Vaginal organoids may unlock new insight into sexually transmitted infections in women

By Sarah Anderson, PhD

A team of UBC researchers has created new vaginal models grown from mouse or human cells and demonstrated that they are capable of being infected with herpes simplex virus type 2 (HSV-2) and Zika virus and responding to antiviral drugs.

Their results establish a valuable experimental system that researchers can leverage to study how sexually transmitted viruses infect, replicate, and respond to treatment in the female reproductive tract.

“Discoveries that were being made about other organ systems decades ago are just now being initiated in a lot of areas of women's health,” said Ananya Saraph, a research technician in the Department of Microbiology and Immunology and first author of the preprint study. “One of these areas is sexually transmitted infections, and I’m hopeful that scientists working in this space can use this tool to drive new breakthroughs.” 

Sexually transmitted viruses such as human papillomavirus, human immunodeficiency virus, herpes simplex virus, and Zika virus disproportionately affect women and often result in adverse outcomes for maternal and fetal health. Understanding how these viruses specifically affect vaginal tissue could help scientists devise new strategies to clear the virus at the site where the infection is acquired. However, immune responses at the vaginal tract have been historically understudied compared to those at other mucous membrane systems such as the lung and gut.

To bridge this gap, researchers have recently begun to develop vaginal organoids — three-dimensional clusters of cells that mimic the structure and function of the vagina. These organoids better represent the complex architecture and spatial organization of the vagina compared to cells grown in a single layer in a flask. Organoids provide a platform that is both physiologically relevant and compatible with efficiently testing large collections of drug candidates, and those made from human cells allow scientists to study viruses that do not infect mice. While ripe with potential, the use of vaginal organoids is still in its infancy and requires further studies to better understand how different components affect function.   

To meet this need, the researchers set out to create and characterize mouse- and human-derived vaginal models. They harvested vaginal tissue from mice, obtained cells including stem cells, and allowed them to grow into a multi-layer structure within a gel-like scaffold. There, the stem cells transformed into the different types of epithelial cells present in the vagina and formed three-dimensional organoids. Because it’s difficult to get access to human vaginal tissue and the stem cells it contains, the team next used cells that were previously isolated from human vaginal lining and modified to grow in culture. “We coaxed these cells into forming spatially organized structures known as spheroids,” said Saraph. “They’re not true organoids because they’re not generated from stem cells and they don’t feature all of the different cell types present in vaginal tissue, but it’s a promising starting point." 

The researchers then focused on evaluating how their three-dimensional cellular clusters responded when they exposed them to sexually transmitted viruses. “The virology expertise that we have in the department was instrumental in giving us access to these viruses in our lab,” said Dr. Maria Tokuyama, a professor in the Department of Microbiology and Immunology and senior author of the study. The team exposed the mouse organoids and human spheroids to HSV-2 and observed that both were susceptible to infection. They then treated the organoids and spheroids with an existing antiviral drug and found that both displayed a significant decrease in virus replication, marking the first time that human vaginal spheroids have been used to model viral infection and response to treatment. They took the same approach with Zika virus and observed that while the two systems were again successfully infected, only the human spheroid showed a drop in virus replication when treated with an approved antiviral. These results indicate that while their vaginal organoid platform reliably reports the effects of antiviral drugs, these effects may vary in cells derived from different species. 

The team then turned their attention to the spatial arrangement of cells in the mouse organoid. The organoids that they and other researchers had thus far generated featured a flipped orientation, where the layer of cells facing the outside or inside of the structure is opposite from what is found in the vagina. Drawing on studies of other organoid systems, the team hypothesized that the physical pressure exerted by the gel-like scaffold might be causing the organoids to adopt this reversed arrangement. When they released the organoid from the scaffold, they found that the structures automatically turned inside-out, establishing for the first time mouse vaginal organoids that preserve the true physiological orientation. 

The team then treated this “apical-out” organoid with HSV-2 and Zika virus and found that, compared to its flipped, “basal-out,” counterpart, a higher amount of virus was required in order to support virus replication and sustain infection. While it’s not yet clear why this is the case, the researchers hypothesize that it may be related to the fact that the apical side features less of a key surface receptor that many viruses use to enter the cell and more keratin protein, which could serve as a physical barrier that blocks viral penetration. “Comparing the apical-out to basal-out organoids will allow us to study how different layers of cells respond to a virus and what this means for the course of infection,” said Saraph. While cells on the apical side are the first to “see” the virus, certain viruses such as HSV-2 can establish a latent infection and, when reactivated, encounter cells on the basal side. Therefore, it is necessary to understand how the virus interacts with these layers from both directions.

While their organoids and spheroids currently include only epithelial cells found in the vaginal lining, the researchers hope to next incorporate immune cells (specifically, lymphocytes) that play a critical role in the body’s response to sexually transmitted infections and antiviral treatments. They hope that with further refinement, their models may be used to not only test new drug candidates, but provide insight into basic questions in the female reproductive tract, such as how the host responds when viral or bacterial pathogens infect at the same time. “It’s really important to understand these co-infection dynamics, and we’ll only be able to do that if we work with an actual vaginal tissue system,” said Dr. Tokuyama. “There is a pressing need for more research into these fundamental issues in women’s health, and I see this as a unique area in which my lab can contribute.”