Ligand-binding fusion proteins

A fusion protein which comprises a ligand-binding moiety and is represented by formula (I):

• [Ligand-binding domain]-[Lx]-[Cx]-[Ly]-[Ligand moiety] (I)
• wherein:
• Lx represents a first peptide linker comprising a first protease cleavage site;
• Cx represents a constant region comprising a second peptide linker and one or more amino acid residues which are modified from or to cysteine;
• Ly represents a third peptide linker, and
• wherein the ligand-binding domain comprises a VH region and a VL region, binds to the ligand moiety, and is capable of releasing the ligand moiety in the presence of a protease,
• wherein the constant region comprises an antibody heavy chain comprising a CHI region and an Fc region and an antibody light chain comprising a CL region,
• (a) wherein the second peptide linker is positioned in a hinge region so that disulfide bond formation between Cys at position 220 of the heavy chain and Cys at position 214 of the light chain is promoted, with all positions according to EU numbering;
• (b) wherein amino acid residues in the heavy chain and the light chain are modified so that no disulfide bond is formed between position 220 of the heavy chain and position 214 of the light chain, with all positions according to EU numbering;
• or
• (c) wherein the heavy chain is modified to allow disulfide bond formation between position 131 of the heavy chain and position 214 of the light chain, with all positions according to EU numbering;
• and
• wherein the first protease cleavage site of Lx is located between the VH or VL region and the CH1 or CL region, respectively.