By Amy Norton HealthDay Reporter

WEDNESDAY, March 5, 2014 (HealthDay News) -- In an early step toward drug-free HIV therapy, researchers are reporting the first success in genetically "editing" T-cells in patients' immune systems to become resistant to the virus.

The findings, published in the March 6 issue of the New England Journal of Medicine, are based on only 12 patients. But experts were cautiously optimistic about what the study accomplished.

Specifically, researchers were able to take T-cells from the HIV patients' blood, then "knock out" a gene known as CCR5, which controls a protein that allows HIV to enter a cell.

The scientists then infused the genetically altered T-cells back into patients' blood, where they expanded in number. What's more, a few patients were taken off their HIV drugs temporarily and saw their virus levels decrease.

"This is impressive," said Rowena Johnston, director of research for amfAR, the Foundation for AIDS Research.

The altered T-cells "actually seem to be doing exactly what [the researchers] wanted them to," said Johnston, who was not involved in the study.

Still, she said, there are plenty of questions left and much research ahead. The investigators on the study agreed.

"This was a first-in-human study," said researcher Bruce Levine, an associate professor of cancer gene therapy at the University of Pennsylvania School of Medicine, in Philadelphia.

That means the trial was designed to see whether it's even safe to use this approach in people with HIV -- and not whether it's an effective therapy.

Read more here:

Gene Therapy for Controlling HIV Shows Early Promise