Mucin-induced apoptosis of monocyte-derived dendritic cells during maturation

The diagnostic effectiveness of serum sialic acid predicts both qualitative and quantitative prostate cancer in patients with prostate-specific antigen between 4 and 20 ng/mL

Introduction

This study aimed to evaluate the predictive value of the serum biochemical index, including alkaline phosphatase (AKP), lactate dehydrogenase (LDH), α-L-fucosidase (AFU), serum sialic acid (SA), and fibrinogen (FIB), for prostate cancer (PCa) and clinically significant prostate cancer (CSPCa) in patients with a prostate-specific antigen (PSA) value between 4 and 20 ng/mL.

Patients and methods

This study retrospectively examined the clinical data of 408 eligible patients who underwent prostate biopsies in our hospital between March 2015 and July 2022. CSPCa was defined as a "Gleason grade group of≥2". For analyzing the association between PCa/CSPCa and serum biochemical index, univariable logistic regression and multivariable logistic regression were conducted. Based on the multivariable logistic regression model, we constructed models and compared the area under the curve (AUC). We generated the nomogram, the ROC curve, the DCA curve, and the calibration curve for PCa.

Results

Overall, we studied 271 patients with PCa (including 155 patients with CSPCa) and 137 non-PCa patients. Patients with PCa were more likely to consume alcohol, have higher total PSA (TPSA) values, and have lower free PSA (FPSA) and free/total PSA (f/T) values. There were higher TPSA values and lower f/T values in the CSPCa group when compared with the non-CSPCa group. The univariate logistic regression analyses did not show significant results. However, AKP, AFU, SA, TPSA, and FPSA all retain significant significance when all factors are included in multifactor logistic regression analysis. This finding suggests that the exposure factor exhibited an independent effect on the outcome after controlling for other factors, including the potential confounding effects that may have been underestimated. Through ROC curves, we found that SA and TPSA levels are more powerful predictors. In contrast, there is a lack of excellent predictive value for PCA and CSPCa using Age, AFU, FIB, and FPSA.

Conclusion

In our study, serum biochemical index is a potential prediction tool for PCa and CSPCa for patients with PSA values between 4 and 20 ng/mL. Additionally, the new serum biochemical index SA is also useful when diagnosing PCa and CSPCa, as we conclude in our study.

Pasture intake protects against commercial diet-induced lipopolysaccharide production facilitated by gut microbiota through activating intestinal alkaline phosphatase enzyme in meat geese

Introduction

Diet strongly affects gut microbiota composition, and gut bacteria can influence the intestinal barrier functions and systemic inflammation through metabolic endotoxemia. In-house feeding system (IHF, a low dietary fiber source) may cause altered cecal microbiota composition and inflammatory responses in meat geese via increased endotoxemia (lipopolysaccharides) with reduced intestinal alkaline phosphatase (ALP) production. The effects of artificial pasture grazing system (AGF, a high dietary fiber source) on modulating gut microbiota architecture and gut barrier functions have not been investigated in meat geese. Therefore, this study aimed to investigate whether intestinal ALP could play a critical role in attenuating reactive oxygen species (ROS) generation and ROS facilitating NF-κB pathway-induced systemic inflammation in meat geese.

Methods

The impacts of IHF and AGF systems on gut microbial composition via 16 sRNA sequencing were assessed in meat geese. The host markers analysis through protein expression of serum and cecal tissues, hematoxylin and eosin (H&E) staining, localization of NF-қB and Nrf2 by immunofluorescence analysis, western blotting analysis of ALP, and quantitative PCR of cecal tissues was evaluated.

Results and Discussion

In the gut microbiota analysis, meat geese supplemented with pasture showed a significant increase in commensal microbial richness and diversity compared to IHF meat geese demonstrating the antimicrobial, antioxidant, and anti-inflammatory ability of the AGF system. A significant increase in intestinal ALP-induced Nrf2 signaling pathway was confirmed representing LPS dephosphorylation mediated TLR4/MyD88 induced ROS reduction mechanisms in AGF meat geese. Further, the correlation analysis of top 44 host markers with gut microbiota showed that artificial pasture intake protected gut barrier functions via reducing ROS-mediated NF-κB pathway-induced gut permeability, systemic inflammation, and aging phenotypes. In conclusion, the intestinal ALP functions to regulate gut microbial homeostasis and barrier function appear to inhibit pro-inflammatory cytokines by reducing LPS-induced ROS production in AGF meat geese. The AGF system may represent a novel therapy to counteract the chronic inflammatory state leading to low dietary fiber-related diseases in animals.

Sweet Immune Checkpoint Targets to Enhance T Cell Therapy

Despite tremendous success against hematological malignancies, the performance of chimeric Ag receptor T cells against solid tumors remains poor. In such settings, the lack of success of this groundbreaking immunotherapy is in part mediated by ligand engagement of immune checkpoint molecules on the surface of T cells in the tumor microenvironment. Although CTLA-4 and programmed death-1 (PD-1) are well-established checkpoints that inhibit T cell activity, the engagement of glycans and glycan-binding proteins are a growing area of interest due to their immunomodulatory effects. This review discusses exemplary strategies to neutralize checkpoint molecules through an in-depth overview of genetic engineering approaches aimed at overcoming the inhibitory programmed death ligand-1 (PD-L1)/PD-1 axis in T cell therapies and summarizes current knowledge on glycoimmune interactions that mediate T cell immunosuppression.

