Myeloid Cell Types Research Articles

The Tumor Immune Microenvironment in Pancreatic Ductal Adenocarcinoma: Neither Hot nor Cold.

Simple SummaryIn this review, we discuss the current understanding of pro- and anticancer immune responses in the tumor immune microenvironment of pancreatic ductal adenocarcinoma. We describe the duality and complexity of immune cell functions in the tumor microenvironment and also illustrate therapeutic approaches that modulate the antitumor immune response.Pancreatic ductal adenocarcinoma (PDAC) is the most common pancreatic tumor and is associated with poor prognosis and treatment response. The tumor microenvironment (TME) is recognized as an important factor in metastatic progression across cancers. Despite extensive study of the TME in PDAC, the cellular and molecular signaling networks remain poorly understood, largely due to the tremendous heterogeneity across tumors. While earlier work characterized PDAC as an immunologically privileged tumor poorly recognized by the immune system, recent studies revealed the important and nuanced roles of immune cells in the pathogenesis of PDAC. Distinct lymphoid, myeloid, and stromal cell types in the TME exert opposing influences on PDAC tumor trajectory, suggesting a more complex organization than the classical “hot” versus “cold” tumor distinction. We review the pro- and antitumor immune processes found in PDAC and briefly discuss their leverage for the development of novel therapeutic approaches in the field.

HDM induces distinct immunometabolic phenotype in macrophages in TLR4-dependent manner

Asthma is one of the most common chronic diseases. In many cases it is preceded by the development of an immune response to allergens such as animal fur, dust, pollens and etc. In human population this disease is heterogeneous, and no selective drugs are available at the moment for some endotypes of asthma. The role of the adaptive immune system in the pathogenesis of asthma was extensively studied, while the role of innate immune cells, in particular myeloid cells, was not sufficiently addressed. Myeloid cells, such as macrophages and dendritic cells, are characterized by high plasticity, heterogenicity and ability to undergo polarization in response to various pathogenic stimuli, including those engaging innate immune receptors. Recently, special attention was drawn to the link between polarization of macrophages and cell metabolism. We hypothesized that immunometabolic reprogramming of myeloid cells, in particular, of macrophages and dendritic cells during sensitization with an allergen may affect further immune response and asthma development. To test this hypothesis, we generated distinct types of myeloid cells in vitro from murine bone marrow and analyzed their immunometabolic profiles upon activation with house dust mite extract (HDM) and its key active components. We found that the combination of lipopolysaccharide (LPS) and beta-glucan is sufficient to upregulate proinflammatory cytokine production as well as respiratory and glycolytic capacity of myeloid cells, comparably to HDM. This specific immunometabolic phenotype was associated with altered mitochondrial morphology and possibly with increased ROS production in macrophages. Moreover, we found that both TNF production and metabolic remodeling of macrophages in response to HDM are TLR4-dependent processes. Altogether, these results expand our understanding of molecular mechanisms underlying asthma induction and pathogenesis and may potentially lead to new therapeutic strategies for the treatment of this disease.

Mouse dendritic cells and other myeloid subtypes in healthy lymph nodes and skin: 26-Color flow cytometry panel for immune phenotyping.

This novel 26-color flow cytometry panel allows the detailed immune phenotyping of the complex network of myeloid cells in murine lymph nodes and skin. With the optimized panel the different murine DC-subsets and other myeloid cell types can be identified and further characterized for co-stimulatory and inhibitory surface molecules.

A Human CD68 Promoter-Driven Inducible Cre-Recombinase Mouse Line Allows Specific Targeting of Tissue Resident Macrophages.

