Epstein-Barr virus infection: the micro and macro worlds

Epstein‒Barr virus (EBV) is a DNA virus that belongs to the human B lymphotropic herpesvirus family and is highly prevalent in the human population. Once infected, a host can experience latent infection because EBV evades the immune system, leading to hosts harboring the virus for their lifetime. EBV is associated with many diseases and causes significant challenges to human health. This review first offers a description of the natural history of EBV infection, clarifies the interaction between EBV and the immune system, and finally focuses on several major types of diseases caused by EBV infection.

Role of Exosomes and Their Potential as Biomarkers in Epstein-Barr Virus-Associated Gastric Cancer

Exosomes are a subtype of extracellular vesicles ranging from 30 to 150 nm and comprising many cellular components, including DNA, RNA, proteins, and metabolites, encapsulated in a lipid bilayer. Exosomes are secreted by many cell types and play important roles in intercellular communication in cancer. Viruses can hijack the exosomal pathway to regulate viral propagation, cellular immunity, and the microenvironment. Cells infected with Epstein-Barr virus (EBV), one of the most common oncogenic viruses, have also been found to actively secrete exosomes, and studies on their roles in EBV-related malignancies are ongoing. In this review, we focus on the role of exosomes in EBV-associated gastric cancer and their clinical applicability in diagnosis and treatment.

Molecular mechanisms underlying the action of carcinogens in gastric cancer with a glimpse into targeted therapy

BACKGROUND

Gastric cancer imposes a substantial global health burden despite its overall incidence decrease. A broad spectrum of inherited, environmental and infectious factors contributes to the development of gastric cancer. A profound understanding of the molecular underpinnings of gastric cancer has lagged compared to several other tumors with similar incidence and morbidity rates, owing to our limited knowledge of the role of carcinogens in this malignancy. The International Agency for Research on Cancer (IARC) has classified gastric carcinogenic agents into four groups based on scientific evidence from human and experimental animal studies. This review aims to explore the potential comprehensive molecular and biological impacts of carcinogens on gastric cancer development and their interactions and interferences with various cellular signaling pathways.

CONCLUSIONS

In this review, we highlight recent clinical trial data reported in the literature dealing with different ways to target various carcinogens in gastric cancer. Moreover, we touch upon other multidisciplinary therapeutic approaches such as surgery, adjuvant and neoadjuvant chemotherapy. Rational clinical trials focusing on identifying suitable patient populations are imperative to the success of single-agent therapeutics. Novel insights regarding signaling pathways that regulate gastric cancer can potentially improve treatment responses to targeted therapy alone or in combination with other/conventional treatments. Preventive strategies such as control of H. pylori infection through eradication or immunization as well as dietary habit and lifestyle changes may reduce the incidence of this multifactorial disease, especially in high prevalence areas. Further in-depth understanding of the molecular mechanisms involved in the role of carcinogenic agents in gastric cancer development may offer valuable information and update state-of-the-art resources for physicians and researchers to explore novel ways to combat this disease, from bench to bedside. A schematic outlining of the interaction between gastric carcinogenic agents and intracellular pathways in gastric cancer H. pylori stimulates multiple intracellular pathways, including PI3K/AKT, NF-κB, Wnt, Shh, Ras/Raf, c-MET, and JAK/STAT, leading to epithelial cell proliferation and differentiation, apoptosis, survival, motility, and inflammatory cytokine release. EBV can stimulate intracellular pathways such as the PI3K/Akt, RAS/RAF, JAK/STAT, Notch, TGF-β, and NF-κB, leading to cell survival and motility, proliferation, invasion, metastasis, and the transcription of anti-apoptotic genes and pro-inflammatory cytokines. Nicotine and alcohol can lead to angiogenesis, metastasis, survival, proliferation, pro-inflammatory, migration, and chemotactic by stimulating various intracellular signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, ROS, and JAK/STAT. Processed meat contains numerous carcinogenic compounds that affect multiple intracellular pathways such as sGC/cGMP, p38 MAPK, ERK, and PI3K/AKT, leading to anti-apoptosis, angiogenesis, metastasis, inflammatory responses, proliferation, and invasion. Lead compounds may interact with multiple signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, DNA methylation-dependent, and epigenetic-dependent, leading to tumorigenesis, carcinogenesis, malignancy, angiogenesis, DNA hypermethylation, cell survival, and cell proliferation. Stimulating signaling pathways such as PI3K/Akt, RAS/RAF, JAK/STAT, WNT, TGF-β, EGF, FGFR2, and E-cadherin through UV ionizing radiation leads to cell survival, proliferation, and immortalization in gastric cancer. The consequence of PI3K/AKT, NF-κB, Ras/Raf, ROS, JAK/STAT, and WNT signaling stimulation by the carcinogenic component of Pickled vegetables and salted fish is the Warburg effect, tumorigenesis, angiogenesis, proliferation, inflammatory response, and migration.

Clinicopathological features of Epstein-Barr virus-associated superficial early stage gastric cancer treated with endoscopic submucosal dissection

BACKGROUND

Epstein-Barr virus (EBV) is known to be involved in gastric carcinogenesis. EBV-associated early gastric carcinoma (EBVEGC) has a lower incidence of lymph node involvement and could be an expanded indication for endoscopic submucosal dissection (ESD) treatment.

AIM

To clarify the prevalence and clinicopathological features of EBVEGC.

METHODS

This study reviewed 618 lesions in 519 patients treated with ESD between 2014 and 2016. Tissue microarray sections were subjected to in situ hybridization staining for EBV-encoded small RNA transcripts (EBER). Lesions positive for EBER were compared with control lesions and were retrospectively analyzed.

RESULTS

12 (1.9%) of the 618 lesions were EBVEGC. EBVEGCs were more frequently located near the atrophic border than control lesions in the middle or upper stomach and were reddish. EBVEGC invasion was deeper and more often histologically undifferentiated. On narrow-band imaging magnifying endoscopy, the EBVEGC group significantly more often showed an endoscopic lace pattern, defined as an absent or obscure microsurface pattern and a microvascular pattern of a tiny, dense, and irregular subepithelial capillary network. The rate of curative resection was significantly lower in the EBVEGC group.

CONCLUSIONS

Only 1.9% of the ESD specimens were EBV-positive. Endoscopic features could raise clinical suspicion of EBV infection.

FastViFi: Fast and accurate detection of (Hybrid) Viral DNA and RNA

DNA viruses are important infectious agents known to mediate a large number of human diseases, including cancer. Viral integration into the host genome and the formation of hybrid transcripts are also associated with increased pathogenicity. The high variability of viral genomes, however requires the use of sensitive ensemble hidden Markov models that add to the computational complexity, often requiring > 40 CPU-hours per sample. Here, we describe FastViFi, a fast 2-stage filtering method that reduces the computational burden. On simulated and cancer genomic data, FastViFi improved the running time by 2 orders of magnitude with comparable accuracy on challenging data sets. Recently published methods have focused on identification of location of viral integration into the human host genome using local assembly, but do not extend to RNA. To identify human viral hybrid transcripts, we additionally developed ensemble Hidden Markov Models for the Epstein Barr virus (EBV) to add to the models for Hepatitis B (HBV), Hepatitis C (HCV) viruses and the Human Papillomavirus (HPV), and used FastViFi to query RNA-seq data from Gastric cancer (EBV) and liver cancer (HBV/HCV). FastViFi ran in <10 minutes per sample and identified multiple hybrids that fuse viral and human genes suggesting new mechanisms for oncoviral pathogenicity. FastViFi is available at https://github.com/sara-javadzadeh/FastViFi.

