The vaginal microbiota, an ally against cancer

Every two weeks, a current scientific topic is explored by a researcher from the Collège de France.

In 2023, France recorded 1,100 deaths from cervical cancer, despite screening campaigns. As these cancers are all caused by papillomaviruses (HPV), the fight against these infections helps to prevent them. A better understanding of the vaginal microbiota could help to improve prevention.
Interview with Samuel ^Alizon*, biology researcher at the Collège de France.

We know how to prevent cervical cancer fairly well. As with other cancers, early detection contributes to the chances of cure. For women over the age of 30 , the new recommendations are to first carry out an HPV screening test to detect the possible presence of a papillomavirus.

Testing for HPV before trying to detect the presence of precancerous cells speeds up diagnosis, saves money for the healthcare system and offers patients a less intrusive method.

Samuel Alizon's team is focused on improving cancer prevention, by seeking to better understand HPV infections. " We have implemented a clinical study to describe the dynamics of genital infections caused by HPV and their interaction with the immune response. " To do this, she set up a continuous follow-up of women with regular biological sampling, which led her to take an interest in this vaginal environment as a whole, and, in particular, the microbiota.

A scientific, health and political issue

All the micro-organisms living in a given ecosystem form the microbiota. They cover all our body's interfaces with the environment, such as the skin and the intestine. If we compare the gut microbiota of two people, we see that they differ completely.   A healthy intestinal microbiota is made up of thousands of highly diverse micro-organisms," explains Samuel Alizon. So diverse, in fact, that it's hard to categorize it for a single person. Vaginal microbiota, on the other hand, are very easy to describe, because they're not very diverse. A healthy vaginal microbiota has virtually only one species of micro-organism. " This greatly facilitates the scientific process, enabling simple hypotheses to be formulated and tested.

However, there is a lack of studies on the subject, particularly in Europe and even more so in France. " We're probably touching on male biases in research and science ", says Samuel Alizon. For example, the researcher was surprised to note the lack of studies on the links between menstrual protection, particularly silicone cups, and the vaginal environment. In his view, an in-depth study of vaginal microbiota could tell us a lot about HPV infections. The microbiota present in the vagina is essentially made up of lactobacilli. "These bacteria get their name from their production of lactic acid, with which athletes are very familiar Lactic acid means acidity and therefore a very low pH. Many bacteria and viruses cannot survive in an acid pH. "However, despite this protective role, we know nothing about the predisposition of certain women to having a vaginal microbiota more or less rich in lactobacilli

Beyond cervical cancer

Studies in North America and Africa have already shown that a vaginal microbiota composition low in lactobacilli is associated with greater susceptibility to certain sexually transmitted infections, such as HPV or human immunodeficiency virus (HIV). However, there is still a great deal of work to be done on this subject. On the one hand, little is known about the reasons why some women have lactobacillus-poor microbiota ; on the other, therapeutic options are limited and have not really changed over the last forty years, with two or three types of antibiotics. But these are tricky questions, as genital infections could also affect the composition of the vaginal microbiota.

This research could also help resolve certain cases of infertility. "  Microbiota composition is associated with significant differences in the success of in vitrofertilization procedures . " Links with endometriosis are also put forward, but evidence is lacking. More broadly, surveys show a correlation between disturbances in vaginal microbiota and women's well-being.

Unfortunately, these are not yet the subject of a large body of scientific literature. " We have effective working tools to go further and describe precisely how the vaginal microbiota functions ", says Samuel Alizon. As well as being an exciting scientific subject, it is associated with major health issues . Despite the funding difficulties he may encounter, this does not prevent him from being optimistic and convinced that this is a field of research for the future.

*Samuel Alizon is director of the Ecology and Evolution of Healthteam in the CIRB unit at the Collège de France, and director of research at the CNRS.