Sialic Acid-binding Lectin Research Articles

Prognostic value of PD-L1 and Siglec-15 expression in patients with nasopharyngeal carcinoma

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) might be involved in the activation of important pathways related to tumor immune escape, along with programmed death-ligand 1 (PD-L1). Here, we aimed to investigate the correlation between the expression of Siglec-15 and PD-L1 in nasopharyngeal carcinoma (NPC) patients. We determined the expression of PD-L1 via immunohistochemical staining and that of Siglec-15 via immunofluorescence staining in 182 NPC tissue samples. A significant correlation was identified between the PD-L1 and Siglec-15 expression (P = 0.000). Moreover, Kaplan–Meier survival curves showed that PD-L1 expression was associated with improved overall survival (OS) (P = 0.025) and Siglec-15 expression was associated with improved distant failure-free survival (D-FFS) (P = 0.048). Moreover, multivariate Cox analysis showed that PD-L1 and Siglec-15 were independent predictors of OS (P = 0.020) and D-FFS (P = 0.047), respectively. The results of the log-rank test and Cox regression analyses showed that patients exhibiting no PD-L1/Siglec-15 expression had significant advantages regarding OS, compared to other groups (P = 0.037). PD-L1 and Siglec-15 may represent novel biomarkers for predicting the prognosis of NPC patients. Siglec-15 may be considered as a potential target for the development of therapeutics for NPC treatment in the future.

Abstract 613: AL009 is a multi-Siglec inhibitor engineered to bind myeloid cells that enhances innate and adaptive immunity to cancer

Abstract Background - Inhibitory sialic acid-binding immunoglobulin-type lectins (Siglecs) are a subset of the Siglec family of cell surface receptors that potentiate immune tolerance. A multitude of inhibitory Siglecs on myeloid cells become engaged in sialic acid-rich tumor microenvironments, suggesting that disrupting Siglec-sialic acid signaling could confer therapeutic benefit in cancer. To accomplish this, we designed AL009, an engineered Siglec-9 extracellular domain-Fc fusion molecule that acts as a sialic acid trap and a multi-Siglec inhibitor, repolarizing suppressive myeloid cells and activating an anti-cancer response. Methods - Cooperative binding of AL009 was analyzed by flow cytometry using cultured human tumor cell lines and myeloid-derived suppressor cells (MDSCs) differentiated from primary human monocytes. Monocytes, MDSCs, and macrophages differentiated from primary human monocytes were assessed for AL009 binding by flow cytometry. AL009m (AL009 with a mouse Fc) was fluorophore-labeled and intravenously injected into B6 mice to analyze biodistribution via ex vivo tissue imaging over time. Initial toxicology screening was conducted in cynomolgus monkeys in a non-terminal study. Results - AL009 displays cooperative binding with sialic acid and Fc gamma receptors on myeloid cells. When comparing binding among myeloid cell subsets, AL009 preferentially binds MDSCs. Analysis of the biodistribution of labeled AL009m in mice showed the greatest accumulation in the spleen, consistent with immune cell targeting in vivo. Further, Fc engineering of AL009 improved the pharmacodynamic profile compared to a non-engineered Fc. In cynomolgus monkeys, single doses of 80 mg/kg appeared safe and without clinically significant findings. Conclusions - The engineered structure of AL009 leads to preferential binding to an immunosuppressive subset of myeloid cells. This targeting leads to repolarization of myeloid cells and activates an innate and adaptive anti-cancer response. Pharmacologically relevant doses of AL009 appear well-tolerated in initial studies in non-human primates, supporting further development for entry into clinical studies. Citation Format: Sam Nalle, Helen Lam, Cheryl Barner, Hua Long, Spencer Liang, Arnon Rosenthal, Daniel Maslyar. AL009 is a multi-Siglec inhibitor engineered to bind myeloid cells that enhances innate and adaptive immunity to cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 613.

