Immunopositivity for Siglec-15 in gastric cancer and its association with clinical and pathological parameters

Study of immunosenescence in the occurrence and immunotherapy of gastrointestinal malignancies

In human beings heterogenous, pervasive and lethal malignancies of different parts of the gastrointestinal (GI) tract viz., tumours of the oesophagus, stomach, small intestine, colon, and rectum, represent gastrointestinal malignancies. Primary treatment modality for gastric cancer includes chemotherapy, surgical interventions, radiotherapy, monoclonal antibodies and inhibitors of angiogenesis. However, there is a need to improve upon the existing treatment modality due to associated adverse events and the development of resistance towards treatment. Additionally, age has been found to contribute to increasing the incidence of tumours due to immunosenescence-associated immunosuppression. Immunosenescence is the natural process of ageing, wherein immune cells as well as organs begin to deteriorate resulting in a dysfunctional or malfunctioning immune system. Accretion of senescent cells in immunosenescence results in the creation of a persistent inflammatory environment or inflammaging, marked with elevated expression of pro-inflammatory and immunosuppressive cytokines and chemokines. Perturbation in the T-cell pools and persistent stimulation by the antigens facilitate premature senility of the immune cells, and senile immune cells exacerbate inflammaging conditions and the inefficiency of the immune system to identify the tumour antigen. Collectively, these conditions contribute positively towards tumour generation, growth and eventually proliferation. Thus, activating the immune cells to distinguish the tumour cells from normal cells and invade them seems to be a logical strategy for the treatment of cancer. Consequently, various approaches to immunotherapy, viz., programmed death ligand-1 (PD-1) inhibitors, Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors etc are being extensively evaluated for their efficiency in gastric cancer. In fact, PD-1 inhibitors have been sanctioned as late late-line therapy modality for gastric cancer. The present review will focus on deciphering the link between the immune system and gastric cancer, and the alterations in the immune system that incur during the development of gastrointestinal malignancies. Also, the mechanism of evasion by tumour cells and immune checkpoints involved along with different approaches of immunotherapy being evaluated in different clinical trials will be discussed.

Expression feature and prognostic function of a novel immune checkpoint Siglec-15 in human colorectal cancer

BACKGROUND

Sialic acid-bound immunoglobulin lectin 15 (Siglec-15) plays an important role in the development of cancer. However, the association between Siglec-15 expression and clinicopathological characteristics of colorectal cancer (CRC) has not been fully investigated.

METHODS

In this present study, a number of bioinformatics analyses were performed to provide an overview and detailed characteristics of Siglec-15. Quantitative real-time polymerase chain reaction (qPCR), western blotting and immunohistochemistry analyses were conducted to characterize the expression of Siglec-15 in CRC. Kaplan-Meier survival and Cox regression analyses were performed to identify the prognostic parameters of CRC.

RESULTS

The results of bioinformatics analyses revealed the expression characteristics and prognostic roles of Siglec-15 in CRC. The data of qCPR, western blotting, and IHC analyses demonstrated that the expression of Siglec-15 in CRC tissues was significantly higher than that in non-cancerous tissues. Moreover, the expression level of Siglec-15 in CRC was significantly associated with lymph node metastasis (p=0.001), TNM stage (p=0.001), and overall survival (p=0.026). COX multi-factor analysis indicated that Siglec-15 expression (p=0.023) and tumor differentiation (p=0.003) were independent prognostic factors for CRC.

CONCLUSIONS

Collectively, the data suggested that Siglec-15 expression may serve as a novel prognostic factor and Siglec-15 might be identified as an ideal candidate for immunotherapy in CRC treatment.

