In 2007, a young American man living in Berlin became a marvel of modern medicine when, 12 years after he was diagnosed with HIV, the virus suddenly disappeared from his body. Timothy Ray Brown had been diagnosed with leukemia and received a stem cell transplant treat it. His stem cell donor, it turned out, had a rare genetic mutation known as CCR5-delta 32 that gave Brown resistance to HIV infection. Brown became known as "the Berlin patient." Ten years later, he is still the only person to have ever been cured of HIV.