Sialic acids on B cells are crucial for their survival and provide protection against apoptosis

Sialic acids (Sias) on the B cell membrane are involved in cell migration, in the control of the complement system and, as sialic acid-binding immunoglobulin-like lectin (Siglec) ligands, in the regulation of cellular signaling. We studied the role of sialoglycans on B cells in a mouse model with B cell-specific deletion of cytidine monophosphate sialic acid synthase (CMAS), the enzyme essential for the synthesis of sialoglycans. Surprisingly, these mice showed a severe B cell deficiency in secondary lymphoid organs. Additional depletion of the complement factor C3 rescued the phenotype only marginally, demonstrating a complement-independent mechanism. The B cell survival receptor BAFF receptor was not up-regulated, and levels of activated caspase 3 and processed caspase 8 were high in B cells of Cmas-deficient mice, indicating ongoing apoptosis. Overexpressed Bcl-2 could not rescue this phenotype, pointing to extrinsic apoptosis. These results show that sialoglycans on the B cell surface are crucial for B cell survival by counteracting several death-inducing pathways.

High Expression Levels of SIGLEC9 Indicate Poor Outcomes of Glioma and Correlate With Immune Cell Infiltration.

ObjectiveThis study aimed to investigate the diagnostic value and underlying mechanisms of sialic acid-binding Ig-like lectin 9 (SIGLEC9) in gliomas.Patients and MethodsThe Cancer Genome Atlas (TCGA) and the Chinese Glioma Genome Atlas (CGGA) databases were used to analyze the association of SIGLEC9 expression levels with tumor stages and survival probability. Immunohistochemical staining of SIGLEC9 and survival analysis were performed in 177 glioma patients. Furthermore, related mechanisms were discovered about SIGLEC9 in glioma tumorigenesis, and we reveal how SIGLEC9 functions in macrophages through single-cell analysis.ResultsTCGA and CGGA databases indicated that patients with high SIGLEC9 expression manifested a significantly shorter survival probability than those with low SIGLEC9 expression. SIGLEC9 was upregulated significantly in malignant pathological types, such as grade III, grade IV, mesenchymal subtype, and isocitrate dehydrogenase wild-type gliomas. The immunohistochemical staining of tissue sections from 177 glioma patients showed that high-SIGLEC9-expression patients manifested a significantly shorter survival probability than low-SIGLEC9-expression patients with age ≧60 years, grade IV, glioblastoma multiforme, alpha thalassemia/intellectual disability syndrome X-linked loss, and without radiotherapy or chemotherapy. Furthermore, the SIGLEC9 expression level was positively correlated with myeloid-derived suppressor cell infiltration and neutrophil activation. The SIGLEC9 expression was also positively correlated with major immune checkpoints, such as LAIR1, HAVCR2, CD86, and LGALS9. Through single-cell analysis, we found that the SIGLEC9 gene is related to the ability of macrophages to process antigens and the proliferation of macrophages.ConclusionThese findings suggested that SIGLEC9 is a diagnostic marker of poor outcomes in glioma and might serve as a potential immunotherapy target for glioma patients in the future.

Study on the effect and mechanisms of SIGLEC-15 on laryngeal squamous cell carcinoma

Objective: To investigate the effect of sialic acid combined with immunoglobulin-like lectin 15 (SIGLEC-15) on laryngeal squamous cell carcinoma (LSCC) and underlying mechanisms. Methods: The Cancer Genome Atlas (TCGA), Cancer Cell Line Encyclopedia (CCLE) and Gene Expression Profiling Interactive Analysis (GEPIA2) databases were used for bioinformatics analysis. Cell Counting Kit-8 (CCK8), flow cytometry, and Transwell method were used respectively to detect proliferation, apoptosis, cell cycle, metastasis and invasion behaviors of the cells. Gene chip method was used for detecting up-regulated and down-regulated genes and performing enrichment analysis of differential genes. Western Blotting (WB) and Quantitative Real-time PCR (qPCR) were used to detect the expressions of proteins. Tumor formation experiments in nude mice were used to detect the effect of SIGLEC-15 on the growth of transplanted tumors. Wilcoxon rank sum test, t-test and Log-rank test were used for statistical analysis. Results: SIGLEC-15 was highly expressed in laryngeal squamous cell carcinoma and closely related to life in being. TU686SIGLEC-15-with low expression of SIGLEC-15 was constructed. Compared to TU686SIGLEC-15+, TU686SIGLEC-15-showed significantly reduced activities of proliferation (48 h: 1.32±0.23 vs. 2.56±0.37, t=6.59, P<0.05), migration (1 036.52±51.22 vs. 1 819.62±180.24, t=7.22, P<0.05) and invasion (469.21±112.25 vs. 961.45±102.03, t=7.85, P<0.05); early increased apoptosis ((23.27±1.12)% vs. (5.64±1.61)%, t=11.32, P<0.05); blocked cell cycle at G0/G1 ((59.32±3.65)% vs. (35.46±3.57)%, t=9.85, P<0.05); the knockdown of SIGLEC-15 resulted in up-regulation of 864 genes, down-regulation of 357 genes, with significant changes in molecules of cell cycle, apoptosis and JAK/STAT signal pathways, and the expressions of p-JAK2, p-STAT3, Caspase-3, Bad, Bcl-2, and Cyclin d1 proteins. Tumor formation experiments in nude mice showed that at 8 weeks after the tumors were implanted, the growth transplanted tumors of TU686 SIGLEC-15-cell group was slower than that of TU686 SIGLEC-15+cell group, with significant difference in the mean tumor weights between two groups ((0.382±0.054) g vs. (1.277±0.126) g, t=8.44, P<0.05), while the expression of SIGLEC-15 was lower in the transplanted tumors of SIGLEC-15 knockdown group compared to control group, with significant difference(11.29±2.17 vs. 36.25±7.56, t=9.28, P<0.05). Conclusion: SIGLEC-15 is highly expressed in LSCC and can promote the progression of LSCC through the JAK2-STAT3 pathway.

