A 3Rs approach to investigate the feto-maternal interface: visualisation of pathogen and antibody in a 3D in vitro human placental model

Why did we fund this project?

This award aims to develop a 3D microphysiological model of the human placenta using a microfluidic system to represent the feto-maternal interface to replace pregnant mammals used in infection and immunity studies.

The placenta acts as an interface between mother and foetus, transferring nutrients and removing waste products. Passive immunity is passed to the foetus through the transfer of antibodies. Some pathogens, such as the Zika virus, can also be transferred. The underlying mechanisms of how these transferals occur are not well understood. and a number of different approaches, including in vitro, ex vivo and in vivo methods, are used in associated research. In vitro models are typically 2D and do not include perfusion whereas ex vivo models are 3D and can be perfused, but only for a number of hours and are difficult to set-up. Pregnant mammals, including mice, rats, rabbits, pigs and sheep, are typically used in infectivity studies where the pathogen is injected or ingested to induce clinical symptoms or to determine doses in vaccine studies.

The student will develop a microphysiological model of the placenta using a commercially available OrganoPlate system. The model will include co-cultured human endothelial cells and trophoblasts, the two main cell types in the placenta, and be perfused to create a 3D microfluidic platform. The OrganoPlate system enables real-time imaging in a high throughput system, which the student will use to investigate maternal passive immunity and disease transmission. They will develop skills in immunohistochemistry and confocal microscopy.  

Background: Immunisation during pregnancy is now recognised as an efficient approach to protect the fetus and/or the infant from life-threatening infection. However, the mechanisms underlying the transmission of pathogens and the transfer of passive immunity from the mother to the fetus remain obscure. The structure that lies at the interface between mother and fetal environment is the placenta, an intricate organ made up of cellular and vascular networks that serve the functions of kidney, lung, gut and liver altogether in order to promote fetal growth and viability. Owing to the ethical issues associated with the study of human pregnancy, a variety of in vivo, ex vivo and in vitro models have been developed. However, while the in vivo animal models fail to match the structural and/or functional properties of the human placenta, ex vivo human models are impractical, difficult to set up, of limited capability, and in vitro models lack physiological relevance by virtue of their monolayer and/or static set-up.

Proposed solution: To address the caveats inherent to current experimental models of the human placenta, we propose to develop a novel and easy-to-set-up in vitro platform that will help reduce and/or replace the use of both murine and non-murine models. Our model will be validated through the analyses of placenta-blood barrier functions and cross-placental transport of pathogens and antibodies using a 3D microfluidic bioengineered platform i.e., the Organoplate® (Mimetas).

Experimental approach: Trophoblasts represent the most outer layer of the placenta whereby nutrients, chemical and gas feto-maternal exchanges are regulated. With the support of our industrial partner, we will develop an unprecedented trophoblast-based microfluidic dynamic model, that mimics the feto-maternal interface. This will be achieved using the commercially available and imaging-friendly 3-line OrganoPlate® system (Mimetas BV), we will create a tubular culture system that mimics the three-dimensional, quasiphysiological environment where (fetal) endothelial cells will be luminally exposed to physiological levels of flow and co-cultured with abluminal trophoblasts to form a functional placental barrier. Our platform will be unique in that it will also offer real-time and high-throughput imaging capability.

The major outcomes of this project will be:

• The development of a microphysiological model that reconstitutes the functional unit of the human placenta, and establishment of SOPs disseminated via local and international networks including the OOAC (organ-on-a-chip) Technologies (MRC-Innovate UK) and iPlacenta (Horizon 2020) and/or via sponsored workshops
• The provision of in vitro platform offering versatility and high predictive value to replace animals that would otherwise be used to investigate maternal passive immunity and vertical disease transmission
• The establishment of optimal methodologies for theimaging of antibodies and pathogens to promote a wider use of dynamic in vitro imaging.

3R impact: An immediate benefit will be the potential for a significant reduction in the number of experimental animals used for research. Our novel platform could be used specifically as in vitro substitutes for infectivity studies where pathogens are injected into or ingested by the host to determine the quantity required to induce clinical symptoms; infection biology studies which are aimed primarily at improving our knowledge of basic pathogen biology, pathogenesis and host-pathogen interaction; drug testing and/or vaccine screening where drugs or vaccines are administered at a range of concentrations to determine effective dose. Although clinical drug and vaccine trials are unlikely to be avoided completely, these could be considerably refined if more relevant in vitro testing were possible.