On chip electrofusion of single human B cells and mouse myeloma cells for efficient hybridoma generation

Antibodies, repertoires and microdevices in antibody discovery and characterization

Therapeutic antibodies are paramount in treating a wide range of diseases, particularly in auto-immunity, inflammation and cancer, and novel antibody candidates recognizing a vast array of novel antigens are needed to expand the usefulness and applications of these powerful molecules. Microdevices play an essential role in this challenging endeavor at various stages since many general requirements of the overall process overlap nicely with the general advantages of microfluidics. Therefore, microfluidic devices are rapidly taking over various steps in the process of new candidate isolation, such as antibody characterization and discovery workflows. Such technologies can allow for vast improvements in time-lines and incorporate conservative antibody stability and characterization assays, but most prominently screenings and functional characterization within integrated workflows due to high throughput and standardized workflows. First, we aim to provide an overview of the challenges of developing new therapeutic candidates, their repertoires and requirements. Afterward, this review focuses on the discovery of antibodies using microfluidic systems, technological aspects of micro devices and small-scale antibody protein characterization and selection, as well as their integration and implementation into antibody discovery workflows. We close with future developments in microfluidic detection and antibody isolation principles and the field in general.

Application of Microfluidic Technology in Antibody Screening

Specific antibodies are widely used in the biomedical field. Current screening methods for specific antibodies mainly involve hybridoma technology and antibody engineering techniques. However, these technologies suffer from tedious screening processes, long preparation periods, high costs, low efficiency, and a degree of automation, which have become a bottleneck for the screening of specific antibodies. To overcome these difficulties, microfluidics has been developed as a promising technology for high-throughput screening and high purity of antibody. In this review, we provide an overview of the recent advances in microfluidic applications for specific antibody screening. In particular, hybridoma technology and four antibody engineering techniques (including phage display, single B cell antibody screening, antibody expression, and cell-free protein synthesis) based on microfluidics have been introduced, challenges, and the future outlook of these technologies are also discussed. This article is protected by copyright. All rights reserved.

Rapid cell pairing and fusion based on oscillating bubbles within an acoustofluidic device

Cell fusion is an essential event in many biological processes and has gained increasing attention in the field of biotechnology. In this study, we demonstrate an effective and convenient strategy for cell capture, pairing, and fusion based on oscillating bubbles within an acoustofluidic device. Multirectangular structures of the same size were fabricated at the sidewall of polydimethylsiloxane to generate monodisperse microbubbles. These microbubbles oscillated with a similar amplitude under single-frequency acoustic excitation. Cells were simultaneously captured and paired on the surface of the oscillating bubbles within 40 ms, and the efficiency reached approximately 90%. Homotypic or heterotypic cell membrane fusion was achieved within 15 and 20 min, respectively. More importantly, the homotypic fused cells enabled migration and proliferation at 24 h, indicating that the important biological functions were not altered.

Highly efficient and precise two-step cell selection method for tetramethylenedisulfotetramine-specific monoclonal antibody production

Monoclonal antibodies (mAbs) are useful biological tools for research, diagnostics, and pharmaceuticals. Here, we proposed a new mAb discovery platform named the two-step cell selection method (TCSM) for mAbs production of some small molecule haptens as antibiotic, toxins, and pesticides. The first step was performed by a fluorescence-activated cell sorter to enrich the hapten-specific B cells, the second step was an image-based precise pick of single hapten-specific hybridoma cells by confocal laser scanning microscopy. In this study, we used tetramethylenedisulfotetramine (TETS) as a model analyte, which is a highly lethal neurotoxic rodenticide. The TETS-specific hybridoma cells selection was completed within 10 days by the TCSM, compared with at least 40 days in the traditional hybridoma method (THM). The half maximal inhibitory concentration (IC₅₀) of the best mAb 1G6 for TETS in the TCSM was 1.98 ng mL^-1, and that of mAb 2B6 in the THM was 11.49 ng mL^-1. Antibody-TETS recognition also showed more interactions in mAb 1G6 than in mAb 2B6. Then, the mAb 1G6 was then successfully applied to develop an icELISA for TETS in biological samples with satisfactory sensitivity, accuracy and precision. The results demonstrated that the TCSM was a feasible and efficient method for mAb discovering of poisonous hapten molecules.

