CD66b-CD64dimCD115- cells in the human bone marrow represent neutrophil-committed progenitors.

Here we report the identification of human CD66b-CD64dimCD115- neutrophil-committed progenitor cells (NCPs) within the SSCloCD45dimCD34+ and CD34dim/- subsets in the bone marrow. NCPs were either CD45RA+ or CD45RA-, and in vitro experiments showed that CD45RA acquisition was not mandatory for their maturation process. NCPs exclusively generated human CD66b+ neutrophils in both in vitro differentiation and in vivo adoptive transfer experiments. Single-cell RNA-sequencing analysis indicated NCPs fell into four clusters, characterized by different maturation stages and distributed along two differentiation routes. One of the clusters was characterized by an interferon-stimulated gene signature, consistent with the reported expansion of peripheral mature neutrophil subsets that express interferon-stimulated genes in diseased individuals. Finally, comparison of transcriptomic and phenotypic profiles indicated NCPs represented earlier neutrophil precursors than the previously described early neutrophil progenitors (eNePs), proNeus and COVID-19 proNeus. Altogether, our data shed light on the very early phases of neutrophil ontogeny.

Identification of a miR-146b-Fas ligand axis in the development of neutropenia in T large granular lymphocyte leukemia.

Tlarge granular lymphocyte leukemia (T-LGLL) is characterized by the expansion of several large granular lymphocyte clones, among which a subset of large granular lymphocytes showing constitutively activated STAT3, a specific CD8+/CD4- phenotype and the presence of neutropenia has been identified. Although STAT3 is an inducer of transcription of a large number of oncogenes, so far its relationship with miRNAs has not been evaluated in T-LGLL patients. Here, we investigated whether STAT3 could carry out its pathogenetic role in T-LGLL through an altered expression of miRNAs. The expression level of 756 mature miRNA was assessed on purified T large granular lymphocytes (T-LGLs) by using a TaqMan Human microRNA Array. Hierarchical Clustering Analysis of miRNA array data shows that the global miRNome clusters with CD8 T-LGLs. Remarkably, CD8 T-LGLs exhibit a selective and STAT3-dependent repression of miR-146b expression, that significantly correlated with the absolute neutrophil counts and inversely correlated with the expression of Fas ligand (FasL), that is regarded as the most relevant factor in the pathogenesis of neutropenia. Experimental evidence demonstrates that the STAT3-dependent reduction of miR-146b expression in CD8 T-LGLs occurs as a consequence of miR-146b promoter hypermethylation and results in the disruption of the HuR-mediated post-transcriptional machinery controlling FasL mRNA stabilization. Restoring miR-146b expression in CD8 T-LGLs lead to a reduction of HuR protein and, in turn, of FasL mRNA expression, thus providing mechanistic insights for the existence of a STAT3-miR146b-FasL axis and neutropenia in T-LGLL.

Histone modifications underlie monocyte dysregulation in patients with systemic sclerosis, underlining the treatment potential of epigenetic targeting.

BACKGROUND AND OBJECTIVE: Systemic sclerosis (SSc) is a severe autoimmune disease, in which the pathogenesis is dependent on both genetic and epigenetic factors. Altered gene expression in SSc monocytes, particularly of interferon (IFN)-responsive genes, suggests their involvement in SSc development. We investigated the correlation between epigenetic histone marks and gene expression in SSc monocytes. METHODS: Chromatin immunoprecipitation followed by sequencing (ChIPseq) for histone marks H3K4me3 and H3K27ac was performed on monocytes of nine healthy controls and 14 patients with SSc. RNA sequencing was performed in parallel to identify aberrantly expressed genes and their correlation with the levels of H3K4me3 and H3K27ac located nearby their transcription start sites. ChIP-qPCR assays were used to verify the role of bromodomain proteins, H3K27ac and STATs on IFN-responsive gene expression. RESULTS: 1046 and 534 genomic loci showed aberrant H3K4me3 and H3K27ac marks, respectively, in SSc monocytes. The expression of 381 genes was directly and significantly proportional to the levels of such chromatin marks present near their transcription start site. Genes correlated to altered histone marks were enriched for immune, IFN and antiviral pathways and presented with recurrent binding sites for IRF and STAT transcription factors at their promoters. IFNα induced the binding of STAT1 and STAT2 at the promoter of two of these genes, while blocking acetylation readers using the bromodomain BET family inhibitor JQ1 suppressed their expression. CONCLUSION: SSc monocytes have altered chromatin marks correlating with their IFN signature. Enzymes modulating these reversible marks may provide interesting therapeutic targets to restore monocyte homeostasis to treat or even prevent SSc.

