FACS profile of marrow cells from a CB17/SCID mouse transplanted 5 weeks previously with 2 × 10⁷ human marrow cells. In the left panel, the cells were stained with an irrelevant mouse IgG isotope control antibody. In the right panel, the cells were stained with antihuman-CD34–FITC (8G12-FITC) and antihuman-Thy–1-PE (5E10-PE). The human CD34⁺ Thy-1⁺ cells seen in the right upper quadrant of this panel comprised approximately 0.4% of all the viable cells in the marrow of that mouse, whereas the total population of human CD34⁺ cells comprised about 8% of the cells.