At high doses, IL2 (Aldesleukin) drives helper and cytotoxic T-cells to combat cancer (but promote autoimmunity).
At low doses, it favours regulatory T-cells, which are obligate IL2-dependent for survival. Tregs downregulate inflammation: good for autoimmunity, bad for cancer and infection.
Anti-IL2 (Basiliximab, Daclizumab) is used in the prevention of acute rejection in transplants, and rarely used off-label in severe autoimmune diseases and graft-vs-host reactions. There is at least a theoretical concern that longterm use may deplete Tregs, rendering perpetuation of rejection and autoimmunity. So, while it may seem counter-intuitive, low dose IL2 may be a more appropriate treatment for rejection and autoimmunity.
IL2 biology is more complex than this differential dose-effect in various T-cell populations. IL2/anti-IL2 immune complexes promote functional Tregs.