What are cancer vaccines?
Cancer vaccines belong to a class of substances known as biological response modifiers. Biological response modifiers work by stimulating or restoring the immune system’s ability to fight infections and disease. There are two broad types of cancer vaccines:
Preventive (or prophylactic) vaccines, which are intended to prevent cancer from developing in healthy people
Treatment (or therapeutic) vaccines, which are intended to treat an existing cancer by strengthening the body’s natural immune response against the cancer. Treatment vaccines are a form of immunotherapy.
Two types of cancer preventive vaccines (human papillomavirus vaccines and hepatitis B virus vaccines) are available in the United States, and one treatment vaccine (for metastatic prostate cancer) is available.
How do cancer preventive vaccines work?
Cancer preventive vaccines target infectious agents that cause or contribute to the development of cancer. They are similar to traditional vaccines, which help prevent infectious diseases, such as measles or polio, by protecting the body against infection. Both cancer preventive vaccines and traditional vaccines are based on antigens that are carried by infectious agents and that are relatively easy for the immune system to recognize as foreign.
Most preventive vaccines, including those aimed at cancer-causing viruses (hepatitis B virus and human papillomavirus), stimulate the production of antibodies that bind to specific targeted microbes and block their ability to cause infection.
How are cancer treatment vaccines designed to work?
Cancer treatment vaccines are used to treat cancers that have already developed. They are intended to delay or stop cancer cell growth; to cause tumor shrinkage; to prevent cancer from coming back; or to eliminate cancer cells that have not been killed by other forms of treatment.
Cancer treatment vaccines are designed to work by activating cytotoxic T cells and directing them to recognize and act against specific types of cancer or by inducing the production of antibodies that bind to molecules on the surface of cancer cells. To do so, treatment vaccines introduce one or more antigens into the body, usually by injection, where they cause an immune response that results in T cell activation or antibody production. Antibodies recognize and bind to antigens on the surface of cancer cells, whereas T cells can also detect cancer antigens inside cancer cells.
Producing effective treatment vaccines has proven more difficult and challenging than developing cancer preventive vaccines. To be effective, cancer treatment vaccines must achieve two goals. First, like preventive vaccines, cancer treatment vaccines must stimulate specific immune responses against the correct target. Second, the immune responses must be powerful enough to overcome the barriers that cancer cells use to protect themselves from attack by killer T cells.