterparts on the APCs. They can inhibit immune responses, including PD1, PD-L1, CTLA-4, VISTA, CD155/TIGIT, TIM-3, and more.