Biological activity of antibodies from clones transformed with the FUT8 and GMD siRNA tandem expression vector. Lysis of antigen-expressing cells targeted by human PBMCs at a target:effector ratio of 1:20 in the presence of different antibody concentrations was quantified by detecting lactate dehydrogenase activity (A). The antigen-binding activity of the antibody was measured by ELISA (B). Antibody purified from the serum-free fed-batch cultures of cells transformed by the FUT8 and GMD tandem siRNA expression vector, FG1 (open circles), FG16 (open squares), and the parental cell line 32-05-12 (filled circles) are shown. Cytotoxicity (%) and absorbance are indicated as the mean values ± SD of triplicates.