Expression signature, prognosis value, and immune characteristics of Siglec-15 identified by pan-cancer analysis

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.

Analysis of the interlink between glucose-6-phosphate dehydrogenase (G6PD) and lung cancer through multi-omics databases

Glucose-6-Phosphate Dehydrogenase (G6PD) is a crucial enzyme that executes the pentose phosphate pathway. Due to its critical nodal position in the metabolic network, it is associated with different forms of cancer tumorigeneses and progression. Nonetheless, its functional role and molecular mechanism in lung cancer remain unknown. The present study provides intricate information associated with G6PD and Lung Cancer. Varieties of public datasets were retrieved by us, including UALCAN, TCGA, cBioPortal, and the UCSC Xena browser. The data obtained were used to assess the expression of G6PD, its clinical features, epigenetic regulation, relationship with tumour infiltration, tumour mutation burden, microsatellite instability, tumour microenvironment, immune checkpoint genes, genomic alteration, and patient's overall survival rate. The present study revealed that the G6PD expression was correlated with the clinical features of lung cancer including disease stage, race, sex, age, smoking habits, and lymph node metastasis. Moreover, the expression profile of G6PD also imparts epigenetic changes by modulating the DNA promoter methylation activity. Methylation of promoters changes the expression of various transcription factors, genes leading to an influence on the immune system. These events linked with G6PD-related mutational gene alterations (FAM3A, LAG3, p53, KRAS). The entire circumstance influences the patient's overall survival rate and poor prognosis. Functional investigation using STRING, GO, and KEGG found that G6PD primarily engages in hallmark functions (metabolism, immunological responses, proliferation, apoptosis, p53, HIF-1, FOXO, PI3K-AKT signaling). This work provides a wide knowledge of G6PD's function in lung cancer, as well as a theoretical foundation for possible prognostic therapeutic markers.

Human-specific elimination of epithelial Siglec-XII suppresses the risk of inflammation-driven colorectal cancers

Carcinomas are common in humans but rare among closely related "great apes." Plausible explanations, including human-specific genomic alterations affecting the biology of sialic acids, are proposed, but causality remains unproven. Here, an integrated evolutionary genetics-phenome-transcriptome approach studied the role of SIGLEC12 gene (encoding Siglec-XII) in epithelial transformation and cancer. Exogenous expression of the protein in cell lines and genetically engineered mice recapitulated approximately 30% of the human population in whom the protein is expressed in a form that cannot bind ligand because of a fixed, homozygous, human-universal missense mutation. Siglec-XII-null cells/mice recapitulated the remaining approximately 70% of the human population in whom an additional polymorphic frameshift mutation eliminates the entire protein. Siglec-XII expression drove several pro-oncogenic phenotypes in cell lines and increased tumor burden in mice challenged with chemical carcinogen and inflammation. Transcriptomic studies yielded a 29-gene signature of Siglec-XII-positive disease and when used as a computational tool for navigating human data sets, pinpointed with surprising precision that SIGLEC12 expression (model) recapitulates a very specific type of colorectal carcinomas (disease) that is associated with mismatch-repair defects and inflammation, disproportionately affects European Americans, and carries a favorable prognosis. They revealed a hitherto-unknown evolutionary genetic mechanism for an ethnic/environmental predisposition of carcinogenesis.

Fourteen years of cellular deconvolution: methodology, applications, technical evaluation and outstanding challenges

Single-cell RNA sequencing (scRNA-Seq) is a recent technology that allows for the measurement of the expression of all genes in each individual cell contained in a sample. Information at the single-cell level has been shown to be extremely useful in many areas. However, performing single-cell experiments is expensive. Although cellular deconvolution cannot provide the same comprehensive information as single-cell experiments, it can extract cell-type information from bulk RNA data, and therefore it allows researchers to conduct studies at cell-type resolution from existing bulk datasets. For these reasons, a great effort has been made to develop such methods for cellular deconvolution. The large number of methods available, the requirement of coding skills, inadequate documentation, and lack of performance assessment all make it extremely difficult for life scientists to choose a suitable method for their experiment. This paper aims to fill this gap by providing a comprehensive review of 53 deconvolution methods regarding their methodology, applications, performance, and outstanding challenges. More importantly, the article presents a benchmarking of all these 53 methods using 283 cell types from 30 tissues of 63 individuals. We also provide an R package named DeconBenchmark that allows readers to execute and benchmark the reviewed methods (https://github.com/tinnlab/DeconBenchmark).

The prognostic value of sialylation-related long non-coding RNAs in lung adenocarcinoma

There has been increasing interest in the role of epigenetic modification in cancers recently. Among the various modifications, sialylation has emerged as a dominant subtype implicated in tumor progression, metastasis, immune evasion, and chemoresistance. The prognostic significance of sialylation-related molecules has been demonstrated in colorectal cancer. However, the potential roles and regulatory mechanisms of sialylation in lung adenocarcinoma (LUAD) have not been thoroughly investigated. Through Pearson correlation, univariate Cox hazards proportional regression, and random survival forest model analyses, we identified several prognostic long non-coding RNAs (lncRNAs) associated with aberrant sialylation and tumor progression, including LINC00857, LINC00968, LINC00663, and ITGA9-AS1. Based on the signatures of four lncRNAs, we classified patients into two clusters with different landscapes using a non-negative matrix factorization approach. Collectively, patients in Cluster 1 (C1) exhibited worse prognoses than those in Cluster 2 (C2), as well as heavier tumor mutation burden. Functional enrichment analysis showed the enrichment of several pro-tumor pathways in C1, differing from the upregulated Longevity and programmed cell death pathways in C2. Moreover, we profiled immune infiltration levels of important immune cell lineages in two subgroups using MCPcounter scores and single sample gene set enrichment analysis scores, revealing a relatively immunosuppressive microenvironment in C1. Risk analysis indicated that LINC00857 may serve as a pro-tumor regulator, while the other three lncRNAs may be protective contributors. Consistently, we observed upregulated LINC00857 in C1, whereas increased expressive levels of LINC00968, LINC00663, and ITGA9-AS1 were observed in C2. Finally, drug sensitivity analysis suggested that patients in the two groups may benefit from different therapeutic strategies, contributing to precise treatment in LUAD. By integrating multi-omics data, we identified four core sialylation-related lncRNAs and successfully established a prognostic model to distinguish patients with different characterizations. These findings may provide some insights into the underlying mechanism of sialylation, and offer a new stratification way as well as clinical guidance in LUAD.

Siglec-15 on macrophages suppress the immune microenvironment in patients with PD-L1 negative non-metastasis lung adenocarcinoma

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is an immune checkpoint molecule with sequence homology to programmed cell death ligand 1 (PD-L1), which is mainly expressed on macrophages and tumor cells. However, whether Siglec-15-induced immunosuppression and poor prognosis are independent of PD-L1 remains unclear. In this study, we collected samples of 135 non-small cell lung cancers and found that Siglec-15 and PD-L1 expression were independent in non-small cell lung cancer by multiple immunofluorescence staining. Siglec-15 on macrophages (Mφ-Siglec-15) was significantly associated with DFS (p < 0.05) in PD-L1- patients with non-metastasis lung adenocarcinoma, not in PD-L1+ or lung squamous cell carcinoma patients. Moreover, stromal Siglec-15+ macrophages of Mφ-Siglec-15+PD-L1- patients were significantly more than those of Mφ-Siglec-15-PD-L1- patients (p = 0.002). We further found that Siglec-15+ macrophages polarized toward M2 and produced more IL-10, negatively associated with inflamed immunophenotype in PD-L1- patients and may inhibit CD8+T cells infiltration. In conclusion, PD-L1-independent Siglec-15+ macrophages contribute to the formation of an immunosuppressive microenvironment in non-metastasis lung adenocarcinoma patients, which may cause a higher risk of recurrence. Siglec-15 could be a potential target for normalizing cancer immunotherapy, benefiting patients who fail to respond to anti-PD-L1 therapy.

