Electrofusion by a bipolar pulsed electric field: Increased cell fusion efficiency for monoclonal antibody production

Influences of pulsed electric field parameters on cell electroporation and electrofusion events: Comprehensive understanding by experiments and molecular dynamics simulations

Electroporation and electrofusion are efficient methods, which have been widely used in different areas of biotechnology and medicine. Pulse strength and width, as an external condition, play an important role in the process of these methods. However, comparatively little work has been done to explore the effects of pulsed electric field parameters on electroporation and electrofusion. Herein, influences of pulse strength and width on the electroporation and electrofusion of phospholipid bilayers were systematically investigated by using experiments combined with molecular dynamics simulations. Experimental results and machine learning-based regression analysis showed that the number of pores is mainly determined by pulse strength, while the sizes of pores were enlarged by increasing the pulse widths. In addition, the formation of large-size pores is the most crucial factor that affects the fusion rate of myeloma cells. The same trend has taken place on coarse-grained and all-atom MD simulations. The result suggested that electroporation events occur only in an electric field exceeding the strength of threshold, and the unbalanced degree of electric potential between two membranes leads to pores formation during the process of electroporation. Generally, this work provides a comprehensive understanding of how pulse strength and width govern the poration event of bilayer lipid membranes, as well as guidance on the experimental design of electrofusion.

Characterization of Mesenchymal and Neural Stem Cells Response to Bipolar Microsecond Electric Pulses Stimulation

In the tissue regeneration field, stem cell transplantation represents a promising therapeutic strategy. To favor their implantation, proliferation and differentiation need to be controlled. Several studies have demonstrated that stem cell fate can be controlled by applying continuous electric field stimulation. This study aims to characterize the effect of a specific microsecond electric pulse stimulation (bipolar pulses of 100 µs + 100 µs, delivered for 30 min at an intensity of 250 V/cm) to induce an increase in cell proliferation on mesenchymal stem cells (MSCs) and induced neural stem cells (iNSCs). The effect was evaluated in terms of (i) cell counting, (ii) cell cycle, (iii) gene expression, and (iv) apoptosis. The results show that 24 h after the stimulation, cell proliferation, cell cycle, and apoptosis are not affected, but variation in the expression of specific genes involved in these processes is observed. These results led us to investigate cell proliferation until 72 h from the stimulation, observing an increase in the iNSCs number at this time point. The main outcome of this study is that the microsecond electric pulses can modulate stem cell proliferation.

Microfluidic Chip for Cell Fusion and In Situ Separation of Fused Cells

Electrofusion is an effective method for fusing two cells into a hybrid cell, and this method is widely used in immunomedicine, gene recombination, and other related fields. Although cell pairing and electrofusion techniques have been accomplished with microfluidic devices, the purification and isolation of fused cells remains limited due to expensive instruments and complex operations. In this study, through the optimization of microstructures and electrodes combined with buffer substitution, the entire cell electrofusion process, including cell capture, pairing, electrofusion, and precise separation of the targeted fused cells, is achieved on a single chip. The proposed microfluidic cell electrofusion achieves an efficiency of 80.2 ± 7.5%, and targeted cell separation could be conveniently performed through the strategic activation of individual microelectrodes via negative dielectrophoresis, which ensures accurate release of the fused cells with an efficiency of up to 91.1 ± 5.1%. Furthermore, the survival rates of the cells after electrofusion and release are as high as 94.7 ± 0.6% and 91.7 ± 1.2%, respectively. These results demonstrate that the in situ cell electrofusion and separation process did not affect the cell activity. This chip offers integrated multifunctional manipulation of cells in situ, and can be applied to multiple fields in the future, thus laying the foundation for the field of precise single-cell analysis.

