HHLA2 overexpression is a novel biomarker of malignant status and poor prognosis in gastric cancer

Identification and Validation of Cytotoxicity-Related Features to Predict Prognostic and Immunotherapy Response in Patients with Clear Cell Renal Cell Carcinoma

Background

Clear cell renal cell carcinoma (ccRCC) is a renal cortical malignancy with a complex pathogenesis. Identifying ideal biomarkers to establish more accurate promising prognostic models is crucial for the survival of kidney cancer patients.

Methods

Seurat R package was used for single-cell RNA-sequencing (scRNA-seq) data filtering, dimensionality reduction, clustering, and differentially expressed genes analysis. Gene coexpression network analysis (WGCNA) was performed to identify the cytotoxicity-related module. The independent cytotoxicity-related risk model was established by the survival R package, and Kaplan-Meier (KM) survival analysis and timeROC with area under the curve (AUC) were employed to confirm the prognosis and effectiveness of the risk model. The risk and prognosis in patients suffering from ccRCC were predicted by establishing a nomogram. A comparison of the level of immune infiltration in different risk groups and subtypes using the CIBERSORT, MCP-counter, and TIMER methods, as well as assessment of drug sensitivity to conventional chemotherapeutic agents in risk groups using the pRRophetic package, was made.

Results

Eleven ccRCC subpopulations were identified by single-cell sequencing data from the GSE224630 dataset. The identified cytotoxicity-related T-cell cluster and module genes defined three cytotoxicity-related molecular subtypes. Six key genes (SOWAHB, SLC16A12, IL20RB, SLC12A8, PLG, and HHLA2) affecting prognosis risk genes were selected for developing a risk model. A nomogram containing the RiskScore and stage revealed that the RiskScore contributed the most and exhibited excellent predicted performance for prognosis in the calibration plots and decision curve analysis (DCA). Notably, high-risk patients with ccRCC demonstrate a poorer prognosis with higher immune infiltration characteristics and TIDE scores, whereas low-risk patients are more likely to benefit from immunotherapy.

Conclusions

A ccRCC survival prognostic model was produced based on the cytotoxicity-related signature, which had important clinical significance and may provide guidance for ccRCC treatment.

Unlocking the potential of HHLA2: identifying functional immune infiltrating cells in the tumor microenvironment and predicting clinical outcomes in laryngeal squamous cell carcinoma

BACKGROUND

HHLA2 (human endogenous retrovirus-H long terminal repeat-associating protein 2) represents a recently identified member of the B7 immune checkpoint family, characterized by limited expression in normal tissues but notable overexpression in various cancer types. Nevertheless, the precise function and interaction with immune cells remain poorly understood, particularly in laryngeal squamous cell carcinoma (LSCC). This investigation endeavored to elucidate the biological significance of HHLA2 within the tumor microenvironment of human LSCC tissues and delineate the clinical relevance and functional roles of HHLA2 in LSCC pathogenesis.

METHODS

Through multiplexed immunohistochemistry analyses conducted on tissue microarrays sourced from LSCC patients (n = 72), the analysis was executed to assess the expression levels of HHLA2, density and spatial patterns of CD68+HLA-DR+CD163- (M1 macrophages), CTLA-4+CD4+FoxP3+ (CTLA-4+Treg cells), CTLA-4+CD4+FoxP3- (CTLA-4+Tcon cells), exhausted CD8+T cells, and terminally exhausted CD8+T cells in LSCC tissues. Survival analysis was conducted to evaluate the prognostic significance of HHLA2 and these immune checkpoints or immune cell populations, employing COX regression analysis to identify independent prognostic factors.

RESULTS

Kaplan-Meier (K-M) survival curves revealed a significant association between HHLA2 expression and overall survival (OS) in LSCC. Elevated levels of HHLA2 were linked to reduced patient survival, indicating its potential as a prognostic marker (HR: 3.230, 95%CI 0.9205-11.34, P = 0.0067). Notably, increased infiltration of CD68+ cells (total macrophages), STING+CD68+HLA-DR+CD163- (STING+M1 macrophages), CTLA-4+CD4+FoxP3+, CTLA-4+CD4+FoxP3-, PD-1+LAG-3+CD8+T cells, and PD-1+LAG-3+TIM-3+CD8+T cells strongly linked to poorer survival outcomes (P < 0.05). A discernible trend was observed between the levels of these immune cell populations, STING+CD68+ (STING+ total macrophages), CD68+HLA-DR+CD163-, STING+CD68+CD163+HLA-DR- (STING+M2 macrophages), PD-1+LAG-3-CD8+T cells, PD-1+TIM-3+CD8+T cells, and PD-1+LAG-3+TIM-3-CD8+T cells and prognosis. Importantly, multivariate COX analysis identified HHLA2 as an independent predictive factor for OS in LSCC patients (HR = 3.86, 95% CI 1.08-13.80, P = 0.038). This underscored the potential of HHLA2 as a critical marker for predicting patient outcomes in LSCC.

CONCLUSIONS

HHLA2 emerged as a detrimental prognostic biomarker for assessing OS in LSCC patients. Relative to other immune checkpoints, HHLA2 exhibited heightened predictive efficacy for the prognosis of LSCC patients.

The Importance of HHLA2 in Solid Tumors-A Review of the Literature

Cancer immunotherapy is a rapidly developing field of medicine that aims to use the host's immune mechanisms to inhibit and eliminate cancer cells. Antibodies targeting CTLA-4, PD-1, and its ligand PD-L1 are used in various cancer therapies. However, the most thoroughly researched pathway targeting PD-1/PD-L1 has many limitations, and multiple malignancies resist its effects. Human endogenous retrovirus-H Long repeat-associating 2 (HHLA2, known as B7H5/B7H7/B7y) is the youngest known molecule from the B7 family. HHLA2/TMIGD2/KIRD3DL3 is one of the critical pathways in modulating the immune response. Recent studies have demonstrated that HHLA2 has a double effect in modulating the immune system. The connection of HHLA2 with TMIGD2 induces T cell growth and cytokine production via an AKT-dependent signaling cascade. On the other hand, the binding of HHLA2 and KIR3DL3 leads to the inhibition of T cells and mediates tumor resistance against NK cells. This review aimed to summarize novel information about HHLA2, focusing on immunological mechanisms and clinical features of the HHLA2/KIR3DL3/TMIGD2 pathway in the context of potential strategies for malignancy treatment.

