For more than 30 years, doctors have been trying to rally the weakened immune systems of cancer patients to fight the disease. Only recently, however, have therapies been developed that bring some of the body's own most potent weapons to bear in the struggle to repel invaders ranging from cancer to the AIDS virus. Those weapons include antibodies, tumor-killing blood cells and the chemical messengers that regulate them.
One promising approach is the use of interleukin-2, one of the proteins called lymphokines, which are produced by the immune system. IL-2 is now being administered in various ways to stimulate the white...