Sialic Acid-binding Ig-like Lectin Research Articles

T-cell dysfunction in CLL is mediated through expression of Siglec-10 ligands CD24 and CD52 on CLL cells

AbstractAutologous T-cell–based therapies, such as chimeric antigen receptor (CAR) T-cell therapy, exhibit low success rates in chronic lymphocytic leukemia (CLL) and correlate with a dysfunctional T-cell phenotype observed in patients. Despite various proposed mechanisms of T-cell dysfunction in CLL, the specific CLL-derived factors responsible remain unidentified. This study aimed to investigate the mechanisms through which CLL cells suppress CAR T-cell activation and function. We found that CLL-derived T cells get activated, albeit in a delayed fashion, and specifically that restimulation of CAR T cells in the presence of CLL cells causes impaired cytokine production and reduced proliferation. Notably, coculture of T cells with CD40-activated CLL cells did not lead to T-cell dysfunction, and this required direct cell contact between the CD40-stimulated CLL cells and T cells. Inhibition of kinases involved in the CD40 signaling cascade revealed that the Spare Respiratory Capacity (SRC) kinase inhibitor dasatinib prevented rescue of T-cell function independent of CD40-mediated increased levels of costimulatory and adhesion ligands on CLL cells. Transcriptome profiling of CD40-stimulated CLL cells with or without dasatinib identified widespread differential gene expression. Selecting for surface receptor genes revealed CD40-mediated downregulation of the Sialic acid-binding Ig-like lectin 10 (Siglec-10) ligands CD24 and CD52, which was prevented by dasatinib, suggesting a role for these ligands in functional T-cell suppression in CLL. Indeed, blocking CD24 and/or CD52 markedly reduced CAR T-cell dysfunction upon coculture with resting CLL cells. These results demonstrated that T cells derived from CLL patients can be reinvigorated by manipulating CLL–T-cell interactions. Targeting CD24- and CD52-mediated CLL–T-cell interaction could be a promising therapeutic strategy to enhance T-cell function in CLL.

Involvement of Siglec-15 in regulating RAP1/RAC signaling in cytoskeletal remodeling in osteoclasts mediated by macrophage colony-stimulating factor

DNAX-associated protein 12 kD size (DAP12) is a dominant immunoreceptor tyrosine-based activation motif (ITAM)-signaling adaptor that activates costimulatory signals essential for osteoclastogenesis. Although several DAP12-associated receptors (DARs) have been identified in osteoclasts, including triggering receptor expressed on myeloid cells 2 (TREM-2), C-type lectin member 5 A (CLEC5A), and sialic acid-binding Ig-like lectin (Siglec)-15, their precise role in the development of osteoclasts and bone remodeling remain poorly understood. In this study, mice deficient in Trem-2, Clec5a, Siglec-15 were generated. In addition, mice double deficient in these DAR genes and FcεRI gamma chain (FcR)γ, an alternative ITAM adaptor to DAP12, were generated. Bone mass analysis was conducted on all mice. Notably, Siglec-15 deficient mice and Siglec-15/FcRγ double deficient mice exhibited mild and severe osteopetrosis respectively. In contrast, other DAR deficient mice showed normal bone phenotype. Likewise, osteoclasts from Siglec-15 deficient mice failed to form an actin ring, suggesting that Siglec-15 promotes bone resorption principally by modulating the cytoskeletal organization of osteoclasts. Furthermore, biochemical analysis revealed that Sigelc-15 activates macrophage colony-stimulating factor (M-CSF)-induced Ras-associated protein-1 (RAP1)/Ras-related C3 botulinum toxin substrate 1 (Rac1) pathway through formation of a complex with p130CAS and CrkII, leading to cytoskeletal remodeling of osteoclasts. Our data provide genetic and biochemical evidence that Siglec-15 facilitates M-CSF-induced cytoskeletal remodeling of the osteoclasts.

