Schlafen 4-expressing myeloid-derived suppressor cells are induced during murine gastric metaplasia

MDSC checkpoint blockade therapy: a new breakthrough point overcoming immunosuppression in cancer immunotherapy

Despite the success of cancer immunotherapy in treating hematologic malignancies, their efficacy in solid tumors remains limited due to the immunosuppressive tumor microenvironment (TME), which is mainly formed by myeloid-derived suppressor cells (MDSCs). MDSCs not only exert potent immunosuppressive effects that hinder the success of immune checkpoint inhibitors (ICIs) and adaptive cellular therapies, but they also promote tumor advancement through non-immunological pathways, including promoting angiogenesis, driving epithelial-mesenchymal transition (EMT), and contributing to the establishment of pre-metastatic environments. While targeting MDSCs alone or in combination with conventional therapies has shown limited success, emerging evidence suggests that MDSC checkpoint blockade in combination with other immunotherapies holds great promise in overcoming both immunological and non-immunological barriers. In this review, we discussed the dual roles of MDSCs, with a particular emphasis on their underexplored checkpoints blockade strategies. We discussed the rationale behind combination strategies, their potential advantages in overcoming MDSC-mediated immunosuppression, and the challenges associated with their development. Additionally, we highlight future research directions aimed at optimizing combination immunotherapies to enhance cancer therapeutic effectiveness, particularly in solid tumor therapies where MDSCs are highly prevalent.

ATP6V1C1, associated with the tumor microenvironment and mTORC1 signaling pathway, is a potential diagnostic, prognostic, and therapeutic biomarker for hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a global health challenge with high mortality. ATP6V1C1, one of the subunit genes of vacuolar adenosine triphosphatase (V-ATPase), is a potential oncogene. However, its role in HCC remains unclear.

MATERIALS AND METHODS

Differential analysis of mRNA and microRNA (miRNA), combined with machine learning, identified ATP6V1C1 as a potential biomarker for HCC. The expression and prognostic role of ATP6V1C1 in HCC were evaluated. Additionally, we explored the distribution of ATP6V1C1 in HCC tumor microenvironment (TME) at single-cell and spatial transcriptome levels. Furthermore, the association between ATP6V1C1 and malignant biological features, TME characteristics, and therapy response in HCC was investigated. Finally, in vitro experiments validated the effects of ATP6V1C1 on the malignant phenotype of HCC.

RESULTS

ATP6V1C1 had higher expression in HCC tissues compared to paired normal tissues. Upregulated ATP6V1C1 was associated with poor HCC prognosis. ATP6V1C1 was primarily expressed in malignant cells and the tumor region in HCC TME. A positive correlation was observed between ATP6V1C1 expression and the activation of cancer-related pathways. The high ATP6V1C1 expression group exhibited increased pro-tumorigenic immune infiltration, inhibited anti-tumor immune activity, and high tumor proliferation rate. HCC patients of low ATP6V1C1 expression group had more clinical response to anti-tumor therapies. Knockdown of ATP6V1C1 impaired the proliferation, migration, and invasion of HCC cells by downregulating the mTORC1 signaling pathway.

CONCLUSION

ATP6V1C1 multifacetedly contributes to the oncogenesis and progression of HCC and is a promising diagnostic and prognostic biomarker with predictive value on therapy response.

LMD: Cluster-Independent Multiscale Marker Identification in Single-cell RNA-seq Data

Identifying accurate cell markers in single-cell RNA-seq data is crucial for understanding cellular diversity and function. Localized Marker Detector (LMD) is a novel tool to identify "localized genes" - genes exclusively expressed in groups of highly similar cells - thereby characterizing cellular diversity in a multi-resolution and fine-grained manner. LMD constructs a cell-cell affinity graph, diffuses the gene expression value across the cell graph, and assigns a score to each gene based on its diffusion dynamics. LMD's candidate markers can be grouped into functional gene modules, which accurately reflect cell types, subtypes, and other sources of variation such as cell cycle status. We apply LMD to mouse bone marrow and hair follicle dermal condensate datasets, where LMD facilitates cross-sample comparisons, identifying shared and sample-specific gene signatures and novel cell populations without requiring batch effect correction or integration methods. Furthermore, we assessed the performance of LMD across nine single-cell RNA sequencing datasets, compared it with six other methods aimed at achieving similar objectives, and found that LMD outperforms the other methods evaluated.

A CXCR4 partial agonist improves immunotherapy by targeting polymorphonuclear myeloid-derived suppressor cells and cancer-driven granulopoiesis

Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are pathologically activated neutrophils that potently impair immunotherapy responses. The chemokine receptor CXCR4, a central regulator of hematopoiesis, represents an attractive PMN-MDSC target1. Here, we fused a secreted CXCR4 partial agonist TFF2 to mouse serum albumin (MSA) and demonstrated that TFF2-MSA peptide synergized with anti-PD-1 to induce tumor regression or eradication, inhibited distant metastases, and prolonged survival in multiple gastric cancer (GC) models. Using histidine decarboxylase (Hdc)-GFP transgenic mice to track PMN-MDSC in vivo , we found TFF2-MSA selectively reduced the immunosuppressive Hdc-GFP + CXCR4 hi tumor PMN-MDSCs while preserving proinflammatory neutrophils, thereby boosting CD8 + T cell-mediated anti-tumor response together with anti-PD-1. Furthermore, TFF2-MSA systemically reduced PMN-MDSCs and bone marrow granulopoiesis. In contrast, CXCR4 antagonism plus anti-PD-1 failed to provide a similar therapeutic benefit. In GC patients, expanded PMN-MDSCs containing a prominent CXCR4 + LOX-1 + subset are inversely correlated with the TFF2 level and CD8 + T cells in circulation. Collectively, our studies introduce a strategy of using CXCR4 partial agonism to restore anti-PD-1 sensitivity in GC by targeting PMN-MDSCs and granulopoiesis.

Regulation of metaplasia and dysplasia in the stomach by the stromal microenvironment

Research on the microenvironment associated with gastric carcinogenesis has focused on cancers of the stomach and often underestimates premalignant stages such as metaplasia and dysplasia. Since epithelial interactions with T cells, macrophages, and type 2 innate lymphoid cells (ILC2s) are indispensable for the formation of precancerous lesions in the stomach, understanding the cellular interactions that promote gastric precancer warrants further investigation. Although various types of immune cells have been shown to play important roles in gastric carcinogenesis, it remains unclear how stromal cells such as fibroblasts influence epithelial transformation in the stomach, especially during precancerous stages. Fibroblasts exist as distinct populations across tissues and perform different functions depending on the expression patterns of cell surface markers and secreted factors. In this review, we provide an overview of known microenvironmental components in the stroma with an emphasis on fibroblast subpopulations and their roles during carcinogenesis in tissues including breast, pancreas, and stomach. Additionally, we offer insights into potential targets of tumor-promoting fibroblasts and identify open areas of research related to fibroblast plasticity and the modulation of gastric carcinogenesis.

Momordicine-I Suppresses Head and Neck Cancer Growth by Reprogrammimg Immunosuppressive Effect of the Tumor-Infiltrating Macrophages and B Lymphocytes

Head and neck cancer (HNC) is prevalent worldwide, and treatment options are limited. Momordicine-I (M-I), a natural component from bitter melon, shows antitumor activity against these cancers, but its mechanism of action, especially in the tumor microenvironment (TME), remains unclear. In this study, we establish that M-I reduces HNC tumor growth in two different immunocompetent mouse models using MOC2 and SCC VII cells. We demonstrate that the anticancer activity results from modulating several molecules in the monocyte/macrophage clusters in CD45+ populations in MOC2 tumors by single-cell RNA sequencing. Tumor-associated macrophages (TAM) often pose a barrier to antitumor effects, but following M-I treatment, we observe a significant reduction in the expression of Sfln4, a myeloid cell differentiation factor, and Cxcl3, a neutrophil chemoattractant, in the monocyte/macrophage populations. We further find that the macrophages must be in close contact with the tumor cells to inhibit Sfln4 and Cxcl3, suggesting that these TAMs are impacted by M-I treatment. Coculturing macrophages with tumor cells shows inhibition of Agr1 expression following M-I treatment, which is indicative of switching from M2 to M1 phenotype. Furthermore, the total B-cell population in M-I-treated tumors is significantly lower, whereas spleen cells also show similar results when cocultured with MOC2 cells. M-I treatment also inhibits PD1, PD-L1, and FoxP3 expression in tumors. Collectively, these results uncover the potential mechanism of M-I by modulating immune cells, and this new insight can help to develop M-I as a promising candidate to treat HNCs, either alone or as adjuvant therapy.

