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Scientists are one step closer to developing a 'living gel' that could be applied to the vaginal or intestinal tracts to protect against HIV/AIDS infection.

The researchers genetically modified bacteria that are normally present in the body to make them produce a protein that stops the HIV virus from infecting cells.

They say that allowing these bacteria to colonise the internal body surfaces where HIV transmission can occur through sexual activity, could offer cost-effective, efficient and long-lasting protection against the virus.

The team, led by Srinivas Rao, chief of laboratory animal medicine at the Vaccine Research Center of the US National Institute of Allergy and Infectious Diseases, published their findings last week (23 August) in Proceedings of the National Academy of Sciences.

Rao's team showed that the modified bacteria colonised the intestines and vaginas of mice for periods of weeks to months, without causing any signs of disease. Furthermore, the modified bacteria produced large quantities of the HIV-blocking protein.

The reproductive and intestinal tracts are prime sites for HIV infection. Various microbes live in each, playing an important role in defending the body against harmful organisms.

The researchers hope that adding modified bacteria to these existing microbes could help prevent HIV transmission, especially in developing countries. They point out that if the bacteria successfully colonise and reproduce, protection can be long-lasting.

Short-lasting creams against HIV/AIDS would need to be applied regularly before sex and this is likely to limit their use, say the researchers.

In an article published yesterday (August 30) in the Proceedings of the National Academy of Sciences, Laurel Lagenaur and Edward Berger of the US National Institutes of Health, point out that modified bacteria would be easy to produce, store and distribute.

But they add that before human trials can begin, researchers will need to ensure that the microbes are better able to colonise the reproductive and intestinal tracts.

Other issues that will need to be addressed include the safety of introducing live, genetically modified microbes into human bodies. Rao's team used a strain of bacterium that is already used in the United States as a live treatment for bowel disorders such as Crohn's disease.

Berger points out, however, that the possibility of genes transferring from the GM bacteria to other microbes in the body carries a potential medical risk that must be assessed.

Although the approach has produced promising results in mice, trials on monkeys exposed to HIV or the primate equivalent (SIV) will have to be successful before the bacteria can be tested in people.

"It is a fascinating concept," says Harold Kessler, associate director of the Infectious Diseases Section at Rush University Medical Center in Chicago, United States. "Obviously there is a great deal of work ahead, but it is certainly a novel approach that deserves further investigation."

Link to abstract of paper in Proceedings of the National Academy of Sciences

Reference: Proceedings of the National Academy of Sciences 102, 11993 (2005)

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