Current genetic tools designed to target macrophages in vivo often target cells from all myeloid lineages. Therefore, we sought to generate a novel transgenic mouse which has a tamoxifen inducible Cre-recombinase under the control of the human CD68 promoter (hCD68-CreERT2). To test the efficiency and specificity of the of Cre-recombinase activity we crossed the hCD68-CreERT2 mice with a loxP-flanked STOP cassette red fluorescent protein variant (tdTomato) mouse. We established that orally dosing mice with 2 mg of tamoxifen for 5 consecutive days followed by a 5-day induction period resulted in robust expression of tdTomato in CD11b+ F4/80+ tissue resident macrophages. Using this induction protocol, we demonstrated tdTomato expression within peritoneal, liver and spleen macrophages and blood Ly6Clow monocytes. Importantly there was limited or no inducible tdTomato expression within other myeloid cells (neutrophils, monocytes, dendritic cells and eosinophils), T cells (CD4+ and CD8+) and B cells (CD19+). We also demonstrated that the level of tdTomato expression can be used as a marker to identify different populations of peritoneal and liver macrophages. We next assessed the longevity of tdTomato expression in peritoneal macrophages, liver and splenic macrophages and demonstrated high levels of tdTomato expression as long as 6 weeks after the last tamoxifen dose. Importantly, hCD68-CreERT2 expression is more restricted than that of LysM-Cre which has significant expression in major myeloid cell types (monocytes and neutrophils). To demonstrate the utility of this novel macrophage-specific Cre driver line we demonstrated tdTomato expression in recruited CD11b+CD64+F4/80+ monocyte-derived macrophages within the atherosclerotic lesions of AAV8-mPCSK9 treated mice, with limited expression in recruited neutrophils. In developing this new hCD68-CreERT2 mouse we have a tool that allows us to target tissue resident macrophages, with the advantage of not targeting other myeloid cells namely neutrophils and inflammatory monocytes.

Abstract 5148: Immune landscapes and interactions in human fallopian tubes and their implications for early high-grade serous ovarian cancers

Abstract The five-year survival rate of ovarian cancer (OC) dramatically rises from below 40% to 90% with patients who are diagnosed early (stage I), when the disease restricts to the ovary. Thus, the ultimate goals of our research are to learn how to detect ovarian cancer at its earliest stages of development and thereby improve patient survival and to learn how the immune microenvironment contributes to the development of OC. Achieving these goals requires us to better characterize the earliest steps in ovarian carcinogenesis. The human fallopian tube harbors the cell-of-origin for most high-grade serous 'ovarian' cancers (HGSOCs), but its cellular composition, particularly the immune component, is poorly characterized. Emerging evidence from several research groups using molecular sequencing technologies of fallopian tube epithelium strongly support this hypothesis. We recently described our use of single-cell transcriptome technology (scRNA-Seq) to profile the heterogeneity of non-malignant FT and define a novel transcriptional gene regulatory network of epithelial differentiation and tumorigenesis in the human FT. Here we present an in-depth characterization of the immune cell atlas for human fallopian tubes, which has not been reported. Our unpublished analyses of our FT dataset and the publicly available HGSOC scRNA-Seq dataset demonstrate a significant difference in the immune cell landscape. There are limited macrophages and a high abundance of monocytes in non-malignant FT and adjacent normal ovaries compared to those in HGSOC tumors. This finding leads us to hypothesize that the macrophage-to-monocyte ratio and their interactions with other immune cell types in human fallopian tubes create a permissive microenvironment allowing for the development of HGSOC and can provide a biomarker for early cancer detection. To test if those myeloid cells could be a marker for early HGSOC, we performed scRNA-seq on FT from women carrying mutant alleles of BRCA1 or BRCA2 who are at high risk of HGSOC. Intriguingly, the ratio of monocytes to macrophages in the FTs from half of these high-risk individuals is more like that found in HGSOC than in normal FT. Furthermore, computational analyses on myeloid cell types and their interactions with different epithelial cells, stromal fibroblast cells, and T and NK cells revealed the extended contribution of the non-epithelial microenvironment in FT, potentially driving early HGSOC development and progression. This cellular and molecular compendium of the human fallopian tube immune landscapes in cancer-free and cancer-high-risk women is expected to advance our understanding of the earliest stages of fallopian epithelial neoplasia. Citation Format: Josh Brand, Marcela Harro, Forough Abbasi, Xianzhi Lin, Matthew Siedhoff, Li Andrew, Bobbie J. Rimel, Fabiola Medeiros, Kate Lawrenson, Huy Q. Dinh. Immune landscapes and interactions in human fallopian tubes and their implications for early high-grade serous ovarian cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5148.