A Metabolic Axis of Immune Intractability

Immune cells in the tumor niche robustly influence disease progression. Remarkably, in cancer, developmental pathways are reenacted. Many parallels between immune regulation of embryonic development and immune regulation of tumor progression can be drawn, with evidence clearly supporting an immune-suppressive microenvironment in both situations. In these ecosystems, metabolic and bioenergetic circuits guide and regulate immune cell differentiation, plasticity, and functional properties of suppressive and inflammatory immune subsets. As such, there is an emerging pattern of intersection across the dynamic process of ontogeny and the ever-evolving tumor neighborhood. In this article, we focus on the convergence of immune programming during ontogeny and in the tumor microenvironment. Exemplifying dysregulation of Hedgehog (Hh) activity, a key player during ontogeny, we highlight a critical convergence of these fields and the metabolic axis of the nutrient sensing hexosamine biosynthetic pathway (HBP) that integrates glucose, glutamine, amino acids, acetyl CoA, and uridine-5'-triphosphate (UTP), culminating in the synthesis of UDP-GlcNAc, a metabolite that functions as a metabolic and bioenergetic sensor. We discuss an emerging pattern of immune regulation, orchestrated by O-GlcNAcylation of key transcriptional regulators, spurring suppressive activity of dysfunctional immune cells in the tumor microenvironment.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

The Cxcr2+ subset of the S100a8+ gastric granylocytic myeloid-derived suppressor cell population (G-MDSC) regulates gastric pathology

INTRODUCTION

Gastric myeloid-derived suppressor cells (MDSCs) are a prominent population that expands during gastric pre-neoplastic and neoplastic development in humans and mice. However, the heterogeneity of this population has circumvented the ability to study these cells or understand their functions. Aside from Schlafen-4+ (Slfn-4+) MDSCs in mouse studies, which constitute a subset of this population, limitations exist in characterizing the heterogeneity of the gastric CD11b+Ly6G+ population and targeting its different subsets. Here we identify S100a8 as a pan-specific marker for this population and utilize it to study the role of the S100a8+Cxcr2+ subset.

METHODS

We profiled gastric CD11b+Ly6G+ versus CD11b+Ly6G- myeloid cells by transcriptomic and single-cell RNA sequencing. We identified S100a8 as a pan-specific marker of the gastric granulocytic MDSC (G-MDSC) population, and generated S100a8CreCxcr2flox/flox to study the effects of Cxcr2 knockdown.

RESULTS

Following 6-months of Helicobacter felis infection, gastric CD11b+Ly6G+ G-MDSCs were highly enriched for the expression of S100a8, S100a9, Slfn4, Cxcr2, Irg1, Il1f9, Hcar2, Retnlg, Wfdc21, Trem1, Csf3R, Nlrp3, and Il1b. The expression of these distinct genes following 6mo H. felis infection marked heterogeneous subpopulations, but they all represented a subset of S100a8+ cells. S100a8 was identified as a pan-marker for CD11b+Ly6G+ cells arising in chronic inflammation, but not neutrophils recruited during acute gut infection. 6mo Helicobacter felis-infected S100a8CreCxcr2flox/flox mice exhibited worsened gastric metaplastic pathology than Cxcr2flox/flox mice, which was associated with dysregulated lipid metabolism and peroxidation.

CONCLUSION

S100a8 is a pan-specific marker that can be used to target gastric G-MDSC subpopulations, of which the Cxcr2+ subset regulates gastric immunopathology and associates with the regulation of lipid peroxidation.

The TLR/MyD88 signalling cascade in inflammation and gastric cancer: the immune regulatory network of Helicobacter pylori

Helicobacter pylori-induced chronic gastritis represents a well-established risk factor for gastric cancer (GC). However, the mechanism by which chronic inflammation caused by H. pylori induces the development of GC is unclear. H. pylori can influence host cell signalling pathways to induce gastric disease development and mediate cancer promotion and progression. Toll-like receptors (TLRs), as pattern recognition receptors (PRRs), play a key role in the gastrointestinal innate immune response, and their signalling has been implicated in the pathogenesis of an increasing number of inflammation-associated cancers. The core adapter myeloid differentiation factor-88 (MyD88) is shared by most TLRs and functions primarily in H. pylori-triggered innate immune signalling. MyD88 is envisioned as a potential target for the regulation of immune responses and is involved in the regulation of tumourigenesis in a variety of cancer models. In recent years, the TLR/MyD88 signalling pathway has received increasing attention for its role in regulating innate and adaptive immune responses, inducing inflammatory activation and promoting tumour formation. In addition, TLR/MyD88 signalling can manipulate the expression of infiltrating immune cells and various cytokines in the tumour microenvironment (TME). In this review, we discuss the pathogenetic regulatory mechanisms of the TLR/MyD88 signalling cascade pathway and its downstream molecules in H. pylori infection-induced-associated GC. The focus is to elucidate the immunomolecular mechanisms of pathogen recognition and innate immune system activation of H. pylori in the TME of inflammation-associated GC. Ultimately, this study will provide insight into the mechanism of H. pylori-induced chronic inflammation-induced GC development and provide thoughts for GC prevention and treatment strategies.

Schlafen4+-MDSC in Helicobacter-induced gastric metaplasia reveals role for GTPases

Introduction

MDSCs express SCHLAFEN 4 (SLFN4) in Helicobacter-infected stomachs coincident with spasmolytic polypeptide-expressing metaplasia (SPEM), a precursor of gastric cancer. We aimed to characterize SLFN4+ cell identity and the role of Slfn4 in these cells.

Methods

Single-cell RNA sequencing was performed on immune cells sorted from PBMCs and stomachs prepared from uninfected and 6-month H. felis-infected mice. Knockdown of Slfn4 by siRNA or PDE5/6 inhibition by sildenafil were performed in vitro. Intracellular ATP/GTP levels and GTPase activity of immunoprecipitated Slfn4 complexes were measured using the GTPase-Glo assay kit. The intracellular level of ROS was quantified by the DCF-DA fluorescent staining, and apoptosis was determined by cleaved Caspase-3 and Annexin V expression. Gli1CreERT2 x Slfn4 fl/fl mice were generated and infected with H. felis. Sildenafil was administered twice over 2 weeks by gavaging H. felis infected mice ~4 months after inoculation once SPEM had developed.

Results

Slfn4 was highly induced in both monocytic and granulocytic MDSCs from infected stomachs. Both Slfn4 +-MDSC populations exhibited strong transcriptional signatures for type-I interferon responsive GTPases and exhibited T cell suppressor function. SLFN4-containing protein complexes immunoprecipitated from myeloid cell cultures treated with IFNa exhibited GTPase activity. Knocking down Slfn4 or PDE5/6 inhibition with sildenafil blocked IFNa induction of GTP, SLFN4 and NOS2. Moreover, IFNa induction of Slfn +-MDSC function was inhibited by inducing their reactive oxygen species (ROS) production and apoptosis through protein kinase G activation. Accordingly, in vivo disruption of Slfn4 in Gli1CreERT2 x Slfn4 fl/fl mice or pharmacologic inhibition by sildenafil after Helicobacter infection also suppressed SLFN4 and NOS2, reversed T cell suppression and mitigated SPEM development.

Conclusion

Taken together, SLFN4 regulates the activity of the GTPase pathway in MDSCs and precludes these cells from succumbing to the massive ROS generation when they acquire MDSC function.

Role of spasmolytic polypeptide-expressing metaplasia in gastric mucosal diseases

Spasmolytic polypeptide-expressing metaplasia (SPEM) is a trefoil factor 2-expressing metaplasia in the fundic glands that resembles the fundic metaplasia of deep antral glandular cells and arises mainly from transdifferentiation of mature chief cells as well as mucous neck cells or isthmic stem cells. SPEM participates in the regulation of gastric mucosal injury, including focal and diffuse injury. This review focuses on the origin, models, and regulatory mechanisms of SPEM and on its role in the development of gastric mucosal injury. We hope to provide new prospects for the prevention and treatment of gastric mucosal diseases from the perspective of cell differentiation and transformation.