Targeting SIGLEC15 as an emerging immunotherapy for anaplastic thyroid cancer

Anaplastic thyroid carcinoma (ATC) is the most aggressive subtype of thyroid cancer with few effective therapies. Though immunotherapies such as targeting PD-1/PD-L1 axis have benefited patients with solid tumor, the druggable immune checkpoints are quite limited in ATC. In our study, we focused on the anti-tumor potential of sialic acid-binding Ig-like lectins (Siglecs) in ATC. Through screening by integrating microarray datasets including 216 thyroid-cancer tissues and single-cell RNA-sequencing, SIGLEC family members CD33, SIGLEC1, SIGLEC10 and SIGLEC15 were significantly overexpressed in ATC, among which SIGLEC15 increased highest and mainly expressed on cancer cells. SIGLEC15high ATC cells are characterized by high expression of serine protease PRSS23 and cancer stem cell marker CD44. Compared with SIGLEC15low cancer cells, SIGLEC15high ATC cells exhibited higher interaction frequency with tumor microenvironment cells. Further study showed that SIGLEC15high cancer cells mainly interacted with T cells by immunosuppressive signals such as MIF-TNFRSF14 and CXCL12-CXCR4. Notably, treatment of anti-SIGLEC15 antibody profoundly increased the cytotoxic ability of CD8+ T cells in a co-culture model and zebrafish-derived ATC xenografts. Consistently, administration of anti-SIGLEC15 antibody significantly inhibited tumor growth and prolonged mouse survival in an immunocompetent model of murine ATC, which was associated with increase of M1/M2, natural killer (NK) cells and CD8+ T cells, and decrease of myeloid-derived suppressor cells (MDSCs). SIGLEC15 inhibited T cell activation by reducing NFAT1, NFAT2, and NF-κB signals. Blocking SIGLEC15 increased the secretion of IFN-γ and IL-2 in vitro and in vivo. In conclusion, our finding demonstrates that SIGLEC15 is an emerging and promising target for immunotherapy in ATC.

Unveiling the hub genes in the SIGLECs family in colon adenocarcinoma with machine learning.

Despite the recognized roles of Sialic acid-binding Ig-like lectins (SIGLECs) in endocytosis and immune regulation across cancers, their molecular intricacies in colon adenocarcinoma (COAD) are underexplored. Meanwhile, the complicated interactions between different SIGLECs are also crucial but open questions. We investigate the correlation between SIGLECs and various properties, including cancer status, prognosis, clinical features, functional enrichment, immune cell abundances, immune checkpoints, pathways, etc. To fully understand the behavior of multiple SIGLECs' co-evolution and subtract its leading effect, we additionally apply three unsupervised machine learning algorithms, namely, Principal Component Analysis (PCA), Self-Organizing Maps (SOM), K-means, and two supervised learning algorithms, Least Absolute Shrinkage and Selection Operator (LASSO) and neural network (NN). We find significantly lower expression levels in COAD samples, together with a systematic enhancement in the correlations between distinct SIGLECs. We demonstrate SIGLEC14 significantly affects the Overall Survival (OS) according to the Hazzard ratio, while using PCA further enhances the sensitivity to both OS and Disease Free Interval (DFI). We find any single SIGLEC is uncorrelated to the cancer stages, which can be significantly improved by using PCA. We further identify SIGLEC-1,15 and CD22 as hub genes in COAD through Differentially Expressed Genes (DEGs), which is consistent with our PCA-identified key components PC-1,2,5 considering both the correlation with cancer status and immune cell abundance. As an extension, we use SOM for the visualization of the SIGLECs and show the similarities and differences between COAD patients. SOM can also help us define subsamples according to the SIGLECs status, with corresponding changes in both immune cells and cancer T-stage, for instance. We conclude SIGLEC-1,15 and CD22 as the most promising hub genes in the SIGLECs family in treating COAD. PCA offers significant enhancement in the prognosis and clinical analyses, while using SOM further unveils the transition phases or potential subtypes of COAD.

Abstract 75: Luciferase reporter cell lines allow simultaneous incorporation of tumor cells, innate immune cells, and adaptive immune cells for in-depth immune checkpoint studies

Abstract Despite the considerable success of immune checkpoint therapies targeting T cells, a sizable proportion of patients experience resistance or relapse due to the immunosuppressive nature of the tumor microenvironment. Myeloid cells, a major component that suppresses effector lymphocytes, have emerged as an alternative and promising therapeutic target. However, there is a deep lack of widely accessible immunological models capable of representing the intricate three-way interaction between tumor cells, T cells, and myeloid cells. To address this need, we conducted a comprehensive protein profiling of human tumor and immune cell lines available at ATCC for various established and novel immune checkpoint molecules. Cell lines with high endogenous expression of the immune checkpoint proteins, such as programmed death-ligand 1 and 2 (PD-L1 and PD-L2), cluster of differentiation 155 (CD155), B7 homolog 3 (B7-H3), sialic acid-binding Ig-like lectin 10 (Siglec-10), or signal-regulatory protein alpha (SIRPα), were selected and constructed into luciferase reporter cell lines. For tumor reporter cell lines, a gamma interferon activation site (GAS) response element was placed upstream of the luciferase gene in the lentiviral vector, enabling the activation of the JAK-STAT signaling pathway within tumor cells to induce luciferase expression. In myeloid reporter cell lines, a nuclear factor kappa B (NF-κB) response element replaced GAS to monitor the activation of the NF-κB signaling pathway. In the presence of corresponding immune checkpoint inhibitors that enhance T cell-mediated anti-tumor activity, these reporter cell lines produce a bioluminescent signal based on luciferase expression. This signal can be easily detected and quantified to assess the efficacy of the inhibitor. Our data revealed that bioluminescence intensity in the tumor and myeloid reporter cell lines increased by >100-fold in a dose-dependent manner in response to interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) stimulation, respectively, and by >50-fold in response to the conditioned media collected from activated primary T cells. Furthermore, in co-culture assays involving various combinations of immune cell and tumor cell types with corresponding immune checkpoint inhibitors, these reporter cell lines demonstrated a significant increase in bioluminescence intensity. In conclusion, these newly established luciferase reporter cell lines offer an excellent ex vivo model for cancer immunotherapy. These cell lines naturally express immune checkpoint proteins, enabling the sensitive and reproducible monitoring of combinatorial responses from various immune cell types. Citation Format: Hyeyoun Chang, Alicia C. Walker, John G. Foulke, Luping Chen, Fang Tian, Zhizhan Gu. Luciferase reporter cell lines allow simultaneous incorporation of tumor cells, innate immune cells, and adaptive immune cells for in-depth immune checkpoint studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 75.

