A bone marrow transplant seems to have suppressed HIV virus levels in blood. These results have been observed in a single patient and have not yet been reported in the peer-reviewed literature. According to news reports, a man infected with the AIDS virus received a bone marrow transplant as part of leukemia treatment. The donor of the bone marrow was naturally resistant to HIV infection because of a mutation in the CCR5 protein that the virus uses to gain entry into the cells it infects. Afterwards, the patient stopped taking his AIDS drugs. Twenty months later, though they cannot conclude that the virus has been vanquished, doctors cannot find evidence of leukemia or HIV in the 42-year-old patient.