Role of MPL expression in determining heterogeneity of leukemia-initiating capacity of chronic myelogenous leukemia stem cells

Using a CML mouse model, we identified differences in gene expression between leukemic compared with non-leukemic LTHSC, including increased expression of the thrombopoietin (THPO) receptor MPL. LTHSC expressing high levels of MPL showed enhanced JAK/STAT signaling and proliferation in response to THPO in vitro, and increased leukemogenic capacity in vivo compared to LTHSC with low MPL expression. Although both G0 and S-phase subpopulations were increased in MPL expressing LTHSC, LSC capacity was restricted to quiescent cells. Inhibition of MPL expression in CML LTHSC resulted in reduced THPO-induced JAK/STAT signaling and leukemogenic potential. Similar observations were made with LTHSC from CML patients. MPL expressing LTHSC demonstrated reduced sensitivity to BCR-ABL TKI treatment but demonstrated increased sensitivity to JAK inhibitors. Our studies identify MPL expression levels as a key determinant of heterogeneous leukemia-initiating capacity and drug sensitivity of CML LTHSC, and suggest that MPL-expressing CML stem cells are critical targets for therapy. Overall design: To evaluate heterogeneity in LSC potential, donor LTHSC from SCL-tTA/BCR-ABL mice (200 cells/mouse) were transplanted into a cohort of congenic FVBN mice. Recipient mice were followed for engraftment of donor CML cells and development of CML. LTHSCs were isolated from leukemic and non-leukemic recipient mice and global gene expression was analyzed using RNA-Seq.

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Zhang B, Li L, Ho Y, Li M, Marcucci G, Tong W, Bhatia R