Murine Myeloid Cells Research Articles

Small-Molecule Disruption of the Myb/p300 Cooperation Targets Acute Myeloid Leukemia Cells.

The transcription factor c-Myb is essential for the proliferation of hematopoietic cells and has been implicated in the development of leukemia and other human cancers. Pharmacologic inhibition of Myb is therefore emerging as a potential therapeutic strategy for these diseases. By using a Myb reporter cell line, we have identified plumbagin and several naphthoquinones as potent low-molecular weight Myb inhibitors. We demonstrate that these compounds inhibit c-Myb by binding to the c-Myb transactivation domain and disrupting the cooperation of c-Myb with the coactivator p300, a major driver of Myb activity. Naphthoquinone-induced inhibition of c-Myb suppresses Myb target gene expression and induces the differentiation of the myeloid leukemia cell line HL60. We demonstrate that murine and human primary acute myeloid leukemia cells are more sensitive to naphthoquinone-induced inhibition of clonogenic proliferation than normal hematopoietic progenitor cells. Overall, our work demonstrates for the first time the potential of naphthoquinones as small-molecule Myb inhibitors that may have therapeutic potential for the treatment of leukemia and other tumors driven by deregulated Myb. Mol Cancer Ther; 15(12); 2905-15. ©2016 AACR.

Distal regulation of c-myb expression during IL-6-induced differentiation in murine myeloid progenitor M1 cells.

The c-Myb transcription factor is a major regulator that controls differentiation and proliferation of hematopoietic progenitor cells, which is frequently deregulated in hematological diseases, such as lymphoma and leukemia. Understanding of the mechanisms regulating the transcription of c-myb gene is challenging as it lacks a typical promoter and multiple factors are involved. Our previous studies identified some distal regulatory elements in the upstream regions of c-myb gene in murine myeloid progenitor M1 cells, but the detailed mechanisms still remain unclear. In the present study, we found that a cell differentiation-related DNase1 hypersensitive site is located at a −28k region upstream of c-myb gene and that transcription factors Hoxa9, Meis1 and PU.1 bind to the −28k region. Circular chromosome conformation capture (4C) assay confirmed the interaction between the −28k region and the c-myb promoter, which is supported by the enrichment of CTCF and Cohesin. Our analysis also points to a critical role for Hoxa9 and PU.1 in distal regulation of c-myb expression in murine myeloid cells and cell differentiation. Overexpression of Hoxa9 disrupted the IL-6-induced differentiation of M1 cells and upregulated c-myb expression through binding of the −28k region. Taken together, our results provide an evidence for critical role of the −28k region in distal regulatory mechanism for c-myb gene expression during differentiation of myeloid progenitor M1 cells.

441 Cell type specific expression and induction of IL-33 mRNA and protein

Key mediators of innate immunity during skin inflammation are cytokines of the interleukin-1 (IL-1) family. While IL-1α and IL-18 are well characterized and are activated via inflammasome activation, the activation of IL-33 is still cryptic and in contrast, IL-33 is claimed to be inactivated by caspases. Recent data suggest that IL-33 acts as an alarm or danger signal and is released after cell damage. Besides binding to its specific receptor ST2, IL-33 can be present in the nucleus and in the cytosol. Here, we aim to elucidate the induction of IL-33 and its receptor ST2 compared to the other IL-1 family members IL-1α and IL-1β in different cell types and studied the cellular localization of the alarmin IL-33. We analyzed human and murine myeloid cells and epithelial cells and tested the expression of IL-33 mRNA and protein after stimulation of different pattern recognition receptors. The cellular localization of IL-33 was identified by Western blotting of nuclear and cytosolic cell extracts and by immunofluorescence. Interestingly, we found very different expression levels of IL-33 in certain myeloid cells and tissue-resident cells in both human and mice. High baseline levels of IL-33 were even present in cells that do not carry an inflammasome and are not able to activate inflammatory caspases. In analogy to IL-1α and IL-1β, IL-33 can be induced in myeloid cells by certain stimuli and signaling pathways. However, expression levels and kinetics of IL-33 seem to be different from IL-1α and IL-1β. In conclusion, we demonstrate a different activation pattern of IL-1α, IL-1β and IL-33 in myeloid and non-myeloid cells. As all these innate mediators are released during cutaneous damage we hypothesize that the activation of inflammasomes or inflammatory caspases influences not only the innate immune response but also the adaptive immune response in very early stages of skin inflammation.

