NEOPLASIA Reintroduction of C/EBP in leukemic CD34 stem/progenitor cells impairs self-renewal and partially restores myelopoiesis

EBP) transcription factor is indispens-able for myeloid differentiation. In various myeloid leukemias, C/EBP is mutated or functionally impaired due to decreased C/EBP expression or phosphorylation. In order to investigate the functional con-sequences of decreased C/EBP func-tion in AML, we reintroduced C/EBP in primary CD34 sorted acute myeloid leu-kemia (AML) cells using a lentiviral ap-proach. Self-renewal and differentiation of primary AML stem cells were studied on long-term MS5 cocultures. Activation of C/EBP immediately led to a growth arrest in all AML cultures (N 7), result-ing in severely reduced expansion com-pared with control cultures. This growth arrest corresponded with enhanced myeloid differentiation as assessed by fluorescence-activated cell sorter (FACS) analysis for CD14, CD15, and CD11b. Myeloid differentiation was further con-firmed by the up-regulation of neutro-phil elastase and granulocyte colony-stimulatingfactor (G-CSF)receptor inC/EBP transduced cells. C/EBP-expressing AML CD34 cells failed to generate second and third leukemic cobblestone areas (L-CAs) in serial replating experiments, while control cultures could be sequen-tially passaged for more than 4 times, indicating that reintroduction of C/EBP impaired the self-renewal capacity of the leukemic CD34 compartment. Together, our data indicate that low C/EBP levels are necessary to maintain self-renewal and the immature character of AML stem cells. (Blood. 2007;110:1317-1325) © 2007 by The American Society of Hematolog