Mobilized hematopoietic progenitor cells are rapidly cleared from the bloodstream.

(A) Representative FACS plots showing the gates used to isolate eGFP⁺ progenitors (Lin^−/loc-kit⁺Sca-1⁺) from day +4 CY/G-CSF–treated eGFP transgenic mice. The sorted populations are boxed. The right panel shows the high level of expression of eGFP in sorted progenitor cells. Data are expressed as contour or histogram plots representing fluorescence intensity for the indicated marker. (B) Clearance from the blood of eGFP⁺ progenitors (♦) and PKH-26⁺ RBC (●). Day +4 CY/G-CSF–treated wild-type mice were anesthetized and injected intravenously with sorted eGFP⁺ progenitor cells and PKH-26–labeled erythrocytes, as described in “Materials and methods.” Samples of peripheral blood were obtained from the recipient mouse at the indicated time points. The frequency of eGFP⁺ or PKH-26⁺ at each time point was determined by flow cytometry. Data are expressed as the number of eGFP⁺ or PKH-26⁺ cells per 10⁶ total nucleated blood cells. (C) In vivo homing of MPB stem and progenitor cells. eGFP⁺ progenitor cells were infused into anesthetized day +4 CY/G-CSF–treated wild-type recipients, as in panel B. After 3 hours, animals were killed and the number of eGFP⁺ cells in each organ was determined by flow cytometry. Data are presented as the percent of total eGFP⁺ cells recovered from each organ, as indicated. ILN indicates inguinal lymph nodes; MLN, mesenteric lymph nodes; PP, Peyer patches.