<p>BST2 antibodies are sorted by employing their ability of binding to splicing variants of a human BST2 antigen as a measure. As a result, a BST2 antibody capable of specifically recognizing BST2D (which is a substance reported to be expressed in a cancer cell at a high level) can be successfully obtained. The antibody can bind to a BST2D-expressing cell specifically. When the antibody is used for therapy, it becomes possible to inhibit the non-specific binding of the antibody to a tissue other than a target tissue (wherein the non-specific binding can cause the decrease in the concentration of the antibody in the blood). Also disclosed is a diagnostic agent comprising the antibody, which can specifically detect a BST2D-expressing tissue.</p>
