A study of Epstein-Barr virus infection in the Chinese tree shrew(Tupaia belangeri chinensis)

RNA-Seq and miRNA-Seq data from Epstein-Barr virus-infected tree shrews reveal a ceRNA network contributing to immune microenvironment regulation

Epstein-Barr virus (EBV) infection in humans is ubiquitous and associated with various diseases. Remodeling of the immune microenvironment is the primary cause of EBV infection and pathogenesis; however, the underlying mechanism has not been fully elucidated. In this study, we used whole-transcriptome RNA-Seq to detect mRNAs, long non-coding RNAs (lncRNA), and microRNA (miRNA) profiles in the control group, 3 days, and 28 days after EBV infection, based on the tree shrew model that we reported previously. First, we estimated the proportion of 22 cell types in each sample using CIBERSORT software and identified 18 high-confidence DElncRNAs related to immune microenvironment regulation after EBV infection. Functional enrichment analysis of these differentially expressed lncRNAs primarily focused on the autophagy, endocytosis, and ferroptosis signalling pathways. Moreover, EBV infection affects miRNA expression patterns, and many miRNAs are silenced. Finally, three competing endogenous RNA regulatory networks were built using lncRNAs that significantly correlated with immune cell types, miRNAs that responded to EBV infection, and potentially targeted the mRNA of the miRNAs. Among them, MRPL42-AS-5 might act as an hsa-miR-296-5p "sponge" and compete with target mRNAs, thus increasing mRNA expression level, which could induce immune cell infiltration through the cellular senescence signalling pathway against EBV infection. Overall, we conducted a complete transcriptomic analysis of EBV infection in vivo for the first time and provided a novel perspective for further investigation of EBV-host interactions.

Study of tree shrew biology and models: A booming and prosperous field for biomedical research

The tree shrew ( Tupaia belangeri) has long been proposed as a suitable alternative to non-human primates (NHPs) in biomedical and laboratory research due to its close evolutionary relationship with primates. In recent years, significant advances have facilitated tree shrew studies, including the determination of the tree shrew genome, genetic manipulation using spermatogonial stem cells, viral vector-mediated gene delivery, and mapping of the tree shrew brain atlas. However, the limited availability of tree shrews globally remains a substantial challenge in the field. Additionally, determining the key questions best answered using tree shrews constitutes another difficulty. Tree shrew models have historically been used to study hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, myopia, and psychosocial stress-induced depression, with more recent studies focusing on developing animal models for infectious and neurodegenerative diseases. Despite these efforts, the impact of tree shrew models has not yet matched that of rodent or NHP models in biomedical research. This review summarizes the prominent advancements in tree shrew research and reflects on the key biological questions addressed using this model. We emphasize that intensive dedication and robust international collaboration are essential for achieving breakthroughs in tree shrew studies. The use of tree shrews as a unique resource is expected to gain considerable attention with the application of advanced techniques and the development of viable animal models, meeting the increasing demands of life science and biomedical research.

Cyclosporine A induces Epstein-Barr virus reactivation in tree shrew (Tupaia belangeri chinensis) model

Epstein-Barr virus (EBV) usually exists as a latent infection in immunocompetent hosts but immunosuppressed individuals are at risk for developing EBV reactivation that leads to the uncontrolled proliferation of B lymphocytes. In this study, we have mimicked the immunosuppressed microenvironment in the tree shrew model of EBV infection by using cyclosporine A (CsA). The results showed that EBV-cocultured peripheral blood mononuclear cells (PBMCs) proliferated vigorously in response to CsA treatment in vitro. However, EBV susceptibility in vivo depended on the timing of CsA administration. Reactivation of EBV occurred in the latently EBV-infected tree shrews after treatment with 25 mg/kg/day CsA (EBV > CsA group), whereas tree shrews were no longer susceptible to infection if CsA was administered for five weeks before EBV injection (CsA > EBV group). RNA-seq analysis of both groups identified a further link between immunosuppression and EBV infection. KEGG pathway enrichment analysis revealed a significant enrichment of viral infection-related pathways in the EBV > CsA group, whereas tumor-related pathways were significantly enriched in the CsA > EBV group. A protein-protein interaction network was constructed using Cytoscape for the purpose of identifying hub genes that were then verified using qRT-PCR. In conclusion, the tree shrew model of EBV infection exhibits certain features of EBV infection in humans and serves as a valuable platform for exploring the underlying mechanisms of EBV infection.

