Recombinant Anti-CD28 x Anti-HN Bispecific Antibody (Tandem scFv) is designed to be expressed as a scFv from an anti-CD28 antibody variable domains fused with a scFv from an anti-HN antibody variable domains. It contains a His-tag at the C/N terminus for affinity purification. The BsAb exits as monomer in reducing and non-reducing conditions. This BsAb can retarget T cells to tumor cells. It is designed for the tumor vaccine modification and the research of Tumors therapy.