The invention relates to branches of biotechnology and, in particular, to mutated polypeptides of the TGFβ molecule, -- the primary sequence of which has 90% sequence identity with that of human TGFβ. The polypeptide comprises a mutation of at least one amino acid residue selected from the group consisting of W30, W32, L101, I51, L51, Q67 and Y6 in native human TGFβ. These muteins lose their ability to interact with ALK5 but retain their ability to interact with the rest of the receptors that form part of the receptor complex (TBRII and TBRIII). In addition, they can antagonise the signalling of all of the natural variants of the TGFβ ligands, dependent on the recruitment of ALK5 in the receptor complex, and they have an immunomodulatory effect. The invention also relates to pharmaceutical compositions comprising, as the active principle, the disclosed polypeptides or fusion proteins and to the therapeutic use of the disclosed polypeptides, fusion proteins and pharmaceutical compositions and medicaments owing to their immunomodulatory effect on diseases such as cancer, diseases associated with fibrosis and chronic infectious diseases.
