William B. Coley is often credited with first recognizing the potential role of the immune system in cancer treatment. Coley, an early twentieth-century New York City surgeon, observed that some of his patients with sarcoma underwent spontaneous regression of their tumor. He associated this tumor regression with preceding bacterial infection. Coley was the first physician to exploit the power of the immune system to fight cancer. He deliberately infected cancer patients with bacteria and actually developed a vaccine consisting of killed bacteria to attempt tumor killing (1). Indeed, complete tumor regression was achieved in some patients. It was not until the late 1970s, however, that IL-2 was identified and cloned, making it possible to study T cells ex vivo. Expanding the understanding of the complex working of the immune system now enables exploration of its potential role in cancer therapy.