IL-10 disrupts the Brd4-docking sites to inhibit LPS-induced CXCL8 and TNF-α expression in monocytes: Implications for chronic obstructive pulmonary disease.

BACKGROUND: IL-10 is well known for its ability to block the expression and production of numerous proinflammatory cytokines, in this manner preventing the development of excessive or chronic immune activation. IL-10-induced transcriptional repression of CXCL8 and TNFA genes consists of 2 distinct phases: an early phase, occurring rapidly and in a protein synthesis-independent manner, followed by a second phase that is more delayed and dependent on protein synthesis. OBJECTIVE: We sought to identify the mechanisms through which IL-10 rapidly and directly suppresses LPS-induced CXCL8 and TNF-α transcription, which might be defective under pathologic conditions. METHODS: The molecular events triggered by IL-10 in LPS-activated monocytes at the CXCL8 and TNFA loci were investigated by using the chromatin immunoprecipitation assay. RESULTS: Inhibition of LPS-induced CXCL8 and TNF-α expression by IL-10 proceeds through a common mechanism targeting LPS-induced phosphorylation of the nuclear factor κB p65 serine 276 residue (pS276p65). As a result, all the pS276p65-dependent events occurring at the CXCL8 and TNFA loci are consistently reduced, ultimately leading to a reduction in transcript elongation. Additionally, IL-10 selectively controls CXCL8 transcript elongation through histone deacetylase (HDAC) 2-dependent covalent chromatin modifications, disrupting the assembly of the transcriptional machinery. Remarkably, PBMCs from patients with acute-phase chronic obstructive pulmonary disease, which express negligible HDAC2 levels, are scarcely affected by IL-10 in terms of inhibition of CXCL8 expression. CONCLUSIONS: This study provides mechanistic evidence that IL-10 creates a chromatin environment that decreases the transcriptional rate of CXCL8 and TNF-α to Toll-like receptor 4-activating signals. Data identify novel molecular targets for therapeutic strategies aimed at dampening inflammation in pathologies such as chronic obstructive pulmonary disease, in which reduced intracellular HDAC2 levels have been described.

Cutting edge: An inactive chromatin configuration at the IL-10 locus in human neutrophils.

To identify the molecular basis of IL-10 expression in human phagocytes, we evaluated the chromatin modification status at their IL-10 genomic locus. We analyzed posttranslational modifications of histones associated with genes that are active, repressed, or poised for transcriptional activation, including H3K4me3, H4Ac, H3K27Ac, and H3K4me1 marks. Differently from autologous IL-10-producing monocytes, none of the marks under evaluation was detected at the IL-10 locus of resting or activated neutrophils from healthy subjects or melanoma patients. By contrast, increased H3K4me3, H4Ac, H3K4me1, and H3K27Ac levels were detected at syntenic regions of the IL-10 locus in mouse neutrophils. Altogether, data demonstrate that human neutrophils, differently from either monocytes or mouse neutrophils, cannot switch on the IL-10 gene because its locus is in an inactive state, likely reflecting a neutrophil-specific developmental outcome. Implicitly, data also definitively settle a currently unsolved issue on the capacity of human neutrophils to produce IL-10.

IL-10-induced microRNA-187 negatively regulates TNF-α, IL-6, and IL-12p40 production in TLR4-stimulated monocytes.

IL-10 is a potent anti-inflammatory molecule that, in phagocytes, negatively targets cytokine expression at transcriptional and posttranscriptional levels. Posttranscriptional checkpoints also represent the specific target of a recently discovered, evolutionary conserved class of small silencing RNAs known as "microRNAs" (miRNAs), which display the peculiar function of negatively regulating mRNA processing, stability, and translation. In this study, we report that activation of primary human monocytes up-regulates the expression of miR-187 both in vitro and in vivo. Accordingly, we identify miR-187 as an IL-10-dependent miRNA playing a role in IL-10-mediated suppression of TNF-α, IL-6, and the p40 subunit of IL-12 (IL-12p40) produced by primary human monocytes following activation of Toll-like receptor 4 (TLR4). Ectopic expression of miR-187 consistently and selectively reduces TNFα, IL-6, and IL-12p40 produced by LPS-activated monocytes. Conversely, the production of LPS-induced TNF-α, IL-6, and IL-12p40 is increased significantly when miR-187 expression is silenced. Our data demonstrate that miR-187 directly targets TNF-α mRNA stability and translation and indirectly decreases IL-6 and IL-12p40 expression via down-modulation of IκBζ, a master regulator of the transcription of these latter two cytokines. These results uncover an miRNA-mediated pathway controlling cytokine expression and demonstrate a central role of miR-187 in the physiological regulation of IL-10-driven anti-inflammatory responses.

