SU5416 inhibits TPO-dependent growth and survival of immature HSCs. Sca-1⁺/c-kit⁺/Gr-1^- cells were purified from murine bone marrow and single-cell cultures were performed in the presence of 100 ng/mL hTPO with (▨) or without (▪)1 μM SU5416. The number of cells in each well was monitored daily. The columns show the percentage of single cells that divided at least once within the 7-day culture period (left panel) and the percentage of wells that contain at least one cell on day 7 (right panel). Each column represents the average ± SD of 3 independent experiments.