Mucin-type sialyl-Tn antigen is associated with PD-L1 expression and predicts poor clinical prognosis in breast cancer

Background

A recent study showed that mucin-type sialylated O-linked glycans could induce the increased expression of PD-L1 via binding to Siglec receptors. However, the relationship between the expression of the mucin-type sialyl-Tn antigen (sTn) and PD-L1 remains unclear in breast cancer (BC). Therefore, we investigate the clinicopathological and prognostic effects of sTn expression and its relationship with PD-L1 expression in BC tissues.

Methods

We retrospectively analyzed the clinical data of 380 invasive BC patients between January 2011 and January 2014. The last follow-up time was January 31, 2019 with a median follow-up of 62 months. The expression of the sTn antigen and PD-L1 in 380 tumor specimens was assessed by immunohistochemistry. Correlations between sTn/PD-L1 expression and clinicopathological features and prognoses were analyzed.

Results

In BC tissues, the positive expression rate of PD-L1 (20.5%) was much lower than that of sTn (41.8%). Pearson's contingency analysis showed that sTn and PD-L1 expression in tumor tissues demonstrated a high correlation (P<0.001). High sTn expression was associated with negative ER expression (P<0.001), positive HER-2 status (P<0.001), advanced tumor stage (P<0.001), high density of CD8+ tumor-infiltrating lymphocytes (TILs) (P=0.028), and positive lymph node metastasis (P=0.002). Moreover, patients with concomitant high expression of both markers had the highest risk of relapse (P<0.001) and mortality (P<0.001). The multivariate Cox regression model revealed that positive sTn expression (HRos: 1.941, 95% CI: 1.168, 3.223, Pos=0.028; HRpfs: 1.739, 95% CI: 1.063, 2.847, Ppfs=0.010) and positive PD-L1 expression (HRos: 1.912, 95% CI: 1.138, 3.212, Pos=0.017; HRpfs: 1.863, 95% CI: 1.116, 3.110, Ppfs=0.014) were independent indicators for poor overall survival (OS) and progression-free survival (PFS), respectively.

Conclusions

BC patients who expressed both sTn and PD-L1 had poorer survival. Therefore, combinational therapy with dual blockade might benefit BC patients with sTn(+)/PD-L1(+) expression, which requires further examination in future clinical trials.

Consequence of distinctive expression of MUC2 in colorectal cancers: How much is actually bad?

Colorectal cancer (CRC) exhibits complex pathogenesis via compromised intestinal mucosal barrier. It is accepted that goblet cells secrete mucin which line the intestinal mucosal barrier and offer wide range protection and maintain the gut integrity. The principal mucin in the small and large intestine which is Mucin2 (MUC2) is predominantly expressed in the goblet cells which play a pivotal role in intestinal homeostasis. Its disruption is associated with diverse diseases and carcinomas. MUC2 has lately been identified as a principal marker in various mechanisms and secretory cell lineage. While MUC2 expression is regulated by various modulators, alterations in its expression are associated with immunomodulation, differences in tumor immunity and also regulation of microbiota. In the light of current literature, the present review explicates the regulation, functional mechanisms and essential role of MUC2 in colorectal cancer and aids in providing deep understanding of pathogenesis of the disease and also specifies the importance of the MUC2 in gaining more insights about the subtypes of colorectal cancer and how it can succour in approximating the prognosis and survival of the patients.

Tools to study and target the Siglec-sialic acid axis in cancer

Siglecs are widely expressed on leucocytes and bind to ubiquitously presented glycans containing sialic acids (sialoglycans). Most Siglecs carry an immunoreceptor tyrosine-based inhibition motif (ITIM) and elicit an inhibitory intracellular signal upon ligand binding. A few Siglec receptors can, however, recruit immunoreceptor tyrosine-based activation motif (ITAM)-containing factors, which activate cells. The role of hypersialylation (the enhanced expression of sialoglycans) has recently been explored in cancer progression. Mechanistic studies have shown that hypersialylation on cancer cells can engage inhibitory Siglecs on the surface of immune cells and induce immunosuppression. These recent studies strongly suggest that the Siglec-sialic acid axis can act as a potential target for cancer immunotherapy. Moreover, the use of new tools and techniques is facilitating these studies. In this review, we summarise techniques used to study Siglecs, including different mouse models, monoclonal antibodies, Siglec fusion proteins, and sialoglycan arrays. Furthermore, we discuss the recent major developments in the study of Siglecs in cancer immunosuppression, tools, and techniques used in targeting the Siglec-sialic acid axis and the possibility of clinical intervention.

