Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (Tandem scFv) is designed to be expressed as a scFv fromti-Ad fiber knob antibody variable domains fused with a scFv from an anti-CEA antibody variable domains. It contains a His-tag at the C/N terminus for affinity purification. The BsAb exits as monomer in reducing and non-reducing conditions. 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.