Multifunctional Microwell Arrays for Single Cell Level Functional Analysis of Lymphocytes

Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation

Crescent-shaped hydrogel microparticles are shown to template uniform volume aqueous droplets upon simple mixing with aqueous and oil media for various bioassays. This emerging "lab on a particle" technique requires hydrogel particles with tunable material properties and dimensions. The crescent shape of the particles is attained by aqueous two-phase separation of polymers followed by photopolymerization of the curable precursor. In this work, the phase separation of poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40 000) for tunable manufacturing of crescent-shaped particles is investigated. The particles' morphology is precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rates of various streams. The fabricated particles with variable dimensions encapsulate uniform aqueous droplets upon mixing with an oil phase. The particles are fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color-coded particles. The blue fluorescent dye shows a moderate response to the pH change. The fluorescently labeled particles are able to tolerate an extremely acidic solution (pH 1) but disintegrate within an extremely basic solution (pH 14). The particle-templated droplets are able to effectively retain the disintegrating particle and the fluorescent signal at pH 14.

Fabrication of Micro Carbon Mold for Glass-Based Micro Hole Array

In glass molding to produce biochips with micro holes, cavities, and channels, it is important to machine micro molds. This study presents a novel process for fabricating micro pin arrays on carbon graphite, one of the glass molding materials. The micro pin array was used as a mold to fabricate a glass-based micro hole array. Using conventional micro endmill tools, machining micro-cylindrical pins requires complex toolpaths and is time-consuming. In order to machine micro pin arrays with high efficiency, a micro eccentric tool was introduced. Micro pin arrays with a diameter of 200 µm and a height of 200 µm were easily fabricated on graphite using the micro eccentric tool. In the machining of micro pin arrays using eccentric tools, the machining characteristics such as cutting force and tool wear were investigated.

Approaches for the isolation and long-term expansion of pericytes from human and animal tissues

Pericytes surround capillaries in every organ of the human body. They are also present around the vasa vasorum, the small blood vessels that supply the walls of larger arteries and veins. The clinical interest in pericytes is rapidly growing, with the recognition of their crucial roles in controlling vascular function and possible therapeutic applications in regenerative medicine. Nonetheless, discrepancies in methods used to define, isolate, and expand pericytes are common and may affect reproducibility. Separating pure pericyte preparations from the continuum of perivascular mesenchymal cells is challenging. Moreover, variations in functional behavior and antigenic phenotype in response to environmental stimuli make it difficult to formulate an unequivocal definition of bona fide pericytes. Very few attempts were made to develop pericytes as a clinical-grade product. Therefore, this review is devoted to appraising current methodologies' pros and cons and proposing standardization and harmonization improvements. We highlight the importance of developing upgraded protocols to create therapeutic pericyte products according to the regulatory guidelines for clinical manufacturing. Finally, we describe how integrating RNA-seq techniques with single-cell spatial analysis, and functional assays may help realize the full potential of pericytes in health, disease, and tissue repair.

Effects of extracellular adhesion molecules on immune cell mediated solid tumor cell killing

Adoptive cell therapy (ACT) using ex vivo engineered/expanded immune cells demonstrated poor efficacy against solid tumors, despite its great success in treating various hematopoietic malignancies. To improve ACT for solid tumors, it is crucial to comprehend how the numerous components of the tumor microenvironment (TME) surrounding solid tumor cells influence killing ability of immune cells. In this study, we sought to determine the effects of extracellular adhesion provided by extracellular matrix (ECM) of TME on immune cell cytotoxicity by devising microwell arrays coated with proteins either preventing or promoting cell adhesion. Solid tumor cells in bovine serum albumin (BSA)-coated microwells did not attach to the surfaces and exhibited a round morphology, but solid tumor cells in fibronectin (FN)-coated microwells adhered firmed to the substrates with a flat shape. The seeding densities of solid tumor cells and immune cells were tuned to maximize one-to-one pairing within a single microwell, and live cell imaging was performed to examine dynamic cell-cell interactions and immune cell cytotoxicity at a single cell level. Both natural killer (NK) cells and T cells showed higher cytotoxicity against round tumor cells in BSA-coated microwells compared to flat tumor cells in FN-coated microwells, suggesting that extracellular adhesion-mediated firm adhesion of tumor cells made them more resistant to immune cell-mediated killing. Additionally, NK cells and T cells in FN-coated microwells exhibited divergent dynamic behaviors, indicating that two distinct subsets of cytotoxic lymphocytes respond differentially to extracellular adhesion cues during target cell recognition.

