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Monoclonal antibodies

Certain cancer cells have specific proteins (antigens) on their surface. Monoclonal antibodies are substances that can find and bind to a specific antigen on a cancer cell. They may be used on their own (naked) or attached to other substances (conjugated).

Monoclonal antibodies are made in the laboratory.

  • Human cancer cells are injected into mice. Their immune systems make antibodies against the cancer cells.
  • Cells in the mice that are producing antibodies are then removed and mixed with cells grown in the laboratory to create hybrid cells (hybridomas).
  • Hybridomas are then used to produce large amounts of monoclonal antibodies.
  • The antibodies made in the mice are changed so that the human immune system cannot recognize them as being foreign (humanization).

Monoclonal antibodies are also called MOABs, MoAbs, MABs or MAbs.

Naked monoclonal antibodies

Naked monoclonal antibodies attach themselves to specific antigens (receptors) on cancer cells. Once attached, they block the growth of cancer cells.

Examples of monoclonal antibodies currently being used to treat cancer include:

  • Rituximab (Rituxan) is used to treat certain types of B-cell non-Hodgkin lymphoma.
  • Trastuzumab (Herceptin) is used to treat HER2-positive breast cancer.

Naked monoclonal antibodies are usually given into a vein (intravenously). The dose and frequency of injections depend on the type of cancer being treated. Monoclonal antibodies may be given alone or along with chemotherapy drugs.

Researchers are studying other monoclonal antibodies in clinical trials.

Conjugated monoclonal antibodies

Monoclonal antibodies can be attached to radioactive substances (radioactive isotopes). Less commonly, they are also attached to toxins or chemotherapy drugs. The antibodies find and bind to cancer cells, and then release the attached substances to destroy the cancer cells.

Radioactive substances

When monoclonal antibodies are used to carry radioactive substances, they are called radiolabelled monoclonal antibodies (or radioimmunoconjugates). This type of therapy is called radioimmunotherapy. Radiolabelled monoclonal antibodies work best in tumours that are sensitive to radiation therapy.

An example of a radiolabelled monoclonal antibody used to treat certain cancers is Ibritumomab (Zevalin). It is made up of a monoclonal antibody and the radioactive isotope yttrium-90. It is used to treat certain types of B-cell non-Hodgkin lymphoma.

Radiolabelled monoclonal antibodies may sometimes be used to find a tumour or a recurrence.


Monoclonal antibodies can be attached to poisonous substances (toxins) made from bacteria or plants. These conjugated monoclonal antibodies are sometimes called immunotoxins.

Toxins can affect both normal cells and cancer cells. Researchers are looking for antigens that occur only on cancer cells so that they can target these cells without harming normal cells. Unfortunately, few of these antigens have been found.

Researchers have made and tested a few immunotoxins, but this is still a very new area of study.

Chemotherapy drugs

When monoclonal antibodies are used to carry chemotherapy drugs, they are called chemolabelled monoclonal antibodies. Researchers are still studying these drugs or they are not currently available in Canada.

Gemtuzumab ozogamicin is an example of a chemolabelled monoclonal antibody that researchers are studying. It uses an antibody to target a specific antigen (CD33) on leukemia cells and delivers a powerful chemotherapy drug (calicheamicin) to them.

For more detailed information on specific drugs, go to sources of drug information.


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