Biological Therapies for Cancer: Questions and Answers
7. What are monoclonal antibodies?
Researchers are evaluating the effectiveness of certain antibodies made in the laboratory called monoclonal antibodies (MOABs or MoABs). These antibodies are produced by a single type of cell and are specific for a particular antigen. Researchers are examining ways to create MOABs specific to the antigens found on the surface of various cancer cells.
To create MOABs , scientists first inject human cancer cells into mice. In response, the mouse immune system makes antibodies against these cancer cells. The scientists then remove the mouse plasma cells that produce antibodies, and fuse them with laboratory-grown cells to create "hybrid" cells called hybridomas. Hybridomas can indefinitely produce large quantities of these pure antibodies, or MOABs.
MOABs may be used in cancer treatment in a number of ways:
MOABs that react with specific types of cancer may enhance a patient's immune response to the cancer.
MOABs can be programmed to act against cell growth factors, thus interfering with the growth of cancer cells.
MOABs may be linked to anticancer drugs, radioisotopes (radioactive substances), other BRMs, or other toxins. When the antibodies latch onto cancer cells, they deliver these poisons directly to the tumor, helping to destroy it.
MOABs carrying radioisotopes may also prove useful in diagnosing certain cancers, such as colorectal, ovarian, and prostate.
Rituxan® (rituximab) and Herceptin® (trastuzumab) are examples of MOABs that have been approved by the FDA. Rituxan is used for the treatment of non-Hodgkin lymphoma. Herceptin is used to treat metastatic breast cancer in patients with tumors that produce excess amounts of a protein called HER-2. (More information about Herceptin is available in the National Cancer Institute (NCI) fact sheet Herceptin® (Trastuzumab): Questions and Answers, which can be found at http://www.cancer.gov/cancertopics/factsheet/Therapy/herceptin on the Internet.) In clinical trials, researchers are testing MOABs to treat lymphoma, leukemia, melanoma, and cancers of the brain, breast, lung, kidney, colon, rectum, ovary, prostate, and other areas.
8. What are cancer vaccines?
Cancer vaccines are another form of biological therapy currently under study. Vaccines for infectious diseases, such as measles, mumps, and tetanus, are injected into a person before the disease develops. These vaccines are effective because they expose the body's immune cells to weakened forms of antigens that are present on the surface of the infectious agent. This exposure causes the immune system to increase production of plasma cells that make antibodies specific to the infectious agent. The immune system also increases production of T cells that recognize the infectious agent. These activated immune cells remember the exposure, so that the next time the agent enters the body, the immune system is already prepared to respond and stop the infection.