Imatinib treatment does not affect the frequency of blood mast cell progenitors in vivo. (A) Peripheral blood mast cell progenitors and mast cells were gated as SSC^loLin⁻CD45^intCD34⁺CD117^int/hiFcεRI⁺ cells and CD45⁺CD14⁻CD34⁻CD117^hiFcεRI^hi cells, respectively. The percentages indicate the frequency of the gated cells normalized to the number of CD45⁺ singlet cells. The frequencies of mast cell progenitors (B) and mast cells (C) from the CD45⁺ cell population in healthy controls (n = 6), patients with CML (n = 5), patients with CML under treatment with imatinib (n = 5), patients with GIST under treatment with imatinib (n = 5), and patients with systemic mastocytosis (SM) carrying the D816V KIT mutation (n = 9) are shown. The lines represent the geometric means. The triangles and squares represent the same patients before and during imatinib treatment. One-way ANOVA with Tukey’s multiple comparisons test on log-transformed data. *Adjusted P < .05; **adjusted P < .01. FSC, forward scatter; SSC, side scatter.