Bronchial asthma from the perspective of glycomics

Bronchial asthma is a widespread disease that is becoming increasingly costly to the medical and financial systems of many countries with each passing year. The rising prevalence of bronchial asthma necessitates a search for the most efficient diagnostic and treatment strategies for various asthma phenotypes, including some that are relatively uncommon.&#x0D; From this point of view, glycomics appears to be one of the most interesting and perspective branches of medicine. This research area studies various carbohydrate complexes and their roles in the development of various diseases.&#x0D; Researchers are interested in the study of the receptors for advanced glycation end products and their soluble variants with regard to bronchial asthma. Furthermore, sialic acid-binding immunoglobulin-type lectins (Siglecs) may play a vital role in the principal novel strategies of the treatment. By affecting Siglecs, a decrease in the proinflammatory activity of immunocompetent cells results, and the bronchial walls are protected. Finally, N- and O-glycans remain almost unresearched. These molecules, on the other hand, have the potential to play a significant role not only in the diagnosis and confirmation of asthma but also in the allergenicity of various molecules. Scientists are interested in N-glycans, not only in the diagnostic context but also in their role as a molecule that can reduce allergenicity, for example, egg white vaccines.&#x0D; Glycomics and glycoproteomics are cutting-edge disciplines of medical science that are opening up new perspectives in the management of patients with diseases of various organs and systems, including diseases of the respiratory tract in general and bronchial asthma in particular. Despite the fast-paced nature of the development of glycoscience, theories about the role of the molecules investigated in the pathophysiology of respiratory disorders are only beginning to emerge.

Validation of disease-specific biomarkers for the early detection of bronchopulmonary dysplasia

ObjectiveTo demonstrate and validate the improvement of current risk stratification for bronchopulmonary dysplasia (BPD) early after birth by plasma protein markers (sialic acid-binding Ig-like lectin 14 (SIGLEC-14), basal cell adhesion molecule (BCAM), angiopoietin-like 3 protein (ANGPTL-3)) in extremely premature infants.Methods and resultsProteome screening in first-week-of-life plasma samples of n = 52 preterm infants <32 weeks gestational age (GA) on two proteomic platforms (SomaLogic®, Olink-Proteomics®) confirmed three biomarkers with significant predictive power: BCAM, SIGLEC-14, and ANGPTL-3. We demonstrate high sensitivity (0.92) and specificity (0.86) under consideration of GA, show the proteins’ critical contribution to the predictive power of known clinical risk factors, e.g., birth weight and GA, and predicted the duration of mechanical ventilation, oxygen supplementation, as well as neonatal intensive care stay. We confirmed significant predictive power for BPD cases when switching to a clinically applicable method (enzyme-linked immunosorbent assay) in an independent sample set (n = 25, p < 0.001) and demonstrated disease specificity in different cohorts of neonatal and adult lung disease.ConclusionWhile successfully addressing typical challenges of clinical biomarker studies, we demonstrated the potential of BCAM, SIGLEC-14, and ANGPTL-3 to inform future clinical decision making in the preterm infant at risk for BPD.Trial registrationDeutsches Register Klinische Studien (DRKS) No. 00004600; https://www.drks.de.ImpactThe urgent need for biomarkers that enable early decision making and personalized monitoring strategies in preterm infants with BPD is challenged by targeted marker analyses, cohort size, and disease heterogeneity.We demonstrate the potential of the plasma proteins BCAM, SIGLEC-14, and ANGPTL-3 to identify infants with BPD early after birth while improving the predictive power of clinical variables, confirming the robustness toward proteome assays and proving disease specificity.Our comprehensive analysis enables a phase-III clinical trial that allows full implementation of the biomarkers into clinical routine to enable early risk stratification in preterms with BPD.

