Recombinant Anti-CD28 x Anti-CD3 Bispecific Antibody (scDiabody-Fc) is a fusion protein of two scDiabodies with an Fc region. In single-chain Diabodies, an additional connecting linker is introduced between chains of the anti-CD28/anti-CD3 diabody. The scDiabody with two specificities is further fused to the Fc domain to form BsAb with 2+2 antigen-binding valency. This BsAb can improve T-cell activation. It is designed for the research of Tumors therapy.