Expansion of a novel myeloid cell subset in cancer patients. (A) In cancer patients, gating on CD14– cells in monocyte-rich fractions elutriated from apheresis products showed expansion of CD11chiCD123– cells (blue box) that are not present in healthy donors. The green box denotes myeloid dendritic cells and the orange box denotes plasmacytoid dendritic cells. The CD14+ fraction is comprised entirely of monocytes (red box) in patients and healthy donors. (B) Percent of CD11c+CD123– cells in the patient cohort (n = 53) vs healthy donors (n = 10). The red dotted line represents the mean, and the error bar represents the SEM. (C) Expression profiles of gated subsets (color coded) are shown. CD11chiCD123–CD14– cells express common MDSC markers, including CD11b, CD15, CD66b, and CD124, but they also express HLA-DR and CD127. Quadrants set based on the background fluorescence using fluorescence minus one (FMO) controls. Representative flow cytometry plots from a representative subject are shown. (D) Hematoxylin and eosin–stained cytospins of electronically sorted subsets (original magnification ×200) from a representative subject. CD11chiCD123–CD14– cells resemble immature monocytes, whereas other subsets show the expected morphology.