What is the immune system?

The human body’s immune system is a complex network of biological structures and processes which has evolved to combat foreign biological, chemical, and physical threats. It operates down to the molecular level via chemical interactions within and between cells. The immune system is always active, monitoring the body for damage (such as a cut in the skin) as well as for infectious agents (such as bacteria and viruses). A person’s health is critically dependent on their immune system’s ability to identify threats, repair damage, and kill invaders.

What is immunotherapy?

The immune system is very powerful—so powerful, in fact, that it can sometimes overreact to a perceived threat and actually damage the body itself. (For example, if a person with a peanut allergy is exposed to peanuts, their body’s immune response may be so strong as to be life-threatening.) In most cases, however, the immune system’s built-in feedback mechanisms restrain its responses after a threat has been addressed.

For decades scientists and physicians have searched for ways to harness the power of the body’s immune system to fight disease, especially cancer. Immunotherapy refers to medical treatments that modify the immune system’s response to achieve better treatment results. Treatments may include special drugs, modified cells, or manmade proteins. Immunotherapy is rapidly emerging as a potent treatment option for metastatic cancer. Metastatic cancer is cancer that has spread to a different part of the body. A wide distribution of many cancers within the body is difficult to treat using surgery or radiation therapy because those approaches are primarily effective at removing or killing tumors that remain confined to a smaller region of the body.

How does radiation interact with the immune system and immunotherapy?

It is known that radiation can suppress or stimulate the immune system. Radiation is very efficient at destroying cancer cells, and the immune system is often suppressed at the same time because the cells responsible for mounting an immune response are also destroyed. However, there have been several documented cases of a patient treated with radiation mounting a very strong anti-cancer immune response. In these cases, not only did the patient’s treated cancer disappear, but other untreated cancers in their body also disappeared.

The molecular mechanisms behind radiation-triggered anti-cancer immune response is an active area of clinical research. It is now understood from studies in mice that daily radiation dose and total radiation dose are important factors in whether radiation stimulates the immune system instead of suppressing it. There is also recent evidence that some types of radiation may be more effective than others in stimulating an immune system anti-cancer response.

In recent studies, radiation has been combined with immunotherapy and chemotherapy in an effort to find new ways to treat cancers that are widespread in the body. There are indications that combining radiation with immunotherapy drugs may further enhance the body’s anti-cancer immune response. One exciting future possibility of such treatments is that patients may not only recover from their cancer, but also maintain a persistent “cancer immunity” as though they had received a vaccine against their particular cancer.

Given the early and highly variable nature of recent study results, researchers are examining their data in an effort to determine which patients are most likely to exhibit a beneficial immune response following radiation treatment and how best to deliver the radiation to achieve that beneficial response. At present we do not fully understand how radiation activates the body’s immune response. However, our knowledge is growing and there is hope and excitement that a deeper understanding of combined radiation and immunotherapy may lead to another breakthrough in cancer treatment.

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