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Immunotherapy seeks to activate the body's own immune system to target and destroy cancerous cells. Although clinical science has recognized the potential of immunology in cancer therapy for over 100 years, only recently has technology advanced to the state where viable treatments seem within reach. Scientists are now producing antibodies directed at specific targets on cancer cells or related tissues that support tumor growth. Some have proven successful in treating cancers. For example, BL22 has been used to treat adult hairy cell leukemia and Herceptin® has been effective in treating certain types of breast cancer. There are many other products that have been approved, or are in late clinical trials.

Currently, novel strategies are being employed to design immunotoxins which are produced by fusing a protein, derived from the immune system, together with a cellular toxin. Alan Wayne, M.D., clinical director of the pediatric oncology branch, National Cancer Institute (NCI), explained, "The antibodies recognize specific proteins on the cell surface. It is similar to our being able to tell the difference in facial appearances (e.g. noses, shape of the eyes). The monoclonal antibodies can then be linked to therapeutic agents that deliver a poison payload specifically to the cancer cells."

An early study of an immuotoxin treatment in children uses a bacterial toxin named BL22 that has shown promise in treating certain types of blood cancers in adults. An NIH phase I study of BL22 is testing this therapy in pediatric patients who have relapsed acute lymphoblastic leukemia (ALL) or non-Hodgkin's lymphoma. Wayne noted, "Although preliminary, we are encouraged by our initial findings."

Adoptive cell transfer, a method in which white blood cells are withdrawn from a patient, activated in a culture to boost their tumor-fighting ability, and then re-infused, has shown promise in treating some patients with melanoma. The technique is now being applied to the treatment of sarcomas in children. "Our study is similar to a melanoma study that was developed at NCI," said Lee Helman, M.D., chief of the pediatric oncology branch, NCI. "We harvest cells from the patient, and then the cells are matured outside of the body. In the case of treating children with sarcomas, we are using the cell that presents proteins to the immune system and says ‘here is the protein you should be attacking.’"

For the past 10 years, much clinical research has focused on development of a variety of cancer vaccines. However, the use of vaccines to treat cancer has yet to achieve widespread success. Increased understanding of the molecular biology of immunity raises hopes of developing a new generation of vaccines. New strategies are being applied to enhance vaccine specificity to tumor proteins and to find ways to circumvent the defense mechanisms that cancer cells use to escape normal immune responses. "The NCI is currently developing a trial that adapts tumor vaccine techniques used in our sarcoma trials. The immune activating cells are taken from the patient's brother or sister, who previously served as the bone marrow transplant donor," concluded Wayne.

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