Construction of an original anoikis-related prognostic model closely related to immune infiltration in gastric cancer

Background: Anoikis is considered as a particular type of programmed cell death, the weakness or resistance of which contributes greatly to the development and progression of most malignant solid tumors. However, the latent impact of anoikis-related genes (ARGs) on gastric cancer (GC) is still ambiguous. Based on these, this study established an anoikis-related prognostic model of GC to identify the prognosis of patients and provide more effective treatment in clinical practice. Methods: First, we extracted four public datasets containing the gene expression and clinicopathological information of GC, which were worked as the training and validating sets, separately. Then, an anoikis-related survival-predicted model of GC was developed via Lasso and COX regression analyses and verified by using the Kaplan-Meier (KM) curve and receiver operating characteristic (ROC) curve analyses. Next, we assigned GC patients to two groups characterized by the risk score calculated and analyzed somatic mutation, functional pathways, and immune infiltration between the different two groups. Finally, a unique nomogram was offered to clinicians to forecast the personal survival probability of GC patients. Results: Based on seven anoikis-related markers screened and identified, a carcinogenic model of risk score was produced. Patients placed in the high-score group suffered significantly worse overall survival (OS) in four cohorts. Additionally, the model revealed a high sensitivity and specificity to prognosticate the prognoses of GC patients [area under the ROC curve (AUC) at 5-year = 0.713; GSE84437, AUC at 5-year = 0.639; GSE15459, AUC at 5-year = 0.672; GSE62254, AUC at 5-year = 0.616]. Apart from the excellent predictive performance, the model was also identified as an independent prediction factor from other clinicopathological characteristics. Combining anoikis-related prognostic model with GC clinical features, we built a more comprehensive nomogram to foresee the likelihood of survival of GC patients in a given year, showing a well-accurate prediction performance. Conclusion: In summary, this study created a new anoikis-related signature for GC, which has potentially provided new critical insights into survival prediction and individualized therapy development.

The interaction of Helicobacter pylori with cancer immunomodulatory stromal cells: New insight into gastric cancer pathogenesis

Gastric cancer is the fourth most common cause of cancer-linked deaths in the world. Gastric tumor cells have biological characteristics such as rapid proliferation, high invasiveness, and drug resistance, which result in recurrence and poor survival. Helicobacter pylori (H. pylori) has been proposed as a first-class carcinogen for gastric cancer according to the 1994 world health organization (WHO) classification. One of the important mechanisms by which H. pylori affects the gastric environment and promotes carcinogenesis is triggering inflammation. H. pylori induces an inflammatory response and a plethora of different signal transduction processes, leading to gastric mucosal disturbance, chronic gastritis, and a multi-step complex pathway that initiates carcinogenesis. It seems undeniable that the interaction between various cell types, including immune cells, gastric epithelium, glands, and stem cells, is vital for the progression and development of carcinogenesis concerning H. pylori. The interactions of H. pylori with surrounding cells play a key role in cancer progression. In this review, we discuss the interplay between H. pylori and tumor-supportive cells, including mesenchymal stem cells (MSCs), cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and myeloid derived-suppressor cells (MDSCs) in gastric cancer. It is hoped that clarifying the specific mechanisms for 'cross-talk' between H. pylori and these cells will provide promising strategies for developing new treatments.

Therapeutic strategies for gastric cancer targeting immune cells: Future directions

Gastric cancer (GC) is a malignancy with a high incidence and mortality, and the emergence of immunotherapy has brought survival benefits to GC patients. Compared with traditional therapy, immunotherapy has the advantages of durable response, long-term survival benefits, and lower toxicity. Therefore, targeted immune cells are the most promising therapeutic strategy in the field of oncology. In this review, we introduce the role and significance of each immune cell in the tumor microenvironment of GC and summarize the current landscape of immunotherapy in GC, which includes immune checkpoint inhibitors, adoptive cell therapy (ACT), dendritic cell (DC) vaccines, reduction of M2 tumor-associated macrophages (M2 TAMs), N2 tumor-associated neutrophils (N2 TANs), myeloid-derived suppressor cells (MDSCs), effector regulatory T cells (eT_regs), and regulatory B cells (B_regs) in the tumor microenvironment and reprogram TAMs and TANs into tumor killer cells. The most widely used immunotherapy strategies are the immune checkpoint inhibitor programmed cell death 1/programmed death-ligand 1 (PD-1/PD-L1) antibody, cytotoxic T lymphocyte–associated protein 4 (CTLA-4) antibody, and chimeric antigen receptor T (CAR-T) in ACT, and these therapeutic strategies have significant anti-tumor efficacy in solid tumors and hematological tumors. Targeting other immune cells provides a new direction for the immunotherapy of GC despite the relatively weak clinical data, which have been confirmed to restore or enhance anti-tumor immune function in preclinical studies and some treatment strategies have entered the clinical trial stage, and it is expected that more and more effective immune cell–based therapeutic methods will be developed and applied.

Schlafen family is a prognostic biomarker and corresponds with immune infiltration in gastric cancer

The Schlafen (SLFN) gene family plays an important role in immune cell differentiation and immune regulation. Previous studies have found that the increased SLFN5 expression in patients with intestinal metaplasia correlates with gastric cancer (GC) progression. However, no investigation has been conducted on the SLFN family in GC. Therefore, we systematically explore the expression and prognostic value of SLFN family members in patients with GC, elucidating their possible biological function and its correlation with tumor immune cells infiltration. TCGA database results indicated that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN13 expression was significantly higher in GC. The UALCAN and KM plotter databases indicated that enhanced the SLFN family expression was associated with lymph node metastasis, tumor stage, and tumor grade and predicted an adverse prognosis. cBioportal database revealed that the SLFN family had a high frequency of genetic alterations in GC (about 12%), including mutations and amplification. The GeneMANIA and STRING databases identified 20 interacting genes and 16 interacting proteins that act as potential targets of the SLFN family. SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 may be implicated in the immunological response, according to Gene Set Enrichment Analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Additionally, Timer and TISIDB databases indicate that SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 are involved in the immune response. Furthermore, Timer, TCGA, and TISIDB databases suggested that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 expression in GC is highly linked with immune cell infiltration levels, immune checkpoint, and the many immune cell marker sets expression. We isolated three samples of peripheral blood mononuclear cell (PBMC) and activated T cells; the results showed the expression of SLFN family members decreased significantly when T cell active. In conclusion, the SLFN family of proteins may act as a prognostic indicator of GC and is associated with immune cell infiltration and immune checkpoint expression in GC. Additionally, it may be involved in tumor immune evasion by regulating T cell activation.

Toll-like Receptor 9 Pathway Mediates Schlafen+-MDSC Polarization During Helicobacter-induced Gastric Metaplasias

BACKGROUND & AIMS

A subset of myeloid-derived suppressor cells (MDSCs) that express murine Schlafen4 (SLFN4) or its human ortholog SLFN12L polarize in the Helicobacter-inflamed stomach coincident with intestinal or spasmolytic polypeptide-expressing metaplasia. We propose that individuals with a more robust response to damage-activated molecular patterns and increased Toll-like receptor 9 (TLR9) expression are predisposed to the neoplastic complications of Helicobacter infection.

METHODS

A mouse or human Transwell co-culture system composed of dendritic cells (DCs), 2-dimensional gastric epithelial monolayers, and Helicobacter were used to dissect the cellular source of interferon-α (IFNα) in the stomach by flow cytometry. Conditioned media from the co-cultures polarized primary myeloid cells. MDSC activity was determined by T-cell suppression assays. In human subjects with intestinal metaplasia or gastric cancer, the rs5743836 TLR9T>C variant was genotyped and linked to TLR9, IFNα, and SLFN12L expression by immunohistochemistry. Nuclear factor-κB binding to the TLR9 C allele was determined by electrophoretic mobility shift assays.

RESULTS

Helicobacter infection induced gastric epithelial and plasmacytoid DC expression of TLR9 and IFNα. Co-culturing primary mouse or human cells with DCs and Helicobacter induced TLR9, IFNα secretion, and SLFN+-MDSC polarization. Neutralizing IFNα in vivo mitigated Helicobacter-induced spasmolytic polypeptide-expressing metaplasia. The TLR9 minor C allele creates a nuclear factor-κB binding site associated with higher levels of TLR9, IFNα, and SLFN12L in Helicobacter-infected stomachs that correlated with a greater incidence of metaplasias and cancer.

