Persistence of early CD34⁺ CD33^dim and CD34⁺ HLA-DR^dim subsets is enhanced by FL. HLA-DR⁺ cells from mobilized peripheral blood were sorted as shown in Fig 4 and cultured for 6 days in stroma-free medium containing [IL-3 + IL-6 + KL] ± FL. Harvested cells were stained for CD34, CD33, and HLA-DR antigens as well as PI. Histograms show PI^low CD34⁺ cells gated for analysis of CD33 and HLA-DR. Growth with (A) or without (B) FL. Inclusion of FL increased the proportion of cells with early phenotypes. Larger number of events in (A) reflects the enhanced production of CD34⁺ cells (and primitive subsets) in the presence of FL. Data representative of 3 separate trials. Data from this trial (including those for the HLA-DR^dim culture not included in this figure) are displayed quantitatively in Fig 7.