Immune Cell Interactions and Immune Checkpoints in the Tumor Microenvironment of Gastric Cancer

Gastric cancer (GC) ranks as the fifth most prevalent malignant neoplasm globally, with an increased death rate despite recent advancements in research and therapeutic options. Different molecular subtypes of GC have distinct interactions with the immune system, impacting the tumor microenvironment (TME), prognosis, and reaction to immunotherapy. Tumor-infiltrating lymphocytes (TILs) in the TME are crucial for preventing tumor growth and metastasis, as evidenced by research showing that patients with GC who have a significant density of TILs have better survival rates. But cancer cells have evolved a variety of mechanisms to evade immune surveillance, both sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) and Programmed Death-Ligand 1 (PD-L1) playing a pivotal role in the development of an immunosuppressive TME. They prevent T cell activation and proliferation resulting in a decrease in the immune system's capacity to recognize and eliminate malignant cells. These immune checkpoint molecules function via different but complementary mechanisms, the expression of Siglec-15 being mutually exclusive with PD-L1 and, therefore, providing a different therapeutic approach. The review explores how TILs affect tumor growth and patient outcomes in GC, with particular emphasis on their interactions within the TME and potential targeting of the PD-L1 and Siglec-15 pathways for immunotherapy.

Stromal immune cells expression of Siglec-15 is associated with lower T stage and better prognosis of urinary bladder cancer

Introduction

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is a novel immune checkpoint, similar to programmed death-ligand (PD-L1), and has emerged as a potential target for cancer immunotherapy. Until recently, little was known about the expression and role of Siglec-15 in bladder cancer (BC).

Methods

In this study, we used immunohistochemical staining to assess the expression of Siglec-15 and PD-L1 in 69 primary BC samples and analyzed their relationship with clinicopathologic characters and prognosis.

Results

The expression rates of Siglec-15 in the tumor cells, stromal immune cells, and both the tumor and stromal cells were 84.1% (58/69), 50.7% (35/69), and 44.9% (31/69), respectively. The PD-L1 expression rate was 52.2% (36/69), with a positive rate of 17.4% (12/69). PD-L1 expression was inversely correlated with Siglec-15 expression, but the statistical significance was not achieved (P = 0.072). Low stromal Siglec-15 expression was associated with advanced tumor stage (P = 0.010). PD-L1 expression was associated with tumor stage (P = 0.008) and perineural invasion (PNI) (P = 0.048). Kaplan-Meier survival curves showed that stromal Siglec-15 expression was associated with a better prognosis (P = 0.012), although it was not an independent prognostic factor after multivariate analysis (P = 0.236) .

Discussion

This study revealed a high expression rate of Siglec-15 in BC and may provide valuable insights for patient selection in future clinical trials.

Siglec15 in blood system diseases: from bench to bedside

Inhibiting the PD-1/PD-L1 pathway using immunomodulators has demonstrated promising outcomes in clinics. Immunomodulators can effectively target immune checkpoints with a strong preference for the tumor microenvironment (TME). Besides, immunomodulators specifically target the recently discovered inhibitory immune checkpoint, sialic acid-binding immunoglobulin-like lectin (Siglec-15). Distinctive in its molecular composition, Siglec-15 has a unique molecular composition and been shown to be highly prevalent in numerous solid tumor tissues and tumor-associated macrophages (TAMs) in human subjects. Notably, Siglec-15 is up-regulated across various cancer types. As a result, Siglec-15 has attracted significant attention due to its exclusive nature concerning PD-L1 expression, suggesting its role in immune evasion in patients lacking PD-L1. Siglec-15 predominantly appears in certain populations and can promote tumor development by repressing T lymphocyte activation and proliferation, thereby facilitating tumor cell immune escape. Furthermore, Siglec-15 is implicated in osteoclast differentiation and bone remodeling, indicating that it is a promising target for next-generation cancer immunotherapies. Additionally, Siglec-15 can modulate immune responses to microbial infections. The current treatment strategies for hematological conditions predominantly include conventional intensive chemotherapy and transplantation methods. However, emerging immunotherapeutic approaches are increasingly recognized for their overall effectiveness, indicating that specific molecular targets should be identified. The expression of Siglec-15 within tumor cells may indicate a novel pathway for treating hematological malignancies. In this study, the biological attributes, expression patterns, and pathogenic mechanisms of Siglec-15 across various diseases were reviewed. The role of Siglec-15 in the pathogenesis and laboratory diagnosis of hematological disorders was also evaluated.