Targeting myeloid cells for cancer immunotherapy: Siglec-7/9/10/15 and their ligands

Advances in immunotherapy have revolutionized cancer treatment, yet many patients do not show clinical responses. While most immunotherapies target T cells, myeloid cells are the most abundant cell type in solid tumors and are key orchestrators of the immunosuppressive tumor microenvironment (TME), hampering effective T cell responses. Therefore, unraveling the immune suppressive pathways within myeloid cells could unveil new avenues for cancer immunotherapy. Over the past decade, Siglec receptors and their ligand, sialic acids, have emerged as a novel immune checkpoint on myeloid cells. In this review, we highlight key findings on how sialic acids modify immunity in the TME through engagement of Siglec-7/9/10/15 expressed on myeloid cells, and how the sialic acid-Siglec axis can be targeted for future cancer immunotherapies.

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.

Analysis of SIGLEC12 expression, immunomodulation and prognostic value in renal cancer using multiomic databases

Siglecs belong to a family of immune regulatory receptors predominantly found on hematopoietic cells. They interact with Sia, resulting in the activation or inhibition of the immune response. Previous reports have suggested that the SIGLEC12 gene, which encodes the Siglec-XII protein, is expressed in the epithelial tissues and upregulated in carcinomas. However, studies deciphering the role of Siglec-XII in renal cancer (RC) are still unavailable, and here we provide insights on this question. We conducted expression analysis using the Human Protein Atlas and UALCAN databases. The impact of SIGLEC12 on RC prognosis was determined using the KM plotter, and an assessment of immune infiltration with SIGLEC12 was performed using the TIMER database. GSEA was conducted to identify the pathways affected by SIGLEC12. Finally, using GeneMania, we identified Siglec-XII interacting proteins. Our findings indicated that macrophages express SIGLEC12 in the kidney. Furthermore, we hypothesize that Siglec-XII expression might be involved in the increase of primary RC, but this effect may not be dependent on the age of the patient. In the tumour microenvironment, oncogenic pathways appeared to be upregulated by SIGLEC12. Similarly, our analysis suggested that SIGLEC12-related kidney renal papillary cell carcinomas may be more suitable for targeted immunotherapy, such as CTLA-4 and PD-1/PD-L1 inhibitors. These preliminary results suggested that high expression of SIGLEC12 is associated with poor prognosis for RC. Future studies to assess its clinical utility are necessitated.

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.

The Potential of Siglecs and Sialic Acids as Biomarkers and Therapeutic Targets in Tumor Immunotherapy

The dysregulation of sialic acid is closely associated with oncogenesis and tumor progression. Most tumor cells exhibit sialic acid upregulation. Sialic acid-binding immunoglobulin-like lectins (Siglecs) are receptors that recognize sialic acid and are expressed in various immune cells. The activity of Siglecs in the tumor microenvironment promotes immune escape, mirroring the mechanisms of the well-characterized PD-1/PD-L1 pathway in cancer. Cancer cells utilize sialic acid-linked glycans to evade immune surveillance. As Siglecs exhibit similar mechanisms as the established immune checkpoint inhibitors (ICIs), they are potential therapeutic targets for different forms of cancer, especially ICI-resistant malignancies. Additionally, the upregulation of sialic acid serves as a potential tumor biomarker. This review examines the feasibility of using sialic acid and Siglecs for early malignant tumor detection and discusses the potential of targeting Siglec-sialic acid interaction as a novel cancer therapeutic strategy.

Nanoparticles (NPs)-mediated Siglec15 silencing and macrophage repolarization for enhanced cancer immunotherapy

T cell infiltration and proliferation in tumor tissues are the main factors that significantly affect the therapeutic outcomes of cancer immunotherapy. Emerging evidence has shown that interferon-gamma (IFNγ) could enhance CXCL9 secretion from macrophages to recruit T cells, but Siglec15 expressed on TAMs can attenuate T cell proliferation. Therefore, targeted regulation of macrophage function could be a promising strategy to enhance cancer immunotherapy via concurrently promoting the infiltration and proliferation of T cells in tumor tissues. We herein developed reduction-responsive nanoparticles (NPs) made with poly (disulfide amide) (PDSA) and lipid-poly (ethylene glycol) (lipid-PEG) for systemic delivery of Siglec15 siRNA (siSiglec15) and IFNγ for enhanced cancer immunotherapy. After intravenous administration, these cargo-loaded could highly accumulate in the tumor tissues and be efficiently internalized by tumor-associated macrophages (TAMs). With the highly concentrated glutathione (GSH) in the cytoplasm to destroy the nanostructure, the loaded IFNγ and siSiglec15 could be rapidly released, which could respectively repolarize macrophage phenotype to enhance CXCL9 secretion for T cell infiltration and silence Siglec15 expression to promote T cell proliferation, leading to significant inhibition of hepatocellular carcinoma (HCC) growth when combining with the immune checkpoint inhibitor. The strategy developed herein could be used as an effective tool to enhance cancer 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.

Novel Siglec-15-Sia axis inhibitor leads to colorectal cancer cell death by targeting miR-6715b-3p and oncogenes

Siglecs are well known immunotherapeutic targets in cancer. Current checkpoint inhibitors have exhibited limited efficacy, prompting a need for novel therapeutics for targets such as Siglec-15. Presently, small molecule inhibitors targeting Siglec-15 are not explored alongside characterised regulatory mechanisms involving microRNAs in CRC progression. Therefore, a small molecule inhibitor to target Siglec-15 was elucidated in vitro and microRNA mediated inhibitor effects were investigated. Our research findings demonstrated that the SHG-8 molecule exerted significant cytotoxicity on cell viability, migration, and colony formation, with an IC50 value of approximately 20µM. SHG-8 exposure induced late apoptosis in vitro in SW480 CRC cells. Notably, miR-6715b-3p was the most upregulated miRNA in high-throughput sequencing, which was also validated via RT-qPCR. MiR-6715b-3p may regulate PTTG1IP, a potential oncogene which was validated via RT-qPCR and in silico analysis. Additionally, molecular docking studies revealed SHG-8 interactions with the Siglec-15 binding pocket with the binding affinity of -5.4 kcal/mol, highlighting its role as a small molecule inhibitor. Importantly, Siglec-15 and PD-L1 are expressed on mutually exclusive cancer cell populations, suggesting the potential for combination therapies with PD-L1 antagonists.