Progress in Prophylactic and Therapeutic EBV Vaccine Development Based on Molecular Characteristics of EBV Target Antigens

Epstein–Barr virus (EBV) was discovered in 1964 in the cell line of Burkitt lymphoma and became first known human oncogenic virus. EBV belongs to the Herpesviridae family, and is present worldwide as it infects 95% of people. Infection with EBV usually happens during childhood when it remains asymptomatic; however, in adults, it can cause an acute infection known as infectious mononucleosis. In addition, EBV can cause wide range of tumors with origins in B lymphocytes, T lymphocytes, and NK cells. Its oncogenicity and wide distribution indicated the need for vaccine development. Research on mice and cultured cells as well as human clinical trials have been in progress for a few decades for both prophylactic and therapeutic EBV vaccines. The main targets of the vaccines are EBV envelope glycoproteins such as gp350 and EBV latent genes. The long wait for the EBV vaccine is due to the complexity of the EBV replication cycle and the wide range of its host cells. Although some strategies such as the use of dendritic cells and recombinant Vaccinia viral vectors have shown success, ongoing clinical trials using mRNA-based vaccines as well as new delivery systems as nanoparticles are yet to show the best choice of vaccine target and its production strategy.

Four Decades of Prophylactic EBV Vaccine Research: A Systematic Review and Historical Perspective

Background

Epstein-Barr virus (EBV) is the causal agent of infectious mononucleosis and has been associated with various cancers and autoimmune diseases. Despite decades of research efforts to combat this major global health burden, there is no approved prophylactic vaccine against EBV. To facilitate the rational design and assessment of an effective vaccine, we systematically reviewed pre-clinical and clinical prophylactic EBV vaccine studies to determine the antigens, delivery platforms, and animal models used in these studies.

Methods

We searched Cochrane Library, ClinicalTrials.gov, Embase, PubMed, Scopus, Web of Science, WHO’s Global Index Medicus, and Google Scholar from inception to June 20, 2020, for EBV prophylactic vaccine studies focused on humoral immunity.

Results

The search yielded 5,614 unique studies. 36 pre-clinical and 4 clinical studies were included in the analysis after screening against the exclusion criteria. In pre-clinical studies, gp350 was the most commonly used immunogen (33 studies), vaccines were most commonly delivered as monomeric proteins (12 studies), and mice were the most used animal model to test immunogenicity (15 studies). According to an adaptation of the CAMARADES checklist, 4 pre-clinical studies were rated as very high, 5 as high, 13 as moderate quality, 11 as poor, and 3 as very poor. In clinical studies, gp350 was the sole vaccine antigen, delivered in a vaccinia platform (1 study) or as a monomeric protein (3 studies). The present study was registered in PROSPERO (CRD42020198440).

Conclusions

Four major obstacles have prevented the development of an effective prophylactic EBV vaccine: undefined correlates of immune protection, lack of knowledge regarding the ideal EBV antigen(s) for vaccination, lack of an appropriate animal model to test vaccine efficacy, and lack of knowledge regarding the ideal vaccine delivery platform. Our analysis supports a multivalent antigenic approach including two or more of the five main glycoproteins involved in viral entry (gp350, gB, gH/gL, gp42) and a multimeric approach to present these antigens. We anticipate that the application of two underused challenge models, rhesus macaques susceptible to rhesus lymphocryptovirus (an EBV homolog) and common marmosets, will permit the establishment of in vivo correlates of immune protection and attainment of more generalizable data.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=198440, identifier PROSPERO I.D. CRD4202019844.