Targeting Suppressive Myeloid Cells Potentiates Checkpoint Inhibitors to Control Spontaneous Neuroblastoma.

Neuroblastoma is the most common extracranial solid cancer type in childhood, and high-risk patients have poor prognosis despite aggressive multimodal treatment. Neuroblastoma-driven inflammation contributes to the induction of suppressive myeloid cells that hamper efficient antitumor immune responses. Therefore, we sought to enhance antitumor immunity by removing immunosuppression mediated by myeloid cells. The prognostic values of myeloid cells are demonstrated by analyzing genomic datasets of neuroblastoma patients. The impact of tumor-derived factors on myelopoiesis and local induction of suppressive myeloid cells is dissected by in vitro culture models using freshly isolated human CD34(+) hematopoietic stem cells, primary human monocytes, and murine bone marrow cells. To test the therapeutic efficacy of BLZ945 as a monotherapy or in combination with checkpoint inhibitors, we used a transgenic murine model (TH-MYCN) that develops aggressive spontaneous neuroblastoma. We report that infiltrating CSF-1R(+) myeloid cells predict poor clinical outcome in patients with neuroblastoma. In vitro, neuroblastoma-derived factors interfere with early development of myeloid cells and enable suppressive functions on human monocytes through M-CSF/CSF-1R interaction. In a transgenic mouse model (TH-MYCN) resembling high-risk human neuroblastoma, antagonizing CSF-1R with a selective inhibitor (BLZ945) modulates the induction of human and murine suppressive myeloid cells and efficiently limit tumor progression. While checkpoint inhibitors are insufficient in controlling tumor growth, combining BLZ945 with PD-1/PD-L1 blocking antibodies results in superior tumor control. Our results demonstrate the essential role of CSF-1R signaling during the induction of suppressive myeloid cells and emphasize its clinical potential as an immunotherapy for human cancers. Clin Cancer Res; 22(15); 3849-59. ©2016 AACR.

Src-like adaptor protein 2 (SLAP2) binds to and inhibits FLT3 signaling

Fms-like tyrosine kinase (FLT3) is a frequently mutated oncogene in acute myeloid leukemia (AML). FLT3 inhibitors display promising results in a clinical setting, but patients relapse after short-term treatment due to the development of resistant disease. Therefore, a better understanding of FLT3 downstream signal transduction pathways will help to identify an alternative target for the treatment of AML patients carrying oncogenic FLT3. Activation of FLT3 results in phosphorylation of FLT3 on several tyrosine residues that recruit SH2 domain-containing signaling proteins. We screened a panel of SH2 domain-containing proteins and identified SLAP2 as a potent interacting partner of FLT3. We demonstrated that interaction occurs when FLT3 is activated, and also, an intact SH2 domain of SLAP2 is required for binding. SLAP2 binding sites in FLT3 mainly overlap with those of SRC. SLAP2 over expression in murine proB cells or myeloid cells inhibited oncogenic FLT3-ITD-mediated cell proliferation and colony formation in vitro, and tumor formation in vivo. Microarray analysis suggests that higher SLAP2 expression correlates with a gene signature similar to that of loss of oncogene function. Furthermore, FLT3-ITD positive AML patients with higher SLAP2 expression displayed better prognosis compared to those with lower expression of SLAP2. Expression of SLAP2 blocked FLT3 downstream signaling cascades including AKT, ERK, p38 and STAT5. Finally, SLAP2 accelerated FLT3 degradation through enhanced ubiquitination. Collectively, our data suggest that SLAP2 acts as a negative regulator of FLT3 signaling and therefore, modulation of SLAP2 expression levels may provide an alternative therapeutic approach for FLT3-ITD positive AML.

