Heterogeneity of leukemia-initiating capacity of chronic myelogenous leukemia stem cells
Bin Zhang, … , Wei Tong, Ravi Bhatia
Bin Zhang, … , Wei Tong, Ravi Bhatia
Published February 15, 2016
Citation Information: J Clin Invest. 2016;126(3):975-991. https://doi.org/10.1172/JCI79196.
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Research Article Oncology

Heterogeneity of leukemia-initiating capacity of chronic myelogenous leukemia stem cells

Abstract

Chronic myelogenous leukemia (CML) results from transformation of a long-term hematopoietic stem cell (LTHSC) by expression of the BCR-ABL fusion gene. However, BCR-ABL–expressing LTHSCs are heterogeneous in their capacity as leukemic stem cells (LSCs). Although discrepancies in proliferative, self-renewal, and differentiation properties of normal LTHSCs are being increasingly recognized, the mechanisms underlying heterogeneity of leukemic LTHSCs are poorly understood. Using a CML mouse model, we identified gene expression differences between leukemic and nonleukemic LTHSCs. Expression of the thrombopoietin (THPO) receptor MPL was elevated in leukemic LTHSC populations. Compared with LTHSCs with low MPL expression, LTHSCs with high MPL expression showed enhanced JAK/STAT signaling and proliferation in response to THPO in vitro and increased leukemogenic capacity in vivo. Although both G0 and S phase subpopulations were increased in LTHSCs with high MPL expression, LSC capacity was restricted to quiescent cells. Inhibition of MPL expression in CML LTHSCs reduced THPO-induced JAK/STAT signaling and leukemogenic potential. These same phenotypes were also present in LTHSCs from patients with CML, and patient LTHSCs with high MPL expression had reduced sensitivity to BCR-ABL tyrosine kinase inhibitor treatment but increased sensitivity to JAK inhibitors. Together, our studies identify MPL expression levels as a key determinant of heterogeneous leukemia-initiating capacity and drug sensitivity of CML LTHSCs and suggest that high MPL–expressing CML stem cells are potential targets for therapy.

Authors

Bin Zhang, Ling Li, Yinwei Ho, Min Li, Guido Marcucci, Wei Tong, Ravi Bhatia

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Figure 3

Enhanced leukemogenic capacity of MPLhi LTHSCs.

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Enhanced leukemogenic capacity of MPLhi LTHSCs. (A) Representative flow ...
(A) Representative flow cytometry plots of LTHSCs with high (MPLhi) and low (MPLlo) levels of cell surface MPL expression. (B) Mpl mRNA expression in MPLhi and MPLlo LTHSCs cells. (C) wbc count and (D) engraftment of CML CD45.1 cells in the PB of CD45.2 recipients after transplantation with CML MPLhi and MPLlo LTHSCs (200 cells per mouse). Red symbols represent the mice that were sick and euthanized or found dead. The dashed lines represent the upper limit of the normal wbc count, distinguishing leukemic from nonleukemic mice. (E) Engraftment of CD45.1 normal cells in the PB of CD45.2 recipients after transplantation with normal MPLhi and MPLlo LTHSCs (50 cells per mouse). Flow cytometry plot and summary graph showing the cell cycle status of MPLhi and MPLlo LTHSCs for (F) normal and (G) CML mice determined by Ki-67 and DAPI staining. HoechstloPyroninlo (quiescent) and Hoechsthi/loPyroninhi (proliferating) (H and I) CD45.1 CML and (J) normal MPLhi LTHSCs were selected by flow cytometry and transplanted into CD45.2 recipients (100 cells per mouse, 10 mice per group). Engraftment in PB was monitored as shown every 4 weeks for 16 weeks or until mice developed CML or had to be euthanized. Results represent mean ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001. 2-way ANOVA was used to assess significance.