Epigenetic mechanisms controlling human leukemia stem cells and therapy resistance

Many human cancers, including acute myeloid leukemia (AML), arise from mutations of stem and progenitor cells. Immunophenotypic profiling has shown that leukemias develop hierarchically, with mutations in leukemia stem cells associated with disease propagation and relapse1,2. Although leukemia initiating cells can be enriched using cell surface markers, their frequency tends to be variable and low, obscuring mechanisms and hindering effective therapies3,4. To define AML stem cells in human patients, we performed functional genomic profiling of diverse leukemias using label tracing techniques designed to preserve hematopoietic stem cell (HSC) function in vivo. We found that propagation of human AML is mediated by a rare but distinct quiescent label-retaining cell (LRC) population that evades detection by currently known immunophenotypic markers. We show that human AML LRC quiescence is reversible, sparing genetic clonal competition that maintains its epigenetic inheritance. LRC quiescence is defined by distinct promoter-centered chromatin and gene expression dynamics and controlled by a distinct AP-1/ETS transcription factor network, including JUN in particular, which is associated with disease persistence and chemotherapy resistance in diverse patients. These results enable prospective isolation and functional genetic manipulation of immunophenotypically-varied leukemia stem cells in human patient specimens, as well as establish key functions of epigenetic plasticity in leukemia development and therapy resistance. We anticipate that these findings will lead to the elucidation of essential properties of leukemia stem cell quiescence and the design of therapeutic strategies for their clinical identification and control.