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A new type of microbicide — a gel or cream designed to block the sexual transmission of HIV — has proved extremely successful in an animal model, according to a new study.

The results, published today in the journal Nature Medicine, are the first concrete evidence that microbicides can prevent the virus from attaching to and entering cells in the vagina.

More than 50 candidate microbicides are currently being investigated around the world. Many researchers are optimistic that they can become an important way of preventing the spread of HIV by offering women a new method to block the disease, particularly as the prospects for an effective vaccine remain a long way off.

The collaborative study between US- and UK-based researchers looked at the b12 human antibody, which binds to a protein on the surface of the virus and stops it from attaching to cells. They found that only a quarter of the macaque monkeys treated with b12 became infected with simian HIV, compared with 12 out of 13 that did not receive the treatment.

The authors say that application of b12 appears to inhibit the entry of the virus into vaginal cells. And although their research is still at the early stages, the researchers emphasise the value of studying animal models.

"Identifying the compounds that succeed or fail in comparative studies in macaques may help identify the most plausible candidates for clinical development," they say.

But the researchers also acknowledge that the study has a number of gaps, leaving questions over how long the protection lasts, and what dosage is required, for example. Additionally, b12 would need to be combined with other general antibodies to act as an effective microbicide, and this would result in a potentially costly product.

So far most of the evidence for microbicide action has been empirical, with none having proved clinically effective against the virus. And three years ago, research suffered a serious setback when a study of the N-9 spermicide carried out in South Africa found that it actually increased the risk of HIV infection.

Nevertheless, the development of microbicides is beginning to be taken seriously by both researchers and funding bodies, such as the Rockefeller Foundation. Five substances are due to go into clinical trials this year including Carraguard, which is based on a seaweed extract. And a new US-based research US$30 million intiative — the International Partnership for Microbicides — was launched last month (see 'Microbicides: raising new barriers against HIV', 3 January 2003).

© SciDev.Net 2003

Link to Nature Medicine research paper (free access)

Photo credit: CDC

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