Prolonged culture times of v-Abl⁺ lymphoid cells correlate with increased STAT5 protein levels and decreased imatinib sensitivity. (A) Cell counts of LTCs (n = 4) and STCs (n = 6) treated with 100nM imatinib. (B) Representative colony-forming assays of LTCs and STCs in growth-factor free methylcellulose without and supplemented with 200nM imatinib. Pictures of colonies were taken after 14 days (LTCs) and 21 days (STCs). (C) Dose-response curves determined by [³H]-thymidine incorporation of LTCs (n = 6) and STCs (n = 4) treated with imatinib for 24 hours. Control values in the absence of imatinib were set to 100%. (D) Immunoblot analysis of STCs and LTCs for STAT transcription factors and v-ABL. (A,C) Error bars represent mean ± SD. ***P < .001.