CONCLUSIONS

TLR9 plays an essential role in the production of IFNα and polarization of SLFN+ MDSCs on Helicobacter infection. Subjects carrying the rs5743836 TLR9 minor C allele are predisposed to neoplastic complications if chronically infected.

Effects of helicobacter pylori on tumor microenvironment and immunotherapy responses

Helicobacter pylori is closely associated with gastric cancer. During persistent infection, Helicobacter pylori can form a microenvironment in gastric mucosa which facilitates the survival and colony formation of Helicobacter pylori. Tumor stromal cells are involved in this process, including tumor-associated macrophages, mesenchymal stem cells, cancer-associated fibroblasts, and myeloid-derived suppressor cells, and so on. The immune checkpoints are also regulated by Helicobacter pylori infection. Helicobacter pylori virulence factors can also act as immunogens or adjuvants to elicit or enhance immune responses, indicating their potential applications in vaccine development and tumor immunotherapy. This review highlights the effects of Helicobacter pylori on the immune microenvironment and its potential roles in tumor immunotherapy responses.

The immune microenvironment in gastric adenocarcinoma

Like most solid tumours, the microenvironment of epithelial-derived gastric adenocarcinoma (GAC) consists of a variety of stromal cell types, including fibroblasts, and neuronal, endothelial and immune cells. In this article, we review the role of the immune microenvironment in the progression of chronic inflammation to GAC, primarily the immune microenvironment driven by the gram-negative bacterial species Helicobacter pylori. The infection-driven nature of most GACs has renewed awareness of the immune microenvironment and its effect on tumour development and progression. About 75-90% of GACs are associated with prior H. pylori infection and 5-10% with Epstein-Barr virus infection. Although 50% of the world's population is infected with H. pylori, only 1-3% will progress to GAC, with progression the result of a combination of the H. pylori strain, host susceptibility and composition of the chronic inflammatory response. Other environmental risk factors include exposure to a high-salt diet and nitrates. Genetically, chromosome instability occurs in ~50% of GACs and 21% of GACs are microsatellite instability-high tumours. Here, we review the timeline and pathogenesis of the events triggered by H. pylori that can create an immunosuppressive microenvironment by modulating the host's innate and adaptive immune responses, and subsequently favour GAC development.

Myeloid-Derived Suppressor Cells: The Expanding World of Helminth Modulation of the Immune System

Infection with helminths or parasitic worms are highly prevalent worldwide especially in developing regions. Helminths cause chronic infections that are associated with suppression of immune responses to unrelated pathogens, vaccines, and by-stander antigens responsible for dysregulated immune responses as occurs in diseases such as allergies. Helminths use multiple mechanisms to modulate the immune system to evade the highly polarized type 2 immune response required to expel adult worms and for immunity to reinfection. Anthelmintic drugs are efficient in reducing adult worm burdens in helminth-infected individuals, but resistance to these drugs is rapidly increasing and vaccines against these pathogens are not available. Emerging evidence indicate that helminths induce myeloid-derived suppressor cells (MDSC), originally described in tumor-bearing mice and cancer patients. MDSC are a heterogenous population of immature cells that consist of two distinct sub-populations, polymorphonuclear (PMN)-MDSC and monocytic (M)-MDSC based on morphology and phenotype. MDSC suppress the function of T cells and other innate and adaptive immune cells including NK cells and B cells. During cancer or infection with bacteria or viruses, there is marked expansion of MDSC. Furthermore, the frequencies of MDSC correlate inversely with the prognosis and survival of tumor-bearing hosts as well as bacterial and viral burdens, persistence, and outcome in infected hosts. Currently, there is a paucity of data on MDSC and helminth infections. Here, we provide a survey of the evidence accumulated so far that overall support a role for MDSC in modulating immune responses during helminth infections. We review data from studies in various helminths, including those that infect humans. Finally, we summarize the progress to date in understanding the role of MDSC in helminth infections and briefly discuss potential host-directed strategies to target MDSC-mediated suppression of immune responses to helminths in favor of development of immunity to eliminate adult worms and possibly induce protection against reinfection.

Helicobacter pylori infection induces stem cell-like properties in Correa cascade of gastric cancer

Gastric cancer (GC) is the fourth leading cause of cancer-related death. Its poor prognosis is attributed to unclear pathogenesis. Currently, the most widely accepted model for elucidating the mechanism of GC is the Correa cascade, which covers several histological lesions of the gastric mucosa. GC stem cells (CSCs) are crucial for oncogenesis in the Correa cascade and GC progression. As Helicobacter pylori (H. pylori) is the etiological factor in the Correa cascade, growing evidence suggests that enhancement of gastric stem cell-like properties and increase in CSCs correlate with H. pylori infection. In this paper, we review recent studies that present pathogenic mechanisms by which H. pylori induces gastric stem cell-like properties and CSCs, which may supplement the existing Correa model of GC. First, the dysfunction of developmental signaling pathways associated with H. pylori infection leads to the enhancement of gastric stemness. Second, H. pylori infection promotes alteration of the gastric mucosal microenvironment. In addition, epithelial-mesenchymal transition (EMT) may contribute to H. pylori-induced gastric stemness. Taken together, understanding these pathogeneses will provide potential therapeutic targets for the treatment of CSCs and malignant GC in H. pylori induced-Correa cascade of GC.

Regulation of the double-stranded RNA response through ADAR1 licenses metaplastic reprogramming in gastric epithelium

Cells recognize both foreign and host-derived double-stranded RNA (dsRNA) via a signaling pathway that is usually studied in the context of viral infection. It has become increasingly clear that the sensing and handling of endogenous dsRNA is also critical for cellular differentiation and development. The adenosine RNA deaminase, ADAR1, has been implicated as a central regulator of the dsRNA response, but how regulation of the dsRNA response might mediate cell fate during injury and whether such signaling is cell intrinsic remain unclear. Here, we show that the ADAR1-mediated response to dsRNA was dramatically induced in 2 distinct injury models of gastric metaplasia. Mouse organoid and in vivo genetic models showed that ADAR1 coordinated a cell-intrinsic, epithelium-autonomous, and interferon signaling–independent dsRNA response. In addition, dsRNA accumulated within a differentiated epithelial population (chief cells) in mouse and human stomachs as these cells reprogrammed to a proliferative, reparative (metaplastic) state. Finally, chief cells required ADAR1 to reenter the cell cycle during metaplasia. Thus, cell-intrinsic ADAR1 signaling is critical for the induction of metaplasia. Because metaplasia increases cancer risk, these findings support roles for ADAR1 and the response to dsRNA in oncogenesis.

Cellular Plasticity, Reprogramming, and Regeneration: Metaplasia in the Stomach and Beyond

The mucosa of the body of the stomach (ie, the gastric corpus) uses 2 overlapping, depth-dependent mechanisms to respond to injury. Superficial injury heals via surface cells with histopathologic changes like foveolar hyperplasia. Deeper, usually chronic, injury/inflammation, most frequently induced by the carcinogenic bacteria Helicobacter pylori, elicits glandular histopathologic alterations, initially manifesting as pyloric (also known as pseudopyloric) metaplasia. In this pyloric metaplasia, corpus glands become antrum (pylorus)-like with loss of acid-secreting parietal cells (atrophic gastritis), expansion of foveolar cells, and reprogramming of digestive enzyme-secreting chief cells into deep antral gland-like mucous cells. After acute parietal cell loss, chief cells can reprogram through an orderly stepwise progression (paligenosis) initiated by interleukin-13-secreting innate lymphoid cells (ILC2s). First, massive lysosomal activation helps mitigate reactive oxygen species and remove damaged organelles. Second, mucus and wound-healing proteins (eg, TFF2) and other transcriptional alterations are induced, at which point the reprogrammed chief cells are recognized as mucus-secreting spasmolytic polypeptide-expressing metaplasia cells. In chronic severe injury, glands with pyloric metaplasia can harbor both actively proliferating spasmolytic polypeptide-expressing metaplasia cells and eventually intestine-like cells. Gastric glands with such lineage confusion (mixed incomplete intestinal metaplasia and proliferative spasmolytic polypeptide-expressing metaplasia) may be at particular risk for progression to dysplasia and cancer. A pyloric-like pattern of metaplasia after injury also occurs in other gastrointestinal organs including esophagus, pancreas, and intestines, and the paligenosis program itself seems broadly conserved across tissues and species. Here we discuss aspects of metaplasia in stomach, incorporating data derived from animal models and work on human cells and tissues in correlation with diagnostic and clinical implications.

