Compared to Brown, the first H.I.V. -positive individual to enter long-term remission, the London patient has responded relatively well to his transplant. He developed Hodgkin lymphoma that year and agreed to a stem cell transplant to deal with the most cancers in 2016.
The "London patient" has not received antiretroviral therapy (ARV) for almost 18 months, yet he showed no trace of the virus.
Rare cases of remission, such as the London and Berlin patients "provide a lot of enthusiasm and motivation" for research teams and show that a cure can be achieved, he said, "but we still have a long way to go".
Gupta who led the medical team that treated the man described the patient as "functionally cured" and "in remission", but cautioned: "It's too early to say he's cured".
The man stopped antiretroviral therapy in a carefully monitored analytic treatment interruption 16 months after the transplant.
A second patient has reportedly been cured of HIV, which could be a major milestone, in the global fight against the AIDS epidemic.
According to the report, the patient was diagnosed with HIV in 2003 and was on anti-HIV drugs since 2012.
A man in London, England is now free of HIV/AIDS after stem cell transplant therapy. There is still no trace of the virus after 18 months off the drugs.
"It's one thing when you hear something is manageable and another thing to live it", said Greg Louganis, the Olympic champion diver who was diagnosed with HIV in 1988, six months before he won two gold medals in Seoul.More news: DNC Rejects Fox News as 2020 Debate Host
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Brown - the first and so far only person known to have been cured of HIV - received two stem cell transplants to treat leukaemia in 2006. Over the three years after the initial transplant, and despite discontinuing antiretroviral therapy, researchers could not detect HIV in Brown's blood.
He added that both the Berlin and London patients had this complication, which could have played a role in the loss of HIV-infected cells.
"They used a reduced intense conditioning regimen but I think that had no influence on the outcome", he said.
But the idea of looking for a cure involving bone marrow transplants to destroy and replace the immune systems of all those infected with HIV is a non-starter.
Now doctors have said that, together, the cases provide proof of concept that a cure may be possible for everyone, although the invasive treatment would have to be adapted radically.
Dr. Sharon Lewin, director of the Peter Doherty Institute for Infection and Immunity and a professor of medicine at the University of Melbourne, said the long remission seen in the London patient is "exciting".
There are 35 million HIV-positive people in the world, and bone marrow transplants from donors with the HIV-resistant CCR5-delta 32 mutation - which both "Berlin Patient" Timothy Ray Brown and the anonymous London Patient received - will not be a likely treatment option for most.
Chemotherapy can be effective at fighting HIV because it kills dividing cells. "Its effectiveness underlines the importance of developing new strategies based on preventing CCR5 expression", said co-author Dr Ian Gabriel (Imperial College Healthcare NHS Trust).
"If we can understand better why the procedure works in some patients and not others, we will be closer to our ultimate goal of curing HIV", said Cooke, who was not involved in the case study.