Critically, because these new donor cells were endowed with the CCR5 mutation, the patient's HIV was unable to infect them.
The key is finding a bone marrow donor with mutated CCR5 proteins, which prevent HIV from entering cells in the immune system, effectively "curing" HIV.
The man is being called "the London patient", in part because his case is similar to the first known case of a functional cure of HIV - in an American man, Timothy Brown, who became known as the Berlin patient when he underwent similar treatment in Germany in 2007 which also cleared his HIV.
"The first is that CCR5-negative cells are resistant to HIV", she said.
Although it is generally thought that HIV/AIDS cannot be cured, many patients with the virus can live a mostly normal life with anti-viral treatment that keeps the virus at a low level. Two men known collectively to the media as the Boston Patients appeared to be "cured" of HIV following bone marrow transplants. In 1997, David Ho of the Aaron Diamond Institute announced that the new crop of anti-retroviral drugs would probably be able to knock out the virus in patients after they continued the regimen for a number of years. He also underwent a bone-marrow transplant to treat his leukemia.
The transplant involves killing nearly all the immune cells and replacing them with donor cells, and is so risky it can only be carried out on people with cancer. But as a concept this case is so significant because it brings hope to scientists who are looking for new ways to tackle HIV and achieve a cure.
Though the news is undoubtedly exciting, the practicality of bone marrow transplants as a widespread cure for HIV isn't high, since the procedure is risky and comes with potentially life-long side effects, according to The New York Times.
"The Human Immunodeficiency Virus (HIV) attacks and weakens the immune system, reducing its ability to fight diseases or infections", Girish Badarkhe, Haematologist at HCG Cancer Centre, Bengaluru, told IANS. Cells without a working CCR5 receptor are essentially locked up to the virus.
Globally, 36.9 million people were living with HIV in 2017. Finding the right regimen and staying on it can make the virus undetectable in a person's blood, meaning both that they stay healthy and that they cannot transmit the virus to other people.
The London patient is one of 38 patients given bone marrow treatment, including six who used donors without the mutation, that a group of researchers is following.
The patient treated by the UCL team was also battling lymphoma, a cancer of immune cells, which is a common complication of long-term HIV infection.
The next big question is how the knowledge gained from CCR5 stem cell transplants might actually help create a true cure for HIV.
After so many failed attempts at replication, the London patient is giving researchers hope that Brown's case was not just luck.