Melanoma-Secreted Lysosomes Trigger Monocyte-Derived Dendritic Cell Apoptosis and Limit Cancer Immunotherapy

The recent success of checkpoint blockade therapies has established immunotherapy as one of the most promising treatments for melanoma. Nonetheless, a complete curative response following immunotherapy is observed only in a fraction of patients. To identify what factors limit the efficacy of immunotherapies, we established mouse models that cease to respond to immunotherapies once their tumors exceed a certain stage. Analysis of the immune systems of the organisms revealed that the numbers of tumor-infiltrating dendritic cells (TIDC) drastically decreased with time. Further, in contrast to the current paradigm, once melanoma was established, TIDC did not migrate into sentinel lymph nodes. Instead, they underwent local cell death due to excessive phagocytosis of lysosomes. Importantly, TIDC were required to license the cytotoxic activity of tumor CD8⁺ T cells, and in their absence, T cells did not lyse melanoma cells. Our results offer a paradigm shift regarding the role of TIDC and a framework to increase the efficacy of immunotherapies. SIGNIFICANCE: This work redefines the role of monocyte-derived dendritic cells in melanoma and provides a novel strategy to increase the efficacy of T-cell-based immunotherapies in nonresponding individuals. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/10/1942/F1.large.jpg.

Dendritic Cells in the Tumor Microenvironment

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) of the immune system. They capture foreign antigens and can present them to lymphocytes, that is, T cells and B cells, to activate them. DCs are the most potent of all immune cells at inducing the adaptive immune system. Thus, the presence of DCs at the anatomical site of the immune challenge is imperative for the immune system to mount an effective immune response. From the anatomical site of the immune challenge, DCs cargo antigens to the draining lymph nodes, specialized immune organs where adaptive immunity is generated. DCs are heterogeneous as a type of immune cell, and various subsets of DCs have been reported and their functions described. In this chapter, we discuss various aspects of DC development and function. We further discuss how various tumor microenvironments can affect DC development, function, and migration, thus evading a strong adaptive immune response.

Modulation of Immune Tolerance via Siglec-Sialic Acid Interactions

One of the key features of the immune system is its extraordinary capacity to discriminate between self and non-self and to respond accordingly. Several molecular interactions allow the induction of acquired immune responses when a foreign antigen is recognized, while others regulate the resolution of inflammation, or the induction of tolerance to self-antigens. Post-translational signatures, such as glycans that are part of proteins (glycoproteins) and lipids (glycolipids) of host cells or pathogens, are increasingly appreciated as key molecules in regulating immunity vs. tolerance. Glycans are sensed by glycan binding receptors expressed on immune cells, such as C-type lectin receptors (CLRs) and Sialic acid binding immunoglobulin type lectins (Siglecs), that respond to specific glycan signatures by triggering tolerogenic or immunogenic signaling pathways. Glycan signatures present on healthy tissue, inflamed and malignant tissue or pathogens provide signals for “self” or “non-self” recognition. In this review we will focus on sialic acids that serve as “self” molecular pattern ligands for Siglecs. We will emphasize on the function of Siglec-expressing mononuclear phagocytes as sensors for sialic acids in tissue homeostasis and describe how the sialic acid-Siglec axis is exploited by tumors and pathogens for the induction of immune tolerance. Furthermore, we highlight how the sialic acid-Siglec axis can be utilized for clinical applications to induce or inhibit immune tolerance.

Intestinal mucin activates human dendritic cells and IL-8 production in a glycan-specific manner

Cross-talk between different components of the intestinal barrier and the immune system may be important in maintaining gut homeostasis. A crucial part of the gut barrier is the mucus layer, a cross-linked gel on top of the intestinal epithelium that consists predominantly of the mucin glycoprotein MUC2. However, whether the mucin layer actively regulates intestinal immune cell responses is not clear. Because recent evidence suggests that intestinal dendritic cells (DCs) may be regulated by the mucus layer, we purified intestinal mucin, incubated it with human DCs, and determined the functional effects. Here we show that expression of the chemokine IL-8 and co-stimulatory DC markers CD86 and CD83 are significantly up-regulated on human DCs in the presence of intestinal mucins. Additionally, mucin-exposed DCs promoted neutrophil migration in an IL-8–dependent manner. The stimulatory effects of mucins on DCs were not due to mucin sample contaminants such as lipopolysaccharide, DNA, or contaminant proteins. Instead, mucin glycans are important for the pro-inflammatory effects on DCs. Thus, intestinal mucins are capable of inducing important pro-inflammatory functions in DCs, which could be important in driving inflammatory responses upon intestinal barrier damage.

Interactions between the breast cancer-associated MUC1 mucins and C-type lectin characterized by optical tweezers

Carbohydrate–protein interactions govern many crucial processes in biological systems including cell recognition events. We have used the sensitive force probe optical tweezers to quantify the interactions occurring between MGL lectins and MUC1 carrying the cancer-associated glycan antigens mucins Tn and STn. Unbinding forces of 7.6±1.1 pN and 7.1±1.1 pN were determined for the MUC1(Tn)—MGL and MUC1(STn)—MGL interactions, at a force loading rate of ~40 pN/s. The interaction strength increased with increasing force loading rate, to 27.1±4.4 and 36.9±3.6 pN at a force loading rate of ~ 310 pN/s. No interactions were detected between MGL and MUC1(ST), a glycoform of MUC1 also expressed by breast carcinoma cells. Interestingly, this glycan (ST) can be found on proteins expressed by normal cells, although in this case not on MUC1. Additionally, GalNAc decorated polyethylene glycol displayed similar rupture forces as observed for MUC1(Tn) and MUC1(STn) when forced to unbind from MGL, indicating that GalNAc is an essential group in these interactions. Since the STn glycan decoration is more frequently found on the surface of carcinomas than the Tn glycan, the binding of MUC1 carrying STn to MGL may be more physiologically relevant and may be in part responsible for some of the characteristics of STn expressing tumours.