Prognostic Value of HHLA2 in Patients with Solid Tumors: A Meta-Analysis

HHLA2 is a checkpoint from the B7 family that can play a co-stimulatory or co-inhibitory role in cancer, depending on the binding receptor. The aim of this meta-analysis was to assess the relationship between HHLA2 levels and its impact on the prognosis of patients with solid cancers. The study used data from PubMed, Embase, Web of Science (WOS), Cochrane and SCOPUS databases. The R studio software was used for the data analysis. The study assessed overall survival (OS), disease-specific survival (DSS), progression-free survival (PFS), recurrence-free survival (RFS), and disease-free survival (DFS) by pooling appropriate hazard ratios (HR). Eighteen studies (2880 patients' data) were included. High expression of HHLA2 was associated with worse OS (HR = 1.58, 95% CI: 1.23-2.03), shorter RFS (HR = 1.95, 95% CI: 1.38-2.77) and worse DFS (HR = 1.45, 95% CI: 1.01-2.09) in patients with solid cancers. The current study suggests that high expression of HHLA2 is associated with poorer prognosis in patients with solid cancers.

HHLA2 is more significantly associated with poor prognosis in TSCC than PD-L1

BACKGROUND

The incidence and mortality of tongue squamous cell carcinoma have shown an alarming increase in recent years. This study aimed to investigate the potential of HHLA2 as an immune checkpoint in comparison to PD-L1.

METHODS

We obtained RNA-seq data from TCGA to study HHLA2 and PD-L1 expression across various tissues. Using the CIBERSORT package, we estimated cell type abundances within mixed populations based on gene expression profiles. Immunohistochemistry was performed to analyze HHLA2 and PD-L1 expression in Tongue squamous cell carcinoma. Prognostic evaluation was carried out with Kaplan-Meier curves and the log-rank test. To explore factors affecting HHLA2, univariate and multivariate Cox regression analyses were conducted with the COX regression model. Additionally, we used single-cell RNA sequencing data from the GEO database for gene set enrichment analysis with genes strongly correlated with HHLA2.

RESULTS

Our analysis of RNA-seq data unveiled a significant upregulation of HHLA2 and PD-L1 expression in primary tumors when compared with normal tissue. HHLA2 exhibited a positive expression rate of 36.9%, while PD-L1 had a positive expression rate of 24.6%. HHLA2 emerged as a noteworthy independent risk factor impacting the overall survival of Tongue squamous cell carcinoma patients. The analysis of scRNA-seq data shed light on the involvement of HHLA2 in key pathways related to cell cycle regulation and interferon alpha/beta signaling.

CONCLUSIONS

This study suggests that in the context of Tongue squamous cell carcinoma, HHLA2 may represent a more promising target for immunotherapy when compared with PD-L1.

siRNA-Mediated B7H7 Knockdown in Gastric Cancer Lysate-Loaded Dendritic Cells Amplifies Expansion and Cytokine Secretion of Autologous T Cells

BACKGROUND

Gastric cancer, ranked as the fifth most common cancer worldwide, presents multiple treatment challenges. These obstacles often arise due to cancer stem cells, which are associated with recurrence, metastasis, and drug resistance. While dendritic cell (DC)-based immunotherapy has shown promise as a therapeutic strategy, its efficacy can be limited by the tumor microenvironment and certain inhibitory immune checkpoint molecules, such as B7H7. SiRNA-medicated knockdown of B7H7 in tumor cell lysate-pulsed DCs can increase cytokine secretion and autologous T lymphocyte expansion. This study aimed to evaluate the impact of B7H7 suppression in gastric cancer cell lysate-pulsed DCs on the stimulatory potential of autologous CD3+ T lymphocytes.

METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated and monocytes were obtained; then, they were differentiated to immature DCs (iDCs) by GM-CSF and IL-4. Tumor cell lysates from human gastric cancer cell lines were harvested, and iDCs were transformed into mature DCs (mDCs) by stimulating iDCs with tumor cell lysate and lipopolysaccharide. B7H7-siRNA was delivered into mDCs using electroporation, and gene silencing efficiency was assessed. The phenotypic characteristics of iDCs, mDCs, and B7H7-silenced mDCs were evaluated using specific surface markers, an inverted light microscope, and flow cytometry. CD3+ T cells were isolated via magnetically activated cell sorting. They were labeled with CFSE dye and co-cultured with mDCs and B7H7-silenced mDCs to evaluate their ability to induce T-cell proliferation. T-cell proliferation was assessed using flow cytometry. The concentration of TGF-β, IL-4, and IFN-γ secreted from CD3+ T cells in the co-cultured supernatant was evaluated to investigate the cytokine secretory activity of the cells.

RESULTS

Transfection of B7H7 siRNA into mDCs was performed in optimal conditions, and the siRNA transfection effectively reduced B7H7 mRNA expression in a dose-dependent manner. SiRNA-mediated B7H7 knockdown in mDCs enhanced maturation and activation of the DCs, as demonstrated by an increased surface expression of CD11c, CD86, and CD40. Co-culture experiments revealed that B7H7-silenced mDCs had more capacity to induce T cell proliferation compared to non-transfected mDCs. The cytokine production patterns of T cells were also altered. Upon examining the levels of TGF-β, IL-4, and IFN-γ released by CD3+ T cells in the co-culture supernatant, we found that silencing B7H7 in mDCs resulted in a rise in IL-4 secretion and a reduction in TGF-β levels compared to mDCs that were not transfected.

