The patient received bone marrow stems from a donor with a rare genetic mutation three years ago, and 18 months after coming off antiretroviral drugs, tests still show no sign of his previous HIV infection, according to the Guardian.
Unexpectedly, the stem cell treatment - from a donor with a mutation of the CCR5 gene, which is a co-receptor for the HIV-1 infection - ended up with Brown's HIV going into remission, where is has remained ever since.
Professor Gupta described his patient as "functionally cured" and "in remission", but cautioned: "It's too early to say he's cured".
The London man was cured after he received a bone marrow transplant from an HIV-resistant donor, his doctors said. That transplant also appeared to clear his HIV infection.
The new patient has chosen to remain anonymous, and the scientists referred to him only as the "London patient".
Scientists have inched closer to finding the real cure for HIV/AIDS after another man who was until recently HIV-positive was successfully cured of the disease in Britain.
Graham Cooke, from Imperial College London, said: "This second London patient, whose HIV has been controlled following bone marrow transplantation, is encouraging".
The London patient, whose case is set to be presented at a medical conference in Seattle on Tuesday, has asked his medical team not to reveal his name, age, nationality or other details.
The CCR5 gene was thrust into the worldwide spotlight recently by the revelation that a Chinese scientist had attempted to edit human embryos to create the same deletion, with the hopes of creating babies that were immune to HIV.
The man, who has been dubbed the "London patient", is the second person to receive the treatment. He received transplant from a donor with a mutation in a protein called CCR5.
"Today's news is a welcome development for many people living with HIV, but we must not take our eye off the ball in ensuring we use the tools we already have that can help us towards zero new transmissions".
There are important limitations to applying the findings of the London patient to a HIV cure, said Anthony Kelleher, director of the Kirby Institute at the University of New South Wales in Sydney.
The London patient has no detectable HIV virus, Gupta and colleagues said.
Similar therapy has been successful once before with "Berlin Patient", a U.S. man treated in Germany 12 years ago who is still free of HIV. But the transplants were meant to treat cancer in the patients, not HIV. "Everybody believed after the Berlin patient that you needed to almost die basically to cure HIV, but now maybe you don't".
While this new patient might not unlock the cure to a disease that has killed millions of people, it does give hope to researchers that it is possible in some circumstances.
HIV has been cured in a second patient, researchers are reporting.
"CCR5 is something essential for the virus to complete its life-cycle and we can't knock out many other things without causing harm to the patient", said Gupta.
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