The chromatin remodeling factor Arid1a cooperates with Jun/Fos to promote osteoclastogenesis by epigenetically upregulating Siglec15 expression.

Osteoporosis is characterized by an imbalance between osteoclast-mediated bone resorption and osteoblast-related bone formation, particularly increased osteoclastogenesis. However, the mechanisms by which epigenetic factors regulate osteoclast precursor differentiation during osteoclastogenesis remain poorly understood. Here, we show that the specific knockout of the chromatin remodeling factor Arid1a in bone marrow-derived macrophages (BMDMs) results in increased bone mass. The loss of Arid1a in BMDM inhibits cell-cell fusion and maturation of osteoclast precursors, thereby suppressing osteoclast differentiation. Mechanistically, Arid1a increases the chromatin access in the gene promoter region of sialic acid-binding Ig-like lectin 15 (Siglec15) by transcription factor Jun/Fos, which results in the upregulation of Siglec15 and promotion of osteoclast differentiation. However, the loss of Arid1a reprograms the chromatin structure to restrict Siglec15 expression in osteoclast precursors, thereby inhibiting BMDM differentiation into mature osteoclasts. Deleting Arid1a after ovariectomy (a model for postmenopausal bone loss) alleviated bone loss and maintained bone mass. In summary, epigenetic reprogramming mediated by Arid1a loss suppresses osteoclast differentiation and may serve as a promising therapeutic strategy for treating bone loss diseases.

484 - Phase 2 trial in progress - lirentelimab in adults with moderate-to-severe atopic dermatitis inadequately controlled by topical treatments

Abstract Background Atopic dermatitis (AD) is a chronic pruritic inflammatory dermatitis that affects approximately 16.5 million (7.3%) adults in the US, of which around 6.6 million (40%) have moderate-to-severe disease. The current standard of care includes topical treatments supplemented with corticosteroids with and without immunosuppressants. Patients with AD inadequately controlled by topical treatments and immunosuppressants are often treated with biologics and/or JAK inhibitors. Some patients do not have an adequate clinical response or are unable to tolerate these treatments prompting the need for novel therapies. Study Rationale Mast cells (MCs) and eosinophils (eos) are implicated in the pathogenesis of AD. Sialic acid-binding Ig-like lectin (Siglec)-8 is expressed selectively on MCs and eos; engagement with an antibody results in broad inhibition of MC activation and eos depletion. Lirentelimab (AK002) is a humanized, nonfucosylated IgG1 monoclonal antibody that binds specifically to Siglec-8. Preclinical data demonstrates that lirentelimab can broadly inhibit multiple modes of mast cell stimulation that drive AD pathogenesis. Lirentelimab, administered every 4 weeks as an infusion (IV), has been tested in over 600 healthy volunteers and patients with inflammatory and allergic diseases; in those with concomitant AD, improvements in AD were observed. Overall, lirentelimab IV has been well-tolerated; the most common AE being infusion related reactions (IRRs) typically associated with the initial infusions. In a phase 1 study, a subcutaneous (SC) formulation of lirentelimab was well-tolerated with no IRRs. The results of these studies provide a strong rationale for conducting this phase 2 proof-of-concept, randomized, double-blind, placebo-controlled study of lirentelimab SC in adults with moderate–severe atopic dermatitis inadequately controlled by topical treatments (NCT05155085, “ATLAS”). Key Inclusion/Criteria Adults (18-80 years) are eligible for screening if they have had chronic AD presented for ≥3 years with moderate-to-severe symptoms defined as: Eczema Area and Severity Index (EASI) score ≥16, involvement of ≥10% of the Body Surface Area (BSA), and Investigator Global Assessment (IGA) score ≥3, documented recent history of inadequate response to treatment with medications such as topical corticosteroids, calcineurin inhibitors, JAK inhibitors, or PDE4 inhibitors (crisaborole), and biologic-naïve or biologic-exposed (secondary loss of response, intolerance, or lack of access). The complete list of inclusion/exclusion criteria will be presented. Study Design 130 patients will be randomized 1:1 to receive either 7 SC injections of 300mg lirentelimab or placebo every two weeks and then followed for 12 weeks after the last dose. The primary endpoint is the proportion of patients who achieve EASI-75 at week 14 (2 weeks after last dose) compared with baseline. All patients who receive study medication will be included in the safety analysis. Secondary endpoints include percent change in EASI at week 14 from baseline and proportion of patients with IGA of 0 or 1 and a 2-point improvement at week 14 compared to baseline. Patients who complete the study (day 99 visit of double-blind period) will be given the option to enroll in an open-label extension (OLE) for 7 doses of 300mg lirentelimab SC for 12 weeks. Qualified participants will receive medication, lab tests and medical care related to the study at no cost. Study Sites This study is currently enrolling in the USA and Germany. Please visit clinicaltrials.gov (NCT05155085) or email atlas.info@allakos.com to learn more about this study.

