An American HIV sufferer living in Berlin has been living free of the virus for nearly two years following a bone marrow transplant that used stem cells from a donor with natural genetic resistance to AIDS.

Dr. Gero Hutter and Thomas Schneider of the Berlin Charite hospital say the 42-year-old man, who had AIDS for more than a decade, also had leukaemia.

The team had sought a bone marrow donor who had a genetic mutation known to help the body resist the AIDS infection – roughly one in 1000 Europeans and Americans has inherited the mutation from both parents.

When they found a donor with the mutation, they used that bone marrow to treat the patient and not only did the leukemia disappear – so did the HIV.

"As of today, more than 20 months after the successful transplant, no HIV can be detected in the patient," the clinic said in a statement.

"We performed all tests, not only with blood but also with other reservoirs," Dr Schneider said to a news conference.

However, the doctors admitted the results could be a fluke, saying “we cannot exclude the possibility that it's still there."

Marrow transplants for treating AIDS or HIV infection have been attempted before.

In 1999, an article in the journal Medical Hypotheses reported two cases out of 32 attempts between 1982 and 1996 were apparently successful.

The researchers played down their result, stressing that it would never become a standard treatment for HIV because marrow stem cell transplants are rigorous and dangerous, requiring the patient to first have their own bone marrow completely destroyed and their immune system disabled.

Between 20% and 30% of recipients of this treatment die.

But the researchers conclude the results suggest that gene therapy, a highly experimental technology, has the potential to block, suppress, or even cure HIV / AIDS.