What are Hybridomas?

Hybridoma technology is used to produce monoclonal antibodies (mAbs). It involves fusing B cells, which produce antibodies, with myeloma cells, which are cancerous cells that grow indefinitely. The resulting hybrid cells, known as hybridomas, canproduce a large quantity of identical mAbs that target a specific antigen.

The general process of creating hybridomas involves several steps, including immunization of an animal with the antigen of interest, harvesting B cells from the spleen, fusing the B cells with myeloma cells using a chemical or electrical method, selecting the hybridomas that produce the desired antibody, and finally, growing and maintaining the selected hybridomas in culture.

Making Antibody-Generating Hybridomas

Immunization: The first step is to immunize an animal with the antigen of interest. The animal's immune system will produce B cells that manufacture antibodies specific to the antigen.

Cell isolation: Plasma B cells and memory B cells are both produced through B cell differentiation, which occurs in the lymphoid tissues of the immune system, including the bone marrow, lymph nodes and spleen. B cells derived from these sources are used for making antibody-producing hybridomas. Myeloma tumor cells that allow continuous cell division are grown in special media conditions and are isolated for hybridization with B cells.

Cell fusion: The B cells are then fused with immortalized myeloma cells. The fusion is typically achieved using chemical or electrical methods:

• Chemical Fusion: Polyethylene glycol (PEG), a water-soluble polymer that can fuse cell membranes together, allows the B cells and myeloma cells to merge into a single hybrid cell. The PEG treatment is usually performed in the presence of a high concentration of calcium ions to help stabilize the newly formed hybrid cell. After the fusion, cells are washed to remove the PEG and any un-fused cells then plated in a culture medium to allow the fused hybridomas to grow.
• Electrical Fusion: Hybridoma fusion occurs using an electric field to create small pores in the cell membranes of the B cells and myeloma cells. The cells are then brought into close proximity to allow the pores to merge, creating a single hybrid cell. The electrical method is usually performed using an electroporator which applies an electrical field across the cells. The electrical pulse conditions, such as voltage, time and number of pulses, can be optimized to achieve the best fusion efficiency.

Selection & Screening: Inactivated hypoxanthine-guanine phosphoribosyltransferase (HGPRT) in myeloma cells allows the selection of hybridoma cells in HAT media, which are screened to identify the hybridomas that produce the desired antibody. Screening is typically done using an enzyme-linked immunosorbent assay (ELISA) or flow cytometry.

• ELISA: The antigen of interest is immobilized on a surface such as a microplate well. The hybridoma culture supernatants are then added to the plate, and any hybridomas that produce the desired antibody will bind to the antigen. Detection reagents, such as a secondary antibody conjugated to an enzyme, are then added to detect the bound antibody. Positive hybridomas can then be identified, indicating that the antibody has bound to the antigen.
• Flow Cytometry: To identify antibody-producing hybridoma cells, the cells are first tagged with fluorescently labeled antibodies that bind specifically to the antigen-binding antibody on the surface of the cells. When the cells are introduced into a flow cytometer, they pass through a laser beam that excites the fluorescent labels on the cells. The flow cytometer then detects the resulting fluorescent emission and the data is collected and analyzed by specialized software. This data from flow cytometry can provide information about different physical properties of the cells, including their size, granularity and surface marker expression.

Cloning: Monoclonality ensures that single cells are selected and expanded so that each cell produces the same mAbs. Several factors can influence the success of hybridoma cell cloning, including the purity and viability of the starting cell population, the selection of appropriate culture conditions and the use of appropriate growth factors and media supplements. Additionally, careful monitoring and screening of the resulting clones are necessary to ensure they continue producing the desired antibody and maintain their stability over time. Master and working hybridoma cell banks are prepared for long-term cryopreservation and immediate usage, respectively.

Characterization: Once the hybridomas have been cloned, they are further characterized to confirm that they produce the desired antibody and to determine the antibody's specificity, affinity and other properties. This can involve additional assays, such as Western blotting, immunoprecipitation, or epitope mapping.

Production: Finally, the selected clones are grown in a GMP environment to produce bulk quantities of mAbs. Scaling to meet demands for increased production is achieved using bioreactors which provide the optimal conditions for cell growth and antibody production for use in research or clinical applications.

Antibody-Producing Hybridoma Applications

The use of hybridoma cells to produce mAbs has provided invaluable insights into life science research, therapeutics and drug discovery. Applications include:

• Targeted therapy: Hybridoma-derived mAbs are used to treat various diseases, including cancer, autoimmune disorders and infectious diseases.
• Drug discovery: Hybridoma-derived mAbs are valuable tools for drug discovery and development, as they can be used to identify and validate new drug targets or as therapeutics themselves.

Advantages & Disadvantages of Antibody-Producing Hybridomas

Hybridoma cells offer a valuable method for producing mAbs. However, their use may be limited by the time-consuming process and requirement for animal use in their production.

Advantages:

• Highly specific: Hybridoma cells produce mAbs that are highly specific for their target antigen, making them valuable tools for research and therapeutics.
• High yield: Hybridoma cells can produce large quantities of mAbs.
• Consistency: Hybridoma cells produce mAbs with consistent affinity and specificity, which is essential for reproducibility.

Limitations:

• Time-consuming: Generating hybridoma cells and screening for mAbs is time-consuming, which may limit their use in applications that require a rapid response.
• Antigen isoforms: While hybridoma cells produce highly specific antibodies, they may not recognize all forms of a target antigen or distinguish between different isoforms or modifications.
• Animal use: Hybridoma cells are typically generated by fusing a B cell with a myeloma cell, which requires animals to produce the cells. This introduces a risk of contamination by adventitious agents.
• Genetic instability: Hybridoma cells can undergo genetic changes over time, leading to the loss of mAb production or changes in antibody properties.

Antibody-producing hybridomas have been an invaluable resource for researchers and clinicians for decades. While many laboratories around the world continue to utilize hybridoma technology, some limitations of this technique have led to the search for newer methods that facilitate mAb production from gene constructs. Genetic engineering is an advanced method that shows promise in reducing some of these challenges. Other advancements are being researched to humanize lab-produced mAbs to a large extent. For now, most mAbs licensed by the US FDA are produced using the hybridoma technique.