A Microfluidic Flip-Chip Combining Hydrodynamic Trapping and Gravitational Sedimentation for Cell Pairing and Fusion

Cancer cell–immune cell hybrids and cancer immunotherapy have attracted much attention in recent years. The design of efficient cell pairing and fusion chips for hybridoma generation has been, subsequently, a subject of great interest. Here, we report a three-layered integrated Microfluidic Flip-Chip (MFC) consisting of a thin through-hole membrane sandwiched between a mirrored array of microfluidic channels and saw-tooth shaped titanium electrodes on the glass. We discuss the design and operation of MFC and show its applicability for cell fusion. The proposed device combines passive hydrodynamic phenomenon and gravitational sedimentation, which allows the transportation and trapping of homotypic and heterotypic cells in large numbers with pairing efficiencies of 75~78% and fusion efficiencies of 73%. Additionally, we also report properties of fused cells from cell biology perspectives, including combined fluorescence-labeled intracellular materials from THP1 and A549, mixed cell morphology, and cell viability. The MFC can be tuned for pairing and fusion of cells with a similar protocol for different cell types. The MFC can be easily disconnected from the test setup for further analysis.

Highly integrated microfluidic device for cell pairing, fusion and culture

In this study, we proposed a microfluidic device with compact structures integrating multiple modalities for cell capture, pairing, fusion, and culture. The microfluidic device is composed of upper and lower parts. The lower part configured with electrodes and capture wells is used for cell trapping/pairing/fusion, while the upper part configured with corresponding culture wells is used for cell culture. Dielectrophoresis is used to enable accurate cell trapping and pairing in capture wells. Moreover, the paired cells are fused flexibly by either electrical pulses or polyethylene glycol (PEG) buffer. The fused cells are then transferred to culture wells for on-chip culture simply by flipping the device. Using the device and HeLa cells, we demonstrated pairing efficiency of ∼78% and fusion efficiencies of ∼ 26% for electrical fusion or ∼ 21% for PEG fusion, and successful cell proliferation and migration after 72 h on-chip culture. We believe that this multifunction-integrated but structure-simplified microfluidic device would largely facilitate cell fusion oriented tasks.

Electrofusion of single cells in picoliter droplets

We present a microfluidic chip that enables electrofusion of cells in microdroplets, with exchange of nuclear components. It is shown, to our knowledge for the first time, electrofusion of two HL60 cells, inside a microdroplet. This is the crucial intermediate step for controlled hybridoma formation where a B cell is electrofused with a myeloma cell. We use a microfluidic device consisting of a microchannel structure in PDMS bonded to a glass substrate through which droplets with two differently stained HL60 cells are transported. An array of six recessed platinum electrode pairs is used for electrofusion. When applying six voltage pulses of 2–3 V, the membrane electrical field is about 1 MV/cm for 1 ms. This results in electrofusion of these cells with a fusion yield of around 5%. The operation with individual cell pairs, the appreciable efficiency and the potential to operate in high-throughput (up to 500 cells sec⁻¹) makes the microdroplet fusion technology a promising platform for cell electrofusion, which has the potential to compete with the conventional methods. Besides, this platform is not restricted to cell fusion but is also applicable to various other cell-based assays such as single cell analysis and differentiation assays.

A microfluidic approach towards hybridoma generation for cancer immunotherapy

Dendritic cells/tumor fusions have shown to elicit anti-cancer immunity in different cancer types. However, the application of these vaccines for human cancer immunotherapy are limited by the instable quality and insufficient quanity of fusion cells. We present a cell electrofusion chip fabricated using soft lithography technique, which combines the rapid and precise cell pairing microstructures and the high yield electrofusion micro-electrodes to improve the cell fusion. The design uses hydrodynamic trapping in combination with positive dielectrophoretic force (pDEP) to achieve cell fusion. The chip consists of total 960 pairs of trapping channels, which are capable of pairing and fusing both homogeneous and heterogeneous types of cells. The fused cells can be easily taken out of the chip that makes this device a distinguishable from other designs. We observe pairing efficiency of 68% with fusion efficiency of 64%.

Optically-Induced Cell Fusion on Cell Pairing Microstructures

Cell fusion is a critical operation for numerous biomedical applications including cell reprogramming, hybridoma formation, cancer immunotherapy, and tissue regeneration. However, unstable cell contact and random cell pairings have limited efficiency and yields when utilizing traditional methods. Furthermore, it is challenging to selectively perform cell fusion within a group of cells. This study reports a new approach called optically-induced cell fusion (OICF), which integrates cell-pairing microstructures with an optically-induced, localized electrical field. By projecting light patterns onto a photoconductive film (hydrogen-rich, amorphous silicon) coated on an indium-tin-oxide (ITO) glass while an alternating current electrical field was applied between two such ITO glass slides, “virtual” electrodes could be generated that could selectively fuse pairing cells. At 10 kHz, a 57% cell paring rate and an 87% fusion efficiency were successfully achieved at a driving voltage of 20  V_pp, suggesting that this new technology could be promising for selective cell fusion within a group of cells.