Disruption of Her2-Induced PD-L1 Inhibits Tumor Cell Immune Evasion in Patient-Derived Gastric Cancer Organoids

Simple Summary

HER2 may contribute to immune evasion in gastric cancer that is associated with PD-L1 expression. Autologous organoid/immune cell co-cultures serve as an appropriate in vitro model to study the effects of anti-HER2 targeted therapy in combination with anti-PD1 immune checkpoint inhibition and may be used as an ex vivo tool for precision medicine.

Abstract

(1) Background: The expression of programmed death-ligand 1 (PD-L1), which interacts with programmed cell death protein 1 (PD-1) on cytotoxic T lymphocytes (CTLs), enables tumors to escape immunosurveillance. The PD-1/PD-L1 interaction results in the inhibition of CTL proliferation, and effector function, thus promoting tumor cell evasion from immunosurveillance and cancer persistence. Despite 40% of gastric cancer patients exhibiting PD-L1 expression, only a small subset of patients responds to immunotherapy. Human epidermal growth factor receptor2 (HER2) is one of the critical regulators of several solid tumors, including metastatic gastric cancer. Although half of PD-L1-positive gastric tumors co-express HER2, crosstalk between HER2 and PD-1/PD-L1 in gastric cancer remains undetermined. (2) Methods: Human gastric cancer organoids (huTGOs) were generated from biopsied or resected tissues and co-cultured with CTLs and myeloid-derived suppressor cells (MDSCs). Digital Spatial Profiling (DSP) was performed on FFPE tissue microarrays of numerous gastric cancer patients to examine the protein expression of immune markers. (3) Results: Knockdown of HER2 in PD-L1/HER2-positive huTGOs led to a concomitant decrease in PD-L1 expression. Similarly, in huTGOs/immune cell co-cultures, PD-L1 expression decreased in huTGOs and was correlated with an increase in CTL proliferation which enhanced huTGO death. Treatment with Nivolumab exhibited similar effects. However, a combinatorial treatment with Mubritinib and Nivolumab was unable to inhibit HER2 expression in co-cultures containing MDSCs. (4) Conclusions: Our study suggested that co-expression of HER2 and PD-L1 may contribute to tumor cell immune evasion. In addition, autologous organoid/immune cell co-cultures can be exploited to effectively screen responses to a combination of anti-HER2 and immunotherapy to tailor treatment for gastric cancer patients.

A Novel Autophagy-Related lncRNA Prognostic Signature Associated with Immune Microenvironment and Survival Outcomes of Gastric Cancer Patients

Purpose

Autophagy plays a crucial role in the initiation and progression of gastric cancer (GC). However, the role of autophagy-related lncRNAs in GC remains unknown. This study aimed to investigate the prognostic value of the autophagy-related lncRNA signature and its role in the tumor immune microenvironment (TIME) of GC.

Methods

RNA-sequencing (RNA-seq) and clinical data of GC patients were extracted from The Cancer Genome Atlas (TCGA) database. Univariate and multivariate Cox regression analyses were performed to identify the autophagy-related lncRNA prognostic signature which was validated in the test set and entire set. The survival and predictive performance were analyzed based on the Kaplan–Meier and ROC curves. Furthermore, the CIBERSORT algorithm was applied to explore the relationship between this signature and the immune cell infiltration. To elucidate the potential functions of autophagy-related lncRNAs in GC, we constructed the lncRNA-mRNA co-expression network and performed enrichment analysis. Principal component analysis (PCA) and Gene Set Enrichment Analysis (GSEA) were further performed to compare the different statuses between the high-risk and low-risk groups.

Results

We identified 5 autophagy-related lncRNAs (AL355574.1, AC010768.2, AP000695.2, AC087286.2, and HAGLR) to construct a prognostic signature. This signature could be an independent prognostic indicator for GC patients and had a higher prediction efficiency than other clinicopathological parameters. Furthermore, patients in the high-risk score group had a stronger immunosuppressive microenvironment than the low-risk group. The enrichment analysis for mRNAs co-expressed with these lncRNAs indicated that autophagy-related signaling pathways were remarkably enriched. PCA and GSEA further revealed different autophagy and immune statuses in the high- and low-risk groups.

Conclusion

The 5 autophagy-related lncRNA signature has significant clinical implications in prognosis prediction of GC. Meanwhile, our study elucidates the critical role of the autophagy-related lncRNA signature in the TIME of GC.

Slfn4 deficiency improves MAPK-mediated inflammation, oxidative stress, apoptosis and abates atherosclerosis progression in apolipoprotein E-deficient mice

BACKGROUND AND AIMS

Atherosclerosis, a progressive inflammatory disease characterized by elevated inflammation and lipid accumulation in the aortic endothelium, arises in part from the infiltration of inflammatory cells into the vascular wall. However, it is not fully defined how inflammatory cells, especially macrophages, affect the pathogenesis of atherosclerosis. Schlafen4 (Slfn4) mRNA is remarkably upregulated upon ox-LDL stimulation in macrophages. Nonetheless, the role of Slfn4 in foam cell formation remains unclear.

METHODS

To determine whether and how Slfn4 regulates lesion macrophage function during atherosclerosis，we engineered ApoE-/-Slfn4-/- double-deficient mice on an ApoE-/- background and evaluated the deficiency of Slfn4 expression in atherosclerotic lesion formation in vivo.

RESULTS

Our results demonstrate that total absence of SLFN4 and the bone marrow-restricted deletion of Slfn4 in ApoE-/- mice remarkably diminish inflammatory cell numbers within arterial plaques as well as limit development of atherosclerosis in moderate hypercholesterolemia condition. This is linked to a marked reduction in the expression of proinflammatory cytokines, the generation of the reactive oxygen species (ROS) and the apoptosis of cells. Furthermore, the activation of MAPKs and apoptosis signaling pathways is compromised in the absence of Slfn4.

CONCLUSIONS

These findings demonstrate a novel role of Slfn4 in modulating vascular inflammation and atherosclerosis, highlighting a new target for the related diseases.

NOX2-Deficient Neutrophils Facilitate Joint Inflammation Through Higher Pro-Inflammatory and Weakened Immune Checkpoint Activities

Immune-mediated arthritis is an important chronic inflammatory disease of joints causing debilitating morbidity in affected patients. The mechanisms underlying immune-mediated arthritis have been intensively investigated, however the cellular and molecular factors contributing to the joint inflammation in different redox conditions have not been clearly elucidated. Previous research showed that phagocyte-produced reactive oxygen species (ROS) plays an anti-inflammatory role in K/BxN serum-transfer arthritis and NOX2-deficient mice tend to have more severe arthritis. Although many leukocytes play critical roles in the development of immune-mediated arthritis, the role of neutrophils, which are the main producers of ROS in inflammation, is still controversial. We hence assessed the immunomodulatory function of neutrophils from arthritic joints of NOX2-deficient and wild type mice in this study. We found more neutrophils accumulation in NOX2-deficient inflamed joints. RNA-sequencing and quantitative PCR revealed significantly increased expression of acute inflammation genes including IL1b, Cxcl2, Cxcl3, Cxcl10 and Mmp3 in activated neutrophils from the inflamed joints of NOX2-deficient mice. Moreover, gene set enrichment analysis (GSEA) showed enriched gene signatures in type I and II IFN responses, IL-6-JAK-STAT3 signaling pathway and TNF-α signaling pathway via NF-κB in NOX2-deficient neutrophils. In addition, we found that NOX2-deficient neutrophils expressed lower levels of PD-L1 and were less suppressive than WT neutrophils. Moreover, treatment of PD-L1-Fc decreased cytokine expression and ameliorated the severity of inflammatory arthritis. Our results suggest that NOX2-derived ROS is critical for regulating the function and gene expression in arthritic neutrophils. Both the strong pro-inflammatory and weakened anti-inflammatory functions of neutrophils due to abnormal redox regulation may be targets of treatment for immune-mediated arthritis.