Tree Shrew Is a Suitable Animal Model for the Study of Epstein Barr Virus

Epstein-Barr virus (EBV) is a human herpesvirus that latently infects approximately 95% of adults and is associated with a spectrum of human diseases including Infectious Mononucleosis and a variety of malignancies. However, understanding the pathogenesis, vaccines and antiviral drugs for EBV-associated disease has been hampered by the lack of suitable animal models. Tree shrew is a novel laboratory animal with a close phylogenetic relationship to primates, which is a critical advantage for many animal models for human disease, especially viral infections. Herein, we first identified the key residues in the CR2 receptor that bind the gp350 protein and facilitate viral entry. We found that tree shrew shares 100% sequence identity with humans in these residues, which is much higher than rabbits (50%) and rats (25%). In vitro analysis showed that B lymphocytes of tree shrews are susceptible to EBV infection and replication, as well as EBV-enhanced cell proliferation. Moreover, results of in vivo experiments show that EBV infection in tree shrews resembles EBV infection in humans. The infected animals exhibited transient fever and loss of weight accompanied by neutropenia and high viremia levels during the acute phase of the viral infection. Thereafter, tree shrews acted as asymptomatic carriers of the virus in most cases that EBV-related protein could be detected in blood and tissues. However, a resurgence of EBV infection occurred at 49 dpi. Nanopore transcriptomic sequencing of peripheral blood in EBV-infected animals revealed the dynamic changes in biological processes occurring during EBV primary infection. Importantly, we find that neutrophil function was impaired in tree shrew model as well as human Infectious Mononucleosis datasets (GSE85599 and GSE45918). In addition, retrospective case reviews suggested that neutropenia may play an important role in EBV escaping host innate immune response, leading to long-term latent infection. Our findings demonstrated that tree shrew is a suitable animal model to evaluate the mechanisms of EBV infection, and for developing vaccines and therapeutic drugs against EBV.

Anatomy and nomenclature of tree shrew lymphoid tissues

The immune response plays a key role in the disease development of the organism, while immune function serves as an important indicator for animal models evaluation. The tree shrew (Tupaia belangeri chinensis), as a new laboratory animal with a close genetic relationship with primates, has been used to construct various disease models. However, the immune system of tree shrews, especially anatomical descriptions of lymph nodes, is still relatively unknown. In this study, a total of 16 different lymph nodes were identified, including superficial lymph nodes and deep lymph nodes. Superficial lymph nodes were located in the head and neck region (submandibular lymph node, parotid lymph node, deep and superficial cervical lymph nodes) and at the forelimb (axillary and accessory axillary lymph nodes, subscapular lymph node) and hindlimb (popliteal, sciatic, and inguinal lymph nodes). Deep lymph nodes comprise mediastinal lymph nodes located in thoracic cavity and abdominal lymph nodes that are mainly located in each mesentery (mesenteric, gastric, pancreatic-duodenal, renal lymph nodes) or along the major vessels (iliac lymph nodes). In addition, we described the spleen and thymus of the tree shrew, as well as two lymphoid tissues in the top wall of the nasal cavity and the oropharynx. This study mainly describes the tree shrew immune system from an anatomical and histopathological perspective and provides fundamental research references for the establishment of various animal models of tree shrews.

Uncovering early events in primary Epstein-Barr virus infection using a rabbit model

Epstein-Barr virus (EBV) is an oncogenic herpesvirus implicated in the pathogenesis of several malignant and non-malignant conditions. However, a number of fundamental aspects about the biology of EBV and the mechanism(s) by which this virus induces pathology remain unknown. One major obstacle has been the lack of a suitable animal model for EBV infection. In this study, using our recently established rabbit model of EBV infection, we examined the early events following primary EBV infection. We show that, both immunocompetent and immunosuppressed animals were readily susceptible to EBV infection. However, immunosuppressed animals showed marked splenomegaly and widespread infection. Following EBV infection, the virus primarily targeted naïve IgM+, CD20+, CD21+ and CD79a+ B cells. Infected cells expressed varying sets of viral latent/lytic gene products. Notably, co-expression of latent and lytic proteins in the same cell was not observed. Infected cells in type 0/1 latency (EBERs+), were small and proliferating (Ki67+). By contrast, cells in type 2/3 latency (LMP1+), were large, non-proliferating (Ki-67-) and p53+. Although infected B-cells were widely present in splenic follicles, they did not express germinal center marker, BCL-6. Taken together, this study shows for the first time, some of the early events following primary EBV infection.