Abstract 2117: IFN-γ signaling in myeloid cells regulates pancreatic cancer growth and progression

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by low survival, early metastasis, and rapidly emerging resistance to therapy. Interferon gamma (IFN-γ) signaling pathway is one of the key regulators of the tumor microenvironment in numerous cancer settings and its possible key role in myeloid cells is suggested. Here we investigated the IFN-y signaling in myeloid cells during PDAC development, progression, and metastasis using mice with conditional ablation of IFNgR2 in myeloid cells (IFNgR2-Delta-Mye). We performed an orthotopical injection of cells derived from conditional murine pancreatic model (Pdx1Cre-Kras-P53, or “KPC” cells) into IFNgR2-LysMCre (IFNgR2-Delta-Mye) mice. Ablation of IFN-γ signaling in myeloid cells led to a higher tumor burden compared to controls. Subsequent RNA sequence analysis demonstrated that IFN-γR2 deficiency in myeloid cells resulted in increased TGFβ1 gene expression as well as changes in metabolic and growth factor pathways in macrophages isolated from tumor tissue. Immunofluorescent analysis demonstrated that IFN-γR2 deletion in myeloid cells led to changes in cancer cell differentiation, resulting in a loss of characteristic epithelial histological pattern and shifting it towards more aggressive phenotype, possible via TGFβ1 dependent mechanism. Using murine model of liver metastasis, we found that loss of IFN-γR2 in myeloid cells leads to increased metastatic outgrowth of PDAC KPC cells. This effect was partially dependent on the gut microbiota, as shown by “separated and co-housed mice” experiments. Deficiency of IFN-γR2 in myeloid cells resulted in increased recruitment and infiltration of monocytes in normal and tumor/metastatic liver tissues. Our data identifies myeloid cell type specific IFN-γ signaling pathway as an important regulator of pancreatic cancer progression and metastasis, that can be potentially exploited as a novel immunooncology target. Citation Format: Elena Ivleva, Natalia Andreeva, Sergei Grivennikov. IFN-γ signaling in myeloid cells regulates pancreatic cancer growth and progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2117.

Unravelling the sex-specific diversity and functions of adrenal gland macrophages.

SummaryDespite the ubiquitous function of macrophages across the body, the diversity, origin, and function of adrenal gland macrophages remain largely unknown. We define the heterogeneity of adrenal gland immune cells using single-cell RNA sequencing and use genetic models to explore the developmental mechanisms yielding macrophage diversity. We define populations of monocyte-derived and embryonically seeded adrenal gland macrophages and identify a female-specific subset with low major histocompatibility complex (MHC) class II expression. In adulthood, monocyte recruitment dominates adrenal gland macrophage maintenance in female mice. Adrenal gland macrophage sub-tissular distribution follows a sex-dimorphic pattern, with MHC class IIlow macrophages located at the cortico-medullary junction. Macrophage sex dimorphism depends on the presence of the cortical X-zone. Adrenal gland macrophage depletion results in altered tissue homeostasis, modulated lipid metabolism, and decreased local aldosterone production during stress exposure. Overall, these data reveal the heterogeneity of adrenal gland macrophages and point toward sex-restricted distribution and functions of these cells.

Stress Keratin 17 Expression in Head and Neck Cancer Contributes to Immune Evasion and Resistance to Immune-Checkpoint Blockade.

