A man from London has become the second person in the world to be cured of HIV, doctors say.

Adam Castillejo is still free of the virus more than 30 months after stopping antiretroviral therapy.

He was not cured by the HIV drugs, however, but by a stem-cell treatment, he received for a cancer he also had, the Lancet HIV journal reports.

The donors of those stem cells have an uncommon gene that gives them, and now Mr Castillejo, protection against HIV.

In 2011, Timothy Brown, the "Berlin Patient" became the first person reported as cured of HIV, three and half years after having similar treatment.

Prof Gupta said: "It is important to note that this curative treatment is high-risk and only used as a last resort for patients with HIV who also have life-threatening haematological malignancies.

"Therefore, this is not a treatment that would be offered widely to patients with HIV who are on successful anti-retroviral treatment."

But it might offer hope of finding a cure, in the future, using gene therapy.

CCR5 is the most commonly used receptor by HIV-1 - the virus strain of HIV that dominates around the world - to enter cells.

But a very small number of people who are resistant to HIV have two mutated copies of the CCR5 receptor.

This means the virus cannot penetrate cells in the body it normally infects.

Researchers say it may be possible to use gene therapy to target the CCR5 receptor in people with HIV.

It is the same receptor the now jailed Chinese scientist He Jiankui worked on when he created the world's first gene-edited babies.

The tests suggest 99% of Mr Castillejo's immune cells have been replaced by donor ones.

But he still has remnants of the virus in his body, as does Mr Brown.

And it is impossible to say with absolute certainty his HIV will never come back.

Mr Castillejo told the New York Times: "This is a unique position to be in, a unique and very humbling position.

"I want to be an ambassador of hope. I don't want people to think, 'Oh, you've been chosen.' No, it just happened. I was in the right place, probably at the right time, when it happened."

Prof Sharon Lewin, from the University of Melbourne, Australia, said: "Given the large number of cells sampled here and the absence of any intact virus, is the London Patient truly cured?

"The additional data provided in this follow-up case report is certainly encouraging but unfortunately, in the end, only time will tell."

-BBC