SIGLEC10+ macrophages drive gastric cancer progression by suppressing CD8+ T cell function

Existing immune checkpoint inhibitors focus on activating T cells and show limited effectiveness in gastric cancer (GC). SIGLEC10 is identified as a novel tumor-associated macrophage-related immune checkpoint in other cancer types. However, its immunosuppressive role and clinical significance in GC remain unclear. In this study, we find a dominant expression of SIGLEC10 on CD68+ macrophages in GC. SIGLEC10 can suppress the proliferation and function of tumor-infiltrating CD8+ T cells in vitro via the Akt/P38/Erk signaling pathway. Furthermore, in ex vivo and in vivo models, SIGLEC10 blockade promotes CD8+ T cell effector function. Finally, SIGLEC10+ macrophages are positively correlated with the adverse prognosis of GC. Our study highlights that SIGLEC10 directly suppresses T cell function and serves as a promising target for immunotherapy and suggests SIGLEC10+ macrophages as a novel potential predictor of the clinical prognosis of GC.

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.

Non-spatial and spatial heterogeneity revealed a suppressive immune feature of Siglec-15 in lung adenocarcinomas

BACKGROUND

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) has emerged as a novel immunotherapy candidate, which deserves a comprehensive investigation in lung adenocarcinoma (LUAD).

METHODS

Multiplex fluorescence-based immunohistochemistry was conducted to assess Siglec-15 expression and tumor-infiltrating immune cells in LUAD from Tianjin cohort, with validation cohorts Xinchao 04 and 07.

RESULTS

This study revealed that Siglec-15 was positively correlated with CD8+ T cells and tumor-associated macrophages (TAMs) infiltration, but CD8+ T cells were mostly infiltrated in the stroma area, not in the tumor area. Spatially, fewer CD8+ T cells surrounded Siglec-15+ tumor cells in PD-L1- cells, and more TAMs surrounded Siglec-15+ tumor cells in PD-L1-/+ cells. Siglec-15+ TAMs infiltrated with more CD8+ T cells, and were closer to CD8+ T cells than Siglec-15- TAMs and Siglec-15+ tumor cells. Siglec-15+ TAMs infiltrated with more Tregs and were closer to Tregs than Siglec-15+ tumor cells. Siglec-15+ tumor cells or TAMs reversed CD8+ T cells prognosis value, and enhanced the prognosis value of Tregs and TAMs. The immunotyping based on Siglec-15 and CD8A / CD8+ T cells revealed that patients with high CD8A and Siglec-15 expression exhibited immune activation. Patients with low CD8A expression / CD8+ T cells infiltration and Siglec-15 overexpression were related to the activation of immunosuppressive signature and metabolism-related pathway, and infiltrated with more TAMs.

CONCLUSIONS

We revealed the distinct characteristics between Siglec-15+ tumor cells and TAMs in relation to CD8+ T cells, and a unique relationship between Siglec-15 and immunosuppressive TIME in LUAD, which may provide potential value for anti-Siglec-15 therapy.

Pan-cancer analysis of G6PD carcinogenesis in human tumors

Glucose-6-phosphate dehydrogenase (G6PD) is involved in the catalytic pentose phosphate pathway (PPP), which is closely related to energy metabolism. G6PD plays a crucial role in many types of cancer, but the specific molecular mechanisms of G6PD in cancer remain unclear. Therefore, we investigated the potential oncogenic role of G6PD in various tumors based on The Cancer Genome Atlas (TCGA), the cBioPortal datasets, the University of California Santa Cruz (UCSC) Xena browser, and the UALCAN-based online tool. G6PD was highly expressed in several cancer tissues (hepatocellular carcinoma, glioma, and breast cancer) compared with normal tissues and was significantly associated with poor prognosis of hepatocellular carcinoma, clear cell renal cell carcinoma, and breast cancer. Promoter methylation levels of G6PD were lower in Bladder Urothelial Carcinoma (BLCA) (P = 2.77e-02), breast invasive carcinoma (BRCA) (P = 1.62e-12), kidney renal clear cell carcinoma (KIRC) (P = 4.23e-02), kidney renal papillary cell carcinoma (KIRP) (P = 2.64e-03), liver hepatocellular carcinoma (LIHC) (P = 1.76e-02), stomach adenocarcinoma (STAD) (P = 3.50e-02), testicular germ cell tumors (TGCT) (P = 1.62e-12), higher in prostate adenocarcinoma (PRAD) (P = 1.81e-09), and uterine corpus endometrial carcinoma (UCEC) (P = 2.96e-04) compared with corresponding normal tissue samples. G6PD expression was positively correlated with the infiltration level of immune cells in most tumors, suggesting that G6PD may be involved in tumor immune infiltration. In addition, the functional mechanism of G6PD also involves 'Carbon metabolism', 'Glycolysis/Gluconeogenesis', 'Pentose phosphate pathway', and 'Central carbon pathway metabolism in cancer signaling pathway'. This pan-cancer study provides a relatively broad understanding of the oncogenic role of G6PD in various tumors and presents a theoretical basis for the development of G6PD inhibitors as therapeutic drugs for multiple cancers.

Core needle biopsies alter the amounts of CCR5, Siglec-15, and PD-L1 positivities in breast carcinoma

Core needle biopsies (CNB) are widely used to diagnose breast cancer, but the procedure is invasive and thus, it changes the tumor microenvironment. The purpose of this study is to see how the expression of three potentially anti-inflammatory molecules, namely, programmed death-ligand 1 (PD-L1), sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15), and C-C chemokine receptor-5 (CCR-5), are expressed in CNB and surgical resection specimens (SRS). To do this, we compared the amounts of tumor-infiltrating lymphocytes and the levels of CCR5, Siglec-15, and PD-L1 in tumor cells and inflammatory cells as assessed by immunohistochemistry in CNB and the corresponding SRS of 22 invasive breast carcinomas of no special type and 22 invasive lobular carcinomas. The Siglec-15 H-score was higher in tumor cells in the SRS than in the CNB groups. There was no change in tumor cells CCR5 or PD-L1 between CNB and SRS. The positive inflammatory cell numbers for all markers rose between CNB and SRS, as did the amount of Tils. Furthermore, higher grade tumors and tumors with a high proliferation rate had more inflammatory cells that were positive for the markers and also more PD-L1+ tumor cells. Although changes in inflammatory cells can partly be attributed to the larger sample size of operation specimens, the differences also mirror a true change in the tumor microenvironment. The changes in inflammatory cells could be partly due to the need to restrict excess inflammation at the site of the biopsy.

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.

Enhancing the Anti-tumor Potency of a Novel Siglec-15 Antibody by Engineering its Fc-mediated Effector Functions

Siglec-15, an inhibitory immune checkpoint, is an emerging target in cancer immunotherapy. Blocking the function of Siglec-15 is an excellent strategy for cancer treatment and antibody blockade has been used to target Siglec-15. However, whether Fc-mediated effector functions contribute to the therapeutic effect of antibodies remains unclear. Herein, we generated a monoclonal antibody, 1-15D1, which had a high binding affinity with Siglec-15 and strongly activated T-cell immune response in vitro. Subsequently, the Fc-mediated effector functions of 1-15D1 were explored in a Siglec-15 humanized mouse model, and further improvement in antitumor efficacy was observed in the mouse IgG2a isotype group. Thus, we demonstrate that the antitumor effects of 1-15D1 were mediated via multiple factors. In addition to the T-cell immune response, 2 novel mechanisms were explored, including the internalization of the cell surface Siglec-15 and Fc-mediated effector functions. In conclusion, our studies not only provide a potential agent for the improvement of cancer immunotherapy but also suggest that a specific role of Fc-mediated immune regulation may improve the therapeutic potency of Siglec-15 monoclonal antibody.

