What is Immune Checkpoint

Fig. 1 Schematic diagram of immune checkpoint interaction

Immune checkpoint is a kind of signal for regulating the antigen recognition of T cell receptor (TCR) in the process of immune responce. Immune checkpoint contains two kinds of signals:
(1) Co-stimulatory immune checkpoint: stimulating immune progress, such as CD28, ICOS, and CD137;
(2) Co-inhibitory immune checkpoint: inhibiting immune progress, such as PD1, CTLA-4, and VISTA.
When immune system is attacking pathogens, these immune checkpoint molecules can protect the normal tissues from damage. The cancer cells cleverly escape from immune attack by dysregulating immune checkpoint related proteins. Immune checkpoint therapy relys on functioning immune system with agonists of co-stimulatory signals or antagonists of inhibitory signals.
Over these years there are two immune checkpoint receptors that have been actively studied: cytotoxic T-lymphocyte-associated antigen 4 (CTLA4; also known as CD152) and programmed cell death protein 1 (PD1; also known as CD279). The corresponding antibodies can inhibit the functioning of the receptors and enhance antitumour immunity. Furthermore, multiple additional immune checkpoints, representing promising targets for anti-cancer therapy are under active development, more therapies based on immune checkpoint for more cancers are on the way to the market.

What is Immune Checkpoint: Reference

Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012; 12:252–64.
Christopher J. Nirschl and Charles G. Drake. y. Molecular Pathways: Coexpression of Immune Checkpoint Molecules: Signaling Pathways and Implications for Cancer Immunotherapy. Clin Cancer Res; 19(18); 4917–24.