A Bitter Sweet Symphony: Immune Responses to Altered O-glycan Epitopes in Cancer

The appearance of aberrant glycans on the tumor cell surface is one of the emerging hallmarks of cancer. Glycosylation is an important post-translation modification of proteins and lipids and is strongly affected by oncogenesis. Tumor-associated glycans have been extensively characterized regarding their composition and tumor-type specific expression patterns. Nevertheless whether and how tumor-associated glycans contribute to the observed immunomodulatory actions by tumors has not been extensively studied. Here, we provide a detailed overview of the current knowledge on how tumor-associated O-glycans affect the anti-tumor immune response, thereby focusing on truncated O-glycans present on epithelial tumors and mucins. These tumor-associated O-glycans and mucins bind a variety of lectin receptors on immune cells to facilitate the subsequently induction of tolerogenic immune responses. We, therefore, postulate that tumor-associated glycans not only support tumor growth, but also actively contribute to immune evasion.

Tissue-resident dendritic cells and diseases involving dendritic cell malfunction

Dendritic cells (DCs) control immune responses and are central to the development of immune memory and tolerance. DCs initiate and orchestrate immune responses in a manner that depends on signals they receive from microbes and cellular environment. Although DCs consist mainly of bone marrow-derived and resident populations, a third tissue-derived population resides the spleen and lymph nodes (LNs), different subsets of tissue-derived DCs have been identified in the blood, spleen, lymph nodes, skin, lung, liver, gut and kidney to maintain the tolerance and control immune responses. Tissue-resident DCs express different receptors for microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs), which were activated to promote the production of pro- or anti-inflammatory cytokines. Malfunction of DCs contributes to diseases such as autoimmunity, allergy, and cancer. It is therefore important to update the knowledge about resident DC subsets and diseases associated with DC malfunction.

MUC5B silencing reduces chemo-resistance of MCF-7 breast tumor cells and impairs maturation of dendritic cells

Mucins participate in cancer progression by regulating cell growth, adhesion, signaling, apoptosis or chemo-resistance to drugs. The secreted mucin MUC5B, the major component of the respiratory tract mucus, is aberrantly expressed in breast cancer, where it could constitute a cancer biomarker. In this study we evaluated the role of MUC5B in breast cancer by gene silencing the MUC5B expression with short hairpin RNA on MCF-7 cells. We found that MUC5B-silenced MCF-7 cells have a reduced capacity to grow, adhere and form cell colonies. Interestingly, MUC5B knock-down increased the sensitivity to death induced by chemotherapeutic drugs. We also show that MUC5B silencing impaired LPS-maturation of DCs, and production of cytokines. Furthermore, MUC5B knock-down also influenced DC-differentiation and activation since it resulted in an upregulation of IL-1β, IL-6 and IL-10, cytokines that might be involved in cancer progression. Thus, MUC5B could enhance the production of LPS-induced cytokines, suggesting that the use of MUC5B-based cancer vaccines combined with DC-maturation stimuli, could favor the induction of an antitumor immune response.

Dendritic Cells in Oncolytic Virus-Based Anti-Cancer Therapy

Dendritic cells (DCs) are specialized antigen-presenting cells that have a notable role in the initiation and regulation of innate and adaptive immune responses. In the context of cancer, appropriately activated DCs can induce anti-tumor immunity by activating innate immune cells and tumor-specific lymphocytes that target cancer cells. However, the tumor microenvironment (TME) imposes different mechanisms that facilitate the impairment of DC functions, such as inefficient antigen presentation or polarization into immunosuppressive DCs. These tumor-associated DCs thus fail to initiate tumor-specific immunity, and indirectly support tumor progression. Hence, there is increasing interest in identifying interventions that can overturn DC impairment within the TME. Many reports thus far have studied oncolytic viruses (OVs), viruses that preferentially target and kill cancer cells, for their capacity to enhance DC-mediated anti-tumor effects. Herein, we describe the general characteristics of DCs, focusing on their role in innate and adaptive immunity in the context of the TME. We also examine how DC-OV interaction affects DC recruitment, OV delivery, and anti-tumor immunity activation. Understanding these roles of DCs in the TME and OV infection is critical in devising strategies to further harness the anti-tumor effects of both DCs and OVs, ultimately enhancing the efficacy of OV-based oncotherapy.

Dendritic cell defects in the colorectal cancer

Colorectal cancer (CRC) results from the accumulation of both genetic and epigenetic alterations of the genome. However, also the formation of an inflammatory milieu plays a pivotal role in tumor development and progression. Dendritic cells (DCs) play a relevant role in tumor by exerting differential pro-tumorigenic and anti-tumorigenic functions, depending on the local milieu. Quantitative and functional impairments of DCs have been widely observed in several types of cancer, including CRC, representing a tumor-escape mechanism employed by cancer cells to elude host immunosurveillance.

