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 CD11c^hiCD123^– 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. CD11c^hiCD123^–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. CD11c^hiCD123^–CD14^– cells resemble immature monocytes, whereas other subsets show the expected morphology.