Suppressing Immune Responses Using Siglec Ligand-Decorated Anti-receptor Antibodies.

The sialic acid-binding immunoglobulin-type lectins (Siglecs) are expressed predominantly on white blood cells and participate in immune cell recognition of self. Most Siglecs contain cytoplasmic inhibitory immunoreceptor tyrosine-based inhibitory motifs characteristic of inhibitory checkpoint co-receptors that suppress cell signaling when they are recruited to the immunological synapse of an activating receptor. Antibodies to activatory receptors typically activate immune cells by ligating the receptors on the cell surface. Here, we report that the conjugation of high affinity ligands of Siglecs to antibodies targeting activatory immune receptors can suppress receptor-mediated activation of immune cells. Indeed, B-cell activation by antibodies to the B-cell receptor IgD is dramatically suppressed by conjugation of anti-IgD with high affinity ligands of a B-cell Siglec CD22/Siglec-2. Similarly, degranulation of mast cells induced by antibodies to IgE, which ligate the IgE/FcεR1 receptor complex, is suppressed by conjugation of anti-IgE to high affinity ligands of a mast cell Siglec, CD33/Siglec-3 (CD33L). Moreover, the anti-IgE-CD33L suppresses anti-IgE-mediated systemic anaphylaxis of sensitized humanized mice and prevents anaphylaxis upon subsequent challenge with anti-IgE. The results demonstrate that attachment of ligands of inhibitory Siglecs to anti-receptor antibodies can suppress the activation of immune cells and modulate unwanted immune responses.

Ligation of Siglec-9 inhibits FcɛRI-dependent mediator release from human mast cells

Abstract Mast cell activation is critical for the development of allergic diseases. Ligation of Sialic acid-binding immunoglobin-like lectins (Siglecs) such as Siglec-7 and 8 has been shown to inhibit mast cell activation and is considered one of the main approaches to reduce mast cell contribution to allergic disease. Recent high throughput studies provided evidence that human mast cells express Siglec-9, an inhibitory receptor that is mainly expressed by innate immune cells such as neutrophils, monocytes and eosinophils. Based on this evidence, we aimed to examine Siglec-9 expression and function in human mast cells. Flow cytometry analysis showed that Siglec-9 is expressed in the human mast cell lines LAD2, LUVA, and HMC-1, and in peripheral blood-derived cultured human mast cells (PBCMCs). The expression of Siglec-9 in PBCMCs peaks at week 5 of culture and correlates positively with the expression of the high affinity receptor for IgE (FcɛRI). Pre-treatment of human mast cells with the Siglec-9 agonists glycophorin A or high molecular weight hyaluronic acid (HMW-HA) followed by FcɛRI-dependent stimulation has an inhibitory effect on mast cell degranulation. SIGLEC9 gene disruption by CRISPR/Cas9 editing resulted in a significant reduction in Siglec-9 expression in LAD2 cells that also became impervious to inhibition by Siglec-9 agonists. Together, our data shows that human mast cells express Siglec-9 and that engaging this inhibitory receptor can reduce mast cell degranulation.

