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A vaccine stimulates the immune system to produce antibodies to fight a disease. Most vaccines are used to prevent infectious diseases caused by viruses, such as the flu, measles or polio. Cancer vaccines are used to:
Most cancer vaccines are still being studied in clinical trials.
Prophylactic cancer vaccines are used to prevent viral infections associated with the development of cancer. They are designed to stimulate the immune system to attack certain viruses before they cause an infection. These vaccines are given to healthy people before cancer develops.
Examples of prophylactic cancer vaccines approved for use in Canada include:
Prophylactic vaccines commonly use proteins on the surface of the virus (antigensantigensA foreign substance that stimulates the immune system to produce antibodies against it.) to trigger an immune system response against the virus.
Therapeutic vaccines are designed to stimulate the body to produce an immune response against cancer cells, rather than prevent viral infections. Therapeutic vaccines may contain whole or parts of cancer cells. They may also contain whole antigens or parts of antigens from cancer cells. The vaccine triggers an immune response against the specific cancer cells present in the body. It activates certain white blood cells, including T cells and B cells. These activated cells either directly kill cancer cells or produce antibodies against them.
Bacillus Calmette-Guérin (BCG) vaccine is an example of a therapeutic vaccine. It is used to treat bladder cancer. Researchers are studying many other types of therapeutic vaccines. These vaccines may eventually be used to treat a particular type of cancer, prevent it from recurring or destroy cancer cells that are not killed by other treatments.
Whole tumour cell vaccines are made from cancer cells collected during a biopsybiopsyThe removal of cells or tissues for examination under a microscope. or surgery. Before they are injected back into the person, the cancer cells are killed with radiation so that they will not form more tumours. Antigens are still present on the surface of the cells and will stimulate an immune response. The immune system recognizes and attacks cancer cells containing these antigens.
Whole tumour cell vaccines may be made from a person’s own tumour cells that were removed (autologous vaccine). Autologous vaccines are custom made for each person. It is often difficult to get enough tumour cells from one person to make a vaccine. Therefore, tumour cells taken from other people who have the same type of cancer are often used to make the vaccine (allogeneic vaccine).
Antigen vaccines use specific proteins or parts of proteins (antigens) from the surface of cancer cells to stimulate the immune system to fight these cells. Cancer cell antigens are sometimes mixed with substances to help the vaccine work better. These substances are called adjuvants. Adjuvants help the body recognize the cells as being foreign, so they boost the immune response. CytokinesCytokinesA substance made by cells of the immune system. Cytokines allow immune system cells to communicate with each other and thus help carry out the body’s immune response (the immune system’s reaction to the presence of foreign substances in the body)., such as interleukin-2interleukin-2A group of natural hormone-like substances produced by white blood cells (which help the body fight infection and diseases)., are a type of adjuvant. The person with cancer is vaccinated with the mixture of cancer cell antigens and adjuvants. The immune system responds to both the adjuvant and the cancer cells that have the antigen.
Some antigen vaccines cause an immune response to a certain cancer. Others produce immune reactions to more than one kind of cancer.
Researchers are looking at ways of changing antigens so that the immune system can recognize them more easily. They are also studying combinations of several antigens in one vaccine to see if it will cause a response to different antigens that may be present on cancer cells.
An idiotype is the part of an antibody that determines the specific antigen the antibody will act against. Anti-idiotype vaccines trigger an immune system response in almost the same way as antigen vaccines. They stimulate the body to produce antibodies against cancer cells. These antibodies act like cancer cell antigens. When the vaccine is injected, it stimulates the immune system to recognize antigens on the cancer cells. B cells then produce antibodies against the cancer cell antigens.
Dendritic cells are a type of white blood cell that helps fight infection by producing signals (antigens) to boost the immune response. A dendritic vaccine uses cancer cells mixed with dendritic cells to stimulate the immune system.
Dendritic cell vaccines are custom made for each person. Some dendritic cells are removed from a person’s blood and are treated to make them reproduce quickly. The cells are exposed to the cancer cell antigen or their genetic makeup is changed so that they make the antigen. The dendritic cells are then injected back into the person. They help the immune system recognize and destroy cancer cells that have the antigen.
The effect of a cancer vaccine often becomes weaker as time goes by because the immune system eventually returns to its normal state of activity. Researchers are studying whether vaccines containing DNADNAThe molecules inside the cell that program genetic information. DNA determines the structure, function and behaviour of a cell. can help the body maintain the immune response longer by providing it with a steady supply of antigens.
DNA inside cancer cells contains the genetic code for the proteins (antigens) that they make. Bits of DNA that contain the genetic instructions for one or more antigens may be used to make the vaccine. The DNA for the vaccine is made in the laboratory, sometimes using a person’s own cells. After a DNA vaccine is injected into a person, cells take up the DNA. These cells now have the instructions to make the specific cancer cell antigen. This constant supply of antigen keeps the immune system actively fighting the cancer cells.
Although researchers have made advances in the development of anti-cancer vaccines, considerable work still needs to be done.
It is not completely known how the body’s immune system will respond to therapeutic cancer vaccine treatment. Long-term side effects of these cancer vaccines are not known. Researchers are also studying ways that cancer vaccines can be used together with other treatments, such as other biological therapies, to boost the immune response.
Researchers are studying other prophylactic cancer vaccines that may have the potential to reduce the risk of certain types of cancer by attacking cancer-causing viruses.
For more detailed information on specific drugs, go to sources of drug information.