Recombinant Anti-CD28 x Anti-HN Bispecific Antibody (Tandem scFv-Fc) is designed to be expressed as a homodimer, which has 2+2 antigen-binding valency. This format consists of one Fc region and two tandem scFv fragments, in which the anti-CD28/HN tandem scFv is fused to the Fc domain. The engineered fragment format is used to extend the half-life. This BsAb can retarget T cells to tumor cells. It is designed for the tumor vaccine modification and the research of Tumors therapy.