Doctors at a Berlin hospital said Wednesday that they appear to have rolled back the AIDS virus in a patient by using bone marrow keyed to a genetic shield against HIV, but stressed it was an unusual case that needed further investigation.
"This is an interesting case for research," said Rodolf Tauber, a professor at the Charite university clinic, where the work was carried out.
"But to promise to millions of people infected with HIV that there is hope of a cure would not be right," he said in a statement.
The patient, an American living in the German capital now 42 years old, came to the clinic three years ago suffering from leukaemia, for which he was given chemotherapy and other treatment. He had also been HIV-positive for a decade.
T-cells are derived from bone marrow.
Acting on a hunch, doctors replenished his bone marrow after the treatment by using marrow from a donor carrying a specific genetic variant known to confers some protection against HIV.
This mutation, already identified in previous research, occurs in one to three percent of the European population.
Known as Delta 32, it occurs in a gene called CCR5, on Chromosome 3.
It reduces the number of docking points, called CCR5, on the surface of so-called T immune cells targeted by the virus, thus lowering the risk of cell penetration by the pathogen.
The bone marrow donor had a double copy of the Delta variant in his genome, meaning he had inherited a copy from both his mother and his father, rather than from just one parent.
The patient was told to stop taking his HIV medication during the process, a move that would normally cause levels of HIV to rise sharply within short time.
"Today, more than 20 months after the successful transplant there is no sign of HIV in the patient," the statement said.
But the case should not lead to "false hopes", Gero Huetter, one of the members of the medical team, stressed at a news conference on Wednesday.
"This process is not adapted for the treatment of patients with HIV, neither today nor in the near future," Huetter said.
AIDS first came to public notice in 1981, when alert US doctors noted an unusual cluster of deaths among young homosexuals in California and New York.
It has since killed at least 25 million people, and 33 million others are living with the disease or HIV, according to the best estimates.
Previous research involving HIV drugs has shown that when HIV is reduced to below detectable levels, the virus holes up in refuges in the body, such as in dormant memory T cells in lymph nodes. It rebounds when treatment is stopped.
The Berlin case has not yet been submitted to a peer-reviewed journal for publication.