Several studies have monitored hOCT1 mRNA expression in the MNC fraction of the leukocytes [3, 9] . However, the MNC is composed of several types of cells (including immature myeloid precursors, mostly tumor cells in CML patients). Although not analyzed, because of a low number of available samples for hOCT mRNA measurement in MNC (required for statistical significance), we expected that the impact of the cell composition found in total leukocytes on the hOCT mRNA expression results would be similar when measured in MNC. Therefore, it is not surprising that Labussiere et al. and White et al. did not dem- letters onstrate a relationship between hOCT1 expression measured in IMA naïve de novo CML patients and the future therapeutic response [3, 9] . Although Wang et al. [5] was able to show this relationship, only 16 of the 70 CML patients from this study were not pretreated. Thus, it is unknown whether the high hOCT1 mRNA expression level seen in Wang et al. could be a real predictor of therapeutic response in the future, or whether patients with a high hOCT1 mRNA expression level had a differential leukocyte and mononuclear count (due to pretreatment) that was close to that of healthy individuals and therefore higher than other patients in the study. In addition, Wang et al. did not clearly define the cell population in which measurements was carried out, which creates additional uncertainty in their results. Similarly, Crossman et al. demonstrated a relationship between of hOCT1 mRNA expression and the achievement of a complete cytogenetic response [4] . However, all patients in that study were pretreated and this fact could explain why there was no observed difference between expression of hOCT1 mRNA in CML patients and healthy donors. Furthermore, Crossman et al. used bone marrow MNC for monitoring hOCT1 mRNA expression. The influence from the higher percentage of different myeloid precursors in these samples, as well as the greater heterogeneity in hOCT1 mRNA expression, is likely to exceed the influence of the immature cells in the PB samples that we have described in the present study.