Knowledge of how the immune system operates has produced two fundamental benefits: (1) an understanding of the cause and progression of many diseases and (2) the development or proposed development of methods to prevent, stop, or even reverse diseases.
Immunotherapy treats disease by altering immune systemfunction or by directly attacking harmful cells. Some approaches attempt to boost immune system function in general. For example, administering cytokines or other agents can promote inflammation and activate immune cells, which can help destroy tumor cells. On the other hand, sometimes inhibiting the immune system is help-ful. For example, multiple sclerosis is an autoimmune disease in which the immune system treats self-antigens as foreign antigens, destroying the myelin that covers axons. A type of cytokine called interferon beta blocks the expression of MHC molecules that dis-play self-antigens and is used to treat multiple sclerosis.
Some immunotherapy takes a more specific approach. For example, vaccination can prevent many diseases (see “Acquired Immunity”). The ability to produce monoclonal antibodies can result in effective therapies for treating tumors. If an antigen unique to tumor cells can be found, then monoclonal antibod-ies can be used to deliver radioactive isotopes, drugs, toxins, enzymes, or cytokines that kill the tumor cell directly or activate the immune system to kill the cell. Unfortunately, so far researchers have found no antigen on tumor cells that is not also present on normal cells. Nonetheless, this approach can be useful if damage to normal cells is minimal.
Some uses of monoclonal antibodies to treat tumors are yield-ing promising results. For example, monoclonal antibodies with radioactive iodine (131I) have been found to cause the regression of B-cell lymphomas while producing few side effects. Herceptin, a monoclonal antibody, binds to a growth factor receptor that is overexpressed in 25–30% of primary breast cancers. The antibody “tags” cancer cells, which are then lysed by natural killer cells. Herceptin slows disease progression and increases survival time, but it is not a cure for breast cancer.
Many other immunotherapy approaches are being studied, and more treatments that use the immune system are sure to develop in the future.