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Last Updated: Saturday, 17 May, 2003, 01:52 GMT 02:52 UK
Secrets of safer HIV
The mutant gene stops the virus killing
In some patients, HIV never turns into full-blown Aids - and now scientists believe they know why.

They think a particular genetic mutation that can occur within the virus stops it killing off our immune cells.

It is the depletion of immune cells that leaves the body vulnerable to the opportunistic infections that characterise Aids.

But if this depletion does not take place, then some people - known as long term nonprogressors - can live with HIV replicating itself inside their bodies without developing signs of disease.

Whether knowledge of the mutation could help patients who have the normal, more dangerous form of HIV, is currently less certain.

Cell death

The finding, by scientists at the Mayo Clinic in Minnesota, US, centres around a gene called Vpr.

This, they say, appears to have a key role in HIV's ability to trigger cell death in immune cells.

The mutant doesn't kill as well as the normal, or wild type HIV
Dr Andrew Badley, Mayo Clinic
Dr Andrew Badley, who led the research, published in the Journal of Clinical Investigation, said: "Clearly, something is going on to help these long term nonprogressors survive the infection - but what?

"Previous studies have explained some of it - but not all."

He added: "The mutant doesn't kill as well as the normal, or wild type HIV."

The Mayo Clinic research team tested this by comparing two versions of HIV - one with the mutant Vpr gene.

They found that, in cell cultures in the laboratory, the mutant Vpr HIV had less ability to induce cell death in the immune cells.

The protein produced by each gene was compared in a similar way - and mutant Vpr protein was also less dangerous for the immune cells.

Dr Badley said: "By further exploring the role of Vpr we may be looking at a mechanism by which patients with long-term nonprogressive HIV disease are able to stay symptom free.

"That information could eventually translate into new treatments."

Protein defence

In another study, researchers from Paris are investigating a human body chemical which they are hoping to harness to attack HIV.

HIV produces its own viral protein, called Vif, to disable the human enzyme which would normally stop the virus in its tracks.

The French team, whose work is detailed in the journal Science, believe that one day they can disable this protein, allowing the enzyme to do its job.

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