Siglec-15/sialic acid axis as a central glyco-immune checkpoint in breast cancer bone metastasis

Immunotherapy is a promising approach for treating metastatic breast cancer (MBC), offering new possibilities for therapy. While checkpoint inhibitors have shown great progress in the treatment of metastatic breast cancer, their effectiveness in patients with bone metastases has been disappointing. This lack of efficacy seems to be specific to the bone environment, which exhibits immunosuppressive features. In this study, we elucidate the multiple roles of the sialic acid-binding Ig-like lectin (Siglec)-15/sialic acid glyco-immune checkpoint axis in the bone metastatic niche and explore potential therapeutic strategies targeting this glyco-immune checkpoint. Our research reveals that elevated levels of Siglec-15 in the bone metastatic niche can promote tumor-induced osteoclastogenesis as well as suppress antigen-specific T cell responses. Next, we demonstrate that antibody blockade of the Siglec-15/sialic acid glyco-immune checkpoint axis can act as a potential treatment for breast cancer bone metastasis. By targeting this pathway, we not only aim to treat bone metastasis but also inhibit the spread of metastatic cancer cells from bone lesions to other organs.

Exosomes secreted by ST3GAL5high cancer cells promote peritoneal dissemination by establishing a premetastatic microenvironment.

Peritoneal dissemination of cancer affects patient survival. The behavior of peritoneal mesothelial cells (PMCs) and immune cells influences the establishment of a microenvironment that promotes cancer cell metastasis in the peritoneum. Here, we investigated the roles of lactosylceramide alpha-2,3-sialyltransferase (ST3G5; also known as ST3GAL5 and GM3 synthase) in the exosome-mediated premetastatic niche in peritoneal milky spots (MSs). Exosomes secreted from ST3G5high cancer cells (ST3G5high -cExos) were found to contain high levels of hypoxia-inducible factor 1-alpha (HIF1α) and accumulated in MSs via uptake in macrophages (MΦs) owing to increased expression of sialic acid-binding Ig-like lectin 1 (CD169; also known as SIGLEC1). ST3G5high -cExos induced pro-inflammatory cytokines and glucose metabolic changes in MΦs, and the interaction of these MΦs with PMCs promoted mesothelial-mesenchymal transition (MMT) in PMCs, thereby generating αSMA+ myofibroblasts. ST3G5high -cExos also increased the expression of immune checkpoint molecules and T-cell exhaustion in MSs, which accelerated metastasis to the omentum. These events were prevented following ST3G5 depletion in cancer cells. Mechanistically, ST3G5high -cExos upregulated chemokines, including CC-chemokine ligand 5 (CCL5), in recipient MΦs and dendritic cells (DCs), which induced MMT and immunosuppression via activation of signal transducer and activator of transcription 3 (STAT3). Maraviroc, a C-C chemokine receptor type 5 (CCR5) antagonist, prevented ST3G5high -cExo-mediated MMT, T-cell suppression, and metastasis in MSs. Our results suggest ST3G5 as a suitable therapeutic target for preventing cExo-mediated peritoneal dissemination.

Immunolocalization and expression of Siglec5 protein in the male reproductive tract of dromedary camel during rutting season.

