Building blocks of microphysiological system to model physiology and pathophysiology of human heart

Microphysiological systems (MPS) are drawing increasing interest from academia and from biomedical industry due to their improved capability to capture human physiology. MPS offer an advanced in vitro platform that can be used to study human organ and tissue level functions in health and in diseased states more accurately than traditional single cell cultures or even animal models. Key features in MPS include microenvironmental control and monitoring as well as high biological complexity of the target tissue. To reach these qualities, cross-disciplinary collaboration from multiple fields of science is required to build MPS. Here, we review different areas of expertise and describe essential building blocks of heart MPS including relevant cardiac cell types, supporting matrix, mechanical stimulation, functional measurements, and computational modelling. The review presents current methods in cardiac MPS and provides insights for future MPS development with improved recapitulation of human physiology.

Sourcing cells for in vitro models of human vascular barriers of inflammation

The vascular system plays a critical role in the progression and resolution of inflammation. The contributions of the vascular endothelium to these processes, however, vary with tissue and disease state. Recently, tissue chip models have emerged as promising tools to understand human disease and for the development of personalized medicine approaches. Inclusion of a vascular component within these platforms is critical for properly evaluating most diseases, but many models to date use "generic" endothelial cells, which can preclude the identification of biomedically meaningful pathways and mechanisms. As the knowledge of vascular heterogeneity and immune cell trafficking throughout the body advances, tissue chip models should also advance to incorporate tissue-specific cells where possible. Here, we discuss the known heterogeneity of leukocyte trafficking in vascular beds of some commonly modeled tissues. We comment on the availability of different tissue-specific cell sources for endothelial cells and pericytes, with a focus on stem cell sources for the full realization of personalized medicine. We discuss sources available for the immune cells needed to model inflammatory processes and the findings of tissue chip models that have used the cells to studying transmigration.

Multiorgan microphysiological systems as tools to interrogate interorgan crosstalk and complex diseases

Metabolic and inflammatory disorders such as autoimmune and neurodegenerative diseases are increasing at alarming rates. Many of these are not tissue-specific occurrences but complex, systemic pathologies of unknown origin for which no cure exists. Such complexity obscures causal relationships among factors regulating disease progression. Emerging technologies mimicking human physiology, such as microphysiological systems (MPSs), offer new possibilities to provide clarity in systemic metabolic and inflammatory diseases. Controlled interaction of multiple MPSs and the scalability of biological complexity in MPSs, supported by continuous multiomic monitoring, might hold the key to identifying novel relationships between interorgan crosstalk, metabolism, and immunity. In this perspective, I aim to discuss the current state of modeling multiorgan physiology and evaluate current opportunities and challenges.

Modeled vascular microenvironments: immune-endothelial cell interactions in vitro

The advancement of in vitro techniques enables a better understanding of biological processes and improves drug screening platforms. In vitro studies allow for enhanced observation of cell behavior, control over the mimicked microenvironment, and the ability to use human cells. In particular, advances in vascular microenvironment recapitulation are of interest given vasculature influence in cardiovascular vascular diseases and cancer. These investigate alterations in endothelial cell behavior and immune cell interactions with endothelial cells. Specific immune cells such as monocytes, macrophages, neutrophils, and T cells influence endothelial cell behavior by promoting or inhibiting vasculogenesis through cell-cell interaction or soluble signaling. Results from these studies showcase cell behavior in vascular diseases and in the context of tumor metastasis. In this review, we discuss examples of in vitro studies modeling immune cell-endothelial cell interactions to present methods and recent findings in the field. Schematic showcasing common methods of in vitro experimentation of endothelial-immune cell interactions, including interactions with flow, static culture, or in-direct contact.