Siglec15 is a prognostic indicator and a potential tumor-related macrophage regulator that is involved in the suppressive immunomicroenvironment in gliomas

Background

Siglec15 is rising as a promising immunotherapeutic target in bladder, breast, gastric, and pancreatic cancers. The aim of the present study is to explore the prognostic value and immunotherapeutic possibilities of Siglec15 in gliomas using bioinformatics and clinicopathological methods.

Methods

The bioinformatics approach was used to examine Siglec15 mRNA expression in gliomas based on TCGA, CGGA, and GEO datasets. Then, the predictive value of Siglec15 expression on progression-free survival time (PFST) and overall survival time (OST) in glioma patients was comprehensively described.The TCGA database was screened for differentially expressed genes (DEGs) between the high and low Siglec15 expression groups, and enrichment analysis of the DEGs was performed. The Siglec15 protein expression and its prognostic impact in 92 glioma samples were explored using immunohistochemistry Next, the relationships between Siglec15 expression and infiltrating immune cells, immune regulators and multiple immune checkpoints were analysed.

Results

Bioinformatics analyses showed that high Siglec15 levels predicted poor clinical prognosis and adverse recurrence time in glioma patients. In the immunohistochemical study serving as a validation set, Siglec15 protein overexpression was found in 33.3% (10/30) of WHO grade II, 56% (14/25) of WHO grade III, and 70.3% (26/37) of WHO grade IV gliomas respectively. Siglec15 protein overexpression was also found to be an independent prognostic indicator detrimental to the PFST and OST of glioma patients. Enrichment analysis showed that the DEGs were mainly involved in pathways associated with immune function, including leukocyte transendothelial migration, focal adhesion, ECM receptor interaction, and T-cell receptor signaling pathways. In addition, high Siglec15 expression was related to M2 tumor-associated macrophages (TAMs), N2 tumor-infiltrating neutrophils, suppressive tumor immune microenvironment, and multiple immune checkpoint molecules. Immunofluorescence analysis confirmed the colocalization of Siglec15 and CD163 on TAMs.

Conclusion

Siglec15 overexpression is common in gliomas and predicts an adverse recurrence time and overall survival time. Siglec15 is a potential target for immunotherapy and a potential TAMs regulator that is involved in the suppressed immunomicroenvironment in gliomas.

Dynamic change in Siglec-15 expression in peritumoral macrophages confers an immunosuppressive microenvironment and poor outcome in glioma

Background

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) was reported to be a novel immune checkpoint molecule comparable to programmed cell death 1 ligand 1 (PD-L1). However, its expression profile and immunosuppressive mechanisms in the glioma tumor microenvironment have not yet been fully explored.

Objectives

To identify the expression profile and potential function of Siglec-15 in glioma tumor microenvironment.

Methods

We investigated Siglec-15 and PD-L1 expression in tumor tissues from 60 human glioma patients and GL261 tumor models. Next, Siglec-15 knockout macrophages and mice were used to elucidate the immunosuppressive mechanism of Siglec-15 impacting macrophage function.

Results

Our results demonstrated that high levels of Siglec-15 in tumor tissues was positively correlated with poor survival in glioma patients. Siglec-15 was predominantly expressed on peritumoral CD68⁺ tumor-associated macrophages, which accumulated to the highest level in grade II glioma and then declined as grade increased. The Siglec-15 expression pattern was mutually exclusive with that of PD-L1 in glioma tissues, and the number of Siglec-15⁺PD-L1^- samples (n = 45) was greater than the number of Siglec-15^-PD-L1⁺ samples (n = 4). The dynamic change in and tissue localization of Siglec-15 expression were confirmed in GL261 tumor models. Importantly, after Siglec15 gene knockout, macrophages exhibited enhanced capacities for phagocytosis, antigen cross-presentation and initiation of antigen-specific CD8⁺ T-lymphocyte responses.

Conclusion

Our findings suggested that Siglec-15 could be a valuable prognostic factor and potential target for glioma patients. In addition, our data first identified dynamic changes in Siglec-15 expression and distribution in human glioma tissues, indicating that the timing of Siglec-15 blockade is critical to achieve an effective combination with other immune checkpoint inhibitors in clinical practice.

Comparison of the molecular mechanisms of Fuzi Lizhong Pill and Huangqin decoction in the treatment of the cold and heat syndromes of ulcerative colitis based on network pharmacology

OBJECTIVE

The aim of this study was to illuminate the similarities and differences of two prescriptions as "cold" and "heat" drugs for treating ulcerative colitis (UC) with the simultaneous occurrence of heat and cold syndrome via network pharmacology.

METHODS

(1) Active compounds of Fuzi-Lizhong Pill (FLP) and Huangqin Decoction (HQT) were retrieved from the TCMSP database, and their common active compounds were compared using the Venn diagram. (2) Potential proteins targeted to three sets of compounds either (i) shared by FLP and HQT, (ii) unique to FLP or (iii) unique to HQT were screened from the STP, STITCH and TCMSP databases, and three corresponding core compound sets were identified in Herb-Compound-Target (H-C-T) networks. (3) Targets related to UC were identified from the DisGeNET and GeneCards databases and compared with the FLP-HQT common targets to identify potential targets of FLP-HQT compounds related to UC. (4) Three potential target sets were imported into the STRING database for protein‒protein interaction (PPI) analysis, and three core target sets were defined. (5) The binding capabilities and interacting modes between core compounds and key targets were verified by molecular docking via Discovery Studio 2019 and molecular dynamics (MD) simulations via Amber 2018. (6) The target sets were enriched for KEGG pathways using the DAVID database.

RESULTS

(1) FLP and HQT included 95 and 113 active compounds, respectively, with 46 common compounds, 49 FLP-specific compounds and 67 HQT-specific compounds. (2) 174 targets of FLP-HQT common compounds, 168 targets of FLP-specific compounds, and 369 targets of HQT-specific compounds were predicted from the STP, STITCH and TCMSP databases; six core compounds specific to FLP and HQT were screened in the FLP-specific and HQT-specific H-C-T networks, respectively. (3) 103 targets overlapped from the 174 predicted targets and the 4749 UC-related targets; two core compounds for FLP-HQT were identified from the FLP-HQT H-C-T network. (4) 103 FLP-HQT-UC common targets, 168 of FLP-specific targets and 369 of HQT-specific targets had shared core targets (AKT1, MAPK3, TNF, JUN and CASP3) based on the PPI network analysis. (5) Molecular docking demonstrated that naringenin, formononetin, luteolin, glycitein, quercetin, kaempferol and baicalein of FLP and HQT play a critical role in treating UC; meanwhile, MD simulations revealed the stability of protein‒ligand interactions. (6) The enriched pathways indicated that most targets were related to anti-inflammatory, immunomodulatory and other pathways. Compared with the pathways identified using traditional methods, FLP-specific pathways included the PPAR signaling pathway and the bile secretion pathway, and HQT-specific pathways included the vascular smooth muscle contraction pathway and the natural killer cell-mediated cytotoxicity pathway etc. CONCLUSION: In this study, we clarified the common mechanisms of FLP and HQT in treating UC and their specific mechanisms in treating cold and heat syndrome in UC through compound, target and pathway distinction and a literature comparison based on network pharmacology; these results provide a new perspective on the detailed mechanism of "multidrugs and single-disease" thought in traditional Chinese medicine.