Lectins are carbohydrate-binding proteins that are highly selective for sugar groups on other molecules. Siglec5 is a cell-surface lectin that belongs to the sialic acid-binding Ig-like lectins (Siglecs) and acts as a suppressor of immune responses. In this study, immunohistochemistry, western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) were used to detect the expression of Siglec5 in the male reproductive tract of dromedary camels during the rutting season. Siglec5 displayed strong immunostaining in the cranial and caudal testicular regions and moderate immunostaining in the rete testis. Different parts of the epididymis showed varying immunoreactions to Siglec5. The spermatozoa in the testes and epididymis also showed positive immunostaining for Siglec5, whereas, the vas deferens showed negative immunostaining for the protein. The results obtained by western blotting confirmed the immunohistochemical detection of the protein in the testicular and epididymal tissues. The results of qRT-PCR showed that Siglec mRNA was expressed differently in each part of the testis and epididymis; the highest levels of expression were observed in the caudal part of the testis and in the head of the epididymis. In conclusion, the present study revealed that Siglec5 is mainly located in the testis and epididymis, where sperm production and maturation occur. Therefore, this protein may play an essential role in the development, maturation and protection of camel sperm.

Low expression of acyl-CoA thioesterase 13 is associated with poor prognosis in ovarian serous cystadenocarcinoma.

Objective: Acyl-CoA thioesterase 13 (ACOT13) encodes a member of the thioesterase superfamily. It has not been reported in ovarian cancer. This research aimed at evaluating the expression and prognostic value of ACOT13 in ovarian serous cystadenocarcinoma (OSC). Methods: We extracted and analyzed TCGA, GEPIA, THPA, GTEx, miRWalk, and GDSC databases to investigate the potential carcinogenic mechanism of ACOT13 in OSC, including the correlation of ACOT13 with prognosis, immune checkpoint, tumor mutational burden (TMB), and 50% inhibition concentration (IC50) score. The incidence of endpoint events was compared with Kaplan-Meier survival analysis. Independent prognostic factors for OSC were evaluated with univariate and multivariate Cox regression analyses, and a nomogram was established. Results: The expression of ACOT13 was increased in OSC and correlated with tumor stage, with higher expression in stages I and II than in stages III and IV. Besides, it was observed that low expression of ACOT13 is correlated with poor overall survival (OS), progression-free survival (PFS), and disease-specific survival (DSS) in patients with OSC. There was a positive correlation between ACOT13 expression and immune checkpoint sialic acid-binding Ig-like lectin (SIGLEC) 15 and TMB. Patients with low ACOT13 expression had higher cisplatin IC50 scores. Conclusion: ACOT13 is an independent prognostic factor and a promising clinical target for OSC. In the future, the carcinogenic mechanism and clinical application value of ACOT13 in ovarian cancer need to be further studied.

365 Phase 2 trial in progress—lirentelimab in adults with moderate-to-severe atopic dermatitis inadequately controlled by topical treatments

Abstract Atopic dermatitis (AD) is a chronic pruritic inflammatory dermatitis that affects approximately 16.5 million (7.3%) adults in the USA, of which around 6.6 million (40%) have moderate-to-severe disease. The current standard of care includes topical treatments supplemented with corticosteroids with and without immunosuppressants. Patients with AD inadequately controlled by topical treatments and immunosuppressants are often treated with biologics and/or JAK inhibitors. Some patients do not have an adequate clinical response or are unable to tolerate these treatments prompting the need for novel therapies. Mast cells (MCs) and eosinophils (eos) are implicated in the pathogenesis of AD. Sialic acid-binding Ig-like lectin (Siglec)-8 is expressed selectively on MCs and eos; engagement with an antibody results in broad inhibition of MC activation and eos depletion. Lirentelimab (AK002) is a humanized, nonfucosylated IgG1 monoclonal antibody that binds specifically to Siglec-8. Preclinical data demonstrate that lirentelimab can broadly inhibit multiple modes of MC stimulation that drive AD pathogenesis. Lirentelimab, administered every 4 weeks as an infusion (IV), has been tested in over 600 healthy volunteers and patients with inflammatory and allergic diseases; in those with concomitant AD, improvements in AD were observed. Overall, lirentelimab IV has been well-tolerated; the most common AE being infusion related reactions (IRRs) typically associated with the initial infusions. In a phase 1 study, a subcutaneous (SC) formulation of lirentelimab was well-tolerated with no IRRs. The results of these studies provide a strong rationale for conducting this phase 2 proof-of-concept, randomized, double-blind, placebo-controlled study of lirentelimab SC in adults with moderate-to-severe AD inadequately controlled by topical treatments (NCT05155085, ‘ATLAS’). Adults (18–80 years) are eligible for screening if they have had chronic AD presented for ≥3 years with moderate-to-severe symptoms defined as: Eczema Area and Severity Index (EASI) score ≥16, involvement of ≥10% of the Body Surface Area and Investigator Global Assessment (IGA) score ≥3, documented recent history of inadequate response to treatment with medications such as topical corticosteroids, calcineurin inhibitors, JAK inhibitors or PDE4 inhibitors (crisaborole), and biologic-naïve or biologic-exposed (secondary loss of response, intolerance or lack of access). The complete list of inclusion/exclusion criteria will be presented. One hundred and thirty patients will be randomized 1 : 1 to receive either seven SC injections of 300-mg lirentelimab or placebo every 2 weeks and then followed for 12 weeks after the last dose. The primary endpoint is the proportion of patients who achieve EASI-75 at week 14 (2 weeks after last dose) compared with baseline. All patients who receive study medication will be included in the safety analysis. Secondary endpoints include percent change in EASI at week 14 from baseline and proportion of patients with IGA of 0 or 1 and a 2-point improvement at week 14 compared with baseline. Patients who complete the study (Day 99 visit of double-blind period) will be given the option to enroll in an open-label extension for seven doses of 300-mg lirentelimab SC for 12 weeks. Qualified participants will receive medication, lab tests and medical care related to the study at no cost. This study is currently enrolling in the USA and Germany. Please visit clinicaltrials.gov (NCT05155085) or email atlas.info@allakos.com to learn more about this study.

