Interleukin-2 (IL2) is a protein initially identified as a T cell growth factor. IL2 is mainly produced by activated CD4+CD25- (helper) T cells, and induces the proliferation of these and others cells like CD8+ T cells, B and NK cells. For this reason, it has been used to treat immune-deficiencies like HIV, and induce immune response against tumors. Nevertheless, it has been shown that IL2 also acts as the main growth factor of CD4+CD25+ Regulatory T cells. Interleukin 2 mediates its functions in the target cell through the interleukin 2 receptor (IL2R). IL2R is a multimeric functional protein consisting of three different chains: Il2Rα, Il2Rβ and γc.