Scientists and funding agencies are pegging gels or creams that prevent the transmission of HIV during sex as the key to stopping the pandemic.

You’re in: AIDS at 25 Coverage / Microbicides

TORONTO—Since a safe and effective HIV vaccine is a long way off, scientists and funding agencies are pegging microbicides—gels or creams that prevent the transmission of HIV during sex—as the key to stopping the AIDS pandemic.

The first microbicide could be available as soon as 2010—years before a vaccine would be available, said Gita Ramjee, director of the South African Medical Research Council (MRC) HIV Prevention Research Unit. “There is urgent need for HIV prevention among women and microbicides would do just that,” said Ramjee.

Microbicides interfere with HIV infection in one of four ways: They enhance the body’s natural defenses, provide a barrier between tissue and the virus, disable the virus or interfere with HIV gaining entrance into a cell. A simulation performed at the London School of Hygiene and Tropical Medicine showed that a microbicide that is 60% effective could prevent 2.5 million infections over three years. Prevention has been a major theme during the first three days of the XVI International AIDS Conference in Toronto. UNAIDS, the Joint United Nations Programme on HIV/AIDS, estimates that more than 38 million people are now infected with HIV, and that more than four million were newly infected in 2005. “We have to do a much better job at prevention, or we’re never going to be able to deal with the numbers of those who will have to go onto treatment,” philanthropist and Microsoft founder Bill Gates said at a press conference on Sunday.

According to UNAIDS, 17.3 million women were living with HIV at the end of 2005. More than three-quarters of these women live in sub-Saharan Africa, where heterosexual intercourse is the predominant mode of transmission. Activists say that a microbicide would put HIV prevention in the hands of women. “The vast majority of women who become infected are infected through sex, and the vast majority of them are infected in the context of an ongoing relationship,” said Lori Heise, director of the Global Campaign for Microbicides.

Despite the increased backing microbicides are receiving, they must still pass through clinical trials. Sixteen products are currently in that phase and five of these are in major advanced studies. More than 17,000 women, mainly in Africa, are enrolled in five large-scale microbicide clinical efficacy trials. One third of these women are participating in a trial in South Africa using the seaweed-derived Carraguard, a long chain anionic polymer that prevents the virus from attaching to receptors on target cells.

But many worry that the first-generation candidates may not be successful. “You always have to plan for failure in the HIV game,” said John Moore, a professor of microbiology and immunology at Cornell University. Moore is conducting preclinical trials on microbicides based on antiretrovirals called “entry inhibitors” that bind to the virus or to the CCR5 receptor on T-cells. At least five second-generation candidates containing antiretroviral compounds are in pre-clinical and early clinical development, including entry inhibitors and those that shut down HIV replication within the cell.

According to UNAIDS, funding remains an issue for the continued research and development of microbicides. The total global investment in research and development of microbicides for 2005 was $168 million, but UNAIDS has called for funding to increase to $280 million per year over the next five to ten years. On Sunday, Bill Gates said his foundation will be “upping its funding” of microbicide research. Since 2000, The Bill and Melinda Gates Foundation has provided $124 million for microbicide research. “Microbicides and oral prevention drugs could be the next big breakthrough in the fight against AIDS,” Gates said.

Originally published August 16, 2006

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