Understanding Vaginal Microbiomes with Vagina-on-a-Chip Models

April 04, 2023 - As organ-on-a-chip technology has advanced, researchers have branched out to model multiple organs. In a new study published in the BMC Microbiome, researchers developed and analyzed the utility of a vagina-on-a-chip, a microfluidic organ culture model of the human vaginal mucosa. The model aimed to mimic the human vaginal microbiome and understand vaginal microbiome host interactions by combining ideas from existing organ-on-a-chip models with data from reproductive health and sexual health research on the vagina’s microbiome.

Organ-on-a-chip

Since the first development of organ-on-a-chip models in 2010, researchers have worked to advance and expand the uses of this biotechnology. In addition to using the model to analyze tissues and how specific nutrients affect development, academic researchers have also used organ chip models to test drug mechanisms and impacts.

Beyond scientific research purposes, organ chip models have been used to test drugs and advance the medication development process in the pharmaceutical industry.

“The drug development model is broken or highly challenged because most drugs fail when they get to the clinic,” said Don Ingber, MD, PhD, founding director of Harvard University’s Wyss Institute for Biologically Inspired Engineering, chair professor at Harvard and Boston Children’s Hospital, and author on the BMC study.

He notes that much of that may be connected to the focus on animals as a preclinical model, which does not necessarily indicate the outcomes in human patients. Furthermore, Ingber postulates that many drugs that could benefit humans may have yet to make it to clinical phases because of bad results in animal models. This understanding drove Ingber and many others to focus on organ-on-a-chip models.

Vagina-on-a-Chip

“An organ chip is a small microdevice, the size of a computer memory stick, made of an optically clear, flexible, rubber-like material,” he explained. “It has hollow channels less than a millimeter wide. A porous membrane separates two hollow channels, and researchers can flow fluids or air through these channels.”

He explained that these channels could be lined with human cells — like cells from human vaginal tissue — and blood vessels on the bottom. Clinicians can then perfuse nutrients through the channels to simulate the interactions in the body.

“The vagina chip happened because I had been working on an intestine chip with the Gates Foundation,” noted Ingber. “We were modeling malnutrition and low-resource nations. That was going so well that they came to us and said, ‘Could you build a vagina chip or a cervix chip?’”

The Gates Foundation wanted to focus on the vagina-on-a-chip model because roughly 25% of people with vaginas experience bacterial vaginosis. Although the condition is a relatively common infection that can be treated with antibiotics, low-resource nations struggle to treat the disease.

According to Ingber, bacterial vaginosis significantly contributes to prenatal death and increased susceptibility to sexually transmitted infections (STI), including HPV, HIV, chlamydia, or gonorrhea. Beyond the risk of STI, the Cleveland Clinic links untreated bacterial vaginosis to pregnancy complications, pelvic inflammatory disease, and infertility.

Developing an inexpensive new treatment for bacterial vaginosis to improve women’s health was a significant driver in developing the human vagina-on-a-chip model.

“They're always looking for inexpensive ways to treat major disease processes endemic in low-source nations. They are trying to pursue the development of a live bio-therapeutic product, which is like a bacterium probiotic formulation that can be sold over the counter and is expensive,” noted Ingber. “However, they have no real way to test it pre-clinically. There's no animal model for this.”

Model Specifications

“In the vagina chip, we get the lining epithelial cells from the vaginal epithelium. We can buy them commercially or get them from patients directly,” explained Ingber.

For this study, he and his teammates concocted a synthetic mixture of microbes to put on the chip and simulate the vaginal microbiome.

“Research over the last ten years has suggested that individuals with good vaginal health are dominated by a complex microbiome that's dominated by a species called lactobacillus,” noted Ingber. “More specifically, Lactobacillus crispatus dominates a healthy person’s vaginal microbiome, whereas a different type of microbiome correlates with bacterial vaginosis.”

In many cases of bacterial vaginosis, there are low levels of lactobacilli bacteria and high levels of unhealthy bacteria, such as Gardnerella vaginalis. Both situations can be modeled on organ-on-a-chip technology.

After developing the model, Ingber and his team could test early formulations of the biotherapeutic product.

“The product is a mixture of the good L. crispatus microbes, which could show that they suppress inflammation,” noted Ingber.

Benefits of Organ Chip Models

Ingber pointed out another vital advantage of human organ-on-a-chip models: the ability to personalize the chip. According to him, clinicians can manipulate the model to replicate interactions across different sexes, ethnic groups, and ages. It could even simulate microbiome interactions in pregnant individuals.

“Researchers can't do this easily in mice in a meaningful way,” emphasized Ingber.

Beyond the ability to model multiple scenarios, investigators can also use the models to test drugs, helping them develop new treatments or therapies.

“For drugs, we could mimic the drug exposure profiles or the change in drug levels over time, focusing on pharmacokinetics,” he added. “We've done this in multiple studies and can mimic the regimen-specific responses seen in patients.”

Using organ chip technology, the ability to model drug interactions or bacterial communities in human vaginal cells — or any human cells — is unparalleled by any existing models.

Some existing standard models include cell cultures or organoids. Although researchers could put microbes with cells in culture, that is considered contamination and leads to cell death.

Alternatively, researchers have also attempted to use organoids to understand this process. Ingber defines organoids as tissue cultures derived from stem cells. These cells grow in a gel and can mimic cell and tissue features. However, there are some limitations to organoids. First, they cannot correctly mimic multi-tissue organ features and the physical microenvironment. Even though researchers can inject microbes into the center of organoids, they will die within 24 hours, preventing researchers from observing longer-term impacts.

“Even with organoids, which we often use as cell sources, when they're just sitting bathed in drug, that's nothing compared to our inpatient responses,” he continued.

Some patients take their medications multiple times a day or at different dosages. It also does not account for various treatment methods modalities, whether an injection or an oral pill.

“The ability to culture microbiomes in contact with living human cells for multiple days is another unique advantage of organ-on-chips,” added Ingber.

Beyond modeling for days, significantly longer than any other in vitro model used in clinical research, clinicians may be able to extend the time. Ingber explained that they have looked at passing viral infections from chip to chip to observe the change over an extended period.

“In a viral infection, we could see the evolution of variants of concern with influenza virus by passing from chip to chip. These are long chips that almost mimic coughing in patient-to-patient transmission,” he remarked.

Future of Organ Chip Models

Although organ chip models may become critical tools for drug development and analysis, some limitations are associated with these models. One of the most obvious limitations is that it only analyzes part of the body.

Ingber explained that investigators have attempted to model a more holistic human body by using human body on chips, which connect multiple organ chips with blood vessel channels.

While the limitations will require some work to overcome, researchers anticipate that organ chip models will be the future of scientific development.

In addition to the benefits of wildlife conservation, the organ chip models will be associated with significant cost savings over time. Although they are more expensive than cell culture plates, the cost of organ chip models is comparable to animal studies, with one added bonus: they’re human. They are also significantly less expensive than non-human primates, which are the closest to humans.

“We have to think of these as replacements for animal testing, not a replacement of a 96-well plate. They're not high throughput. We use higher throughput methods to work out doses, and then we'll do the important experiments on the chips,” said Ingber.

Although the current costs are relatively expensive, since the technology is in its early stages, it will likely decrease as more companies commercialize the models and improve development procedures.

“The way big pharma works now is they'll spend tens of millions of dollars on clinical trials that almost always fail. Then they go back, and they do get their statisticians to analyze. If they're lucky, they do a targeted trial with a group that responds better, and they get approved for a new application,” said Ingber

“With organ-on-chips and cells from patients, you could flip it on its head and start with a particular ethnic group,” he added.