Single-cell sorting based on secreted products for functionally defined cell therapies

Cell therapies have emerged as a promising new class of "living" therapeutics over the last decade and have been particularly successful for treating hematological malignancies. Increasingly, cellular therapeutics are being developed with the aim of treating almost any disease, from solid tumors and autoimmune disorders to fibrosis, neurodegenerative disorders and even aging itself. However, their therapeutic potential has remained limited due to the fundamental differences in how molecular and cellular therapies function. While the structure of a molecular therapeutic is directly linked to biological function, cells with the same genetic blueprint can have vastly different functional properties (e.g., secretion, proliferation, cell killing, migration). Although there exists a vast array of analytical and preparative separation approaches for molecules, the functional differences among cells are exacerbated by a lack of functional potency-based sorting approaches. In this context, we describe the need for next-generation single-cell profiling microtechnologies that allow the direct evaluation and sorting of single cells based on functional properties, with a focus on secreted molecules, which are critical for the in vivo efficacy of current cell therapies. We first define three critical processes for single-cell secretion-based profiling technology: (1) partitioning individual cells into uniform compartments; (2) accumulating secretions and labeling via reporter molecules; and (3) measuring the signal associated with the reporter and, if sorting, triggering a sorting event based on these reporter signals. We summarize recent academic and commercial technologies for functional single-cell analysis in addition to sorting and industrial applications of these technologies. These approaches fall into three categories: microchamber, microfluidic droplet, and lab-on-a-particle technologies. Finally, we outline a number of unmet needs in terms of the discovery, design and manufacturing of cellular therapeutics and how the next generation of single-cell functional screening technologies could allow the realization of robust cellular therapeutics for all patients.

A rare monoclonal antibody discovery based on indirect competitive screening of a single hapten-specific rabbit antibody secreting cell

A rare antibody that is able to tolerate physio-chemical factors is preferred and highly demanded in diagnosis and therapy. Rabbit monoclonal antibodies (RmAbs) are distinguished owing to their high affinity and stability. However, the efficiency and availability of traditional methods for RmAb discovery are limited, particularly for small molecules. Here, we present an indirect competitive screening method in nanowells, named CSMN, for single rabbit antibody-secreting cells (ASCs) selection with 20.6 h and propose an efficient platform for RmAb production against small molecules within 5.8 days for the first time. Chloramphenicol (CAP) as an antibacterial agent poses a great threat to public health. We applied CSMN to select CAP-specific ASCs and produced one high-affinity RmAb, surprisingly showed extremely halophilic properties with an IC₅₀ of 0.08 ng mL^-1 in the saturated salt solution, which has not yet been seen for other antibodies. The molecular dynamic simulation showed that the negatively charged surface improved the stability of the RmAb structure with additional disulfide bonds compared with mouse antibodies. Moreover, the reduced solvent accessible surface area of the binding pocket increased the interactions of RmAb with CAP in a saturated salt solution. Furthermore, RmAb was used to develop an immunoassay for the detection of CAP in real biological samples with simple pretreatment, shorter assay time, and higher sensitivity. The results demonstrated that the practical and efficient CSMN is suitable for rare RmAb discovery against small molecules.

Selective retrieval of antibody-secreting hybridomas in cell arrays based on the dielectrophoresis

A cascade of the formation of cell arrays, the discrimination of cells secreting specific molecules, and the selective retrieval of cells has been developed to harvest antibody-secreting hybridomas in heterogeneous cell populations simply and rapidly. The microwell array device consisted of three-dimensional microband electrodes by assembling both upper and lower substrates perpendicularly. Arrays of hybridomas secreting specific antibodies were prepared by aligning hybridomas in each microwell based on the attractive force of positive dielectrophoresis (p-DEP). Antibody secreted by the hybridomas in the microwells was recognized by the antigen immobilized on the microwells or the membrane surfaces of hybridomas to discriminate hybridomas with the secretion ability. Thereafter, a repulsive force of negative dielectrophoresis (n-DEP) was applied to release the target hybridomas from the microwell array. To harvest the target hybridoma, AC signals could be modulated in the n-DEP frequency region and applied to a pair of microband electrodes located above and below each microwell containing target hybridoma. Thus, the cell-based array system described in this study allowed selective retrieval of single target hybridomas by merely switching from p-DEP to n-DEP after selecting the antibody-secreting hybridomas trapped in each microwell. The development of this high-affinity device could be useful to recover hybridomas producing antibodies in large populations of cells rapidly and effectively.

