Article by Maria Samaritano & Roberta Lock
Engineering the Human Vagina On-a-Chip
Vaginal microbiome-host interactions modeled in a human vagina-on-a-chip, Microbiome, 2022
Gautam Mahajan et al., Don Ingber Lab
The vagina is a muscular tube-like structure that is part of the female reproductive system. It connects the cervix to the outside of the body and serves as a passage for menstrual blood, sexual intercourse, and childbirth. Since the vaginal environment is constantly exposed to different microorganisms, this organ has a diverse array of bacteria, fungi, and viruses that live within it. These microorganisms can be both beneficial and harmful, depending on their type and quantity. This community is called the vaginal microbiome, and its interactions with the body’s immune system are still not fully understood. This study uses techniques from the field of organs-on-chip engineering to create a novel in vitro vaginal model to mimic the vaginal microenvironment in order to identify and understand key interactions that may lead to vaginal infections and other gynecological conditions.
What did these researchers do?
In this study, researchers created a novel human vagina-on-a-chip model that allows for the study of complex interactions between the vaginal microbiome and the host. They then used the model to investigate the effects of two bacterial species commonly found in the vaginal microbiome, Lactobacillus crispatus and Gardnerella vaginalis, on the vaginal epithelium. By analyzing gene expression changes in the vaginal epithelium and the composition of the bacterial culture, key interactions between the vaginal microbiome and the host could be identified. For example, the study found that the vaginal epithelial cells responded differently to different bacterial species; Lactobacillus crispatus promoted epithelial cell proliferation and differentiation, while Gardnerella vaginalis disrupted the epithelial barrier and induced inflammation. Overall, the study demonstrates the potential of a human vagina-on-a-chip model for studying the interactions between the vaginal microbiome and the host, as well as for testing new therapies for vaginal conditions that adversely affect patients, like vaginal dysbiosis.
Why is this important?
Despite its critical role for female health, the vaginal organ remains relatively understudied. Although developments in gynecologic health research continue to advance, relatively few groups specifically focus on vaginal tissue research. As a result, there is insufficient data for researchers to use for the development of targeted therapeutics, thus leaving vaginal conditions with limited treatments. Specifically, non-optimal vaginal microbiota are associated with an increased risk of infections, such as bacterial vaginosis, as well as adverse reproductive outcomes, like preterm birth. Therefore, there is a major need to create novel research methods to study this organ and model its dynamic microenvironment. Thus, the model developed in this study represents a significant improvement over traditional methods of studying vaginal tissue, such as 2D cell culture on flat plastic, or in vivo mouse models, which often fail to fully replicate the human in vivo environment. Furthermore, this model has the potential to be used in pre-clinical drug testing, allowing for the development of new treatments. Therefore, the development of this device serves as a crucial first step in the creation of a novel platform to study the dynamic vaginal microbiome interactions and accelerate the development of therapeutics to improve female healthcare outcomes.
How did the researchers do this?
To develop this vagina-on-a-chip model, the authors of this paper used a combination of microfabrication techniques, cell culture, microbiology, and molecular biology. First, they designed a microfluidic device that mimics the structure and function of the human vaginal epithelium. These researchers decided to recreate key components of vaginal tissue, including the epithelial layer, microbiome, pH, and mucus secretion. In order to do so, this device consisted of two compartments, one for the epithelial cells and the other for the bacterial culture. The two compartments were separated by a porous membrane that allowed for the exchange of molecules and metabolites but prevented direct contact between the epithelial cells and the bacterial culture.
Diagram of Vaginal Organ Chip
Next, to create the epithelial layer, a microfabrication technique called soft lithography was used to pattern a layer of polydimethylsiloxane (PDMS) (a biocompatible polymer) on glass. They then seeded the PDMS layer with primary human vaginal epithelial cells obtained from hysterectomy samples. The cells were cultured until they formed a continuous, dense epithelial layer that was similar to the natural vaginal epithelium. For the bacterial culture, the researchers used a combination of two bacterial species commonly found in the vaginal microbiome, Lactobacillus crispatus and Gardnerella vaginalis. They introduced the bacterial culture into the compartment adjacent to the epithelial layer and allowed it to interact with the epithelial cells for up to 48 hours. To study the interactions between the vaginal microbiome and the host, the researchers analyzed gene expression changes in the epithelial cells using RNA sequencing and analyzed the composition of the bacterial culture using 16S rRNA sequencing, which is a special type of sequencing that is used to identify and compare bacterial diversity in a sample. Overall, the methods used in this study allowed for the development of a complex human vagina-on-a-chip model that mimics the structure and function of the vaginal epithelium.
What comes next?
While this study provides important insights into vaginal microbiome interactions, there are a few limitations that should be considered. The model aims to mimic the structure and function of the vagina, but only recapitulates a few key characteristics. While a more simplistic in vitro model allows for more control over every aspect of the study, the lack of complexity means the model can’t fully recapitulate what happens in a person in vivo. There are several ways the model’s complexity could be increased in the future to make it even more representative of the native organ. The bacterial culture could be expanded to include a wider range of bacterial species. While the composition of the vaginal microbiome can vary widely between individuals and over time, more than 20 different species of Lactobacillus have been detected within it. Additionally, the cells representing the vagina were limited to epithelial cells, whereas the native vagina has a complex cell landscape composition. For example, immune cells would be an interesting addition, as they play an important role in regulating the vaginal microbiome and responding to infections. Finally, as with all in vitro models and studies, it is important to remember that in vivo studies and clinical benchmarks will be needed to validate the in vitro findings to ensure clinical relevance. Overall, while the development of the vagina-on-a-chip model presented in this paper represents a significant improvement over traditional models, there is much work to be done to elucidate the information necessary to develop treatments that will significantly reduce the burden of gynecological diseases.