IgG-IgG is a type of bispecific antibody conjugates, antibody-antibody conjugates. Crosslinking of IgGs is a direct approach to generate BsAbs. It is generated by conjugating two full length antibodies. IgG-IgG conjugate has a MW of ~300 kDa and is bivalent for each antigen. Usually, the generation of IgG-IgG conjugate relies on the amino-reactive reagents. And the widely used crosslinkers include SPDP, Traut’s reaget/SMCC, etc. In some conditions, IgG-IgG conjugates generated are high heterogeneity, which may be a backbone to get high-purity homogeneous antibody.