Lessons from the clinical trials of interleukin-2

The initial results of interleukin-2 (IL-2) therapy in man are reviewed from the perspective of how they conform to predictions from preclinical studies. These preclinical models predict that tumors will vary in their susceptibility to IL-2 therapy and will be most successfully treated at lower tumor burdens. In addition, the dose and schedule of IL-2 are important for successful therapy. Host-related factors, including the presence of suppressor activities, may also be important. In these models, the addition of other cytokines, including interferon-alpha or tumor necrosis factor, to IL-2 can enhance antitumor activity. The concomitant administration of ex vivo IL-2-activated lymphokine-activated killer cells or tumor-infiltrating lymphocytes also enhances the IL-2 antitumor effect. Clinical trials addressing all of these issues have been completed or are underway; the results suggest overall that the preclinical models are predictive, with both host- and tumor-related factors as well as such IL-2-therapy-related factors as dose, schedule, route and the use of additional agents all playing a role in the success of therapy. A more complete understanding of the mechanisms of response and resistance involved in this therapy will facilitate the rational development of more effective and less toxic IL-2-based therapy of human malignancy.