Recombinant Anti-CD3 x Anti-CD4 Bispecific Antibody (Fab-Fv) is designed to be expressed as two polypeptide chains. The heavy chain Fd fragment and light chain of an anti-CD3 antibody are fused with the VL and VH domains of an anti-CD4 antibody respectively. It can form natural in vivo heterodimerization. This BsAb can retarget T cells to HIV-1 infected cells. It is designed for the research of HIV-1 infection, AIDS therapy.