The immune system contains a number of cell types, such as [[NK cells]] and [[cytotoxic T cell|killer T cells]] that have the capability to destroy other cells that have become infected with viruses or have become cancerous. [[Immunotherapy]] involves the enhancement or potentiation of these natural defenses against tumor cells. | The immune system contains a number of cell types, such as [[NK cells]] and [[cytotoxic T cell|killer T cells]] that have the capability to destroy other cells that have become infected with viruses or have become cancerous. [[Immunotherapy]] involves the enhancement or potentiation of these natural defenses against tumor cells. |