IgM⁺ B cells generated in cultures from pre-B cell precursors obtained from embryo cell lines in the presence of rIL-7.

(A) CD19⁺IgM⁻ B-cell precursors were purified by immunomagnetic depletion of IgM⁺ B cells from an embryo cell line, and they were replated in ST2/rIL-7 culture conditions. The numbers displayed in the contour plots correspond to the percentages of B cells inside the window, at the indicated time points. (B) CD19⁺IgM⁻ B-cell precursors were purified as above from 2 embryo cell lines (circles) and one LFL/BM cell line (triangles) as control. The cells were cultured for 96 hours in the presence of ST2 cells and the indicated doses of rIL-7. At the end of the culture, the recovered cells were counted and analyzed as in Figure 5.