Monoclonal Antibodies

So we understand how antibodies are made in the body. Plasma cells are generated through the cloning of B lymphocytes when they recognise the correct antigen and are stimulated to divide by activated helper T cells. Lots of plasma cells are cloned and these plasma cells make lots and lots of antibodies. These antibodies bind to the non-self antigen. Easy! (Click here for a clearer explanation, and here for an animation)

Antibodies are very useful to scientist because they are antigen specific, meaning they will only bind to one antigen or cells containing that antigen. So antibodies can be adapted to act as markers. For example, an antibody that attaches to antigens on cancer cells can be manufactured in the lab and labeled with a radioactive marker. When this antibody is introduced into the body it attaches to the antigens on the cancer cells. A radioisotope scan will then locate all of the cancer cells in the body with that particular antigen. This makes it easy for doctors to track the spread of a cancer and check success rates after surgery, for example.

So the question is how can we manufacture antibodies outside of the body? Plasma cells only live for a short time and cannot clone themselves. So we need to find a way of extracting the correct plasma cells from the body and giving them a way of reproducing so that they can produce enough antibodies to be of medical use.

Antibodies produced in large quantities outside of the body are called monoclonal antibodies. This is how they are produced:

1. The target antigen is injected into a mouse.
2. The antigen is recognised by a few B lymphocytes in the mouse spleen and these lymphocytes multiply to form a clone of plasma cells.
3. A sample of the mouse spleen is extracted which should contain these plasma cells.
4. The plasma cells are mixed with mouse myeloma (cancer) cells. These two types of cells fuse to produce a cell called a ‘hybridoma’.
5. Non-hybridised plasma cells soon die, and unhybridised myeloma cells are killed by removing a metabolite from the culture medium which is vital to their survival. The hybridoma cells can produce this metabolite, therefore they survive.
6. The surviving cells are subcultured. This means putting each hybridoma cell into a separate culture.
7. Lots of different plasma cells (for lots of different antigens) will have be collected from the spleen (step 3) so there will be lots of different hybridomas each producing a different antibody. The antibodies from each culture are tested against the target antigen. If the culture is producing the correct antibodies they will cause agglutination when exposed to the antigen.
8. Hybridoma cells which cause agglutination of the specific antigen are identified and then mass cultured in large fermenters. These fermenters will produce large quantities of the specific antibody.

There is an excellent animation of monoclonal antibody production from the good people at Sumanas Inc here.

So we can produce large quantities of antibodies outside the body for scientific use. These can be used in a number of different ways, such as;

• As markers to identify specific cells in the body (such as cancer cells).
• As markers for cell surface proteins (such as carrier proteins)
• To carry drugs to specific cells in the body. This allows targeted medication, particularly useful in the treatment of cancers.
• As diagnostic tools for diseases, used in blood or urine analyses.
• To identify hormones (such as in pregnancy tests).

Monoclonal antibodies have a huge range of uses in medicine and in research labs. They are often referred to as ‘magic bullets‘ as they can be made to target specific antigens.

Of course, the use of mice to produce the initial plasma cells is controversal. It would be unethical to induce disease in humans to extract plasma cell, and some people think it is unethical to do this mice. On the other hand, many human lives have been saved by the use of monoclonal antibody technology. What do you think?