Stem-cell parameters in AML patients with a different course of the disease. Cells were analyzed at diagnosis and at different time points during follow-up of 2 AML patients. (A,B) Patient 1. (C,D) Patient 2. (A,C) Malignant CD34⁺CD38⁻ cells (defined by CLL-1) as a fraction of the total CD34⁺CD38⁻ population. The solid line represents the background expression in RBM for CLL-1. (B,D) The frequency of CD34⁺CD38⁻CLL-1⁺ cells as percentage of the total WBC count. D indicates diagnosis; R, relapse; 1st, after first course of chemotherapy; and 2nd and 3rd, after the second and third course of chemotherapy, respectively. Patient 1 reached complete remission after the first course of chemotherapy and has been in continuous complete remission now for 3 years. Percentage of CLL-1 expression on the total CD34⁺CD38⁻ compartment declined rapidly (A) as did the frequency of CD34⁺CD38⁻CLL-1⁺cells (B). Patient 2 reached complete remission after the first course of chemotherapy; however, a relapse occurred after the second course of chemotherapy. Although CR was reached, there was a continuous expression of CLL-1 on the CD34⁺CD38⁻ cells (C). Also, the frequency of CD34⁺CD38⁻CLL-1⁺ cells did not decrease after chemotherapy, but even increased (D).