Since Ca15Mab-1 exhibits a superior reactivity among Ca15Mabs (supplementary Fig. 1 and Fig. 2A), we next investigated the reactivity of Ca15Mab-1 against endogenous CDH15-expressing cell lines, human osteosarcoma Saos-2 and mouse myoblast C2C12. The gene discussed is CDH15; the disease is osteosarcoma.