The therapeutic use of agents that stimulate immune function (immunostimulants). These agents include cytokines and cytokine antagonists, monoclonal antibodies, compounds obtained from bacteria, and hormones from the thymus. The most successful immunostimulants have been laboratory-prepared cytokines, the protein mediators of immune responses. Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are used widely to increase white blood cell production in the bone marrow after cancer therapy, bone marrow transplantation, and AIDS. Erythropoietin is effective in treating anemia in patients with chronic renal failure, AIDS, and bone marrow depression following cancer therapy. Transforming growth factor beta seems to enhance wound healing and reduce fibrotic changes following inflammation. Interleukins and interferons are being studied for their beneficial effects in patients with certain leukemias and other malignant tumors. Lymphocyte-activated killer (LAK) cells and tumor-infiltrating lymphocytes (TILs), which are lymphocytes that have been removed from the patient and stimulated with interleukin-2, also show promise in treating malignant tumors. Monoclonal antibodies against mediators of inflammation have been created in the laboratory from hybridomas and are being studied for clinical use.
Bacteria-based compounds, which produce nonspecific stimulation, have been used the longest. Attenuated (weak) solutions of Mycobacterium bovis (bacille Calmette-Guérin) and endotoxins from Staphylococcus aureus and OK432, prepared from Streptococcus pyogenes, are being used as adjunct cancer therapy because of their ability to activate natural killer cells, T cells, and macrophages. New techniques have enabled researchers to isolate hormones from the thymus gland, where T lymphocytes mature, to treat viral infections and cancers. Their clinical effectiveness has not been established. See: cytokine; monoclonal antibody