Doctors in Germany say a man appears to have been cured of AIDS by a bone marrow transplant from a donor who had a genetic resistance to HIV.
The researchers at the Berlin Charite hospital say the patient, who suffered from leukaemia as well as AIDS, had shown no sign of either disease since the transplant was completed two years ago.
The result is expected to encourage further interest in gene therapy as a treatment for AIDS. So far all efforts to find a cure have been unsuccessful.
Roughly one in 1,000 Europeans and Americans have an inherited genetic mutation, which prevents HIV from attaching itself to cells.
Two million people die of AIDS every year and the virus is estimated to have infected 33 million people worldwide.