Understanding the interactions between DCs and tumors is important for comprehending the mechanisms of tumor immune surveillance and escape, and provides novel approaches to therapy of cancer. This review summarizes updated information on the role of the DCs in colon cancer development and/or progression.

Molecular and functional characterization of porcine Siglec-3/CD33 and analysis of its expression in blood and tissues

A cDNA clone encoding a 380 a-a type 1 transmembrane protein with homology to human Siglec-3/CD33 was obtained from a swine small intestine library. An analysis of protein sequence identified two immunoglobulin-like domains, a transmembrane region, and a carboxi-terminal tail with two tyrosine-based signalling motifs. Binding assays of Siglec-3 transfected CHO cells to polyacrylamide glycoconjugates showed a preference for α2-6-linked sialic acids. Using mAbs raised against a fragment containing the two Ig-like domains, porcine Siglec-3 was found to be expressed on monocytes and granulocytes, and their bone marrow precursors. It was also detected in lymph node, splenic and alveolar macrophages. MAbs immunoprecipitated, from granulocyte lysates, a protein of 51-60 kDa under both non-reducing and reducing conditions. MAbs were also used to analyse functional activity of Siglec-3 on bone marrow and blood cells. Engagement of Siglec-3 by mAb had no apparent effect on cell proliferation or cytokine production.

The Breast Cancer-Associated Glycoforms of MUC1, MUC1-Tn and sialyl-Tn, Are Expressed in COSMC Wild-Type Cells and Bind the C-Type Lectin MGL

Aberrant glycosylation occurs in the majority of human cancers and changes in mucin-type O-glycosylation are key events that play a role in the induction of invasion and metastases. These changes generate novel cancer-specific glyco-antigens that can interact with cells of the immune system through carbohydrate binding lectins. Two glyco-epitopes that are found expressed by many carcinomas are Tn (GalNAc-Ser/Thr) and STn (NeuAcα2,6GalNAc-Ser/Thr). These glycans can be carried on many mucin-type glycoproteins including MUC1. We show that the majority of breast cancers carry Tn within the same cell and in close proximity to extended glycan T (Galβ1,3GalNAc) the addition of Gal to the GalNAc being catalysed by the T synthase. The presence of active T synthase suggests that loss of the private chaperone for T synthase, COSMC, does not explain the expression of Tn and STn in breast cancer cells. We show that MUC1 carrying both Tn or STn can bind to the C-type lectin MGL and using atomic force microscopy show that they bind to MGL with a similar dead adhesion force. Tumour associated STn is associated with poor prognosis and resistance to chemotherapy in breast carcinomas, inhibition of DC maturation, DC apoptosis and inhibition of NK activity. As engagement of MGL in the absence of TLR triggering may lead to anergy, the binding of MUC1-STn to MGL may be in part responsible for some of the characteristics of STn expressing tumours.

Endogenous airway mucins carry glycans that bind Siglec-F and induce eosinophil apoptosis

BACKGROUND

Sialic acid-binding, immunoglobulin-like lectin (Siglec) F is a glycan-binding protein selectively expressed on mouse eosinophils. Its engagement induces apoptosis, suggesting a pathway for ameliorating eosinophilia in the setting of asthma and other eosinophil-associated diseases. Siglec-F recognizes sialylated sulfated glycans in glycan-binding assays, but the identities of endogenous sialoside ligands and their glycoprotein carriers in vivo are unknown.

OBJECTIVES

To use mouse lung-derived materials to isolate, biochemically identify, and biologically characterize naturally occurring endogenous glycan ligands for Siglec-F.

METHODS

Lungs from normal and mucin-deficient mice, as well as mouse tracheal epithelial cells, were investigated in vitro and in vivo for the expression of Siglec-F ligands. Western blotting and cytochemistry used Siglec-F-Fc as a probe for directed purification, followed by liquid chromatography-tandem mass spectrometry of recognized glycoproteins. Purified components were tested in mouse eosinophil-binding assays and flow cytometry-based cell death assays.

RESULTS

We detected mouse lung glycoproteins that bound to Siglec-F; binding was sialic acid dependent. Proteomic analysis of Siglec-F binding material identified Muc5b and Muc4. Cross-affinity enrichment and histochemical analysis of lungs from mucin-deficient mice assigned and validated the identity of Muc5b as one glycoprotein ligand for Siglec-F. Purified mucin preparations carried sialylated and sulfated glycans, bound to eosinophils and induced their death in vitro. Mice conditionally deficient in Muc5b displayed exaggerated eosinophilic inflammation in response to intratracheal installation of IL-13.

CONCLUSIONS

These data identify a previously unrecognized endogenous anti-inflammatory property of airway mucins by which their glycans can control lung eosinophilia through engagement of Siglec-F.

