Health

Vital clues that might lead to an AIDS vaccine have been discovered by researchers studying the genetic code of HIV-2 - the less virulent and less common form of the virus.

Although both forms of the virus infect humans, HIV-2 goes on to cause AIDS in only 20 per cent of infected people. In contrast, HIV-1, which has spread disastrously through sub-Saharan Africa, goes on to cause AIDS in 98 per cent of people who do not take anti-viral drugs.

A team from Oxford University and the UK Medical Research Council (MRC) unit in the Gambia set out to determine why the human immune system is better able to resist HIV-2, which is largely confined to West Africa. Their studies centred on a group of women infected with the virus for over a decade.

They discovered that a tiny part of one viral gene called gag makes HIV-2 vulnerable to attack from the human immune system. What's more, this gene hardly ever mutates.

The gag gene, which codes for just 18 amino acids, provides a signal for white blood cells, called T-cells, to attack the virus and sweep it out of the blood stream before it can do further damage.

"Clearly there is something special about the gag region - and it looks like vaccine researchers should be focusing on it," says Aleksandra Leligdowicz who leads the MRC unit. The thinking is that a vaccine containing the right part of the gag gene could trigger the body's immune response, making it better able to prevent HIV-2 infection developing into full blown AIDS.

Vaccine key

Leligdowicz notes that the two per cent of people infected with HIV-1 who do not progress to AIDS show a strong T-cell response to the gag region as well.

Even more intriguing, most strains of HIV-1 also have a highly-conserved gag gene. The key to better vaccines could be finding just the right part of this region to include, she says.

The findings also indicate that a T-cell based or "cell mediated" defence against HIV is enough to render HIV harmless. For over a decade researchers have argued whether or not an immune response that involved antibodies in addition to T-cells was also vital.

According to Leligdowicz, the latest results suggest it is possible to devise a vaccine to treat HIV, which although not preventing infection or eradicating the virus, will stop the wearing down of the immune system that leads to AIDS.

Virologist Robin Weiss who researches HIV vaccines at University College London says. "Ultimately, I think that a vaccine that actually prevents infection will need to make an anti-body response as well as cell-mediated one.

"But the idea of a therapeutic vaccine does have legs. Not only would it treat people, it might make them less able to infect other people, so you would get a double dividend. The study of HIV-2, although a less important pathogen, might well teach us some valuable lessons."

Journal reference: Journal of Clinical Investigation (DOI:10.1172/JCI32380)

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