the powers of the immune system to treat cancer
Recognizing the immune system's remarkable ability to defend the body against disease, medical scientists have long dreamed of developing a new form of treatment for cancer -- immunotherapy. The aim of cancer immunotherapy is to bolster the immune system so that it is better able to combat cancer cells. Currently, several forms of immunotherapy are being explored in research laboratories and clinical trials. The majority of these approaches use natural biological substances to activate the immune system. Researchers are able to reproduce these natural substances outside the body through genetic engineering and hybridoma techniques. The various forms of immunotherapy fall into three main categories: immune response modifiers, monoclonal antibodies and vaccines.
Immune response modifiers. These are substances, either extrinsic or intrinsic to the body, that affect the immune response. One group of extrinsic modifiers is referred to as immune potentiators. These include BCG, C. parvum and endotoxin, which are all microbes or microbial products that have been shown to modify the immune response and, under certain conditions, to cause tumors to regress or grow more slowly than usual.
The intrinsic group, known as biological response modifiers , includes interleukin-1 and interleukin-2, interferon (alpha, beta, and gamma), tumor necrosis factor, B-cell growth factors and hematopoietic growth factors (such as colony-stimulating factors). These agents exert their influence at different stages of the immune response.
The interleukins activate the body's own lymphocytes to do their work. IL-2 has been found to be effective in some patients with melanoma or with renal cancer when it is administered alone or with a patient's own lymphocytes that have been treated with Il-2 outside the body.
The interferons act on the immune system by stimulating both T cells and macrophages. They also prevent cells from multiplying. Scientists believe that these two properties together enable interferon to fight some tumors effectively. Alpha interferon was the first FDA-approved biological response modifier for the treatment of cancer (it is effective against a rare form of leukemia).
Tumor necrosis factor directly attacks and kills tumor cells. Currently, it is being tested alone and in conjunction with gamma interferon to determine its potential efficacy in the treatment of human cancers. B-cell growth factors stimulate the multiplication of antibody-producing cells. The hematopoietic growth factors step up the production of both red and white blood cells in the bone marrow, thereby giving the body additional ammunition to fight disease and protect itself against the suppressive effects on the bone marrow of radiation and chemotherapy.
Monoclonal antibodies. One of the most important developments in immunology is the ability to produce pure antibodies in large amounts. These antibodies, called monoclonal antibodies, can be targeted to specific cancer antigens. Monoclonals can be used in both the diagnosis and treatment of cancer. In the laboratory, monoclonals serve as powerful tools to define tumor antigens that distinguish cancer cells from normal cells. When linked to radioactive isotopes, they can detect groups of cancer cells throughout the body. When attached to anticancer drugs and natural toxins, they can serve as "guided missiles" by directing these substances toward their malignant prey. They can also be used to treat cancer on their own by inducing an immune cell response at the tumor site. Monoclonals have shown promise in the treatment of lymphoma, leukemia and colon cancer.
Vaccines. Vaccines are being developed and tested in patients to prevent recurrences of previously treated cancers. Cancer vaccines are composed molecules, called antigens, which are found in cancer cells. These are being injected with appropriate chemical boosters to stimulate an immune response to a specific type of cancer. Current development efforts are centered on vaccines for melanoma, rectal cancer and breast cancer, as well as other cancers. |