Molecular fusion events in carcinogenic organisms: a bioinformatics study for the detection of fused proteins between viruses, bacteria and eukaryotes

Molecular fusion events have a prominent role in the initial steps of carcinogenesis. In this study, a bioinformatics analysis was performed between four organisms that are known to induce cancer development in humans: two viruses, Human Herpesvirus 4, and Human T-cell leukaemia virus, one bacterium, Helicobacter Pylori, and one trematode, Schistosoma mansoni. The annotated proteomes from these organisms were analysed using the SAFE software to identify protein fusion events, which may provide insight into protein function similarities and possible merging events during the course of evolution. Based on the results, five fused proteins with very similar functions were detected, whereas proteins with different functions that might act in the same molecular complex or biochemical pathway were not found. Thus, this study analysed the above four well-known cancer-related organisms with de novo bioinformatics programs and provided useful information on protein fusion events, hopefully leading to deeper understanding of carcinogenenesis.

PD-L1 expression in EBV associated gastric cancer: a systematic review and meta-analysis

OBJECTIVES

The aim of this systematic review and meta-analysis is to the summarize the evidence on programmed cell death protein ligand 1 (PD-L1) in Epstein-Barr virus associated gastric cancer (EBVaGC) and to estimate the expression rate of PD-L1 among this subtype of Gastric Cancer (GC).

MATERIALS AND METHODS

For this study, PubMed^®, EMBASE^® and Web of Science^® databases were searched for articles published until 1st November 2021. A total of 43 eligible publications with a total of 11,327 patients were included analysis based on inclusion and exclusion criteria. A total of 41 publications present data for proportion estimation and 33 for comparison of PD-L1 between EBV positive and negative GC. DerSimonian-Laird random-effects model was used for meta-analysis.

RESULTS

The analysis showed that in EBVaGC the pooled positivity rate for PD-L1 was 54.6% (p < 0.001), with a high heterogeneity between the included studies, which was associated with variation on positivity criteria for PD-L1 expression. Overall, the study reveals an increased association between PD-L1 and EBVaGC (OR = 6.36, 95% CI 3.91-10.3, p < 0.001). Furthermore, the study revealed that GC with lymphoid stroma (GCLS) is highly associated with EBV (OR = 17.4, 95% CI 6.83-44.1, p < 0.001), with a pooled EBV positivity rate of 52.9% (p < 0.001).

CONCLUSIONS

Patients with EBVaGC tend to show higher PD-L1 expression, which enhances EBV positivity as a promising marker for patient selection for immunotherapy targeted agents. A uniform criteria for PD-L1 positivity in tumor cells is needed, as well as further prospective studies to validate our findings and their prognostic significance.

EBV-associated diseases: Current therapeutics and emerging technologies

EBV is a prevalent virus, infecting >90% of the world's population. This is an oncogenic virus that causes ~200,000 cancer-related deaths annually. It is, in addition, a significant contributor to the burden of autoimmune diseases. Thus, EBV represents a significant public health burden. Upon infection, EBV remains dormant in host cells for long periods of time. However, the presence or episodic reactivation of the virus increases the risk of transforming healthy cells to malignant cells that routinely escape host immune surveillance or of producing pathogenic autoantibodies. Cancers caused by EBV display distinct molecular behaviors compared to those of the same tissue type that are not caused by EBV, presenting opportunities for targeted treatments. Despite some encouraging results from exploration of vaccines, antiviral agents and immune- and cell-based treatments, the efficacy and safety of most therapeutics remain unclear. Here, we provide an up-to-date review focusing on underlying immune and environmental mechanisms, current therapeutics and vaccines, animal models and emerging technologies to study EBV-associated diseases that may help provide insights for the development of novel effective treatments.

Epstein-Barr Virus-Associated Gastric Cancer: Old Entity with New Relevance

Gastric cancer (GC) represents a major public health issue worldwide, being the fifth most common cancer and one of the leading causes of death by cancer. In 2014, The Cancer Genome Atlas (TCGA) established that tumors positive for Epstein-Barr virus (EBV) are considered a specific subtype of GC (EBVaGC). Several meta-analyses have shown that EBVaGC represents almost 10% of all gastric cancer worldwide, with small differences in the geographic distribution. This tumor subtype has a high potential of being clinically relevant and studies have shown that it has specific features, a better prognosis, and increased overall survival. In this review, we summarize some of the most frequent aspects of EBVaGC, including the specific features of this GC subtype, data regarding the potential steps of EBVaGC carcinogenesis, and perspectives on treatment opportunities.

Epstein Barr Virus: Development of Vaccines and Immune Cell Therapy for EBV-Associated Diseases

Epstein-Barr virus (EBV) is the first human tumor virus discovered and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. Each year EBV associated cancers account for over 200,000 new cases of cancer and cause 150,000 deaths world-wide. EBV is also the primary cause of infectious mononucleosis, and up to 70% of adolescents and young adults in developed countries suffer from infectious mononucleosis. In addition, EBV has been shown to play a critical role in the pathogenesis of multiple sclerosis. An EBV prophylactic vaccine that induces neutralizing antibodies holds great promise for prevention of EBV associated diseases. EBV envelope proteins including gH/gL, gB and gp350 play key roles in EBV entry and infection of target cells, and neutralizing antibodies elicited by each of these proteins have shown to prevent EBV infection of target cells and markedly decrease EBV titers in the peripheral blood of humanized mice challenged with lethal dose EBV. Recent studies demonstrated that immunization with the combination of gH/gL, gB and/or gp350 induced markedly increased synergistic EBV neutralizing activity compared to immunization with individual proteins. As previous clinical trials focused on gp350 alone were partially successful, the inclusion of gH/gL and gB in a vaccine formulation with gp350 represents a promising approach of EBV prophylactic vaccine development. Therapeutic EBV vaccines have also been tested clinically with encouraging results. Immunization with various vaccine platforms expressing the EBV latent proteins EBNA1, LMP1, and/or LMP2 promoted specific CD4+ and CD8+ cytotoxic responses with anti-tumor activity. The addition of EBV envelope proteins gH/gL, gB and gp350 has the potential to increase the efficacy of a therapeutic EBV vaccine. The immune system plays a critical role in the control of tumors, and immune cell therapy has emerged as a promising treatment of cancers. Adoptive T-cell therapy has been successfully used in the prevention and treatment of post-transplant lymphoproliferative disorder. Chimeric antigen receptor T cell therapy and T cell receptor engineered T cell therapy targeting EBV latent proteins LMP1, LMP2 and/or EBNA1 have been in development, with the goal to increase the specificity and efficacy of treatment of EBV associated cancers.

