How Immunotherapy Works

How Immunotherapy Works. Illustration of Keytruda in the immune system.
Mode of Action

Understanding Immunotherapy1

The use of immunotherapy drugs (“immuno-oncology” or “cancer immunotherapy”) represents a recent development in the fight against cancer. Immunotherapy uses certain parts of a person’s immune system to fight diseases such as cancer, this can be done in a number of ways:

  • Stimulating the patient’s immune system to work harder and smarter to attack cancer cells.
  • Improving the patient’s immune system by introducing different immune system components that are produced in a laboratory setting.

Immune checkpoint inhibitors 2

Immune checkpoint inhibitors function by helping to take the ‘brakes’ off the immune system, this allows the immune system to recognise and attack the cancer cells.

How immune checkpoint inhibitors work2

An important part of the immune system is its ability to tell between normal cells in the body and those it sees as “foreign”. This lets the immune system attack the foreign cells while leaving the normal cells alone.

To do this, it uses “checkpoints” – molecules on certain immune cells that need to be activated (or inactivated) to start an immune response.

Cancer cells sometimes find ways to use these checkpoints to avoid being attacked by the immune system. Immunotherapy drugs target these checkpoints.


  1. American Cancer Society How Immunotherapy Is Used to Treat Cancer. Last accessed April 2022
  2. American Cancer Society Immune Checkpoint Inhibitors and Their Side Effects (cancer.org) Last accessed April 2022