What are monoclonal antibodies?

Whenever any of us has an infection the white blood cells in our body are able to detect foreign proteins, called antigens, on the bacteria or virus causing the infection. Our blood cells then make another protein, called an antibody, which locks on to, and reacts with, the foreign antigen, leading to the destruction of the bacteria or virus.

In the mid 1970s it became possible to produce antibodies in the laboratory. These artificially produced antibodies were called monoclonal antibodies.

With this new technology researchers wondered if they could use monoclonal antibodies to help treat cancer. To do this they would need to find antigens on the surface of cancer cells which were found only on those cancer cells and were not found on normal tissues, and then produce monoclonal antibodies to those particular antigens.

The theory was that these monoclonal antibodies could then recognise the antigen on the cancer cells and lock on to it (like a key in a lock). This might then trigger the body's immune system to attack the cancer cells or even cause the cancer cells to destroy themselves. Alternatively the monoclonal antibody could have a cancer drug or a radioactive substance attached to it and be used to deliver treatment directly to the cancer cell (this was called targeted therapy or the 'magic bullet').
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In the last twenty five years a great deal of research as gone into both looking for antigens on cancer cells and improving production of monoclonal antibodies so that the large quantities necessary for medical use could be made.

There have been a number of difficulties which have hindered the use of monoclonal antibodies as a possible treatment. Firstly it is very difficult to find antigens that are specific only for cancer cells as most of the antigens found on cancers are also found to a lesser extent on normal tissues. Secondly the antibodies are treated as foreign substances by the body and some of the antibody will be mopped up by the body's defence mechanisms in organs such as the liver and the spleen.

In the last few years some useful antigens have been identified in some types of cancer and monoclonal antibodies suitable for use in patients (therapeutic monoclonal antibodies), mainly lymphomas and breast cancer, have been produced.

The early results of treatment with these therapeutic monoclonal antibodies have been quite promising. Sometimes they have been given on their own and sometimes in combination with normal chemotherapy.

At the moment the only monoclonal antibodies available for routine use are for lymphomas and in some types of breast cancer but the hope is that further research will increase the number and range of these therapeutic monoclonal antibodies so that other types of cancer can be treated.