Virus-host interactions in carcinogenesis of Epstein-Barr virus-associated gastric carcinoma: Potential roles of lost ARID1A expression in its early stage

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is a distinct molecular subtype of gastric cancer characterized by viral infection and cellular abnormalities, including loss of AT-rich interaction domain 1A (ARID1A) expression (lost ARID1A). To evaluate the significance of lost ARID1A in the development of EBVaGC, we performed in situ hybridization of EBV-encoded RNA (EBER) and immunohistochemistry of ARID1A in the non-neoplastic gastric mucosa and intramucosal cancer tissue of EBVaGC with in vitro infection analysis of ARID1A-knockdown and -knockout gastric cells. Screening of EBER by in situ hybridization revealed a frequency of approximately 0.2% EBER-positive epithelial cells in non-neoplastic gastric mucosa tissue samples. Six small foci of EBV-infected epithelial cells showed two types of histology: degenerated (n = 3) and metaplastic (n = 3) epithelial cells. ARID1A was lost in the former type. In intramucosal EBVaGC, there were ARID1A-lost (n = 5) and -preserved tumors (n = 7), suggesting that ARID1A-lost carcinomas are derived from ARID1A-lost precursor cells in the non-neoplastic mucosa. Lost ARID1A was also observed in non-neoplastic mucosa adjacent to an ARID1A-lost EBVaGC. In vitro experiments using siRNA knockdown and the CRISPR/Cas9-knockout system demonstrated that transient reduction or permanent loss of ARID1A expression markedly increased the efficiency of EBV infection to stomach epithelial cells. Taken together, lost ARID1A plays a role in initiating EBV-driven carcinogenesis in stomach epithelial cells, which develop to a distinct subtype of EBVaGC within the proper mucosal layer. Lost ARID1A is one of the constituents of virus-host interactions in the carcinogenesis of EBVaGC.

Human Herpesvirus and the Immune Checkpoint PD-1/PD-L1 Pathway: Disorders and Strategies for Survival

The immune system has evolved as a complex and efficient means of coping with extrinsic materials, such as pathogens and toxins, as well as intrinsic abnormalities, such as cancers. Although rapid and timely activation of the immune system is obviously important, regulated downregulation of the system is almost as significant as activation to prevent runaway immunity, such as allergies and hypercytokinemia. Therefore, the immune checkpoint programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway is beneficial for the host. On the other hand, pathogens have evolved to evade host immunity by taking advantage of the PD-1/PD-L1 pathway. This review is focused on human herpesviruses, such as herpes simplex virus (HSV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV), which cause various types of disorders, and their relationships with the PD-1/PD-L1 pathway. Understanding such relationships will be useful for developing preventative and therapeutic methods for disorders caused by herpesviruses.

Ephrin receptor A2, the epithelial receptor for Epstein-Barr virus entry, is not available for efficient infection in human gastric organoids

Epstein-Barr virus (EBV) is best known for infection of B cells, in which it usually establishes an asymptomatic lifelong infection, but is also associated with the development of multiple B cell lymphomas. EBV also infects epithelial cells and is associated with all cases of undifferentiated nasopharyngeal carcinoma (NPC). EBV is etiologically linked with at least 8% of gastric cancer (EBVaGC) that comprises a genetically and epigenetically distinct subset of GC. Although we have a very good understanding of B cell entry and lymphomagenesis, the sequence of events leading to EBVaGC remains poorly understood. Recently, ephrin receptor A2 (EPHA2) was proposed as the epithelial cell receptor on human cancer cell lines. Although we confirm some of these results, we demonstrate that EBV does not infect healthy adult stem cell-derived gastric organoids. In matched pairs of normal and cancer-derived organoids from the same patient, EBV only reproducibly infected the cancer organoids. While there was no clear pattern of differential expression between normal and cancer organoids for EPHA2 at the RNA and protein level, the subcellular location of the protein differed markedly. Confocal microscopy showed EPHA2 localization at the cell-cell junctions in primary cells, but not in cancer cell lines. Furthermore, histologic analysis of patient tissue revealed the absence of EBV in healthy epithelium and presence of EBV in epithelial cells from inflamed tissue. These data suggest that the EPHA2 receptor is not accessible to EBV on healthy gastric epithelial cells with intact cell-cell contacts, but either this or another, yet to be identified receptor may become accessible following cellular changes induced by inflammation or transformation, rendering changes in the cellular architecture an essential prerequisite to EBV infection.

Selective sensitivity of EZH2 inhibitors based on synthetic lethality in ARID1A-deficient gastric cancer

BACKGROUND

AT-rich interactive domain 1A (ARID1A) is a tumor suppressor gene that is frequently mutated in gastric cancer (GC). Although ARID1A mutations are not a druggable target for conventional treatments, novel therapeutic strategies based on a synthetic lethal approach are effective for ARID1A-deficient cancers. The histone methyltransferase EZH2 acts in a synthetic lethal manner in ARID1A-mutated ovarian cancer, although its role in GC remains unknown.

METHODS

The selective sensitivity of the EZH2 inhibitors for ARID1A-deficient GC cells was evaluated using cell viability and colony formation assays. The expression of PI3K/AKT signaling genes were investigated using TCGA's cBioPortal database to determine whether the homeostasis between ARID1A and EZH2 is related to cell proliferation and survival via the PI3K/AKT signaling pathway. We also evaluated the phosphorylation of PI3K/AKT signaling proteins in ARID1A knock downed ARID1A-WT GC cells.

RESULTS

EZH2 inhibitors decreased the viability of ARID1A-deficient cells in a dose-dependent manner and demonstrated the selective sensitivity to ARID1A-deficient cells in vitro experiment system. Bioinformatics approach revealed that the PI3K/AKT signaling was tended to be activated in ARID1A-deficient GC enhancing cell viability and, furthermore, down-regulation of EZH2 in ARID1A-deficient GC was related to normalization of PI3K/AKT signaling pathway. The cell experiment revealed that phosphorylated AKT was upregulated in ARID1A-deficent GC cells.

CONCLUSIONS

The present findings provide a rationale for the selective sensitivity of EZH2 inhibitors against ARID1A-deficient GC and suggest the potential efficacy of targeted therapy using EZH2 inhibitors in this patient population.

Overview of Epstein-Barr-Virus-Associated Gastric Cancer Correlated with Prognostic Classification and Development of Therapeutic Options

Gastric cancer (GC) is a deadly disease with poor prognosis that is characterized by heterogeneity. New classifications based on histologic features, genotypes, and molecular phenotypes, for example, the Cancer Genome Atlas subtypes and those by the Asian Cancer Research Group, help understand the carcinogenic differences in GC and have led to the identification of an Epstein–Barr virus (EBV)-related GC subtype (EBVaGC), providing new indications for tailored treatment and prognostic factors. This article provides a review of the features of EBVaGC and an update on the latest insights from EBV-related research with a particular focus on the strict interaction between EBV infection and the gastric tumor environment, including the host immune response. This information may help increase our knowledge of EBVaGC pathogenesis and the mechanisms that sustain the immune response of patients since this mechanism has been demonstrated to offer a survival advantage in a proportion of patients with GC.