Evasion of immunosurveillance by the upregulation of Siglec15 in bladder cancer

Immunotherapy resistance in bladder cancer (BLCA) is associated with elevated levels of sialic acid-binding immunoglobulin-like lectin (Siglec15). This protein plays a crucial role in fostering a noninflammatory tumor microenvironment (TME), which is conducive to cancer progression. Our study confirmed that the overexpression of Siglec15 led to a reduction in CD8+ T cell infiltration. This effect was mediated by the downregulation of pro-inflammatory cytokines and chemokines, which in turn exacerbated BLCA malignancy. Furthermore, Siglec15 inhibited the cytotoxicity of effector T cell, contributing to immune evasion. An in vivo study demonstrated that Siglec15 overexpression induced a non-inflammatory TME and promoted resistance to immunotherapy. These findings highlight Siglec15 as a potential therapeutic target for BLCA. By modulating inflammation in the TME and CD8+ T cell function, targeting Siglec15 may offer a novel strategy for overcoming immunotherapy resistance and improving patient outcomes.

Siglec-15 expression in diffuse gliomas and its correlation with MRI morphologic features and apparent diffusion coefficient

BACKGROUND

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) enhances tumor immune escape and leads to tumor growth.

PURPOSE

To investigate the expression of Siglec-15 in diffuse gliomas and its correlation with tumor magnetic resonance imaging (MRI) features.

MATERIAL AND METHODS

This study included 57 patients with gliomas. Morphological MRI features, including the largest tumor diameter, enhancement category, location, calcification, cysts, and hemorrhage, were visually rated. Apparent diffusion coefficient (ADC) values were calculated in tumor region. MRI morphologic features and ADC were compared between patients with positive and negative Siglec-15 expression. Receiver operating characteristic (ROC) curves were further constructed to assess the diagnostic performance.

RESULTS

Siglec-15 was expressed in immunocytes, such as macrophages in the peritumoral area. Siglec-15 expression was positive in 20/57 (35.09%) patients, with higher expression in patients with IDH-mutant gliomas and lower grade gliomas. The tumor diameter was significantly smaller in patients with positive Siglec-15 expression than in those with negative expression for all patients (P = 0.017) and for patients with IDH-mutant gliomas (P = 0.020). Moreover, ADC values of the tumor were significantly higher in patients with positive Siglec-15 expression than in those with negative expression for all patients (P = 0.027). The areas under the ROC curve (AUCs) of the diameter and ADC were 0.702 and 0.686, respectively. A combination of these two parameters generated an improved AUC of 0.762.

CONCLUSION

Siglec-15 was expressed in immunocytes such as macrophages in the peritumoral area, with a positive rate of 35.09%. Positive Siglec-15 expression in diffuse gliomas was correlated with smaller tumor size and higher ADC values.

SIGLEC15, negatively correlated with PD-L1 in HCC, could induce CD8+ T cell apoptosis to promote immune evasion