Modeling Immunity In Vitro: Slices, Chips, and Engineered Tissues

Modeling immunity in vitro has the potential to be a powerful tool for investigating fundamental biological questions, informing therapeutics and vaccines, and providing new insight into disease progression. There are two major elements to immunity that are necessary to model: primary immune tissues and peripheral tissues with immune components. Here, we systematically review progress made along three strategies to modeling immunity: ex vivo cultures, which preserve native tissue structure; microfluidic devices, which constitute a versatile approach to providing physiologically relevant fluid flow and environmental control; and engineered tissues, which provide precise control of the 3D microenvironment and biophysical cues. While many models focus on disease modeling, more primary immune tissue models are necessary to advance the field. Moving forward, we anticipate that the expansion of patient-specific models may inform why immunity varies from patient to patient and allow for the rapid comprehension and treatment of emerging diseases, such as coronavirus disease 2019.

Discrimination of cell-differentiation using a cell-binding assay based on the conversion of cell-patterns with dielectrophoresis

We developed a simple, rapid, and label-free method to obtain the ratio of cells with a specific surface protein from heterogeneous cell populations, and applied it to estimate the cell differentiation states. The repulsive force of negative dielectrophoresis was used to form the first pattern of HL60 cells on a substrate immobilized with anti-CD13 or anti-CD11b antibody. Next, the patterned cells were converted to form the second pattern by switching the pattern of the electric field. The cells exhibiting a specific protein remained in the original position due to the immunorecognition event, while the unwanted cells that were not bound to the antibody on the substrates could be simply removed. The cell-binding efficiencies of substrates modified with anti-CD13 and anti-CD11b decreased and increased, respectively, with increasing duration of cell culture in medium containing differentiation-inducing agents, including all-trans retinoic acid. This is explained by the downregulation of CD13 and upregulation of CD11b throughout the differentiation process of HL60 cells. Furthermore, the assay was applied to investigate the effects of various differentiation-inducing agents. The total assay time required for discriminating the proteins expressed on the cell surface in each differentiation state was as short as 120 s. No fluorescence label is required for the proposed assay. The method could be useful to estimate the cell differentiation and factors that influence the differentiation trajectory for numerous cell types.

Engineering approaches for studying immune-tumor cell interactions and immunotherapy

This review describes recent research that has advanced our understanding of the role of immune cells in the tumor microenvironment (TME) using advanced 3D in vitro models and engineering approaches. The TME can hinder effective eradication of tumor cells by the immune system, but immunotherapy has been able to reverse this effect in some cases. However, patient-to-patient variability in response suggests that we require deeper understanding of the mechanistic interactions between immune and tumor cells to improve response and develop novel therapeutics. Reconstruction of the TME using engineered 3D models allows high-resolution observation of cell interactions while allowing control of conditions such as hypoxia, matrix stiffness, and flow. Moreover, patient-derived organotypic models are an emerging tool for prediction of drug efficacy. This review highlights the importance of modeling and understanding the immune TME and describes new tools for identifying new biological targets, drug testing, and strategies for personalized medicine.

Analysis of Transcriptomic Changes in Bovine Endometrial Stromal Cells Treated With Lipopolysaccharide

Endometritis adversely affects the ability of cattle to reproduce and significantly reduces milk production. The is mainly composed of epithelial and stromal cells, and they produce the first immune response to invading pathogens. However, most of the epithelial cells are disrupted, and stromal cells are exposed to an inflammatory environment when endometritis occurs, especially postpartum. Many bacteria and toxins start attacking stromal cell due to loss of epithelium, which stimulates Toll-like receptor (TLRs) on stromal cells and causes upregulated expression of cytokines. Understanding the genome-wide characterization of bovine endometritis will be beneficial for prevention and treatment of endometritis. In this study, whole-transcriptomic gene changes in bovine endometrial stromal cells (BESCs) treated with LPS were compared with those treated with PBS (control group) and were analyzed by RNA sequencing. Compared with the control group, a total of 366 differentially expressed genes (DEGs) were identified in the LPS-induced group (234 upregulated and 132 downregulated genes), with an adjusted P < 0.05 by DESeq. Gene Ontology (GO) enrichment analysis revealed that DEGs were most enriched in interleukin-1 receptor binding, regulation of cell activation, and lymphocyte-activated interleukin-12 production. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed DEGs were most enriched in the TNF signaling pathway, Toll-like receptor signaling pathway, cytokine-cytokine receptor interaction, NF-κB signaling pathway, and chemokine signaling pathway. The results of this study unraveled BESCs affected with LPS transcriptome profile alterations, which may have a significant effect on treatment inflammation by comprehending molecular mechanisms and authenticating unique genes related to endometritis.

