ervation. He made deliberate attempts to infect cancer patients with bacteria and later devised a vaccine consisting of killed bacteria to prompt a tumor-killing response (Old, 1999). These treatments-which we would now consider immunotherapies because they aimed to attack disease with the body's own defenses-brought about complete tumor regressions in some individuals. But they were not broadly accepted because the results were unpredictable. Although the idea of fortifying or stimulating the immune system to fight cancer has been around for many years, new technologies and a better understanding of immune-system mechanisms have worked together !
             to cause an explosion of research and development in industry, government, and major universities (NIH, 1995).
             Components of the immune system that are capable of recognizing cancer cells have been identified in patients with certain cancers. In the laboratory, it has been found that cells of the immune system can kill tumor cells. Even more convincing are clinical re
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