The technique also holds promise for people suffering from the various types of cancers that suppress the immune system

Dr Bruce Levine

So far it has only been tried in eight people but the results appear to have long-term promise.

The treatment involves taking the kind of immune cell which HIV targets out of the infected person's body, modifying them to make them more resistant to HIV infection, and then putting them back.

These cells are known as CD4-positive T-cells, a vital component of the body's defences.

Usually HIV is able to sneak inside these cells and wipe them out.

Revamped cells

But by modifying them outside the body with a process known as co-stimulation - priming them for action - and then putting them back into the patient's body, they are able to do their job again properly.

Writing in the journal Nature Medicine, the researchers at the Abramson Institute report that the treatment successfully kept CD4 T cell levels up for a period of several months.

More intriguingly, the cells, which had been modified to mimic a genetic lesion that renders some people resistant to HIV infection, seemed to be reproducing inside the patient's body, suggesting that protection might be long-term.

HIV infects CD4 cells by attaching to a number of receptors on the cell surface, including a critical receptor called CCR5.

The modified CD4 cells had fewer of these vital receptors.

Increasing numbers of people are becoming infected with drug resistant strains of the virus

Mark Graver

Further studies are now being conducted which will yield more information into whether this kind of treatment could prove a useful addition to the drugs already in use.

Researcher Dr Bruce Levine said: "The technique not only holds promise for people who are HIV positive, but also for those suffering from the various types of cancers that suppress the immune system."

Mark Graver, of the UK HIV charity the Terrence Higgins Trust, told BBC News Online: "Any new HIV treatment developments are to be welcomed, especially as increasing numbers of people are becoming infected with drug resistant strains of the virus.

"However, further trials will be needed in order to determine how well it will work and what potential longer term effects it could have."