Comparison of the frequency of infected SRCs with and without SFSD culture. (A) The infected cells were divided into 2 groups consisting of the same number of cells (5 × 10², 1 × 10³, 5 × 10³, 1 × 10⁴, 5 × 10⁴, 1 × 10⁵, 3 × 10⁵ cells/mouse). One group was instantly transplanted (n = 41), and the other was cultured for 4 days in SFSD culture, and then transplanted into NOD/SCID mice (n = 75). At 10 weeks after transplantation, the mice were killed and the percentages of CD45⁺EGFP⁺ cells in the mouse bone marrow cells were determined by flow cytometry. The presence of cells was also confirmed by PCR using EGFP primers to rule out the false-positive results by flow cytometry (data not shown). (B) Representative FACS profiles. Data from mouse, indicated by the triangle in panel A, are shown. The numbers in the top left and right quadrants show the percentage of CD45⁺EGFP^- and CD45⁺EGFP⁺ populations, respectively. Multilineage repopulation capacity of transduced SRCs was also examined. The numbers in the right panel show the percentage of CD33⁺ and CD19⁺ populations within CD45⁺EGFP⁺ cells from bone marrow. (C) The frequency of infected SRCs before and after culture. The number shown within each box indicates the calculated frequency of SRCs using L-Calc software (StemCell Technologies).