Pancreas-on-a-Chip Technology for Transplantation Applications

PURPOSE OF REVIEW

Human pancreas-on-a-chip (PoC) technology is quickly advancing as a platform for complex in vitro modeling of islet physiology. This review summarizes the current progress and evaluates the possibility of using this technology for clinical islet transplantation.

RECENT FINDINGS

PoC microfluidic platforms have mainly shown proof of principle for long-term culturing of islets to study islet function in a standardized format. Advancement in microfluidic design by using imaging-compatible biomaterials and biosensor technology might provide a novel future tool for predicting islet transplantation outcome. Progress in combining islets with other tissue types gives a possibility to study diabetic interventions in a minimal equivalent in vitro environment. Although the field of PoC is still in its infancy, considerable progress in the development of functional systems has brought the technology on the verge of a general applicable tool that may be used to study islet quality and to replace animal testing in the development of diabetes interventions.

3D Immunocompetent Organ-on-a-Chip Models

In recent years, engineering of various human tissues in microphysiologically relevant platforms, known as organs-on-chips (OOCs), has been explored to establish in vitro tissue models that recapitulate the microenvironments found in native organs and tissues. However, most of these models have overlooked the important roles of immune cells in maintaining tissue homeostasis under physiological conditions and in modulating the tissue microenvironments during pathophysiology. Significantly, gradual progress is being made in the development of more sophisticated microphysiologically relevant human-based OOC models that allow the studies of the key biophysiological aspects of specific tissues or organs, interactions between cells (parenchymal, vascular, and immune cells) and their extracellular matrix molecules, effects of native tissue architectures (geometry, dynamic flow or mechanical forces) on tissue functions, as well as unravelling the mechanism underlying tissue-specific diseases and drug testing. In this Progress Report, we discuss the different components of the immune system, as well as immune OOC platforms and immunocompetent OOC approaches that have simulated one or more components of the immune system. We also outline the challenges to recreate a fully functional tissue system in vitro with a focus on the incorporation of the immune system.

An inflammatory vascular endothelium-mimicking microfluidic device to enable leukocyte rolling and adhesion for rapid infection diagnosis

Recruitment of circulating leukocytes to sites of infection is of utmost importance in the development, propagation, and outcome of sepsis. These multi-step processes are mediated by interactions between adhesion receptors of leukocytes and cell adhesion molecules (CAMs) of endothelial cells, such as P-selectin, E-selectin and ICAM-1. However, the potential utility of the CAMs-facilitated leukocyte capture has not been thoroughly investigated as an index of the host response to infection for diagnostic purposes. Here, we report that the systemic infection affects the expression of CAMs ligands on leukocytes, upregulating the expression of P-selectin ligand-1 (PSGL-1) and increasing the number of PSGL-1- and E-selectin ligand-1 (ESL-1)-expressing leukocyte levels in septic blood. We leveraged this finding to determine infection by measuring the increased adhesion of leukocytes to an inflammatory vascular endothelium-mimicking microchannel coated with CAMs. We successfully validated that the proposed method can significantly differentiate infection in bacteremia and endotoxemia models in rats as early as an hour post-infection using a finger-prick volume of blood (50 μL), which were unachievable with the conventional diagnostic methods.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