Surface CD52, CD84, and PTGER2 mark mature PMN-MDSCs from cancer patients and G-CSF-treated donors.

Precise molecular characterization of circulating polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) is hampered by their mixed composition of mature and immature cells and lack of specific markers. Here, we focus on mature CD66b+CD10+CD16+CD11b+ PMN-MDSCs (mPMN-MDSCs) from either cancer patients or healthy donors receiving G-CSF for stem cell mobilization (GDs). By RNA sequencing (RNA-seq) experiments, we report the identification of a distinct gene signature shared by the different mPMN-MDSC populations under investigation, also validated in mPMN-MDSCs from GDs and tumor-associated neutrophils (TANs) by single-cell RNA-seq (scRNA-seq) experiments. Analysis of such a gene signature uncovers a specific transcriptional program associated with mPMN-MDSC differentiation and allows us to identify that, in patients with either solid or hematologic tumors and in GDs, CD52, CD84, and prostaglandin E receptor 2 (PTGER2) represent potential mPMN-MDSC-associated markers. Altogether, our findings indicate that mature PMN-MDSCs distinctively undergo specific reprogramming during differentiation and lay the groundwork for selective immunomonitoring, and eventually targeting, of mature PMN-MDSCs.

The slan antigen identifies the prototypical non-classical CD16+-monocytes in human blood.

Introduction: Peripheral monocytes in humans are conventionally divided into classical (CL, CD14++CD16-), intermediate (INT, CD14++CD16+) and non-classical (NC, CD14dim/-CD16++) cells, based on their expression levels of CD14 and CD16. A major fraction of the NC-monocytes has been shown to express the 6-sulfo LacNAc (slan) antigen, but whether these slan+/NC-monocytes represent the prototypical non-classical monocytes or whether they are simply a sub-fraction with identical features as the remainder of NC monocytes is still unclear. Methods: We analyzed transcriptome (by bulk and single cell RNA-seq), proteome, cell surface markers and production of discrete cytokines by peripheral slan+/NC- and slan-/NC-monocytes, in comparison to total NC-, CL- and INT- monocytes. Results: By bulk RNA-seq and proteomic analysis, we found that slan+/NC-monocytes express higher levels of genes and proteins specific of NC-monocytes than slan-/NC-monocytes do. Unsupervised clustering of scRNA-seq data generated one cluster of NC- and one of INT-monocytes, where all slan+/NC-monocytes were allocated to the NC-monocyte cluster, while slan-/NC-monocytes were found, in part (13.4%), within the INT-monocyte cluster. In addition, total NC- and slan-/NC-monocytes, but not slan+/NC-monocytes, were found by both bulk RNA-seq and scRNA-seq to contain a small percentage of natural killer cells. Conclusion: In addition to comparatively characterize total NC-, slan-/NC- and slan+/NC-monocyte transcriptomes and proteomes, our data prove that slan+/NC-, but not slan-/NC-, monocytes are more representative of prototypical NC-monocytes.

Uncovering an IL-10-dependent NF-kappaB recruitment to the IL-1ra promoter that is impaired in STAT3 functionally defective patients.

The interleukin 1 receptor antagonist (IL-1ra) is an important negative regulator of the inflammatory response, whose genetic deficiency has been recently shown to cause a severe autoinflammatory syndrome in humans. In this study we characterized the molecular mechanisms whereby interleukin 10 (IL-10) potentiates IL-1ra transcription in LPS-stimulated monocytes and neutrophils. Using chromatin immunoprecipitation, we show that although NF-kappaBp65 and NF-kappaBp50 proteins accumulate into the nuclei and bind to the IkappaB alpha promoter during LPS stimulation, they are not recruited to the kappaB sites of the IL-1ra promoter. However, in response to LPS plus IL-10, which were found to induce chromatin acetylation, recruitment of both NF-kappaBp65 and NF-kappaBp50 to the IL-1ra promoter efficiently occurs in a STAT3-dependent manner. Accordingly, in neutrophils from hyper-IgE syndrome patients, who carry a nonfunctional STAT3, IL-10 failed to promote NF-kappaBp65 recruitment to the IL-1ra promoter and consequently to potentiate LPS-induced IL-1ra transcription. Altogether our findings uncover a novel mechanism whereby IL-10-activated STAT3 modulates IL-1ra transcription in LPS-treated phagocytes by making IL-1ra promoter accessible to readily available nuclear NF-kappaB.