High-affinity monoclonal antibodies against the porcine epidemic diarrhea virus S1 protein

The porcine epidemic diarrhea virus (PEDV) infection inflicted substantial economic losses upon the global pig-breeding industry. This pathogen can infect all pigs and poses a particularly high fatality risk for suckling piglets. The S1 subunit of spike protein is a crucial target protein for inducing the particularly neutralizing antibodies that can intercept the virus-host interaction and neutralize virus infectivity. In the present study, the HEK293F eukaryotic expression system was successfully utilized to express and produce recombinant S1 protein. Through quantitative analysis, five monoclonal antibodies (mAbs) specifically targeting the recombinant S1 protein of PEDV were developed and subsequently evaluated using enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence assay (IFA), and flow cytometry assay (FCA). The results indicate that all five mAbs belong to the IgG1 isotype, and their half-maximal effective concentration (EC50) values measured at 84.77, 7.42, 0.89, 14.64, and 7.86 pM. All these five mAbs can be utilized in ELISA, FCA, and IFA for the detection of PEDV infection. MAb 5-F9 exhibits the highest sensitivity to detect as low as 0.3125 ng/mL of recombinant PEDV-S1 protein in ELISA, while only 0.096 ng/mL of mAb 5-F9 is required to detect PEDV in FCA. The results from antigen epitope analysis indicated that mAb 8-G2 is the sole antibody capable of recognizing linear epitopes. In conclusion, this study has yielded a highly immunogenic S1 protein and five high-affinity mAbs specifically targeting the S1 protein. These findings have significant implications for early detection of PEDV infection and provide a solid foundation for further investigation into studying virus-host interactions.

Mechanism study on the influences of buffer osmotic pressure on microfluidic chip-based cell electrofusion

Cell electrofusion is a key process in many research fields, such as genetics, immunology, and cross-breeding. The electrofusion efficiency is highly dependent on the buffer osmotic pressure properties. However, the mechanism by which the buffer osmotic pressure affects cell electrofusion has not been theoretically or numerically understood. In order to explore the mechanism, the microfluidic structure with paired arc micro-cavities was first evaluated based on the numerical analysis of the transmembrane potential and the electroporation induced on biological cells when the electrofusion was performed on this structure. Then, the numerical model was used to analyze the effect of three buffer osmotic pressures on the on-chip electrofusion in terms of membrane tension and cell size. Compared to hypertonic and isotonic buffers, hypotonic buffer not only increased the reversible electroporation area in the cell-cell contact zone by 1.7 times by inducing a higher membrane tension, but also significantly reduced the applied voltage required for cell electroporation by increasing the cell size. Finally, the microfluidic chip with arc micro-cavities was fabricated and tested for electrofusion of SP2/0 cells. The results showed that no cell fusion occurred in the hypertonic buffer. The fusion efficiency in the isotonic buffer was about 7%. In the hypotonic buffer, the fusion efficiency was about 60%, which was significantly higher compared to hypertonic and isotonic buffers. The experimental results were in good agreement with the numerical analysis results.

Advances in hybridoma preparation using electrofusion technology

As a rapidly developing cell engineering technique, cell electrofusion has been increasingly applied in the field of hybridoma preparation in recent years. However, it is difficult to completely replace the polyethylene glycol-mediated cell fusion using electrofusion due to the high operation requirements, high cost of electrofusion instruments, and lack of prior reference research work. The key elements limiting electrofusion in the field of hybridoma preparation also introduce practical complications, such as the use/choice of electrofusion instruments, setup/optimization of electrical parameters, and precise control of cells. This review summarizes the state of the art of cell electrofusion in hybridoma preparation based on recent published literature, mainly focusing on electrofusion instruments and their components, process control and characterization, and cell treatment. It also provides new information and insightful commentary critically important for further electrofusion development in the field of hybridoma preparation.

Characterization of monoclonal antibodies against porcine epidemic diarrhea virus S1/S2 junction protein

Pig producers have faced considerable economic losses due to porcine epidemic diarrhea virus (PEDV) infection, emphasizing the need for PEDV antibody development. The S1/S2 junction (S1S2J) cleavage site of the S protein of PEDV is one of the major determinants of coronavirus infection success. In this study, we specifically selected the S1S2J protein of PEDV-AJ1102 (a representative strain of the G2 type) as a target protein to immunize mice and generated monoclonal antibodies (mAbs) using hybridoma technology. Three mAbs with high-binding activities to the S1S2J protein and were obtained and further analyzed. To reveal the characterization of these mAbs, variable region genes of antibodies were studied by using DNA sequencing, thereby revealing differences in their CDR3 amino acid sequences. We then developed a new method to identify the isotypes of these three mAbs. Results showed that these three antibodies were of the IgM type. As for the functions of these three mAbs, indirect immunofluorescence assay confirmed their good binding ability to Vero E6 cells infected with the PEDV-SP-C strain (G1 type). Epitope analysis showed linear epitopes for all three mAbs. These antibodies were also used to detect infected cells via flow cytometry analysis. In summary, we prepared and examined three mAbs against PEDV-S1S2J. These mAbs can be employed as detection antibodies for diagnostic reagents and further developed for other applications. We also designed a novel technique for easy and cost-saving identification of isotypes of mouse mAbs. Our results lay a good foundation for the development of research on PEDV.

