A HIV-positive man in Britain has become the second known adult worldwide to be cleared of the AIDS virus after he received a bone marrow transplant from a HIV-resistant donor.
Almost three years after receiving bone marrow stem cells from a donor with a rare genetic mutation that resists HIV infection - and more than 18 months after coming off anti-retroviral drugs - highly sensitive tests still show no trace of the man's previous HIV infection.
"There is no virus there that we can measure. We can't detect anything," said Ravindra Gupta, a professor and HIV biologist who co-led a team of doctors treating the man.
Doctors say the case is a proof of the concept that scientists will one day be able to end AIDS - but that does not mean a cure for HIV has been found.
Prof Gupta described his patient as "functionally cured" and "in remission", but cautioned: "It's too early to say he's cured."
The man is being called "the London patient", in part because his case is similar to the first known case of a functional cure of HIV - in an American man, Timothy Brown, who became known as the Berlin patient when he underwent similar treatment in Germany in 2007 which also cleared his HIV.
Mr Brown, who had been living in Berlin, has since moved to the United States and, according to HIV experts, is still HIV-free.
Some 37 million people worldwide are currently infected with HIV and the AIDS pandemic has killed around 35 million people worldwide since it began in the 1980s.
Scientific research into the complex virus has in recent years led to the development of drug combinations that can keep it at bay in most patients.
The London patient, whose case was set to be reported in the journal Nature and presented at a medical conference in Seattle today, has asked his medical team not to reveal his name, age, nationality or other details.