Recombinant immunotoxin targeting mesothelin

A chimeric molecule comprising a fusion polypeptide having the formula M-L1-FCS-FL-functional PE domain III, wherein

• M is an antibody which specifically binds to mesothelin, or a fragment thereof that specifically binds mesothelin;
• L1 consists of from 1 to 10 continuous amino acid residues;
• FCS is a furin cleavage site consisting of continuous amino acid residues capable of being cleaved by furin;
• FL consists of from 3 to 8 continuous amino acid residues selected independently from glycine and serine;
• Functional PE domain III consists of continuous amino acid residues identical in sequence to SEQ ID NO:1 from position 395 to 613, optionally comprising (i) substitutions in one or more residues corresponding to 609-613 of SEQ ID NO:1, (ii) a substitution of glycine, alanine, valine, leucine, or isoleucine for arginine at a position corresponding to position 490 of SEQ ID NO:1, (iii) a substitution of one or more residues corresponding to residues of SEQ ID NO:1, which residues of SEQ ID NO:1 maintain immunogenicity of an epitope or subepitope of PE domain III, or (iv) a combination of any of (i)-(iii).