In vivo G-CSF administration increases 67LR expression in circulating CD34⁺ cells compared with normal unstimulated marrow CD34⁺ cells. (A) 67LR expression in circulating CD34⁺ cells during G-CSF–induced stem-cell mobilization in 2 representative donors (nos. 1 and 20 in Figure 2A-B). Immunophenotyping of 67LR expressing CD34⁺ cells was performed by 3-color flow cytometry on mononuclear cells gated for side light scatter (SSC-H) and CD45⁺, with an anti-67LR polyclonal antibody detected by a FITC-conjugated antirabbit antibody. PBMNCs were collected before (day 0) or at various time points (day 3 and 5) during G-CSF administration. (B) Immunophenotyping of 67LR-expressing CD34⁺ cells on BMMNCs from 3 representative healthy subjects. (C) Percentage of 67LR expressing CD34⁺ cells in BMMNCs from 15 healthy subjects and in PBMNCs collected from 35 healthy donors before G-CSF administration (day 0, ▪) or at the time of cell harvesting (day 5, □). (D) Immunophenotyping of 67LR expressing CD34⁺ cells performed by 3-color flow cytometry on mononuclear cells gated for side light scatter (SSC-H) and CD45⁺, with an anti-67LR polyclonal antibody on PBMNCs collected before (day 0), during (days 3 and 5) G-CSF administration, and at G-CSF withdrawal (days 6 and 9). Increased 67LR expression in circulating CD34⁺ cells is strictly dependent on G-CSF administration.