Gene expression profiles of mouse BM LSKs, wild-type as well as Ezh2 KO mouse CML leukemia initiating cells (LICs). Mus musculus

Tyrosine kinase inhibitors (TKIs) have revolutionized chronic myelogenous leukemia (CML) management. Disease eradication, however, is hampered by innate resistance of leukemia initiating cells (LICs) to TKI-induced killing, which also provides the basis for subsequent emergence of TKI-resistant mutants. We report that EZH2, the catalytic subunit of Polycomb Repressive Complex 2 (PRC2), is overexpressed in CML LICs, required for colony formation, and survival and cell cycle progression of CML cell lines. A critical role for Ezh2 is supported by genetic studies in a mouse CML model. Inactivation of Ezh2 in conventional conditional mice and through CRISPR/Cas9-mediated gene editing prevents initiation and maintenance of disease and survival of LICs, irrespective of BCR/ABL1 mutational status, and extends survival. Expression of the Ezh2 homolog Ezh1 is reduced in Ezh2-deficient CML LICs, creating a scenario resembling complete loss of PRC2. EZH2-dependence of CML LICs raises prospects for improved therapy of TKI-resistant CML and/or eradication of disease by addition of EZH2 inhibitors. Overall design: Bone marrow LSK (Lin-Sca1+Kit+) cells were FACS sorted from 12 weeks old C57/BL6 mice. Wild type and Ezh2 KO CML LICs (GFP+Lin-Sca1+Kit+) were FACS sorted from a retroviral CML mouse model, at 14 days post bone marrow transplantation. Each sample was double sorted to ensure high purify.