Functional roles of SIGLEC15 in hepatocellular carcinoma (HCC) were not clear, which was recently found to be an immune inhibitor with similar structure of inhibitory B7 family members. SIGLEC15 expression in HCC was explored in public databases and further examined by PCR analysis. SIGLEC15 and PD-L1 expression patterns were examined in HCC samples through immunohistochemistry. SIGLEC15 expression was knocked-down or over-expressed in HCC cell lines, and CCK8 tests were used to examine cell proliferative ability in vitro. Influences of SIGLEC15 expression on tumor growth were examined in immune deficient and immunocompetent mice respectively. Co-culture system of HCC cell lines and Jurkat cells, flow cytometry analysis of tumor infiltrated immune cells and further sequencing analyses were performed to investigate how SIGLEC15 could affect T cells in vitro and in vivo. We found SIGLEC15 was increased in HCC tumor tissues and was negatively correlated with PD-L1 in HCC samples. In vitro and in vivo models demonstrated inhibition of SIGLEC15 did not directly influence tumor proliferation. However, SIGLEC15 could promoted HCC immune evasion in immune competent mouse models. Knock-out of Siglec15 could inhibit tumor growth and reinvigorate CD8+ T cell cytotoxicity. Anti-SIGLEC15 treatment could effectively inhibit tumor growth in mouse models with or without mononuclear phagocyte deletion. Bulk and single-cell RNA sequencing data of treated mouse tumors demonstrated SIGLEC15 could interfere CD8+ T cell viability and induce cell apoptosis. In all, SIGLEC15 was negatively correlated with PD-L1 in HCC and mainly promote HCC immune evasion through inhibition of CD8+ T cell viability and cytotoxicity.

The expression characteristic and prognostic role of Siglec-15 in lung adenocarcinoma

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) has been identified as an immune suppressor and a promising candidate for immunotherapy of cancer management. However, the association between Siglec-15 expression and clinicopathological features of lung adenocarcinoma (LUAD), especially the prognostic role, is not fully elucidated. In this present study, a serial of bioinformatics analyses in both tissue and cell levels were conducted to provide an overview of Siglec-15 expression. Real-time quantitative PCR (qPCR) test, western blotting assay, and immunohistochemistry (IHC) analyses were conducted to evaluate the expression of Siglec-15 in LUAD. Survival analysis and Kaplan-Meier curve were employed to describe the prognostic parameters of LUAD. The results of bioinformatics analyses demonstrated the up-regulation of Siglec-15 expression in LUAD. The data of qPCR, western blotting, and IHC analyses further proved that the expression of Siglec-15 in LUAD tissues was significantly increased than that in noncancerous tissues. Moreover, the expression level of Siglec-15 protein in LUAD was substantially associated with TNM stage. LUAD cases with up-regulated Siglec-15 expression, positive N status, and advance TNM stage suffered a critical unfavorable prognosis. In conclusion, Siglec-15 could be identified as a novel prognostic biomarker in LUAD and targeting Siglec-15 may provide a promising strategy for LUAD immunotherapy.

Identification of BACH1-IT2-miR-4786-Siglec-15 immune suppressive axis in bladder cancer

The sialic acid binding Ig like lectin 15 (Siglec-15) was previously identified as tumor immune suppressor gene in some human cancers with elusive molecular mechanism to be elucidated. The continuous focus on both clinical and basic biology of bladder cancer leads us to characterize aberrant abundance of BACH1-IT2 associating with stabilization of Siglec-15, which eventually contributes to local immune suppressive microenvironment and therefore tumor advance. This effect was evidently mediated by miR-4786-5p. BACH1-IT2 functions in this scenario as microRNA sponge, and competitively conceals miR-4786 and up-regulates cancer cell surface Siglec-15. The BACH1-IT2-miR-4786-Siglec-15 axis significantly influences activation of immune cell co-culture. In summary, our data highlights the critical involvements of BACH1-IT2 and miR-4786 in immune evasion in bladder cancer, which hints the potential for both therapeutic and prognostic exploitation.

Bioinformatic analysis reveals prognostic value and immunotherapy potential of Siglec-15 in laryngeal squamous cell carcinoma

Background

Laryngeal squamous cell carcinoma (LSCC) is the ultimate common malignant head and neck cancer with dismal prognosis. The expression pattern and clinical significance of Siglec-15 (Sialic acid-binding immunoglobulin-like lectin 15) in LSCC are poorly understood. In order to lay the groundwork for future immune-related research on Siglec-15 in LSCC, we set out to study its expression and prognostic importance in the disease, as well as to use bioinformatics to investigate the immune features modulated by Siglec-15 in LSCC.

