The invention relates to variants of interleukin-2 (IL2). In particular, the invention relates to a polypeptide comprising a mutein of human IL2 or of a functional variant of human IL2, wherein the human IL2 or functional variant thereof is substituted such that affinity for the βγ IL2 receptor complex (IL2Rβγ) is enhanced. In one embodiment, the human IL2 or functional variant thereof is further substituted such that affinity for the αβγ IL2 receptor complex (IL2αβγ) is reduced. In one embodiment, the polypeptide activates effector T cells over regulatory T cells. The invention also relates to polynucleotides coding for the polypeptides of the invention, host cells comprising the polynucleotides, pharmaceutical compositions comprising the polypeptides, polynucleotides or host cells, therapeutic or prophylactic methods of treatment using the polypeptides, polynucleotides, host cells or pharmaceutical compositions and medical preparations comprising the polypeptides, polynucleotides, host cells or pharmaceutical compositions.