Multimolecular characteristics and role of BRCA1 interacting protein C-terminal helicase 1 (BRIP1) in human tumors: a pan-cancer analysis

BACKGROUND

The aberrant expression of BRIP1 was associated with several cancers; however, the panoramic picture of BRIP1 in human tumors remains unclear. This study aims to explore the pan-cancerous picture of the expression of BRIP1 across 33 human cancers.

METHODS

Based on the data from TCGA and GTEx, a series of bioinformatic analyses were applied to systematically explore the genetic landscape and biologic function of BRIP1 in 33 human tumors.

RESULTS

We observed prognosis-related differential BRIP1 expressions between various carcinomas and the corresponding normal tissues. "Basal transcription factors," "homologous recombination," "nucleotide excision repair," and DNA metabolism pathways may play a role in the functional mechanisms of BRIP1. Patients with uterine corpus endometrial carcinoma presented with the highest alteration frequency of BRIP1 (nearly 10%). Single-nucleotide and copy number variations of BRIP1 were noticed in multiple cancers, and the expression of BRIP1 is significantly regulated by copy number variation in breast invasive carcinoma and lung squamous cell carcinoma. BRIP1 expression is negatively correlated with the DNA methylation levels in many tumors and is associated with the activation of apoptosis, cell cycle, DNA damage response, and inhibition of hormone ER and RNS/MARK signaling pathways. Moreover, a positive correlation was observed between BRIP1 expression and the immune infiltration levels of cancer-associated fibroblasts and CD8+ T cells in lung adenocarcinoma.

CONCLUSION

Our pan-cancer analysis of BRIP1 provides a valuable resource for understanding the multimolecular characteristics and biological function of BRIP1 across human cancers.

Construction and characterization of a cuproptosis- and immune checkpoint-based LncRNAs signature for breast cancer risk stratification

BACKGROUND

Cuproptosis is the most recently identified form of cell death, and copper homeostasis is an important cancer therapeutic target. However, the therapeutic benefits of cuproptosis-targeted treatment in BRCA remain undetermined. This study utilized LncRNAs linked to cuproptosis genes and immune checkpoint genes to generate a BRCA predictive signature.

METHODS

We screened a population of LncRNAs that correlated with both cuproptosis genes and immune checkpoint genes and used ten of these LncRNAs to construct a prognosis-predictive signature. We then validated and proved the efficacy of the signature in predicting the prognosis of BRCA patients. We also unraveled the relationship between the signature and the immunological milieu, immune function, and susceptibility to chemotherapy.

RESULTS

The signature derived from the ten cuproptosis- and immune-related prognostic LncRNAs (CuImP-LncRNAs) can be implied to categorize patients into two groups, including the high- and low-risk groups. The value of the signature was validated, and the risk score was verified as an independent prognostic indicator. The TIME and TMB distribution patterns and chemosensitivity were depicted in the high- and low-risk groups, respectively. Patients of the high-risk group with a suppressive immunological intratumor context were more sensitive to a broad range of antitumor agents. In contrast, low-risk individuals with active immune function responded more favorably to immunotherapy.

CONCLUSION

Our findings provided a novel and effective model for predicting BRCA prognosis and the propensity to different treatment modalities, thus contributing to the optimization of personalized BRCA therapy in the future.

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.

Association of Sialic Acid-Binding Immunoglobulin-Like Lectin 15 With Phenotypes in Esophageal Squamous Cell Carcinoma in the Setting of Neoadjuvant Chemoradiotherapy

IMPORTANCE

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is a novel immune checkpoint molecule that is highly homologous to programmed cell death ligand 1 (PD-L1), but information remains limited about its role in esophageal squamous cell carcinoma (ESCC).

OBJECTIVE

To explore the expression pattern and association of Siglec-15 with outcomes among patients with ESCC who received neoadjuvant chemoradiotherapy (CRT).

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study was conducted at an academic institution in China. Participants included patients with ESCC who underwent neoadjuvant CRT and esophagectomy between June 2002 and December 2018. Multiplexed immunofluorescence staining was used to evaluate the expression of Siglec-15 and PD-L1 in tumor cells (TCs) or tumor-associated macrophages based on pre-CRT biopsies. Different immune phenotypes have been proposed and further validated in an independent cohort. Data analysis was conducted from January to May 2021.

EXPOSURES

Siglec-15 or PD-L1 positivity vs negativity.

MAIN OUTCOMES AND MEASURES

Pathologic complete response (pCR), overall survival (OS), and recurrence-free survival (RFS).

RESULTS

Of 130 participants (median [range] age, 56 [42-73] years; 108 [83.1%] male participants) in the primary cohort, 58 patients (44.6%) achieved a pCR after neoadjuvant CRT. Siglec-15 and PD-L1 were detected in both TCs and macrophages. The percentage of Siglec-15-positive macrophages was notably higher than that of Siglec-15-positive TCs (median [IQR]: 34.4% [12.7%-64.3%] vs 4.8% [0.7%-25.6%]; P < .001). TC-Siglec-15 expression was significantly and positively associated with macrophage-Siglec-15 expression (r = 0.78; P < .001). Siglec-15 positivity was significantly associated with a higher rate of pCR (37 of 70 [52.9%] vs 21 of 60 [35.0%]; P = .04), more favorable OS (hazard ratio [HR], 0.46; 95% CI, 0.25-0.85; P = .01), and RFS (HR, 0.48; 95% CI, 0.26-0.88; P = .02). However, PD-L1 positivity in TCs was negatively associated with survival. Stratification analysis further revealed that patients with combined Siglec-15 positivity and PD-L1 negativity had better survival than those with other phenotypes. Major findings were reproducible in a validation cohort with 55 patients.

CONCLUSIONS AND RELEVANCE

In this cohort study of patients with ESCC receiving neoadjuvant CRT, Siglec-15 positivity was associated with a better pathological response and more favorable survival. Siglec-15 could serve as a novel biomarker to identify potential candidates that may benefit from immunotherapy combined with CRT.

Transcriptional Regulation of Siglec-15 by ETS-1 and ETS-2 in Hepatocellular Carcinoma Cells

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) has been identified as a crucial immune suppressor in human cancers, comparable to programmed cell death 1 ligand (PD-L1). However, the regulatory mechanisms underlying its transcriptional upregulation in human cancers remain largely unknown. Here, we show that the transcription factors ETS-1 and ETS-2 bound to the Siglec-15 promoter to enhance transcription and expression of Siglec-15 in hepatocellular carcinoma (HCC) cells and that transforming growth factor β-1 (TGF-β1) upregulated the expression of ETS-1 and ETS-2 and facilitated the binding of ETS-1 and ETS-2 to the Siglec-15 promoter. We further demonstrate that TGF-β1 activated the Ras/C-Raf/MEK/ERK1/2 signaling pathway, leading to phosphorylation of ETS-1 and ETS-2, which consequently upregulates the transcription and expression of Siglec-15. Our study defines a detailed molecular profile of how Siglec-15 is transcriptionally regulated which may offer significant opportunity for therapeutic intervention on HCC immunotherapy.

