ABSTRACT
The availability of highly purified proteins has permitted the evaluation of cytokine function in vitro and in vivo as well as the clinical application of cytokines in human disease. The pleiotropic activity and intricate interactions of the cytokines form a system containing positive and negative feedback signals and redundancy which function to maintain homeostasis. Attempts to influence the immune system or the cellular functions of tumor cells with cytokines in the treatment of human cancer are limited by feedback mechanisms which bring the immune system and cellular function back toward equilibrium following provocation. The concept of combination cytokine therapy is well founded in numerous in vitro and animal models. Clinical progress in the application of these agents will be slow due to the need to determine for each cytokine the maximum tolerated dose and the individual toxicity spectrum.