We investigated whether in human head and neck squamous cell carcinoma (HNSCC) high levels of expression of stress keratin 17 (K17) are associated with poor survival and resistance to immunotherapy. We investigated the role of K17 in regulating both the tumor microenvironment and immune responsiveness of HNSCC using a syngeneic mouse HNSCC model, MOC2. MOC2 gives rise to immunologically cold tumors that are resistant to immune-checkpoint blockade (ICB). We engineered multiple, independent K17 knockout (KO) MOC2 cell lines and monitored their growth and response to ICB. We also measured K17 expression in human HNSCC of patients undergoing ICB. MOC2 tumors were found to express K17 at high levels. When knocked out for K17 (K17KO MOC2), these cells formed tumors that grew slowly or spontaneously regressed and had a high CD8+ T-cell infiltrate in immunocompetent syngeneic C57BL/6 mice compared with parental MOC2 tumors. This phenotype was reversed when we depleted mice for T cells. Whereas parental MOC2 tumors were resistant to ICB treatment, K17KO MOC2 tumors that did not spontaneously regress were eliminated upon ICB treatment. In a cohort of patients with HNSCC receiving pembrolizumab, high K17 expression correlated with poor response. Single-cell RNA-sequencing analysis revealed broad differences in the immune landscape of K17KO MOC2 tumors compared with parental MOC2 tumors, including differences in multiple lymphoid and myeloid cell types. We demonstrate that K17 expression in HNSCC contributes to immune evasion and resistance to ICB treatment by broadly altering immune landscapes of tumors.

TREM-2 mediates dendritic cell-induced NO to suppress Th17 activation and ameliorate chronic kidney diseases.

Chronic kidney disease (CKD) is a global public health issue. CKD is caused by the infiltration of various myeloid cell types into renal tissue, resulting in renal fibrosis and tubular atrophy. Unilateral ureteral obstruction (UUO) surgery in mice is a model of CKD and characterized by high expression of the anti-inflammatory receptor, Triggering receptor expressed on myeloid cells 2 (TREM-2), on myeloid cells in affected kidneys. Here, we show that iNOS expression and nitric oxide (NO) induction were decreased in Trem-2-/- bone marrow-derived DCs (BMDCs) and in Trem-2 knockdown DC2.4 cells stimulated in vitro with LPS. The nitration of RORγt was decreased in T cells co-cultured with LPS-stimulated Trem-2-/- BMDCs, enhancing IL-17 production. UUO-treated Trem-2-/- mice displayed aggravated renal pathogenesis accompanied by greater neutrophil infiltration and enhanced Th17 cells differentiation, phenotypes that could be rescued by the administration of L-arginine (a biological precursor of NO). Our data identify a key mechanism underlying TREM-2-mediated NO to modulate the cellular crosstalk between dendritic cells, Th17, and neutrophils. Furthermore, we also reveal TREM-2 as a potential novel target for the development of anti-inflammatory drugs in CKD treatment. KEY MESSAGES: The expression of TREM-2 is increased in nephritis TREM-2+ DCs maintain NO production to negatively regulate Th17 differentiation The severe pathologies of nephritis can be rescued by L-arginine supplementation.

Abstract 412: Transcriptomic Analysis Reveals That Lipid Loading Of Distinct Intimal Myeloid Cell Subpopulations Precedes Inflammation In Early Atherogenesis

