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APCs are essential for innate and adaptive immunity as well as self-immune tolerance. Here, we show that the Cap'n'collar member Bach1 regulates the generation of APCs, specifically macrophages and dendritic cells, in mice. The impaired APC development in Bach1−/−mice was accompanied by defects in downstream T-cell responses and partial protection from experimental autoimmune encephalomyelitis. Genomewide analyses identified a panel of Bach1 target genes and ablation of the direct Bach1 target gene HO-1 exacerbated the impaired APC development observed in Bach1−/−mice. This was attributed to the impaired ability of HO-1−/−Bach1−/−double mutants to produce upstream APC progenitor cells, including common myeloid progenitor (CMP)–Flk2+. By contrast, we observed an increase in hematopoietic stem-progenitor cells (HSPCs) in these mice, suggesting a developmental block in the progression of HSPCs to CMP-Flk2+and subsequently APCs.

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm resulting from the BCR-ABL1fusion gene that encodes a constitutively activated tyrosine kinase (TK). Although TK inhibitors (TKIs) induce disease remission and prolonged survival in CML patients, a subset are resistant and progress from chronic phase (CP) to blast crisis (BC) with poor prognosis. Understanding the molecular mechanisms of transformation from CP to BC is necessary in the development of effective treatments.

Stein: Celgene: Speakers Bureau; Amgen Inc.: Speakers Bureau. Jin:The National Natural Science Foundation of China: Research Funding; College of Medicine, Zhejiang University: Employment.

Wang: Mustang Therapeutics: Other: Licensing Agreement, Patents & Royalties, Research Funding. Forman:Mustang Therapeutics: Other: Licensing Agreement, Patents & Royalties, Research Funding. Kortylewski:N/A: Patents & Royalties: I am an inventor on the US patent 9,976,147.

NF-kB signaling plays central role in the regulation of immune cell activity. The microRNA-146a-5p (miR-146a) provides negative feedback inhibition of the NF-kB pathway to prevent either excessive immunity, such as cytokine release syndrome. Low expression of miR-146a is also implicated in certain types of leukemia, especially in del(5q)-syndrome myelodysplastic and acute myeloid leukemia (MDS/AML). While miR-146a is a potential therapeutic target, the lack of efficient miRNA delivery methods limits clinical translation. We previously developed a strategy for targeted delivery of oligonucleotide therapeutics, such as siRNA, into human and mouse myeloid cells and B cells, using partly or completely phophorothioated (PS) single-stranded oligodeoxynucleotides containing CpG motif (CpG ODN). Here, we demonstrate that similar strategy, using CpG ODN optimized for targeting human monocytes, can be employed for the delivery of functional miR-146a mimic. The CpG-miR146a mimic conjugate, but not unconjugated miR-146a, was quickly internalized by target human and mouse myeloid cells, such as dendritic cells, macrophages and leukemic cells. In vitroCpG-miR146a mimic reduced protein levels of downstream targets, Irak1 and Traf6, as well as the inhibition of DNA binding and transcriptional activity of NF-kB in myeloid cells. We further verified functional activity of CpG-miR146a mimic against several models of acute inflammation. The intravenous injections of this oligonucleotide reduced myeloproliferation and excessive cytokine response to bacterial endotoxin or to live Listeriachallenge in miR-146a-/-mice. Furthermore, CpG-miR146a mimic had similar anti-inflammatory effect also in a human model of cytokine release syndrome induced by CD19 chimeric antigen receptor (CAR) T-cell activity. CpG-miR146a effectively abrogated CAR T-cell induced IL-6 production by human monocytes in vitro. Finally, our studies indicated that CpG-miR146a mimic can target del(5q) MDS and AML cells in vitroand in vivoresulting in growth inhibition of MDSL and HL-60 acute myeloid leukemia. Our results suggest that CpG-miR146a strategy can be provide a new-in-class immunomodulatory therapeutics for treatment of acute inflammatory disorders, myeloproliferative diseases and myeloid leukemia.

Eaves: Experimental Hematology: Other: Editor of journal; StemCell Technologies Inc: Other: Wife of owner.

