Recombinant Anti-CD3 x Anti-CD4 Bispecific Antibody (Tandem scFv-Fc) is designed to be expressed as a homodimer, which has 2+2 antigen-binding valency. This format consists of one Fc region and two tandem scFv fragments, in which the anti-CD3/CD4 tandem scFv is fused to the Fc domain. The engineered fragment format is used to extend the half-life. This BsAb can retarget T cells to HIV-1 infected cells. It is designed for the research of HIV-1 infection, AIDS therapy.