The total volume of PB was used for the leukocyte (LEU) separation and for fractionation into polymorphonuclear cells (PMNCs) and mononuclear cells (MNCs) using gradient centrifugation Histopaque 1 1077/1119 (Sigma Diagnostics, St. Louis, USA). The fractionation was performed according to the manufacturer's recommendations. For verification of the composition of leukocyte fractions obtained by separation, microscopic analysis of individual cell groups (PMNC and MNC) was performed. Smears were processed using May-Grünwald and Giemsa-Romanowski solutions. Interestingly, the MNC fraction from CML patients whose PB was collected at the time of diagnosis also contained immature cells (e.g. myelocytes, promyelocytes, and metamyelocytes).