32.4: Hybridoma Technology
Hybridoma technology is used for the large-scale production of monoclonal antibodies. Monoclonal antibodies bind to only a single antigenic determinant or epitope. Such antibodies are used in research, diagnostics, and disease therapy. The hybridoma technology established in 1975 by Georges Köhler and Cesar Milstein was awarded the Nobel Prize in Medicine in 1984 for revolutionizing research and therapy.
Commonly used fusion techniques — electroporation, polyethylene glycol (PEG) mediated fusion, and the use of fusogenic viruses — generally produce hybridomas at a very low frequency. Fusion products thus have a high ratio of self-fused B-cells and myeloma cells, or unfused cells, with a low number of hybrid cells.
The hypoxanthine-aminopterin-thymidine (HAT) medium is used to select hybridomas by selectively allowing their growth. The aminopterin blocks the default nucleotide synthesis in cells. However, cells can utilize hypoxanthine and thymidine from the medium to synthesize nucleotides via the salvage pathway.
Myeloma cells deficient in the HGPRT enzyme cannot synthesize nucleotides via this pathway and thus, do not grow in HAT medium. Although B-cells produce functional HGPRT enzymes, they cannot divide indefinitely. Thus, only the hybrid cells with functional HGPT from the B-cells and immortality from the myeloma line can grow on the HAT selection medium. Such a culture of hybrid cells is called a hybridoma, which can be screened for monoclonal antibody production.
Hybridoma cultures from the HAT selection are plated onto a 96-well plate; each well containing only one cell. Using Enzyme-linked Immunosorbent Assay (ELISA), each cell is screened for the production of antibodies specific to the epitope of interest. Cells that test positive are then selected and grown in a larger culture vessel to establish hybridoma cell lines. These cell lines are a permanent source of unlimited monoclonal antibodies. Thus hybridoma technology is a convenient and cost-effective method for mass production of monoclonal antibodies.