(Image source from: The Straits Times)

An HIV-positive man in London has become the second known adult worldwide to be cleared of the AIDS virus after a received a bone marrow transplant from an HIV resistant doctor, according to his doctors.

Nearly 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 antiretroviral drugs, extremely sensitive tests still show no hint 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.

The doctors said, the case is proof of the concept that scientists will one day be able to end AIDS but does not mean a cure for HIV has been found.

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 identified as "the London patient", in part since his case is akin to the first known case of a functional cure of HIV - in an American man, Timothy Brown, who turned out to be known as the Berlin patient when he underwent similar treatment in Germany in 2007 which also cured his HIV.

Brown, who had been living in Berlin, has since moved to the United States and, according to HIV experts, is still HIV-free.

Around 37 million people worldwide are currently infected with HIV and the AIDS pandemic has killed around 35 million people across the world since it began in the 1980s. In recent years, Scientific research into the complex virus led to the development of drug combinations that can keep it at bay in most cases.

Gupta, now at Cambridge University, treated the London patient when he was working at University College London. The man had contracted HIV in 2003, Gupta said, and in 2012 was also diagnosed with a type of blood cancer named Hodgkin's Lymphoma.

Last Chance of Survival

In 2016, when he was afflicted with cancer, doctors made up their mind to seek a transplant match for him. "This was really his last chance of survival," Gupta told Reuters in an interview.

The donor - who was unrelated - had a genetic mutation known as 'CCR5 delta 32', which confers resistance to HIV.

The transplant went relatively smoothly, Gupta said, but there were some side effects, including the patient suffering a period of "graft-versus-host" disease - a condition in which donor immune cells attack the recipient's immune cells.

According to most of the experts, it is out of the question that such treatments could be a way of curing all patients. The procedure is costly, complex and risky as well.

To do this in others, exact match donors would have to be found in the small proportion of people, who have the CCR5 mutation that makes them immune to the virus.

Specialists said it is also not yet distinct whether the CCR5 resistance is the only key - or whether the graft versus host disease may have been just as important. Both the Berlin and London patients had this complication, which may have played a role in the loss of HIV-infected cells, Gupta said.

Sharon Lewin, an expert at Australia's Doherty Institute and co-chair of the International AIDS Society's cure research advisory board, told Reuters the London case points to new avenues for study.

"We haven't cured HIV, but (this) gives us hope that it's going to be feasible one day to eliminate the virus," she said.

Gupta said his team is thinking to use these findings to look into potential new HIV treatment strategies. "We need to understand if we could knock out this (CCR5) receptor in people with HIV, which may be possible with gene therapy," he said.

The case of London patient is set to be reported in the journal Nature and presented at a medical conference in Seattle on Tuesday. The patient has asked his medical team not to reveal his personal details like name, age, nationality etc.

-Sowmya Sangam