Reprogramming of Notch1-induced acute lymphoblastic leukemia cells into pluripotent stem cells in mice

Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells using the reprogramming factors (Oct4, Sox2, Klf4 and c-Myc, also called OSKM).1 Cellular reprogramming and oncogenesis share many common features. The application of the iPS technology in cancers help us better understand the mechanism underlying the initiation and progression of cancer. Therefore, defining the reprogramming potential of cancer cells would provide unique opportunities to reveal epigenetic mechanisms and develop novel therapeutics for cancer. Because the reprogramming efficiency of cancer cells is paradoxically much lower than that of normal cells in general, only some handful types of cancer cells have been explored using the iPS technology.2 To date, in the hematopoietic system, Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines, human chronic myeloid leukemia cells, juvenile myelomonocytic leukemia cells and primary murine mixed lineage leukemia-AF9 acute myeloid leukemia cells have been successfully generated into iPS cells.3, 4, 5, 6 However, whether the primary malignant leukemic T cells can be reprogrammed into the iPS cells is still a mystery.

Calreticulin-mutant proteins induce megakaryocytic signaling to transform hematopoietic cells and undergo accelerated degradation and Golgi-mediated secretion.

BackgroundSomatic calreticulin (CALR), Janus kinase 2 (JAK2), and thrombopoietin receptor (MPL) mutations essentially show mutual exclusion in myeloproliferative neoplasms (MPN), suggesting that they activate common oncogenic pathways. Recent data have shown that MPL function is essential for CALR mutant-driven MPN. However, the exact role and the mechanisms of action of CALR mutants have not been fully elucidated.MethodsThe murine myeloid cell line 32D and human HL60 cells overexpressing the most frequent CALR type 1 and type 2 frameshift mutants were generated to analyze the first steps of cellular transformation, in the presence and absence of MPL expression. Furthermore, mutant CALR protein stability and secretion were examined using brefeldin A, MG132, spautin-1, and tunicamycin treatment.ResultsThe present study demonstrates that the expression of endogenous Mpl, CD41, and the key megakaryocytic transcription factor NF-E2 is stimulated by type 1 and type 2 CALR mutants, even in the absence of exogenous MPL. Mutant CALR expressing 32D cells spontaneously acquired cytokine independence, and this was associated with increased Mpl mRNA expression, CD41, and NF-E2 protein as well as constitutive activation of downstream signaling and response to JAK inhibitor treatment. Exogenous expression of MPL led to constitutive activation of STAT3 and 5, ERK1/2, and AKT, cytokine-independent growth, and reduction of apoptosis similar to the effects seen in the spontaneously outgrown cells. We observed low CALR-mutant protein amounts in cellular lysates of stably transduced cells, and this was due to accelerated protein degradation that occurred independently from the ubiquitin-proteasome system as well as autophagy. CALR-mutant degradation was attenuated by MPL expression. Interestingly, we found high levels of mutated CALR and loss of downstream signaling after blockage of the secretory pathway and protein glycosylation.ConclusionsThese findings demonstrate the potency of CALR mutants to drive expression of megakaryocytic differentiation markers such as NF-E2 and CD41 as well as Mpl. Furthermore, CALR mutants undergo accelerated protein degradation that involves the secretory pathway and/or protein glycosylation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-016-0275-0) contains supplementary material, which is available to authorized users.

MiRNA dynamics in tumor-infiltrating myeloid cells modulating tumor progression in pancreatic cancer

ABSTRACTMyeloid cells including tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) are known as important mediators of tumor progression in solid tumors such as pancreatic cancer. Infiltrating myeloid cells have been identified not only in invasive tumors, but also in early pre-invasive pancreatic intraepithelial precursor lesions (PanIN). The functional dynamics of myeloid cells during carcinogenesis is largely unknown. We aimed to systematically elucidate phenotypic and transcriptional changes in infiltrating myeloid cells during carcinogenesis and tumor progression in a genetic mouse model of pancreatic cancer. Using murine pancreatic myeloid cells isolated from the genetic mouse model at different time points during carcinogenesis, we examined both established markers of macrophage polarization using RT-PCR and FACS as well as transcriptional changes focusing on miRNA profiling. Myeloid cells isolated during carcinogenesis showed a simultaneous increase of established markers of M1 and M2 polarization during carcinogenesis, indicating that phenotypic changes of myeloid cells during carcinogenesis do not follow the established M1/M2 classification. MiRNA profiling revealed distinct regulations of several miRNAs already present in myeloid cells infiltrating pre-invasive PanIN lesions. Among them miRNA-21 was significantly increased in myeloid cells surrounding both PanIN lesions and invasive cancers. Functionally, miRNA-21-5p and -3p altered expression of the immune-modulating cytokines CXCL-10 and CCL-3 respectively. Our data indicate that miRNAs are dynamically regulated in infiltrating myeloid cells during carcinogenesis and mediate their functional phenotype by facilitating an immune-suppressive tumor-promoting micro-milieu.