Schlafens: Emerging Proteins in Cancer Cell Biology

Schlafens (SLFN) are a family of genes widely expressed in mammals, including humans and rodents. These intriguing proteins play different roles in regulating cell proliferation, cell differentiation, immune cell growth and maturation, and inhibiting viral replication. The emerging evidence is implicating Schlafens in cancer biology and chemosensitivity. Although Schlafens share common domains and a high degree of homology, different Schlafens act differently. In particular, they show specific and occasionally opposing effects in some cancer types. This review will briefly summarize the history, structure, and non-malignant biological functions of Schlafens. The roles of human and mouse Schlafens in different cancer types will then be outlined. Finally, we will discuss the implication of Schlafens in the anti-tumor effect of interferons and the use of Schlafens as predictors of chemosensitivity.

Plasmacytoid dendritic cells-derived IFN-α is involved in Helicobacter pylori infection-induced differentiation of Schlafen 4-expressing myeloid-derived suppressor cells

During chronic infection with Helicobacter pylori, Schlafen 4-expressing myeloid-derived suppressor cells (SLFN4⁺ MDSCs) create a microenvironment favoring intestinal metaplasia and neoplastic transformation. SLFN4 can be induced by IFN-α, which is mainly secreted from plasmacytoid dendritic cells (pDCs). This study tested the hypothesis that Helicobacter pylori infection promotes SLFN4⁺ MDSC differentiation by inducing pDCs to secrete IFN-α. C57BL/6 mice were gavaged with H. pylori and infection lasted 2, 4, or 6 months. The mouse pDCs were isolated from the bone marrow from wild type C57BL/6J mice. The results showed that H. pylori infection increased the number of SLFN4⁺ MDSCs by inducing IFN-α expression in mice. Further mechanistic experiments unraveled that IFN-α induced SLFN4 transcription by binding to the SLFN4 promoter. Furthermore, H. pylori infection stimulated pDCs to secrete IFN-α by activating the TLR9-MyD88-IRF7 pathway. Collectively, Helicobacter pylori infection promotes SLFN4⁺ MDSC differentiation by inducing secretion of IFN-α from pDCs.

Bacterial-Driven Inflammation and Mutant BRAF Expression Combine to Promote Murine Colon Tumorigenesis That Is Sensitive to Immune Checkpoint Therapy

Colorectal cancer is multifaceted, with subtypes defined by genetic, histologic, and immunologic features that are potentially influenced by inflammation, mutagens, and/or microbiota. Colorectal cancers with activating mutations in BRAF are associated with distinct clinical characteristics, although the pathogenesis is not well understood. The Wnt-driven multiple intestinal neoplasia (MinApcΔ716/+) enterotoxigenic Bacteroides fragilis (ETBF) murine model is characterized by IL17-dependent, distal colon adenomas. Herein, we report that the addition of the BRAF V600E mutation to this model results in the emergence of a distinct locus of midcolon tumors. In ETBF-colonized BRAF V600E Lgr5 CreMin (BLM) mice, tumors have similarities to human BRAF V600E tumors, including histology, CpG island DNA hypermethylation, and immune signatures. In comparison to Min ETBF tumors, BLM ETBF tumors are infiltrated by CD8+ T cells, express IFNγ signatures, and are sensitive to anti-PD-L1 treatment. These results provide direct evidence for critical roles of host genetic and microbiota interactions in colorectal cancer pathogenesis and sensitivity to immunotherapy. SIGNIFICANCE: Colorectal cancers with BRAF mutations have distinct characteristics. We present evidence of specific colorectal cancer gene-microbial interactions in which colonization with toxigenic bacteria drives tumorigenesis in BRAF V600E Lgr5 CreMin mice, wherein tumors phenocopy aspects of human BRAF-mutated tumors and have a distinct IFNγ-dominant immune microenvironment uniquely responsive to immune checkpoint blockade.This article is highlighted in the In This Issue feature, p. 1601.

Long-term survivors of murine sepsis are predisposed to enhanced LPS-induced lung injury and proinflammatory immune reprogramming

Millions of people who survive sepsis each year are rehospitalized and die due to late pulmonary complications. To prevent and treat these complications, biomarkers and molecular mediators must be identified. Persistent immune reprogramming in the form of immunoparalysis and impaired host defense is proposed to mediate late pulmonary complications after sepsis, particularly new pulmonary infections. However, immune reprogramming may also involve enhanced/primed responses to secondary stimuli, although their contribution to long-term sepsis complications remains understudied. We hypothesize that enhanced/primed immune responses in the lungs of sepsis survivors are associated with late pulmonary complications. To this end, we developed a murine sepsis model using cecal ligation and puncture (CLP) followed 3 wk later by administration of intranasal lipopolysaccharide to induce inflammatory lung injury. Mice surviving sepsis exhibit enhanced lung injury with increased alveolar permeability, neutrophil recruitment, and enhanced Ly6C^hi monocyte Tnf expression. To determine the mediators of enhanced lung injury, we performed flow cytometry and RNA sequencing of lungs 3 wk after CLP, prior to lipopolysaccharide. Sepsis survivor mice showed expanded Ly6C^hi monocytes populations and increased expression of many inflammatory genes. Of these, S100A8/A9 was also elevated in the circulation of human sepsis survivors for months after sepsis, validating our model and identifying S100A8/A9 as a potential biomarker and therapeutic target for long-term pulmonary complications after sepsis. These data provide new insight into the importance of enhanced/primed immune responses in survivors of sepsis and establish a foundation for additional investigation into the mechanisms mediating this response.

Hedgehog transcriptional effector GLI mediates mTOR-Induced PD-L1 expression in gastric cancer organoids

Tumors evade immune surveillance by expressing Programmed Death-Ligand 1 (PD-L1), subsequently inhibiting CD8⁺ cytotoxic T lymphocyte function. Response of gastric cancer to immunotherapy is relatively low. Our laboratory has reported that Helicobacter pylori-induced PD-L1 expression within the gastric epithelium is mediated by the Hedgehog (Hh) signaling pathway. The PI3K/AKT/mTOR pathway is activated in gastric cancer and may have immunomodulatory potential. We hypothesize that Hh signaling mediates mTOR-induced PD-L1 expression. Patient-derived organoids (PDOs) were generated from gastric biopsies and resected tumor tissues. Autologous organoid/immune cell co-cultures were used to study the immunosuppressive function of MDSCs. NanoString Digital Spatial Profiling (DSP) of immune-related protein markers using FFPE slide-mounted tissues from gastric cancer patients was performed. DSP analysis showed infiltration of immunosuppressive MDSCs expressing Arg1, CD66b, VISTA and IDO1 within cancer tissues. Orthotopic transplantation of patient derived organoids (PDOs) resulted in the engraftment of organoids and the development of histology similar to that observed in the patient's tumor tissue. PDO/immune cell co-cultures revealed that PD-L1-expressing organoids were unresponsive to nivolumab in vitro in the presence of PMN-MDSCs. Depletion of PMN-MDSCs within these co-cultures sensitized the organoids to anti-PD-1/PD-L1-induced cancer cell death. Rapamycin decreased phosphorylated S6K, Gli2 and PD-L1 expression in PDO/immune cell co-cultures. Transcriptional regulation of PD-L1 by GLI1 and GLI2 was blocked by rapamycin. In conclusion, the PDO/immune cell co-cultures may be used to study immunosuppressive MDSC function within the gastric tumor microenvironment. The mTOR signaling pathway mediates GLI-induced PD-L1 expression in gastric cancer.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

The role of myeloid-derived suppressor cells in gastrointestinal cancer

Gastrointestinal (GI) cancer encompasses a range of malignancies that originate in the digestive system, which together represent the most common form of cancer diagnosed worldwide. However, despite numerous advances in both diagnostics and treatment, the incidence and mortality rate of GI cancer are on the rise. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that increase in number under certain pathological conditions, such as infection and inflammation, and this expansion is of particular relevance to cancer. MDSCs are heavily involved in the regulation of the immune system and act to dampen its response to tumors, favoring the escape of tumor cells from immunosurveillance and increasing both metastasis and recurrence. Several recent studies have supported the use of MDSCs as a prognostic and predictive biomarker in patients with cancer, and potentially as a novel treatment target. In the present review, the mechanisms underlying the immunosuppressive functions of MDSCs are described, and recent researches concerning the involvement of MDSCs in the progression, prognosis, and therapies of GI cancer are reviewed. The aim of this work was to present the development of novel treatments targeting MDSCs in GI cancer in the hope of improving outcomes for patients with this condition.

