Types of Biological Therapy
There are two basic categories of biological therapy: immunotherapy and cytotoxic therapy. Immunotherapy uses a variety of methods and drugs to manipulate the immune system. This creates a hostile environment for the existence or growth of cancer in the body. Cytotoxic therapy involves changing the cancer cells' biology so that they become weak and die.
Immunotherapy can be either active or passive. Active immunotherapy involves setting an immune response in the cancer patient to fight cancer cells. In passive immunotherapy, immune molecules are given to patients who do not produce them on their own. Both approaches can be specific or nonspecific.
Specific Active Immunotherapy
One way the immune system can recognize differences among cells is by molecules called antigens that appears on the cell surface. In active immunotherapy, cancer cells are analyzed in the lab and their antigens are identified. Then, a treatment is designed to stimulate a specific immune response against them. This is called specific active immunotherapy. Despite its theoretical worthiness, results of this approach have been disappointing and it has been generally abandoned by clinicians.
Nonspecific Active immunotherapy
The nonspecific active approach uses agents that set in motion a general immune response, activating a wide range of immune cells. The approach aims at strengthening the overall activity of the immune system instead of selectively arousing those elements most able to fight cancer. This approach has achieved some success.
The agents used in this method include interferons and interleukins (IL-2 and IL-12, for example), as well as bacillus (or bacilli) Calmette-Guerin (BCG), the organism that causes tuberculosis. The immune response to tuberculosis can cause certain cancers to regress. Researchers have achieved some success by injecting nonspecific agents directly into body cavities where tumors are located. In two studies, for example, the use of BCG led to the complete remission of recurrent bladder tumors in about 70 percent of the patients.
Passive immunotherapy, sometimes called adoptive immunotherapy, gives the cancer patient antibodies and other agents so that the patient adopts an immune response that has been developed in a test tube.
The passive approach can be specific or nonspecific. Specific treatments include monoclonal antibodies (MABs), the so-called magic bullets, which can be designed to target certain cancer cells.
One nonspecific technique involves removing some of the person's T-cells, culturing the cells in the lab, and then injecting expanded populations of the treated cells into cancer patients.
An alternative approach is to activate lymphocytes taken from a person's tumor to create yet another agent, called tumor-infiltrating lymphocytes (TILs) and returning these "stranger" cells to the patient where they can fight the cancer cells.
Cytotoxic Therapy (Tumor Cell Modulation)
The second main category of biological therapy is sometimes called cytotoxic (cell-killing) therapy. This approach uses proteins called cytotoxins that are produced by the body's cells to attack the cancer either by destroying the cancer cells or by making it difficult for them to grow and reproduce. Another term for this approach is tumor cell modulation.
Tumor cell modulation changes the cancer cell's biology so that they become weak and die. Some of the agents used in this approach are called cytotoxins. Perhaps the best-known cytotoxin in this category is tumor necrosis factor (TNF), a toxin secreted by activated macrophages to selectively kill tumor cells, principally by interfering with their blood supply.
Certain agents make the antigens on cancer cells more recognizable to antibodies or make them stickier so that antibodies bind to them more easily. Other compounds interfere with the cell's ability to metastasize.