Deciphering the state of immune silence in fatal COVID-19 patients.

Since the beginning of the SARS-CoV-2 pandemic, COVID-19 appeared as a unique disease with unconventional tissue and systemic immune features. Here we show a COVID-19 immune signature associated with severity by integrating single-cell RNA-seq analysis from blood samples and broncho-alveolar lavage fluids with clinical, immunological and functional ex vivo data. This signature is characterized by lung accumulation of naïve lymphoid cells associated with a systemic expansion and activation of myeloid cells. Myeloid-driven immune suppression is a hallmark of COVID-19 evolution, highlighting arginase-1 expression with immune regulatory features of monocytes. Monocyte-dependent and neutrophil-dependent immune suppression loss is associated with fatal clinical outcome in severe patients. Additionally, our analysis shows a lung CXCR6+ effector memory T cell subset is associated with better prognosis in patients with severe COVID-19. In summary, COVID-19-induced myeloid dysregulation and lymphoid impairment establish a condition of 'immune silence' in patients with critical COVID-19.

Anti-viral state segregates two molecular phenotypes of pancreatic adenocarcinoma: potential relevance for adenoviral gene therapy.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) remains a leading cause of cancer mortality for which novel gene therapy approaches relying on tumor-tropic adenoviruses are being tested. METHODS: We obtained the global transcriptional profiling of primary PDAC using RNA from eight xenografted primary PDAC, three primary PDAC bulk tissues, three chronic pancreatitis and three normal pancreatic tissues. The Affymetrix GeneChip HG-U133A was used. The results of the expression profiles were validated applying immunohistochemical and western blot analysis on a set of 34 primary PDAC and 10 established PDAC cell lines. Permissivity to viral vectors used for gene therapy, Adenovirus 5 and Adeno-Associated Viruses 5 and 6, was assessed on PDAC cell lines. RESULTS: The analysis of the expression profiles allowed the identification of two clearly distinguishable phenotypes according to the expression of interferon-stimulated genes. The two phenotypes could be readily recognized by immunohistochemical detection of the Myxovirus-resistance A protein, whose expression reflects the activation of interferon dependent pathways. The two molecular phenotypes discovered in primary carcinomas were also observed among established pancreatic adenocarcinoma cell lines, suggesting that these phenotypes are an intrinsic characteristic of cancer cells independent of their interaction with the host's microenvironment. The two pancreatic cancer phenotypes are characterized by different permissivity to viral vectors used for gene therapy, as cell lines expressing interferon stimulated genes resisted to Adenovirus 5 mediated lysis in vitro. Similar results were observed when cells were transduced with Adeno-Associated Viruses 5 and 6. CONCLUSION: Our study identified two molecular phenotypes of pancreatic cancer, characterized by a differential expression of interferon-stimulated genes and easily recognized by the expression of the Myxovirus-resistance A protein. We suggest that the detection of these two phenotypes might help the selection of patients enrolled in virally-mediated gene therapy trials.

Chromatin remodelling and autocrine TNFα are required for optimal interleukin-6 expression in activated human neutrophils.

Controversy currently exists about the ability of human neutrophils to produce IL-6. Here, we show that the chromatin organization of the IL-6 genomic locus in human neutrophils is constitutively kept in an inactive configuration. However, we also show that upon exposure to stimuli that trigger chromatin remodelling at the IL-6 locus, such as ligands for TLR8 or, less efficiently, TLR4, highly purified neutrophils express and secrete IL-6. In TLR8-activated neutrophils, but not monocytes, IL-6 expression is preceded by the induction of a latent enhancer located 14 kb upstream of the IL-6 transcriptional start site. In addition, IL-6 induction is potentiated by endogenous TNFα, which prolongs the synthesis of the IκBζ co-activator and sustains C/EBPß recruitment and histone acetylation at IL-6 regulatory regions. Altogether, these data clarify controversial literature on the ability of human neutrophils to generate IL-6 and uncover chromatin-dependent layers of regulation of IL-6 in these cells.