Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (scFv4-Ig) is an appended IgG format, which includes four scFv moieties at the N-termini of the constant regions. It is a bivalent homodimer, in which one anti-Ad fiber knob scFv is fused to the CH1 domain of a heavy chain and another anti-CEA scFv to the CL domain of a light chain, or vice versa. The resulting leads to 2+2 antigen-binding valency. This BsAb can retarget of adenoviral vectors to tumour cells. It can be used in cancer gene therapy to transfer a therapeutic gene into tumour cells aiming at selective and efficient cell killing.