CONCLUSIONS

The study found that suppressing B7H7 expression in DCs significantly enhances their maturation and stimulatory activity when exposed to gastric cancer cell lysate. These B7H7-silenced DCs can substantially increase cytokine production and promote co-cultured T-cell expansion. Consequently, inhibiting B7H7 in DCs may offer a practical strategy to enhance the ability of DCs to initiate T lymphocyte responses and improve the effectiveness of DC-based cell therapy for cancer patients.

Cooperative Treatment of Gastric Cancer Using B7-H7 siRNA and Docetaxel; How Could They Modify Their Effectiveness?

Purpose

Despite the high prevalence of gastric cancer (GC), drug resistance is a major problem for effective chemotherapy. B7-H7 is a novel member of the B7 superfamily and is expressed in most common cancers. However, the role of B7-H7 on the aggressiveness of GC and chemosensitivity has remained unknown. Therefore, this study was designed to assess the effect of B7-H7 suppression using small interference RNA (siRNA) in combination with docetaxel on GC cells.

Methods

MTT test was applied to determine the IC50 of docetaxel and the combined effect of B7-H7 siRNA and docetaxel on the viability of the MKN-45 cells. To determine B7-H7, BCL-2, BAX, and caspase-3-8-9 genes expression, qRT-PCR was performed. Furthermore, flow cytometry was applied to evaluate apoptosis and the cell cycle status. Finally, to evaluate the effect of this combination therapy on migratory capacity and colony-forming ability, wound healing assay and colony formation test were employed, respectively.

Results

B7-H7 suppression increased the chemo-sensitivity of MKN-45 cells to docetaxel. The expression of B7-H7 mRNA was reduced after using B7-H7 siRNA and docetaxel in MKN-45 GC cells. Also, B7-H7 suppression alongside docetaxel reduced cell migration and colony formation rate, arrested the cell cycle at the G2-M phase, and induced apoptosis by modulating the expression of apoptotic target genes.

Conclusion

B7-H7 plays a significant role in the chemo-sensitivity and pathogenesis of GC. Therefore, B7-H7 suppression, in combination with docetaxel, may be a promising therapeutic approach in treating GC.

B7-H7: A potential target for cancer immunotherapy

Cancer immunotherapy enhances the body's immunity against tumors by mitigating immune escape. Compared with traditional chemotherapy, immunotherapy has the advantages of fewer drugs, a wider range of action and fewer side effects. B7-H7 (also known as HHLA2, B7y) is a member of the B7 family of costimulatory molecules that was discovered more than 20 years ago. B7-H7 is mostly expressed in organs such as the breast, intestine, gallbladder and placenta and is detected predominantly in monocytes/macrophages in the immune system. Its expression is upregulated after stimulation by inflammatory factors such as lipopolysaccharide and interferon-γ. B7-H7/transmembrane and immunoglobulin domain containing 2 (TMIGD2) and killer cell immunoglobulin-like receptor, three Ig domains and long cytoplasmic tail 3 (KIR3DL3)-B7-H7 are the two currently confirmed signaling pathways for B7-H7. An increasing number of studies have demonstrated that B7-H7 is widely present in a variety of human tumor tissues, especially in programmed cell death-1 (PD-L1)-negative human tumors. B7-H7 promotes tumor progression, disrupts T-cell-mediated antitumor immunity, and inhibits immune surveillance. B7-H7 also triggers tumor immune escape and is associated with clinical stage, depth of tumor infiltration, metastasis, prognosis, and survival related to different tumor types. Multiple studies have shown that B7-H7 is a promising immunotherapeutic target. Herein, review the current literature on the expression, regulation, receptors and function of B7-H7 and its regulation/function in tumors.

HHLA2 immune-regulatory roles in cancer

Human endogenous retrovirus H long terminal repeat-associating protein 2 (HHLA2 or B7-H7) is a newly discovered B7 family member. HHLA2 is aberrantly expressed in solid tumors and exerts co-stimulatory or co-inhibitory activities dependent on interaction with counter receptors. HHLA2 represents co-stimulatory effects upon interaction with transmembrane and immunoglobulin domain containing 2 (TMIGD2, also called CD28H), but its interaction with killer cell Ig-like receptor, three Ig domains and long cytoplasmic tail 3 (KIR3DL3) renders co-inhibitory effects. TMIGD2 is mainly expressed on resting or naïve T cells, whereas expression of KIR3DL3 occurs on activated T cells. HHLA2/KIR3DL3 attenuates responses from both innate and adaptive anti-tumor immunity, and the activity within this axis is regarded as a biomarker of weak prognosis in cancer patients. HHLA2/KIR3DL3 promotes CD8⁺ T cell exhaustion and induces macrophage polarity toward pro-tumor M2 phenotype. HHLA2 represents diverse expression profile and activity in tumor and stroma. Tumoral expression of HHLA2 is presumably higher compared with programmed death-ligand 1 (PD-L1), and HHLA2 co-expression with PD-L1 is indicative of more severe outcomes. A suggested strategy in patients with HHLA2^high cancer is to use monoclonal antibodies for specifically suppressing the HHLA2 inhibitory receptor KIR3DL3, not the HHLA2 ligand. TMIGD2 can be a target for development of agonistic bispecific antibodies for hampering tumor resistance to the programmed death-1 (PD-1)/PD-L1 blockade therapy.

Downregulation of HHLA2 inhibits ovarian cancer progression via the NF-κB signaling pathway and suppresses the expression of CA9

HHLA2 has been recently demonstrated to play multifaceted roles in several types of cancers. However, its underlying mechanism in the progression of human ovarian cancer (OC) remains largely unexplored. In the present study, we aimed to determine whether downregulation of HHLA2 inhibited malignant phenotypes of human OC cells and explore its specific mechanism. Our results revealed that downregulation of HHLA2 by transfection with a lentiviral vector significantly suppressed the viability, invasion, and migration of OC cells. Interaction study showed that downregulation of HHLA2 in OC cells reduced the expression of CA9 and increased the expressions of p-IKKβ and p-RelA. Conversely, the viability, invasion, and migration of HHLA2-depleted OC cells were increased when CA9 was upregulated. In vivo, we found that downregulation of HHLA2 significantly inhibited tumor growth, which was reversed by CA9 overexpression. In addition, downregulation of HHLA2 inhibited the OC progression via activating the NF-κB signaling pathway and decreasing the expression of CA9. Collectively, our data suggested a link between HHLA2 and NF-κB axis in the pathogenesis of OC, and these findings might provide valuable insights into the development of novel potential therapeutic targets for OC.

