FACS analysis of BB9 expression on subpopulations of CD34⁺ cells in umbilical cord blood and fetal liver. (A) The relative expression of BB9 on CD34⁺ cells is shown for (i) FL, (ii) UCB, and (iii) adult BM. UCB (B) and 16- to 22-week FL cells (C) were stained with BB9 and antibodies against CD34 and either CD38, Thy-1, or CD133 (top panels). The most primitive populations, CD34⁺CD38⁻, Thy-1⁺, CD133⁺ (black sort regions, top panels), express high levels of BB9 (filled histograms, bottom panels). BB9 expression on more mature CD34⁺ cells (gray sort regions, top panels) is represented by unfilled histograms (bottom panels).