Three scientists who uncovered key secrets of how the body's immune system works have won the 2011 Nobel prize for medicine or physiology, the prize-awarding institute said on Monday. Sweden's Karolinska Institute said in a statement that the prize went to U.S. scientist Bruce Beutler, Luxembourg-born Jules Hoffmann, based in France, and Canadian-born Ralph Steinman, based in the United States. "This year's Nobel Laureates have revolutionized our understanding of the immune system by discovering key principles for its activation," the institute said. Beutler and Hoffmann shared one half of the prize of 10 million Swedish crowns ($1.46 million) and Steinman won the other half. The work of the three scientists has been pivotal to the development of improved types of vaccines against infectious diseases and novel approaches to fighting cancer. The research has helped lay the foundations for a new wave of so-called "therapeutic vaccines" that stimulate the immune system to attack tumors.