Recombinant Anti-CD28 x Anti-CD3 Bispecific Antibody (Miniantibody) is a fusion protein of two scFv fragments combined with distinct specificity. One scFv of an anti-CD28 antibody variable domain is linked to another scFv of an anti-CD3 antibody variable domain by a flexible hinge region. This BsAb format has the decreased size and better penetration than conventional IgGs in the clinical diagnostics and potentially therapy. This BsAb can improve T-cell activation. It is designed for the research of Tumors therapy.