Structural insights into Siglec-15 reveal glycosylation dependency for its interaction with T cells through integrin CD11b

Sialic acid-binding Ig-like lectin 15 (Siglec-15) is an immune modulator and emerging cancer immunotherapy target. However, limited understanding of its structure and mechanism of action restrains the development of drug candidates that unleash its full therapeutic potential. In this study, we elucidate the crystal structure of Siglec-15 and its binding epitope via co-crystallization with an anti-Siglec-15 blocking antibody. Using saturation transfer-difference nuclear magnetic resonance (STD-NMR) spectroscopy and molecular dynamics simulations, we reveal Siglec-15 binding mode to α(2,3)- and α(2,6)-linked sialic acids and the cancer-associated sialyl-Tn (STn) glycoform. We demonstrate that binding of Siglec-15 to T cells, which lack STn expression, depends on the presence of α(2,3)- and α(2,6)-linked sialoglycans. Furthermore, we identify the leukocyte integrin CD11b as a Siglec-15 binding partner on human T cells. Collectively, our findings provide an integrated understanding of the structural features of Siglec-15 and emphasize glycosylation as a crucial factor in controlling T cell responses.

Ablation of Siglec-E enhances adipose tissue inflammation through CXCR3 activation and induces monocytic myeloid-derived suppressor cells

Abstract Obesity is a worldwide epidemic associated with dysregulated metabolism and chronic low-grade inflammation in adipose tissue (AT). AT infiltrates with several immune cells, which secrete proinflammatory cytokines that mediate the severity of AT inflammation during obesity. During our ongoing studies, we observed the downregulation of various genes, particularly sialic acid-binding Ig-like lectin E (Siglec-E) by RNA-seq analysis in AT immune cells isolated from high-fat diet (HFD) fed mice as compared to normal diet (ND) mice. Siglec-E is mainly expressed in the cells of myeloid lineages, including macrophages, dendritic cells (DCs), and neutrophils. We confirmed the RNA-seq data of downregulation of Siglec-E in AT derived from HFD-fed mice by RT-PCR analysis. To determine the role of Siglec-E in mediating AT inflammation, we fed ND and HFD to wild-type (WT) and Siglec-E knockout mice (Siglec-E −/−), respectively. HFD consumption increased the body weight and blood glucose levels in Siglec-E −/−mice as compared to WT mice. Further, we observed increased infiltration of macrophages and decreased frequency of DCs in HFD-fed Siglec-E −/−mice AT compared to WT HFD-fed mice. We also noticed an increase in the frequency of CD8 +CXCR3 +cells and monocytic myeloid-derived suppressor cells (M-MDSCs) in AT of HFD-fed Siglec-E −/−mice as compared to WT HFD-fed mice. We also noticed the increased expression of AKT, and TNF receptor-associated factor 3 (TRAF3) in HFD-fed Siglec-E −/−mice. These results suggest that Siglec-E deletion plays a role in AT inflammation and obesity through the activation of CXCR3 and M-MDSCs. This study supports the notion that modulating Siglec-E pathways protect from AT inflammation and metabolic disorders. This research is supported by NIH grant R01 AI140405

An Agonistic Monoclonal Antibody Against Siglec-6 Broadly Inhibits Mast Cell Activation in Transgenic Mice

Mast cells (MCs) regulate chronic inflammation through a myriad of activating cell surface receptors. Dysregulation of MC activation through IgE-dependent and -independent mechanisms (ie cytokines, neuropeptides) contributes to allergic and non-allergic diseases. MC-targeting strategies have focused on neutralizing individual mediators or activating receptors which may be insufficient to broadly reduce MC activity. Molecules that dampen multiple pathways of MC activation, such as sialic acid-binding Ig-like lectins (Siglecs), represent novel therapeutic options for inflammatory diseases.

