polypeptides are disclosed comprising , in n - terminal - to - c - terminal order : an n - terminal segment of ad5 fiber tail sequence ; at least 2 pseudorepeats of an ad5 fiber shaft domain sequence ; a portion of a third ad5 fiber shaft domain sequence ; a carboxy - terminal segment of a 14 fibritin bacteriophage trimerization domain sequence ; a linker sequence ; and a camelid single chain antibody sequence . a camelid single chain antibody sequence can be against a human carcinoembryonic antigen . also disclosed are nucleic acids encoding these polypeptides , and adenovirus vectors comprising the polypeptides . methods are disclosed for treating a neoplastic disease . these methods can comprise administering an adenovirus vector comprising a disclosed polypeptide . also disclosed are methods of targeting a vector to cea - expressing cells . these methods comprise administering an adenovirus vector comprising a disclosed polypeptide . methods can further comprise subjecting a subject to ionizing radiation in an amount effective for inducing cea overexpression .