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.
Although the finding is exciting, it is not offering up a new treatment for the millions of people around the world living with HIV.
This is the second time a patient treated this way has ended up in remission from HIV. After chemotherapy, he underwent a stem cell transplant in 2016 and subsequently remained on antiretroviral therapy for 16 months. But HIV drugs have become so effective that many people carrying this infection have a normal lifespan if they take these medications for a lifetime.
After more than a decade - and with over half a trillion United States dollars spent on HIV/AIDS research this century - we finally know that this incredible result can be replicated.
That didn't happen with the London patient.
Ten years after the first confirmed case of an HIV-infected person being rid of the deadly disease, a man known only as the "London patient" has shown no sign of the virus for almost 19 months, they reported in the journal Nature.
"CCR5 is something essential for the virus to complete its life-cycle and we can't knock out many other things without causing harm to the patient", said Gupta.
Adalja noted that although the Berlin patient and the London patient received similar treatments, the Berlin patient's treatment was more intense - he received two bone-marrow transplants in addition to whole-body irradiation (radiation exposure to the whole body).
He's being the only one thought to have been cured of HIV.
Any story about an HIV cure is bound to stir excitement.
The London patient has been free of the virus for a substantial amount of time, he acknowledges, but at this point, "it's still possible for the virus to come back". He has now been in remission for 18 months, and regular testing has confirmed that his HIV viral load remains undetectable. "Anything lower than that reads 'Lower than the Limit of Detection or Target not Detected", Dr Mwau explained. The gene is known to create a protein that is crucial for HIV to invade blood cells.
The identification of the HIV virus ultimately led to the development of therapies that specifically target the virus' ability to make new copies of itself.
In the blood, the CCR5 is the most commonly used receptor by HIV-1 - the virus strain of HIV that dominates around the world - to enter cells. The team also found that his white blood cells now can not be infected with CCR5-dependent HIV strains, indicating the donor's cells had engrafted. "This means the virus can not get into the cells".
Researchers from eight countries are tracking 45 patients with cancer and HIV who have or will soon have stem cell transplants.
But McKnight cautioned that this won't necessarily lead to a treatment for all HIV individuals.
However, Gupta described his patient as "functionally cured" and "in remission", rather than "cured".
The Aids disease has killed about 35 million people worldwide since the 1980s, when it was first discovered.
The fact that this second patient has gone into remission can give researchers more confidence they're on the right path, Kiem said.