By UTMB’s David Niesel and Norbert Herzog: Millions of people around the world are infected with HIV, the virus that causes AIDS, but only one has ever been cured. Known as the “Berlin Patient,” Timothy Ray Brown is a 48-year-old American living in Germany. Scientists and physicians have wondered how he was cured, and some recently published studies in monkeys have provided one clue. Brown had been HIV positive since 1995. Brown’s HIV was held at bay by antiretroviral drugs that have made this infection survivable. However, in 2006 he was diagnosed with acute myeloid leukemia, a cancer unrelated to HIV. AML affects a group of blood cells in bone marrow called the myeloid cells. Brown underwent grueling chemotherapy that failed. In the hope of saving his life, he received two bone marrow transplants. The year of his first transplant, he stopped taking the antiretrovirals, which would normally cause a patient’s HIV levels to skyrocket. Yet, years later, there is no sign of the virus returning. Only traces of HIV’s genetic material have been found in his blood, and those pieces are unable to replicate. The big question now is: how was this accomplished?