Recombinant Anti-CD28 x Anti-CD3 Bispecific Antibody (scFv-Fc-scFv) is designed to be expressed as one chain, then assembled to a homodimer of bivalent scFv fragments and the Fc region of IgG. The anti-CD28 scFv is fused to the N-terminus of Fc via a hinge region while another anti-CD3 scFv is linked to the C-terminus of Fc. This scFv-Fc-scFv format has 2+2 antigen-binding valency by employing different scFv fragments. This BsAb can improve T-cell activation. It is designed for the research of Tumors therapy.