Double-stranded RNA analog and type I interferon regulate expression of Trem paired receptors in murine myeloid cells.

BackgroundTriggering receptors expressed on myeloid cells (Trem) proteins are a family of cell surface receptors used to control innate immune responses such as proinflammatory cytokine production in mice. Trem genes belong to a rapidly expanding family of receptors that include activating and inhibitory paired-isoforms.ResultsBy comparative genomic analysis, we found that Trem4, Trem5 and Trem-like transcript-6 (Treml6) genes typically paired receptors. These paired Trem genes were murine-specific and originated from an immunoreceptor tyrosine-based inhibition motif (ITIM)-containing gene. Treml6 encoded ITIM, whereas Trem4 and Trem5 lacked the ITIM but possessed positively-charged residues to associate with DNAX activating protein of 12 kDa (DAP12). DAP12 was directly associated with Trem4 and Trem5, and DAP12 coupling was mandatory for their expression on the cell surface. In bone marrow-derived dendritic cells (BMDCs) and macrophages (BMDMs), and splenic DC subsets, polyinosinic-polycytidylic acid (polyI:C) followed by type I interferon (IFN) production induced Trem4 and Treml6 whereas polyI:C or other TLR agonists failed to induce the expression of Trem5. PolyI:C induced Treml6 and Trem4 more efficiently in BMDMs than BMDCs. Treml6 was more potentially up-regulated in conventional DC (cDCs) and plasmacytoid DC (pDCs) than Trem4 in mice upon in vivo stimulation with polyI:C.DiscussionTreml6-dependent inhibitory signal would be dominant in viral infection compared to resting state. Though no direct ligands of these Trem receptors have been determined, the results infer that a set of Trem receptors are up-regulated in response to viral RNA to regulate myeloid cell activation through modulation of DAP12-associated Trem4 and ITIM-containing Treml6.Electronic supplementary materialThe online version of this article (doi:10.1186/s12865-016-0147-y) contains supplementary material, which is available to authorized users.

HSP90B1 Regulates TLR-dependent Monocyte Signaling and its Common Variants are Associated with BCG-specific T-cell Responses and Protection from Pediatric TB Disease

Abstract Introduction HSP90B1 is a chaperone for multiple Toll-like receptors (TLRs), regulates innate immune signaling in murine myeloid cells and is expressed in T-cells. We hypothesized human HSP90B1 regulates monocyte responses to Mycobacterium tuberculosis (Mtb) and that its variants are associated with T-cell responses to the BCG vaccine and susceptibility to TB disease. Methods & Results We screened 17 haplotype-tagging HSP90B1 gene region SNPs for association with BCG-induced immune responses in South African infants vaccinated with BCG at birth. We stimulated peripheral blood drawn at 10 weeks of age with BCG in a whole blood cytokine assay. Three HSP90B1 SNPs (rs10507172, 10507173, and 2164747) were associated with increased IL-2 secretion (P<0.05, generalized linear model). SNPrs10507173 was associated with increased IL-2 production in the CD4+ T-cell subset (p=0.028, ANOVA) based on intracellular cytokine staining and flow cytometry. The same three alleles were associated with protection from pediatric TB disease in a gene association study of 226 children who contracted tuberculosis compared with 626 controls who remained healthy (dominant model, unadjusted p<0.05, OR 0.58–0.72; after adjusting for ethnicity, p<0.05 for 2/3 SNPs). We used CRISPR/Cas9 gene editing to reduce HSP90B1 expression in U937 monocyte cells. Relative to controls, HSP90B1-deficient cells secreted less TNF when exposed to TLR1/2/6 (p=0.02) and TLR4 (p=0.01) ligands and Mtb whole cell lysate (p=0.001). Conclusion These data suggest HSP90B1 deficiency is associated with an impaired monocyte response to Mtb ligands. In infants, HSP90B1 variants are associated with increased BCG-specific IL-2 responses T-cells and protection from TB disease.