Remodeling of the ARID1A tumor suppressor

In recent years, AT-rich interactive domain-containing protein 1A (ARID1A) has been widely accepted as a bona fide tumor suppressor due to its essential role in preventing tumorigenesis and tumor progression in both mouse and human contexts. ARID1A shows high mutation frequencies in both cancers and preneoplastic lesions. The loss of ARID1A expression in cancer cells leads to increases in cell proliferation, invasion and migration and reductions in cell apoptosis and chemosensitivity. The tumor-suppressive role of ARID1A is mainly attributed to its regulation of gene transcription, which can be induced either directly by chromatin remodeling or indirectly by affecting histone modifications. ARID1A also acts independently of its cardinal transcription-regulating mechanisms, which include interfering with protein-protein interactions. Interestingly, nonmutational mechanisms, such as regulation by DNA hypermethylation, microRNAs, and ubiquitinases/deubiquitinases, have provided another perspective on ARID1A inactivation in cancer. Since the critical tumor-suppressive role of ARID1A has been revealed, several studies have attempted to identify synthetic lethal targets with ARID1A mutation/inactivation as an alternative strategy for cancer treatment.

The Clinicopathological Features and Genetic Alterations in Epstein-Barr Virus-Associated Gastric Cancer Patients after Curative Surgery

Background: Epstein–Barr virus (EBV)-associated gastric cancer (GC) is one of four major gastric cancer types and is traditionally considered to be related to lymphoepithelioma-like GC. Few studies have investigated the clinical significance of EBV infection in intestinal/solid type, diffuse (poorly cohesive) type, and lymphoepithelioma-like GC. Methods: A total of 460 GC patients receiving curative surgery were enrolled. The clinicopathological features, genetic alterations and prognoses were compared between patients with and without EBV infection. Results: EBV-positive GC patients (n = 43) had more tumors located in the upper and middle stomach, more common in lymphoepithelioma-like carcinoma, more lymphoid stroma, fewer Helicobacter pylori infections, and higher programmed death-ligand 1 (PD-L1) expression than EBV-negative GC patients. For intestinal/solid type GC, EBV-positive tumors were more likely to be located in the upper and middle stomach, have more lymphoid stroma, fewer Helicobacter pylori infections, higher PD-L1 expression, and more liver metastases than EBV-negative tumors. For diffuse (poorly cohesive) type GC, EBV-positive tumors were more likely to be located in the upper stomach, and have more lymphoid stroma than EBV-negative tumors. For lymphoepithelioma-like GC, EBV-positive tumors had more PI3K/AKT pathway mutations than EBV-negative tumors. Conclusions: Intestinal/solid type GC patients with EBV-positive tumors were associated with higher PD-L1 expression and more liver metastases, while lymphoepithelioma-like GC patients with EBV-positive tumors had more PI3K/AKT pathway mutations. Immunotherapy and targeted therapy may be beneficial for these groups of patients. Routine EBV survey is recommended in GC.

Thirty years of Epstein-Barr virus-associated gastric carcinoma

Thirty years have passed since a possible association of Epstein-Barr virus (EBV) with gastric carcinoma was reported. We now know EBV-associated gastric carcinoma to be a specific subtype of gastric carcinoma. Global epigenetic methylation and counteraction of the antitumour microenvironment are two major characteristics of this subtype of gastric carcinoma. Recent development of therapeutic modalities for gastric carcinoma, such as endoscopic mucosal dissection and immune checkpoint inhibitor therapy, has made the presence of EBV infection a biomarker for the treatment of gastric carcinoma. This review presents a portrait of EBV-associated gastric carcinoma from initiation to maturity that we define as the 'gastritis-infection-cancer sequence', followed by its molecular abnormalities and interactions with immune checkpoint molecules and the microenvironment. EBV non-coding RNAs (microRNA and circular RNA) and exosomes derived from EBV-infected cells that were previously behind the scenes are now recognized for their roles in EBV-associated gastric carcinoma. The virus utilizes cellular machinery skilfully to control infected cells and their microenvironment. We should thus strive to understand virus-host interactions more fully in the following years to overcome this virus-driven subtype of gastric carcinoma.

Clinicopathological characteristics of Epstein-Barr virus-positive gastric cancer in Latvia

OBJECTIVE

Epstein-Barr virus (EBV)-associated gastric cancer has been proposed to be a distinct gastric cancer molecular subtype. The prognostic significance of EBV infection in gastric cancer remains unclear and needs further investigation. Our study aimed to analyze EBV-positive and EBV-negative gastric cancer patients regarding their personal and tumor-related characteristics, and compare their overall survival.

METHODS

Gastric cancer patients consecutively treated at the Riga East University Hospital during 2009-2016 were identified retrospectively. Tumor EBV status was determined by in-situ hybridization for EBV-encoded RNA (EBER). Information about clinicopathological characteristics was obtained from patient questionnaires, hospital records. Overall survival was ascertained through 30 July 2017. Cox proportional hazard regression models adjusted for personal and tumor-related covariates compared survival between EBV-positive and EBV-negative patients.

RESULTS

There were a total of 302 gastric cancer patients (61% males) with mean and SD age 63.6 ± 11.5 years. EBER positivity was present in 8.6% of tumors. EBV-positive gastric cancer patients had better survival at 80 months [adjusted hazard ratio = 0.37, 95% confidence interval (CI) = 0.19-0.72] compared to EBV-negative patients. Worse survival was observed for patients with stage III (hazard ratio = 2.76, 95% CI = 1.67-4.56) and stage IV (hazard ratio = 10.02, 95% CI = 5.72-17.57) compared to stage I gastric cancer, and overlapping and unspecified subsite (hazard ratio = 1.85; 95% CI = 1.14; 3.00) compared to distal tumors.

CONCLUSION

Tumor EBV positivity is a favorable prognostic factor in gastric cancer.

