Fab-IgG (also tandem Fab-Fc in the construct) is a format of appended IgGs, the IgG scaffold with Fab fragment in the N terminus. In some conditions, scFv misfolding can cause the non-function. Fab-IgG only contains Fab antigen-binding fragment, so there is no such problem respect to scFv. Meanwhile, less artificial construct and sequence design makes it easier to express. In Fab-IgG, standard Fab and Fc domains are used, with no mutations, which can maintain the function and natural characteristics of conventional IgGs. Fab-IgGs are symmetric bispecific and tetravalent molecules, 2+2 antigen-binding valency.