Siglec-15 as multifunctional molecule involved in osteoclast differentiation, cancer immunity and microbial infection

Siglec-15 is a highly conserved member of the Siglec family, expressed on osteoclasts, a subset of myeloid cells and some cancer cells. Except for regulating osteoclast differentiation, Siglec-15 engages in immunoregulation as an immune suppressor. Siglec-15 functions as an immunosuppressive molecule in tumor-associated macrophage-mediated T cell immunity in the tumor microenvironment (TME), which makes Siglec-15 to be an emerging and promising target for normalization cancer immunotherapy. Besides, Siglec-15 interacts with sialylated pathogens and modulates host immune response against microbial pathogens by altering cytokine production and/or phagocytosis, which further broadens the underlying pathophysiological roles of Siglec-15. The fact that N-glycosylation and sialylation of Siglec-15 play a pivotal role in Siglec-15 biological function indicates that targeting certain post-translational modification may be an effective strategy for targeting Siglec-15 therapy. In-depth exploring Siglec-15 biology function is crucial for better design of Siglec-15-based therapy according to different clinical indications.

Prognostic value of TMEM59L and its genomic and immunological characteristics in cancer

Background

TMEM59L is a newly discovered transmembrane protein; its functions in cancer remain unknown. This study was designed to reveal the prognostic value and the functional role of TMEM59L in cancer.

Methods

The gene expression profiles, methylation data, and corresponding clinical data of TMEM59L were retrieved from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression database. Survival analysis was employed to calculate the pan-cancer prognostic value of TMEM59L. The correlation between TMEM59L expression and tumor immune microenvironment, as well as DNA methylation dynamics and genomic heterogeneity across cancers were assessed based on data from TCGA.

Results

Our findings revealed that distinct differences of TMEM59L mRNA expression were observed in different cancer types and that higher TMEM59L expression was observed in the advanced pathological stage and associated with worse prognosis in kidney renal papillary cell carcinoma, bladder urothelial carcinoma, colon adenocarcinoma, and kidney renal clear cell carcinoma. Pathway analysis indicated that TMEM59L exerted a key influence in cancer development and in immune- and cancer-associated pathways such as epithelial-mesenchymal transition and TGF-β signaling. Moreover, correlation analysis hinted at a negative correlation of TMEM59L expression with CD8 T cells, activated CD4 T cells, and several immunomodulators, including IDO1, TIGIT, PD-L1, CTLA-4, and BTLA in various cancers. Survival analysis indicated that the hypermethylation of TMEM59L gene was associated with longer survival times. A significant correlation was also observed between TMEM59L expression and immunophenoscore, homologous recombination deficiency, loss of heterozygosity, tumor stemness score, and neoantigens in various cancers. Importantly, we also identified numerous potential agents that may target TMEM59L.

Conclusion

Our study revealed the prognostic value as well as the genomic and immunological characteristics of TMEM59L in cancers, highlighting the promising potential for TMEM59L as a prognostic cancer biomarker and a therapeutic target.

Alterations in cellular metabolisms after TKI therapy for Philadelphia chromosome-positive leukemia in children: A review

Incidence rates of chronic myeloid leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) are lower but more aggressive in children than in adults due to different biological and host factors. After the clinical application of tyrosine kinase inhibitor (TKI) blocking BCR/ABL kinase activity, the prognosis of children with CML and Ph+ ALL has improved dramatically. Yet, off-target effects and drug tolerance will occur during the TKI treatments, contributing to treatment failure. In addition, compared to adults, children may need a longer course of TKIs therapy, causing detrimental effects on growth and development. In recent years, accumulating evidence indicates that drug resistance and side effects during TKI treatment may result from the cellular metabolism alterations. In this review, we provide a detailed summary of the current knowledge on alterations in metabolic pathways including glucose metabolism, lipid metabolism, amino acid metabolism, and other metabolic processes. In order to obtain better TKI treatment outcomes and avoid side effects, it is essential to understand how the TKIs affect cellular metabolism. Hence, we also discuss the relevance of cellular metabolism in TKIs therapy to provide ideas for better use of TKIs in clinical practice.

Bioinformatics analysis of prognosis and immune microenvironment of immunological cell death-related gemcitabine-resistance genes in bladder cancer

Background

Bladder cancer (BC) is the most common malignant tumor of the urinary system. Gemcitabine resistance partly accounts for treatment failure and recurrence in BC. Immunological cell death (ICD) is correlated with chemoresistance. The prognosis of patients with similar tumor stage still varies in response to chemotherapy, recurrence, and disease progression. Therefore, our study aimed to provide a prognostic model based on ICD-related and gemcitabine-resistance genes for BC.

Methods

The data of BC patients were obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs), and differentially expressed gemcitabine resistance-related genes (DEGRRGs) were identified using the edgeR package. The survival-associated DEGRRGs were identified by univariate Cox analysis. A prognostic model was established by univariate Cox regression analysis and validated by GEO dataset. The outcome of low-risk group and high-risk group was analyzed by the Kaplan-Meier curve. The relationship between risk score and immune cell infiltration was investigated using the TIMER online database.

Results

The prognosis of patients in the ICD-high group was significantly better than ICD-low group. A prognostic model containing 5 gemcitabine resistance-related ICD-associated genes, including PTPRR, HOXB3, SIGLEC15, UNC5CL, and CASQ1, was established. In both TCGA prognostic model and GEO validation model, patients in the low-risk group had better outcomes than high-risk group. According to the receiver operating characteristic (ROC) curves, the risk score area under ROC curve (AUC) of the TCGA prognostic model were calculated to be 0.705, while the risk score of the GEO validation model were calculated to be 0.716. Patients in the high-risk group had a significantly higher immune score, stromal score, and infiltration of M0 macrophages, M1 macrophages, M2 macrophages, and activated CD4⁺ T cells. Patients in the high-risk group had significantly lower infiltration of the regulatory T cells, resting dendritic cell (DCs), and activated DCs.

Conclusions

The present study highlighted the functional role of gemcitabine resistance-related ICD-associated genes, constructed a prognostic score for the outcome evaluation and searched for potential targets to overcome gemcitabine chemoresistance in BC.

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.

Quantitative assessment of Siglec-15 expression in lung, breast, head, and neck squamous cell carcinoma and bladder cancer

Immune checkpoint blockade with programmed cell death (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors has resulted in significant progress in the treatment of various cancer types. However, not all patients respond to PD-1/PD-L1 blockade, underscoring the importance of identifying new potential targets for immunotherapy. One promising target is the immune system modulator Siglec-15. In this study, we assess Siglec-15 expression in solid tumors, with a focus on lung, breast, head and neck squamous and bladder cancers. Using quantitative immunofluorescence (QIF) with a previously validated antibody, we found increased Siglec-15 expression in both tumor and immune cells in all the four cancer types. Siglec-15 was seen to be predominantly expressed by the stromal immune cells (83% in lung, 70.1% in breast, 95.2% in head and neck squamous cell and 89% in bladder cancers). Considerable intra-tumoral heterogeneity was noted across cancer types. As previously described for non-small cell lung cancer (NSCLC), Siglec-15 expression was seen to be mutually exclusive to PD-L1 in all the four cancer types, although this differential expression was maintained but somewhat diminished in head and neck squamous cell carcinoma (HNSCC). Siglec-15 was not prognostic either for overall survival (OS) or progression-free survival (PFS). In summary, we show broad expression of this potential immune modulatory target in a wide range of cancer types. These data suggest potential future clinical trials in these tumor types.

