Monoclonal antibodies – GCSE Combined Science Biology

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Monoclonal antibodies are special proteins made in a laboratory. Each one is an exact copy of the others, and each one sticks to just one target. The name sounds hard, but we will build it up slowly.

They matter because doctors use them every day. They are in pregnancy tests, in tests that find disease, and in some cancer treatments.

By the end you will be able to describe how they are made. You will describe how they are used. You will also weigh up the good and bad points of using them to treat cancer.

Antibodies and antigens

An antigen is a molecule on the surface of a cell or germ. Your body sees a foreign antigen as a warning sign. An antibody is a protein that sticks to one antigen.

Antibodies are made by white blood cells called lymphocytes. Each lymphocyte can make only one kind of antibody. Think of a key that fits just one lock.

Monoclonal antibodies are antibodies that are all identical. They come from one clone, which means a group of cells that are exact copies of one cell. They can be made to stick to any antigen we choose.

Making them: the mouse

To make monoclonal antibodies, scientists start with a mouse. They inject the mouse with the antigen they want to target.

The mouse's lymphocytes then make antibodies against that antigen. The scientists collect these lymphocytes from the mouse.

There is a problem. A lymphocyte makes the right antibody, but it will not divide many times in the lab. One cell alone would give us only a tiny amount of antibody. We need a way to make lots.

Making them: the hybridoma

The answer is to join each lymphocyte to a tumour cell. A tumour cell is a cancer cell. It has one useful skill, which is dividing very quickly. Joining two cells together is called fusing them.

The fused cell is called a hybridoma. Think of a footballer who scores goals and never gets tired. The hybridoma makes the antibody and keeps dividing.

The hybridoma divides again and again to make many identical cells. They all make the same antibody. The antibodies are then collected and purified.

Using them to find molecules

A monoclonal antibody sticks to one molecule only. So it can find that molecule for us.

A pregnancy test strip holds antibodies that bind a hormone called hCG. A pregnant woman's body puts hCG into her urine. The antibodies carry coloured beads. When hCG is present, the beads collect in a line and show a positive result.

Antibodies with a fluorescent dye attached can show where a molecule is in a tissue. Doctors use this to diagnose disease. Scientists use it in research.

Treating cancer

Cancer cells have molecules on their surface that normal cells do not have. These are called tumour markers. We can make an antibody that sticks to a tumour marker.

Now we attach a drug to the antibody. The drug could be a toxic drug, a radioactive substance, or a chemical that stops cells dividing. The antibody carries the drug to the cancer cells.

Think of a delivery driver who knows exactly one address. The drug reaches the cancer cells and does much less harm to healthy cells.

Advantages and limits

The big advantage is that monoclonal antibodies are very specific. They can aim a treatment at exact cells. Traditional chemotherapy can harm healthy cells as well as cancer cells.

There are limits too. Monoclonal antibodies have been less successful than hoped. They cause more side effects than scientists first expected, such as fever, vomiting and low blood pressure. They are also costly to produce.

A good answer gives both sides. Say they are specific, then say they have side effects and cost a lot.

Recap

Monoclonal antibodies are identical antibodies made from one clone of hybridoma cells.

A hybridoma is a lymphocyte fused with a tumour cell. It makes the antibody and divides quickly.

They are used in pregnancy tests, diagnosis, research and treating cancer.

They are specific, but costly and can cause side effects.