Abstract: A triple expression vector is disclosed for expressing an antibody molecule comprising an Fc domain in prokaryotic cells and in eukaryotic cells. The triple expression vector comprises a polynucleotide encoding an Fc domain; a polynucleotide encoding a phage coat protein; a cloning site for cloning genes encoding an antibody molecule or a part thereof wherein the antibody molecule or part thereof does not comprise an Fc domain; a prokaryotic secretion signal sequence and a eukaryotic secretion signal sequence, or a secretion signal sequence that drives efficient secretion in both prokaryotic and eukaryotic cells; a promoter for mediating expression in eukaryotic cells; and a stop codon for preventing expression of the phage coat protein in eukaryotic cells.