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The Immune System Recognizes Cancer
How does the immune system recognize cancer? Although much has been learned about interactions between the immune system and cancer, many questions remain unanswered. We know that in order to fight off colds or flu, our immune system must recognize the foreign proteins (antigens) produced by these infections. The same is true for cancer. Some cancers are capable of inducing a measurable immune response, but this response may not be sufficient to prevent tumor growth. Cancers may grow in spite of a normal immune system for several reasons. One potential reason is that cancers are not very immunogenic, meaning they don’t stimulate immune system recognition despite being composed of abnormal cells. Cancers may also suppress the immune system directly.

We do have clues that vigorous immune responses may be protective against some types of cancer. Evidence comes from studies in both mice and humans using different immune-stimulating chemicals. For example, if antibodies are made to bind to cancer antigens, the tumor may become more recognizable for immune destruction. An example of this is the monoclonal antibody Herceptin(r) (trastuzumab). This is an antibody against HER-2/neu, an antigen present in overabundance in some breast cancers and other tumors. Trastuzumab has been found to be an effective treatment for this kind of breast cancer when used either with chemotherapy or alone. There are several ways in which trastuzumab is thought to work, one of which is by increasing immune recognition. Similarly, T cells can directly recognize an antigen on a tumor cell and may assist in destruction of that cell. 		SEM of T Cell Attacking Tumor
Cytotoxic Lymphocyte Destroying a Tumor Cell. ©
John Ding-E Young, Chau-Ching Lin, and Gilla Kaplan
authors. Licensed for use, ASM MicrobeLibrary.org.
We know that tumor antigens exist. Some cancer cells make abnormal or excessive amounts of protein that can serve as a tumor antigen. One example of tumor antigen used in our studies is HER-2/neu (also known as c-erbB-2).

In the picture to your right, the outer membrane of the tumor cell (right) has been shot full of holes by a protein, perforin, secreted from the cytotoxic cell (left). The tumor target cell has become leaky and an influx of water has made it expand in volume; it has also lost many of its surface villi. In addition, there is a large cavity in the membrane of the tumor target cell.
Page last updated 3/25/09