One of the major issues in current antibody
therapy is insufficient efficacy. Various
biological factors relating to the host's immune system or
tumor cells have been suggested to reduce the efficacy of anti-CD20
therapy in B-cell
malignancies. In this study, we characterized the in vitro anti-
lymphoma activity of anti-CD20
antibodies having a novel engineered heavy chain with enhanced
complement-dependent cytotoxicity (CDC). Anti-CD20
antibodies having a variant heavy constant region of mixed
IgG1/
IgG3 isotype, which have previously been found to enhance CDC, were investigated for their in vitro CDC against
lymphoma cells and whole blood B-cell depletion activity. Use of the variant constant region greatly increased the CDC of an anti-CD20 antibody having variable regions identical to those of
rituximab to the level shown by an
IgG1 antibody of
ofatumumab. Although the whole blood assay showed different cytotoxicity patterns among individual blood donors, the CDC-enhancing variant of
rituximab showed higher activity than the parent
IgG1 and consistently showed maximized activity when further combined with antibody-dependent cellular cytotoxicity (ADCC)-enhancing modification by
fucose removal from Fc-linked
oligosaccharides. In addition, the
rituximab variant showed potent CDC against transfectant cells with lower CD20 expression and
chronic lymphocytic leukemia-derived cell lines with higher
complement regulatory
proteins. These findings suggest that CDC enhancement, both alone and in combination with ADCC enhancement, increases the anti-
lymphoma activity of anti-CD20
antibodies irrespective of individual differences in effector functions, and renders current anti-CD20
therapy capable of overcoming the potential resistance mechanisms.