Introduction to Biological Therapy
Biological therapy began with the discovery of immunization more than 200 years ago. Edward Jenner discovered the benefits of injecting humans with fluid taken from sores on cattle infected with cowpox, a disease also known as vaccinia. This fluid contains the organisms that produce the disease. His inoculation worked because the cells of the immune system developed antibodies against the cowpox organism.
About a century later, William Coley, a New York surgeon, started using biological therapy to treat cancer patients. He noticed that people with some kinds of cancer appeared to enter remission after developing certain bacterial infections. He concluded that the body's response to the infection must be exerting some effect on the cancer. He injected cancer patients with live bacteria, then later with filtered toxins. This induced an infectious response that sometimes led to a remission of their cancer. This method of treatment became known as Coley's toxins and was used for decades.
Paul Ehrlich, a German Nobel Prize winner in 1908, theorized that the surfaces of cells carried receptor molecules, or side chains as he called them. He pointed out that antibodies attached to these "side chains" triggered the release of antitoxins. He also believed that antibodies might be developed that could target invaders.
In the mid-1980s, encouraging results were seen in the use of interferon to treat a rare blood disorder called hairy-cell leukemia. The FDA has approved interferon for this disease, as well as chronic myelogenous leukemia, AIDS-related Kaposi's sarcoma, and genital warts.
More recently, Steven Rosenberg, a researcher at the U.S. National Cancer Institute, proved that the human immune system could be directed to discriminate between healthy cells and cancerous ones. Handled properly, immunotherapy could indeed stimulate the body's defenses. In 1992 genetically engineered IL-2 received the FDA's approval for treating advanced kidney cancer. In 1994 clinical trials were started to determine whether another interleukin, interleukin ("IL-12"), might have some benefit against metastatic cancer and AIDS.
To understand biological therapy, it helps to know some basics about the immune system, a complex network of organs and cells.
There are two basic types of defense protecting the body from foreign invaders such as bacteria, viruses, or cancer cells. The first line of defense is a physical barrier involving the skin, mucous membranes, the lining of the respiratory tract. This line of defense produces a nonspecific response because it works regardless of the invader.
The second line of defense, unlike the physical barrier, recognizes these invaders and then develops the specific weapons to fight them. It is even able to remember what the invader looked like so that the next time its response will be even swifter. This line of defense that produces a specific response is made by immune system cells. The immune system cells circulate throughout the body and defend the body against attacks by foreign invaders.
This immune network is one of the body's main defenses against disease. It works against diseases, including cancer, in a variety of ways. For example, the immune system may recognize the difference between healthy cells and cancer cells in the body and work to eliminate those that become cancerous.
Immune system cells include lymphocytes (white blood cells) and other immune cells. Lymphocytes are the most important cells of the immune system and can be categorized into T-cells, B-cells, and NK (Natural Killer) cells.
T-cells directly attack infected, foreign, or cancerous cells. T-cells also regulate the immune response by signaling other immune system defenders. B-cells secrete antibodies, the proteins that recognize and attach to foreign substances known as antigens. Natural Killer cells produce powerful chemical substances that bind to and kill any foreign invader. They attack without first having to recognize a specific antigen. Monocytes are white blood cells that circulate in the bloodstream. When they settle in tissue, the macrophages engulf the invaders and actually digest them.
Understanding how immune system cells exchange messages and finding ways to make these messages clearer and stronger are the goals of research in immunology. Each of these components, and each step in the immune response, represents a potential avenue for the development of a cancer therapy.
Biological therapy research focuses on isolating specific cells of the immune system and their chemical products, then manipulating them in the laboratory to target their activity and control their effects.
In summary, biological therapies use the body's immune system, either directly or indirectly, to fight cancer or to reduce the side effects that may be caused by some cancer treatments.