PURPOSE: To obtain a (poly)peptide containing an amino acid sequence specific to an α-subunit of a T-cell antigen receptor, useful for in vivo diagnosis, in vitro diagnosis, a site specific therapy agent, etc.

CONSTITUTION: This peptide or polypeptide comprises an amino acid sequence preferably to an α-subunit of a T-cell antigen receptor and is shown by the formula (S and L are each a secretion leader sequence; V-seq is a polypeptide in a variable region of an α-subunit of a T-cell antigen receptor or a polypeptide except in a variable range of an α-subunit of a T-cell antigen receptor; J is a joining region; C is a constant region; TM is a transmembrane sequence; Cy is a cytoplasmic region; (c), (d) and (e) are each 0 or 1). The peptide or the polypeptide is obtained by transferring a recombinant nucleic acid constituent encoding a peptide or a polypeptide to a host cell and culturing the host cell in a medium.