Also called gene editing, the process acts like molecular scissors to snip off an entry portal for HIV so the virus cannot enter these key immune cells.
Once the cells lack the CCR5 protein, the immune system behaves much the way it does in a rare set of people -- about one percent of the population -- who are born with a genetic mutation that prevents them from getting HIV.
Experts say the development puts researchers a step closer on the path toward curing AIDS, which has infected nearly 70 million people and killed some 35 million worldwide.
"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," said senior author Carl June of the University of Pennsylvania.
- Repopulating the immune system -
Researchers re-infused 12 patients with their own modified cells and saw them persist in the body, essentially repopulating their immune systems.
Based on the phase I trial results reported in the New England Journal of Medicine, the technique was described as "generally safe."
One serious adverse event was reported in a patient who was rushed to the emergency room with fever, chills, joint pain and back pain within 24 hours of infusion.
Researchers said the problem was likely a reaction to the study drug. All patients completed the 36-week study and are being monitored for the next 10 years.
The treatment also decreased, at least temporarily, the viral loads of some patients taken off antiretroviral drug therapy, or ART.
The patients were each given a single infusion of about 10 billion cells between May 2009 and July 2012.
A dramatic spike in modified T cells was seen in the patients' bodies a week after the infusion.
Six people were taken off ART for up to 12 weeks, beginning four weeks after infusion, and the other six patients remained on treatment.
Four of the patients who stopped ART saw their viral loads drop.
One patient's viral load dropped so low that it became undetectable. Researchers later discovered the person had inherited the CCR5 delta-32 gene mutation from one parent, essentially giving the patient a head start on the treatment.
- A step toward a cure? -
Co-authors on the study came from the Albert Einstein College of Medicine and Sangamo BioSciences, which developed approach for editing the cells, known as zinc finger nuclease (ZFN) technology.
June said he hopes that modified T cells, an experimental approach that has also shown promise against some forms of leukemia, could one day lead to a functional cure for HIV/AIDS and eliminate the need for daily antiretroviral therapy.
So far, only one man -- American Timothy Brown, often called the Berlin patient -- has been cautiously considered cured of HIV after undergoing a bone marrow transplant from a donor with a natural genetic mutation against HIV. He has been off ART since 2008.
Researchers have been trying for years to find a way to replicate those results for the wider population, in a way that might be safer than a risky bone marrow transplant, which carries a 30 percent risk of death.
While the road to a cure is still long, experts praised the research for making significant advances.
"If gene therapy were found to be a way to cure HIV, I really do believe that somebody is going to come up with a way that it could be delivered," Rowena Johnston, vice president and director of research at The Foundation for AIDS Research, or amfAR, told AFP.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which contributed funding to the research, described it as "clearly promising."
"But you have got to be careful that you don't at this point declare any victory because we are still far from any widespread applicability," Fauci said.
[Image via Agence France-Presse]