Identification and validation of an immunological microenvironment signature and prediction model for epstein-barr virus positive lymphoma: Implications for immunotherapy

Background

Epstein-Barr virus (EBV) is considered a carcinogenic virus, which is associated with high risk for poor prognosis in lymphoma patients, and there has been especially no satisfying and effective treatment for EBV+ lymphoma. We aimed to identify the immunological microenvironment molecular signatures which lead to the poor prognosis of EBV+ lymphoma patients.

Methods

Differential genes were screened with microarray data from the GEO database (GSE38885, GSE34143 and GSE13996). The data of lymphoid neoplasm diffuse large B-cell lymphoma (DLBC) from the TCGA database and GSE4475 were used to identify the prognostic genes. The data of GSE38885, GSE34143, GSE132929, GSE58445 and GSE13996 were used to eluate the immune cell infiltration. Formalin-fixed, paraffin-embedded tissue was collected for Real Time Quantitative PCR from 30 clinical samples, including 15 EBV+ and 15 EBV- lymphoma patients.

Results

Four differential genes between EBV+ and EBV- lymphoma patients were screened out with the significance of the survival and prognosis of lymphoma, including CHIT1, SIGLEC15, PLA2G2D and TMEM163. Using CIBERSORT to evaluate immune cell infiltration, we found the infiltration level of macrophages was significantly different between EBV+ and EBV- groups and was closely related to different genes. Preliminary clinical specimen verification identified that the expression levels of CHIT1 and TMEM163 were different between EBV+ and EBV- groups.

Conclusions

Our data suggest that differences in expression levels of CHIT1 and TMEM163 and macrophage infiltration levels may be important drivers of poor prognosis of EBV+ lymphoma patients. These hub genes may provide new insights into the prognosis and therapeutic target for EBV+ lymphoma.

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.

Characterization of the immune cell infiltration landscape in myxofibrosarcoma to aid immunotherapy

Myxofibrosarcoma (MFS) is a highly malignant subtype of soft tissue sarcoma, accounting for 5% of cases. Immunotherapy guided by immune cell infiltration (ICI) is reportedly a promising treatment strategy. Here, MFS samples (n = 104) from two independent databases were classified as ICI clusters A/B/C and gene clusters A/B/C. Then, a close relationship between ICI and gene clusters was established. We found that the features of these clusters were consistent with the characteristics of immune-inflamed tumors (cluster C), immune-desert tumors (cluster B), and immune-excluded tumors (cluster A). Moreover, cluster C was sensitive to immunotherapy. Finally, an independent ICI score was established to predict the therapeutic effect, which has prospects for application in guiding immunotherapy during clinical practice.

Development of an immunohistochemical assay for Siglec-15

Siglec-15, a member of sialic-acid binding immunoglobulin type lectins, is normally expressed by myeloid cells and upregulated in some human cancers and represents a promising new target for immunotherapy. While PD-L1 blockade is an important strategy for immunotherapy, its effectiveness is limited. The expression of Siglec-15 has been demonstrated to be predominantly mutually exclusive to PD-L1 in certain cancer histologies. Thus, there is significant opportunity for Siglec-15 as an immunotherapeutic target for patients that do not respond to PD-1/PD-L1 inhibition. The aim of this study was to prospectively develop an immunohistochemical (IHC) assay for Siglec-15 to be used as a companion diagnostic for future clinical trials. Here, we create and validate an IHC assay with a novel recombinant antibody to the cytoplasmic domain of Siglec-15. To find an enriched target, this antibody was first used in a quantitative fluorescence (QIF) assay to screen a broad range of tumor histologies to determine tumor types where Siglec-15 demonstrated high expression. Based on this and previous data, we focused on development of a chromogenic IHC assay for lung cancer. Then we developed a scoring system for this assay that has high concordance amongst pathologist readers. We then use this chromogenic IHC assay to test the expression of Siglec-15 in two cohorts of NSCLC. We found that this assay shows a higher level of staining in both tumor and immune cells compared to previous QIF assays utilizing a polyclonal antibody. However, similar to that study, only a small percentage of positive Siglec-15 cases showed high expression for PD-L1. This validated assay for Siglec-15 expression may support development of a companion diagnostic assay to enrich for patients expressing the Siglec-15 target for therapy.

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

Siglec-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 5 representative sequences were selected for further study. The results showed the binding activity of 5 antibodies to siglec-15 (EC₅₀ ranged from 0.02368μg /mL to 0.07949 μg /mL) and in 2 siglec-15 overexpressed cell lines, 3 antibodies had the strongest binding activity, so the 2 clones were discarded for further study. Subsequently the affinity of 3 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, CD44, MAG and LRRC4C can be blocked by 3 of the antibodies. Among these, 3F1 had a competitive advantage. Then, the antibody 3F1 showed an obvious ADCC effect (EC₅₀ were 0.85 μg/mL). Further, antibody 3F1 can reverse the inhibitory effect of siglec-15 on lymphocyte proliferation (especially CD4⁺T, CD8⁺T) and cytokine release (IFN-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 anti-tumor effects (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 anti-tumor 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 anti-tumor drugs.

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.

A novel immune checkpoint siglec-15 antibody inhibits LUAD by modulating mφ polarization in TME

BACKGROUND

Siglec-15 (S15) is a type-I transmembrane protein and is considered a new candidate of immune checkpoint inhibitor for cancer immunotherapy.

METHODS

In the present study, we first constructed and characterized a chimeric S15-specific monoclonal antibody (S15-4E6A). Then, the antitumor effectiveness and modulatory role of S15-4E6A in macrophages (mφs) were explored in vitro and in vivo. Finally, the underlying mechanism by which S15mAb inhibits LUAD was preliminarily explored.

RESULTS

The results demonstrated the successful construction of S15-4E6A, and S15-4E6A exerted an efficacious tumor-inhibitory effect on LUAD cells and xenografts. S15-4E6A could promote M1-mφ polarization while inhibiting M2-mφ polarization, both in vitro and in vivo.

CONCLUSIONS

S15-based immunotherapy that functions by modulating mφ polarization may be a promising strategy for the treatment of S15-positive LUAD.

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.

Resistance Mechanisms to Anti-PD Cancer Immunotherapy

The transformative success of antibodies targeting the PD-1 (programmed death 1)/B7-H1 (B7 homolog 1) pathway (anti-PD therapy) has revolutionized cancer treatment. However, only a fraction of patients with solid tumors and some hematopoietic malignancies respond to anti-PD therapy, and the reason for failure in other patients is less known. By dissecting the mechanisms underlying this resistance, current studies reveal that the tumor microenvironment is a major location for resistance to occur. Furthermore, the resistance mechanisms appear to be highly heterogeneous. Here, we discuss recent human cancer data identifying mechanisms of resistance to anti-PD therapy. We review evidence for immune-based resistance mechanisms such as loss of neoantigens, defects in antigen presentation and interferon signaling, immune inhibitory molecules, and exclusion of T cells. We also review the clinical evidence for emerging mechanisms of resistance to anti-PD therapy, such as alterations in metabolism, microbiota, and epigenetics. Finally, we discuss strategies to overcome anti-PD therapy resistance and emphasize the need to develop additional immunotherapies based on the concept of normalization cancer immunotherapy.

