After the first cellular division mitosis , the cells are known as synkaryons in which the nuclear membrane is fused as well. When cells with different numbers of chromosomes fuse, the resultant cell is unstable and further mitosis results in chromosome loss. This presents a unique challenge to scientists engineering hybridomas [ 1 ].
Producing stable hybridomas is crucial. The myeloma cells used have four sets of chromosomes tetraploid and the spleen cells have two sets diploid. The resulting hybridoma cells can vary in ploidy [ 12 ].
After several weeks of downstream processing, the hybridoma DNA stabilizes [ 13 ]. Here we describe the standard fusion techniques viral, PEG and electrofusion which rely on random cell pairings, unstable cell contact and low yields, as well as two newly devised methods gold nano-particle laser and distortion-based. Viral fusion methods In , scientists learned to effectively fuse cells using the Sendai virus, a respiratory tract virus that affects mice. Sendai virus fuses cells by the secretion of fusion proteins that are normally used by the virus to fuse with, and gain entry into a cell.
Two cells held in close proximity with cell fusion proteins will also fuse. Other viruses, or even extracted fusion protein, may also be used to fuse cells for hybridoma production, however, antibody secretions from the fused hybridomas can vary with these other options leading researchers to mainly choose the Sendai virus [ 14 ]. Sendai virus is commercially available and still used in experiments with hybridoma production. The efficiency seen with Sendai virus is very low, with tens of thousands of cells needed to produce each viable hybridoma [ 14 ].
PEG fusion methods Considered more reliable than using the Sendai virus, PEG has become the preferred method for fusing cells in hybridoma production [ 15 ]. Using PEG is a one-step process of simply placing the cells to be fused into a flask containing PEG and shaking [ 1 ].
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PEG dehydrates the cells and fuses cell membranes as well as intracellular membranes . A disadvantage to using PEG is that it causes unwanted fusions to occur [ 16 ].
PEG fusion products must be carefully assayed over the course of several weeks in the post-fusion phase to ensure the desired hybridomas are produced. It is estimated that only one in every 10, PEG fusion attempts leads to hybridoma formation [ 14 ]. Additionally, PEG fusion is not easily reproducible and different cell types act differently when exposed to PEG making experimentation and scale-up difficult [ 14 ]. Cell electrofusion methods First used in , and with a poor survival rate, electrofusion techniques have benefitted greatly from newly devised microfluidics platforms of the past several years [ 17 ].
Advances in bioinformatics have also made electrofusion a more precise method [ 17 ]. Electrofusion is accomplished by applying carefully controlled bursts of electricity to cells in suspension. The cell surface is first prepared through electroporation and then the cells are brought into close contact using the magnetic properties of dialelectrophoresis [ 17 ].
Properly designed, electrofusion results in a cell with a fused membrane and cytoplasm. Modern electrofusion produces more reliable fusion than PEG or Sendai virus techniques, but is not widely used due to its complexity and the technical skill required [ 17 ]. Laser fusion methods Cell fusion using laser technology was first used in the s with good results, but achieved no greater successful fusions than viruses, PEG or electrofusion [ 18 ].
Laser fusion technology is based on the principle that cells held in close proximity and bombarded with UV light will fuse [ 18 ]. Techniques available to researchers in the s offered little control of the system and the fusions most often failed. An experimental technique was released in from the University of Copenhagen, Denmark. This novel fusion system is based on laser application of near infrared NIR light pulsed into cells held in close proximity to gold nano-particles [ 18 ]. Optically heated gold nano-particle fusion appears to offer the greatest success yet seen in cell fusion.
Deformity-based microfluidic fusion method This method of cell fusion may revolutionize the hybridoma platform [ 19 ]. A major drawback to all other techniques is the lack of cell-to-cell contact required for proper fusion.
Other methods rely on random pairings and high numbers of fusions, with lengthy post-fusion screening steps to determine suitability for mAb production. The deformity-based microfluidic technique allows for precise control of the fusion partners and holds the resultant hybridoma in a growth medium while it is checked for proper fusion and post-fusion secretions.
This is considered a high throughput device and is compatible with several different fusion techniques including viral, PEG, electrofusion, and laser.
The Story of César Milstein and Monoclonal Antibodies: The making of monoclonal antibodies
Downstream processes of the hybridoma platform include the production of mAbs. Antibodies were first described in the late s. An antibody Ab , also known as an immunoglobulin Ig , is a Y-shaped protein produced naturally by most animals.
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Cesar Milstein and other researchers pioneered antibody therapies for use in cancer and immune system disorders in the s. They first used animal models for antibody production, but these generally caused unwanted immune reactions when administered to human patients [ 1 ]. When injected into a patient, antibodies can help the immune system fight disease. The first antibodies produced by researchers were made by injecting animals with antigens and collecting serum containing antibodies. These are known as polyclonal antibodies pAb as they produced naturally from multiple immune B cells.
PAbs are used mainly in experiments and diagnostics, and have seen some success in treating human disease. Mabs — monoclonal antibodies are a completely natural antibody produced in laboratory experiments. MAbs are highly specific immune cells produced by cloned parent cells carefully selected for their antibody secretions. Hybridoma technology was instrumental in the early work on mAbs. MAbs also find use throughout the fields of molecular biology and biotechnology as tools for detecting and purifying molecular substances.
The most beneficial use of hybridomas is the production of antibodies made from human cells. Humanized and fully human mAbs — human hybridomas offer many benefits over CHO and phage-display technologies for mAb production. Additionally, the possibility of contamination risk is lower using human hybridomas [ 12 ]. Animal viruses are not always apparent in animal model hybridomas but have been known to cause complications when used in human applications [ 12 ]. Both CHO and phage platforms have issues that could be resolved by the use of human hybridomas.
The humanized hybridomas may use an animal for one, or both, and may involve genetic engineering to make the animal more human-like [ 12 ]. In terms of safety and efficacy, there is little difference between humanized and fully human antibodies produced by hybridomas [ 12 ].
Fully human hybridomas are more difficult to produce because there is a scarcity of human spleen cells producing desired antibodies.
In animal models, the animal is injected with an antigen to cause a secretion of a specific antibody. Hybridoma technology often gets lost amidst larger discussions on mAbs in scientific papers. Researchers who wish to study mAb production could benefit from considering the use of hybridomas for their experiments. Pharmaceutical companies looking to produce new classes and types of mAbs could benefit from using a hybridoma platform over the industry standard CHO, E.
FDA has shown great willingness to approve new biologicals made from the stable hybridoma platform. There are 50 FDA approved mAbs on the market today, of these, 18 are produced using hybridoma technology. The possibility of producing biosimilars with hybridomas to compete with existing mAbs should not go unnoticed by enterprising small-capital drug companies in light of recent developments on the hybridoma platform.
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Deformity-based microfluidics, gold nano-particle laser fusion and HyLiTe software for cell selection are now available for labs to use. Combined, these technologies could revolutionize the mAb industry or lead to breakthroughs in humanized or fully human mAbs. Hybridoma technology, though 40 years old, holds promise for great impact on future biotechnology industry as a platform for drug discovery and development.
As bioinformatics become more powerful and nanotechnology expands into biologicals, the possibilities of using hybridomas to study cellular interactions on a scale never before envisioned becomes a reality. Researchers in all areas of molecular biology can look to the hybridoma for clues related to cell fusion, allopolyploids, or gene expression in fused cells.