286 Phase 2 proof-of-concept trial in progress—lirentelimab in adults with moderate-to-severe atopic dermatitis inadequately controlled by topical treatments

Abstract Atopic dermatitis (AD) is a chronic pruritic inflammatory dermatitis that affects approximately 16.5 million (7.3%) adults in the US, of which around 6.6 million (40%) have moderate-to-severe disease. The current standard of care includes topical treatments supplemented with corticosteroids with and without immunosuppressants. Patients with AD inadequately controlled by topical treatments and immunosuppressants are often treated with biologics and/or JAK inhibitors. Some patients do not have an adequate clinical response or are unable to tolerate these treatments prompting the need for novel therapies. Mast cells (MCs) and eosinophils (eos) are implicated in the pathogenesis of AD. Sialic acid-binding Ig-like lectin (Siglec)-8 is expressed selectively on MCs and eos; engagement with an antibody results in broad inhibition of MC activation and eos depletion. Lirentelimab (AK002) is a humanized, nonfucosylated IgG1 monoclonal antibody that binds specifically to Siglec-8. Preclinical data demonstrates that lirentelimab can broadly inhibit multiple modes of mast cell stimulation that drive AD pathogenesis. Lirentelimab, administered every 4 weeks as an infusion (IV), has been tested in over 600 healthy volunteers and patients with inflammatory and allergic diseases; in those with concomitant AD, improvements in AD were observed. Overall, lirentelimab IV has been well-tolerated; the most common AE being infusion-related reactions (IRRs) typically associated with the initial infusions. In a phase 1 study, a subcutaneous (SC) formulation of lirentelimab was well-tolerated with no IRRs. The results of these studies provide a strong rationale for conducting this phase 2 proof-of-concept, randomized, double-blind, placebo-controlled study of lirentelimab SC in adults with moderate-to-severe atopic dermatitis inadequately controlled by topical treatments (NCT05155085, ‘ATLAS’). Adults (18–80 years) are eligible for screening if they have had chronic AD presented for ≥ 3 years with moderate-to-severe symptoms defined as Eczema Area and Severity Index (EASI) score ≥ 16, involvement of ≥ 10% of the Body Surface Area (BSA) and Investigator Global Assessment (IGA) score ≥ 3, documented recent history of inadequate response to treatment with medications such as topical corticosteroids, calcineurin inhibitors, JAK inhibitors, or PDE4 inhibitors (crisaborole) and biologic-naïve or biologic-exposed (secondary loss of response, intolerance or lack of access). The complete list of inclusion/exclusion criteria will be presented. 130 patients will be randomized 1 : 1 to receive either seven SC injections of 300 mg lirentelimab or a placebo every 2 weeks and then followed for 12 weeks after the last dose. The primary endpoint is the proportion of patients who achieve EASI-75 at week 14 (2 weeks after the last dose) compared with baseline. All patients who receive study medication will be included in the safety analysis. Secondary endpoints include a percent change in EASI at week 14 from baseline and a proportion of patients with IGA of 0 or 1 and a 2-point improvement at week 14 compared to baseline. Patients who complete the study (day 99 visit of double-blind period) will be given the option to enroll in an open-label extension (OLE) for seven doses of 300 mg lirentelimab SC for 12 weeks. Qualified participants will receive medication, lab tests and medical care related to the study at no cost. This study is currently enrolling in the USA and Germany. Please visit clinicaltrials.gov (NCT05155085) or email atlas.info@allakos.com to learn more about this study.

