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Antibodies that arise from a single clone of cells (e.g., myeloma) are homogenous and are called monoclonal antibodies. For example, in multiple myeloma, antibodies are produced by a single clone of plasma cells against a single antigenic determi-nant, and hence antibodies are monoclonal. The monoclonal antibodies differ from polyclonal antibodies, which are heter-ologous and are formed by several different clones of plasma cells in response to antigen.
◗ Method of production of monoclonal antibodies
Kohler and Milstein (1975) were the first to describe a method for production of monoclonal antibodies against a desired antigen for which they were awarded Nobel Prize in 1984. Monoclonal antibodies are produced by fusion of myeloma cells with antibody-producing cells, resulting in production of hybridomas. Such hybridomas produce virtually unlimited quantities of antibodies that are useful in research and diag-nostics. In this procedure, mouse splenic lymphocytes are first fused with mouse myeloma cells to produce hybrid cells or hybridomas. Myeloma cell provides the hybrid cell immortality,
whereas splenic plasma cell provides the antibody-producing capacity. These hybridomas can be maintained indefinitely in culture and continue to produce monoclonal antibodies. Hybridoma cells are prepared in following ways (Fig. 17-2)
· First, an animal (e.g., mouse) is immunized with the antigen of interest.
· Spleen cells (lymphocytes) are then fused with mouse myeloma cells and grown in culture, which are deficient in the enzyme hypoxanthine phosphoribosyl transferase (HPRT).
· Fusion of the cells is facilitated by addition of certain chemi-cals, such as polyethylene glycol. The fused cells are grown in a special culture medium (HAT medium) that supports the growth of the fused hybrid cells but not of the parent cells.
· Finally, the resulting clones of cells are screened for the production of antibody to the antigen of interest.
· These clones are then selected for continuous cultivation. The hybridomas can be maintained indefinitely and will continue to produce monoclonal antibodies.
Human monoclonal antibodies, such as chimeric antibodies, have been produced with modification of the original tech-nique for therapeutic use, since mouse monoclonal antibod-ies are not suitable. The chimeric antibodies consisting of human constant regions and mouse variable regions are being prepared for use in treatment of leukemia. Chimeric antibodies are also used to kill tumor cells either by delivering toxins, such as diphtheria to tumor cells, or by killing tumor cells through complement-mediated cytotoxicity.
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