The Global Landscape of EBV-Associated Tumors

Epstein-Barr virus (EBV), a gamma-1 herpesvirus, is carried as a life-long asymptomatic infection by the great majority of individuals in all human populations. Yet this seemingly innocent virus is aetiologically linked to two pre-malignant lymphoproliferative diseases (LPDs) and up to nine distinct human tumors; collectively these have a huge global impact, being responsible for some 200,000 new cases of cancer arising worldwide each year. EBV replicates in oral epithelium but persists as a latent infection within the B cell system and several of its diseases are indeed of B cell origin; these include B-LPD of the immunocompromised, Hodgkin Lymphoma (HL), Burkitt Lymphoma (BL), Diffuse Large B cell Lymphoma (DLBCL) and two rarer tumors associated with profound immune impairment, plasmablastic lymphoma (PBL) and primary effusion lymphoma (PEL). Surprisingly, the virus is also linked to tumors arising in other cellular niches which, rather than being essential reservoirs of virus persistence in vivo, appear to represent rare cul-de-sacs of latent infection. These non-B cell tumors include LPDs and malignant lymphomas of T or NK cells, nasopharyngeal carcinoma (NPC) and gastric carcinoma of epithelial origin, and leiomyosarcoma, a rare smooth muscle cell tumor of the immunocompromised. Here we describe the main characteristics of these tumors, their distinct epidemiologies, histological features and degrees of EBV association, then consider how their different patterns of EBV latency may reflect the alternative latency programmes through which the virus first colonizes and then persists in immunocompetent host. For each tumor, we discuss current understanding of EBV's role in the oncogenic process, the identity (where known) of host genetic and environmental factors predisposing tumor development, and the recent evidence from cancer genomics identifying somatic changes that either complement or in some cases replace the contribution of the virus. Thereafter we look for possible connections between the pathogenesis of these apparently different malignancies and point to new research areas where insights may be gained.

Viral loads correlate with upregulation of PD-L1 and worse patient prognosis in Epstein-Barr Virus-associated gastric carcinoma

Epstein–Barr virus (EBV)-associated gastric carcinoma (EBVaGC), one of four major gastric cancer types, consists of clonal growth of EBV-infected epithelial cells. However, the significance of viral loads in each tumor cell has not been evaluated. EBV-DNA is stably maintained in episomal form in the nucleus of each cancer cell. To estimate EBV copy number per genome (EBV-CN), qPCR of viral EBNA1 and host GAPDH, standardized by Namalwa DNA (one copy/genome), was applied to the formalin-fixed paraffin embedded (FFPE) surgically resected EBVaGC specimens (n = 43) and EBVaGC cell lines (SNU-719 and NCC-24). In surgical specimens, the cancer cell ratio (CCR) was determined with image analysis, and EBV-CN was obtained by adjusting qPCR value with CCR. Fluorescent in situ hybridization (FISH) was also applied to the FFPE sections using the whole EBV-genome as a probe. In surgical specimens, EBV-CN obtained by qPCR/CCR was between 1.2 and 185 copies with a median of 9.9. EBV-CN of SNU-719 and NCC-24 was 42.0 and 1.1, respectively. A linear correlation was observed with qPCR/CCR data up to 20 copies/genome (40 signals/nucleus), the limit of FISH analysis. In addition, substantial variation in the number of EBV foci was observed. Based on qPCR/CCR, high EBV-CN (>10 copies) correlated with PD-L1 expression in cancer cells (P = 0.015), but not with other pathological indicators. Furthermore, EBVaGC with high EBV-CN showed worse disease-specific survival (P = 0.041). Our findings suggest that cancer cell viral loads may contribute to expression of the immune checkpoint molecule and promotion of cancer progression in EBVaGC.

Expression and significance of EBV, ARID1A and PIK3CA in gastric carcinoma

AT-rich interaction domain 1A (ARID1A) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α (PIK3CA) serve important roles in the formation and development of numerous malignancies including gastric cancer. Accumulating evidence has demonstrated that Epstein-Barr virus (EBV) is a pathogenic virus associated with gastric cancer. The present study aimed to investigate the association between EBV infection, and the expression levels of ARID1A and PIK3CA in gastric cancer. EBER in situ hybridization was performed to detect EBV infection. Immunohistochemistry was used to assess the expression levels of ARID1A and PIK3CA in gastric cancer and adjacent normal tissues. A total of 58 gastric cancer and 10 adjacent normal tissues were tested for genetic mutations via single nucleotide polymorphism genotyping assays. Fluorescent polymerase chain reaction was used to detect EBV infection; 9.3% (28/300) of gastric cancer samples were positive for EBV, whereas, all adjacent normal tissues were negative. ARID1A and PIK3CA were negatively correlated in gastric cancer (r=−0.167). The expression levels of ARID1A and PIK3CA in gastric cancer were significantly associated with the depth of invasion of gastric cancer. A total of 62.1% (36/58) of tumor samples exhibited mutations in ARID1A, whereas, 13.8% (8/58) presented mutations in PIK3CA. Notably, EBV-associated gastric cancer (EBVaGC) samples with PIK3CA mutations additionally exhibited ARID1A mutations. Although in the present study it was identified that ARID1A and PIK3CA were negatively correlated in EBVaGC, further studies are required to investigate the association among ARID1A, PIK3CA and EBV in gastric cancer.

Gastritis-Infection-Cancer Sequence of Epstein-Barr Virus-Associated Gastric Cancer

Epstein-Barr virus-associated gastric cancer (EBVaGC) is a representative EBV-infected epithelial neoplasm, which is now included as one of the four subtypes of The Cancer Genome Atlas molecular classification of gastric cancer. In this review, we portray a gastritis-infection-cancer sequence of EBVaGC. This virus-associated type of gastric cancer demonstrates clonal growth of EBV-infected epithelial cells within the mucosa of atrophic gastritis. Its core molecular abnormality is the EBV-specific hyper-epigenotype of CpG island promoter methylation, which induces silencing of tumor suppressor genes. This is due to the infection-induced disruption of the balance between DNA methylation and DNA demethylation activities. Abnormalities in the host cell genome, including phosphatidylinositol-4,5-biphosphate 3-kinase catalytic subunit α (PIK3CA), AT-rich interaction domain 1A (ARID1A), and programmed death-ligand 1 (PD-L1), are associated with the development and progression of EBVaGC. Furthermore, posttranscriptional modulation affects the transformation processes of EBV-infected cells, such as epithelial mesenchymal transition and anti-apoptosis, via cellular and viral microRNAs (miRNAs). Once established, cancer cells of EBVaGC remodel their microenvironment, at least partly, via the delivery of exosomes containing cellular and viral miRNAs. After exosomes are incorporated, these molecules change the functions of stromal cells, tuning the microenvironment for EBVaGC. During this series of events, EBV hijacks and uses cellular machineries, such as DNA methylation and the miRNA delivery system. This portrait of gastritis-infection-cancer sequences highlights the survival strategies of EBV in the stomach epithelial cells and may be useful for the integration of therapeutic modalities against EBV-driven gastric cancer.

Porphyromonas endodontalis reactivates latent Epstein-Barr virus

AIM

To determine whether Porphyromonas endodontalis can reactivate latent Epstein-Barr virus (EBV).

METHODOLOGY

The concentrations of short-chain fatty acids (SCFAs) in P. endodontalis culture supernatants were determined using high-performance liquid chromatography. A promoter region of BamHI fragment Z leftward open reading frame 1 (BZLF-1), which is a transcription factor that controls the EBV lytic cycle, was cloned into luciferase expression vectors. Then, the luciferase assay was performed using P. endodontalis culture supernatants. Histone acetylation using Daudi cells treated with P. endodontalis culture supernatants was examined using Western blotting. BZLF-1 mRNA and BamHI fragment Z EB replication activator (ZEBRA) protein were also detected quantitatively using real-time polymerase chain reaction (PCR) and Western blotting. Surgically removed periapical granulomas were examined to detect P. endodontalis, EBV DNA, and BZLF-1 mRNA expression using quantitative real-time PCR. Statistical analysis using Steel tests was performed.