Regulation of Siglec-7-mediated varicella-zoster virus infection of primary monocytes by cis-ligands

Varicella-zoster virus (VZV) first infects hematopoietic cells, with the infected cells then acting to distribute the virus throughout the body. Sialic acid-binding immunoglobulin-like lectin (Siglec) family molecules recognize sialic acid-containing molecules on the same cell surface, called cis-ligands, or molecules on other cells or soluble agents, called trans-ligands. Among the Siglec family molecules, Siglec-4 and Siglec-7 mediate VZV infection through association with glycoprotein B (gB). As Siglec-7, but not Siglec-4, is expressed on hematopoietic cells such as monocytes, the regulatory mechanism by which Siglec-7 associates with gB is important to our understanding of VZV infection of blood cells. Here, we found that Siglec-7 is required for VZV to infect human primary monocytes. Furthermore, treatment of primary monocytes with sialidase enhanced both VZV gB binding to monocytes and VZV infectivity. Calcium influx in primary monocytes decreased the expression of Siglec-7 cis-ligands and increased VZV infectivity. These results demonstrate that the Siglec-7 cis-ligands present on primary monocytes play an important role in VZV infection through regulation of the interaction between gB and Siglec-7.

Transgenic mouse models to study the physiological and pathophysiological roles of human Siglecs.

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are important immunomodulatory receptors. Due to differences between human and mouse Siglecs, defining the in vivo roles for human Siglecs (hSiglecs) can be challenging. One solution is the development and use of hSiglec transgenic mice to assess the physiological roles of hSiglecs in health and disease. These transgenic mice can also serve as important models for the pre-clinical testing of immunomodulatory approaches that are based on targeting hSiglecs. Four general methods have been used to create hSiglec-expressing transgenic mice, each with associated advantages and disadvantages. To date, transgenic mouse models expressing hSiglec-2 (CD22), -3 (CD33), -7, -8, -9, -11, and -16 have been created. This review focuses on both the generation of these hSiglec transgenic mice, along with the important findings that have been made through their study. Cumulatively, hSiglec transgenic mouse models are providing a deeper understanding of the differences between human and mice orthologs/paralogs, mechanisms by which Siglecs regulate immune cell signaling, physiological roles of Siglecs in disease, and different paradigms where targeting Siglecs may be therapeutically advantageous.

Siglec-5 is an inhibitory immune checkpoint molecule for human T cells.

Sialic acid-binding immunoglobulin-type lectins (Siglecs) are a family of immunoglobulin-type lectins that mediate protein-carbohydrate interactions via sialic acids attached to glycoproteins or glycolipids. Most of the CD33-related Siglecs (CD33rSiglecs), a major subfamily of rapidly evolving Siglecs, contain a cytoplasmic signaling domain consisting of the immunoreceptor tyrosine-based inhibitory motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM) and mediate suppressive signals for lymphoid and myeloid cells. While most CD33rSiglecs are expressed by innate immune cells, such as monocytes and neutrophils, to date, the expression of Siglecs in human T cells has not been well appreciated. In this study, we found that Siglec-5, a member of the CD33rSiglecs, is expressed by most activated T cells upon antigen receptor stimulation. Functionally, Siglec-5suppresses T cell activation. In support of these findings, we found that Siglec-5 overexpression abrogates antigen receptor induced activation of NFAT and AP-1. Furthermore, we show that GBS β-protein, a known bacterial ligand of Siglec-5, reduces the production of cytokines and cytolytic molecules by activated primary T cells in a Siglec-5 dependent manner. Our data also show that some cancer cell lines express a putative Siglec-5ligand(s), and that the presence of soluble Siglec-5 enhances tumor-cell specific T cell activation, suggesting that some tumor cells inhibit T cell activation via Siglec-5. Together, our data demonstrate that Siglec-5 is a previously unrecognized inhibitory T cell immune checkpoint molecule and suggest that blockade of Siglec-5 could serve as a new strategy to enhance anti-tumor T cell functions.

Siglec Receptors Modulate Dendritic Cell Activation and Antigen Presentation to T Cells in Cancer.

