One of the most important innovations in Immunology during the second half of the 20th century was the development of monoclonal antibodies, by Georges Kohler and Cesar Milstein. Kohler and Milstein were awarded the Nobel Prize in Physiology or Medicine in 1984, which they shared with Niels K. Jerne for discoveries about the control and specificity of the immune system.
I first learned of the work of Kohler and Milstein as an undergraduate. In 1986, the process of making monoclonal antibodies was still very new and cutting edge, but as with most stories in science, the hybridoma process did not originate so suddenly or cleanly. Studies of leukemic cell lines in the late 1960’s and early 1970’s indicated that a B-cell produced only one kind of an antibody molecule, but there was no way to alter the kind of antibody made by an existing B-cell. The leukemia cell lines did offer the clue to the method for developing a cell line which could make a monoclonal antibody recognizing a specific, desired antigen. As we learned in lecture, antibody-producing (plasma) B cells have a limited lifespan in the circulation; it is the memory B-cells that have an extended lifespan, but they do not produce antibody until stimulated by antigen and differentiate back into plasma cells.
Kohler and Milstein’s innovation was this: a mouse is immunized with an antigen, so that B-cells present in the mouse would be stimulated to produce antibody capable of recognizing that antigen. Once antibody production is verified by measurement of serum antibody levels, the mouse is sacrificed, and it’s B-cells are isolated. These B-cells would normally only last for a limited period of time before they begin to die. Kohler and Milstein fused these normal B-cells from the immunized mouse with an immortal cancerous cell line, which had lost the ability to make antibody. Cells which have not fused with a cancerous partner are killed by administration of a drug, and the only surviving cells are B-cells which have fused with the cancer cell.
The B-cell/cancer cells fusions (called hybridomas) are diluted and dispensed into growth chambers, so that only one hybridoma is present in each chamber. Consequently, only one antibody is produced in each growth chamber. The scientist laboriously examines each chamber for chambers that are positive for an antibody of interest, by adding the antigen of interest. Once that has been accomplished, the positive “clone” can be grown essentially indefinitely, and the antibody harvested in massive amounts.
I alluded to a bit of back story up above. In 1973, two years before Kohler and Milstein’s seminal publication, Schwaber and Cohen at the University of Chicago published the fusion of a mouse cell line with human non-antibody producing cells, resulting in a hybrid cell capable of making human antibody. Some historians of science have suggested that significantly more credit should have been given to the first two scientists, however the innovation brought in by Kohler and Milstein (the ability to make an immortalized cell line secreting a single antibody of desired specificity,) while utilizing the basic principle of Schwaber and Cohen, extended and adapted that work in a new direction. And this is the way science works!
BONUS: Describe the use of a monoclonal antibody from a clinical setting. There’s a million of them!