Substantially Improved Electrofusion Efficiency of Hybridoma Cells: Based on the Combination of Nanosecond and Microsecond Pulses

As the initial antibody technology, the preparation of hybridoma cells has been widely used in discovering antibody drugs and is still in use. Various antibody drugs obtained through this technology have been approved for treating human diseases. However, the key to producing hybridoma cells is efficient cell fusion. High-voltage microsecond pulsed electric fields (μsHVPEFs) are currently one of the most common methods used for cell electrofusion. Nevertheless, the membrane potential induced by the external microsecond pulse is proportional to the diameter of the cell, making it difficult to fuse cells of different sizes. Although nanosecond pulsed electric fields (nsPEFs) can achieve the fusion of cells of different sizes, due to the limitation of pore size, deoxyribonucleic acid (DNA) cannot efficiently pass through the cell pores produced by nsPEFs. This directly causes the significant loss of the target gene and reduces the proportion of positive cells after fusion. To achieve an electric field environment independent of cell size and enable efficient cell fusion, we propose a combination of nanosecond pulsed electric fields and low-voltage microsecond pulsed electric fields (ns/μsLVPEFs) to balance the advantages and disadvantages of the two techniques. The results of fluorescence experiments and hybridoma culture experiments showed that after lymphocytes and myeloma cells were stimulated by a pulse (ns/μsLVPEF, μsHVPEF, and control), compared with μsHVPEF, applying ns/μsLVPEF at the same energy could increase the cell fusion efficiency by 1.5–3.0 times. Thus far, we have combined nanosecond and microsecond pulses and provided a practical solution that can significantly increase cell fusion efficiency. This efficient cell fusion method may contribute to the further development of hybridoma technology in electrofusion.

Electrofusion preparation of anti-triazophos monoclonal antibodies for development of an indirect competitive enzyme-linked immunosorbent assay

Immunoassays have been widely used to detect small molecular contaminants due to the advantages of simplicity, high throughout and low-cost. Antibodies are essential reagents of immunoassays, their quality directly determines the characteristics of immunoassays. In this study, the monoclonal antibodies (mAbs) of triazophos were prepared by electrofusion, and used to develop an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). Under the optimal electrofusion conditions (cells treatment with pronase, the alternating electric field strength of 45 V cm^-1, the direct current voltage of 3 kV), the fusion efficiency was 1.104 ± 0.063‱, which was improved more than 4-fold compared with the chemical fusion method (0.255 ± 0.089‱). Three hybrid cell lines that can stably secrete the anti-triazophos mAbs were obtained. The cell line 4G6F10 showed the highest sensitivity, which was used to generate mAb and develop an ic-ELISA. After optimization, the 50% inhibition concentration (IC₅₀), limit of detection (LOD) and linear range (IC₁₀-IC₉₀) of the ic-ELISA were 0.32 ng mL^-1, 0.08 ng mL^-1 and 0.08-2.17 ng mL^-1, respectively. There was no significant cross-reactivity with the analogues of triazophos. The average recoveries of triazophos in spiked samples were 77.5%-89.3% with the relative standard deviations of 0.1%-9.2%. In addition, the ic-ELISA showed good repeatability, reproducibility and accuracy for the analysis of apple samples spiked with triazophos.

Biological effects of ultrashort electric pulses in a neuroblastoma cell line: the energy density role

BACKGROUND

Despite the numerous literature results about biological effects of electromagnetic field (EMF) exposure, the interaction mechanisms of these fields with organisms are still a matter of debate. Extremely low frequency (ELF) MFs can modulate redox homeostasis and we showed that 24 h exposure to 50 Hz-1 mT has a pro-oxidant effect and effects on the epigenome of SH-SY5Y cells, decreasing miR-34b/c expression through the hypermethylation of their promoter.

