Crystal structure of a novel asymmetrically engineered Fc variant with improved affinity for FcγRs

Enhancing the effector function by optimizing the interaction between Fc and Fc gamma receptor (Fc gamma R) is a promising approach to enhance the potency of anticancer monoclonal antibodies (mAbs). To date, a variety of Fc engineering approaches to modulate the interaction have been reported, such as afucosylation in the heavy chain Fc region or symmetrically introducing amino acid substitutions into the region, and there is still room to improve Fc gamma R binding and thermal stability of the C(H)2 domain with these approaches. Recently, we have reported that asymmetric Fc engineering, which introduces different substitutions into each Fc region of heavy chain, can further improve the Fc gamma R binding while maintaining the thermal stability of the C(H)2 domain by fine-tuning the asymmetric interface between the Fc domain and Fc gamma R. However, the structural mechanism by which the asymmetrically engineered Pc improved Fc gamma R binding remained unclear. In order to elucidate the mechanism, we solved the crystal structure of a novel asymmetrically engineered Fc, asym-mAb23, in complex with Fc gamma RIIIa. Asym-mAb23 has enhanced binding affinity for both Fc gamma RIIIa and Fc gamma RIIa at the highest level of previously reported Fc variants. The structural analysis reveals the features of the asymmetrically engineered Fc in comparison with symmetric Fc and how each asymmetrically introduced substitution contributes to the improved interaction between asym-mAb23 and Fc gamma RIIIa. This crystal structure could be utilized to enable us to design a more potent asymmetric Fc. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.