Two scientists, one from Australia and one from the U.S., just won a $600,000 prize for figuring out how the body stops itself from developing autoimmune diseases like lupus, arthritis, and multiple sclerosis. Their research explained how certain immune cells called B cells are trained not to attack the body’s own tissues. This discovery helps explain why most people don’t get autoimmune diseases—and it’s already helped lead to better treatments for those who do. The award they won, the Crafoord Prize, is one of the biggest honors in science.