The present invention relates generally to polypeptides whose primary sequence has high sequence homology with human interleukin 2 (IL-2) with some punctual mutations in the sequence of native IL-2. The polypeptides of the present invention have an immunomodulatory effect on the immune system, which is selective/preferential on regulatory T cells. The present invention also relates to specific polypeptides whose amino acid sequence is disclosed herein. In another aspect the present invention relates to pharmaceutical compositions comprising as active ingredient the polypeptides disclosed. Finally, the present invention relates to the therapeutic use of the polypeptides and pharmaceutical compositions disclosed due to their immune modulating effect on diseases such as cancer and chronic infectious diseases.