The intriguing roles of Siglec family members in the tumor microenvironment

Sialic acid-binding receptors are expressed on the surfaces of a variety of immune cells and have complex and diverse immunoregulatory functions in health and diseases. Recent studies have shown that Siglecs could play diverse immune and nonimmune regulatory roles in the tumor microenvironment (TME) and participate in tumor progression through various mechanisms, such as regulating tumor growth and metastasis, mediating the inflammatory response, and promoting tumor immune escape, thereby affecting the prognoses and outcomes of patients. However, depending on the cell type in which they are expressed, each Siglec member binds to corresponding ligands in the microenvironment milieu to drive diverse cell physiological and pathological processes in tumors. Therefore, we herein summarize the expression spectra and functions of the Siglec family in human diseases, particularly cancer, and highlight the possibility of therapeutic interventions targeting the TME in the future.

Abnormal ECA-Binding Membrane Glycans and Galactosylated CAT and P4HB in Lesion Tissues as Potential Biomarkers for Hepatocellular Carcinoma Diagnosis

Hepatocellular carcinoma (HCC) is one of the most common types of cancer. Despite decades of research efforts, the search for novel biomarkers is still urgently needed for the diagnosis of HCC and the improvement of clinical outcomes. Previous studies of HCC clinical biomarkers have usually focused on serum and urine samples (e.g., serum Alpha-fetoprotein (AFP). However, cellular membrane proteins in lesion tissues are less used in HCC diagnosis. The abnormal expression of membrane glycoproteins in tumor lesions are considered as potential targets for tumor diagnosis and tumor therapies. Here, a lectin array has been employed to screen and identify abnormal glycopatterns and cellular membrane glycans in HCC lesion tissues compared with adjacent non-tumor tissues. We found that there was significantly less expression of Erythrina cristagalli (ECA) lectin binding (Galβ1-3/β1-4) glycans on the cellular membrane of HCC lesion tissues compared with those of adjacent non-tumor tissues. Immunohistochemistry analysis further showed that ECA-binding ability on the membrane proteins of HCC tissues progressively decreased in different tumor-node-metastasis (TNM) stages (stage I to stage III) as the malignancy of liver cancer increased. Receiver operating curve (ROC) analysis showed ECA-binding ability yielding a sensitivity of 85% and specificity of 75%, and a combination of ECA and AFP has better clinical diagnostic efficiency, yielding a sensitivity of 90% and specificity of 85%, than ECA or AFP assay alone. ECA pull-down followed by mass spectrometry further showed that there was significantly less expression of ECA binding membrane catalase (CAT) and prolyl 4-hydroxylase beta polypeptide (P4HB) in HCC tissues compared with the adjacent non-tumor tissues. The abnormally increased expression of total CAT and P4HB and decreased expression of galactosylated membrane CAT and P4HB in HCC cell lines were correlated with an HCC metastasis status. Our findings suggest that abnormal declined ECA-binding galatosylated membrane glycans and two galactosylated-CAT and P4HB glycoproteins in lesion tissues are potential biomarkers in the diagnosis and/or metastasis prediction for HCC.

Expression and function of Siglec-15 in RLPS and its correlation with PD-L1: Bioinformatics Analysis and Clinicopathological Evidence

Purpose: Retroperitoneal liposarcoma (RLPS) is a rare malignancy without effective treatment. Since current treatment for unresectable RLPS is unsatisfactory, immunotherapy and targeted therapy are urgently needed. Siglec-15 is a transmembrane protein highly homologous to PD-L1 and is involved in tumor immune escape. The biological function of Siglec-15 in RLPS, its prognostic relevance and its relationship with PD-L1 need to be further clarified. In this study, we aimed to explore the biological function of Siglec-15 in sarcomas through bioinformatics analysis, and we also evaluated Siglec-15 and PD-L1 expression in RLPS samples. The relationship between the expression of Siglec-15 and PD-L1 and their clinicopathological relevance and prognostic value were also investigated in clinical RLPS patients. Methods: The RNA sequencing data of 259 sarcoma cases and 48 RLPS cases from TCGA were used to analyze the Siglec-15 expression and the differentially expressed genes (DEG) related with Siglec-15 expression. In addition, DEGs were subsequently analyzed through the gene ontology (GO)/ Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction (PPI) network. Tumor specimens were obtained from 91 RLPS patients of our sarcoma center, and Siglec-15 and PD-L1 expression were evaluated using immunohistochemistry. The correlation between the expression level of these two markers as well as their correlation with clinicopathological factors and prognosis of RLPS patients was also assessed. Results: GEPIA analysis showed that the high expression of Siglec-15 was associated with poor sarcoma OS (P=0.034). A total of 682 differential genes were identified between the high and low expression groups of Siglec-15 in RLPS. Enrichment analysis of the KEGG pathway showed that Siglec-15 was related to the Hippo signaling pathway and the neuroactive ligand-receptor interaction. GO annotation analysis showed that the expression of Siglec-15 may thus be able to affect serine hydrolase activity, alongside signal receptor activator activity. The top 5 genes with the largest number of connection points are APOA1, F2, AHSG, AMBP, SERPINC1. In subsequent studies, we used 91 liposarcoma samples from our center for verification. Siglec-15 was expressed in 84.6% of RLPS cases, whereas PD-L1 was expressed in 17.6% of RLPS cases. A negative correlation was observed between Siglec-15 and PD-L1 expression (P=0.020). In this group of RLPS patients, high Siglec-15 expression was correlated with poorer disease-free survival (DFS) (P=0.021), and it was an independent predictor of DFS (hazard ratio: 2.298; 95% confidence interval: 1.154-4.576; P=0.018). However, we did not find a correlation between PD-L1 expression and overall survival or DFS in RLPS patients. Conclusion: The DEG and signaling pathways identified in the study could provide a preliminary understanding of the underlying molecular mechanisms of Siglec-15 in the development and progression of RLPS. High expression of Siglec-15 was a negative independent predictive factor for DFS of RLPS. The negative relationship between Siglec-15 and PD-L1 expression suggested that the Siglec-15 pathway might be an important supplement to PD-L1 treatment.

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.

Siglecs as Therapeutic Targets in Cancer

Hypersialylation is a common post-translational modification of protein and lipids found on cancer cell surfaces, which participate in cell-cell interactions and in the regulation of immune responses. Sialic acids are a family of nine-carbon α-keto acids found at the outermost ends of glycans attached to cell surfaces. Given their locations on cell surfaces, tumor cells aberrantly overexpress sialic acids, which are recognized by Siglec receptors found on immune cells to mediate broad immunomodulatory signaling. Enhanced sialylation exposed on cancer cell surfaces is exemplified as "self-associated molecular pattern" (SAMP), which tricks Siglec receptors found on leukocytes to greatly down-regulate immune responsiveness, leading to tumor growth. In this review, we focused on all 15 human Siglecs (including Siglec XII), many of which still remain understudied. We also highlighted strategies that disrupt the course of Siglec-sialic acid interactions, such as antibody-based therapies and sialic acid mimetics leading to tumor cell depletion. Herein, we introduced the central roles of Siglecs in mediating pro-tumor immunity and discussed strategies that target these receptors, which could benefit improved cancer immunotherapy.