Three-dimensional models of the cervicovaginal epithelia to study host–microbiome interactions and sexually transmitted infections

Two-dimensional (2D) cell culture systems have provided controlled, reproducible means to analyze host-pathogen interactions. Although inexpensive, straightforward, and requiring very short time commitment, these models recapitulate neither the functionality of multi-layered cell types nor the microbial diversity of an infected human. Animal models have commonly been used to recreate the complexity of human infections. However, extensive modifications are commonly required to recreate interactions that resemble those in the human reproductive tract microbiologically and physiologically. Three-dimensional (3D) cell culture models have emerged as alternative means of reproducing key elements of human infections at a fraction of the cost of animal models and on a scale that allows for replicative experiments to be readily performed. Here we describe a new 3D model that utilizes transwells with epithelial cells seeded apically and a basolateral extra cellular matrix (ECM)-like layer containing collagen and fibroblasts. In this system, basal feeding creates a liquid/air interface on the apical side. The model produced tissues with close morphologic and physiological resemblance to human cervical and vaginal epithelia, including observable levels of mucus produced by cervical cells. Infection by both Chlamydia trachomatis and Neisseria gonorrhoeae was demonstrated as well as the growth of bacterial species observed in the human vaginal microbiota, enabling controlled mechanistic analyses of the interactions between host cells, vaginal microbiota and STI pathogens. Future experiments may include immune cells to mimic more closely the genital environment. Finally, the modular set up of the model makes it fully applicable to the analysis of non-genital host-microbiome-pathogen interactions. IMPORTANCE Infected sites in humans are a complex mix of host and microbial cell types interacting with each other to perform specific and necessary functions. The ability to understand the mechanism(s) that facilitate these interactions, and interactions with external factors is paramount to being able to develop preventative therapies. Models that attempt to faithfully replicate the complexity of these interactions are time intensive, costly, and not conducive to high throughput analysis. Two-dimensional (2D) models that have been used as a platform to understand these interactions, while cost effective, are generally limiting in experimental flexibility and structural/physiological relevance. Our three-dimensional (3D) models of the cervicovaginal epithelium can facilitate analysis of interactions between the host epithelium, sexually transmitted pathogens and bacteria present in the vaginal microbiota. Due to the modular design, additional cell types and environmental modulators can be introduced to the system to provide added complexity, approaching conditions in the infected human host.