Explainer: what is cancer immunotherapy?

Immunotherapy boosts the body’s ability to fight disease. Rob Schultz/Flickr, CC BY-NC

Immunotherapy is treatment that boosts the body’s immune system by producing more infection-fighting agents, such as white blood cells and antibodies, to help fight disease.

While it may seem a modern idea, its use in cancer treatment can be traced back to the 1890s. Dr William Coley was the first to try it when he injected bacteria into a cancer patient to stimulate her immune system to attack her bone cancer.

Since then we’ve developed more sophisticated ways to use immunotherapy including vaccinations, antibodies (proteins that bind to foreign objects to mark them for destruction), cytokines (molecules used in the body’s immune response) and colony-stimulating factors (proteins that stimulate the production of blood cells).

But while progress is being made, immunotherapy is not sufficient on its own and needs to be used in conjunction with other cancer treatments.

Vaccination

The best way to fight cancer is to prevent it forming in the first place. Some cancers are known to be caused by viruses and the development of vaccines means we can stop the infections before they have a chance to initiate the disease.

The best example of a vaccine as immunotherapy is one for human papilloma viruses (HPV). These viruses are known to cause some types of cervical cancer and are spread by sexual contact.

Australia has a policy of vaccinating girls against HPV when they are around 12 or 13 years old, before they become sexually active. More recently, the federal government has introduced a policy of vaccinating boys against HPV at around the same age.

Antibodies

Vaccines can cause patients to experience symptoms from irritation and pain at the injection site to allergic reactions. Nikita Kashner/Flickr, CC BY-NC-ND

Antibodies are a type of protein created by the body to help the immune system identify foreign and abnormal organisms, which can include cancers. They’re able to recognise specific markers located on the outer surface of cancer cells. Antibodies bind to these markers to either flag to the immune system that the cell should be destroyed, to stop the binding of signalling molecules or to prevent the uptake of essential nutrients into the cancer cells.

Antibody-based drugs are used particularly in treating breast cancer. One example is the drug trastuzumab (pronounced tras-tuz-u-mab), which recognises the human epidermal growth factor two (HER2) marker.

HER2 is a receptor that is over-expressed on the surface of some breast cancers and lead to an abnormally strong response to growth signals from the body. Cancers that are positive for the HER2 marker are very fast growing, even compared with other cancers.

Before trastuzumab is given to a breast cancer patient, the doctor will request immuno-screening of the tumour to see if the HER2 marker is over-expressed.

Cytokines

Cytokines are a large family of messenger molecules released by infected cells to warn surrounding cells. The release of these types of molecules by cells stimulates the immune system.

It’s now known that some types of cancers are able to actively suppress the immune system to help their growth and spread. Restarting the immune system by giving the patient cytokines can then help to slow or stop cancer growth.

These drugs are particularly useful in treating skin cancers. Two drugs called interferon-alpha and interleukin 2 signal to the body to make a type of white blood cell called a lymphocyte, which is able to destroy abnormally functioning cells.

Colony stimulating factors

These are proteins that stimulate bone marrow to produce more red and white blood cells. While this type of immunotherapy doesn’t attack cancer cells directly, the increase in blood cells means patients are generally able to better tolerate chemotherapy drugs and are less susceptible to infections.

Benefits and drawbacks

Unfortunately, cancer immunotherapy is not without its problems. Cancers are not an infection, they are cells from the body that have begun to work abnormally. This often makes it difficult for the immune system to differentiate between normal and cancerous cells, and many types of cancers don’t respond to immunotherapy.

Immunotherapy can also have side effects. Vaccines can cause patients to experience symptoms from irritation and pain at the injection site to allergic reactions.

Side effects from cytokine therapy include fever, chills, aches, depression, fatigue and fluid retention, and while these may not seem so bad, their intensity in some patients can be so high that treatment has to be stopped.

Because of these drawbacks, immunotherapy is rarely used as a stand-alone treatment and will generally be given in combination with radiotherapy or chemotherapy. But the application of cancer immunotherapy continues to grow as scientists better understand cancers at their microscopic level.