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A monoclonal antibody is a single kind of antibody, made by one clone of B-cell-derived cells, that binds one epitope on one antigen. Georges Köhler and César Milstein made the first monoclonal antibodies in 1975 by fusing antibody-producing B cells with immortal myeloma cells to create hybridomas. Because they are uniform and highly specific, monoclonal antibodies are used as detection tools in immunoassays such as ELISA, flow cytometry and rapid tests, and as drugs for cancer, autoimmune disease and infection. Engineering mouse antibodies into chimeric, humanized or fully human forms reduces immune reactions against the drug itself.
Walk through hybridoma production as a flowchart and ask at each step why the cells that are not wanted die. Then draw a sandwich ELISA layer by layer, from the plate to the colored product, and run the same logic on a home pregnancy test strip. Finish by decoding a few drug names ending in -mab.
When an animal is immunized, many B-cell clones respond, each making antibodies against a different part of the antigen. The resulting serum is polyclonal, a mixture that varies from animal to animal. A single, defined antibody is often more useful, but a B cell making one antibody dies after a short time in culture.
In 1975 Georges Köhler and César Milstein solved this. They immunized a mouse, collected B cells from its spleen, and fused them with myeloma cells, cancerous plasma cells that divide indefinitely. The myeloma cells lacked the enzyme HGPRT. Later work used myeloma lines that also make no antibody of their own, so each hybrid secretes only the B cell's antibody. The cells were then grown in HAT medium, which contains hypoxanthine, aminopterin and thymidine. Aminopterin blocks the cell's main route to making nucleotides, leaving only a salvage route that needs HGPRT. Unfused myeloma cells die. Unfused B cells die on their own. Only hybrid cells, called hybridomas, survive, with HGPRT from the B cell and immortality from the myeloma. Researchers then screen the hybridomas, pick one that makes the desired antibody, and grow it as a clone. Köhler and Milstein shared the 1984 Nobel Prize in Physiology or Medicine with Niels Jerne.
Monoclonal antibodies became standard laboratory tools. In an ELISA (enzyme-linked immunosorbent assay), an antibody or antigen is attached to a plastic plate. In a sandwich ELISA, a capture antibody holds the antigen, and an enzyme-linked detection antibody binds a second site. A substrate turns colored where the enzyme is present, and the color intensity measures the antigen. Lateral-flow strips, used in home pregnancy tests and rapid antigen tests, apply the same sandwich idea along a paper strip, with colored particles in place of an enzyme. In flow cytometry, cells tagged with fluorescent antibodies stream past a laser one at a time, so researchers can count, for example, the CD4 T cells in a blood sample.
Monoclonal antibodies are also drugs. Mouse antibodies, however, provoke an immune response in people. Genetic engineering produced chimeric antibodies, with mouse variable regions and human constant regions, then humanized antibodies, in which only the antigen-binding loops are from the mouse, and finally fully human antibodies. Rituximab, a chimeric antibody against CD20 on B cells, treats some lymphomas. Trastuzumab, a humanized antibody against HER2, treats HER2-positive breast cancer. Adalimumab, a fully human antibody against the cytokine TNF, treats rheumatoid arthritis and other inflammatory diseases.