Methods

① In order to get the gene expression profile and clinical data for TCGA head and neck cancer (TCGA-HNSC), you may access the relevant data from UCSC xena and use 110 cases of laryngeal cancer as a training set. Two datasets, GSE27020 and GSE25727, were obtained from the GEO databank and utilized as validation sets. These datasets include expression profiles and clinical information. The Siglec-15 gene and immune characteristics were analyzed by bioinformatics methods. ② Retrospectively collected routine paraffin specimens from patients with pathological diagnosis of squamous cell carcinoma from December 2012 to November 2015 in Sun Yat-sen Memorial Hospital and fresh frozen tissue of patients from June 2021 to March 2022. Immunohistochemistry method, immunofluorescence technique and real-time quantitative PCR was used to examine the difference of Siglec-15 appearance in LSCC tissue and adjacent tissue, and its correlation of prognosis, clinic pathological characteristics and CD8+T lymphocyte infiltration. Using human laryngeal cancer cell line (LCC), we studied the influence of Siglec-15 in cell proliferation and invasion.

Results

We identified Siglec-15 was upregulated in LSCC. The patients in Siglec-15 high expression group had a poor overall survival (OS) based on the clinical information from TGCA and 111 LSCC patients that hospitalized in Sun Yat-sen Memorial Hospital. The COX regression analysis indicated Siglec-15 as an independent predictor for poor prognosis of LSCC. Bioinformatic analysis suggested that the high expression of Siglec-15 shape an immune suppressive tumor microenvironment (TEM), leading to poor response to immunotherapy in LSCC. Siglec-15 enhanced cell invasion and proliferation, as we showed in vitro.

Conclusion

Our study support Siglec-15 as a potential predictor for LSCC prognosis and an attractive target for LSCC immunotherapy.

The expression of two immunosuppressive SIGLEC family molecules in papillary thyroid cancer and their effect on prognosis

BACKGROUND

The thyroid cancer (THCA) subtype that occurs more frequently is papillary thyroid cancer (PTC). Despite a favorable postoperative outcome, traditional antitumor therapy does not offer ideal results for patients with metastasis, relapse, and radioiodine resistance. Recent studies demonstrated the remarkable effects of immune checkpoint inhibitors on solid tumors, of which the immunoglobulin superfamily member SIGLEC10 and SIGLEC15 act as novel immunotherapy targets for tumors. Nevertheless, their role in PTC prognosis is still indefinite.

METHODS

Immunohistochemistry was utilized to examine the expression of SIGLEC10 and SIGLEC15 in 244 PTC tissue specimens. Then the expression correlation between the two was analyzed in normal tissues (NT), tumor cells (TC), and tumor stroma (TS), respectively. Subsequently, the retrospective data on patients with PTC were collected to examine whether the two immunosuppressive SIGLEC family members could affect their prognosis.

RESULTS

We confirmed that TC expressed higher levels of SIGLEC10 than NT. However, SIGLEC10 was down-regulated in TS and predicted poor outcomes. Meanwhile, down-regulation of SIGLEC15 expression was observed in both TC and TS, indicating a favorable prognosis. PTC patients with both SIGLEC10-SIGLEC15+ expression in TC and TS had a significantly higher recurrence risk. The expression of SIGLEC10 in TS and SIGLEC15 in TC or TS was an independent predictor of PFS, and a positive correlation was shown between SIGLEC10 and SIGLEC15 expression in TS.

CONCLUSIONS

Therefore, our results indicate that SIGLEC10 and SIGLEC15 may be applied as significant prognostic markers for PTC and attractive targets for THCA immunotherapy.

Prognostic value of Siglec-15 expression in patients with solid tumors: A meta-analysis

Background

Siglec-15 is expressed in a variety of cancers. However, the role of Siglec-15 in the prognosis of cancer patients remains controversial. Therefore, we conducted a meta-analysis to clarify the potential prognostic value of Siglec-15 in solid tumors.

