Restoration of sensitivity to STI571.

(A) Viability (3 upper panels) and proliferation (bottom panel) of LAMA84-r cells in the presence (gray line) or absence (black line) of 1 μM STI571 after the indicated periods of withdrawal of the drug. Results are shown as the mean and range percentage of viable cells or absolute number of cells, respectively. (B) Flow cytometric histograms of LAMA84-s (S), LAMA84-r cells grown continuously in STI571 (R), and LAMA84-r grown in the absence of STI571 for the indicated periods (thick dark line) and stained with an anti-Abl antibody. One representative histogram of the 3 cell populations stained with an isotype control (IC) is shown. Note that the anti-Abl staining is due entirely to the Bcr-Abl protein, because LAMA84 does not express the normal ABL gene (no normal chromosome 9).8