Both the Berlin and London patients had this complication, which may have played a role in the loss of HIV-infected cells, Gupta said.
Researchers report that a man with HIV, dubbed the "London patient", appears to have been cured of the infection, following a bone marrow transplant.
Steven Deeks, an HIV researcher at UCSF, says the results could also boost cure efforts to cripple CCR5 "without the need for heroic interventions such as in the Berlin and London cases".
"We haven't cured HIV, but (this) gives us hope that it's going to be feasible one day to eliminate the virus", she said.
"This poses a particular challenge in developing countries", where millions are still not receiving adequate treatment, he added.
As of March 2019, some 37 million people globally were said to be living with the AIDS virus. Almost one million people die every year from HIV-related causes. The transplanted immune cells, now resistant to HIV, seem to have fully replaced his vulnerable cells.
Gupta and his team emphasized that bone marrow transplant - a risky and painful procedure - is not a viable option for HIV treatment.
The London-based patient was confirmed HIV-free following a bone marrow transplant from a HIV-resistant donor.
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"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", Gupta explained.
Gupta's patient, a male resident of the United Kingdom who prefers to remain anonymous, was diagnosed with HIV infection in 2003 and began antiretroviral therapy in 2012.
The transplant went relatively smoothly, Gupta said, but there were some side effects, including the patient suffering a period of "graft-versus-host" disease - a condition in which donor immune cells attack the recipient's immune cells.
CCR5 is the most commonly used receptor by HIV-1.
Reuters reports that the man, whose identity has not been revealed, has tested negative for the virus nearly three years after he received a bone marrow transplant from a donor with an HIV-resistant genetic mutation. Beforehand, each had been treated with toxic chemicals in a "conditioning" regimen meant to kill off their existing cancerous bone marrow cells.
The London patient has been in remission for 18 months since he stopped taking antiretroviral drugs.
It's the second such success since "Berlin patient" Timothy Ray Brown more than a decade ago.
"This is a long time to be in remission off ART, so this is exciting", infectious diseases expert Sharon Lewin from the University of Melbourne, who wasn't involved with the study, explains.
"We can try to tease out which part of the transplant might have made a difference here, and allowed this man to stop his anti-viral drugs".