Early TNFα signaling results in pulmonary DC1 polarization and programing of murine myeloid precursor cells in the bone marrow towards DC1 polarization throughout Cryptococcus neoformans infection

Abstract TNFα is required for protective Th1/Th17 immunity to Cryptococcus neoformans (CN), an opportunistic pulmonary fungal pathogen. The effects of TNFα are linked to the stable, early classical activation of dendritic cells (DC1), preventing alternative (DC2) activation. We hypothesized that TNFα signaling facilitates epigenetic modification of key DC genes during CN infection. We tested this hypothesis using CBA/J mice infected intratracheally with CN and injected once on day 0 intraperitoneally with control or a TNFα-depleting antibody (αTNFα). αTNFα mice had no difference in pulmonary CFU at 7 days post-infection (dpi), but had significantly higher fungal burden and extrapulmonary dissemination at 14 and 28 dpi. DCs from the lungs of control mice at 7 dpi had increased association of iNOS and IL-12b promoters with the activating modification histone 3 lysine 4 trimethylation (H3K4me3), while DCs from αTNFα mice did not. Because DCs have a relatively short half-life during infection, we assessed the bone marrow (BM) myeloid precursor cells (MPCs) from infected animals with and without TNFα. Intranuclear flow cytometry for H3K4me3 showed distinct patterns of global trimethylation between infected control and αTNFα mice as early as 7 dpi. We next tested whether BM-derived DCs (BMDCs) matured ex vivo from infected animals would yield DC1 or DC2 cells. BMDCs from control animals became DC1, and resisted changes to polarization when challenged with the DC2-skewing IL-4, while BMDCs matured from TNFα-depleted mice maintained DC2 polarization when challenged with IFNγ. We conclude that TNFα epigenetically modifies key DC1 genes in MPCs, thereby sustaining lasting DC1 programing of DCs required for clearance of CN from the infected lungs.

Stromal cells and myeloid leukemic cells: Are they friends? Or foes?

An important question when designing targeted therapy by modulation of stromal cells in the leukemic microenvironment is whether the stromal-derived support of tumor cell growth can be halted by drugs including originally tumor supportive agents. We recently used an in vitro system to show that either bone marrow stromal cells as a feeder layer or lipopolysaccharides (LPS) in culture medium is required for the proliferation of murine myeloid tumor cells. However, the stromal-derived support of leukemic growth is strongly suppressed when LPS is coupled in the same culture. This opposing effect of stromal cells or LPS on the myeloid leukemic growth is due, at least in part, to the rapid secretion of interleukin 12, Fas ligand and tissue inhibitor of metalloproteinases-2 from stromal cells upon LPS stimulation. These results provide a proof of principle that stromal cells can be “re-educated” by therapeutic drugs to attenuate tumor cell proliferation through re-wiring the cytokine network in the tumor microenvironment, thus diverting the disease course of myeloid leukemia in the opposite direction.

Dual effect of LPS on murine myeloid leukemia cells: Pro-proliferation and anti-proliferation

Modification of the bone marrow microenvironment is considered as a promising strategy to control leukemic cell proliferation, diseases progression and relapse after treatment. However, due to the diversity and complexity of the cellular and molecular compartments in the leukemic microenvironment, it is extremely difficult to dissect the role of each individual molecule or cell type in vivo. Here we established an in vitro system to dissect the role of lipopolysaccharide (LPS), stromal cells and endothelial cells in the growth of mouse myeloid tumor cells and B-lymphoma cells. We found that either LPS or bone marrow stromal cells as a feeder layer in culture is required for the proliferation of myeloid tumor cells. Surprisingly, the growth of myeloid leukemic cells on stromal cells is strongly inhibited when coupled with LPS in culture. This opposing effect of LPS, a complete switch from pro-proliferation to antitumor growth is due, at least in part, to the rapidly increased production of interleukin 12, Fas ligand and tissue inhibitor of metalloproteinases-2 from stromal cells stimulated by LPS. These results demonstrate that LPS can either facilitate or attenuate tumor cell proliferation, thus changing the disease course of myeloid leukemias through its direct effect or modulation of the tumor microenvironment.

