An iPSC based xeno-free platform to assess the foreign body response against new biomaterials

Implantable biomaterials and medical devices have become mainstream solutions for a variety of health problems and their use is constantly increasing. However, the materials used in these devices can be seen as foreign by the immune system triggering adverse immune reactions that could harm the patient and stop the device from working. These responses (generally known as foreign body response or FBR) are initiated by immune cells circulating in the blood (e.g. T cells and monocytes) and those that are resident (e.g. macrophages) in the tissues where the devices are implanted. Macrophages attack implants in an attempt to clear them from the body which leads to complications including inflammation and formation of dense tissues (fibrotic capsules) that surround the devices. Such complications are major causes of corrective surgeries costing the health system billions annually and causing significant suffering for millions of patients. There is therefore significant interest in investigating FBR for new biomaterials, unfortunately however, there is a heavy reliance on animal models in the biomaterials discovery pipeline with thousands of animals used in both academia and industry each year. In addition to ethical issues, these models are expensive, and have poor physiological relevance to human not least due to fundamental differences between the immune system in humans and the animals. Thus, there is an unmet need for developing better in vitro models to investigate FBR.

To address this need we will build a stem cell based, microfluidic device that can model the FBR and be used to test new biomaterials for compatibility with implantation. We will achieve this via 4 interlinked tasks:

Task 1: Development of Xeno-free hIPSC differentiation of immune and stromal cells. We have developed and validated an efficient, xeno-free stem cell differentiation platform to create all of the necessary cell types required for our model (endothelium, fibroblasts, macrophages and T-cells) in a single media and will finalise development of T-cells in our xeno-free system.

Task 2: Optimising static co-cultures of different cell types and cell supply. Our differentiation platform is based on a single cell culture media for all cell types making coculture of the different cell types more simplified. We will mix different cell types together at ratios that reflect healthy human tissue and assess baseline levels of cell metabolism, proliferation, death and inflammatory profiles.

Task 3: Microfluidic platform assembly and optimisation. We will build the microfluidic device containing compartments replicating vascular networks, stromal tissue and pumps simulating blood flow. We will further optimise long term cellular function of the device to achieve a functional life span of at least 2 weeks.

Task 4: Validation of in the new platform using a selection of well characterised biomaterials. We will compare the performance of the new platform by investigating FBR to a selection of clinically relevant biomaterials where we have access to existing in vivo data from well established animal models. This will enable us to fine tune different aspects of the new device (cell numbers, rations, flow rates) to optimise the device performance if necessary.

Together these objectives will deliver a stem cell based, microfluidic FBR model that will recapitulate the three-dimensionality of the target tissue and the dynamic events occurring in immune responses to implanted devices, including recruitment of circulating immune cells to the site of the implant, immune cell migration through blood vessels and connective tissues and their interactions with other cells in the local area. The model will not be reliant on primary cell types/donors and therefore reduce variability of the platform. Ultimately, this will allow more accurate biomaterial discovery while replacing the need to use tens of thousands of animals per year in biomaterial testing.

Modern medicine is increasingly moving towards implantable devices to facilitate management of disease. Their use, however, is limited by rejection of the device due to inflammation and fibrosis, collectively known as the foreign body response (FBR). Overreliance on animal models of the FBR has left significant gaps in our understanding of the FBR in humans, increasing costs and approval times of new devices. A human specific, animal-free model of the FBR would be transformative both in our understanding of the FBR and our efficiency in delivery of new implantable devices, while simultaneously reducing the significant burden on animals.

To address this, we will bring together our xeno-free, stem-cell-derived macrophages, T cells fibroblasts, and endothelial cells and assemble them in a modular microfluidic device that will closely simulate key cell-cell and cell-stroma interactions during the FBR via four interlinked tasks:

Task. 1. Optimising a xeno-free hIPSC differentiation and maintenance platform for generating fully functional monocytes/macrophages, T cells, endothelial cells and fibroblasts
Task. 2. Establishing static co-cultures of different cell types with focus on optimising culture conditions, common media and cell ratios that support functional properties of all cell types.
Task. 3. Incorporating different cell types into the modular microfluidic platform to develop a foreign-body-on-chip device.
Task. 4. Validation of in the new platform using a selection of well characterised biomaterials.

This model for the first time will enable investigating the FBR in a hIPSC derived animal-free model that simulates key immunological events and initial tissue response to biomaterials and can serve as a viable alternative to use of animals in biomaterial development and safety studies in both academia and industry replacing thousands of animal experiments.