Recombinant Anti-CD3 x Anti-CD4 Bispecific Antibody (scFv-CH3) contains two chains. The anti-CD3 scFv is fused to the Knob-CH3 domain via a hinge region and the same as the anti-CD4 scFv to the Hole-CH3 domain, or vice versa. The KIH CH3 domains can facilitate to form a heterodimer and this bivalent binding leads to improvement in avidity. This BsAb can retarget T cells to HIV-1 infected cells. It is designed for the research of HIV-1 infection, AIDS therapy.