(12) The production of monoclonal antibodies

You need to have read about antibodies before studying this section.

How do you make monoclonal antibodies?

As we have seen, antibodies are produced by the type of white blood cell called B-lymphocytes. It is proving useful to medicine to produce lots of a specific antibody from multiple clones of a single white blood cell. The antibodies will be identical and only target one specific antigen protein molecule. Unfortunately, lymphocyte cells do not divide easily, but tumour cells can be readily cultured to undergo rapid cell division, so they are used instead.

The process starts by (i) injecting a mouse with a specific antigen, this stimulates the production of antibodies against the antigen and then extracting the B-lymphocytes produced.

(ii) Culturing fast dividing tumour cells called myeloma cells.

(iii) You then fuse a mouse B-lymphocyte with a tumour cell to create a 'hybrid' cell called a hybridoma cell - which can be cloned to make lots of identical cells. It is these cells that produce identical monoclonal antibodies, which can be collected and purified for research or direct medical use.

If possible, you can produce monoclonal antibodies that bind to anything you want e.g. an antigen that is only found on the surface of a one specific type of cell.

Because monoclonal antibodies only bind to a specific antigen molecule, you can therefore target a specific cell and destroy it (e.g. a cancer cell) or 'neutralise' a chemical in the body to inhibit its poisonous action.

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(12b) Uses of monoclonal antibodies

1. Treating diseases using monoclonal antibody techniques

As we have seen, different cells in the body have different antigen molecules on their surface, which gives them a unique molecular signature.

This means you can make monoclonal antibodies that will bind to ('target') specific cells with that specific antigen.

Cancer cells have antigens on their cell membranes that you do not find on normal healthy body cells and they are known as tumour markers.

In the laboratory you can culture cells to produce monoclonal antibodies (see above) that will bind to these tumour marker antigens, but the real trick is other things you can do with the monoclonal antibody e.g. diagnose and treat cancer.

An anticancer drug-agent can be attached to the monoclonal antibody - see the diagram below.

The anti-cancer agent might be a toxic drug or radioactive substance (radioisotope) or any chemical that inhibits the growth and division of cancer cells.

Any toxic effect will only kill the cancer cells, not the healthy non-cancerous cells, because the anti-cancer agent is only attached to the cancer cell antibody, which itself, will only attach itself to the cancer cells - that's the way the antigen-antibody mechanism works.

Advantages and problems with using monoclonal antibodies to treat disease

Despite the wonderful advantages of applying monoclonal antibodies to medical treatments, there are the 'usual' pros and cons.

In other cancer treatments e.g. chemotherapy and radiotherapy you inadvertently damage neighbouring healthy cells as well as killing the cancer cells because of the high energy of the radiation (often gamma radiation). This doesn't happen with monoclonal antibody drug cancer treatment where the side effects are much less and healthy cells are not damaged.

Disadvantages: Unfortunately, monoclonal antibodies do cause more side effects than expected.

Symptoms exhibited include breathlessness, fever, itchy rashes, head aches, low blood pressure and nausea and vomiting.

These side effects have limited the use of monoclonal antibody drug treatments.

 

2. Tests for tracing and measuring specific substances to help in medical diagnosis

e.g. monoclonal antibody applications include ...

(a) Binding them to a specific hormone or other molecule in the blood to measure the concentration ('level' of a chemical).

(b) Testing blood samples for the presence of specific pathogens.

(c) Tracing and locating specific molecules on cell or tissue.

You first make monoclonal antibodies that bind to the specific molecule X you are investigating.

The monoclonal antibodies are then reacted chemically to bind with a fluorescent dye molecule to facilitate an analysis.

If the molecule X is present in your analysis sample, the monoclonal antibody will attach itself to it.

Therefore the presence, location and concentration of molecule X can be obtained using uv light to cause a fluorescent effect.

(d) Testing for cancer

You first make the specific antibody that will bind to the cancer cells, but this antibody is labelled with a radioisotope.

The radioactive labelled antibody is fed into the patient through a drip into the bloodstream and carried all the way around the body.

When the antibody encounters a cancer cell it will bind to it because it recognises the antigen of the cancer cell (the tumour marker).

The radiation emitted from the radioactive tracer is monitored by a special camera (linked to a computer and screen) and where the cancer cells are concentrated, the emitted radiation will be the greatest - this will show up as a bright 'hot spot' on the screen.

Therefore doctors can see exactly where the cancer is, the size of the tumour and, from previous scans, whether the cancer is spreading e.g. secondary cancers from prostate cancer i.e. cancer spreading out of the prostate gland.

(e) Using monoclonal antibodies to find blood clots

Blood clots form when proteins in the blood join together to form a solid mesh that restricts `blood flow.

You can make monoclonal antibodies, labelled with a radioactive tracer, that bind to these particular proteins.

After injection of these monoclonal antibodies into the bloodstream, a special camera (linked to a computer and screen) can pick out a where the blood clot is where there is a high concentration of the radioisotope - shown by a bright 'hot spot' on the screen from the nuclear radiation emitted by the radioisotope.

Blood clots are very potentially dangerous and this technique is able to detect them and allow the doctor to remove them before the patient comes to harm.

 

3. Pregnancy testing using monoclonal antibodies

Monoclonal antibodies are used in a pregnancy test strip/stick which can detect the HCG hormone which is only present in the urine of pregnant women.

The science behind the test is illustrated in the diagram below.

1. You wee onto the end of the strip or dip it into a collected sample of urine - the method is up to you!

2. The reaction zone is impregnated with the HCG antibody which has been modified with an enzyme (e) to facilitate a colour effect if HCG hormone is present.

As the urine diffuses up the strip this 1st antibody combines with any HCG hormone in the urine and continues moving along the strip.

3. In the test zone the HCG combination encounters and attaches itself to a 2nd, but immobile antibody.

If the HCG hormone is present in the urine the enzyme triggers a chemical reaction to give a colour change e.g. the appearance of blue colour would signify a positive pregnancy test.

If the HCG hormone is not present, no colour change is seen, indicating a negative pregnancy result

4. The control zone is to check that the strip is working correctly, irrespective of a positive result.

As the urine diffuses further up the strip it carries along some of the first HCG antibody (with enzyme e) that has not combined with the HCG hormone. It then encounters an immobile version of the 2nd antibody which already has the HCG hormone attached to it

If the pregnancy stick is behaving correctly, you should get the same colour change whether it is a positive or negative pregnancy test result.

 

Note: You can impregnate the strip with different antibodies to test for the presence of other substances in the urine e.g. the antigens on other pathogens.

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