Sweet escape: sialic acids in tumor immune evasion

Sialic acids represent a family of sugar molecules derived from neuraminic acid that frequently terminate glycan chains and contribute to many biological processes. Already five decades ago, aberrantly high expression of sialic acids has been proposed to protect cancer cells from recognition and eradication by the immune system. Today, increased understanding at the molecular level demonstrates the broad immunomodulatory capacity of tumor-derived sialic acids that is, at least in part, mediated through interactions with immunoinhibitory Siglec receptors. Here we will review current studies from a sialic acid sugar perspective showing that tumor-derived sialic acids disable major killing mechanisms of effector immune cells, trigger production of immune suppressive cytokines and dampen activation of antigen-presenting cells and subsequent induction of anti-tumor immune responses. Furthermore, strategies to modulate sialic acid expression in cancer cells to improve cancer immunotherapy will be discussed.

Sialyl Tn-expressing bladder cancer cells induce a tolerogenic phenotype in innate and adaptive immune cells

Despite the wide acceptance that glycans are centrally implicated in immunity, exactly how they contribute to the tilt immune response remains poorly defined. In this study, we sought to evaluate the impact of the malignant phenotype-associated glycan, sialyl-Tn (STn) in the function of the key orchestrators of the immune response, the dendritic cells (DCs). In high grade bladder cancer tissue, the STn antigen is significantly overexpressed and correlated with the increased expression of ST6GALNAC1 sialyltransferase. Bladder cancer tissue presenting elevated expression of ST6GALNAC1 showed a correlation with increased expression of CD1a, a marker for bladder immature DCs and showed concomitant low levels of Th1-inducing cytokines IL-12 and TNF-α. In vitro, human DCs co-incubated with STn(+) bladder cancer cells, had an immature phenotype (MHC-II(low), CD80(low) and CD86(low)) and were unresponsive to further maturation stimuli. When contacting with STn(+) cancer cells, DCs expressed significantly less IL-12 and TNF-α. Consistent with a tolerogenic DC profile, T cells that were primed by DCs pulsed with antigens derived from STn(+) cancer cells were not activated and showed a FoxP3(high) IFN-γ(low) phenotype. Blockade of STn antigens and of STn(+) glycoprotein, CD44 and MUC1, in STn(+) cancer cells was able to lower the induction of tolerance and DCs become more mature. Overall, our data suggest that STn-expressing cancer cells impair DC maturation and endow DCs with a tolerogenic function, limiting their capacity to trigger protective anti-tumour T cell responses. STn antigens and, in particular, STn(+) glycoproteins are potential targets for circumventing tumour-induced tolerogenic mechanisms.

Dendritic cells: a spot on sialic Acid

Glycans decorating cell surface and secreted proteins and lipids occupy the juncture where critical host–host and host-pathogen interactions occur. The role of glycan epitopes in cell–cell and cell-pathogen adhesive events is already well-established, and cell surface glycan structures change rapidly in response to stimulus and inflammatory cues. Despite the wide acceptance that glycans are centrally implicated in immunity, exactly how glycans and their changes contribute to the overall immune response remains poorly defined. Sialic acids are unique sugars that usually occupy the terminal position of the glycan chains and may be modified by external factors, such as pathogens, or upon specific physiological cellular events. At cell surface, sialic acid-modified structures form the key fundamental determinants for a number of receptors with known involvement in cellular adhesiveness and cell trafficking, such as the Selectins and the Siglec families of carbohydrate recognizing receptors. Dendritic cells (DCs) preside over the transition from innate to the adaptive immune repertoires, and no other cell has such relevant role in antigen screening, uptake, and its presentation to lymphocytes, ultimately triggering the adaptive immune response. Interestingly, sialic acid-modified structures are involved in all DC functions, such as antigen uptake, DC migration, and capacity to prime T cell responses. Sialic acid content changes along DC differentiation and activation and, while, not yet fully understood, these changes have important implications in DC functions. This review focuses on the developmental regulation of DC surface sialic acids and how manipulation of DC surface sialic acids can affect immune-critical DC functions by altering antigen endocytosis, pathogen and tumor cell recognition, cell recruitment, and capacity for T cell priming. The existing evidence points to a potential of DC surface sialylation as a therapeutic target to improve and diversify DC-based therapies.

The dark side of dendritic cells: development and exploitation of tolerogenic activity that favor tumor outgrowth and immune escape

Dendritic cells (DC) play a central role in the regulation of the immune responses by providing the information needed to decide between tolerance, ignorance, or active responses. For this reason different therapies aim at manipulating DC to obtain the desired response, such as enhanced cell-mediated toxicity against tumor and infected cells or the induction of tolerance in autoimmunity and transplantation. In the last decade studies performed in these settings have started to identify (some) molecules/factors involved in the acquisition of a tolerogenic DC phenotype as well as the underlying mechanisms of their regulatory function on different immune cell populations.

