The case of a HIV-positive man becoming the second known adult to be cleared of the AIDS virus strengthens the idea "that a cure is feasible", according to director of the Peter Doherty Institute for Infection and Immunity and the University of Melbourne Sharon Lewin.

The man in the UK has was cleared of the AIDS virus after he received a bone marrow transplant from a HIV-resistant donor.

"We can try to tease out which part of the transplant might have made a difference here, and allowed this man to stop his anti-viral drugs."

The International AIDS Society said in a statement today that results from the second patient "reaffirm our belief that there exists a proof of concept that HIV is curable".

Mark Dybul, co-chair of the Towards an HIV Cure initiative, said the London case "is as important as it is exciting".

Both patients received stem cell transplants from donors carrying a genetic mutation that prevents expression of an HIV receptor, known as CCR5.

The study describes an anonymous male patient in Britain who was diagnosed with HIV infection in 2003 and had been on antiretroviral therapy since 2012.

Later that year, he was diagnosed with advanced Hodgkin's Lymphoma, a deadly cancer.

He underwent a so-called haematopoietic stem cell transplant in 2016 from a donor with two copies of a CCR5 gene variant, which is resistant to most HIV-1 virus strains.

"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. 

"We know that CCR5 can be knocked out without any serious consequences because people are walking around without that gene."

CCR5 was the target in the genome of the controversial gene-edited twins born last year in China, whose father is HIV-positive.

New communities

After the bone marrow transplant, the London patient remained on ARV for 16 months, at which point treatment was stopped.

Regular testing has confirmed that the patient's viral load remained undetectable since then.

Timothy Brown, the first sustained remission survivor known as the "Berlin patient", was given two transplants and underwent total body irradiation to treat leukaemia, while the British patient received just one transplant and less intensive chemotherapy.

"I did not want to be the only person in the world cured of HIV," Brown wrote in a medical journal in 2015, explaining why he decided to reveal his identity. 

Gupta said he hoped to expand research on the stem-cell transplant technique to focus on communities in Africa, where the HIV-beating mutation does not naturally occur. 

"Expanding remission to populations that are affected disproportionately is quite important," he told AFP.

The research team for the London patient will present their findings at the annual Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle, Washington, later today.