Methods

The PubMed, Web of Science, Embase and CNKI databases were comprehensively searched to identify studies assessing the effect of Siglec-15 on the survival of cancer patients. Hazard ratios (HRs) with 95% confidence intervals (CIs) for overall survival (OS), progression-free survival (PFS) and disease-specific survival (DSS) from individual studies were evaluated.

Results

The data from 13 observational studies consisting of 1376 patients were summarized. Elevated baseline Siglec-15 expression was significantly correlated with poor OS (pooled HR = 1.28, 95% CI: 1.05-1.56; P = 0.013). However, high Siglec-15 expression predicted a significantly better DSS (pooled HR = 0.73 (95% CI: 0.57-0.94; P = 0.015) but not PFS (pooled HR = 1.49, 95% CI: 0.46-4.87; P=0.510). In addition, high Siglec-15 expression was not associated with PD-L1 (OR=0.64, 95% CI: 0.42-0.95; P = 0.028). High Siglec-15 expression was associated with male sex (OR = 1.39, 95% CI: 1.05-1.84; P = 0.022), larger tumor size (OR = 1.896, 95% CI: 1.26-2.9; P = 0.002), and advanced tumor-node-metastasis (TNM) stage (OR = 1.84; 95% CI: 1.19-2.84; P =0.006) in solid tumors.

Conclusions

This updated study suggested the expression of Siglec-15 is significantly associated with poor outcomes in human solid tumors, but further studies are needed to determine the prognostic value of Siglec-15 in solid tumors.

Significance of Siglec-15 expression in colorectal cancer: association with advanced disease stage and fewer tumor-infiltrating lymphocytes

Siglec-15, a novel immune suppressor, is upregulated in many human cancers. The aim of this study was to explore the expression of Siglec-15 in colorectal cancer (CRC), and investigate whether Siglec-15 could be a potential target for cancer immunotherapy in patients with CRC. We performed immunohistochemical analyses of Siglec-15 on a cohort of 805 patients with CRC and made comparisons between clinicopathological characteristics, PD-L1 expression, CD3, CD8, CD45RO tumor-infiltrating lymphocytes (TILs), and prognosis. We found that Siglec-15 expression was commonly detected in tumor cells (48.3%) and tumor-associated stromal cells (33.4%), and was more frequently observed than PD-L1 expression in tumor cells. In contrast, Siglec-15 expression was weakly and scarcely found in normal mucosa (13%). Siglec-15 overexpression in tumor cells was associated with advanced TNM stage (p = 0.020). Co-expression of Siglec-15 and PD-L1 in tumor cells was found in 14.4% of patients, and Siglec-15 expression was detected in almost half of PD-L1 negative cases. Elevated Siglec-15 expression in tumor and stromal cells was associated with sparser CD45RO and CD8 TILs (p = 0.035 and p = 0.004, respectively). The expression of Siglec-15 did not have prognostic significance. In summary, compared to PD-L1, Siglec-15 protein expression is more prevalent in CRC and is associated with advanced disease stage and fewer TILs. These findings support Siglec-15 as a potential cancer immunotherapy target, in addition to PD-1/PD-L1 inhibitors, in patients with CRC.

Unveiling the molecular features, relevant immune and clinical characteristics of SIGLEC15 in thyroid cancer

