Setback for women’s anti-HIV gel
Vaginal bacteria thwarts medication’s effectiveness
WASHINGTON — Creating new HIV prevention tools for women has proven frustratingly slow and researchers have found another hurdle: bacteria in the reproductive tract. A new study published June 1, examined what stalled an early attempt at an anti-HIV gel, and found certain types of vaginal bacteria broke down the protective medication before it had time to work.
“This is an important study,” said microbiologist Sharon Hillier of the University of Pittsburgh, who wasn’t involved in Thursday’s report but leads the Microbicide Trials Network that tests potentially protective products. “It does tell us that this is another factor we have to consider.”
Women make up about half of the nearly 37 million people worldwide living with HIV. They’re particularly at risk in hard-hit Africa. Scientists have long sought unobtrusive ways for women to protect themselves when their partners won’t use a condom.
The research re-examined an early vaginal gel containing the AIDS drug tenofovir that had seemed partially protective in one study only to fail in another. Puzzled scientists thought maybe some women simply didn’t use the gel properly.
Samples saved from 688 South African women who tested that gel tell a different tale.
Some of those women had a reproductive tract dominated by species of “friendly” bacteria from the Lactobacillus family. Others harboured less healthy species that lead to bacterial vaginosis, inflammation that can increase risk of certain health problems.
The tenofovir gel reduced HIV infection by 61 per cent in women who harboured the mostly healthy lactobacilli — but by only 18 per cent in women with the less healthy vaginal bacteria, researchers reported in the journal Science.
Why? The team mixed tenofovir with different types of bacteria in lab dishes. Tenofovir stayed around longer when mixed with healthy lactobacilli, while concentrations plummeted rapidly when mixed with a particularly bad bug named Gardnerella vaginalis. The unhealthy bacteria were breaking down the drug before it could do its job, the study found.
“We have to look at biological variability in each person,” said microbiologist Nichole Klatt of the University of Washington, who led Thursday’s research with a team of U.S. and Canadian scientists.
Microbicides aside, scientists have linked bacterial vaginosis to a higher risk of HIV infection — begging the question of whether it ever will be possible to make vaginal bacteria healthier to lower risk in the first place.
Klatt said simple, relatively inexpensive pH tests can indicate if a woman lacks protective vaginal bacteria.
“What’s really important is understanding this moving forward and being able to advise women more,” Klatt said. Some women might be told, “this prevention might work for you because you have lots of lactobacillus” while others “might need a backup.”