Galactose 6-O-sulfotransferases are not required for the generation of Siglec-F ligands in leukocytes or lung tissue

Eosinophil accumulation is a characteristic feature of the immune response to parasitic worms and allergens. The cell surface carbohydrate-binding receptor Siglec-F is highly expressed on eosinophils and negatively regulates their accumulation during inflammation. Although endogenous ligands for Siglec-F have yet to be biochemically defined, binding studies using glycan arrays have implicated galactose 6-O-sulfate (Gal6S) as a partial recognition determinant for this receptor. Only two sulfotransferases are known to generate Gal6S, namely keratan sulfate galactose 6-O-sulfotransferase (KSGal6ST) and chondroitin 6-O-sulfotransferase 1 (C6ST-1). Here we use mice deficient in both KSGal6ST and C6ST-1 to determine whether these sulfotransferases are required for the generation of endogenous Siglec-F ligands. First, we characterize ligand expression on leukocyte populations and find that ligands are predominantly expressed on cell types also expressing Siglec-F, namely eosinophils, neutrophils, and alveolar macrophages. We also detect Siglec-F ligand activity in bronchoalveolar lavage fluid fractions containing polymeric secreted mucins, including MUC5B. Consistent with these observations, ligands in the lung increase dramatically during infection with the parasitic nematode, Nippostrongylus brasiliensis, which is known to induce eosinophil accumulation and mucus production. Surprisingly, Gal6S is undetectable in sialylated glycans from eosinophils and BAL fluid analyzed by mass spectrometry. Furthermore, none of the ligands we describe are diminished in mice lacking KSGal6ST and C6ST-1, indicating that neither of the known galactose 6-O-sulfotransferases is required for ligand synthesis. These results establish that ligands for Siglec-F are present on several cell types that are relevant during allergic lung inflammation and argue against the widely held view that Gal6S is critical for glycan recognition by this receptor.

The role of lung epithelial ligands for Siglec-8 and Siglec-F in eosinophilic inflammation

PURPOSE OF REVIEW

Siglec-8 and Siglec-F are single pass transmembrane inhibitory receptors found on the surface of human and mouse eosinophils, respectively, but very little is known about their physiologic glycan ligands. This article reviews the latest knowledge on this topic and outlines the strategies being used to further define the production and glycobiochemical nature of these molecules in the lung.

RECENT FINDINGS

Both Siglec-8 and Siglec-F recognize the same glycan structure, namely 6'-sulfated sialyl Lewis X, as determined using glycan array technologies. Studies have identified α2,3-linked sialylated glycoprotein structures localized to mouse airway epithelium in tissue sections, where their constitutive expression requires the specific sialyltransferase St3gal3. Expression of these ligands in lung is enhanced during allergic inflammation and by cytokines such as IL-13, and is maintained in primary air-liquid interface cultures of mouse lung epithelium. Further characterization suggests that they are high molecular weight sialylated proteins, putatively mucins. By combining analytic glycomics, glycoproteomic mapping, and further in-vitro eosinophil experimentation including the ability of candidate structures to enhance eosinophil apoptosis, a finely detailed appreciation of the structural requirements for productive Siglec-8 and Siglec-F engagement should soon emerge.

SUMMARY

An enhanced understanding of Siglec-F, Siglec-8, and their ligands should improve our understanding of endogenous lung pathways limiting the survival of eosinophils within the airway in diseases such as asthma. Knowledge of this biology may also result in novel opportunities for drug development involving glycans and glycomimetics that selectively bind to Siglec-8 and induce eosinophil death.

Dendritic cells in the cancer microenvironment

The complexity of the tumor immunoenvironment is underscored by the emergence and discovery of different subsets of immune effectors and regulatory cells. Tumor-induced polarization of immune cell differentiation and function makes this unique environment even more intricate and variable. Dendritic cells (DCs) represent a special group of cells that display different phenotype and activity at the tumor site and exhibit differential pro-tumorigenic and anti-tumorigenic functions. DCs play a key role in inducing and maintaining the antitumor immunity, but in the tumor environment their antigen-presenting function may be lost or inefficient. DCs might be also polarized into immunosuppressive/tolerogenic regulatory DCs, which limit activity of effector T cells and support tumor growth and progression. Although various factors and signaling pathways have been described to be responsible for abnormal functioning of DCs in cancer, there are still no feasible therapeutic modalities available for preventing or reversing DC malfunction in tumor-bearing hosts. Thus, better understanding of DC immunobiology in cancer is pivotal for designing novel or improved therapeutic approaches that will allow proper functioning of DCs in patients with cancer.

Siglec-8 and Siglec-F, the new therapeutic targets in asthma

The recruitment of eosinophils from the circulation into the airway is a prominent feature of allergic asthma. Persistent inflammatory responses may arise from inefficient mechanisms for resolution of inflammation, including delayed apoptosis. Several studies suggest that eosinophil apoptosis is delayed in asthma. Sialic acid-binding immunoglobulin-like lectins are characterized by their sequence similarities and abilities to bind sialic acids in glycoproteins and glycolipids. Siglec-8 is uniquely expressed on eosinophils, mast cells, and basophils. Engagement of Siglec-8 on blood eosinophils results in caspase- and mitochondria-dependent apoptosis. Eosinophil apoptosis is an important therapeutic target for the development of novel anti-asthma treatments that specifically target the eosinophil.

Down-regulation of mast cell responses through ITIM containing inhibitory receptors

The multiple cell types that comprise the immune system provide an efficient defense system against invading pathogens and micro-organisms. In general, immune cells are activated for disparate functions, such as proliferation, production and release of mediators and chemotaxis, as a result of interactions between ligands and their matching immunoreceptors. This in turn leads to the recruitment and activation of a cascade of second messengers, via their regulators/adaptors, that determine the net effect of the initial response. However, activation of cells of the immune system must be tightly regulated by a finely tuned interplay between activation and inhibition to avoid excessive or inappropriate responsiveness and to maintain homeostasis. Loss of inhibitory signals may disrupt this balance, leading to various pathological processes such as allergic and auto-immune diseases. In this chapter, we will discuss down-regulating mechanisms of mast cells focusing on immunoreceptor tyrosine-based inhibition motifs (ITIM)-containing inhibitory receptors (IR).

