Drug profiling reveals leukemia-intrinsic features. (A) Coculturing on MSCs supports survival of T-ALL (n = 22) and BCP-ALL (n = 25). Data at day 4 are given, normalized to seeded viable cell numbers at day 0 in both monoculture and coculture (left panel). The symbols identify the patients in the 2 culture conditions. Cell cycle and apoptosis rates of primary T-ALL (n = 18) and BCP-ALL (n = 14) cells in coculture are provided on the right. Samples are ranked from highest (top) to lowest (bottom) survival. Ratio of cells in S phase and apoptosis is given on the far right. (B) Engraftment kinetics for ALL cases with >40% and <40% of cells in S phase are given (i). Time to engraftment with 25% ALL blasts in the 2 groups is indicated in the lower panel (ii). (C) In vitro ALL proliferation correlates with drug response to cytarabine (antimetabolite), docetaxel (antimitotic), and other drugs that target the cell cycle (supplemental Figure 4). ALL cells with >40% of cells in S phase respond to cytarabine and docetaxel with lower IC₅₀ compared with samples with <40% of cells in S phase. (D) Cytarabine and docetaxel response profiles predict in vivo ALL response (n = 8). ****P < .001 (paired Student t test); ***P < .001 (2-sided Student t test); **P = .0087. i.p., intraperitoneal; i.v., intraveous; PB, peripheral blood.