Microfluidic Compartmentalization Platforms for Single Cell Analysis

Many cellular analytical technologies measure only the average response from a cell population with an assumption that a clonal population is homogenous. The ensemble measurement often masks the difference among individual cells that can lead to misinterpretation. The advent of microfluidic technology has revolutionized single-cell analysis through precise manipulation of liquid and compartmentalizing single cells in small volumes (pico- to nano-liter). Due to its advantages from miniaturization, microfluidic systems offer an array of capabilities to study genomics, transcriptomics, and proteomics of a large number of individual cells. In this regard, microfluidic systems have emerged as a powerful technology to uncover cellular heterogeneity and expand the depth and breadth of single-cell analysis. This review will focus on recent developments of three microfluidic compartmentalization platforms (microvalve, microwell, and microdroplets) that target single-cell analysis spanning from proteomics to genomics. We also compare and contrast these three microfluidic platforms and discuss their respective advantages and disadvantages in single-cell analysis.

Fabrication approaches for high-throughput and biomimetic disease modeling

There is often a tradeoff between in vitro disease modeling platforms that capture pathophysiologic complexity and those that are amenable to high-throughput fabrication and analysis. However, this divide is closing through the application of a handful of fabrication approaches-parallel fabrication, automation, and flow-driven assembly-to design sophisticated cellular and biomaterial systems. The purpose of this review is to highlight methods for the fabrication of high-throughput biomaterial-based platforms and showcase examples that demonstrate their utility over a range of throughput and complexity. We conclude with a discussion of future considerations for the continued development of higher-throughput in vitro platforms that capture the appropriate level of biological complexity for the desired application. STATEMENT OF SIGNIFICANCE: There is a pressing need for new biomedical tools to study and understand disease. These platforms should mimic the complex properties of the body while also permitting investigation of many combinations of cells, extracellular cues, and/or therapeutics in high-throughput. This review summarizes emerging strategies to fabricate biomimetic disease models that bridge the gap between complex tissue-mimicking microenvironments and high-throughput screens for personalized medicine.

Edge-Enhanced Microwell Immunoassay for Highly Sensitive Protein Detection

Highly sensitive biosensors that can detect low concentrations of protein biomarkers at the early stages of diseases or proteins secreted from single cells are of importance for disease diagnosis and treatment assessment. This work reports a new signal amplification mechanism, that is, edge enhancement based on the vertical sidewalls of microwells for ultra-sensitive protein detection. The fluorescence emission at the edge of the microwells is highly amplified due to the microscopic axial resolution (depth of field) and demonstrates a microring effect. The enhanced fluorescence intensity from microrings is calibrated for bovine serum albumin detection, which shows a 6-fold sensitivity enhancement and a lower limit of detection at the microwell edge, compared to those obtained on a flat surface. The microwell chip is used to separate single cells, and the wall of each microwell is used to detect interferon-γ secretion from T cells stimulated with a peptide and whole cancer cells. Given its edge-enhancement ability, the microwell technique can be a highly sensitive biosensing platform for disease diagnosis at an early stage and for assessing potential treatments at the single-cell level.

Selective Trapping and Retrieval of Single Cells Using Microwell Array Devices Combined with Dielectrophoresis

We proposed selective manipulation techniques for retrieving and retaining target cells arrayed in microwells based on dielectrophoresis (DEP). The upper substrate with microband electrodes was mounted on the lower substrate with microwells based on the same design of microband electrodes by 90 degree relative to the lower substrate. A repulsive force of negative dielectrophoresis (n-DEP) was employed to retrieve the target cells from the microwell array selectively. Furthermore, the target cells were retained in the microwells after other cells were removed by n-DEP. Thus, the system described in this study could make it possible to retrieve and recover single target cells from a microwell array after determining the function of cells trapped in each microwell.

Time-resolved microwell cell-pairing array reveals multiple T cell activation profiles

The differences in behaviour between individual cells in a large population are often important, yet are masked in bulk analyses where only average parameters are measured. One unresolved question in the field of immunology is the extent to which important immunological phenomena such as immunodominance to cancer antigens correlates with the average activity of a population of antigen-specific T lymphocytes, or with the activity of individual "outlier" cells. Despite progress in single cell technologies, few platforms are available that can deliver time-resolved, functional analysis at single cell resolution, for these investigations. We have developed an accessible high-throughput platform to measure single T cell signalling in real time following time-controlled stimulation by live antigen presenting cells. The cell-trap array consists of thousands of individual microwells cast in an agarose block, which is biocompatible and permeable to nutrients. Single T cells are isolated in wells via passive sedimentation and size exclusion, achieving up to 90% occupancy. The device enables simultaneous activation of thousands of single CD8⁺ cells. Stimulation with soluble reagents (ionomycin, anti-CD3 antibodies) or antigen presenting cells leads to changes in intracellular calcium concentrations which were measured using calcium-chelating fluorophore dyes. The platform was used to demonstrate a range of activation profiles among individual cells of a cloned, antigen specific CD8⁺ T cell hybridoma in response to both nonspecific stimuli and specific, physiologically relevant antigen stimulation. The presence of two different activation profiles was demonstrated, together with rare outlier behaviour among cells that are essentially clonal.

