Chronic myeloid leukemia (CML) is a stem cell (SC) neoplasm which originates from an incomplete process of differentiation of the hematopoietic stem cells (HSCs) to the adult cells which lead to accumulation of their immature form into the BM and the peripheral blood. It is characterized by the reciprocal translocation. The resulting oncoprotein, BCR/ABL1, is considered essential for the initiation and manifestation of the disease . In CML, leukemic stem cell (LSC) supposedly resides within the CD45+/ CD34+/CD38-/Lin- fraction of the leukemic clone (3). However, normal hematopoietic SC also exhibit this phenotype so that additional markers are required to discriminate CML LSC from normal SC. CD34+/CD38-/Lin- CML LSC specifically co-express dipeptidylpeptidase IV(DPPIV=CD26). This enzyme disrupts LSC-niche interactions by degrading stroma derived factor-1 (SDF-1). Moreover, CD26 is a robust biomarker for the quantification and isolation of CML LSC (4). It was reported that CD26+ LSCs were significantly correlated with BCR-ABL1 transcript level at diagnosis and after three months of treatment with tyrosine kinase inhibitor (TKI) .

Inclusion Criteria:

• : All suspected patients for CML diagnosis aged more than 18 years who presented with high white blood cells(WBCs) count , marked shift to left in peripheral blood with or without splenomegaly .

Exclusion Criteria:

• Patients on treatment or presence of blasts in peripheral blood sample.

All suspected patients for CML diagnosis aged more than 18 years who presented with high white blood cells(WBCs) count , marked shift to left in peripheral blood with or without splenomegaly .