Organ-on-a-Chip for Cancer and Immune Organs Modeling

Bridging the gap between findings in preclinical 2D cell culture models and in vivo tissue cultures has been challenging; the simple microenvironment of 2D monolayer culture systems may not capture the cellular response to drugs accurately. Three-dimensional organotypic models have gained increasing interest due to their ability to recreate precise cellular organizations. These models facilitate investigation of the interactions between different sub-tissue level components through providing physiologically relevant microenvironments for cells in vitro. The incorporation of human-sourced tissues into these models further enables personalized prediction of drug responses. Integration of microfluidic units into the 3D models can be used to control their local environment, dynamic simulation of cell behaviors, and real-time readout of drug testing data. Cancer and immune system related diseases are severe burdens to our health care system and have created an urgent need for high-throughput, and effective drug development plans. This review focuses on recent progress in the development of "cancer-on-a-chip" and "immune organs-on-a-chip" systems designed to study disease progression and predict drug-induced responses. Future challenges and opportunities are also discussed.

Designing natural and synthetic immune tissues

Vaccines and immunotherapies have provided enormous improvements for public health, but there are fundamental disconnects between where most studies are performed-in cell culture and animal models-and the ultimate application in humans. Engineering immune tissues and organs, such as bone marrow, thymus, lymph nodes and spleen, could be instrumental in overcoming these hurdles. Fundamentally, designed immune tissues could serve as in vitro tools to more accurately study human immune function and disease, while immune tissues engineered for implantation as next-generation vaccines or immunotherapies could enable direct, on-demand control over generation and regulation of immune function. In this Review, we discuss recent interdisciplinary strategies that are merging materials science and immunology to create engineered immune tissues in vitro and in vivo. We also highlight the hurdles facing these approaches and the need for comparison to existing clinical options, relevant animal models, and other emerging technologies.

Spatially resolved microfluidic stimulation of lymphoid tissue ex vivo

The lymph node is a structurally complex organ of the immune system, whose dynamic cellular arrangements are thought to control much of human health. Currently, no methods exist to precisely stimulate substructures within the lymph node or analyze local stimulus-response behaviors, making it difficult to rationally design therapies for inflammatory disease. Here we describe a novel integration of live lymph node slices with a microfluidic system for local stimulation. Slices maintained the cellular organization of the lymph node while making its core experimentally accessible. The 3-layer polydimethylsiloxane device consisted of a perfusion chamber stacked atop stimulation ports fed by underlying microfluidic channels. Fluorescent dextrans similar in size to common proteins, 40 and 70 kDa, were delivered to live lymph node slices with 284 ± 9 μm and 202 ± 15 μm spatial resolution, respectively, after 5 s, which is sufficient to target functional zones of the lymph node. The spread and quantity of stimulation were controlled by varying the flow rates of delivery; these were predictable using a computational model of isotropic diffusion and convection through the tissue. Delivery to two separate regions simultaneously was demonstrated, to mimic complex intercellular signaling. Delivery of a model therapeutic, glucose-conjugated albumin, to specific regions of the lymph node indicated that retention of the drug was greater in the B-cell zone than in the T-cell zone. Together, this work provides a novel platform, the lymph node slice-on-a-chip, to target and study local events in the lymph node and to inform the development of new immunotherapeutics.

Vasculature-On-A-Chip for In Vitro Disease Models

Vascularization, the formation of new blood vessels, is an essential biological process. As the vasculature is involved in various fundamental physiological phenomena and closely related to several human diseases, it is imperative that substantial research is conducted on characterizing the vasculature and its related diseases. A significant evolution has been made to describe the vascularization process so that in vitro recapitulation of vascularization is possible. The current microfluidic systems allow elaborative research on the effects of various cues for vascularization, and furthermore, in vitro technologies have a great potential for being applied to the vascular disease models for studying pathological events and developing drug screening platforms. Here, we review methods of fabrication for microfluidic assays and inducing factors for vascularization. We also discuss applications using engineered vasculature such as in vitro vascular disease models, vasculature in organ-on-chips and drug screening platforms.

