Image: Burnet Instiute Head of Life Sciences, Professor Gilda Tachedjian

Burnet Institute HIV scientists have identified a metabolite produced by bacteria in the vaginal tract that could help protect women at increased risk for HIV, including women from sub-Saharan Africa, from contracting the virus.

The diverse nature of naturally occurring vaginal bacteria in women from sub-Saharan Africa makes them more susceptible to acquiring HIV, and they’re generally lacking in beneficial lactobacillus bacteria that’s been shown to help protect against HIV and other sexually transmitted infections.

This is a serious problem for young women in particular. Eighty percent of all young women living with HIV live in sub-Saharan Africa, and HIV is the leading cause of death of women of reproductive age in the region.

More broadly, women represent almost half the global HIV burden of 37 million infected individuals, and are up to eight times more likely than men to acquire HIV following vaginal intercourse.

The Burnet study, led by Professor Gilda Tachedjian and published in the Nature journal Mucosal Immunology, found that a metabolite called lactic acid, which occurs at high concentrations in women with beneficial lactobacillus bacteria, plays a key role in the dampening of inflammation that can be caused by an imbalance in the vaginal microbiome due to an overgrowth of highly diverse anaerobic bacteria.

Reducing vaginal inflammation can help protect against HIV since it can prevent the activation and recruitment of HIV target cells to the vagina as well as prevent breakdown in the mucosal barrier that can allow virus to penetrate and establish infection.

“What we showed in the laboratory is that not only did lactic acid dampen the production of pro-inflammatory mediators from epithelial cells that provide a physical and immunological barrier in vaginal tract, it also resulted in the production of an anti-inflammatory mediator,” Professor Tachedjian said.

“That would suggest a mechanism whereby these women, in part, are likely to be protected if they have this beneficial bacteria, compared to women who have vaginal dysbiosis where they have this high-diversity, anaerobic bacteria.”

Professor Tachedjian said the study has important translational implications and opens up a number of avenues for further research to address the needs of women with this particular susceptibility to HIV.

“It may be that we could take a probiotic approach using a species that can make high levels of this product as a way to prevent HIV in these women in combination with strategies such as pre-exposure prophylaxis (PrEP), which we know works,” she said.

“Of course we need to consider that probiotics may not successfully colonise in some women due to competition with existing bacteria or sexual intercourse.”

An alternative strategy could be to deliver lactic acid into the vagina using a daily gel or in a sustained way through an intravaginal ring or a sustained release formulation that may offer wider benefits.

“We’re working on a formulation that’s cheap and can be used with women in developing countries to prevent HIV acquisition, but also potentially other sexually transmitted infections (STIs), Professor Tachedjian said.

“If you’re reducing inflammation, and inflammation affects the mucosal barrier, then you could imagine that you could potentially prevent herpes infections and bacterial STIs as well, such as gonorrhea.

“That’s why we do these studies, to understand how things work. We start with an observation that we know these bacteria are protective, and the mechanism behind that can lead to ways to develop interventions for the improvement of women’s health.”

This study led by the Burnet Institute is a collaboration with US-based investigators at Johns Hopkins University and Boston University School of Medicine.

LISTEN to Professor Tachedjian’s interview about this research with SBS’s African Radio Service.