German researchers believe they have cured a man of HIV by using a stem cell transplant.

Timothy Ray Brown, 42, was also being treated for acute myeloid leukaemia – a cancer of the immune system. Three and a half years later, he apparently shows no sign of either disease.

He stopped taking HIV medication and was given the stem cell transplant in February 2007. He also underwent high-dose chemotherapy and radiation treatment, which wiped out his immune system.

Mr Brown received another round of treatment and a new stem cell transplant from the same donor just over a year later, when his leukaemia relapsed.

Researchers at Charite-University Medicine Berlin said that the donor’s stem cells had a rare inherited genetic mutation that made them resistant to HIV infection.

It was expected that his HIV would return but this has not happened yet.

Dr Gero Huetter, a hematologist and professor at the University of Heidelberg, and a co-author of the new paper, told Deutsche Welle: “We weren’t able to find HIV in his cells. The new cells have a natural resistance against HIV.”

The study, published in the journal Blood, said his immune system has returned to normal health and concluded: “Our results strongly suggest that cure of HIV has been achieved in this patient.”

However, HIV experts said that while the results were promising, they did not represent a potential cure for all patients.

Dr Michael Saag, professor of medicine and director of the University of Alabama at Birmingham AIDS Center, told CNN: “This probably is a cure, but it comes at a bit of a price.”

“For him to receive the donor cells, his body had to have all of his immune system wiped out. . . . The Catch-22 here is that the best candidates for a cure, ideally, are people who are healthy.”

”I would call this a functional cure,” Dr Margaret Fischl, an AIDS researcher at the University of Miami, told the Brisbane Times.

”It’s on the level and a very remarkable case. But would we do this with an HIV patient? No.”