In vivo flow cytometry and confocal microscopy imaging of MM.1S in the presence or absence of AMD3100. (A) In vivo confocal flow cytometry. DiD-labeled cells (treated with 50 μM AMD3100 for 2 hours or untreated control) were injected in the tail veins of 2 BALB/c mice. Cells were counted every 5 minutes for 1 hour. The cell count decreased by 86% in the control and by 47% in the AMD3100-treated mouse (P = .002). (B) In vivo confocal imaging of 4 quadrants of the skulls of mice showing BM niches on each side of the sagittal sinus (center of each picture). Fluorescent cells homed to the parasagittal vascular segments in the untreated control mouse; the number of cells that homed to the BM was significantly lower in the AMD3100-treated mouse. (C) Mean cell count of fluorescent cells that homed to BM niches in areas 3 and 4 in 3 experiments of the untreated (CTRL) and treated AMD3100 mice. The cell count in the AMD3100-treated mice decreased to 38% compared with control (P = .01).