MicroRNA miR-146ais frequently depleted in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Loss of miR-146amay be an initiating event in tumorigenesis, as miR-146aloss in mouse models is sufficient to cause features of MDS and eventual progression to AML. To define how miR-146aloss initiates tumorigenesis, we analyzed hematopoietic stem cell (HSC) function from miR-146aknockout (KO) mice prior to onset of an overt malignant phenotype. Tracking cell division kinetics, proliferation, and differentiation of single long-term HSC (LT-HSC; EPCR+CD45+CD48-CD150+) in culture, we found evidence that miR-146aKOreduces HSC quiescence and promotes differentiating cell divisions. Our data show that miR-146aKO HSC dysfunction may stem from loss of a CD150-bright EPCR-bright sub-population, which has previously been associated with robust HSC activity. In line with this, single cell DNA methylation profiling revealed a reduction in a primitive sub-population of LT-HSCs in miR-146aKO animals. In addition, single cell LT-HSC transplants revealed a myeloid repopulation bias. As reduced HSC cell cycle quiescence has been linked to impaired HSC self-renewal upon hematopoietic stress, such as serial transplantation, we assessed the frequency of serially transplantable HSCs by performing secondary transplants with limiting dilution. Serially transplantable HSC frequency was reduced in miR-146aKO compared to wild type, suggesting impaired HSC self-renewal. Transcriptome profiling of miR-146a KO hematopoietic stem and progenitor cells identified tumor necrosis factor (TNF) signaling activation as a potential driver of HSC dysfunction. LT-HSC cell cycle quiescence and the CD150-bright EPCR-bright LT-HSC sub-population were restored in miR-146a/TNFdouble KO mice, suggesting that aberrant TNF signaling activation drives HSC dysfunction upon loss of miR-146a.Gene expression levels in the TNF signaling network are inversely correlated with miR-146alevels in human AML, implying that TNF signaling may similarly disrupt HSC function in miR-146a-depleted myeloid malignancies. Overall, our findings suggest that miR-146apromotes HSC cell cycle quiescence and inhibits differentiation by antagonizing TNF signaling, in order to maintain a primitive sub-population of long-term self-renewing HSCs.

An epigenetic modification prevents the production of a tumor-suppressing and anti-inflammatory microRNA in receptor-negative breast cancers.

Taganov: Regulus Therapeutics Inc: Employment.

Recent discoveries have implicated microRNAs, which are small 22–24 nucleotide long RNA molecules, as important regulators of many cellular processes, including differentiation and development. The microRNA-155 (miR-155) is known to be overexpressed in subsets of B-cell neoplasms and is thought to be important in the activation and function of B-lymphocytes. Here, we show that miR-155 is signficantly overexpressed in human acute myeloid leukemia and that its overexpression is most consistently seen in acute myelomonocytic leukemia. These findings led us to investigate the effects of overexpression of miR-155 in hematopoietic cells. By utilizing retroviral infection and transfer of murine bone marrow, we introduced miR-155 overexpressing hematopoietic stem cells into lethally irradiated recipient mice. Following reconstitution of hematopoietic organs, the mice demonstrated a profound myeloproliferative condition in the bone marrow characterized by replacement of the marrow by proliferating and dysplastic myelomonocytic cells. In addition, extramedullary hematopoiesis was observed in the spleen and examination of the peripheral blood revealed anemia and thrombocytopenia. To begin to explore the mechanisms whereby miR-155 overexpression results in this myeloproliferative phenotype, we utilized computational methods to identify targets predicted to be regulated by miR-155. This revealed several genes that have previously been implicated in myeloid development and neoplasia, which were confirmed to be targets of miR-155 by reverse-transcription/quantitative polymerase chain reaction (RT/QPCR) and by downregulation of luciferase protein upon fusion of the luc gene with the respective 3′ untranslated regions. These studies show a hitherto uncharacterized role of miR-155 in myeloid development and proliferation. Importantly, these findings lay the groundwork for understanding the complex regulatory networks underlying myeloid development in the context of microRNAs, and may point to new therapeutic opportunities in the treatment of myeloid malignancies.