METHODS

Here, we investigated the role of the electromagnetic deposited energy density (ED) during exposures lasting 24 h to 1 mT amplitude MFs at a frequency of 50 Hz in inducing the above mentioned effects. To this end, we delivered ultrashort electric pulses, in the range of microsecond and nanosecond duration, with the same ED of the previously performed magnetic exposure to SH-SY5Y cells. Furthermore, we explored the effect of higher deposited energy densities. Analysis of i) gene and microRNA expression, ii) cell morphology, iii) reactive oxygen species (ROS) generation, and iv) apoptosis were carried out.

RESULTS

We observed significant changes in egr-1 and c-fos expression at very low deposited ED levels, but no change of the ROS production, miR-34b/c expression, nor the appearance of indicators of apoptosis. We thus sought investigating changes in egr-1 and c-fos expression caused by ultrashort electric pulses at increasing deposited ED levels. The pulses with the higher deposited ED caused cell electroporation and even other morphological changes such as cell fusion. The changes in egr-1 and c-fos expression were more intense, but, again, no change of the ROS production, miR-34b/c expression, nor apoptosis induction was observed.

CONCLUSIONS

These results, showing that extremely low levels of electric stimulation (never investigated until now) can cause transcriptional changes, also reveal the safety of the electroporating pulses used in biomedical applications and open up the possibility to further therapeutic applications of this technology.

制备人脐静脉内皮细胞和人肺腺癌细胞融合细胞的新方法

Purpose:

Human umbilical endothelial cells (HUVECs) have been proved to be an effective whole-cell vaccine inhibiting tumor angiogenesis. In this study, we fused HUVECs with human lung adenocarcinoma cells A549 s, aiming at preparing lung cancer vaccine to achieve dual effects of anti-tumor angiogenesis and specific immunity to tumor cells.

Methods:

A549 cells were induced by ethyl methane sulfonate (EMS) and 8-azaguanine (8-AG) to get hypoxanthine guanine phosphoribosyl transferase (HGPRT) auxotrophic A549 cells. Then Fused HGPRT auxotrophic A549 cells with primary HUVEC cells by combining electrofusion with polyethylene glycol (PEG). Afterward the fusion cells were screened by HAT and HT selective medium and sorted by flow cell sorter to obtain high-purity HUVEC-A549 cells. Finally, HUVEC-A549 cells were identified by karyotype analysis and western blotting.

Results:

The fusion efficiency of HUVEC-A549 cells prepared by combining electrofusion with polyethylene glycol (PEG) was significantly higher than that of electrofusion and PEG (43.0% vs 17.60% vs 2.71%, P < 0.05). After screened by HAT and HT selective medium and sorted by flow cell sorter, the proportion of HUVEC-A549 cells can count for 71.2% ± 3.2%. The mode of chromosomes in HUVEC-A549 cells was 68, and the chromosome was triploid. VE-cadherin and platelet endothelial cell adhesion molecule-1 (CD31) were highly expressed in HUVECs and HUVEC-A549 cells, but not in A549 cells.

Conclusions:

These results indicate that HUVEC-A549 cells retain the biological characteristics of human umbilical vein endothelial cells and A549 cells. It can be used in the experimental study of lung cancer cell vaccine.

Recent advances in critical nodes of embryo engineering technology

The normal development and maturation of oocytes and sperm, the formation of fertilized ova, the implantation of early embryos, and the growth and development of foetuses are the biological basis of mammalian reproduction. Therefore, research on oocytes has always occupied a very important position in the life sciences and reproductive medicine fields. Various embryo engineering technologies for oocytes, early embryo formation and subsequent developmental stages and different target sites, such as gene editing, intracytoplasmic sperm injection (ICSI), preimplantation genetic diagnosis (PGD), and somatic cell nuclear transfer (SCNT) technologies, have all been established and widely used in industrialization. However, as research continues to deepen and target species become more advanced, embryo engineering technology has also been developing in a more complex and sophisticated direction. At the same time, the success rate also shows a declining trend, resulting in an extension of the research and development cycle and rising costs. By studying the existing embryo engineering technology process, we discovered three critical nodes that have the greatest impact on the development of oocytes and early embryos, namely, oocyte micromanipulation, oocyte electrical activation/reconstructed embryo electrofusion, and the in vitro culture of early embryos. This article mainly demonstrates the efforts made by researchers in the relevant technologies of these three critical nodes from an engineering perspective, analyses the shortcomings of the current technology, and proposes a plan and prospects for the development of embryo engineering technology in the future.