The present invention relates to an IL-2 protein sequence of the formula Ala-SEQ A-Cys*-SEQ B (I), wherein SEQ A has at least 94% sequence identity to SEQ ID NO:1; SEQ B has at least 94% sequence identity to SEQ ID NO:2; Ala is an alanine residue; and Cys* is a cysteine residue; to conjugates thereof and their uses in the treatment of cancer.