Monoclonal Antibodies
You only need to know about monoclonal antibodies if you’re studying the triple award spec (for AQA at least). They sound complicated, but they’re just antibodies that bind to a single type of antigen.
Producing monoclonal antibodies
Monoclonal antibodies are antibodies which are produced by a single clone of a specific white blood cell. They are specific to one binding site on one protein antigen (the molecules that are found on the surface of pathogens) so they are able to target specific cells. For example, monoclonal antibodies can be produced which bind specifically to the HIV antigen. Other monoclonal antibodies are able to bind to the antigens expressed on the surface of cancer cells.
Monoclonal antibodies are used in medicine and research and can be made in the following process:
A mouse is injected with the antigen that we want the monoclonal antibody to be specific to.
White blood cells secrete antibodies with a complementary shape to the antigen.
Spleen cells are extracted from the mouse – these cells produce the lymphocytes (white blood cells) which secrete the complementary antibody.
The lymphocytes are fused with a myeloma (cancer) cell to form a hybridoma cell. The hybridoma cell is able to divide rapidly and secrete the antibody.
The hybridoma cells are screened to make sure they are producing the correct antibody.
The hybridoma cell divides by mitosis to form a group of cloned cells that all produce the same antibody.
A large amount of the antibody is collected and purified.
Uses of monoclonal antibodies
Monoclonal antibodies are useful in research and medicine. For example:
Pregnancy tests – monoclonal antibodies bind to a hormone called HCG which is only found in the urine of pregnant people. The antibodies are attached to the end of a pregnancy stick which a woman urinates on. If her urine contains the hormone, it will bind to the antibodies and cause a colour change. This appears on the pregnancy stick as a solid line to indicate a positive result.
To measure the levels of hormones or other chemicals in the blood
To detect the presence of pathogens in the blood – e.g. monoclonal antibodies which specifically bind to the HIV virus can be used to diagnose HIV/AIDS
To treat diseases – e.g. the monoclonal antibody can be attached to a cancer drug. The antibody is designed to bind to antigens expressed on the surface of cancer cells. This enables the drug to be delivered specifically to cancer cells where it will release the cancer drug. This minimises the toxic effects on non-cancerous cells.
In research – e.g. the monoclonal antibody can be attached to a fluorescent dye which allows scientists to visualise structures within the cell. For example, if you wanted to look at cells of the liver, you could use a monoclonal antibody that is designed to bind to antigens on the surface of liver cells. The fluorescent tag that the antibody is attached to will make these cell fluoresce under the microscope.
When monoclonal antibodies were first developed, scientists expected them to be used widely and have a huge impact on science and healthcare. Unfortunately, monoclonal antibodies have not turned out to be very effective because they tend to bind to other molecules or cells of the body, resulting in unwanted side effects. For example, a 2006 drug trial to treat arthritis and leukaemia had to be stopped prematurely when many participants suffered organ failure, even though the monoclonal antibodies were shown to be safe in animal trials.
Other concerns about the use of monoclonal antibodies include the removal of spleen cells from the mouse. Since this involves harm to an animal, animal-rights groups tend to disagree with the use of monoclonal antibodies.