BCR: a new target in resistance mediated by BCR/ABL-315I?

Targeting BCR/ABL with Tyrosine kinase inhibitors (TKIs) is a proven concept for the treatment of Philadelphia chromosome-positive (Ph+) leukemias but the "gatekeeper" mutation T315I confers resistance against all approved TKIs, with the only exception of ponatinib, a multi-targeted kinase inhibitor. Besides resistance to TKIs, T315I also confers additional features to the leukemogenic potential of BCR/ABL, involving endogenous BCR. Therefore we studied the role of BCR on BCR/ABL mutants lacking functional domains indispensable for the oncogenic activity of BCR/ABL. We used the factor independent growth of murine myeloid progenitor 32D cells and the transformation of Rat-1 fibroblasts both mediated by BCR/ABL. Here we report that T315I restores the capacity to mediate factor-independent growth and transformation potential of loss-of-function mutants of BCR/ABL. Targeting endogenous Bcr abrogated the capacity of oligomerization deficient mutant of BCR/ABL-T315I to mediate factor independent growth of 32D cells and strongly reduced their transformation potential in Rat-1 cells, as well as led to the up-regulation of mitogen activated protein kinase (MAPK) pathway. Our data show that the T315I restores the capacity of loss-of-function mutants to transform cells which is dependent on the transphosphorylation of endogenous Bcr, which becomes a putative therapeutic target to overcome resistance by T315I.

PD-1 Blunts the Function of Ovarian Tumor-Infiltrating Dendritic Cells by Inactivating NF-κB.

The PD-1:PD-L1 immune signaling axis mediates suppression of T-cell-dependent tumor immunity. PD-1 expression was recently found to be upregulated on tumor-infiltrating murine (CD11c(+)CD11b(+)CD8(-)CD209a(+)) and human (CD1c(+)CD19(-)) myeloid dendritic cells (TIDC), an innate immune cell type also implicated in immune escape. However, there is little knowledge concerning how PD-1 regulates innate immune cells. In this study, we examined the role of PD-1 in TIDCs derived from mice bearing ovarian tumors. Similar to lymphocytes, TIDC expression of PD-1 was associated with expression of the adapter protein SHP-2, which signals to NF-κB; however, in contrast to its role in lymphocytes, we found that expression of PD-1 in TIDC tonically paralyzed NF-κB activation. Further mechanistic investigations showed that PD-1 blocked NF-κB-dependent cytokine release in a SHP-2-dependent manner. Conversely, inhibition of NF-κB-mediated antigen presentation by PD-1 occurred independently of SHP-2. Collectively, our findings revealed that PD-1 acts in a distinct manner in innate immune cells compared with adaptive immune cells, prompting further investigations of the signaling pathways controlled by this central mediator of immune escape in cancer.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

The Impact of NFAT Inhibition on Neutrophil Antifungal Defense and Myelopoiesis in Cyclosporine A Treated and NFATc1LysM Mice

