Recombinant Anti-BAFF x Anti-B7RP1 Bispecific Antibody (Fab-IgG) is designed to be expressed as three chains, assembling in vivo and resulting in the construct of Fab-IgG (Tandem Fab-Fc). Fab-IgG has standard Fab and Fc domains, with no mutations, which may permit it has similar affinity binding and PK profile comparable to the parental antibodies. This BsAb can bind and inactivate two ligands simultaneously. It can inhibit B cell survival and T cell costimulation. It is designed for the research of Systemic lupus erythematosus (SLE) therapy.