Definition

A type of protein found on some immune cells, such as T cells and antigen-presenting cells, and some cancer cells. These proteins help keep the body’s immune response from being so strong that it harms healthy cells. Some immune checkpoint proteins on T cells bind with partner immune checkpoint proteins on cancer cells, which signals the T cells to stay in an inactive state, preventing them from killing the cancer cells. Drugs that block these proteins can help T cells find and kill cancer cells and are being used in the treatment of some types of cancer. Examples of immune checkpoint proteins are PD-1 and CTLA-4 on T cells and PD-L1 on some cancer cells.