Differentiation of HOXB4-transduced ES cells. (A) Representative flow cytometric analysis and phase-contrast microscopy of HOXB4-transduced ES cells under hematopoietic differentiation medium show increased expression of GFP and CD45 as their differentiation progressed from day 0 to day 26. The fully differentiated HPCs showed various sizes of single cells at day 26. Numbers indicate percentages of cells within the culture. Original magnification ×200 for photographs. Numbers on plots are percentages of total cells in that quadrant. (B) Total number of viable cells was counted at different days after differentiation. HOXB4-transduced ES cells survived and eventually robustly expanded up to nearly 100-fold after 26 days of differentiation. In contrast, nontransduced control CCE-GFP ES cells failed to thrive and progressively regressed in viable cell numbers. Days 1 through 6 represent period of EBs formation.