Hypercholesterolemia (HC) is a key risk factor of atherosclerosis, a chronic inflammatory disease that causes myocardial infarction and stroke. Although all regions of arteries are exposed to HC, atherosclerosis develops in discrete regions, such as the lesser curvature (LC) of the mouse aortic arch. Dietary HC in Ldlr -/- mice induces intimal myeloid cells to develop into foam cells, constituting nascent lesions. The purpose of this study is to characterize the transcriptomic changes occurring in the aortic intima during the earliest stages of atherogenesis, and correlate them to cellular responses. Using en face enzymatic digestion and intimal cell microisolation, transcriptomic analysis was performed on the LC. Intimal cells were isolated from the LC of the ascending aortic arch of Ldlr -/- mice at 0, 5, and 14 days of CRD feeding. Bulk RNA-seq and RT-qPCR found that genes associated with lipid-loaded macrophages (e.g., Abcg1, Lgals3 ) were progressively elevated at 5 and 14 days of CRD. Atherogenesis-associated inflammatory transcripts and pathways, such as leukocyte transendothelial migration, cell adhesion, and cytokine/chemokine signalling were significantly elevated after 14d of CRD, but not detected at 5d. Single cell transcriptomic analysis of the mouse aortic arch intima of Ldlr -/- mice revealed multiple sub-populations of myeloid, endothelial, and other cell types. A shift in the C1qb + , Mmp12 + myeloid subpopulations was observed as the duration of cholesterol feeding increased - with expansion of a macrophage population rich in lipid-responsive transcripts. This finding is consistent with an increase in macrophage number and the presence of Nile Red + CD68 + foam cells observed by immunoconfocal microscopy at 5 days of CRD. However, a robust inflammatory signature was not detected in this macrophage cluster. Interestingly, an inflammatory signature similar to that reported in early atherogenesis was identified in a distinct Ccr2 + myeloid population with no signature of lipid loading. This suggests that the inflammation associated with atherogenesis may be a result of intercellular crosstalk between distinct myeloid subpopulations within the intima and may not originate directly from lipid loaded macrophages.

Specialized interferon action in COVID-19

The impacts of interferon (IFN) signaling on COVID-19 pathology are multiple, with both protective and harmful effects being documented. We report here a multiomics investigation of systemic IFN signaling in hospitalized COVID-19 patients, defining the multiomics biosignatures associated with varying levels of 12 different type I, II, and III IFNs. The antiviral transcriptional response in circulating immune cells is strongly associated with a specific subset of IFNs, most prominently IFNA2 and IFNG. In contrast, proteomics signatures indicative of endothelial damage and platelet activation associate with high levels of IFNB1 and IFNA6. Seroconversion and time since hospitalization associate with a significant decrease in a specific subset of IFNs. Additionally, differential IFN subtype production is linked to distinct constellations of circulating myeloid and lymphoid immune cell types. Each IFN has a unique metabolic signature, with IFNG being the most associated with activation of the kynurenine pathway. IFNs also show differential relationships with clinical markers of poor prognosis and disease severity. For example, whereas IFNG has the strongest association with C-reactive protein and other immune markers of poor prognosis, IFNB1 associates with increased neutrophil to lymphocyte ratio, a marker of late severe disease. Altogether, these results reveal specialized IFN action in COVID-19, with potential diagnostic and therapeutic implications.

Entinostat Decreases Immune Suppression to Promote Antitumor Responses in a HER2+ Breast Tumor Microenvironment.

Therapeutic combinations to alter immunosuppressive, solid tumor microenvironments (TME), such as in breast cancer, are essential to improve responses to immune checkpoint inhibitors (ICI). Entinostat, an oral histone deacetylase inhibitor, has been shown to improve responses to ICIs in various tumor models with immunosuppressive TMEs. The precise and comprehensive alterations to the TME induced by entinostat remain unknown. Here, we employed single-cell RNA sequencing on HER2-overexpressing breast tumors from mice treated with entinostat and ICIs to fully characterize changes across multiple cell types within the TME. This analysis demonstrates that treatment with entinostat induced a shift from a protumor to an antitumor TME signature, characterized predominantly by changes in myeloid cells. We confirmed myeloid-derived suppressor cells (MDSC) within entinostat-treated tumors associated with a less suppressive granulocytic (G)-MDSC phenotype and exhibited altered suppressive signaling that involved the NFκB and STAT3 pathways. In addition to MDSCs, tumor-associated macrophages were epigenetically reprogrammed from a protumor M2-like phenotype toward an antitumor M1-like phenotype, which may be contributing to a more sensitized TME. Overall, our in-depth analysis suggests that entinostat-induced changes on multiple myeloid cell types reduce immunosuppression and increase antitumor responses, which, in turn, improve sensitivity to ICIs. Sensitization of the TME by entinostat could ultimately broaden the population of patients with breast cancer who could benefit from ICIs.

Challenges and Opportunities for Immunotherapeutic Intervention against Myeloid Immunosuppression in Glioblastoma.

