The study involved painstaking molecular analysis of blood samples taken annually from the patients, who participated in separate studies begun in 2000, 2002, and 2004.

"We were astonished that we could detect the modified cells for so long. It's a relatively small number of patients, but more than 500 years of patient data," said University of Pennsylvania pathologist Bruce Levine, a leader of the research. "But it's difficult to separate with certainty the effectiveness of this treatment from the antiretrovirals."

Gene therapy harnesses the insidious ability of viruses to slip their DNA into the cells they infect. By neutralizing a virus and then using it as a "vector" to insert DNA that is helpful rather than harmful, gene therapy can theoretically treat ailments ranging from arthritis to infections and cancer.

Levine, his Penn colleague Carl June, and their team have tested a variety of ways to outwit HIV with gene therapy. Their approach has focused on T cells, which are the big guns of the immune system but also the cells that HIV infects. The researchers took some of the patients' T cells and inserted a gene that makes them better at recognizing and killing HIV-infected cells. Then these super-T cells were multiplied using growth-stimulation technology and put back into the patient.

Over the years, many other research groups have tried using modified T cells, but the patient's immune system perceived them as invaders and wiped them out, sometimes within hours.

Read this article:

Penn researchers report a gene-therapy success