Engineered antibodies with increased activity to recruit complement

This manuscript describes two sites in a human IgG1 that, when mutated indi vidually or in combination, result in a dramatic increase in Clq binding an d complement-dependent cytotoxicity activity. These two residues, K326 and E333, are located at the extreme ends of the C1q binding epicenter in the C (H)2 domain of a human IgG. A mutation to tryptophan at K326 debilitates Ab -dependent cell-mediated cytotoxicity activity. In addition, substitutions of the residues E333 with serine and of K326 with tryptophan in a human IgG 2 confer biological activity in the complement-dependent cytotoxicity assay in which the wild-type IG2 is inactive. This study reveals that the residu es K326 and E333 play a significant role in the control of the biological a ctivity of an IgG molecule and can rescue the activity of an inactive IgG i sotype. The Journal of Immunology, 2001, 166: 2571-2575.