The Surprising Story of IL-2: From Experimental Models to Clinical Application.

Equilibrium in the immune system is maintained by a balance between activation, which generates effector and memory cells, and suppression, which is mediated mainly by regulatory T cells. Understanding this balance and how to exploit it therapeutically is one of the dominant themes of modern immunology. The cytokine IL-2 was discovered as a growth factor for T cells and thus a key component of immune activation. It was initially used to boost immune responses in patients with cancer. Studies in experimental models and humans showed that the major function of IL-2 is to maintain functional regulatory T cells, and thus its essential function is in immune suppression. How the same cytokine can serve two opposing roles is a subject of current investigation. Because of these advances, IL-2 is now being tested as a cytokine for suppressing pathologic immune responses in autoimmune diseases and graft rejection. Fully understanding the biology of IL-2 may enable us to custom-design this cytokine for different applications in humans.