DPP4 and chronic myelogenous leukemia, BCR-ABL1 positive: Since CD26 is not observed in normal SCs or in LSCs from other hematological malignancies, it may be thought as a robust, specific marker of CML LSCs, but little is known about circulating CD26+ LSCs; their role, if they even play one, as an active reservoir of disease; or their potential significance in terms of MRD [23].