Glioblastoma multiforme (GBM), the most common and deadly brain cancer, exemplifies the paradigm that cancers grow with help from an immunosuppressive tumor microenvironment (TME). In general, TME includes a large contribution from various myeloid lineage-derived cell types, including (in the brain) altered pathogenic microglia as well as monocyte-macrophages (Macs), myeloid-derived suppressor cells (MDSC) and dendritic cell (DC) populations. Each can have protective roles, but has, by definition, been coopted by the tumor in patients with progressive disease. However, evidence demonstrates that myeloid immunosuppressive activities can be reversed in different ways, leading to enthusiasm for this therapeutic approach, both alone and in combination with potentially synergistic immunotherapeutic and other strategies. Here, we review the current understanding of myeloid cell immunosuppression of anti-tumor responses as well as potential targets, challenges, and developing means to reverse immunosuppression with various therapeutics and their status. Targets include myeloid cell colony stimulating factors (CSFs), insulin-like growth factor 1 (IGF1), several cytokines and chemokines, as well as CD40 activation and COX2 inhibition. Approaches in clinical development include antibodies, antisense RNA-based drugs, cell-based combinations, polarizing cytokines, and utilizing Macs as a platform for Chimeric Antigen Receptors (CAR)-based tumor targeting, like with CAR-T cells. To date, promising clinical results have been reported with several of these approaches.

Feasibility of administering human pancreatic cancer chemotherapy in a spontaneous pancreatic cancer mouse model

BackgroundBoth modified FOLFIRINOX (mFFX) and gemcitabine/nab-paclitaxel chemotherapy regimens have been shown to improve clinical outcomes in patients with pancreatic cancer, and are often used interchangeably as the standard of care. Preclinical studies often do not use these regimens, since administering these multiagent approaches can be difficult. In this study, we assessed the feasibility of administering these two chemotherapy regimens in spontaneous pancreatic tumors using KPC mice with the ultimate goal of advancing preclinical studies.MethodsKPC mice were created by breeding KrasLSL−G12D/+ to Trp53fl/fl;Ptf1αCre/+, resulting in KrasLSL−G12D/+;p53fl/+;Ptf1αCre/+ mice. At 14 weeks of age, mice were palpated for spontaneous tumor growth that was verified using ultrasounds. Mice with tumors under 15 mm in diameter were used. The mice were assigned to one of seven treatment regimens: 1 cycle of mFFX (FFX X1), 2 cycles of mFFX (FFX X2), 1 cycle of mFFXwith 40 Gy SBRT (FFX SBRT), 1 cycle of gemcitabine/nab-paclitaxel (GEM/AB X1), 2 cycles of gemcitabine/nab-paclitaxel (GEM/AB X2), 2 cycles of gemcitabine/nab-paclitaxel with 40 Gy SBRT (GEM/AB SBRT), or saline only (control).ResultsIn total, 92 mice were included. The median OS in the FFX X2 group was slightly longer that the median OS in the FFX X1 group (15 days vs 11 days, P = 0.003). Mice in the GEM/AB X2 group had longer OS when compared to mice in the GEM/AB X1 group (33.5 vs 13 days, P = 0.001). Mice treated with chemotherapy survived longer than untreated control animals (median OS: 6.5 days, P < 0.001). Moreover, in mice treated with chemotherapy, mice that received 2 cycles of GEM/AB X2 had the longest survival, while the FFX X1 group had the poorest OS (P < 0.001). The addition of chemotherapy was associated with reduced number of myeloid and lymphoid cell types, except for CD4 + cells whose levels were largely unaltered only in tumors treated with gemcitabine/nab-paclitaxel. Lastly, chemotherapy followed by consolidative SBRT trended towards increased local control and survival.ConclusionsWe demonstrate the utility and feasibility of clinically relevant mFOLFIRINOX and gemcitabine/nab-paclitaxel in preclinical models of pancreatic cancer.