Increased co-expression of stromal HHLA2 and fibroblast activation protein in upper tract urothelial carcinoma

BACKGROUND

The human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2; also known as B7 homolog 7 [B7-H7]) regulates immune responses. However, its immunoregulatory role in upper tract urothelial carcinoma (UTUC) remains unclear.

METHODS

We evaluated the immunohistochemical expression of HHLA2 and fibroblast activation protein (FAP), which is a marker of cancer-associated fibroblasts, in UTUC tissues from 85 patients who underwent nephroureterectomy. The associations between the expressions of HHLA2 and FAP and clinicopathological characteristics were investigated.

RESULTS

The increased expression of HHLA2 in tumor cells (t-HHLA2) was associated with a low histological grade, a negative lymphovascular invasion (LVI), and a low neutrophil-to-lymphocyte ratio, whereas an increased expression of HHLA2 in stromal cells (s-HHLA2) was associated with a high histological grade. No correlation was observed between the expression of t-HHLA2 and s-HHLA2. FAP was expressed only in the stromal cells (s-FAP). Positive s-FAP expression was significantly associated with increased s-HHLA2 expression, higher histological grade, higher pathological T stage, and positive LVI. Higher t-HHLA2 was associated with longer cancer-specific and progression-free survival. In contrast, positive s-FAP was associated with short progression-free survival.

CONCLUSION

These findings suggest that the progression of UTUC may involve increased co-expression of HHLA2 and FAP in the tumor stroma.

Silencing tumor-intrinsic HHLA2 potentiates the anti-tumoral effect of paclitaxel on MG63 cells: Another side of immune checkpoint

BACKGROUND

Osteosarcoma is common type of bone cancer; however, the prognosis of patients with metastatic osteosarcoma is poor. As a new inhibitory immune checkpoint molecule, HHLA2 is upregulated in osteosarcoma. Herein, we studied the significance of tumor-intrinsic HHLA2 in MG-63 growth. Also, we examined the influence of combined therapy of HHLA2 knockdown with paclitaxel on the apoptosis, cell cycle, migration, and stemness of MG-63 cells.

METHODS

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was performed to study the half-maximal inhibitory concentration (IC50) of paclitaxel and the cytotoxicity of HHLA2-small interfering RNA (siRNA) on MG-63 cells. The apoptosis and cell cycle were analyzed using flow cytometry. The wound-healing and colony formation assays were conducted to investigate the effect of paclitaxel and HHLA2 knockdown on the migration and stemness of MG-63 cells, respectively. QRT-PCR was used to determine the Bax, caspase-3, and Bcl-2 mRNA expression levels.

RESULTS

HHLA2 silencing has enhanced the chemosensitivity of MG-63 cells to paclitaxel. Besides, HHLA2 knockdown has increased the paclitaxel-induced cytotoxic effect on MG-63 cells. In terms of stimulating apoptosis, decreasing clonogenicity, halting the cell cycle at the sub G1 phase, and inhibiting migration, tumor-intrinsic HHLA2 silencing has increased these anti-tumor effects of paclitaxel on MG-63 cells. Besides, HHLA2 knockdown has potentiated paclitaxel-mediated Bcl-2 downregulation and paclitaxel-mediated caspase-3 and Bax upregulation in MG-63 cells.

CONCLUSION

Tumor-intrinsic HHLA2 knockdown increases the anti-tumoral effect of paclitaxel on MG-63 cells and enhances the chemosensitivity of MG-63 cells to paclitaxel.

The integrated landscape of eRNA in gastric cancer reveals distinct immune subtypes with prognostic and therapeutic relevance

The comprehensive regulation effect of eRNA on tumor immune cell infiltration and the outcome remains obscure. We comprehensively identify the eRNA-mediated immune infiltration patterns of gastric cancer (GC) samples. We creatively proposed a random forest machine-learning (ML) algorithm to map eRNA to mRNA expression patterns. The eRNA score was constructed using principal component analysis algorithms and validated in an independent cohort. Three subtypes with distinct eRNA expression patterns were determined in GC. There were significant differences between the three subtypes in the overall survival rate, immune cell infiltration characteristics, and immunotherapy response indicators. The patients in the high eRNA score group have a higher overall survival rate and might benefit from immunotherapy. This work revealed that eRNA regulation might be a new prognostic index and might offer a potential biomarker in the response of immunotherapy. Evaluating the eRNA regulation manner of GC will contribute to guiding more effective immunotherapy strategies.

Crosstalk between the B7/CD28 and EGFR pathways: Mechanisms and therapeutic opportunities

Somatic activating mutations in the epidermal growth factor receptor (EGFR) are one of the most common oncogenic drivers in cancers such as non-small-cell lung cancer (NSCLC), metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Molecular-targeted agents against EGFR signaling pathways have shown robust clinical efficacy, but patients inevitably experience acquired resistance. Although immune checkpoint inhibitors (ICIs) targeting PD-1/PD-L1 have exhibited durable anti-tumor responses in a subset of patients across multiple cancer types, their efficacy is limited in cancers harboring activating gene alterations of EGFR. Increasing studies have demonstrated that upregulation of new B7/CD28 family members such as B7-H3, B7x and HHLA2, is associated with EGFR signaling and may contribute to resistance to EGFR-targeted therapies by creating an immunosuppressive tumor microenvironment (TME). In this review, we discuss the regulatory effect of EGFR signaling on the PD-1/PD-L1 pathway and new B7/CD28 family member pathways. Understanding these interactions may inform combination therapeutic strategies and potentially overcome the current challenge of resistance to EGFR-targeted therapies. We also summarize clinical data of anti-PD-1/PD-L1 therapies in EGFR-mutated cancers, as well as ongoing clinical trials of combination of EGFR-targeted therapies and anti-PD-1/PD-L1 immunotherapies.