Advances in single cell technologies in immunology

The immune system is composed of heterogeneous populations of immune cells that regulate physiological processes and protect organisms against diseases. Single cell technologies have been used to assess immune cell responses at the single cell level, which are crucial for identifying the causes of diseases and elucidating underlying biological mechanisms to facilitate medical therapy. In the present review we first discuss the most recent advances in the development of single cell technologies to investigate cell signaling, cell-cell interactions and cell migration. Each technology's advantages and limitations and its applications in immunology are subsequently reviewed. The latest progress toward commercialization, the remaining challenges and future perspectives for single cell technologies in immunology are also briefly discussed.

Advances in ultrahigh-throughput screening for directed enzyme evolution

Enzymes are versatile catalysts and their synthetic potential has been recognized for a long time. In order to exploit their full potential, enzymes often need to be re-engineered or optimized for a given application. (Semi-) rational design has emerged as a powerful means to engineer proteins, but requires detailed knowledge about structure function relationships. In turn, directed evolution methodologies, which consist of iterative rounds of diversity generation and screening, can improve an enzyme's properties with virtually no structural knowledge. Current diversity generation methods grant us access to a vast sequence space (libraries of >1012 enzyme variants) that may hide yet unexplored catalytic activities and selectivity. However, the time investment for conventional agar plate or microtiter plate-based screening assays represents a major bottleneck in directed evolution and limits the improvements that are obtainable in reasonable time. Ultrahigh-throughput screening (uHTS) methods dramatically increase the number of screening events per time, which is crucial to speed up biocatalyst design, and to widen our knowledge about sequence function relationships. In this review, we summarize recent advances in uHTS for directed enzyme evolution. We shed light on the importance of compartmentalization to preserve the essential link between genotype and phenotype and discuss how cells and biomimetic compartments can be applied to serve this function. Finally, we discuss how uHTS can inspire novel functional metagenomics approaches to identify natural biocatalysts for novel chemical transformations.

Facile Method for Fabricating Microfluidic Chip Integrated with Microwell Arrays for Cell Trapping

With the development of biomedical technology, personalized diagnosis and treatment at the single-cell level are becoming more important in the medical field. As one of the most powerful tools, microfluidic chips have shown significant potential for various applications related to cell separation, cell proliferation, and cell behavior analysis. However, fabricating microfluidic devices requires complicated procedures and high-cost equipment. In this study, an optofluidic maskless lithography method was proposed for rapid fabrication of microfluidic devices integrated with microwells. Through the use of this approach, microwells can be on-line designed and the exposure patterns can be modulated. Single or multi polystyrene microspheres were successfully trapped by using the designed microwells. The capture of MCF-7 cells and cell arrays indicated that the microfluidic devices fabricated in the present study can be applied for cell research.

Single cell arrays of hematological cancer cells for assessment of lymphocyte cytotoxicity dynamics, serial killing, and extracellular molecules

Cytotoxicity exerted by cytotoxic lymphocytes against cancer cells is an essential cellular function for successful cancer immunotherapy. Standard cytotoxicity assays mostly provide population level information, whereas live cell imaging-based cytotoxicity assays can assess single cell level heterogeneity. However, long term tracking of individual cytotoxic lymphocyte-hematological cancer cell interactions is technically challenging because both cells can float around and form multi-cellular aggregates. To overcome this limitation, single hematological cancer cell arrays with immobilized hematological cancer cells are fabricated using microwell arrays. Using this new platform, single cell level natural killer (NK) cell cytotoxicity against leukemic cells is quantitatively assessed. Depending on microwell surface adhesiveness and inter-microwell distances, distinct modes of NK-leukemic cell interactions that result in different NK cell cytotoxicity are observed. For microwell arrays coated with bovine serum albumin, which prevents cell adhesion, NK cells stably contacted cancer cells with rounded morphologies, whereas for microwell arrays coated with fibronectin (FN), which triggers integrin signals, NK cells contacting cancer cells exhibited dynamic behaviors with elongated morphologies and constantly explored extracellular spaces by membrane extension. In addition, FN on extracellular spaces facilitate NK cell detachment from leukemic cells after killing by providing anchorage for force transmission, and promote cytotoxicity and serial killing. Single hematologic cell arrays are not only an efficient method for lymphocyte cytotoxicity analysis but also a useful tool to study the role of signaling molecules in extracellular spaces on lymphocyte cytotoxicity.