Hetero heavy chain/Common light chain-Asymmetric reengineering technology immunoglobulin (ART-Ig)

Since an IgG antibody has two antigen-binding fragments (Fab) both of which link to an Fc region, there had long been a concept of an asymmetric bispecific IgG antibody capable of binding to two different antigens or epitopes. The asymmetric reengineering technology immunoglobulin (ART-Ig) is a humanized asymmetric bispecific IgG antibody. An asymmetric bispecific IgG antibody typically has 2 kinds of heavy chain and 2 kinds of light chain. If the 4 chains were simultaneously expressed in a recombinant cell to produce the desired asymmetric bispecific IgG antibody, as many as 9 kinds of unwanted byproduct IgG molecules would also be assembled and secreted. A method of reducing the byproduct IgG molecules using a common light chain in the asymmetric bispecific IgG antibody and also by introducing “knobs-into-holes” mutations in its Fc region to prioritize a specific hetero-dimerization of the heavy chains.

Schematic illustration of the molecular structure of asymmetric reengineering technology immunoglobulin (ART-Ig), emicizumab. CDR: complementarity determining region, pI: isometric point. (Adopted from: Kitazawa, T., Shima, M. (2020) Emicizumab, a humanized bispecific antibody to coagulation factors IXa and X with a factor VIIIa-cofactor activity. Int J Hematol 111, 20–30)

Formats of bispecific antibodies (BsAbs)

Many formats have been developed for BsAb generation as listed in the following table.