RESULTS

The concentrations of n-butyric acid in P. endodontalis culture supernatants were significantly higher than those of other SCFAs (P = 0.0173). Using B-95-8-221 Luc cells treated with P. endodontalis culture supernatants, the luciferase assay demonstrated that P. endodontalis induced BZLF-1 expression. Hyperacetylation of histones was also observed with the culture supernatants. BZLF-1 mRNA and ZEBRA protein were expressed by Daudi cells in a dose-dependent manner after the treatment with P. endodontalis culture supernatants. P. endodontalis and BZLF-1 in periapical granulomas were also detected. The expression levels of BZLF-1 mRNA were similar to the numbers of P. endodontalis cells in each specimen.

CONCLUSIONS

n-butyric acid produced by P. endodontalis reactivated latent EBV.

Proposed Molecular and miRNA Classification of Gastric Cancer

Gastric cancer (GC) is a common malignant neoplasm worldwide and one of the main cause of cancer-related deaths. Despite some advances in therapies, long-term survival of patients with advanced disease remains poor. Different types of classification have been used to stratify patients with GC for shaping prognosis and treatment planning. Based on new knowledge of molecular pathways associated with different aspect of GC, new pathogenetic classifications for GC have been and continue to be proposed. These novel classifications create a new paradigm in the definition of cancer biology and allow the identification of relevant GC genomic subsets by using different techniques such as genomic screenings, functional studies and molecular or epigenetic characterization. An improved prognostic classification for GC is essential for the development of a proper therapy for a proper patient population. The aim of this review is to discuss the state-of-the-art on combining histological and molecular classifications of GC to give an overview of the emerging therapeutic possibilities connected to the latest discoveries regarding GC.

Curcuminoids as EBV Lytic Activators for Adjuvant Treatment in EBV-Positive Carcinomas

Epstein-Barr virus (EBV) persists in nasopharyngeal (NPC) and gastric carcinomas (EBVaGC) in a tightly latent form. Cytolytic virus activation (CLVA) therapy employs gemcitabine and valproic acid (GCb+VPA) to reactivate latent EBV into the lytic phase and antiviral valganciclovir to enhance cell death and prevent virus production. CLVA treatment has proven safe in phase-I/II trials with promising clinical responses in patients with recurrent NPC. However, a major challenge is to maximize EBV lytic reactivation by CLVA. Curcumin, a dietary spice used in Asian countries, is known for its antitumor property and therapeutic potential. Novel curcuminoids that were developed to increase efficacy and bioavailability may serve as oral CLVA adjuvants. We investigated the potential of curcumin and its analogs (curcuminoids) to trigger the EBV lytic cycle in EBVaGC and NPC cells. EBV-reactivating effects were measured by immunoblot and immunofluorescence using monoclonal antibodies specific for EBV lytic proteins. Two of the hit compounds (41, EF24) with high lytic inducing activity were further studied for their synergistic or antagonistic effects when combined with GCb+VPA and analyzed by cytotoxicity and mRNA profiling assays to measure the EBV reactivation. Curcuminoid as a single agent significantly induced EBV reactivation in recombinant GC and NPC lines. The drug effects were dose- and time-dependent. Micromolar concentration of curcuminoid EF24 enhanced the CLVA effect in all cell systems except SNU719, a naturally infected EBVaGC cell that carries a more tightly latent viral genome. These findings indicated that EF24 has potential as EBV lytic activator and may serve as an adjuvant in CLVA treatment.

Clinical utility of circulating cell-free Epstein-Barr virus DNA in patients with gastric cancer

Recent comprehensive molecular subtyping of gastric cancer (GC) identified Epstein-Barr virus (EBV)-positive tumors as a subtype with distinct salient molecular and clinical features. In this study, we aimed to determine the potential utility of circulating cell-free EBV DNA as a biomarker for the detection and/or monitoring of therapeutic response in patients with EBV-associated gastric carcinoma (EBVaGC). The EBV genes-to-ribonuclease P RNA component H1 ratios (EBV ratios) in the GC tumors and plasma samples were determined by quantitative real-time polymerase chain reaction in 153 patients with GC, including 14 patients with EBVaGC diagnosed by the conventional method. Circulating cell-free EBV DNA was detected in 14 patients with GC: the sensitivity and specificity of detection were 71.4% (10/14) and 97.1% (135/139), respectively. Plasma EBV ratios were significantly correlated with the size of EBVaGC tumors, and the plasma EBV DNA detected before surgery in EBVaGC cases disappeared after surgery. Patients with EBVaGC may have a better prognosis, but circulating cell-free EBV DNA had no or little impact on prognosis. In addition, repeated assessment of the plasma EBV ratio in EBVaGC showed a decrease and increase in plasma EBV DNA after treatment and during tumor progression/recurrence, respectively. These results suggest the potential utility of circulating cell-free DNA to reveal EBV DNA for the identification of the EBVaGC subtype and/or for real-time monitoring of tumor progression as well as treatment response in patients with EBVaGC.

CD47 expression in Epstein-Barr virus-associated gastric carcinoma: coexistence with tumor immunity lowering the ratio of CD8+/Foxp3+ T cells

Epstein-Barr virus-associated gastric carcinoma (EBVaGC) frequently harbors dense lymphocytic infiltration, suggesting a specific microenvironment allowing coexistence with tumor immunity. CD47, which mediates the "do not eat me" signal in innate immunity, is also important in adaptive anti-tumor immunity. We investigated the significance of CD47 in EBVaGC compared with EBV-negative gastric cancer and the correlation with various immune cells. By immunohistochemistry of CD47, high, low, and negative expression was observed in 24, 63, and 12% of EBVaGC (n = 41), while 11, 49, and 39% of EBV-negative gastric cancer (n = 262), respectively, indicating that high expression of CD47 in cancer cells was significantly frequent and increased in EBVaGC (P = 0.043). In contrast to EBV-negative gastric carcinoma in which no significant correlation was observed between CD47 and survival, high expression of CD47 correlated significantly with worse disease-specific survival (P = 0.011) and overall survival (P = 0.013) in EBVaGC. To further clarify the role of CD47 expression in EBVaGC, digital image analysis of immune cell infiltration revealed that high CD47 expression was correlated with a lower ratio of CD8⁺/Foxp3⁺ T cells (P = 0.021), a sensitive indicator of tumor immunity. Thus, CD47 lowers anti-tumor immunity in EBVaGC by finely tuning profile of infiltrating T cells, suggesting that CD47 is an additional target for cancer immunotherapy against this virus-driven gastric cancer.