The groundbreaking research work about SIGLEC15 has raised it as a potential promising target in cancer immunotherapy. Unfortunately, the role of SIGLEC15 in thyroid carcinoma (THCA) remains obscure. Public and home multi-omics data were collected to investigate the role of SIGLEC15 in THCA in our study. SIGLEC15 was upregulated in THCA tumor tissue compared to nontumor tissue in both mRNA and protein levels; gene set enrichment analysis (GSEA) results showed that high SIGLEC15 mRNA expression was positively correlated to many immune pathways. Results of the examination of immunological landscape characteristics displayed high SIGLEC15 mRNA expression that mainly positively correlated with a large number of cancer immunity immunomodulators and pathways. In addition, upregulation of SIGLEC15 was positively correlated with an enhanced immune score, stromal score, and estimate score. However, higher SIGLEC15 mRNA also met high immune exhausted status. The majority of CpG methylation sites negatively correlated with SIGLEC15 mRNA expression. Analysis of clinical characteristics supported increased SIGLEC15 expression that was positively correlated with more extrathyroid extension and lymph node metastasis. We observed different single nucleotide variant (SNV) and copy number variation (CNV) patterns in high and low SIGLEC15 mRNA expression subgroups; some vital DNA damage repair deficiency scores addressed a negative correlation with SIGLEC15 mRNA expression. We also found that some commonly used chemotherapy drugs might be suitable for different SIGLEC15 mRNA expression subgroups. This study highlighted the vital role of SIGLEC15 in THCA. Targeting SIGLEC15 may offer a potential novel therapeutic opportunity for THCA patients. However, the detailed exact cellular mechanisms of SIGLEC15 in THCA still needed to be elucidated by further studies.

Screening and Identification of a Novel Anti-Siglec-15 Human Antibody 3F1 and Relevant Antitumor Activity

Sialic acid-binding Ig-like lectin-15 is an important immunosuppressive molecule considered to be a key target in next-generation tumor immunotherapy. In this study, we screened 22 high-affinity antibodies that specifically recognize human Siglec-15 by using a large human phage antibody library, and five representative sequences were selected for further study. The results showed the binding activity of five antibodies to Siglec-15 (EC50 ranged from 0.02368 μg/mL to 0.07949 μg/mL), and in two Siglec-15-overexpressed cell lines, three antibodies had the strongest binding activity, so the two clones were discarded for further study. Subsequently, the affinity of three antibodies were measured by bio-layer interferometry technology (5-9 × 10E-09M). As the reported ligands of Siglec-15, the binding activity of Siglec-15 and sialyl-Tn, cluster of differentiation 44, myelin-associated glycoprotein, and leucine-rich repeat-containing protein 4C can be blocked by three of the antibodies. Among these, 3F1 had a competitive advantage. Then, the antibody 3F1 showed an obvious antibody-dependent cell-mediated cytotoxicity effect (EC50 was 0.85 μg/mL). Further, antibody 3F1 can reverse the inhibitory effect of Siglec-15 on lymphocyte proliferation (especially CD4+T and CD8+T) and cytokine release Interferon-γ. Given the above results, 3F1 was selected as a candidate for the in vivo pharmacodynamics study. In the tumor model of Balb/c Nude mice, 3F1 (10 mg/kg) showed certain antitumor effects [tumor growth inhibition (TGI) was 31.5%], while the combination of 3F1 (5 mg/kg) and Erbitux (5 mg/kg) showed significant antitumor effects (TGI was 48.7%) compared with the PBS group. In conclusion, novel human antibody 3F1 has antitumor activity and is expected to be an innovative candidate drug targeting Siglec-15 for tumor immunotherapy. SIGNIFICANCE STATEMENT: Siglec-15 is considered as an important target in the next generation of tumor immunotherapy. 3F1 is expected to be the most promising potential candidate for targeting Siglec-15 for cancer treatment and could provide a reference for the development of antitumor drugs.

Exploration of the Tumor Immune Landscape and Identification of Two Novel Immunotherapy-Related Genes for Epstein-Barr virus-associated Gastric Carcinoma via Integrated Bioinformatics Analysis