Hedgehog signaling in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment

The Hedgehog (HH) signaling pathway plays important roles in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment (TME). Aberrant HH signaling activation may accelerate the growth of gastrointestinal tumors and lead to tumor immune tolerance and drug resistance. The interaction between HH signaling and the TME is intimately involved in these processes, for example, tumor growth, tumor immune tolerance, inflammation, and drug resistance. Evidence indicates that inflammatory factors in the TME, such as interleukin 6 (IL-6) and interferon-γ (IFN-γ), macrophages, and T cell-dependent immune responses, play a vital role in tumor growth by affecting the HH signaling pathway. Moreover, inhibition of proliferating cancer-associated fibroblasts (CAFs) and inflammatory factors can normalize the TME by suppressing HH signaling. Furthermore, aberrant HH signaling activation is favorable to both the proliferation of cancer stem cells (CSCs) and the drug resistance of gastrointestinal tumors. This review discusses the current understanding of the role and mechanism of aberrant HH signaling activation in gastrointestinal carcinogenesis, the gastrointestinal TME, tumor immune tolerance and drug resistance and highlights the underlying therapeutic opportunities.

Cellular plasticity at the nexus of development and disease

In October 2020, the Keystone Symposia Global Health Series hosted a Keystone eSymposia entitled 'Tissue Plasticity: Preservation and Alteration of Cellular Identity'. The event synthesized groundbreaking research from unusually diverse fields of study, presented in various formats, including live and virtual talks, panel discussions and interactive e-poster sessions. The meeting focused on cell identity changes and plasticity in multiple tissues, species and developmental contexts, both in homeostasis and during injury. Here, we review the key themes of the meeting: (1) cell-extrinsic drivers of plasticity; (2) epigenomic regulation of cell plasticity; and (3) conserved mechanisms governing plasticity. A salient take-home conclusion was that there may be conserved mechanisms used by cells to execute plasticity, with autodegradative activity (autophagy and lysosomes) playing a crucial initial step in diverse organs and organisms.

Myeloid-derived suppressor cells in gastrointestinal cancers: A systemic review

Gastrointestinal (GI) cancers are one of the most common malignancies worldwide, with high rates of morbidity and mortality. Myeloid-derived suppressor cells (MDSCs) are major components of the tumor microenvironment (TME). MDSCs facilitate the transformation of premalignant cells and play roles in tumor growth and metastasis. Moreover, in patients with GI malignancies, MDSCs can lead to the suppression of T cells and natural killer cells. Accordingly, a better understanding of the role and mechanism of action of MDSCs in the TME will aid in the development of novel immune-targeted therapies.

Interleukin-1β Suppresses Gastrin via Primary Cilia and Induces Antral Hyperplasia

BACKGROUND & AIMS

Helicobacter pylori infection in humans typically begins with colonization of the gastric antrum. The initial Th1 response occasionally coincides with an increase in gastrin secretion. Subsequently, the gastritis segues to chronic atrophic gastritis, metaplasia, dysplasia and distal gastric cancer. Despite these well characterized clinical events, the link between inflammatory cytokines and non-cardia gastric cancer remains difficult to study in mouse models. Prior studies have demonstrated that overexpression of the Hedgehog (HH) effector GLI2 induces loss of gastrin (atrophy) and antral hyperplasia. To determine the link between specific cytokines, HH signaling and pre-neoplastic changes in the gastric antrum.

METHODS

Mouse lines were created to conditionally direct IL1β or IFN-γ to the antrum using the Gastrin-CreERT2 and Tet activator. Primary cilia, which transduces HH signaling, on G cells were disrupted by deleting the ciliary motor protein KIF3a. Phenotypic changes were assessed by histology and western blots. A subclone of GLUTag enteroendocrine cells selected for gastrin expression and the presence of primary cilia was treated with recombinant SHH, IL1β or IFN-γ with or without kif3a siRNA.

RESULTS

IFN-γ increased gastrin and induced antral hyperplasia. However, antral expression of IL1β suppressed tissue and serum gastrin, while also inducing antral hyperplasia. IFN-γ treatment of GLUTAg cells suppressed GLI2 and induced gastrin, without affecting cilia length. By contrast, IL1β treatment doubled primary cilia length, induced GLI2 and suppressed gastrin gene expression. Knocking down kif3a in GLUTAg cells mitigated SHH or IL1β suppression of gastrin.

CONCLUSIONS

Overexpression of IL1β in the antrum was sufficient to induce antral hyperplasia coincident with suppression of gastrin via primary cilia. ORCID: #0000-0002-6559-8184.

Murine- and Human-Derived Autologous Organoid/Immune Cell Co-Cultures as Pre-Clinical Models of Pancreatic Ductal Adenocarcinoma

Purpose: Pancreatic ductal adenocarcinoma (PDAC) has the lowest five-year survival rate of all cancers in the United States. Programmed death 1 receptor (PD-1)-programmed death ligand 1 (PD-L1) immune checkpoint inhibition has been unsuccessful in clinical trials. Myeloid-derived suppressor cells (MDSCs) are known to block anti-tumor CD8+ T cell immune responses in various cancers including pancreas. This has led us to our objective that was to develop a clinically relevant in vitro organoid model to specifically target mechanisms that deplete MDSCs as a therapeutic strategy for PDAC. Method: Murine and human pancreatic ductal adenocarcinoma (PDAC) autologous organoid/immune cell co-cultures were used to test whether PDAC can be effectively treated with combinatorial therapy involving PD-1 inhibition and MDSC depletion. Results: Murine in vivo orthotopic and in vitro organoid/immune cell co-culture models demonstrated that polymorphonuclear (PMN)-MDSCs promoted tumor growth and suppressed cytotoxic T lymphocyte (CTL) proliferation, leading to diminished efficacy of checkpoint inhibition. Mouse- and human-derived organoid/immune cell co-cultures revealed that PD-L1-expressing organoids were unresponsive to nivolumab in vitro in the presence of PMN-MDSCs. Depletion of arginase 1-expressing PMN-MDSCs within these co-cultures rendered the organoids susceptible to anti-PD-1/PD-L1-induced cancer cell death. Conclusions: Here we use mouse- and human-derived autologous pancreatic cancer organoid/immune cell co-cultures to demonstrate that elevated infiltration of polymorphonuclear (PMN)-MDSCs within the PDAC tumor microenvironment inhibit T cell effector function, regardless of PD-1/PD-L1 inhibition. We present a pre-clinical model that may predict the efficacy of targeted therapies to improve the outcome of patients with this aggressive and otherwise unpredictable malignancy.

MiR130b from Schlafen4+ MDSCs stimulates epithelial proliferation and correlates with preneoplastic changes prior to gastric cancer

The myeloid differentiation factor Schlafen4 (Slfn4) marks a subset of myeloid-derived suppressor cells (MDSCs) in the stomach during Helicobacter-induced spasmolytic polypeptide-expressing metaplasia (SPEM).

OBJECTIVE

To identify the gene products expressed by Slfn4⁺-MDSCs and to determine how they promote SPEM.

DESIGN

We performed transcriptome analyses for both coding genes (mRNA by RNA-Seq) and non-coding genes (microRNAs using NanoString nCounter) using flow-sorted SLFN4⁺ and SLFN4^- cells from Helicobacter-infected mice exhibiting metaplasia at 6 months postinfection. Thioglycollate-elicited myeloid cells from the peritoneum were cultured and treated with IFNα to induce the T cell suppressor phenotype, expression of MIR130b and SLFN4. MIR130b expression in human gastric tissue including gastric cancer and patient sera was determined by qPCR and in situ hybridisation. Knockdown of MiR130b in vivo in Helicobacter-infected mice was performed using Invivofectamine. Organoids from primary gastric cancers were used to generate xenografts. ChIP assay and Western blots were performed to demonstrate NFκb p65 activation by MIR130b.

