Stephen Crohn, renowned for helping scientists study genetic resistance to HIV, died in New York City at age 66, The New York Times reports. The cause was suicide. In 1978, his boyfriend was one of the first people to die of the disease later called AIDS. Soon after that many friends also died, but Crohn never got sick. Researchers exposed his CD4 cells to HIV, but the virus could not infect them. Years later, researchers found the reason: Crohn had a malfunctioning CCR5 receptor on his CD4 cells. He subsequently shared his story in documentaries and interviews worldwide. The discovery of his genetic anomaly, known as the delta 32 mutation, has led to the creation of Selzentry (maraviroc), a drug that blocks the CCR5 receptor. It also led to a bone marrow transplant, using a donor with the mutation, that cured Timothy Brown (a.k.a. the Berlin Patient) of leukemia and HIV.

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