The emerging role of biologics in rheumatic disease.

Biologically based therapeutics may be classified as agents which (1) restore altered immunoregulatory, hematopoietic or other disease resistant functions, (2) modulate immunologic effector mechanisms (immunomodulators), or (3) upregulate or downregulate a specific cell function. There are several characteristics which differentiate biologic agents from more traditional pharmaceutical drugs. Administered parenterally, they often generate systemic effects, and may be associated with a higher placebo response. Many are administered not at pharmacologic, but "industrial strength" doses. The specific desired effect may be obscured by cytokine and other immunoregulatory networks. A host immune response typically occurs with repetitive administration; this may alter the pharmacokinetics of the agent but not necessarily the biologic or clinical effects. The use of biologic markers, both disease specific and agent specific, may allow more efficient clinical development of these agents. A variety of biologic agents are in clinical trials for the treatment of autoimmune diseases. These include interferon gamma, the IL-1 receptor antagonist and monoclonal antibodies to the T cell surface antigens CD4 and CD7. Two immunotoxins, CD5-ricin A chain, and diphtheria AB toxin-IL-2 are undergoing evaluation in rheumatoid arthritis. Data regarding these agents will be reviewed. Issues specific to their use in pediatric clinical applications will be discussed.