HIV: the vaginal flora affects the effectiveness of a preventative treatment
The composition of the vaginal microbiota influences how effective a topical tenofovir treatment is in preventing HIV infection in women. So say researchers who analyzed the impact of the vaginal microbiota on the response to this treatment, whose effectiveness can vary between 0 and 40% according to previously published studies.
By studying the vaginal microbiota of 688 women in South Africa who were not infected with HIV and used a tenofovir gel, they identified two groups of women: one for which the vaginal microbiota is largely dominated by the genus Lactobacillus (over 90%) and the other for which this genus is less important (less than 30% of bacteria). The same bacterial distribution was found in the general population. After two and a half years of monitoring, researchers observed a reduction in the rate of HIV infection by 61% in the Lactobacillus group, and only 18% in the non-Lactobacillus group. Their investigations showed that the concentration of tenofovir decreased rapidly one hour after application in non-Lactobacillus women, and that this drop negatively correlated with the presence of Gardnerella vaginalis and other anaerobic bacteria associated with a risk of vaginosis, like Prevotella. The metabolism of these bacteria is believed to restrict the absorption of tenofovir by the target cells and therefore its conversion into an active molecule. These results confirm the importance of the vaginal microbiota in the response to this preventive treatment, and suggest that this factor should be taken into consideration in future attempts to improve its effectiveness.
Nichole R. Klatt et al. Vaginal bacteria modify HIV tenofovir microbicide efficacy in African women. Science 356, 938–945 (2017)