The intercell dynamics of T cells and dendritic cells in a lymph node-on-a-chip flow device

T cells play a central role in immunity towards cancer and infectious diseases. T cell responses are initiated in the T cell zone of the lymph node (LN), where resident antigen-bearing dendritic cells (DCs) prime and activate antigen-specific T cells passing by. In the present study, we investigated the T cell : DC interaction in a microfluidic device to understand the intercellular dynamics and physiological conditions in the LN. We show random migration of antigen-specific T cells onto the antigen-presenting DC monolayer independent of the flow direction with a mean T cell : DC dwell time of 12.8 min and a mean velocity of 6 μm min(-1). Furthermore, we investigated the antigen specific vs. unspecific attachment and detachment of CD8(+) and CD4(+) T cells to DCs under varying shear stress. In our system, CD4(+) T cells showed long stable contacts with APCs, whereas CD8(+) T cells presented transient interactions with DCs. By varying the shear stress from 0.01 to 100 Dyn cm(-2), it was also evident that there was a much stronger attachment of antigen-specific than unspecific T cells to stationary DCs up to 1-12 Dyn cm(-2). The mechanical force of the cell : cell interaction associated with the pMHC-TCR match under controlled tangential shear force was estimated to be in the range of 0.25-4.8 nN. Finally, upon performing attachment & detachment tests, there was a steady accumulation of antigen specific CD8(+) T cells and CD4(+) T cells on DCs at low shear stresses, which were released at a stress of 12 Dyn cm(-2). This microphysiological model provides new possibilities to recreate a controlled mechanical force threshold of pMHC-TCR binding, allowing the investigation of intercellular signalling of immune synapses and therapeutic targets for immunotherapy.

Microfluidic models for adoptive cell-mediated cancer immunotherapies

Current adoptive T cell therapies have shown promising results in clinical trials but need further development as an effective cancer treatment. Here, we discuss how 3D microfluidic tumour models mimicking the tumour microenvironment could help in testing T cell immunotherapies by assessing engineered T cells and identifying combinatorial therapy to improve therapeutic efficacy. We propose that 3D microfluidic systems can be used to screen different patient-specific treatments, thereby reducing the burden of in vivo testing and facilitating the rapid translation of successful T cell cancer immunotherapies to the clinic.

Microelectrical Impedance Spectroscopy for the Differentiation between Normal and Cancerous Human Urothelial Cell Lines: Real-Time Electrical Impedance Measurement at an Optimal Frequency

PURPOSE

To distinguish between normal (SV-HUC-1) and cancerous (TCCSUP) human urothelial cell lines using microelectrical impedance spectroscopy (μEIS).

MATERIALS AND METHODS

Two types of μEIS devices were designed and used in combination to measure the impedance of SV-HUC-1 and TCCSUP cells flowing through the channels of the devices. The first device (μEIS-OF) was designed to determine the optimal frequency at which the impedance of two cell lines is most distinguishable. The μEIS-OF trapped the flowing cells and measured their impedance at a frequency ranging from 5 kHz to 1 MHz. The second device (μEIS-RT) was designed for real-time impedance measurement of the cells at the optimal frequency. The impedance was measured instantaneously as the cells passed the sensing electrodes of μEIS-RT.

RESULTS

The optimal frequency, which maximized the average difference of the amplitude and phase angle between the two cell lines (p < 0.001), was determined to be 119 kHz. The real-time impedance of the cell lines was measured at 119 kHz; the two cell lines differed significantly in terms of amplitude and phase angle (p < 0.001).

CONCLUSION

The μEIS-RT can discriminate SV-HUC-1 and TCCSUP cells by measuring the impedance at the optimal frequency determined by the μEIS-OF.

Microfluidics: A new tool for modeling cancer-immune interactions

In recognition of the enormous potential of immunotherapies against cancer, research into the interactions between tumor and immune cells has accelerated, leading to the recent FDA approval of several drugs that reduce cancer progression. Numerous cellular and molecular interactions have been identified by which immune cells can intervene in the metastatic cascade, leading to the development of several in vivo and in vitro model systems that can recapitulate these processes. Among these, microfluidic technologies hold many advantages in terms of their unique ability to capture the essential features of multiple cell type interactions in three-dimensions while allowing tight control of the microenvironment and real-time monitoring. Here, we review current assays and discuss the development of new microfluidic technologies for immunotherapy.

