NB1 and PR3 surface expression in an in vitro model of neutrophil differentiation. CD34⁺ stem cells were isolated from umbilical cord blood, expanded, and differentiated into neutrophils. Morphology is shown using Wright-Giemsa staining and microscopy. Surface expression of differentiation markers was assessed by flow cytometry. Seven days of differentiation resulted in identical PR3 and NB1 percentages as shown for a typical of 10 independent experiments.