KIR3DL3-HHLA2 and TMIGD2-HHLA2 pathways: The dual role of HHLA2 in immune responses and its potential therapeutic approach for cancer immunotherapy

BACKGROUND

T cells and natural killer (NK) cells are essential components of the immune system and are regulated by coinhibitory and costimulatory molecules in which the B7 family and CD28 family play significant roles. Previous immune checkpoint studies on B7/CD28 family members, such as PD-1, have led to remarkable success in cancer immunotherapy. However, there is still a need to find new immune checkpoint molecules. Recent studies have demonstrated that HHLA2 exerts inhibitory and stimulatory functions on the immune system by binding to different receptors on different sites. However, the pathways between HHLA2 and its two receptors on T cells and NK cells remain controversial.

AIM OF REVIEW

Here, we reviewed recent studies about HHLA2 ligand interactions with KIR3DL3 and TMIGD2. We focused on elucidating the pathways between KIR3DL3/TMIGD2 and HHLA2 as well as their function in tumour progression. We also addressed the relationship between HHLA2 expression and the clinical prognosis of cancer patients.

KEY SCIENTIFIC CONCEPTS OF REVIEW

KIR3DL3/TMIGD2-HHLA2 may represent novel pathways within the tumour microenvironment and serve as crucial immune checkpoints for developing novel therapeutic drugs against human cancer.

Human endogenous retrovirus-H long terminal repeat-associating 2: The next immune checkpoint for antitumour therapy

Human endogenous retrovirus-H long terminal repeat-associating 2 (HHLA2) is a newly emerging immune checkpoint that belongs to B7 family. HHLA2 has a co-stimulatory receptor transmembrane and immunoglobulin domain containing 2 (TMIGD2) and a newly discovered co-inhibitory receptor killer cell Ig-like receptor, three Ig domains, and long cytoplasmic tail (KIR3DL3), which endows it with both immunostimulant and immunosuppression functions in cancer development. In this review, we summarize the HHLA2 expression profile in human cancers, its association with cancer prognosis and clinical features, and its dual roles in regulating cancer immune response through up-to-date literatures. Furthermore, we highlight that precision cancer immunotherapy through manipulating HHLA2-KIR3DL3/TMIGD2 interaction is a promising antitumour strategy.

Comprehensive Analysis of HHLA2 as a Prognostic Biomarker and Its Association With Immune Infiltrates in Hepatocellular Carcinoma

Background

Inhibitory immune checkpoint proteins promote tumor immune escape and are associated with inferior patient outcome. However, the biological functions and regulatory roles of one of its members, HHLA2, in the tumor immune microenvironment have not been explored.

Methods

RandomForest analyses (371 cases), qRT-PCR (15 cases), and immunohistochemical staining (189 cases) were used to validate the prognostic value of HHLA2 in hepatocellular carcinoma (HCC) patients. Bioinformatic analyses were further performed to explore the biological functions and potential signaling pathways affected by HHLA2. Moreover, ESTIMATE, single sample gene set enrichment analysis, CIBERSORT, TIMER, and other deconvolution methods were used to analyze the composition and infiltration level of immune cells. Multiplex immunofluorescence assays were employed to validate the fractions of suppressive immune cells, and HHLA2-related molecular alterations were investigated. Finally, the clinical response to chemotherapy and immune checkpoint blockade was predicted by TIDE, Submap, and several other in silico analyses.

Results

RandomForest analysis revealed that HHLA2 was the most important inhibitory immune checkpoint associated with HCC patient prognosis (relative importance = 1). Our HCC cohorts further revealed that high HHLA2 expression was an independent prognostic biomarker of shorter overall survival (P<0.01) and time to recurrence (P<0.001) for HCC patients. Bioinformatics experiments revealed that HHLA2 may accelerate the cell cycle of cancer cells. Additionally, we found that high expression of HHLA2 was associated with immune infiltrates, including some immunosuppressive cells, cytokines, chemokines, and corresponding receptors, resulting in an immunosuppressive environment. Notably, HHLA2 expression was positively correlated with the infiltration of exhausted CD8+ T cells, which was validated by immunofluorescence. Genomic alteration analyses revealed that promoter hypermethylation of HHLA2 may be associated with its low expression. More importantly, patients with high HHLA2 expression may be more sensitive to chemotherapy and have better responses to immunotherapy.

Conclusions

High expression of HHLA2 is an independent prognostic biomarker for HCC patients. It can activate the cell cycle and foster an immunosuppressive tumor microenvironment by enriching exhausted CD8+ T cells. Promoter hypermethylation might lead to low expression of HHLA2 in HCC. Thus, targeting HHLA2 may be a practical therapeutic strategy for HCC patients in the future.

Expression of HHLA2, TMIGD2, and GITR in salivary gland adenoid cystic carcinoma and mucoepidermoid carcinoma

BACKGROUND

Mucoepidermoid carcinoma and adenoid cystic carcinoma are the two most common malignancies of salivary gland. Our study aims to explore the role of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced tumor necrosis factor receptor in adenoid cystic carcinoma and mucoepidermoid carcinoma, and the relationship between human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, glucocorticoid-induced TNF receptor, oncogenic signaling molecules, and cluster of differentiation 8.

METHODS

Custom-made human salivary gland tissue microarrays included 81 Adenoid cystic carcinoma, 52 mucoepidermoid carcinoma, 76 normal salivary gland, and 14 pleomorphic adenoma samples. Immunohistochemical analysis of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor, oncogenic phosphorylated Erk_1/2 , the epithelial-mesenchymal transition (EMT) molecule transforming growth factor β1, and cluster of differentiation 8 was performed with salivary gland tissue microarray of human samples.

RESULTS

According to a digital pathological system, we analyzed the correlation of immunostaining. The expression levels of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were significantly enhanced in the adenoid cystic carcinoma and mucoepidermoid carcinoma, compared with those of pleomorphic adenoma and NSG samples. However, the expression levels of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were independent of the pathological grade of malignancy of mucoepidermoid carcinoma and histological pattern of adenoid cystic carcinoma. They were closely related to phosphorylated Erk1/2 and transforming growth factor β1, but negligibly related to cluster of differentiation 8.