Background and Aims: Immunodeficient patients after allogeneic stem cell transplantation (HSCT) are heavily threatened by opportunistic fungal infections like invasive pulmonary aspergillosis (IPA), partly due to immunosuppressive medication e.g. by calcineurin inhibitors like cyclosporine A (CsA) or tacrolimus. It is well known that the nuclear factor of activated T cells (NFAT) is an important transcription factor downstream of calcineurin in the adaptive immune system especially in T cells. Additionally, there is a growing body of evidence that NFAT also plays a substantial role in innate immune response against invasive fungal diseases by polymorphonuclear neutrophils (PMN), as well as in regulation of myelopoiesis and myeloid differentiation, as indicated by recent data in rodent models.Methods: Firstly, we used a murine IPA model (C57BL/6) to clarify the role of NFAT in antifungal innate immune response in vivo. To do so, we treated mice intraperitoneally with CsA (18mg/kg/d) or vehicle for 2 weeks and challenged them with Aspergillus fumigatus (A. f.) conidia intratracheally. 24 hours later, some mice were sacrificed and PMN recruitment to the lungs and pulmonary fungal clearance were examined by analyzing bronchoalveolar lavages (BAL) and peripheral blood (PB) by flow cytometry and murine lungs by fungal culture assays and histopathologic examination. In addition, survival of remaining infected mice was studied with neutropenic animals (by depletion with anti-Gr1) serving as positive controls. Secondly, LysM-specific NFATc1 knockout (NFATc1LysM) mice were bred lacking NFATc1 expression solely in myelomonocytic cells (i.e. PMN and monocytes). Furthermore, these animals were infected with A. f. and analyzed as described above. Secondly, we investigated myelopoiesis and myeloid differentiation under steady state conditions by quantifying bone marrow derived myeloid progenitor cells from CsA treated or NFATc1LysM mice using flow cytometry and simultaneously counting PMN in PB.Results: While the infection was lethal in CsA or vehicle treated neutropenic mice, all CsA or vehicle treated mice survived the infection. CsA treated mice showed enhanced PMN recruitment in BAL by trend (55.2% +/- 12.0 (CsA) vs. 33.7% +/- 8.0 (control), mean +/- SEM, p=0.053), whereas pulmonary inflammation and PMN counts in PB were comparable to controls. In contrast, fungal clearance was clearly impaired in animals after CsA treatment (2.1 x 105 CFU/lung after 48 hours +/- 0.5 (CsA) vs. 1.7 x 105 +/- 0.2 (control), p<0.005). Along with that, NFATc1LysM mice infected with A. f. showed unimpaired survival. However, there were no detectable differences in PMN recruitment or fungal clearance, whereas pulmonary inflammation and PMN counts in PB seemed to be more pronounced in knockout mice (1.0 inflammation points/lung +/- 0.12 (NFATc1LysM) vs. 0.7 +/- 0.07 (control), p=0.057; 1.5 x 103 PMN/µl +/- 0.2 (NFATc1LysM) vs. 0.9 +/- 0.1 (control), p=0.036). Distribution of bone marrow derived murine myeloid progenitor cells was unaffected through NFAT inhibition by CsA but clearly impaired in NFATc1LysM mice especially in megakaryocyte-erythroid progenitor cells (1.2 x 105 cells +/- 0.2 (NFATc1LysM) vs. 2.7 +/- 0.6, p=0.015) whereas PMN blood counts in PB were unchanged.Conclusions: In a mouse model, NFAT inhibition via treatment with CsA does not influence survival after infection with A. f. in vivo but affects PMN recruitment and local fungal clearance. To some extent this may be due to impaired PMN phagocytic and migratory capabilities as indicated by our in vitro and ex vivo studies (data not shown). However, solely NFATc1 downregulation in PMN apparently results in slightly different effects given that infected NFATc1LysM mice displayed enhanced pulmonary inflammation and elevated PMN blood counts compared to controls. Additionally, NFATc1 inhibition in NFATc1LysM mice leads to constrained myelopoiesis under steady state conditions without affecting peripheral PMN blood counts compared to untreated wild type controls. Further studies are needed to clarify underlying mechanisms and clinical relevance in HSCT of our findings. DisclosuresNo relevant conflicts of interest to declare.

Mtss1 is a critical epigenetically regulated tumor suppressor in CML.

Chronic myeloid leukemia (CML) is driven by malignant stem cells that can persist despite therapy. We have identified Metastasis suppressor 1 (Mtss1/MIM) to be downregulated in hematopoietic stem and progenitor cells from leukemic transgenic SCLtTA/Bcr-Abl mice and in patients with CML at diagnosis, and Mtss1 was restored when patients achieved complete remission. Forced expression of Mtss1 decreased clonogenic capacity and motility of murine myeloid progenitor cells and reduced tumor growth. Viral transduction of Mtss1 into lineage-depleted SCLtTA/Bcr-Abl bone marrow cells decreased leukemic cell burden in recipients, and leukemogenesis was reduced upon injection of Mtss1-overexpressing murine myeloid 32D cells. Tyrosine kinase inhibitor (TKI) therapy and reversion of Bcr-Abl expression increased Mtss1 expression but failed to restore it to control levels. CML patient samples revealed higher DNA methylation of specific Mtss1 promoter CpG sites that contain binding sites for Kaiso and Rest transcription factors. In summary, we identified a novel tumor suppressor in CML stem cells that is downregulated by both Bcr-Abl kinase-dependent and -independent mechanisms. Restored Mtss1 expression markedly inhibits primitive leukemic cell biology in vivo, providing a therapeutic rationale for the Bcr-Abl-Mtss1 axis to target TKI-resistant CML stem cells in patients.

