Antigen-binding polypeptides and their uses

A method of making a bispecific antigen-binding polypeptide (ABP) comprising a sequence selected from SEQ ID NO:

• 19, 21, 23, 24, 26, 28, 30, 31, and comprising a ribosomally incorporated non-naturally encoded amino acid substitution, wherein the bispecific ABP is directed against a tumor cell antigen and a cytotoxic trigger molecule and the bispecific antigen-binding polypeptide is linked to a linker, polymer, or biologically active molecule, wherein the method comprises contacting the bispecific antigen-binding polypeptide comprising the ribosomally incorporated non-naturally encoded amino acid, and allowing for an oxime bond to form between the non-naturally encoded amino acid and a linker, polymer, or biologically active molecule, wherein the non-naturally encoded amino acid has the structure:
• and wherein the R group is any substituent other than one used in the twenty natural amino acids.