LINC01004-SPI1 axis-activated SIGLEC9 in tumor-associated macrophages induces radioresistance and the formation of immunosuppressive tumor microenvironment in esophageal squamous cell carcinoma

Radioresistance and immunosuppression remain the major obstacles in the anti-cancer treatments. This work studies the functions of sialic acid binding Ig like lectin 9 (SIGLEC9) and its related molecules in radioresistance and immunosuppression in esophageal squamous cell carcinoma (ESCC). The single-cell analysis showed that SIGLEC9 was mainly expressed on tumor-associated macrophages (TAMs). Monocytes-derived macrophages were co-cultured with ESCC cells and subjected to radiotherapy. High or low doses of radiotherapy induced SIGLEC9 upregulation and M2 polarization of TAMs. Artificial inhibition of SIGLEC9 in TAMs suppressed the radioresistance and immunosuppressive tumor microenvironment (TME) in the co-cultured ESCC cells. Upstream molecules of SIGLEC9 were predicted via bioinformatics. LINC01004 recruited Spi-1 proto-oncogene (SPI1) in nucleus of TAMs to induce transcriptional activation of SIGLEC9. SIGLEC9 interacted with mucin 1 (MUC1). MUC1 overexpression in ESCCs induced M2 skewing of TAMs, enhanced radioresistance and immunosuppression, and promoted nuclear translocation of β-catenin to suppress radiotherapy-induced ferroptosis of ESCC cells. These effects were blocked upon SIGLEC9 suppression. In vitro results were reproduced in the animal models with xenograft tumors. Taken together, this study demonstrates that the LINC01004-SPI1 axis-activated SIGLEC9 in TAMs induces radioresistance and the formation of immunosuppressive TME in ESCC.

Complement Regulatory Protein CD46 Manifests a Unique Role in Promoting the Migration of Bladder Cancer Cells.

CD46 is a membrane-bound complement regulatory protein (mCRP) possessing a regulatory role with the complement system. CD46 protects the host cells from damage by complement. Expression of CD46 is also highly maintained in many cancers, including bladder cancers, and thus functions as a receptor for many cancer therapeutic viruses. In this study we report a unique role of CD46 as a progression factor of cancer cells in bladder cancers. Resulting data from a DNA microarray using CD46-altered HT1376 bladder cancers demonstrated a pool of target genes, including complement C3 α chain (C3α), matrix Gla protein (MGP), AFAP-AS1, follicular dendritic cell secreted protein (FDCSP), MAM domain containing 2 (MAMDC2), gamma-aminobutyric acid A receptor pi (GABRP), transforming growth factor, beta-induced (TGFBI), a family of cytochrome P450 (CYP24A1), sialic acid binding Ig-like lectin 6 (SIGLEC6), metallothionein 1E (MT1E), and several members of cytokeratins. Subsequent studies using quantitative RT-PCR and Western blot analyses confirmed CD46-mediated regulation of C3α, MGP, and keratin 13 (KRT13). MGP and KRT13 are known to be involved in cell migration and cancer cell metastasis. A cell migration assay demonstrated that CD46 enhanced migratory potential of bladder cancer cells. Taken all together, this report demonstrated that CD46 is generally overexpressed in bladder cancers and plays a unique role in the promotion of cancer cell migration. Further detailed studies are needed to be performed to clarify the action mechanism of CD46 and its application to cancer therapeutics.

Tumor stroma Siglec15 expression is a poor prognosis predictor in colon adenocarcinoma.

Sialic acid binding Ig-like lectin 15 (Siglec15) is considered a novel immune checkpoint and an emerging target for next-generation cancer immunotherapy. However, the significance of Siglec15 and its relationship with programmed death-ligand 1 (PD-L1) in colon adenocarcinoma (COAD) remain unknown. In this study, we analyzed Siglec15 expression within stromal area (SA) and tumor area (TA), and its relationship with tumor-infiltrating lymphocytes (TILs) in COAD and mismatch repair-proficient (MMR-p) COAD. Siglec15 expression was significantly higher in COAD tissues than in normal tissues, and elevated Siglec15(SA) expression, rather than Siglec15(TA) and Siglec15 (whole) expression, was correlated with poor prognosis and inversely correlated with the density of CD8+ T cell, both in COAD and MMR-p COAD. Moreover, there were no correlations between Siglec15(SA) and PD-L1(SA), and between Siglec15(TA) and PD-L1(TA), whereas there was positive correlation between Siglec15(whole) and PD-L1(whole). A new immune classification based on the Siglec15(SA)/PD-L1(SA) expression, indicated that patients with Siglec15(SA)Low/PD-L1(SA)+ status had the longest survival times in COAD. Our study highlights that Siglec15(SA) is an independent predictor of poor prognosis and has an immunosuppressive role in COAD and MMR-p COAD tissues. These findings may provide insights into improving responses to immunotherapy-included comprehensive treatments for COAD in the future.

T-Cell Dysfunction in CLL Can be Alleviated By Blocking Sialic Acid-Binding Ig-like Lectin 10 (Siglec-10) Ligation

T-Cell Dysfunction in CLL Can be Alleviated By Blocking Sialic Acid-Binding Ig-like Lectin 10 (Siglec-10) Ligation