What are checkpoint inhibitors?

Checkpoint inhibitors seek to overcome one of cancer’s main defenses against an immune system attack. Immune system T cells patrol the body constantly for signs of disease or infection. When they encounter another cell, they probe certain proteins on its surface, which serve as insignia of the cell’s identity. If the proteins indicate the cell is normal and healthy, the T cell leaves it alone. If the proteins suggest the cell is infected or cancerous, the T cell will lead an attack against it.
Tumor cells often wear proteins that reveal the cells’ cancerous nature. But they sometimes commit what amounts to identity theft, arraying themselves in proteins of normal cells. Recent research has shown that cancer cells often utilize immune checkpoint molecules to suppress and evade an immune system attack. T cells, deceived by these normal-looking proteins, may allow the tumor cell to go unmolested.

Checkpoint inhibitors block these normal proteins on cancer cells, or the proteins on T cells that respond to them. The result is to remove the blinders that prevented T cells from recognizing the cells as cancerous and leading an immune system assault on them.