A previously HIV-positive man in London has become the second person worldwide to be cleared of the virus after receiving a successful bone marrow transplant from an HIV-resistant donor, doctors say.

The man, who three years ago received bone marrow stem cells from a donor with a rare genetic mutation which confers HIV resistance, is still testing as virus-free – even after ceasing his treatment of retroviral drugs.

“There is no virus there that we can measure,” said Ravindra Gupta, a professor and HIV biologist who is on the team treating the man. We can’t detect anything.”

Speaking to Reuters, Gupta clarified that it is still too early to say that the man is actually permanently virus-free, but that he is “functionally cured” and “in remission.” 

The only other person to successfully undergo the experimental bone marrow transplant procedure is American Timothy Brown, who is still HIV-free after his treatment in 2007.

The language being used by the scientists involved in the man’s treatment, is very careful. Though they are calling it a ‘cure’ in some public statements, the New York Times reports that in writing, and the forthcoming publication in science journal Nature, it will be referred to as “long-term remission.”

This is because, as there are only two known cases, it is hard to really concretely define the word ‘cured’.

This is obviously mind-blowing news, but there’s a caveat: most experts agree that it can’t be a solution for many HIV patients. It’s a complex and risky procedure – even this successful patient suffered a period of graft versus host disease – and requires exact match donors from the minuscule portion of people who have the CCR5 mutation.

The vast majority of people who express the CCR5 mutation live in Northern Europe, and there aren’t many of them.

Scientists still aren’t entirely sure why it worked so well with these two men. Some argue it is possible the graft versus host disease, which both men endured after the procedure, might have been key to the success.

This isn’t a universal cure for HIV, but it’s a pretty incredible development which indicates new avenues for research.

Image: Getty Images