Dr Bruce Levine, from the University of Pennsylvania, a study co-author, told The Guardian the team was 'absolutely encouraged' by the results which, he said, showed gene editing to be 'potentially a new therapy for HIV'.
Scientists collected white blood cells from 12 HIV-positive patients and modified them to carry a mutation in the gene for CCR5, a protein which acts as a 'docking station' for the virus and allows it to infect cells. The modified cells were then injected back into the patients in the hope that they would spread and confer resistance.
The approach mimics a rare natural mutation in the CCR5 gene that makes about one percent of the population resistant to the most common strains of HIV. HIV primarily infects T-cells, white blood cells that fight viral infections, and it is these cells that are genetically modified in the new therapy.
When the patients in the study were taken off their anti-viral medication, there was a brief increase in the amount of HIV virus in the body. However, once the modified cells began to multiply and circulate, the level began to drop. The trial began in 2009 and some of the modified cells survived for several years. Today, all of the participants in the trial are back on antiretroviral drugs.
'This study shows that we can safely and effectively engineer an HIV patient's own T-cells to mimic a naturally occurring resistance to the virus, infuse those engineered cells, have them persist in the body, and potentially keep viral loads at bay without the use of drugs', said senior author Professor Carl June.
The researchers hope gene editing could be a 'functional cure' for HIV: the virus would still be present in the body, but it would no longer infect cells.
All the same, Dr Levine told the Guardian, '"cure" is a four-letter word. We don't like to use it, particularly with HIV. We are looking at improving the health and immune function of people with HIV'.
In 2012, the World Health Organisation estimated that 35.3 million people were infected with HIV worldwide, with 1.5 million dying from AIDS-related complications. Although anti-viral treatments now have the ability to control the disease for decades, there is no cure. Side-effects associated with these drugs and their considerable financial cost remain a significant concern.
Researchers have been investigating the use of genetically-modified immune cells since 2008 when Timothy Brown, also known as the Berlin patient, was functionally cured of his HIV. His recovery occurred after a bone marrow transplant for leukaemia from a donor who had the rare protective CCR5 mutation in both alleles. Since then, Brown has apparently been HIV-free.
Scientists are now attempting to replicate Brown's story without bone marrow transplants as they carry a high risk of death and require lengthy hospitalisation.