"Yes. At first, we thought the Delta 32 mutation must have arisen during the Black Death in Europe-about four to sixteen percent of Europeans have at least one copy. But we've traced it back further. We thought perhaps smallpox, but we've found Bronze Age DNA samples that carry it. The mutation's origins are a mystery, but one thing is certain: the bone marrow transplant with CCR5-Delta 32 cured both Brown's leukemia and HIV. After the transplant, he stopped taking his antiretrovirals and has never again tested positive for HIV."