CONCLUSIONS

These results described that certain immune checkpoint molecules, namely, human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were overexpressed in Adenoid cystic carcinoma and mucoepidermoid carcinoma, but were independent of pathological grade, and may relate to transforming growth factor β1, phosphorylated Erk1/2, and cluster of differentiation 8.

High expression of HHLA2 predicts poor prognosis in medullary thyroid carcinoma

Background

Human endogenous retrovirus-H long terminal repeat-associating protein 2 is a newly identified immune checkpoint molecule that was aberrantly expressed in many malignant tumors. However, its expression in medullary thyroid carcinoma is still unclear. This study aimed to investigate the human endogenous retrovirus-H long terminal repeat-associating protein 2 expression in medullary thyroid carcinoma tissues and to evaluate the relationships between its expression and clinicopathologic together with prognostic relevance.

Methods

Using 51 surgical specimens obtained from medullary thyroid carcinoma patients, the expression levels of the human endogenous retrovirus-H long terminal repeat-associating protein 2 protein in medullary thyroid carcinoma tumor tissues and adjacent noncancerous tissues were measured by immunohistochemistry, and its correlations with clinicopathologic and prognostic features were analyzed. Status of CD8+ tumor infiltrating lymphocytes was also investigated.

Results

The results showed that human endogenous retrovirus-H long terminal repeat-associating protein 2 was only detected in tumor tissues, and 31.4% of the medullary thyroid carcinoma patients had high expression of human endogenous retrovirus-H long terminal repeat-associating protein 2. High human endogenous retrovirus-H long terminal repeat-associating protein 2 expression was significantly associated with lymph node metastasis and advanced American Joint Committee on Cancer stages (P = 0.005). There existed an inverse trend between human endogenous retrovirus-H long terminal repeat-associating protein 2 expression and CD8+ tumor infiltrating lymphocytes infiltration in medullary thyroid carcinoma tumor samples (P = 0.042). The log-rank test showed a shorter disease-free survival in patients with high human endogenous retrovirus-H long terminal repeat-associating protein 2 expression (P = 0.002). The disease-free survival rates were also significantly low in cases of medullary thyroid carcinoma with lymph node metastasis, American Joint Committee on Cancer stages III–IV and multifocality. Multivariate Cox analysis confirmed that human endogenous retrovirus-H long terminal repeat-associating protein 2 acted as an independent predictive factor in the disease-free survival of medullary thyroid carcinoma patients (hazard ratio = 4.138, 95% confidence interval: 1.027–16.667, P = 0.046).

Conclusions

Taken together, human endogenous retrovirus-H long terminal repeat-associating protein 2 is highly expressed in medullary thyroid carcinoma patients and is a poor prognostic biomarker of disease-free survival of medullary thyroid carcinoma patients.

HHLA2 Used as a Potential Prognostic and Immunological Biomarker and Correlated with Tumor Microenvironment in Pan-Cancer

Background

The role of HERV–H LTR-associating 2 (HHLA2) in cancer remains still unclear. This study analyzed the correlation between the prognosis and immune infiltrate function of HHLA2 in pan-cancers.

Methods

HHLA2 expression in pan-cancers was analyzed using the databases of TCGA, GTEx, TIMER, GEPIA, UALCAN, and GSEA databases. Multiple bioinformatic methods were used to investigate the correlation of HHLA2 expression with survival, pathological stage, tumor mutation burden (TMB), microsatellite instability (MSI), tumor microenvironment (TME), immune cell infiltration, and immune checkpoint gene (ICG), and gene functional enrichment was performed by Gene Set Enrichment Analysis (GSEA) and Gene Set Variation Analysis (GSVA).

Results

HHLA2 was aberrantly expressed and was strongly correlated with positive or negative prognosis in multiple human cancers, which revealed that HHLA2 might play a vital role during cancer formation and development. Kaplan–Meier (KM) curves across cancers revealed that HHLA2 expression was correlated with overall survival (OS) in eight cancers, disease-specific survival (DSS) in seven cancers, disease-free interval (DFI) in four cancers, and progression-free interval (PFI) in nine cancers. Furthermore, HHLA2 expression was positively correlated with TMB in 6 cancer types and negatively associated with TMB in 7 cancer types, respectively. The former included ESCA, HNSC, KIRP, PAAD, PRAD, and PCPG; the latter contained COAD, LGG, LUAD, LUSC, THYM, THCA, and UCEC. Additionally, we found HHLA2 expression was negatively related to MSI in ACC, COAD, PAAD, and UCEC. More importantly, HHLA2 expression was remarkably correlated with the degree of tumor-infiltrating immune in many cancers, including B cells, CD4+ T cells, CD8+ T cells, neutrophils, macrophages, and dendritic cells and strongly associated with immune checkpoint genes in 13 tumor types. Furthermore, KEGG pathway analyses indicated that HHLA2 could potentially impact cancer etiology or pathogenesis by functioning in amino sugar and nucleotide sugar metabolism, cytosolic DNA sensing pathway, and peroxisome pathways. Meanwhile, GSVA analysis results all indicate that HHLA2 was correlated with TSC/mTOR, RTK, RAS/MAPK, PI3K/AKT, EMT, DNA Damage Response, Cell Cycle, and Apoptosis pathways in various cancers.

Conclusion

HHLA2 can function as a prognostic biomarker and correlate with tumor immunity in human pan-cancer due to its important role in tumorigenesis and immune infiltration, which provides new insight into developing new targeted treatments in cancers.

Human Endogenous Retrovirus-H Long Terminal Repeat-Associating Protein 2 Possesses Prognostic Significance and Promotes Progression of Papillary Thyroid Cancer

Purpose

Patients and Methods

Results

Conclusion

Expression and prognosis of the B7 family in acute myeloid leukemia

Background

B7 family molecules affect both immune responses and cancer progression via immunological and non-immunological pathways. However, the specific expression and prognostic value of B7 members in acute myeloid leukemia (AML) remains unclear; hence, an investigation using online bioinformatics databases is required.

