Phenotype of CD19⁺ B cells produced in cocultures of CD34⁺CD338^lowCD19⁻ cord blood cells with MS-5 murine stromal cells. One thousand CD34⁺CD38^lowCD19⁻ cells were seeded in 24-well plates on preestablished MS-5 cell underlayers. Cells were grown in either switch conditions (A and B) or lymphoid conditions (C through J) for 6 weeks. At the end of the culture period, the total content of the well (adherent and nonadherent cells) was analyzed by flow cytometry after labeling with human MoAbs recognizing human B-cell antigens. Quadrants limits defining positivity and negativity were set up using cells labeled with isotype-matched FITC- (D) and PE-labeled (E) control antibodies. Analysis is shown in the lymphoid gate circled in (A) and (C). (A) and (B) are from one experiment and (C) through (J) are from a separate experiment.