Infection and immunity on a chip: a compartmentalised microfluidic platform to monitor immune cell behaviour in real time

Cells respond to their environments and self-organise into multicellular assemblies with dedicated functions. The migratory and homing response of cells to soluble ligands can be studied by using different techniques, but for real time studies of complex multicellular self-organisation, novel and simpler systems are required. We fabricated a flexible open access microsystem and tested the design by studying cell recruitment from an immune cell reservoir towards an infectious compartment. The two compartments were connected by a network of bifurcated microchannels allowing diffusion of signalling molecules and migration of cells. Bacterial filters were incorporated in the design to prevent bacteria and activated cells from entering the network, permitting migration only from the recruitment reservoir. The fabricated microsystem allows real-time continuous monitoring of cellular decision-making based on biologically produced gradients of cytokines and chemokines. It is a valuable tool for studying cellular migration and self-organisation in relation to infections, autoimmunity, cancer, stem cell homing, and tissue and wound repair.

Microfluidic single-cell analysis for systems immunology

The immune system constantly battles infection and tissue damage, but exaggerated immune responses lead to allergies, autoimmunity and cancer. Discrimination of self from foreign and the fine-tuning of immunity are achieved by information processing pathways, whose regulatory mechanisms are little understood. Cell-to-cell variability and stochastic molecular interactions result in diverse cellular responses to identical signaling inputs, casting doubt on the reliability of traditional population-averaged analyses. Furthermore, dynamic molecular and cellular interactions create emergent properties that change over multiple time scales. Understanding immunity in the face of complexity and noisy dynamics requires time-dependent analysis of single-cells in a proper context. Microfluidic systems create precisely defined microenvironments by controlling fluidic and surface chemistries, feature sizes, geometries and signal input timing, and thus enable quantitative multi-parameter analysis of single cells. Such qualities allow observable dynamic environments approaching in vivo levels of biological complexity. Seamless parallelization of functional units in microfluidic devices allows high-throughput measurements, an essential feature for statistically meaningful analysis of naturally variable biological systems. These abilities recapitulate diverse scenarios such as cell-cell signaling, migration, differentiation, antibody and cytokine production, clonal selection, and cell lysis, thereby enabling accurate and meaningful study of immune behaviors in vitro.

Intercellular adhesion molecule 1/2 and E-selectin in plasma cell mastitis: immunohistochemical study of 35 cases

Plasma cell mastitis (PCM) is one of the most frequently encountered inflammatory diseases of the nonlactating breast. Histologically, PCM is characterized by infiltration of relatively abundant plasma cells into the mammary ducts. Its pathogenesis has remained unknown. In this study, we immunolocalized intercellular adhesion molecule (ICAM) 1 and 2 and E-selectin, all of which play pivotal roles in the inflammatory process, in 35 cases of PCM. We then compared the results with those of non-PCM and nonpathologic breast tissue. In the ductal epithelium, ICAM-1 immunoreactivity was significantly more pronounced in PCM than in non-PCM (P = .045). Both ICAM-1 (P < .001) and ICAM-2 (P = .001) were significantly more pronounced in PCM than in nonpathologic breast tissue. However, no significant differences in ICAM-2 and E-selectin immunoreactivity were detected between ductal epithelium of PCM and non-PCM. ICAM-1, but not ICAM-2 or E-selectin, demonstrated significantly higher immunoreactivity in endothelial cells of PCM than in nonpathologic breast (P < .001). These results all suggest that ICAM-1 in both ductal epithelium and endothelium plays important roles in the inflammatory process of PCM, possibly through margination, extravasation, and attachment of plasma cells and lymphocytes, which may result in continuous inflammatory cell homing to ductal epithelial cells.