Methods

In this study, we explored the expression of B7 molecules using the ONCOMINE, Gene Expression Profiling Interactive Analysis 2 (GEPIA2), and UALCAN databases, while the prognostic value of B7 molecules in AML was analyzed using the LinkedOmics, GEPIA2, UALCAN, and TCGAportal databases. Additionally, genetic alteration and gene co-expression analysis of the B7 family was performed via the cBioPortal and LinkedOmics databases, while functional and pathway enrichment analyses were conducted using the Metascape databases for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses.

Results

The message RNA (mRNA) levels of B7 family members varied in AML patients, and aberrant highly expressed B7 members were correlated with poor prognosis in AML, including B7.1, B7-DC, B7-H3, B7-H5, and B7-H7. B7-H6 acted as a protective molecule for overall survival (OS), while B7-H1 overexpression was inclined to predict poor prognosis. B7 family gene alteration occurred frequently in AML, and the altered B7 group seemed to exhibit a trend towards worse OS. The co-expression genes and relative signaling pathways of the B7 family might be involved in oncogenesis and be associated with prognosis in AML.

Conclusions

Our study showed that aberrantly expressed B7 family molecules affected the prognosis of AML patients, and thus, could be promising prognostic biomarkers and new therapeutic targets.

The Positive and Negative Immunoregulatory Role of B7 Family: Promising Novel Targets in Gastric Cancer Treatment

Gastric cancer (GC), with a heterogeneous nature, is the third leading cause of death worldwide. Over the past few decades, stable reductions in the incidence of GC have been observed. However, due to the poor response to common treatments and late diagnosis, this cancer is still considered one of the lethal cancers. Emerging methods such as immunotherapy with immune checkpoint inhibitors (ICIs) have transformed the landscape of treatment for GC patients. There are presently eleven known members of the B7 family as immune checkpoint molecules: B7-1 (CD80), B7-2 (CD86), B7-H1 (PD-L1, CD274), B7-DC (PDCD1LG2, PD-L2, CD273), B7-H2 (B7RP1, ICOS-L, CD275), B7-H3 (CD276), B7-H4 (B7x, B7S1, Vtcn1), B7-H5 (VISTA, Gi24, DD1α, Dies1 SISP1), B7-H6 (NCR3LG1), B7-H7 (HHLA2), and Ig-like domain-containing receptor 2 (ILDR2). Interaction of the B7 family of immune-regulatory ligands with the corresponding receptors resulted in the induction and inhibition of T cell responses by sending co-stimulatory and co-inhibitory signals, respectively. Manipulation of the signals provided by the B7 family has significant potential in the management of GC.

Interferon Gamma-Induced Interferon Regulatory Factor 1 Activates Transcription of HHLA2 and Induces Immune Escape of Hepatocellular Carcinoma Cells

Immunosuppression developed by cancer cells remains a leading cause of treating failure of immunotherapies. This study aimed to explore the function of human endogenous retrovirus-H long terminal repeat-associating 2 (HHLA2), an immune checkpoint molecule from the B7 family, in the immune escape in hepatocellular carcinoma (HCC). Mouse models with primary HCC or with xenograft tumors were established. The portion of tumor-associated macrophages (TAMs) and the level of PD-L1 in the tumor tissues were examined. THP-1 cells were treated with PMA to obtain a macrophage-like phenotype. The PMA-treated THP-1 cells were co-cultured with the HCC cells in Transwell chambers to examine the function of HHLA2 in chemotactic migration and polarization of macrophages. HHLA2 expression was correlated with infiltration of immune cells, especially macrophages, and was linked to poor prognosis of patients with HCC. HHLA2 knockdown reduced incidence rate of primary HCC in mice. It also reduced tumor metastasis, the portion of M2 macrophages, and the expression of PD-L1 in primary and xenograft tumors. In vitro, HHLA2 upregulation increased expression of PD-L1 in HCC cells indirectly by inducing M2 polarization and chemotactic migration of macrophages. Interferon gamma (IFNG) enhanced expression of interferon regulatory factor 1 (IFR1) in HCC cells, and IFR1 bound to the promoter region of HHLA2 to activate HHLA2 expression. This study suggested that the IFNG/IFR1/HHLA2 axis in HCC induces M2 polarization and chemotactic migration of macrophages, which leads to immune escape and development of HCC.

HHLA2 Expression is Associated with Poor Survival in Patients with Hepatocellular Carcinoma

Background

Human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2) is a member of the B7 family; however, little is known regarding its expression and clinical relevance in hepatocellular carcinoma (HCC).

Methods

To better characterize HHLA2 expression in HCC, we analyzed its expression by in situ staining and further investigated its correlation with immune infiltration and patient prognosis.

Results

HHLA2 was primarily expressed in the peri-tumor region of HCC tissues and co-localized with CD68⁺ monocytes/macrophages. In vitro analysis and multi-immunofluorescence staining showed up-regulated HHLA2 expression in tumor-activated monocytes/macrophages, and HHLA2⁺ monocytes/macrophages expressed high levels of HLA-DR in HCC tissue. A correlation analysis showed that samples displaying high HHLA2 expression in the peri-tumor region had significant tumor infiltration of CD204⁺ and CD11b⁺ cells, and low expression of genes associated with an anti-tumor immune response. The high level of peri-tumoral HHLA2 expression was associated with a poor patient overall survival (OS; P = 0.008). A multivariate analysis revealed that HHLA2 expression in the peri-tumor region was an independent prognostic factor for OS (hazard ratio = 1.872, p = 0.003). Moreover, the expression of HHLA2 was negatively correlated with PD-L1, and patients exhibiting HHLA2 and programmed cell death-ligand 1(PD-L1) co-expression had the shortest survival time.

Conclusion

HHLA2 expression represented an immunosuppressive microenvironment in HCC, and may serve as a potential target for immunotherapy.

