Transformation of ICSBP^-/- myeloid progenitor cells by p210 Bcr/Abl. (A) Wright-Giemsa stain of parental Tot2 cells and Tot2 cells transduced with p210 Bcr/Abl retrovirus (Tot2p210 cells) (original magnification × 600). Tot2 cells were cultured in media containing GM-CSF, whereas Tot2p210 cells were cultured without GM-CSF. (B) Cell cycle analysis. Tot2 and Tot2p210 cells were analyzed for DNA content. (C) Immunoblot analysis for p210 Bcr/Abl and phosphotyrosine-containing proteins. (D) Effect of a Bcr/Abl kinase inhibitor, imatinib mesylate (STI571), on the growth and survival of Tot2 and Tot2p210 cells. Imatinib mesylate was added at indicated concentrations and viable cell number was monitored.