Schematic structures of DNL modules and HexAb. (A) The design of CH1-DDD2-Fab module. (B) The design of CH3-AD2-IgG module. (C) The structure of bispecific HexAb construct generated by DNL from reacting CH3-AD2-IgG and CH1-DDD2-Fab. The DDD2 and AD2 are shown in blue and red, respectively.