Modeling Host-Microbiome Interactions using Organ-On-A-Chip Technology

September is National Ovarian Cancer Awareness Month, a time to raise awareness about ovarian cancer, one of the leading causes of cancer deaths among women. It is predicted that close to 20,000 women in the United States will be diagnosed with ovarian cancer in 2024. Fortunately, heightened awareness and advancements in early detection and prevention have led to a steady decline in death rates, averaging a 2.4% reduction per year since 2013.

The prevalence of ovarian cancer emphasizes the importance of women’s gynecologic health. Regular gynecologic check-ups are essential in preventing bacterial infections, addressing hormonal imbalances, and treating reproductive diseases before they can lead to more severe health issues. A growing body of evidence shows the microbiome as a key regulator of vaginal health and disease. Yet, there is a lack of relevant human vaginal epithelium models to study host-microbiota interactions. A new publication describes an organ-on-a-chip culture model of the human vaginal mucosa to better understand the composition and function of the vaginal microbiome.

Modeling Host-Microbiome Interactions using Organ-On-A-Chip Technology

Mahajan and colleagues describe a new preclinical culture model of the human vaginal mucosa developed using organ-on-a-chip technology to interrogate host-microbiome interactions and host innate immune responses, which could potentially be used for the discovery and assessment of microbiome-based therapeutics.

Organs-on-a-chip are systems containing engineered or natural miniature tissues grown inside microfluidic chip devices. Microfluidic two-channel co-culture organ chip devices were used to create the human vagina chip. Primary human vaginal epithelial cells obtained from Lifeline® Cell Technology and uterine fibroblasts were seeded on the top and bottom surface of a porous membrane within top channel of the chip to recreate the vaginal epithelial-stromal interface in vitro. Differentiation medium was continuously perfused to mimic episodic flow of mucus through the vagina, inducing spontaneous differentiation to form a multilayered, stratified, vaginal epithelial cells and underlying stromal fibroblasts, which sustains a low physiological oxygen concentration in the epithelial lumen.

Vagina Chip Characterization: The vagina chip was first characterized using immunofluorescence staining, revealing the expression of various structural and functional markers that closely mimic those observed in human vaginal epithelium in vivo. The device exhibited a tight tissue permeability barrier, quantified by the apparent permeability (Papp), and was responsive to estrogen. These hallmarks are critical for supporting a living microbiome and maintaining vaginal health.

Co-Culture Establishment: To determine if the model could support a living microbiome, co-cultures in the vagina chip were initiated with single- and multi-strain consortia containing Lactobacillus crispatus (OC1, OC2, and OC3), as well as dysbiotic Gardnerella-containing bacterial strains (BVC1 and BVC2). A dominance of Lactobacillus-containing microbiota is known to be ideal for optimal gynecological health, while the presence of Gardnerella vaginalis is associated with sub-optimal health outcomes, such as those observed in bacterial vaginosis (BV). Live culturable bacteria could be isolated from the chip effluents daily throughout a 72-h period, demonstrating successful microbiota growth in the vagina chip.

Colonization with Optimal and Non-Optimal Consortia: The researchers then assessed the effects of microbiota composition on host cell immune responses. Co-culture and growth of the L. crispatus consortia in the chip maintained epithelial cell viability, produced D- and L-lactic acid (known for their antimicrobial effects in vivo), and sustained a physiologically relevant low pH. Additionally, there was a downregulation of proinflammatory cytokines, including interleukin-6 (IL-6), IL-8, IL-1α, IL-1β, and interferon-γ inducible protein-10 (IP-10), compared to control vagina chips. This demonstrated the modulation of innate immune responses by optimal vaginal consortia. In contrast, co-culture of pathogenic G. vaginalis-containing consortia resulted in epithelial cell injury, a rise in pH, and upregulation of proinflammatory cytokines.

These findings highlight the adverse effects of non-optimal microbiota on vaginal health and the potential of the vagina chip model as an effective human in vitro preclinical model that can be used to advance host-microbiome research and accelerate development of microbiome-targeted therapeutics including live biotherapeutic products.

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Modeling Host-Microbiome Interactions using Organ-On-A-Chip Technology