Coordinate Regulation of TET2 and EBNA2 Controls the DNA Methylation State of Latent Epstein-Barr Virus

Epstein-Barr virus (EBV) latency and its associated carcinogenesis are regulated by dynamic changes in DNA methylation of both virus and host genomes. We show here that the ten-eleven translocation 2 (TET2) gene, implicated in hydroxymethylation and active DNA demethylation, is a key regulator of EBV latency type DNA methylation patterning. EBV latency types are defined by DNA methylation patterns that restrict expression of viral latency genes. We show that TET2 mRNA and protein expression correlate with the highly demethylated EBV type III latency program permissive for expression of EBNA2, EBNA3s, and LMP transcripts. We show that short hairpin RNA (shRNA) depletion of TET2 results in a decrease in latency gene expression but can also trigger a switch to lytic gene expression. TET2 depletion results in the loss of hydroxymethylated cytosine and a corresponding increase in cytosine methylation at key regulatory regions on the viral and host genomes. This also corresponded to a loss of RBP-jκ binding and decreased histone H3K4 trimethylation at these sites. Furthermore, we show that the TET2 gene itself is regulated in a fashion similar to that of the EBV genome. Chromatin immunoprecipitation high-throughput sequencing (ChIP-seq) revealed that the TET2 gene contains EBNA2-dependent RBP-jκ and EBF1 binding sites and is subject to DNA methylation-associated transcriptional silencing similar to what is seen in EBV latency type III genomes. Finally, we provide evidence that TET2 colocalizes with EBNA2-EBF1-RBP-jκ binding sites and can interact with EBNA2 by coimmunoprecipitation. Taken together, these findings indicate that TET2 gene transcripts are regulated similarly to EBV type III latency genes and that TET2 protein is a cofactor of EBNA2 and coregulator of the EBV type III latency program and DNA methylation state.IMPORTANCE Epstein-Barr virus (EBV) latency and carcinogenesis involve the selective epigenetic modification of viral and cellular genes. Here, we show that TET2, a cellular tumor suppressor involved in active DNA demethylation, plays a central role in regulating the DNA methylation state during EBV latency. TET2 is coordinately regulated and functionally interacts with the viral oncogene EBNA2. TET2 and EBNA2 function cooperatively to demethylate genes important for EBV-driven B-cell growth transformation.

Exome sequencing identifies recurrent BCOR alterations and the absence of KLF2, TNFAIP3 and MYD88 mutations in splenic diffuse red pulp small B-cell lymphoma

Splenic diffuse red pulp lymphoma is an indolent small B-cell lymphoma recognized as a provisional entity in the World Health Organization 2008 classification. Its precise relationship to other related splenic B-cell lymphomas with frequent leukemic involvement or other lymphoproliferative disorders remains undetermined. We performed whole-exome sequencing to explore the genetic landscape of ten cases of splenic diffuse red pulp lymphoma using paired tumor and normal samples. A selection of 109 somatic mutations was then evaluated in a cohort including 42 samples of splenic diffuse red pulp lymphoma and compared to those identified in 46 samples of splenic marginal zone lymphoma and eight samples of hairy-cell leukemia. Recurrent mutations or losses in BCOR (the gene encoding the BCL6 corepressor) – frameshift (n=3), nonsense (n=2), splicing site (n=1), and copy number loss (n=4) – were identified in 10/42 samples of splenic diffuse red pulp lymphoma (24%), whereas only one frameshift mutation was identified in 46 cases of splenic marginal zone lymphoma (2%). Inversely, KLF2, TNFAIP3 and MYD88, common mutations in splenic marginal zone lymphoma, were rare (one KLF2 mutant in 42 samples; 2%) or absent (TNFAIP3 and MYD88) in splenic diffuse red pulp lymphoma. These findings define an original genetic profile of splenic diffuse red pulp lymphoma and suggest that the mechanisms of pathogenesis of this lymphoma are distinct from those of splenic marginal zone lymphoma and hairy-cell leukemia.

Cytokine expression associated with Helicobacter pylori and Epstein-Barr virus infection in gastric carcinogenesis

Helicobacter pylori and Epstein-Barr virus (EBV) infection, and associated cytokines are involved in gastric carcinogenesis. We investigated the expression of these cytokines and their relationship with clinicopathological characteristics. The study included specimens from 207 patients with gastric adenocarcinoma, 56 with chronic gastritis, 32 with metaplasia, and 30 with low-grade epithelial dysplasia. Tissue microarrays were constructed and immunohistochemical staining for IL-1β, IL-6, IL-10, IL-17, p16, p21, TNF-α, and TNFR1 was performed. EBV and H. pylori infection status was determined. IL-1β, IL-6, IL-17, p16, and p21 protein expression was significantly higher in adenocarcinoma cases than in the other cases (p < 0.05). EBV was only noted in adenocarcinoma (13 cases, 6.3%). The H. pylori infection rate in adenocarcinoma was significantly higher than that in the other cases (p < 0.005). IL-6 expression was associated with improved survival (p < 0.05), whereas IL-17 expression was associated with decreased survival (p < 0.05). IL-6 expression was inversely associated with angioinvasion, and disease stage (p < 0.05), whereas IL-17 expression was associated with disease stage (p < 0.05). IL-10 expression was correlated with IL-1β and TNF-α expression, and p16 expression was correlated with IL-17 and EBV status. Our results indicate that IL-6 and IL-17 are associated with gastric carcinogenesis and may be considered prognostic factors.

Aberrant expression of AID and AID activators of NF-κB and PAX5 is irrelevant to EBV-associated gastric cancers, but is associated with carcinogenesis in certain EBV-non-associated gastric cancers

Epstein-Barr virus-associated gastric carcinoma (EBVaGC) is a distinct subtype of gastric cancer characterized by clinicopathological features including lymphoepithelioma-like histology. Aberrant expression of activation-induced cytidine deaminase (AID) as a genomic modulator was demonstrated through pathogen-related nuclear factor κB (NF-κB) signaling in Helicobacter pylori-associated gastric cancer. To elucidate whether or not AID expression is relevant to carcinogenesis in EBVaGC, immunohistochemical expression of AID and AID-regulatory factors between EBVaGC and EBV-non-associated gastric carcinoma (GC) were evaluated, each using 15 cases of GC with lymphoid stroma (GCLS) and other types of GC. Aberrant expression of AID, NF-κB and paired box 5 (PAX5) were significantly decreased in EBVaGC (0/11, 1/11 and 1/11) compared with in EBV-non-associated GC (7/19, 12/19 and 11/19) (P=0.025, 0.005 and 0.01, respectively); however, no significant difference in c-Myb proto-oncogene expression was identified. AID expression was also decreased in EBV-associated GCLS (0/10) compared with in EBV-non-associated GCLS (3/5). Unexpectedly, decreased expression of NF-κB and PAX5 was observed in GCLS (1/15 and 2/15) compared with in GC without LS (12/15 and 10/15) (P<0.001 and P=0.003, respectively). Decreased AID expression observed in EBVaGC is consistent with the reported molecular characterization of hypermethylation and rare somatic gene mutation in EBVaGC. Only PAX5 was identified to be significantly associated with venous invasion (P=0.022). The results of the present study suggest that pathogen-induced AID expression may be irrelevant to carcinogenesis of EBVaGC, whereas it contributes to carcinogenesis in certain types of EBV-non-associated GC.