One-to-one encapsulation based on alternating droplet generation

This paper reports the preparation of encapsulated particles as models of cells using an alternating droplet generation encapsulation method in which the number of particles in a droplet is controlled by a microchannel to achieve one-to-one encapsulation. Using a microchannel in which wettability is treated locally, the fluorescent particles used as models of cells were successfully encapsulated in uniform water-in-oil-in-water (W/O/W) emulsion droplets. Furthermore, 20% of the particle-containing droplets contained one particle. Additionally, when a surfactant with the appropriate properties was used, the fluorescent particles within each inner aqueous droplet were enclosed in the merged droplet by spontaneous droplet coalescence. This one-to-one encapsulation method based on alternating droplet generation could be used for a variety of applications, such as high-throughput single-cell assays, gene transfection into cells or one-to-one cell fusion.

A Cell Electrofusion Chip for Somatic Cells Reprogramming

Cell fusion is a potent approach to explore the mechanisms of somatic cells reprogramming. However, previous fusion methods, such as polyethylene glycol (PEG) mediated cell fusion, are often limited by poor fusion yields. In this study, we developed a simplified cell electrofusion chip, which was based on a micro-cavity/ discrete microelectrode structure to improve the fusion efficiency and to reduce multi-cell electrofusion. Using this chip, we could efficiently fuse NIH3T3 cells and mouse embryonic stem cells (mESCs) to induce somatic cells reprogramming. We also found that fused cells demethylated gradually and 5-hydroxymethylcytosine (5hmC) was involved in the demethylation during the reprogramming. Thus, the cell electrofusion chip would facilitate reprogramming mechanisms research by improving efficiency of cell fusion and reducing workloads.

Bidirectional microfluidic pumping using an array of magnetic Janus microspheres rotating around magnetic disks

We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL min(-1) was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in the pumping direction is offered by the rotational direction of the external magnetic field. This method is especially suited for flow-controlled recirculation of chemical and biological species in microchannels - for example, medium recirculation in culture chambers - opening the way towards novel, portable, on-chip applications without the need for external fluidic or electrical connections.

Deformability-based microfluidic cell pairing and fusion

We present a microfluidic cell pairing device capable of sequential trapping and pairing of hundreds of cells using passive hydrodynamics and flow-induced deformation. We describe the design and operation principles of our device and show its applicability for cell fusion. Using our device, we achieved both homotypic and heterotypic cell pairing, demonstrating efficiencies up to 80%. The platform is compatible with fusion protocols based on biological, chemical and physical stimuli with fusion yields up to 95%. Our device further permits its disconnection from the fluidic hardware enabling its transportation for imaging and culture while maintaining cell registration on chip. Our design principles and cell trapping technique can readily be applied for different cell types and can be extended to trap and fuse multiple (>2) cell partners as demonstrated by our preliminary experiments.

Cell electrofusion using nanosecond electric pulses

Electrofusion is an efficient method for fusing cells using short-duration high-voltage electric pulses. However, electrofusion yields are very low when fusion partner cells differ considerably in their size, since the extent of electroporation (consequently membrane fusogenic state) with conventionally used microsecond pulses depends proportionally on the cell radius. We here propose a new and innovative approach to fuse cells with shorter, nanosecond (ns) pulses. Using numerical calculations we demonstrate that ns pulses can induce selective electroporation of the contact areas between cells (i.e. the target areas), regardless of the cell size. We then confirm experimentally on B16-F1 and CHO cell lines that electrofusion of cells with either equal or different size by using ns pulses is indeed feasible. Based on our results we expect that ns pulses can improve fusion yields in electrofusion of cells with different size, such as myeloma cells and B lymphocytes in hybridoma technology.

Prototype for automatable, dielectrophoretically-accessed intracellular membrane-potential measurements by metal electrodes

Functional access to membrane proteins, for example, ion channels, of individual cells is an important prerequisite in drug discovery studies. The highly sophisticated patch-clamp method is widely used for electrogenic membrane proteins, but is demanding for the operator, and its automation remains challenging. The dielectrophoretically-accessed, intracellular membrane-potential measurement (DAIMM) method is a new technique showing high potential for automation of electrophysiological data recording in the whole-cell configuration. A cell suspension is brought between a mm-scaled planar electrode and a μm-scaled tip electrode, placed opposite to each other. Due to the asymmetric electrode configuration, the application of alternating electric fields (1-5 MHz) provokes a dielectrophoretic force acting on the target cell. As a consequence, the cell is accelerated and pierced by the tip electrode, hence functioning as the internal (working) electrode. We used the light-gated cation channel Channelrhodopsin-2 as a reporter protein expressed in HEK293 cells to characterize the DAIMM method in comparison with the patch-clamp technique.