Immunotherapy is used to stimulate the body's immune system against cancer. For example, vaccines composed of antigens derived from tumor cells can boost the body's production of antibodies or immune cells (T cells, or T lymphocytes). Extracts of weakened tuberculosis bacteria, which are known to boost the immune response, have been successful when instilled into the bladder to prevent recurrence of bladder tumors.
Monoclonal antibody therapy involves the use of experimentally produced antibodies to target specific proteins on the surface of cancer cells. Trastuzumab is one such antibody, which attacks the HER-2/neu receptor present on the surface of cancer cells in 25% of women with breast cancer. Trastuzumab enhances the effect of chemotherapy drugs. Rituximab is highly effective in treating lymphomas and chronic lymphocytic leukemia. Rituximab linked to a radioactive isotope can be used to deliver radiation directly to lymphoma cells. Gemtuzumab ozogamicin, a combined antibody and drug, is effective in some people with acute myelocytic leukemia.
Biologic response modifiers improve the immune system's ability to find and destroy cancer cells, such as by stimulating normal cells to produce chemical messengers (mediators). Interferon (of which there are several types) is the best-known and most widely used biologic response modifier. Almost all human cells produce interferon naturally, but interferon can also be made through biotechnology. Although its precise mechanisms of action are not totally clear, interferon has a role in the treatment of several cancers, such as Kaposi sarcoma and malignant melanoma. Interleukin 2, which is produced by certain white blood cells, also can be helpful in renal cell carcinoma and metastatic melanoma.