Interactions between sialylated glycans and sialic acid-binding immunoglobulin-like lectin (Siglec) receptors have been recently described as potential new immune checkpoint that can be targeted to improve anticancer immunity. Myeloid cells have been reported to express a wide range of different Siglecs; however, their expression and functions on cancer-associated dendritic cells (DCs) were not fully characterized. We found that classical conventional DCs (cDCs) from cancer patient samples have a high expression of several inhibitory Siglecs including Siglec-7, Siglec-9, and Siglec-10. In subcutaneous murine tumor models, we also found an upregulation of the inhibitory Siglec-E receptor on cancer-associated cDCs. DC lines and bone marrow-derived DCs (BMDCs) with expression of these inhibitory Siglecs showed impaired maturation states on transcriptome and protein level. Furthermore, ablation of these inhibitory Siglecs from DCs enhanced their capability to prime antigen-specific T cells and induce proliferation. Our work provides a deeper understanding of the influence of inhibitory Siglecs on DCs and reveals a potential new target to improve cancer immunotherapy.

Identification and characterization of three Siglec15-related immune and prognostic subtypes of breast-invasive cancer

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec15) is an immune checkpoint molecule that can inhibit T cell proliferation and have anti-tumor immunity. We explored the correlation between Siglct15 and the clinical features, mutation frequency, and prognosis of breast cancer. 122 upregulated and 11 downregulated genes between Siglet15-high and -low expression groups of 1109 breast invasive cancer samples (BRCA) obtained from the Cancer Genome Atlas (TCGA) were identified. Three subtypes (C1-C3) of BRCA based on Siglec15 were identified from TCGA datasets via consensus cluster plus analysis. The clinical characteristics, functional enrichments, immune environment, mutation frequency, prognosis were compared among these subgroups and were verified using GSE20685 and GSE31448 cohorts. C3 with highest level of Siglec15 expression was correlated with early tumor stage, hormone receptor-positive tumors, luminal A molecular subtype, lowest tumor mutational burden (TMB) score, lowest programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) expression, upregulated PI3K-Akt pathway and advantage of prognosis. C2 with lowest level of Siglec15 was associated with advanced stage, basal-like subtype, highest TMB score, highest PD-1 and PD-L1 expression, upregulated p53 signaling pathway and worse prognosis. Univariate and multivariate Cox regression analysis demonstrated that Siglec15-related subtype was an independent prognostic factor for breast cancer patients. Siglec15 related immunotherapy may be an important candidate for breast cancer patients especially for luminal subtype, independently of blockade of PD-1/PD-L1 immunotherapy. In conclusion, we identified three Siglec15-related subtypes of BRCA, helping us to understand the immunological function and significance of Siglec15 in the BRCA.

Platelets as Key Factors in Inflammation: Focus on CD40L/CD40.

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

Discovery of antitumor effects of leczymes

Sialic-acid binding lectin from bullfrog (Rana catesbeiana) eggs, cSBL, is a cytotoxic ribonuclease (RNase) belonging to the RNase A superfamily. cSBL is cytotoxic to tumor cells, such as malignant pleural mesothelioma by inducing apoptotic cell death caused by the degradation of RNA in tumor cells. In addition, we have reported some data that cSBL could be involved in the endoplasmic reticulum stress pathway, and it was also assumed to cause apoptotic cell death. The most significant property of cSBL is its specificity toward malignant cells. Furthermore, since the antitumor activity of cSBL was confirmed by in vivo experiments using mouse xenograft models, it is expected to be a candidate for clinical chemotherapy. Here, we summarize the history of cSBL, alternatively called "leczyme," with its present and future.

Polymer-tethered glycosylated gold nanoparticles recruit sialylated glycoproteins into their protein corona, leading to off-target lectin binding.

Upon exposure to biological fluids, the fouling of nanomaterial surfaces results in non-specific capture of proteins, which is particularly important when in contact with blood for in vivo and ex vivo applications. It is crucial to evaluate not just the protein components but also the glycans attached to those proteins. Polymer-tethered glycosylated gold nanoparticles have shown promise for use in biosensing/diagnostics, but the impact of the glycoprotein corona has not been established. Here we investigate how polymer-tethered glycosylated gold nanoparticles interact with serum proteins and demonstrate that the protein corona introduces new glycans and hence off-specific targeting capability. Using a panel of RAFT-derived polymers grafted to the gold surface, we show that the extent of corona formation is not dependent on the type of polymer. In lectin-binding assays, a glycan (galactose) installed on the chain-end of the polymer was available for binding even after protein corona formation. However, using sialic-acid binding lectins, it was found that there was significant off-target binding due to the large density of sialic acids introduced in the corona, confirmed by western blotting. To demonstrate the importance, we show that the nanoparticles can bind Siglec-2, an immune-relevant lectin post-corona formation. Pre-coating with (non-glycosylated) bovine serum albumin led to a significant reduction in the total glycoprotein corona. However, sufficient sialic acids were still present in the residual corona to lead to off-target binding. These results demonstrate the importance of the glycans when considering the protein corona and how 'retention of the desired function' does not rule out 'installation of undesired function' when considering the performance of glyco-nanomaterials.

