Here's what to know about the landmark case.
The patient is known as "London Man" has been in the sustained remission for the past 19 months in London.
He was diagnosed with HIV in 2003 and started taking drugs to control the infection in 2012.
In these two cases, doctors selected a donor who had an uncommon mutation that made them virtually immune to HIV infection and this mutation was passed on to the recipient.
Both men received stem cells from donors with this mutation.
Brown, apart from being HIV-positive, had leukemia and had bone marrow transplant after chemotherapy proved futile. "After a ten year gap it provides important confirmation that the "Berlin patient" was not simply an anomaly".
Sixteen months after the procedure (which notably didn't include radiotherapy, unlike the Berlin patient), the London patient discontinued ARV drugs (aka ART therapy), and has now been in HIV remission for over 18 months.
However, most of the patients have died due to the cancer, side effects of the transplant, or saw a return of the virus after quitting antiretroviral drugs.
"We've always wondered whether all that conditioning. a massive amount of destruction to his immune system. explained why Timothy was cured but no one else".
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. "Is that a cure?"
His case was published in Nature journal yesterday, and simultaneously announced by University College London researchers at the annual Conference on Retroviruses and Opportunistic Infections in Seattle. That's when it can also mutate to evade drugs. Because it's a virus, it can't replicate on its own, but instead needs to co-opt the machinery of another cell in order to reproduce, so it can only replicate when it infects other cells.
A mutation in the door's CCR5 gene stops HIV entering. "I never thought that there would be a cure during my lifetime", he added.
This is the second time a patient treated this way has ended up in remission from HIV.
Could the patient's HIV come back?It's only the second time this has been accomplished, despite many attempts over more than a decade. A second, less common form of HIV, could still cause infection despite a transplant like this.
The patient, who prefers to remain anonymous, remains HIV-free to date. To prevent the virus rebounding, he was given a double Δ32 stem cell transfusion, although initially this was combined with ongoing antiretroviral treatment.
Three months after his first treatment, the HIV in his body dropped dramatically and he was soon listed as undetectable.
The study's lead author, Professor Ravindra Gupta, said: "Finding a way to eliminate the virus entirely is an urgent global priority, but is particularly hard because the virus integrates into the white blood cells of its host". He developed Hodgkin lymphoma that year and agreed to a stem cell transplant to treat the cancer in 2016. "Bone marrow transplants are risky". "Two factors are likely at play: The new bone marrow is resistant to HIV, and also, the new bone marrow is actively eliminating any HIV-infected cells".
The donor was resistant because of a mutation in his CCR5 gene. He also naturally had one Δ32 copy, and when similar efforts failed with other patients, there was speculation this, or some other rare feature of Brown's case, was required for success.
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