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What is a cancer vaccine?
The idea of a cancer vaccine began with the observations of William Coley, a surgeon at Sloan-Kettering Cancer Center in the late 19th century. Dr. Coley noted that rare cases of spontaneous cancer regression occurred in patients with previous infectious episodes. It seemed that the infection had stimulated the immune system to attack the cancer as well as the infectious agent. In order to stimulate the immune system, the antigen must be present on the surface of the infectious agent (bacterium) where it can be detected. This understanding led to a search for unique antigens present on the surface of cancer cells that are not present on normal cells. This search is more challenging than is the case for infectious agents, since there are few structural differences between cancer and normal cells. Problems in developing a cancer vaccine A cancer vaccine is an attractive concept, since it is viewed as a natural process, namely, the mobilization of the body's immune system to fight the cancer. It holds promise to destroy the errant cancer cells remaining in the body after previous treatments. However, the field has been marked by continuous failures to develop effective vaccines in spite of extensive research. This article is an update on my previous article on cancer vaccines, and focuses on the problems in developing cancer vaccines, and new approaches that appear promising. Antigen Immunogenicity 1 Laboratory procedures are available to detect antigens in vitro (laboratory apparatus), or in animals, but they provide no direct evidence for their value in stimulating an immune response in humans. Furthermore, there can be a striking heterogeneity in immune responses to an antigen among patients. Finally, researchers found that simply because an antigen stimulates an immune response does not mean that this response results in a protective effect against the tumor. Stimulating the immune response 2 In the 1990's, researchers realized that the presence of an antigen by itself is not sufficient to elicit an immune response. The focus instead was directed towards the components of the immune system known as dendritic cells and cytotoxic CD8 lymphocytes. Dendritic cells are few in number, but perform an essential role. They engulf and break down foreign substances and present antigens on their surfaces. This antigen presentation stimulates the CD8 cells to attack the cancer cells directly, or to secrete substances such as interferon that activate CD4 helper cells or other components of the immune system. The activated immune system reinforces itself enhancing the immune response. The task of the researcher is to improve on the weak immune response typically seen in the cancer condition.
The copyright of the article Can Effective Cancer Vaccines be Developed? in Cancer Treatment is owned by . Permission to republish Can Effective Cancer Vaccines be Developed? in print or online must be granted by the author in writing.
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