Monoclonal Antibodies

Producing monoclonal antibodies

Monoclonal antibodies are identical antibodies made by a single clone of cells. Each one binds to just one site on one protein antigen, so it can be used to target a particular chemical or a particular type of cell.

They are produced in four stages:

• A mouse is injected with the chosen antigen, and its lymphocytes begin making the matching antibody.
• Lymphocytes are collected from the mouse. On their own they do not divide well.
• Each lymphocyte is fused with a fast-dividing tumour cell, forming a hybridoma cell that can both divide and make the antibody.
• A single hybridoma cell is cloned. All the cells in the clone produce the same antibody, which is collected and purified.

The key idea examiners look for is why the cells are fused: the lymphocyte supplies the ability to make the antibody, and the tumour cell supplies the ability to divide rapidly.

Uses of monoclonal antibodies

• Pregnancy tests — the test detects the hormone hCG, which is present in the urine of a pregnant woman. Antibodies carrying a coloured label attach to hCG, and fixed antibodies at the test line trap them, producing a coloured line. A control line shows the test has worked.
• Diagnosis and measurement — in hospitals and laboratories they are used to measure levels of hormones and other chemicals in the blood, and to detect pathogens.
• Research — attached to a fluorescent dye, they can locate or identify specific molecules in cells or tissues.
• Treating disease — for some cancers, the antibody is bound to a radioactive substance, a toxic drug or a chemical that stops cells dividing. It carries this to the cancer cells, so normal body cells are largely unharmed.

Monoclonal antibodies have caused more side effects than was originally expected, so they are not yet as widely used as was first hoped.