Prognostic value of HHLA2 expression in solid tumors: A meta-analysis based on the Chinese population

BACKGROUND

Human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2), a newly discovered member of the B7 family, is overexpressed in numerous tumors. However, the prognostic impact of HHLA2 in human cancers remains controversial. Thus, we performed this meta-analysis to explore the prognostic value of HHLA2 in Chinese patients with solid tumors.

METHODS

PubMed, Embase, Web of Science, Chinese National Knowledge Infrastructure, and WanFang databases were systematically searched for eligible studies that evaluated the impact of HHLA2 on overall survival (OS) in patients with cancer. Hazard ratios (HRs) and 95% confidence intervals (CIs) were combined to evaluate the association between HHLA2 expression and OS in solid tumors. Odds ratios (ORs) and 95% CIs were pooled to assess the correlation between HHLA2 expression and clinicopathological characteristics in solid tumors.

RESULTS

A total of 12 studies, including 15 cohorts and 1747 patients, were included in this meta-analysis. We found that high HHLA2 expression was significantly associated with shorter OS (HR = 1.65, 95% CI: 1.12-2.43). Subgroup analysis by cancer type demonstrated that high HHLA2 expression was associated with poor OS in patients with clear cell renal cell carcinoma (HR = 3.42, 95% CI: 2.39-4.91), gastric cancer (HR = 2.03, 95% CI: 1.31-3.16), intrahepatic cholangiocarcinoma (HR = 1.77, 95% CI: 1.24-2.53), lung cancer (HR = 2.14, 95% CI: 1.33-3.44) and other cancer types (HR = 2.08, 95% CI: 1.34-3.24), but not in patients with epithelial ovarian cancer (HR = 0.52, 95% CI: 0.08-3.56). Nevertheless, high HHLA2 expression was associated with better OS in patients with pancreatic ductal adenocarcinoma (HR = 0.45, 95% CI: 0.32-0.64). Furthermore, high HHLA2 expression was associated with old age (OR = 1.30, 95% CI: 1.03-1.63), lymph node metastasis (OR = 1.99, 95% CI: 1.41-2.81), and vascular invasion (OR = 1.69, 95% CI: 1.18-2.42).

CONCLUSIONS

HHLA2 may serve as a potential prognostic biomarker for solid tumors in Chinese population, by predict the prognosis of cancer patients based on their tumor types.

KIR3DL3-HHLA2 is a human immunosuppressive pathway and a therapeutic target

The B7 family ligand HERV-H LTR-associating protein 2 (HHLA2) is an attractive target for cancer immunotherapy because of its coinhibitory function, overexpression in human cancers, and association with poor prognoses. However, the knowledge of the HHLA2 pathway is incomplete. HHLA2 has an established positive receptor transmembrane and immunoglobulin (Ig) domain containing 2 (TMIGD2) but a poorly characterized negative receptor human killer cell Ig-like receptor, three Ig domains, and long cytoplasmic tail (KIR3DL3). Here, KIR3DL3 and TMIGD2 simultaneously bound to different sites of HHLA2. KIR3DL3 was mainly expressed on CD56dim NK and terminally differentiated effector memory CD8+ T (CD8+ TEMRA) cells. KIR3DL3+ CD8+ TEMRA acquired an NK-like phenotype and function. HHLA2 engagement recruited KIR3DL3 to the immunological synapse and coinhibited CD8+ T and NK cell function and killing, inducing immune-evasive HHLA2+ tumors. KIR3DL3 recruited SHP-1 and SHP-2 to attenuate Vav1, ERK1/2, AKT, and NF-κB signaling. HHLA2+ tumors from human kidney, lung, gallbladder, and stomach were infiltrated by KIR3DL3+ immune cells. KIR3DL3 blockade inhibited tumor growth in multiple humanized mouse models. Thus, our findings elucidated the molecular and cellular basis for the inhibitory function of KIR3DL3, demonstrating that the KIR3DL3-HHLA2 pathway is a potential immunotherapeutic target for cancer.

Human Endogenous Retroviruses in Clear Cell Renal Cell Carcinoma: Biological Functions and Clinical Values

Human endogenous retroviruses (HERVs) form an important part of the human genome, commonly losing their coding ability and exhibiting only rare expression in healthy tissues to promote the stability of the genome. However, overexpression of HERVs has been observed in various malignant tumors, including clear cell renal cell carcinoma (ccRCC), and may be closely correlated with tumorigenesis and progression. HERVs may activate the interferon (IFN) signaling pathway by a viral mimicry process to enhance antitumor immune responses. There is increasing interest in the diagnostic and prognostic value of HERVs in cancers, and they may be candidate targets for tumor immunotherapy. The review will introduce the biological functions of HERVs in ccRCC and their clinical value, especially in regard to immunotherapy.

Phenotypical and potential functional characteristics of different immune cells expressing CD28H/B7-H5 and their relationship with cancer prognosis

CD28H and B7-H5 have been identified as receptor-ligand pairs in the B7/CD28 family, and have co-stimulatory activity in immune cells. Here, we have systematically reviewed the research reports concerning the CD28H/B7-H5 pathway. It was found that CD28H is mainly expressed in T cells and natural killer (NK) cells with naive and poorly differentiated properties, and repeated antigen stimulation leads to permanent loss of CD28H. In tumors, CD28H is mainly expressed in tissue-resident memory (T_RM ) lymphocyte T cells, which is associated with improved tumor prognosis. B7-H5 is a ligand for CD28H and is widely expressed in tumor cells. B7-H5 expression is closely related to the prognosis of the tumor. Studies have shown that high expression of B7-H5 in tumor is related to a worse prognosis for lung cancer, osteosarcoma, oral squamous cell carcinoma (OSCC), breast carcinoma, human clear cell renal cell carcinoma (ccRCC), intrahepatic cholangiocarcinoma (ICC), bladder urothelial carcinoma (BUC) and colorectal cancer (CRC), but is associated with a better prognosis for pancreatic ductal adenocarcinoma (PDAC) and glioma. Controversial views exist in studies on gastric cancer prognosis.