ABSTRACT
Cytokines have emerged as an important new class of drugs for the treatment of malignancies, infectious diseases, hematological cytopenias, and other disorders.' Currently nine different recombinant and natural cytokines are approved for systemic administration in the United States, including erythropoietin, granulocyte colony stimulating factor, granulocyte-macrophage colony stimulating factor, interleukin-2, interferon an3, interferon a2a, interferon a2b, interferon fHb, and interferon y lB. Several dozen other cytokines are now available as recombinant proteins suitable for in vivo evaluation. Many therapeutic applications have been explored at the preclinical level with encouraging results. However, a number of cytokines with therapeutic effects in experimental models have failed to enter the mainstream of medical practice, either because they have had limited clinical benefit or because they have been associated with prohibitive toxicities. The pleiotropic biological activity of most cytokines has complicated the use of cytokines as systemic drugs. The following review focuses on the nature of the biology of cytokines and its implications for the evaluation, application, and benefit/risk analysis of cytokines as pharmacological agents.
