CD34⁺CD38⁻ progenitor cells were seeded at a density of 1 cell per well in 10 μL serum-depleted medium alone, in the putative viability factors, or a multifactor combination (containing IL-1, IL-3, IL-6, G-CSF, GM-CSF, CSF-1, FL, KL, Epo, and Tpo), as indicated. After 116 hours of preincubation, 10 μL of serum-depleted medium supplemented with the same multifactor combination or the indicated cytokine alone was added to all wells as indicated. Clonal growth was evaluated after an additional 14 days of incubation at 37°C and 5% CO₂ in air. Scoring criteria: 1, clones with 5 to 50 cells; 2, more than 50 cells but covering less than 10% of well; 3, colonies covering 10% to 50% of well; 4, colonies covering more than 50% of well. One hundred eighty wells were scored in each group and experiment. The results represent the means (±SEM) of four individual experiments.