In vivo effects of C/EBPα activation in STI571-sensitive and -resistant 32D-BCR/ABL cells. Mice were injected with C/EBPα-ER^TAM-expressing 32D-BCR/ABL cells (A), C/EBPα-ER^TAM–expressing 32D-BCR/ABL^Y253H cells (B), or Δ177-191 C/EBPα-ER^TAM 32D-BCR/ABL^T315I cells (C) and were treated with vehicle alone or with 4-HT for 15 consecutive days. (left panels) Morphology, (middle panels) GFP positivity, and (right panels) colony formation of bone marrow and spleen cells isolated at the end of treatment. Colony number values represent mean ± SD of 3 different experiments.