During 'emergency' situations such as infections, host defense requires rapid mobilization of bone marrow granulocyte progenitors. 'Steady-state' granulopoiesis is absolutely dependent on the C/EBPalpha transcription factor, but the transcriptional mechanisms underlying emergency granulopoiesis remain unclear. Here we show that large numbers of granulocytes were generated from C/EBPalpha-deficient progenitors after cytokine stimulation in vivo. Cytokine treatment or fungal infection induced upregulation of C/EBPbeta but not C/EBPalpha or C/EBPepsilon transcripts in granulocyte progenitors, and C/EBPbeta-deficient progenitors showed decreased emergency-induced granulopoiesis in vitro and in vivo. C/EBPbeta inhibited proliferation less severely than did C/EBPalpha. These data suggest a critical function for C/EBPbeta in emergency granulopoiesis, which demands both differentiation and proliferation of granulocyte precursors.

Monocyte differentiation involves the participation of lineage-restricted transcription factors, although the mechanisms by which this process occurs are incompletely defined. Within the hematopoietic system, members of the Kruppellike family of factors (KLFs) play essential roles in erythrocyte and T lymphocyte development. Here we show that KLF4/GKLF is expressed in a monocyte-restricted and stage-specific pattern during myelopoiesis and functions to promote monocyte differentiation. Overexpression of KLF4 in HL-60 cells confers the characteristics of mature monocytes. Conversely, KLF4 knockdown blocked phorbol ester-induced monocyte differentiation. Forced expression of KLF4 in primary common myeloid progenitors (CMPs) or hematopoietic stem cells (HSCs) induced exclusive monocyte differentiation in clonogenic assays, whereas KLF4 deficiency inhibited monocyte but increased granulocyte differentiation. Mechanistic studies demonstrate that KLF4 is a target gene of PU.1. Consistently, KLF4 can rescue PU.1À/À fetal liver cells along the monocytic lineage and can activate the monocytic-specific CD14 promoter. Thus, KLF4 is a critical regulator in the transcriptional network controlling monocyte differentiation.

Both PU.1 (also called SFPI1), an Ets-family transcription factor, and AML1 (also called RUNX1), a DNA-binding subunit of the CBF transcription factor family, are crucial for the generation of all hematopoietic lineages, and both act as tumor suppressors in leukemia. An upstream regulatory element (URE) of PU.1 has both enhancer and repressor activity and tightly regulates PU.1 expression. Here we show that AML1 binds to functionally important sites within the PU.1 upstream regulatory element and regulates PU.1 expression at both embryonic and adult stages of development. Analysis of mice carrying conditional AML1 knockout alleles and knock-in mice carrying mutations in all three AML1 sites of the URE proximal region demonstrated that AML1 regulates PU.1 both positively and negatively in a lineage dependent manner. Dysregulation of PU.1 expression contributed to each of the phenotypes observed in these mice, and restoration of proper PU.1 expression rescued or partially rescued each phenotype. Thus, our data demonstrate that PU.1 is a major downstream target gene of AML1.

Myeloid-derived suppressor cells (MDSCs) are of myeloid origin and are able to suppress T cell responses. The role of MDSCs in autoimmune diseases remains controversial, and little is known about the function of MDSCs in autoimmune arthritis. In this study, we clarify that MDSCs play crucial roles in the regulation of proinflammatory immune response in a collagen-induced arthritis (CIA) mouse model. MDSCs accumulated in the spleens of mice with CIA when arthritis severity peaked. These MDSCs inhibited the proliferation of CD4+ T cells and their differentiation into Th17 cells in vitro. Moreover, MDSCs inhibited the production of IFN-γ, IL-2, TNF-α, and IL-6 by CD4+ T cells in vitro, whereas they promoted the production of IL-10. Adoptive transfer of MDSCs reduced the severity of CIA in vivo, which was accompanied by a decrease in the number of CD4+ T cells and Th17 cells in the draining lymph nodes. However, depletion of MDSCs abrogated the spontaneous improvement of CIA. In conclusion, MDSCs in CIA suppress the progression of CIA by inhibiting the proinflammatory immune response of CD4+ T cells. These observations suggest that MDSCs play crucial roles in the regulation of autoimmune arthritis, which could be exploited in new cell-based therapies for human rheumatoid arthritis.

