immunotherapies

passive immunization of an individual by administration of preformed antibodies (serum or gamma globulin) actively produced in another individual. By extension, the term has come to include the use of immunopotentiators, replacement with immunocompetent lymphoid tissue (e.g., bone marrow or thymus), and infusion of specially treated white blood cells. Because the immune response is a process of surveillance, recognition, and attack of foreign cells, immunotherapy has emerged as a promising mode of treatment for cancer. In general, there are three basic approaches to immunotherapy: active (specific and nonspecific), passive, and adoptive.

Nonspecific immunotherapy relies on general immune stimulants to activate the whole immune system. In the past decade, immunotherapy against cancer has involved the use of the bacille Calmette-Guérin vaccine (bcg vaccine), which is evolved from strains of Mycobacterium tuberculosis, and is used to provide some immunity to tuberculosis. A growing body of knowledge allows scientists to devise mechanisms to utilize an individual's own defenses to attack foreign cells, such as cancer cells. One drawback to the use of general immune stimulants is that there is a limit to how much the immune system can be forced to respond. At some point there is an automatic dampening of the response which controls immunologic activities so as to protect the body from attack by its own destructive immune cells.

Specific immunotherapy is being actively investigated. Particularly promising is the technique that involves the use of specific antibodies for types of tumor cells, which have been “loaded” with either antineoplastic drugs or radioactive materials. When injected into the bloodstream of a patient with that particular kind of tumor, the “loaded” antibodies attach to the surface of the malignant cells. Thus, the antineoplastic drug or radiation does more damage to the malignant cells than to nonmalignant cells that the antibody does not bind to.

Adaptive immunotherapy is a technique in which a cancer patient's white blood cells are withdrawn and cultured in the laboratory with interleukin-2. The leukocytes thus treated are infused into the patient's bloodstream to stimulate the immune system.

Immunotherapy is also used in the desensitization or hyposensitization of individuals allergic to specific allergens. Minute amounts of allergen to which the person is allergic are administered by injection in increasing doses over prolonged periods of time, in order to provoke production of large quantities of blocking antibody (predominantly IgG), which prevents an immediate hypersensitivity reaction from occurring. Presumably, the blocking antibody prevents the reaction by competing locally or in the circulation for the antigen.