Recombinant Anti-CD3 x Anti-CD4 Bispecific Antibody (scDiabody-Fc) is a fusion protein of two scDiabodies with an Fc region. In single-chain Diabodies, an additional connecting linker is introduced between chains of the anti-CD3/anti-CD4 diabody. The scDiabody with two specificities is further fused to the Fc domain to form BsAb with 2+2 antigen-binding valency. This BsAb can retarget T cells to HIV-1 infected cells. It is designed for the research of HIV-1 infection, AIDS therapy.