A TIM-3/Gal-9 Autocrine Stimulatory Loop Drives Self-Renewal of Human Myeloid Leukemia Stem Cells and Leukemic Progression

SummarySignaling mechanisms underlying self-renewal of leukemic stem cells (LSCs) are poorly understood, and identifying pathways specifically active in LSCs could provide opportunities for therapeutic intervention. T-cell immunoglobin mucin-3 (TIM-3) is expressed on the surface of LSCs in many types of human acute myeloid leukemia (AML), but not on hematopoietic stem cells (HSCs). Here, we show that TIM-3 and its ligand, galectin-9 (Gal-9), constitute an autocrine loop critical for LSC self-renewal and development of human AML. Serum Gal-9 levels were significantly elevated in AML patients and in mice xenografted with primary human AML samples, and neutralization of Gal-9 inhibited xenogeneic reconstitution of human AML. Gal-9-mediated stimulation of TIM-3 co-activated NF-κB and β-catenin signaling, pathways known to promote LSC self-renewal. These changes were further associated with leukemic transformation of a variety of pre-leukemic disorders and together highlight that targeting the TIM-3/Gal-9 autocrine loop could be a useful strategy for treating myeloid leukemias

Identification of the human eosinophil lineage-committed progenitor: revision of phenotypic definition of the human common myeloid progenitor

To establish effective therapeutic strategies for eosinophil-related disorders, it is critical to understand the developmental pathway of human eosinophils. In mouse hematopoiesis, eosinophils originate from the eosinophil lineage-committed progenitor (EoP) that has been purified downstream of the granulocyte/macrophage progenitor (GMP). We show that the EoP is also isolatable in human adult bone marrow. The previously defined human common myeloid progenitor (hCMP) population (Manz, M.G., T. Miyamoto, K. Akashi, and I.L. Weissman. 2002. Proc. Natl. Acad. Sci. USA. 99:11872–11877) was composed of the interleukin 5 receptor α chain+ (IL-5Rα+) and IL-5Rα− fractions, and the former was the hEoP. The IL-5Rα+CD34+CD38+IL-3Rα+CD45RA− hEoPs gave rise exclusively to pure eosinophil colonies but never differentiated into basophils or neutrophils. The IL-5Rα− hCMP generated the hEoP together with the hGMP or the human megakaryocyte/erythrocyte progenitor (hMEP), whereas hGMPs or hMEPs never differentiated into eosinophils. Importantly, the number of hEoPs increased up to 20% of the conventional hCMP population in the bone marrow of patients with eosinophilia, suggesting that the hEoP stage is involved in eosinophil differentiation and expansion in vivo. Accordingly, the phenotypic definition of hCMP should be revised to exclude the hEoP; an “IL-5Rα–negative” criterion should be added to define more homogenous hCMP. The newly identified hEoP is a powerful tool in studying pathogenesis of eosinophilia and could be a therapeutic target for a variety of eosinophil-related disorders

造血前駆細胞増幅中に誘導される機能的Fas抗原

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Hematopoietic Cell Fate and the Initiation of Leukemic Properties in Primitive Primary Human Cells Are Influenced by Ras Activity and Farnesyltransferase Inhibition

The Ras pathway transduces divergent signals determining normal cell fate and is frequently activated in hematopoietic malignancies, but the manner in which activation contributes to human leukemia is poorly understood. We report that a high level of activated H-Ras signaling in transduced primary human hematopoietic progenitors reduced their proliferation and enhanced monocyte/macrophage differentiation. However, the exposure of these cells to a farnesyltransferase inhibitor and establishment of a moderate level of Ras activity showed increased proliferation, an elevated frequency of primitive blast-like cells, and progenitors with enhanced self-renewal capacity. These results suggest that the amplitude of Ras pathway signaling is a determinant of myeloid cell fate and that moderate Ras activation in primitive hematopoietic cells can be an early event in leukemogenesis