The Gastric Microbiome and Its Influence on Gastric Carcinogenesis: Current Knowledge and Ongoing Research

Gastric malignancies are a leading cause of cancer-related death worldwide. At least 2 microbial species are currently linked to carcinogenesis and the development of cancer within the human stomach. These include the bacterium Helicobacter pylori and the Epstein-Barr virus. In recent years, there has been increasing evidence that within the human gastrointestinal tract it is not only pathogenic microbes that impact human health but also the corresponding autochthonous microbial communities. This article reviews the gastrointestinal microbiome as it relates primarily to mechanisms of disease and carcinogenesis within the upper gastrointestinal tract.

Status of Epstein-Barr Virus Coinfection with Helicobacter pylori in Gastric Cancer

Epstein-Barr virus is a ubiquitous human herpesvirus whose primary infection causes mononucleosis, Burkett's lymphoma, nasopharyngeal carcinoma, autoimmune diseases, and gastric cancer (GC). The persistent infection causes malignancies in lymph and epithelial cells. Helicobacter pylori causes gastritis in human with chronic inflammation. This chronic inflammation is thought to be the cause of genomic instability. About 45%-word population have a probability of having both pathogens, namely, H. pylori and EBV. Approximately 180 per hundred thousand population is developing GC along with many gastric abnormalities. This makes GC the third leading cause of cancer-related death worldwide. Although lots of research are carried out individually for EBV and H. pylori, still there are very few reports available on coinfection of both pathogens. Recent studies suggested that EBV and H. pylori coinfection increases the occurrence of GC as well as the early age of GC detection comparing to individual infection. The aim of this review is to present status on coinfection of both pathogens and their association with GC.

Overexpression and gene amplification of PD-L1 in cancer cells and PD-L1+ immune cells in Epstein-Barr virus-associated gastric cancer: the prognostic implications

Cancer cells use PD-L1 to evade antitumor immunity through interaction with programmed cell death protein 1 (PD-1) on T cells. Recent whole-genome sequence studies revealed frequent gene amplification of PD-L1 in Epstein-Barr virus-associated gastric cancer (EBVaGC). To investigate the significance of PD-L1 in cancer cells and their microenvironment in EBVaGC, we studied PD-L1 expression by analysis of the public database and immunohistochemistry with fluorescent in situ hybridization (FISH) of the PD-L1 gene. Analysis of the database from The Cancer Genome Atlas also disclosed high expression of PD-L1 in EBVaGC compared with other molecular subtypes of GC. Expression of PD-L1 was frequently detected in cancer cells of EBVaGC (33/96; 34%), with infiltration of PD-L1⁺ immune cells in its stroma (43/96; 45%). Both expression of PD-L1 in cancer cells and PD-L1⁺ immune cell infiltration in EBVaGC were significantly correlated with diffuse histology according to Lauren's classification and tumor invasion (pT1b or more). As a prognostic indicator, PD-L1 expression in cancer cells correlated with poor outcomes in both overall survival and disease-specific survival (P=0.0498, 0.007). PD-L1-positive cancers had dense infiltration of PD-L1⁺ immune cells as well as CD8⁺ and PD-1⁺ cells in EBVaGC. FISH analysis of representative samples of the tumor demonstrated gene amplification of PD-L1 in 11% of cases. PD-L1-amplified cells corresponded to PD-L1-positive cells showing high-intensity immunohistochemical staining among cancer cells showing weak or moderate intensities. Taken together, PD-L1 expression in cancer cells and their microenvironment may contribute to the progression of EBVaGC, and gene amplification occurs as clonal evolution during progression. This specific subtype of GC infected with EBV is potentially a good candidate for immunotherapy targeting of the PD-L1/PD-1 axis.

Loss of ARID1A expression predicts poor survival prognosis in gastric cancer: a systematic meta-analysis from 14 studies

The chromatin remodeling gene, AT-rich interactive domain 1A gene (ARID1A), frequently mutates inactively in gastric cancer (GC). However, its prognostic value remains controversial. To address this issue, a comprehensive meta-analysis was performed. Studies published until March 2016 were systematically searched. A total of 15 cohorts from 14 literatures involving 3183 patients were subjected to this meta-analysis. The pooled data showed that ARID1A expression loss predicted poor overall survival (OS) in GC (Hazard Ratio (HR) = 1.60; 95% Confidence Interval (CI) = 1.40-1.81; P < 0.001), with low heterogeneity among these studies (I(2) = 21.5%; P = 0.214). Stratification analyses revealed that ARID1A expression loss was associated with poor OS in Asians (HR = 1.65, 95% CI = 1.44-1.89), proportion of proximal disease ≤30% subgroup (HR = 1.80, 95% CI = 1.36-2.38) and Epstein-Barr virus (EBV) (+) > 5% subgroup (HR = 1.59, 95% CI = 1.18-2.15). The robust results were suggested by sensitivity analyses and no evidence of significant publication bias was detected. This study demonstrated a significant relationship between deletion of ARID1A expression and poor OS in GC. Moreover, ethnicity, tumor location and EBV infection status might be potential key factors influencing this correlation.

Low density of CD204-positive M2-type tumor-associated macrophages in Epstein-Barr virus-associated gastric cancer: a clinicopathologic study with digital image analysis

Recent studies suggest that CD204-positive (CD204(+)) M2-type tumor-associated macrophages (TAMs) are associated with the aggressive behavior of various cancers. However, the clinicopathologic significance of tumor-infiltrating CD204(+) macrophages and their correlation with Epstein-Barr virus (EBV) in gastric cancer is unclear. Tissue microarrays were constructed from 119 surgically resected gastric cancer specimens (86 EBV-negative and 28 EBV-positive cases). After immunohistochemistry of CD204, the density of CD204(+) cells was calculated using image analysis software, and associations between CD204 and clinicopathologic factors including patient survival were examined. High CD204(+) cell density was significantly associated with several adverse prognostic factors, including older age (P = .008), advanced tumor depth (P < .001), lymph node metastasis (P < .001), presence of venous invasion (P < .001), and lymphatic invasion (P = .03). Low CD204(+) cell density was significantly associated with EBV infection. Advanced tumor depth and presence of lymph node metastasis were significantly associated with high CD204(+) cell density in both EBV-positive and EBV-negative subgroups. High CD204(+) cell density was significantly associated with shorter cancer-specific survival (P = .0015). In conclusion, a high density of CD204(+) TAMs was associated with the aggressive behavior and worse survival of gastric cancer. Low density of CD204(+) TAMs was associated with infection of EBV, which may explain the favorable outcome of EBV-associated gastric carcinoma. Our results suggest that a specific immune microenvironment may be associated with the biological behavior of gastric cancer and that EBV-associated gastric carcinoma is distinctive from other gastric carcinomas in tumor immunity.