We identified that the treatment of CD26+ SP fractions in both CD26+ RPMI8226 and KMS11 cells with huCD26mAb revealed sensitivity to ADCC and that huCD26mAb in conjunction with Lena resulted in additive cytotoxicity by ADCC, indicating that huCD26mAb could eradicate drug-resistant CD26+ CSCs in MM. Here, DPP4 is linked to Miyoshi myopathy.