CD123 is frequently expressed in primary AML. (A) Primary patient AML samples express CD123. AML blasts were gated using standard side scatter^low CD45^dim characteristics (n = 35-46, from a diverse range of AML subtypes; see supplemental Table 1). (B) CD123 expression levels vary among leukemia samples, as revealed by gating on blasts and using residual normal lymphocytes or isotype-matched controls (not shown) to establish negative and positive gating for CD123. Two examples of blasts stained with CD123 and CD34 are shown (top), and a panel of 9 representative leukemias is shown (bottom). The median fluorescence intensity (MFI) for CD123 was adjusted for cell size by dividing MFI by the forward scatter (FSC). (C) Sorted CD123^dim and CD123^bright leukemia cells form methylcellulose colonies with an identical CD123 phenotype. MFI of CD123 is shown adjacent to each peak. PE, phycoerythrin.