Lin⁻Sca-1⁺c-kit⁺ cells were plated at a concentration of one cell per well and cultured in the presence of optimal concentrations of cytokines as indicated. Approximately 30 clones in each group were picked and analyzed for B220 and GR-1 expression by flow cytometry from a total of three experiments. A B220⁺ colony was scored as such when >95% of the cells in a single clone were positive for B220 and negative for GR-1 as compared with irrelevant isotype-matched control antibodies. Similarly, clones containing >95% GR-1⁺ cells were classified as GR-1⁺. If clones contained more than 5% of B220⁺, as well as GR-1⁺ cells, they were classified as mixed.