The vaginal microbiome may impact the efficacy of HIV prevention therapy

By Sarah MooreReviewed by Emily Henderson, B.Sc.Dec 3 2020

A new study conducted by Dr. Nichole Klatt of the University of Minnesota, and colleagues, has revealed that vaginal microbial communities are linked with an increased risk of HIV acquisition and may also impact the efficacy of PrEP.

Image Credit: https://doi.org/10.1371/journal.ppat.1009024

A need to study the efficacy of PrEP in women

While antiretroviral-based pre-exposure prophylactics (PrEP) has been well studied in men who have sex with men, and evidence has demonstrated its efficacy in this population, PrEP studies in women have generated various data that doesn’t always align.

According to the World Health Organization (WHO), there were around 38 million people around the world living with HIV infection in 2019. These figures highlight the global impact of the virus, and the need to understand the function of preventative techniques in all populations.

With no current effective vaccine or cure for HIV infection, prevention strategies such as PrEp have become vitally important to preventing the spread of the virus. Studies have shown the efficacy of PrEP in preventing men from acquiring an HIV infection. However, data has also revealed that this strategy is less effective at preventing infection in women.

Emerging evidence points to the potential role of vaginal microbial communities in augmenting a person’s risk of acquiring HIV, and is thought to do this by impacting the efficacy of PrEP. Just like in the gut, bacteria play a vital role in maintaining the health of the vaginal environment. Most of the bacteria found in the vagina are from the Lactobacillus genus.

Healthy Lactobacillus bacteria are crucial for numerous functions, such as inhibiting the binding of other bacteria to epithelial cells and producing lactic acid to kill other bacteria. However, the existence and proliferation of other bacterial genera can induce an unhealthy imbalance in the vaginal ecosystem. Researchers led by Klatt at the University of Minnesota investigated the role of this bacterial imbalance on the efficacy of PrEP.

In a paper published this month in the open-access journal PLOS Pathogens, a team of researchers describes the findings of their new study which suggest the potential influence of vaginal bacteria on the efficacy of PrEP. The study was designed to gather much needed in-depth data on HIV prevention in women, specifically looking at how the vaginal microbiome impacts the efficacy of therapeutic drugs.

The impact of the vaginal microbiome on PrEP

The team of US-based scientists analyzed how vaginal bacteria altered both PrEP drug levels and rates of HIV infection. To do this, they collected cervicovaginal lavage samples from a total of 44 women, some of whom had bacterial vaginosis (BV) and some who didn’t. The scientists were interested in comparing the results of those with BV to those without it due to the bacterial imbalance that causes the syndrome’s itching, discharge, and discomfort.

BV has also been associated with a higher risk of sexually transmitted infections, as well as negative reproductive tract outcomes in women. The study found that the bacteria involved in BV was not healthy Lactobacillus bacteria and that this bacteria was able to metabolize PrEP drugs, therefore, reducing its availability and potentially resulting in a reduction in PreP’s efficacy.

The team’s findings demonstrate the impact of vaginal microbial communities on the efficacy of PrEP and the risk of acquisition of HIV.

The study’s authors stress that women require enhanced measurement techniques and interventions for BV, given that it may be crucial for improving the efficacy of PrEP in some women. Dr. Klatt, the study’s lead, comments, "women's health, and factors that contribute to health and disease prevention in women are grossly understudied. This study demonstrates the critical need to develop better treatments for bacterial vaginosis, and in general, to promote more studies of women's health.”