Fig. 4: LSCs in the spleen are more quiescent than in the BM and resistant to TKI therapy.

A BrdU incorporation of LSCs in the spleen and BM 18 days after CML induction and 12 h after intraperitoneal BrdU administration. One representative of 4 independent experiments with n = 4–6 mice per group is shown. B Frequency of viable and apoptotic LSCs in the BM and spleen of CML mice 18 days after CML induction. Viable cells are defined as Annexin V⁻, 7-AAD⁻, early apoptotic cells as Annexin V ⁺, 7-AAD⁻, and late apoptotic cells as Annexin V ⁺, 7-AAD⁺. One representative out of two independent experiments with n = 5 mice per group is shown. C Experimental model. BL/6 CML mice were treated with imatinib (100 mg/kg BW) or vehicle (H₂O) twice daily by oral gavage starting 4 days after CML induction. D Degree of BM infiltration with leukemic cells at day 18 after CML induction. E To compare resistance between BM and spleen, the spleen:BM-ratio of LSPCs was calculated. F Relationship between leukemia load in the BM and the spleen:BM-ratio of LSPCs. Straight lines represent linear regression calculations, dashed lines represent upper and lower 95% confidence intervals. Pooled data from two independent experiments with n = 5–8 mice per group are shown. G Leukemia load at day 25 in peripheral blood of lethally irradiated secondary recipient mice that received 2 × 10⁶ whole-BM or -spleen cells from imatinib- or vehicle-treated primary CML mice (n = 3). H Kaplan–Meier survival curve of imatinib-treated CML mice that were splenectomized or sham-operated prior to CML induction. n = 8 mice per group. If not otherwise stated, data are displayed as mean ± SEM. Statistics: unpaired Student’s t test, (A, D, E), one-way ANOVA (B, G), linear regression (F), and log-rank test (H).