The London man was cured after he received a bone marrow transplant from an HIV-resistant donor, his doctors said. Bone marrow from a similarly CCR5 negative donor was given to the "London Patient". HIV is at its most unsafe when it is actively replicating, furiously producing as many copies of itself as possible so it can penetrate immune cells and spread infection.
Blood cells of an infected person are replaced by someone who is immune to HIV through a genetic mutation which stops the virus attaching to cells. Her group has been working on a way to mutate the CCR5 gene directly in the bone marrow of a person to simulate the effect of the transplants. The London patient, in contrast, had a milder regimen that targeted his lymphoma.
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 on Tuesday.
CCR5 was the target in the genome of the controversial gene-edited twins born a year ago in China, whose father is HIV-positive.
Brown in 2007 was an HIV-positive man with acute myeloid leukaemia, a type of blood cancer that begins in the very cells that become the white blood cells.
A new drug-resistant form of HIV is also a growing concern. Essentially, the mutation prevents HIV from being able to get inside people's cells, so it can not cause infection.
It's a matter of semantics, says Dr. Steven Deeks, professor of medicine at the University of California, San Francisco and one of the doctors who treated Brown. The Berlin and London patients both had this complication, which may have played a role in the loss of HIV-infected cells, Gupta said.
"The so-called London Patient has now been off ART for 19 months with no viral rebound which is impressive, but I would still be closely monitoring his viral load".
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The circumstances of this cure do not apply to those of us who have been living with a HIV diagnosis for many years; the risks involved are too great. "Everybody believed after the Berlin patient that you needed to almost die basically to cure HIV, but now maybe you don't".
The man - who wishes to remain anonymous - was given stem cells from a donor with genetic resistance to the disease and he has now been in long term remission for 18 months without medication. He said the treatment used is not appropriate for all patients but it offers hope for new treatment strategies, including gene therapies.
"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".
As with cancer, chemotherapy can be effective against HIV as it kills cells that are dividing.
However, Gupta described his patient as "functionally cured" and "in remission, " rather than "cured".
Brown hopes that the "London patient" will survive as long as he has.
To learn more about the factors that favor a cure, amfAR, the Foundation for AIDS Research, a New York City-based foundation, in 2014 began to fund a consortium of global researchers who do transplants in HIV-infected people with blood cancers.