Figure 5.

B220⁺iMLL-ENL leukemic blasts are enriched for leukemia initiating cells. (A) BM-derived leukemic blasts were cultured overnight in medium with hIL-6 (10 ng/mL), mIL-3 (6 ng/mL), mIL-7 (10 ng/mL), mSCF (100 ng/mL), and mFlt-3L (100 ng/mL) and DOX, then sorted (left panel) according to B220⁺ versus B220⁻ expression and transferred into secondary recipients. Kaplan-Meier plot (right panel): the difference of the latency periods was assessed by a log-rank test (P < 0.0028). (B) Histopathology of spleen, lungs, and liver revealed massive infiltration of leukemic blasts in mice transplanted with 1 × 10⁵iMLL-ENL B220⁻ versus B220⁺ ex vivo cultured mBM cells with complete loss of normal organ architecture in the latter. (C) Pair-wise correlation maps and hierarchical clustering of human patients with the t(11;19) (in purple) and germline MLL (in gray) genotypes. Correlations and clustering of patient samples were computed using expression values of human genes that are orthologous to mouse genes being part of the following 3 gene sets. Left panel: genes significantly differentially expressed between iMLL-ENL B220⁺ and iMLL-ENL B220⁻ samples. Right panel: a control set of genes with the same expression distribution as the genes from the iMLL-ENL B220⁺/B220⁻ signature. (D) Distribution of normalized expression levels (log₂ CPM) in the 2 gene sets used in (C). The distribution of normalized expression values of all genes expressed in both samples is given as a comparison. BM = bone marrow, DOX = doxycycline, hIL-6 = human interleukin-6, mSCF = murine stem cell factor.