A substantial proportion of patients with acute graft-versus-host disease (aGVHD) respond to cell therapy with culture-expanded human bone marrow mesenchymal stromal/stem cells (BM-MSCs). However, the mechanisms by which these cells can ameliorate aGVHD-associated complications remain to be clarified. We show here that BM-MSC-derived extracellular vesicles (EVs) recapitulated the therapeutic effects of BM-MSCs against aGVHD. Systemic infusion of human BM-MSCderived EVs prolonged the survival of mice with aGVHD and reduced the pathologic damage in multiple GVHD-targeted organs. In EV-treated GVHD mice, CD41 and CD81 T cells were suppressed. Importantly, the ratio of CD62L-CD441 to CD62L 1 CD44-T cells was decreased, suggesting that BM-MSC-derived EVs suppressed the functional differentiation of T cells from a naive to an effector phenotype. BM-MSC-derived EVs also preserved CD4 1 CD25 1 Foxp31 regulatory T cell populations. In a culture of CD3/CD28-stimulated human peripheral blood mononuclear cells with BM-MSC-derived EVs, CD31 T cell activation was suppressed. However, these cells were not suppressed in cultures with EVs derived from normal human dermal fibroblasts (NHDFs). NHDF-derived EVs did not ameliorate the clinical or pathological characteristics of aGVHD in mice, suggesting an immunoregulatory function unique to BM-MSC-derived EVs. Microarray analysis of microRNAs in BM-MSCderived EVs versus NHDF-derived EVs showed upregulation of miR-125a-3p and downregulation of cell proliferative processes, as identified by Gene Ontology enrichment analysis. Collectively, our findings provide the first evidence that amelioration of aGVHD by therapeutic infusion of BM-MSCderived EVs is associated with the preservation of circulating naive T cells, possibly due to the unique microRNA profiles of BM-MSC-derived EVs. STEM CELLS 2018;36:434-445 SIGNIFICANCE STATEMENTCell therapy with human bone marrow mesenchymal stromal/stem cells (BM-MSCs) is clinically effective for patients with intractable acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation. This study revealed that BM-MSC-derived extracellular vesicles (EVs) recapitulated the therapeutic effects of BM-MSCs against aGVHD by inhibiting effector T cell induction and preserving peripheral naive T cells. Gene Ontology analysis of microRNAs differentially expressed in BM-MSC-derived EVs suggested that these microRNAs may downregulate cell proliferative processes. These findings suggest that BM-MSC-derived EVs mediate the anti-aGVHD effects of BM-MSCs, thereby raising the possibility of using EVs as a cell-free therapy for the treatment of aGVHD.

In human CRC cells, loss of SMAD4 leads to up-regulation of CCL15 expression. Human liver metastases that express CCL15 contain higher numbers CCR1(+) cells; patients with these metastases have shorter times of disease-free survival. Reagents designed to block CCL15 recruitment of CCR1(+) cells could prevent metastasis of CRC to liver.

No abstract

Purpose: We previously reported that loss of SMAD4 promotes chemokine CCL15 expression to recruit CCR1 þ myeloid cells via the CCL15-CCR1 axis, which facilitates metastasis of colorectal cancer to the liver. The purposes of this study were to investigate whether essentially the same mechanism works in tumor invasion of the primary colorectal cancer and to evaluate the clinical importance of CCL15 expression and CCR1 þ cell accumulation.Experimental Design: Using human colorectal cancer cell lines with reduced expression of SMAD4 or CCL15, we investigated tumor growth activities in vivo. We used immunohistochemistry (IHC) to investigate expression of SMAD4, CCL15, and CCR1 with 333 clinical specimens of primary colorectal cancer. We next characterized the CCR1 þ cells using double immunofluorescence staining with several specific cell-type markers. Finally, we determined the serum CCL15 levels in 132 colorectal cancer patients. Results:In an orthotopic xenograft model, CCL15 secreted from SMAD4-deficient colorectal cancer cells recruited CCR1