IL2 and cancer: The principle of using low doses of IL-2 for the treatment of immunological diseases, instead of high doses as long time approved for cancer therapy, was introduced because of the assumption, and meanwhile convincingly proven fact, that Treg are more sensitive to IL-2 and require by far much lower doses of IL-2 for their stimulation compared to anti-tumor T cells and NK cells, because they constitutively express high levels of the heterotrimeric high affinity IL-2 receptor complex which is composed of CD25 (α-chain), CD122 (β-chain) and CD132 (common γ-chain) (3, 8, 15, 16).