Recombinant Anti-CD28 x Anti-HN Bispecific Antibody (Tandem Fab) is designed to be expressed as three chains derived from the variable domains of anti-CD28 and anti-HN parental antibodies. It contains a His-tag for affinity purification. And the two Fd regions are connected by a flexible linker. This BsAb can retarget T cells to tumor cells. It is designed for the tumor vaccine modification and the research of Tumors therapy.