Attenuation of the BTLA/HVEM Regulatory Network in the Circulation in Primary Sjögren's Syndrome.

Primary Sjögren’s syndrome (SjS) is an inflammatory autoimmune disorder which targets the lacrimal and salivary glands, resulting in glandular dysfunction. Currently, the immune drivers of SjS remain poorly understood and peripheral biomarkers of disease are lacking. The present study therefore sought to investigate the immune cell constituents of the SjS peripheral blood, and to assess the role of the BTLA/HVEM/CD160 co-stimulatory network by characterizing expression within the periphery. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood of n = 10 patients with SjS and n = 10 age- and sex-matched healthy control donors. Cells were divided and stained with three panels of antibodies, allowing assessment of T, B, and myeloid cell subsets, and measurement of BTLA, HVEM, and CD160 surface expression by flow cytometry. We identified distinct alterations in proportions of peripheral T, B, and myeloid cell types in SjS compared with healthy controls. Expression of BTLA/CD160/HVEM and frequency of BTLA/CD160/HVEM-expressing cells were significantly altered in peripheral SjS lymphocytes. The proportion of T cells co-expressing BTLA/HVEM and CD160/HVEM were significantly reduced in SjS. We found decreased BTLA and HVEM levels on peripheral B and T cells of SjS patients, and decreased BTLA/HVEM and CD160/HVEM co-expression, demonstrating dysregulation of the BTLA/HVEM axis in the peripheral blood of SjS patients. These results indicate the potential of targeting the BTLA-HVEM axis for the treatment of SjS.

Expansion of Fcγ Receptor IIIa-Positive Macrophages, Ficolin 1-Positive Monocyte-Derived Dendritic Cells, and Plasmacytoid Dendritic Cells Associated With Severe Skin Disease in Systemic Sclerosis.

In this study, we sought a comprehensive understanding of myeloid cell types driving fibrosis in diffuse cutaneous systemic sclerosis (dcSSc) skin. We analyzed the transcriptomes of 2,465 myeloid cells from skin biopsy specimens from 12 dcSSc patients and 10 healthy control subjects using single-cell RNA sequencing. Monocyte-derived dendritic cells (mo-DCs) were assessed using immunohistochemical staining and immunofluorescence analyses targeting ficolin-1 (FCN-1). A t-distributed stochastic neighbor embedding analysis of single-cell transcriptome data revealed 12 myeloid cell clusters, 9 of which paralleled previously described healthy control macrophage/DC clusters, and 3 of which were dcSSc-specific myeloid cell clusters. One SSc-associated macrophage cluster, highly expressing Fcγ receptor IIIA, was suggested on pseudotime analysis to be derived from normal CCR1+ and MARCO+ macrophages. A second SSc-associated myeloid population highly expressed monocyte markers FCN-1, epiregulin, S100A8, and S100A9, but was closely related to type 2 conventional DCs on pseudotime analysis and identified as mo-DCs. Mo-DCs were associated with more severe skin disease. Proliferating macrophages and plasmacytoid DCs were detected almost exclusively in dcSSc skin, the latter clustering with B cells and apparently derived from lymphoid progenitors. Transcriptional signatures in these and other myeloid populations indicate innate immune system activation, possibly through Toll-like receptors and highly up-regulated chemokines. However, the appearance and activation of myeloid cells varies between patients, indicating potential differences in the underlying pathogenesis and/or temporal disease activity in dcSSc.

Myeloid Cell-Derived Oxidized Lipids and Regulation of the Tumor Microenvironment.

Immunosuppressive myeloid cells play a major role in cancer by negatively regulating immune responses, promoting tumor progression, and limiting the efficacy of cancer immunotherapy. Immunosuppression is mediated by various mechanisms dependent upon the type of myeloid cell involved. In recent years, a more universal mechanism of immunosuppressive activity of myeloid cells has emerged: Generation of oxidized lipids. Oxidized lipids accumulate in all types of myeloid cells and are often transferred between cells. In this review, we discuss mechanisms involved in the generation and biological role of myeloid cell-derived oxidized lipids in cancer.

