B-lineage lymphocytes arise from early precursors under defined culture conditions.

Sorted Lin⁻ c-kit^Hi (7500 cells/well), Lin⁻ c-kit^Lo (3000 cells/well), or Lin⁻ c-kit⁻ cells (10 000 cells/well) were placed in serum-free, stromal cell-free cultures. After 7 days cells were collected, counted, and analyzed by flow cytometry. Each dot represents absolute numbers of CD19⁺ cells per input in a single experiment. This was determined by simply dividing numbers of recovered lymphocytes by the numbers of precursors used to initiate the cultures.