Immunotherapy: Looking through cancer's invisibility cloak

The Antibody Assault Weapon

Another important biological therapy involves monoclonal antibodies which act against cancer cells or on ‘antigens’, particular targets on cancer cells. Antigens are a part of a virus or cancer cell which stimulate an immune response in the human body. In response to the detection of an antigen the immune system produces antibodies which then attempt to attack and destroy the virus or cancer cell on which the antigen is located.

Monoclonal antibodies are artificial antibodies produced in the laboratory. They are specific for a particular antigen - one designed for lung cancer will not work on cells of ovarian cancer for example.

Monoclonal antibodies work on cancer cells in the same way natural antibodies work, by identifying and binding to the target cells. The antigen specific structure of the antibodies help it identify and bind target cells similar to putting puzzle pieces together. The antibodies then alert other cells in the immune system to the presence of the cancer cells. This acts as a marker for the body’s immune system to destroy them. In order to prevent damage to normal tissue, it is crucial that the antigen has a unique molecular structure on the tumor cells which is not found on normal tissue.

However, some monoclonal antibodies don't really interact with a person's own immune system. Instead of alerting immune cells of the presence of cancer, their therapeutic effects come from the ability to attach to specific antigens, which are functional parts of the tumor and block growth proteins that are normally made by the tumor.

When coupled to drugs or radioactive molecules, antibodies can become full-fledged assault weapons. Because each antibody is specific for a unique target, it can carry the killing power of chemotherapy or radiation directly to a tumor cell – ignoring the normally functioning cells nearby. Instead of ‘bombing’ the target area with a clumsy dose of chemicals or radiation, this new method works more like a sniper, killing only the specific target cell.

Cancer Vaccines

Most of us know about vaccines given to healthy people for viruses, such as measles and mumps. These vaccines use composed of weakened or killed viruses which are intended to start an immune response in the body. The immune system reacts to a vaccine by going into ‘alert status’, on guard against a particular virus, which prevents people from being infected.

A cancer vaccine is very similar in that it is given to healthy people to prevent the development of cancer. Cancer develops because the immune system doesn't recognize cancer cells as something foreign. Rather, cancer cells are once-normal cells that have gone awry. Cancer vaccines try to get the immune system to overcome its tolerance of cancer cells so that it can recognize them and attack them.

Similar to monoclonal antibody therapy, vaccines used to treat cancers take advantage of the fact that certain molecules on the surface of cancer cells are either unique or more abundant than those found on normal or non-cancerous cells. These molecules act as antigens, meaning that they can stimulate the immune system to make a specific immune response thereby putting the immune system on alert to these cancer related molecules.

A Possible Treatment

Immunotherapy seems to offer great promise as a new dimension in cancer treatment, but it is still very much in its infancy. While monoclonal antibodies, tumor antigen specific T cells, and vaccines have individually shown some promise, it is likely that our best strategy to combat cancer will be to attack on all fronts. It may be that the best results are obtained with vaccines in combination with a variety of antigens, or vaccine and antibody combinations.

For more information

Cancer Index - Immunology and Immunotherapy
http://www.cancerindex.org

Meds.com - Immunotherapy
http://www.meds.com