Sugar-decorated carbon dots: a novel tool for targeting immunomodulatory receptors.

Interactions between sialic acid (Sia) and sialic acid-binding immunoglobulin-like lectins (siglecs) regulate the immune system, with aberrations contributing to pathologies such as autoimmunity, infectious disease and cancer. Over the last decade, several multivalent Sia ligands have been synthesized to modulate the Sia-binding affinity of proteins/lectins. Here, we report a novel class of multivalent siglec probes through the decoration of α(2,6)-sialyllactose ligands on inherently fluorescent carbon dots (CD). We show that the preference of α(2,3)-linked Sia for siglec-1 can be altered by increasing the multivalence of Sia ligands present on the CD, and that a locally high glycan concentration can have a direct effect on linkage specificity. Additionally, micromolar (IC50 ∼ 70 μM) interaction of α(2,6)-sialyllactose-CD (6-CD) with siglec-2 (CD22) revealed it was capable of generating a significant cytotoxic effect on Burkitt's Lymphoma (BL) Daudi B cells. This phenonomen was attributed to 6-CD's ability to form trans interactions with CD22 on masked BL Daudi cells as a direct result of clustering of the Sia moiety on the CD surface. Overall, our glycoengineered carbon dots represent a novel high affinity molecular probe with multiple applications in sialoglycoscience and medicine.

HIV-1 trans-Infection Mediated by DCs: The Tip of the Iceberg of Cell-to-Cell Viral Transmission

HIV-1 cell-to-cell transmission is key for an effective viral replication that evades immunity. This highly infectious mechanism is orchestrated by different cellular targets that utilize a wide variety of processes to efficiently transfer HIV-1 particles. Dendritic cells (DCs) are the most potent antigen presenting cells that initiate antiviral immune responses, but are also the cells with highest capacity to transfer HIV-1. This mechanism, known as trans-infection, relies on the capacity of DCs to capture HIV-1 particles via lectin receptors such as the sialic acid-binding I-type lectin Siglec-1/CD169. The discovery of the molecular interaction of Siglec-1 with sialylated lipids exposed on HIV-1 membranes has enlightened how this receptor can bind to several enveloped viruses. The outcome of these interactions can either mount effective immune responses, boost the productive infection of DCs and favour innate sensing, or fuel viral transmission via trans-infection. Here we review these scenarios focusing on HIV-1 and other enveloped viruses such as Ebola virus or SARS-CoV-2.

Siglec Signaling in the Tumor Microenvironment.

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are a family of receptors that recognize sialoglycans – sialic acid containing glycans that are abundantly present on cell membranes. Siglecs are expressed on most immune cells and can modulate their activity and function. The majority of Siglecs contains immune inhibitory motifs comparable to the immune checkpoint receptor PD-1. In the tumor microenvironment (TME), signaling through the Siglec-sialoglycan axis appears to be enhanced through multiple mechanisms favoring tumor immune evasion similar to the PD-1/PD-L1 signaling pathway. Siglec expression on tumor-infiltrating immune cells appears increased in the immune suppressive microenvironment. At the same time, enhanced Siglec ligand expression has been reported for several tumor types as a result of aberrant glycosylation, glycan modifications, and the increased expression of sialoglycans on proteins and lipids. Siglec signaling has been identified as important regulator of anti-tumor immunity in the TME, but the key factors contributing to Siglec activation by tumor-associated sialoglycans are diverse and poorly defined. Among others, Siglec activation and signaling are co-determined by their expression levels, cell surface distribution, and their binding preferences for cis- and trans-ligands in the TME. Siglec binding preference are co-determined by the nature of the proteins/lipids to which the sialoglycans are attached and the multivalency of the interaction. Here, we review the current understanding and emerging conditions and factors involved in Siglec signaling in the TME and identify current knowledge gaps that exist in the field.