When Decio Eizirik began treating patients with type 1 diabetes in the 1980s, he was pretty sure about what was behind the disease: an immune system gone haywire. People with the illness lacked insulin, a crucial hormone, because beta cells in the pancreas—the body’s insulin factories—were being attacked and destroyed by immune system cells. “At that time, the idea was that if you could control the immune system, perhaps you could prevent diabetes” says the endocrinologist, who now has research appointments at the Indiana Biosciences Research Institute and at the Free University of Brussels in Belgium. (He no longer sees patients.)