|
'Living condom' could block HIV
Genetically-modified vaginal bacteria may be able to serve as a "living condom", secreting proteins that protect women against HIV, suggests a new report.
The bacteria have already been used to cripple the virus in test tube experiments. Now the researchers are verifying whether the unmodified parental strain - a natural component of the vaginal microbial flora - can successfully colonise the vaginal tissues of rhesus macaque monkeys. And the researchers have launched a company to study the potential of the approach.
"We are working on production, delivery and efficacy simultaneously to try and bring this to the clinic as soon as possible," says research leader Peter Lee of Stanford University in California.
With an effective HIV vaccine at best years away, many researchers are turning to novel strategies to keep the virus at bay. One approach is to develop vaginal medications which could act as "chemical condoms" to kill or inhibit the virus (New Scientist print edition, 8 February 2003). These would be especially valuable in countries where cultural conventions make it difficult for women to demand their partners use condoms.
However, one problem has haunted the field. Some medications that destroy the virus also damage the mucus membranes of the vagina, making it more susceptible to infection. Lee wondered if a better approach would be to enhance a natural, living barrier - the bacteria already present in healthy vaginal membranes. "The trick is to empower them to fight a particular microbe even more effectively," he says.
Freeze-dried tablets
Lee and his colleagues chose the vaginal native Lactobacillus jensenii and genetically-engineered it to secrete soluble CD4, a protein HIV grabs hold of to break into cells.
In test tube experiments, the enhanced L. jensenii was able to completely block laboratory strains of HIV from infecting human cells, and blocked infection by a strain recently isolated from patients by more than half.
Subscribe to New Scientist for more news and features
Related Stories
Docking blocking drug hope for HIV
19 August 2003
Spermicide offers no HIV protection
27 September 2002
Lemon juice 'is HIV-killing spermicide'
10 October 2002
For more related stories
search the print edition Archive
Weblinks
Peter Lee, Stanford University
Osel
AIDS, MedlinePlus
Microbicides, World Health Organization
Proceedings of the National Academy of Sciences
Alan Stone, chairman of the International Working Group on Microbicides, likes the approach because it mimics the natural vaginal environment and because it is flexible. "If the system works, you can put other genes in like antibody genes or other microbicides," he says.
Finding more effective microbicidal proteins against clinical isolates of HIV is high on Lee's agenda. And in preparation for use of the drug in the developing world his company, Osel, has already developed freeze-dried tablets of bacteria that can be stored up to a year without refrigeration.
Human trials of other strains of natural lactobacillus suggest these microbes can successfully colonise the vagina for days or even weeks. Chemical microbicides must be applied shortly before intercourse.
But one factor the researchers cannot control is the wariness some developing countries have already voiced about genetically modified organisms, such as Zambia's rejection of food aid shipments containing GM corn earlier in 2003. "We've thought about that," says Lee. "We hope preventing HIV infection is a situation where the benefit to risk ratio is so high, that it would overcome those objections."
Philip Cohen
|
Linear Mode
