What is immunotherapy?
Immunotherapy, also called biological therapy, is a type of treatment that uses the body's immune system to fight cancer. The therapy mainly consists of stimulating the immune system to help it do its job more effectively. Immunotherapy is a comparatively new type of therapy in the fight against many cancers. Much of this therapy is still in clinical trials.
To help understand the role that biological agents play in cancer treatment, some understanding of how the normal immune system works is helpful.
How the immune system works
The immune system is a complex network of cells and organs that work together to defend the body against foreign substances (antigens), such as bacteria, viruses, and cancer cells. When the body discovers such a substance, several kinds of cells go into action in what is called an immune response. Below is a description of some of the cells that are part of the immune system:
- Lymphocytes: Lymphocytes are one of the main types of immune cells. They are divided mainly into B and T cells. B lymphocytes produce antibodies – proteins (gamma globulins) that recognize antigens and attach themselves to the substances. Each B cell is programmed to make one specific antibody. When a B cell comes across its triggering antigen, it gives rise to many large cells known as plasma cells. Each plasma cell is essentially a factory for producing an antibody. An antibody matches an antigen much like a key matches a lock. Whenever the antibody and antigen interlock, the antibody marks the antigen for destruction. B cells are powerless to penetrate the cell, so the job of attacking these target cells is left to T lymphocytes.
- T lymphocytes: T lymphocytes are cells that are programmed to recognize, respond to, and remember antigens. T cells contribute to the immune defenses in two major ways. Some direct and regulate the immune responses. When stimulated by the antigenic material presented by the macrophages, the T cells make lymphokines that signal other cells. Other T cells are able to destroy targeted cells on direct contact.
- Dendritic cells: Dendritic cells are known as the most efficient antigen-presenting cell type, with the ability to interact with T cells and initiate an immune response. Dendritic cells are receiving increasing scientific and clinical interest because of their key role in the immune response and potential use with tumor vaccines.
- Granulocytes: There are three types of white blood cells, known as granulocytes, which are part of the immune response. Neutrophils are the most common white blood cells in the body. With an infection, their number increases rapidly. They are the major components of pus and are found around most common inflammations. Their job is to eat and destroy foreign material. Basophils and eosinophils interact with certain foreign materials. Their increased activity may lead to an allergic reaction.
The immune response is a coordinated effort. All of the immune cells work together, so they need to communicate with each other. They do this by secreting a large number of special protein molecules, called cytokines, which act on other cells. There are many different cytokines. Examples of these are interleukins, interferons, tumor necrosis factors, and colony-stimulating factors. Some immunotherapy treatment strategies involve giving larger amounts of these proteins by an injection or infusion. This is done in the hope of stimulating the cells of the immune system to act more effectively or to make the tumor cells more recognizable to the immune system.
Caution: There are people who promote unproven therapies as immune system boosters. Be careful when evaluating these claims.
Types of immunotherapy
The following are types of immunotherapies that are commonly and legitimately used in traditional and scientific medical practice.
- Biological response modifiers: Biological response modifiers are substances that have no direct anti-tumor effect, but are able to trigger the immune system to indirectly affect tumors. These include cytokines such as interferons and interleukins. As mentioned above, this strategy involves giving larger amounts of these substances by injection or infusion in the hope of stimulating the cells of the immune system to act more effectively.
- Colony-stimulating factors: Blood cells are produced in the body's bone marrow (the soft, sponge-like material found inside bones). There are three major types of blood cells: white blood cells, which fight infection; red blood cells, which carry oxygen to and remove waste products from organs and tissues; and platelets, which enable the blood to clot. Cancer treatments such as chemotherapy and radiation therapy can affect these cells, putting the patient at risk for developing infections, anemia, and bleeding problems. Colony-stimulating factors are substances that stimulate the production of blood cells. They do not directly affect tumors, but through their role in stimulating blood cells, they can be helpful in supporting the person's immune system during cancer treatment.
- Tumor vaccines: Researchers are developing vaccines that may encourage the patient's immune system to recognize cancer cells. In theory, these work in a similar way as vaccines for measles, mumps, and smallpox. The difference in cancer treatment is that vaccines are used after someone has cancer. The vaccines would be given to prevent the cancer from returning or to get the body to reject tumor lumps. This is much more difficult than preventing a viral infection. The use of tumor vaccines continues to be studied in clinical trials.
- Monoclonal antibodies: Monoclonal antibodies are laboratory-produced substances that can locate and bind to certain proteins. They do this by reacting against tumor-associated proteins on the surface of certain cells. These antibodies can be used to see where the tumor is in the body (detection), or as therapy to deliver drugs, toxins, or radioactive material directly to a tumor. Monoclonal antibodies can be given to target particular molecules on the cell surface. Examples of these antibodies are rituximab to target lymphoma cells and herceptin to target cells, including breast cancer cells.