Recombinant Anti-CD28 x Anti-CD3 Bispecific Antibody (Bi-nanobody) is designed to be expressed as a VHH from anti-CD28 antibody variable domains fused with a VHH from an anti-CD3 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 improve T-cell activation. It is designed for the research of Tumors therapy.