Recombinant Anti-BAFF x Anti-B7RP1 Bispecific Antibody (CrossMab) is designed to be expressed as four chains with knobs-into-holes mutations and domain crossover. After one or multi-steps purification, high-purity antibody can be obtained. 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.