(A) Growth curves of TF1-neo, TF1-S, and TF1-L clones. Cells were plated at 7 × 10⁴ cells/mL in 96-well plates in complete medium (GM-CSF at 5 ng/mL). Viable cell number was determined daily using a colorimetric assay (see Materials and Methods) with the day 0 value set at 100%. The results are the averages (±SEM) of values for 3 TF1-neo, 6 TF1-S, and 5 TF1-L clones. (B) Growth inhibition in response to ATRA. Cells were plated in 96-well plates at 5,000 cells/well in 100 μL of complete medium, and cultured for 96 hours in the presence of ATRA (10⁻⁶ mol/L) or an equal volume of vehicle control (ethanol, EtOH). Viable cell number at 96 hours was quantitated as in (A). The final plotted value is the average (±SEM) for 4 TF1-neo, 9 TF1-S, and 8 TF1-L clones.