RESULTS

MicroRNA analysis identified an increase in MiR130b in gastric SLFN4⁺ cells. Moreover, MIR130b colocalised with SLFN12L, a human homologue of SLFN4, in gastric cancers. MiR130b was required for the T-cell suppressor phenotype exhibited by the SLFN4⁺ cells and promoted Helicobacter-induced metaplasia. Treating gastric organoids with the MIR130b mimic induced epithelial cell proliferation and promoted xenograft tumour growth.

CONCLUSION

Taken together, MiR130b plays an essential role in MDSC function and supports metaplastic transformation.

Interleukin 27 Protects From Gastric Atrophy and Metaplasia During Chronic Autoimmune Gastritis

BACKGROUND & AIMS

The association between chronic inflammation and gastric carcinogenesis is well established, but it is not clear how immune cells and cytokines regulate this process. We investigated the role of interleukin 27 (IL27) in the development of gastric atrophy, hyperplasia, and metaplasia (preneoplastic lesions associated with inflammation-induced gastric cancer) in mice with autoimmune gastritis.

METHODS

We performed studies with TxA23 mice (control mice), which express a T-cell receptor against the H+/K+ adenosine triphosphatase α chain and develop autoimmune gastritis, and TxA23xEbi3-/- mice, which develop gastritis but do not express IL27. In some experiments, mice were given high-dose tamoxifen to induce parietal cell atrophy and spasmolytic polypeptide-expressing metaplasia (SPEM). Recombinant IL27 was administered to mice with mini osmotic pumps. Stomachs were collected and analyzed by histopathology and immunofluorescence; we used flow cytometry to measure IL27 and identify immune cells that secrete IL27 in the gastric mucosa. Single-cell RNA sequencing was performed on immune cells that infiltrated stomach tissues.

RESULTS

We identified IL27-secreting macrophages and dendritic cell in the corpus of mice with chronic gastritis (TxA23 mice). Mice deficient in IL27 developed more severe gastritis, atrophy, and SPEM than control mice. Administration of recombinant IL27 significantly reduced the severity of inflammation, atrophy, and SPEM in mice with gastritis. Single-cell RNA sequencing showed that IL27 acted almost exclusively on stomach-infiltrating CD4+ T cells to suppress expression of inflammatory genes.

CONCLUSIONS

In studies of mice with autoimmune gastritis, we found that IL27 is an inhibitor of gastritis and SPEM, suppressing CD4+ T-cell-mediated inflammation in the gastric mucosa.

The Physiology of the Gastric Parietal Cell

Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.

Aim2-mediated/IFN-β-independent regulation of gastric metaplastic lesions via CD8+ T cells

Development of gastric cancer is often preceded by chronic inflammation, but the immune cellular mechanisms underlying this process are unclear. Here we demonstrated that an inflammasome molecule, absent in melanoma 2 (Aim2), was upregulated in patients with gastric cancer and in spasmolytic polypeptide-expressing metaplasia of chronically Helicobacter felis-infected stomachs in mice. However, we found that Aim2 was not necessary for inflammasome function during gastritis. In contrast, Aim2 deficiency led to an increase in gastric CD8+ T cell frequency, which exacerbated metaplasia. These gastric CD8+ T cells from Aim2-/- mice were found to have lost their homing receptor expression (sphingosine-1-phosphate receptor 1 [S1PR1] and CD62L), a feature of tissue-resident memory T cells. The process was not mediated by Aim2-dependent regulation of IFN-β or by dendritic cell-intrinsic Aim2. Rather, Aim2 deficiency contributed to an increased production of CXCL16 by B cells, which could suppress S1PR1 and CD62L in CD8+ T cells. This study describes a potentially novel function of Aim2 that regulates CD8+ T cell infiltration and retention within chronically inflamed solid organ tissue. This function operates independent of the inflammasome, IFN-β, or dendritic cells. We provide evidence that B cells can contribute to this mechanism via CXCL16.

Human Gastrointestinal Organoid Models for Studying Microbial Disease and Cancer

One of the major discoveries in stem cell research in the past decade embraces the development of "organs in a dish," also known as "organoids." Organoids are three-dimensional cellular structures derived from primary stem cells of different organ-specific cell types which are capable of self-renewal and maintenance of the parental lineages. Researchers have developed in vitro organoid models to mimic in vivo host-microbial interactions and disease. In this review, we focus on the use of gastrointestinal organoids as models of microbial disease and cancer.

Hedgehog/GLI signaling in tumor immunity - new therapeutic opportunities and clinical implications

Uncontrolled activation of the Hedgehog/Glioma-associated oncogene (HH/GLI) pathway is a potent oncogenic driver signal promoting numerous cancer hallmarks such as proliferation, survival, angiogenesis, metastasis and metabolic rewiring. Several HH pathway inhibitors have already been approved for medical therapy of advanced and metastatic basal cell carcinoma and acute myeloid leukemia with partially impressive therapeutic activity. However, de novo and acquired resistance as well as severe side effects and unexplained lack of therapeutic efficacy are major challenges that urgently call for improved treatment options with more durable responses. The recent breakthroughs in cancer immunotherapy have changed our current understanding of targeted therapy and opened up promising therapeutic opportunities including combinations of selective cancer pathway and immune checkpoint inhibitors. Although HH/GLI signaling has been intensely studied with respect to the classical hallmarks of cancer, its role in the modulation of the anti-tumoral immune response has only become evident in recent studies. These have uncovered HH/GLI regulated immunosuppressive mechanisms such as enhanced regulatory T-cell formation and production of immunosuppressive cytokines. In light of these exciting novel data on oncogenic HH/GLI signaling in immune cross-talk and modulation, we summarize and connect in this review the existing knowledge from different HH-related cancers and chronic inflammatory diseases. This is to provide a basis for the investigation and evaluation of novel treatments combining immunotherapeutic strategies with approved as well as next-generation HH/GLI inhibitors. Further, we also critically discuss recent studies demonstrating a possible negative impact of current HH/GLI pathway inhibitors on the anti-tumoral immune response, which may explain some of the disappointing results of several oncological trials with anti-HH drugs.

Additional file 1

Hepatoma-derived growth factor participates in Helicobacter Pylori-induced neutrophils recruitment, gastritis and gastric carcinogenesis

Helicobacter pylori (Hp) infection and overexpression of hepatoma-derived growth factor (HDGF) are involved in gastric carcinogenesis. However, the relationship between Hp-induced gastric diseases and HDGF upregulation is not yet completely clear. This study aimed to elucidate the role of HDGF in Hp-induced gastric inflammation and carcinogenesis. HDGF expression in gastric biopsy and serum from patients was analyzed by immunohistochemical and ELISA analysis, respectively. Hp and gastric cells coculture system was employed to delineate the mechanism underlying HDGF overexpression during Hp infection. The gastric pathologies of wild type and HDGF knockout mice after Hp infection were investigated by immunohistochemical, immunoblot, and immunofluorescence analyses. HDGF level was significantly elevated in patients with Hp infection or intestinal metaplasia (IM, a precancerous lesion), and HDGF overexpression was positively correlated with Hp load, IM, and neutrophil infiltration in gastric biopsy. Consistently, patients with Hp infection or IM had significantly higher serum HDGF level. By using coculture assay, Hp infection led to HDGF upregulation and secretion in gastric cells. In mice model, HDGF ablation significantly suppressed the Hp-induced neutrophil infiltration and inflammatory TNF-α/COX-2 signaling, thereby relieving the tissue damage in stomach. This was further supported by that recombinant HDGF (rHDGF) stimulated the differentiation/chemotaxis of cultured neutrophils and oncogenic behaviors of gastric cells. Time series studies showed that Hp infection elicited an inflammatory TNF-α/HDGF/COX-2 cascade in stomach. HDGF secretion by Hp infection promotes the neutrophils infiltration and relays Hp-induced inflammatory signaling. Thus, HDGF may constitute a novel diagnostic marker and therapeutic target for Hp-induced gastritis and carcinogenesis.

MDSCs in infectious diseases: regulation, roles, and readjustment

Many pathogens, ranging from viruses to multicellular parasites, promote expansion of MDSCs, which are myeloid cells that exhibit immunosuppressive features. The roles of MDSCs in infection depend on the class and virulence mechanisms of the pathogen, the stage of the disease, and the pathology associated with the infection. This work compiles evidence supported by functional assays on the roles of different subsets of MDSCs in acute and chronic infections, including pathogen-associated malignancies, and discusses strategies to modulate MDSC dynamics to benefit the host.