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Immunotherapy is an emerging treatment that uses the body’s own immune system to destroy cancer cells, shrink tumors, treat symptoms, and possibly cure cancer. There are various ways to use the immune system to fight cancer, including strengthening the body’s immune system and adding synthetic immune system components. All types of immunotherapy involve the immune system, although some types are called biologic therapy or gene therapy.
For patients living with mesothelioma, immunotherapy may be used in conjunction with surgery, radiation, or chemotherapy. This treatment has helped some patients live longer and find relief from symptoms. However, there has been no proof that immunotherapy cures mesothelioma.
How the Immune System Works
The immune system is the biological system responsible for protecting the body from pathogens like viruses and bacteria. The immune system fights infections and prevents disease. This system also recycles and removes dead and damaged cells. From the moment of birth, the immune system recognizes foreign agents in the body. However, the immune system also develops as a person is exposed to pathogens. As a person ages, the immune system becomes more refined and learns to attack new agents.
The immune system includes several types of immune cells, including antibodies and cytokines. Antibodies are proteins that recognize antigens, which are compounds on the surfaces of infectious agents. Antibodies signal the immune system to attack a pathogen by recognizing antigens. Cytokines are also proteins which work to coordinate the immune response. Lymphocytes are immune system cells. B cells lymphocytes produce antigens, while T cells produce cytokines that clean up dead and diseased cells. Macrophages are large immune system cells that consume dead cells and cellular debris.
The immune system is essential for survival but is complicated and imperfect. In some people, the immune system damages and attacks healthy tissue for unknown reasons. This is often referred to as an autoimmune disorder. Examples include rheumatoid arthritis and multiple sclerosis.
What is Immunotherapy?
Immunotherapy is a cancer treatment strategy that uses the body’s immune system to fight cancer cells. There are two main ways this is done. The first is by stimulating the immune system to make it work harder or to target cancer cells specifically. Another is by adding immune system components to instigate an attack on cancer cells. The treatment may be specific, encouraging immune cells to target one type of cancer cell or general, boosting the actions of the immune system overall.
The immune system produces proteins called antibodies that circulate in the body, attaching to antigens wherever they encounter them. Once attached to the antigens, the antibodies recruit other cells to fight the invader. Antibodies can be created in the lab to specifically target an antigen. If cancer researchers know what antigen is present on the cancer, they can design an antibody to trigger the immune system to attack the cancer cells. Antibodies created in this way are known as monoclonal antibodies.
Monoclonal antibodies work better for some types of cancer than others. It is important to identify an antigen, but this is not always easy. For mesothelioma, a possible targeted antigen is mesothelin. Using monoclonal antibodies is not a cure for mesothelioma. However, they can be used in conjunction with other treatments, like surgery. The strategy can be more effective for some patients than others.
Vaccines are manipulated pathogens, like viruses, administered to prevent illness. For instance, millions of people get the flu vaccine each year. The flu vaccine uses inactivated flu viruses to stimulate the immune system to recognize and attack the active flu virus to prevent infection. Cancer vaccines work in a similar manner. They are used to stimulate the immune system to attack cancer cells so as to actively treat the cancer or prevent regrowth of tumors after remission.
Immune Checkpoint Modulators
The immune system should be able to distinguish between healthy cells and pathogens. To distinguish between the two, certain molecules on immune cells must be activated to attack pathogens. Cancer cells can develop molecular strategies to get around these checkpoints, effectively avoiding attack from immune system cells. One emerging immunotherapy strategy targets checkpoints with specially-designed drugs. One drug, atezolizumab, has been successful in treating lung cancer.
A passive approach to immunotherapy involves using strategies to boost the immune system without specificity. This approach is often called non-specific immunotherapy. These strategies may be used alone, with other types of immunotherapy, or with other types of cancer treatments.
One passive strategy is to inject the body with cytokines, immune system proteins that promote the growth and development of immune cells. There are also synthetic drugs that boost the immune system, although how they work is not fully understood.
There is also a type of bacterium that can be used to boost the immune response. BCG, or Bacille Calmette-Guérin, is commonly used in bladder and skin cancers. A solution of the bacteria is injected into the bladder, attracting immune cells which then attack the cancer. There were studies in the 1970’s to 1980’s looking at the possible effectiveness in treating other cancers. It is not currently used to treat mesothelioma unless as part of a clinical trial. BCG does not cause infections in people, although does stimulate inflammatory symptoms. These are similar to flu symptoms and are relatively mild.
BCG has been tested in mesothelioma patients. In one study, the treatment helped prevent pleural effusions, the buildup of fluid in the chest cavity. Another study involved mesothelioma patients who had undergone a thoracotomy. These patients received regular injections of BCG after the surgery. Results of the study showed this treatment could significantly reduce symptoms.
Immunotherapy for Mesothelioma
Using immunotherapy to treat mesothelioma has been tricky. For instance, targeting antigens is difficult because mesothelioma cells seem to produce few antigens. Mesothelin is one of the few recognized, but it is not produced in all cases of mesothelioma. BCG showed some success in early studies, but has not become a regular treatment for mesothelioma.
Immunotherapy continues to be a promising line of treatment. Continuing research should lead to developments that help more patients with cancer, specifically those with mesothelioma. Boosting the immune system seems to have some impact on patient outcome. However, to have a positive effect, immunotherapy often must be used with other treatments. As research continues, more advances should be found, giving patients hope and comfort as they fight mesothelioma.
Page Medically Reviewed and Edited by Anne Courtney, AOCNP, DNP
Anne Courtney has a Doctor of Nursing Practice degree and is an Advanced Oncology Certified Nurse Practitioner. She has years of oncology experience working with patients with malignant mesothelioma, as well as other types of cancer. Dr. Courtney currently works at University of Texas LIVESTRONG Cancer Institutes.