Immunomodulation of monocyte-derived dendritic cells through ligation of tumor-produced mucins to Siglec-9

Dendritic cells (DCs) play an essential role in the induction and maintenance of an effective immune response and express multiple siglecs. In the present study, we investigated whether or not the ligation of tumor-produced mucins with Siglec-9 expressed on immature DCs is related to escape from immunosurveillance in the tumor-bearing state. Expression of Siglec-9 was up-regulated on the development of monocytes into immature DCs and was decreased in mature DCs. Binding of various mucins and artificial glycopolymers carrying poly (NeuAc α2,6 LacNAc) or poly (NeuAc α2,3 LacNAc) to Siglec-9 was demonstrated by means of a plate assay. These mucins also bound to the surface of immature DCs. When immature DCs were treated with LPS in the presence of these mucins or artificial glycopolymers, the production of IL-12 was significantly reduced, but that of IL-10 was not. Furthermore, IL-12 production was decreased to a similar level on treatment with anti-Siglec-9 mAb. Mucins prepared from serum of cancer patients actually could bind to Siglec-9. These results suggest that Siglec-9 expressed on DCs is involved in immunoregulation through ligation with mucins in an epithelial cancer patient.

MUC1 immunotherapy

The overexpression and aberrant glycosylation of MUC1 is associated with a wide variety of cancers, making it an ideal target for immunotherapeutic strategies. This review highlights the main avenues of research in this field, focusing on adenocarcinomas, from the preclinical to clinical; the problems and possible solutions associated with each approach; and speculates on the direction of MUC1 immunotherapeutic research over the next 5-10 years.

Siglec-8 on human eosinophils and mast cells, and Siglec-F on murine eosinophils, are functionally related inhibitory receptors

Siglecs (sialic acid-binding, Ig-like lectins) are a family of single-pass transmembrane cell surface proteins found predominantly on leucocytes. Their unique structural characteristics include an N-terminal carbohydrate-binding ('lectin') domain that binds sialic acid, followed by a variable number of Ig-like domains, hence these structures are a subset of the Ig gene superfamily. Another unique feature of Siglecs is that most, but not all, possess so-called immunoreceptor tyrosine-based inhibitory motifs in their cytoplasmic domains, suggesting that these molecules function in an inhibitory capacity. Siglec-8, the eighth member identified at the time, was discovered as part of an effort initiated almost a decade ago to identify novel human eosinophil and mast cell proteins. Since that time, its selective expression on human eosinophils and mast cells has been confirmed. On eosinophils, Siglec-8 engagement results in apoptosis, whereas on mast cells, inhibition of FcepsilonRI-dependent mediator release, without apoptosis, is seen. It has subsequently been determined that the closest functional paralog in the mouse is Siglec-F, selectively expressed by eosinophils but not expressed on mast cells. Despite only modest homology, both Siglec-8 and Siglec-F preferentially recognize a sulphated glycan ligand closely related to sialyl Lewis X, a common ligand for the selectin family of adhesion molecules. Murine experiments in normal, Siglec-F-deficient mice and hypereosinophilic mice have resulted in similar conclusions that Siglec-F, like Siglec-8, plays a distinctive and important role in regulating eosinophil accumulation and survival in vivo. Given the resurgent interest in eosinophil-directed therapies for a variety of disorders, plus its unique additional ability to also target the mast cell, therapies focusing on Siglec-8 could some day prove to be a useful adjunct to our current armamentarium for the treatment of asthma, allergies and related disorders where overproduction and overactivity of eosinophils and mast cells is occurring.

Molecular mimicry of host sialylated glycans allows a bacterial pathogen to engage neutrophil Siglec-9 and dampen the innate immune response

Human neutrophil Siglec-9 is a lectin that recognizes sialic acids (Sias) via an amino-terminal V-set Ig domain and possesses tyrosine-based inhibitory motifs in its cytoplasmic tail. We hypothesized that Siglec-9 recognizes host Sias as "self," including in cis interactions with Sias on the neutrophil's own surface, thereby dampening unwanted neutrophil reactivity. Here we show that neutrophils presented with immobilized multimerized Siaalpha2-3Galbeta1-4GlcNAc units engage them in trans via Siglec-9. The sialylated capsular polysaccharide of group B Streptococcus (GBS) also presents terminal Siaalpha2-3Galbeta1-4GlcNAc units, and similarly engages neutrophil Siglec-9, dampening neutrophil responses in a Sia- and Siglec-9-dependent manner. Reduction in the neutrophil oxidative burst, diminished formation of neutrophil extracellular DNA traps, and increased bacterial survival are also facilitated by GBS sialylated capsular polysaccharide interactions with Siglec-9. Thus, GBS can impair neutrophil defense functions by coopting a host inhibitory receptor via sialoglycan molecular mimicry, a novel mechanism of bacterial immune evasion.