Recombinant Anti-CD28 x Anti-HN Bispecific Antibody (Fab-Fv) is designed to be expressed as two polypeptide chains. The heavy chain Fd fragment and light chain of an anti-CD28 antibody are fused with the VL and VH domains of an anti-HN antibody respectively. It can form natural in vivo heterodimerization. This BsAb can retarget T cells to tumor cells. It is designed for the tumor vaccine modification and the research of Tumors therapy.