Immune Regulatory Functions of IgG in the Ontogeny of Human Natural Regulatory T Cells

The heavy constant region of IgG (Fc) is highly immunogenic for human natural regulatory T cells (nTreg). Mature IgG+ B cells prime Fc-specific Treg via recycling of surface immunoglobulin with an antigen-processing pathway that is very efficient in presenting immunodominant Fc peptides to Treg. Some of these peptides are pan-HLA binders, explaining the presence of Fc-specific Treg in circulation in healthy pediatric and adult subjects. Following IgG+ B cell priming, further Treg expansion occurs with the presentation of Fc peptides following IgG uptake and processing by CD14+ myeloid dendritic cells type 2 (cDC2) and CD4+ immunoglobulin-like transcript 4 (ILT-4+) tolerogenic DC that secretes IL-10 when stimulated by the Fc that enters cells prevalently via Fcg receptor II. Fc-specific Treg are important in regulating naive T cell differentiation and account for a key mechanism of success for intravenous immunoglobulin therapy (IVIG) in several inflammatory conditions, including Kawasaki disease (KD) a pediatric acute vasculitis of the coronary arteries.

A Single-Cell Transcriptome Profiling of Anterior Kidney Leukocytes From Nile Tilapia (Oreochromis niloticus).

Teleost fish anterior kidney (AK) is an important hematopoietic organ with multifarious immune cells, which have immune functions comparable to mammalian bone marrow. Myeloid and lymphoid cells locate in the AK, but the lack of useful specific gene markers and antibody-based reagents for the cell subsets makes the identification of the different cell types difficult. Single-cell transcriptome sequencing enables single-cell capture and individual library construction, making the study on the immune cell heterogeneity of teleost fish AK possible. In this study, we examined the transcriptional patterns of 11,388 AK leukocytes using 10× Genomics single-cell RNA sequencing (scRNA-seq). A total of 22 clusters corresponding to five distinct immune cell subsets were identified, which included B cells, T cells, granulocytes, macrophages, and dendritic cells (DCs). However, the subsets of myeloid cells (granulocytes, macrophages, and DCs) were not identified in more detail according to the known specific markers, even though significant differences existed among the clusters. Thereafter, we highlighted the B-cell subsets and identified them as pro/pre B cells, immature/mature B cells, activated B/plasmablasts, or plasma cells based on the different expressions of the transcription factors (TFs) and cytokines. Clustering of the differentially modulated genes by pseudo-temporal trajectory analysis of the B-cell subsets showed the distinct kinetics of the responses of TFs to cell conversion. Moreover, we classified the T cells and discovered that CD3+CD4−CD8−, CD3+CD4+CD8+, CD4+CD8−, and CD4−CD8+ T cells existed in AK, but neither CD4+CD8− nor CD4−CD8+ T cells can be further classified into subsets based on the known TFs and cytokines. Pseudotemporal analysis demonstrated that CD4+CD8− and CD4−CD8+ T cells belonged to different states with various TFs that might control their differentiation. The data obtained above provide a valuable and detailed resource for uncovering the leukocyte subsets in Nile tilapia AK, as well as more potential markers for identifying the myeloid and lymphoid cell types.

Regulation of Tim-3 function by binding to phosphatidylserine.

Tim-3 is a transmembrane protein that is highly expressed on subsets of chronically stimulated CD4+ helper and CD8+ cytotoxic T cells, with more transient expression during acute activation and infection. Tim-3 is also constitutively expressed by multiple types of myeloid cells. Like other TIM family members, Tim-3 can bind to phosphatidylserine displayed by apoptotic cells, and this interaction has been shown to mediate uptake of such cells by dendritic cells and cross-presentation of antigens to CD8+ T cells. In contrast, how the recognition of PS by Tim-3 might regulate the function of Tim-3+ T cells is not known. In their recent paper, Lemmon and colleagues demonstrate for the first time that recognition of PS by Tim-3 leads to enhanced T cell activation.