Dr. Carl June at the University of Pennsylvania tested it in 12 HIV patients who had their blood filtered to remove some of their cells. The treated cells were infused back into the patients.
Four weeks later, half of the patients were temporarily taken off AIDS medicines to see the gene therapy's effect. The virus returned in all but one of them; that patient turned out to have one copy of the protective gene.
"We knew that the virus was going to come back in most of the patients," but the hope is that the modified cells eventually will outnumber the rest and give the patient a way to control viral levels without medicines, said Dr. Pablo Tebas, one of the Penn researchers.
The National Institute of Allergy and Infectious Diseases sponsored the work with Sangamo and Penn.
"The ultimate goal is to create an immune system in the body that's been edited genetically so the cells are not capable of being infected with HIV," said director Dr. Anthony Fauci, "but we are a long way from there at this point."
Jay Johnson, 53, who works for Action AIDS, an advocacy and service organization in Philadelphia, had the treatment more than three years ago. Although the virus rebounded when he temporarily went off HIV medicines, tests show his modified blood cells are still multiplying.
"Hopefully one day I'll be able to say I'm HIV negative again," he said.