Epstein–Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is a specific molecular subtype of gastric carcinoma with a high proportion of tumor-infiltrating lymphocytes. It is a highly immunogenic tumor that may benefit from immunotherapy. Hence, it is imperative to analyze the immune landscape and identify immunotherapy biomarkers for EBVaGC. In our study, we investigated the immune landscape and identified 10 hub genes for EBVaGC via integrated bioinformatics analysis. We found that EBVaGC expressed more immune-related genes, including common immune checkpoints and human leukocyte antigen (HLA) genes than EBV-negative gastric carcinoma (EBVnGC). The immune score in EBVaGC was higher, which means EBVaGC has greater immune cell infiltration. Ten hub genes (CD4, STAT1, FCGR3A, IL10, C1QA, CXCL9, CXCL10, CXCR6, PD-L1, and CCL18) were detected as candidate biomarkers for EBVaGC. Two hub genes, CXCL9 and CXCR6, were identified as novel immunotherapy-related genes. Taken together, the results of our comprehensive analysis of the immune microenvironment of EBVaGC revealed its unique immune landscape, demonstrating that it is a highly immunogenic tumor. Moreover, we identified hub genes that may serve as potential immunotherapy biomarkers for EBVaGC.

Analysis of a novel immune checkpoint, Siglec-15, in pancreatic ductal adenocarcinoma

Siglec‐15, a novel immune checkpoint, is an emerging target for next‐generation cancer immunotherapy. However, the role of Siglec‐15 in pancreatic ductal adenocarcinoma (PDAC) remains poorly understood. We investigated the expression of Siglec‐15 and its association with clinicopathological characteristics, programmed cell death‐ligand 1 (PD‐L1), immune cells, and DNA damage repair (DDR) molecules in a cohort of 291 patients with PDAC. Positive tumour cell expression of Siglec‐15 and PD‐L1 was observed in 18.6 and 30.3% of the samples, respectively. We also detected Siglec‐15 positivity in macrophages in 3.4% of patients. Co‐expression of Siglec‐15 with PD‐L1 was observed in 6.1% of the patients. A total of 33 PD‐L1‐negative samples (18.0%) were Siglec‐15‐positive. Siglec‐15 was observed more frequently in moderate‐to‐well‐differentiated tumours. Siglec‐15 was associated with a low density of Tregs and CD45RO T cells, high BRCA1 expression, and improved survival. Both Siglec‐15 and PD‐L1 are independent factors of patient outcomes. The prognostic significance of Siglec‐15 for survival was more discriminative in lymph node‐negative, high BRCA1 expression, or low BRCA2 expression tumours than in lymph node‐positive, low BRCA1 expression, or high BRCA2 expression tumours. In conclusion, we identified Siglec‐15 as a promising predictor for prognosis combined with different DDR molecular statuses and complex tumour‐infiltrating cells in PDAC. Targeting Siglec‐15 may be a novel therapeutic option for patients who are unresponsive to anti‐PD‐1 therapy. Future studies are needed to validate the prognostic significance of Siglec‐15 and to investigate its regulatory mechanisms in this disease.

Expression of Immune Checkpoints in Malignant Tumors: Therapy Targets and Biomarkers for the Gastric Cancer Prognosis

To increase the effectiveness of anticancer therapy based on immune checkpoint (IC) inhibition, some ICs are being investigated in addition to those used in clinic. We reviewed data on the relationship between PD-L1, B7-H3, B7-H4, IDO1, Galectin-3 and -9, CEACAM1, CD155, Siglec-15 and ADAM17 expression with cancer development in complex with the results of clinical trials on their inhibition. Increased expression of the most studied ICs—PD-L1, B7-H3, and B7-H4—is associated with poor survival; their inhibition is clinically significant. Expression of IDO1, CD155, and ADAM17 is also associated with poor survival, including gastric cancer (GC). The available data indicate that CD155 and ADAM17 are promising targets for immune therapy. However, the clinical trials of anti-IDO1 antibodies have been unsatisfactory. Expression of Galectin-3 and -9, CEACAM1 and Siglec-15 demonstrates a contradictory relationship with patient survival. The lack of satisfactory results of these IC inhibitor clinical trials additionally indicates the complex nature of their functioning. In conclusion, in many cases it is important to analyze the expression of other participants of the immune response besides target IC. The PD-L1, B7-H3, B7-H4, IDO1 and ADAM17 may be considered as candidates for prognosis markers for GC patient survival.

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.