MONOCLONAL ANTIBODIES

Antibodies are normally obtained by injecting an animal with the antigen for which an immune response is sought. A variety of antibodies appear, each specific to a different part of the injected antigen molecule. Blood serum taken from such animals contains the antibody mixture, called polyclonal antibodies. Most immunogens tend to be rather weak heterogeneous nature of the immune response which result in each antiserum being a mixture of antibodies with varying affinity, cross reactivities, and effector functions. However, it is possible to enrich antigen-specific lymphocytes.
One of the most important contributions to immunology, that has a strong impact on biotechnology, was made by Kohler and Milstean in 1976. This work has made possible to create pure and uniform antibodies against specific antigens. This technology of producing pure (monoclonal) antibodies is called hybridoma technology. This technology is greatly helping the development of effective vaccines against diseases of humans, animals, and even plants. The modern approach is to fuse an antibody forming cell (B Lymphocyte) with an immortal cell, capable of everlasting proliferation. A mouse is repeatedly immunized with an antigen of choice. As a result, there is proliferation of B lymphocytes making antibodies specific for that antigen. Thereafter, these highly potent B lymphocytes are removed from the mouse and are fused to a mutant myeloma cells whose own antibody synthesis has been stopped. The fused product gives us pure and homogeneous bodies regularly. Hybridoma or Fused cells is a hybrid cell that produces monoclonal antibodies in culture. Hybridoma cells are mainly formed by the fusion of a myeloma (cancer) cell with a normal antibody producing lymphocyte.
Cultured myeloma (cancer) cells are fused to spleen cells (lymphocytes) from an immunized animal. The spleen cells are the source of antibodies. One spleen produce only one type of antibody. This means that one hybridoma clone (that is fused product of cancer cells and lymphocytes) will produce only one type of specific antibody. Later the parental myeloma cells are killed by growing the hybrids in appropriate selective media. The normal spleen cells fail to survive in the culture. Several spleen X myeloma hybrids arise and a few of them survive in culture. These hybrids phenotypically resembles the myeloma cell parent, and they produce large quantities of the antibodies expressed by the lymphocytes derived from the immunized animal.

Applications of Monoclonal Antibodies

Monoclonal antibodies can be used in diagnostic systems to identify serologically similar microorganisms. The merits of monoclonal antibodies as diagnostic reagents is that they provide a standardized product with greatly reduced non-specific reactions. Monoclonal antibodies with markers such as fluorescein, peroxidase-anti peroxidase or radioactive isotopes can be used to identify microbial agents (pathogens) in tissues or cultured cells. Some other clinical applications of monoclonal antibodies are as follows:

• Selective elimination of undesired cells, such as tumour cells or activated T lymphocytes in transplantation patients was one of the first possible therapeutic applications of monoclonal antibodies.
• Potential use in radiological scanning for tumor localization.
• Counting and distinction of human lymphocyte subsets, using monoclonal antibodies that distinguish human helper and suppressor T cells and thymic lymphocytes at different stages of differentiation.
• Depletion of a particular type of T cell subsets from a mixed population of bone marrow cells to prevent graft verses host reaction.
• Analysis of complex antigen mixtures or of embryological relationships .
• Treatment of drug overdose.
• Definition of tumor antigens such as human renal antigen.