Although the finding is exciting, it is not offering up a new treatment for the millions of people around the world living with HIV.
However, the researchers caution that the approach is not appropriate as a standard HIV treatment due to the toxicity of chemotherapy, but it offers hope for new treatment strategies that might eliminate HIV altogether.
The researchers say it is too early to say the patient is "cured" of HIV.
Gupta and his team emphasised that bone marrow transplant - a unsafe and painful procedure - is not a viable option for HIV treatment. While the virus was under control, he was diagnosed with Hodgkin's lymphoma.
16 months after the stem-cell transplant, September 2017, the man went off his antiretroviral drugs for HIV.
The London patient was diagnosed with HIV infection in 2003 and had been on antiretroviral therapy since 2012.
CCR5 is a white blood cell receptor that acts as an entry point for the HIV-1 virus, the more common form of the disease. "Continuing our research, we need to understand if we could knock out this receptor in people with HIV, which may be possible with gene therapy", he added. Any sign of the virus remains undetectable.More news: To the Batmobile! Bugatti’s new $19mn ‘hypercar’ sets new price record
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He received a bone marrow transplant from a donor who was naturally resistant to HIV infection.
The fact that this second patient has gone into remission can give researchers more confidence they're on the right path, Kiem said.
"So, if the bone marrow has disabled CCR5, half of the viruses loiter "aimlessly" with intent to infect, meaning half of these viruses still have a door open for them".
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 worldwide researchers who do transplants in HIV-infected people with blood cancers. When drugs are stopped, the virus roars back, usually in two to three weeks. "If something has happened once in medical science, it can happen again", he said.
As far as scientists can tell, eighteen months he received his intervention, the London patient is still completely free of HIV.
However, now that science has determined that the earlier Berlin patient's HIV cure wasn't merely a unusual fluke, it could open up the doors to new gene-level treatments for the disease.
The patient remained on ARV for 16 months after the transplant, at which point the clinical team and the patient made a decision to interrupt ARV therapy to test if the patient was truly in HIV-1 remission.
In both cases, the doctor used a a genetic mutation that leads to HIV immunity.