Genetically altered AIDS cells that prevent HIV from reproducing may form the basis for an effective new method of fighting the deadly disease.

The treatment appears to have helped restore the immune systems of four of the five study participants, in whom the virus remains partly suppressed after three years. 

Gene therapy offers great promise, but previous trials have produced inconsistent results. Cures have been produced in only a few patients, while some have developed leukemia, and one participant died as a consequence of treatment in 1999.

Researchers hoped to demonstrate that gene therapy can be safe. For the first phase of the study, the team selected five patients whose HIV infections had resisted conventional treatment.

In the study, immune cells were removed from the patients' bodies, modified with a disabled AIDS virus known as a lentivirus, and then intravenously returned. The genetically altered cells disseminated anti-HIV material and prevented HIV from reproducing.

"The goal of this phase I trial was safety and feasibility and the results established that," said Dr. Carl June, who led the study. "But the results also hint at something much more," he added. "It seemed to have a vaccine-like effect in that the immune system was better in most of the patients than when they enrolled. We are trying to study the mechanism."

One great advantage of the therapy is that unlike most HIV medications that have to be taken daily or several times a day, this treatment can be done once and will then automatically keep fighting the infection.

The approach needs years more study, researchers caution, but the encouraging results represent an important step forward in the fight against the deadly AIDS virus, as well as in the general field of gene therapy.

The AIDS virus infects close to 40 million people worldwide and has killed 25 million.