Relationship between Monoclonal Antibodies and Hybridomas

If cells taken from various clones of normal antibody- producing and secreting lymphocytes could be grown in culture, it would be possible to have ready sources of various antibodies at one’s disposal.

There is, however, an abnormal and cancerous form of lymphocyte called a melanoma cell that can be cultured in the laboratory. Melanoma tumors can be produced in experimental animals by infra peritoneal injection of mineral oil.

In 1975, C. Milstein and G. Koehler were able to fuse myeloma cells with normal B lymphocytes, thereby producing a hybrid cell that could be grown in culture. Moreover, the hybrid cell, called a hybridism, pro­duces and secretes antibodies characteristic of the clone from which the normal lymphocyte is taken. The procedure for producing a hybridism is de­picted in Figure 25-11. First, an immune response is induced in a normal animal by exposure to a specific antigen (either by injecting the purified antigen or by injecting bacteria or viruses).

Lymphocytes are then obtained from the animal’s spleen or other lymphoid tissue. Among the cells that are removed will be some from clones that were activated by exposure to the an­tigen (many, perhaps most, of the cells will be from clones not selected by the antigen).

The normal lym­phocytes are then mixed with myeloma cells in a solu­tion of polyethylene glycol. The myeloma cells to be used lack the enzyme phosphoribosyl transferase, which catalyzes the synthesis of inosine monophosphate  and guano- sine monophosphate . Polyethylene glycol in­duces fusion of the two families of cells, thereby forming hybridomas.

The un-fused lymphocytes will fail to grow (or grow so slowly that they produce insignificant num­bers of progeny) when the cells are subcultured. If subculturing is carried out in a medium containing hypoxanthine, aminopterin, and thymidine (i.e., HAT medium), un-fused myeloma cells will also die out be­cause they cannot produce HGPRT.

Thus, the end result is a culture of cells producing a single type of antibody—a monoclonal antibody. Such cultures can be maintained indefinitely and be used as a continuous source of antibody.