The field of immunotherapy traces its origins to the theories of a pioneering American surgeon, William Coley, in the late 19th century but has hit its stride only in the last decade. Though they cover a breadth of different approaches, targets and biological agents, all immunotherapies have this in common: they enlist the body’s own defense program, the immune system, in destroying, controlling and even preventing cancer. Tumor vaccines are one example of such immunotherapy. The most encouraging tumor vaccines used to treat active cancer consist of a patient’s own immune cells, armed to recognize that patient’s cancer and to kill it as well as to stimulate other immune cells to do the same. Such vaccines appear to spare the patient the collateral damage and unpleasant side effects associated with traditional cancer therapies.