Over the past ten years, the human microbiome has attracted a lot of attention due to research suggesting that disturbed bacterial communities are to blame for a variety of illnesses, including irritable bowel syndrome, dermatitis, and autoimmune diseases. The majority of research has concentrated on the microbiome found in the human stomach. Still, there is a growing consensus that another frequently understudied bacterial population, that of the vagina, merits equal study.
Bacterial vaginosis (BV), which affects about 30 percent of reproductive-aged women worldwide and is expected to cost USD 4.8 billion to cure each year, is brought on by disturbances of the vaginal microbiome. Pre-term birth, the second-leading cause of newborn death, and several sexually transmitted infections, including HIV, are both made more likely by BV in pregnant women.
Antibiotics are now used to treat BV, but the condition frequently returns and can result in more serious problems such as pelvic inflammatory disease and even infertility.
Living biotherapeutics are being investigated for the treatment of BV, just as probiotics are now being prescribed to treat gut problems. The human vaginal microbiome differs significantly from those of popular animal models, making it challenging to undertake preclinical experiments. According to studies, lactobacilli bacteria make up more than 70 percent of the vaginal microbiome in healthy humans, but less than 1 percent in the vaginal microbiomes of other mammals.
Researchers at the Wyss Institute at Harvard University have created a solution to that problem in the form of a new Organ Chip that replicates the human vaginal tissue microenvironment including its microbiome in vitro. Composed of the human vaginal epithelium and underlying connective tissue cells, the Vagina Chip replicates many of the physiological features of the vagina and can be inoculated with different strains of bacteria to study their effects on the organ's health. The chip is described in a new paper published in Microbiome.
Modeling the vaginal microbiome: The Bill and Melinda Gates Foundation provided financing for the creation of the Vagina Chip, which had the goal of developing a biotherapeutic therapy for BV and advancing it into human clinical trials in order to lower the incidence of infant mortality, genital infections, and pregnancy problems. especially in countries with few resources.
"A major stumbling block for that effort was that there were no good preclinical models that could be used to study which therapies can actually treat BV in human tissues. Our team's project was to create a human Vagina Chip to aid in the development and testing of new therapies for BV," said co-author Aakanksha Gulati, Ph.D., a Postdoctoral Researcher at the Wyss Institute.
The scientists seeded the top channel of a polymer chip with human vaginal epithelial cells using the microfluidic Organ Chip technology, which was created at the Wyss Institute and then licensed to Emulate. The other side of the permeable membrane between the top and bottom channels was then supplemented with human uterine fibroblast cells. The 3D design resembled the human vaginal wall in structure.
The Vagina Chip has grown several unique layers of differentiated cells after five days that mirrored those in human vaginal tissue. The Vagina Chip's gene expression patterns varied in response to the introduction of the female sex hormone estradiol (a kind of estrogen), showing that it was hormone sensitive--another essential quality for in vitro reproduction of human reproductive organs.
The scientists then moved to study the vaginal microbiome armed with a living replica of the human vagina. They collaborated with Dr. Jacques Ravel, Ph.D., and his group at the University of Maryland School of Medicine, who had developed three different consortia, each of which contained multiple strains of Lactobacillus crispatus, in light of recent research showing that healthy human vaginal microbiomes typically contain multiple strains of Lactobacillus bacteria.
After three days, all three of these consortia successfully colonized the Vagina Chip after being introduced. Lactic acid, which contributes to maintaining the vagina's low pH and prevents the growth of other microbes, was also started by the consortia.
Beyond helping to maintain an acidic environment, the presence of the L. crispatus bacteria also affected the Vagina Chip's innate immune responses. Chips with bacterial consortia produced lower levels of several inflammation-causing cytokine molecules than chips without the bacteria, which is consistent with the current theory that these "good" microbes help keep inflammation in check in healthy human vaginas.
Bad bacterial tenants, on a chip: Having created a healthy Vagina Chip with optimal bacterial residents, the team then conducted a new experiment in which they inoculated chips with different species of bacteria that are associated with BV: Gardnerella vaginalis, Prevotella bivia, and Atopobium vaginae.
A consortium of those three "bad" microbes caused the chips' pH to increase, damaging the vaginal epithelial cells and significantly increasing the production of multiple proinflammatory cytokines - all responses that were similar to what has been observed in human patients with BV.
"It was very striking that the different microbial species produced such opposite effects on the human vaginal cells, and we were able to observe and measure those effects quite easily using our Vagina Chip," said co-author Abidemi Junaid, Ph.D., a Research Scientist at the Wyss Institute.
"The success of these studies demonstrate that this model can be used to test different combinations of microbes to help identify the best probiotic treatments for BV and other conditions."
The team is now using the Vagina Chip to test new and existing treatments for BV to identify effective therapies that can be advanced into clinical trials. They are also working on integrating immune cells into the chip to study how the vaginal microbiome might drive systemic immune system responses.
"There is growing recognition that taking care of women's health is critical for the health of all humans, but the creation of tools to study human female physiology is lagging," said senior author Don Ingber, M.D., Ph.D., who is the Wyss Institute's Founding Director. "We're hopeful that this new preclinical model will drive the development of new treatments for BV as well as new insight into female reproductive health." Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Boston Children's Hospital and the Hansjorg Wyss Professor of Bioinspired Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences.
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