Abstract A04: Systemic agonistic anti-CD40 treatment of tumor bearing mice modulates hepatic myeloid suppressive cells and causes immune-mediated liver damage

Abstract Immune stimulatory monoclonal antibodies are currently evaluated as antitumor agents in clinical trials. Although overall toxicity appears to be moderate, liver toxicities have been reported and are not completely understood. Therefore, we decided to study the effect of systemic CD40 antibody treatment on the liver immune microenvironment. Agonistic CD40 antibody or isotype control was injected intraperitoneally into naïve and tumor-bearing mice. Liver enzymes, histologies and immune infiltrates were analyzed after antibody administration. The effect of agonistic CD40 administration was evaluated using bone marrow chimeras and genetically modified mouse strains Cd40-/- and Nox2-/-. Mouse and human tumor-induced myeloid suppressive cells were cultured to address changes in their immune function upon CD40 ligation. Agonistic CD40 antibody caused liver damage within 24 hours after injection in two unrelated tumor models and mice strains. Using bone marrow chimeras we could demonstrate that CD40 antibody-induced hepatitis in tumor-bearing mice was dependent on the presence of CD40+ immune cells. Agonistic CD40 ligation-dependent liver damage was induced by the generation of reactive oxygen species. Furthermore, agonistic CD40 antibody resulted in increased CD80 and CD40 positive liver CD11b+Gr-1+ immature myeloid cells. CD40 ligation on tumor-induced hepatic myeloid cells or CD14+HLA-DRlow PBMC from cancer patients reduced their immune suppressor function. Collectively, agonistic CD40 antibody activates the tumor-induced liver myeloid suppressive compartment, enhancing acute inflammation and thus liver damage. Our data in murine and human myeloid suppressive cells point towards a pivotal role for CD40 as a key molecule in modulating myeloid suppressive cell plasticity. Citation Format: Jose Medina-Echeverz, Chi Ma, Tobias Eggert, Tim F. Greten. Systemic agonistic anti-CD40 treatment of tumor bearing mice modulates hepatic myeloid suppressive cells and causes immune-mediated liver damage. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A04.

Defining New Therapeutics Using a More Immunocompetent Mouse Model of Antibody-Enhanced Dengue Virus Infection.

ABSTRACTWith over 3.5 billion people at risk and approximately 390 million human infections per year, dengue virus (DENV) disease strains health care resources worldwide. Previously, we and others established models for DENV pathogenesis in mice that completely lack subunits of the receptors (Ifnar and Ifngr) for type I and type II interferon (IFN) signaling; however, the utility of these models is limited by the pleotropic effect of these cytokines on innate and adaptive immune system development and function. Here, we demonstrate that the specific deletion of Ifnar expression on subsets of murine myeloid cells (LysM Cre+ Ifnarflox/flox [denoted as Ifnarf/f herein]) resulted in enhanced DENV replication in vivo. The administration of subneutralizing amounts of cross-reactive anti-DENV monoclonal antibodies to LysM Cre+ Ifnarf/f mice prior to infection with DENV serotype 2 or 3 resulted in antibody-dependent enhancement (ADE) of infection with many of the characteristics associated with severe DENV disease in humans, including plasma leakage, hypercytokinemia, liver injury, hemoconcentration, and thrombocytopenia. Notably, the pathogenesis of severe DENV-2 or DENV-3 infection in LysM Cre+ Ifnarf/f mice was blocked by pre- or postexposure administration of a bispecific dual-affinity retargeting molecule (DART) or an optimized RIG-I receptor agonist that stimulates innate immune responses. Our findings establish a more immunocompetent animal model of ADE of infection with multiple DENV serotypes in which disease is inhibited by treatment with broad-spectrum antibody derivatives or innate immune stimulatory agents.