Establishment of Tree Shrew Animal Model for Kaposi's Sarcoma-Associated Herpesvirus (HHV-8) Infection

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the most common cause of Kaposi’s sarcoma (KS) and other malignant growths in humans. However, the lack of a KSHV-infected small animal model has hampered understanding of the mechanisms of KSHV infection, virus replication, pathogenesis, and persistence. This study was designed to explore the susceptibility of tree shrews as a possible KSHV-infected small animal model. A recombinant GFP (latent)/RFP (lytic)-positive rKSHV.219 strain was used to infect primary cells cultured from different tissues of tree shrews as an in vitro model and adult tree shrews as an in vivo model. KSHV latent nuclear antigen (LANA) and DNA were successfully detected in primary cells of tree shrews. Among them, tree shrew kidney epithelial cells (TSKEC) were the most susceptible cells to KSHV infection compared to other cells. KSHV genomic DNA, mRNA, and KSHV-specific proteins were readily detected in the TSKEC cultured up to 32 dpi. Moreover, KSHV DNA and mRNA transcription were also readily detected in the peripheral blood mononuclear cells (PBMCs) and various tissues of tree shrews infected with KSHV. Haematoxylin and eosin (HE) staining showed lymphocyte infiltration, lymphoid tissue focal aggregation, alveolar wall thickening, hepatocyte edema, hepatic necrosis in the spleen, lung, and liver of KSHV-infected animals. Additionally, immune-histochemical (IHC) staining showed that LANA or ORF62-positive cells were present in the spleen, lung, liver, and kidney of KSHV-infected tree shrews. Here, we have successfully established in vitro and in vivo KSHV latent infection in tree shrews. This small animal model is not only useful for studying the pathogenesis of KSHV in vivo but can also be a useful model to study transmission routes of viral infection and a useful platform to characterize the novel therapeutics against KSHV.

The Status and Prospects of Epstein-Barr Virus Prophylactic Vaccine Development

Epstein–Barr virus (EBV) is a human herpesvirus that is common among the global population, causing an enormous disease burden. EBV can directly cause infectious mononucleosis and is also associated with various malignancies and autoimmune diseases. In order to prevent primary infection and subsequent chronic disease, efforts have been made to develop a prophylactic vaccine against EBV in recent years, but there is still no vaccine in clinical use. The outbreak of the COVID-19 pandemic and the global cooperation in vaccine development against SARS-CoV-2 provide insights for next-generation antiviral vaccine design and opportunities for developing an effective prophylactic EBV vaccine. With improvements in antigen selection, vaccine platforms, formulation and evaluation systems, novel vaccines against EBV are expected to elicit dual protection against infection of both B lymphocytes and epithelial cells. This would provide sustainable immunity against EBV-associated malignancies, finally enabling the control of worldwide EBV infection and management of EBV-associated diseases.

Antibody-Mediated Immune Subset Depletion Modulates the Immune Response in a Rabbit (Oryctolagus cuniculus) Model of Epstein-Barr Virus Infection

Epstein-Barr Virus (EBV) is a γ-herpesvirus which infects over 90% of the adult human population. Most notably, this virus causes infectious mononucleosis but it is also associated with cancers such as Hodgkin and Burkitt lymphoma. EBV is a species-specific virus and has been studied in many animal models, including nonhuman primates, guinea pigs, humanized mice, and tree shrews. However, none of these animal models are considered the "gold standard" for EBV research. Recently, rabbits have emerged as a viable alternative model, as they are susceptible to EBV infection. In addition, the EBV infection progresses after immune suppression with cyclosporine A (CsA), modeling the reactivation of EBV after latency. We sought to refine this model for acute or active EBV infections by performing antibody-mediated depletion of certain immune subsets in rabbits. Fourteen 16 to 20-wk old, NZW rabbits were intravenously inoculated with EBV and concurrently treated with either anti-CD4 T-cell antibody, anti-pan-T-cell antibody (anti CD45), CSA, or, as a control, anti-HPV antibody. Rabbits that received the depleting antibodies were treated with CsA 3 times at a dose of 15 mg/kg SC once per day for 4 d starting at the time of EBV inoculation then the dose was increased to 20 mg/kg SC twice weekly for 2 wk. Weights, temperatures, and clinical signs were monitored, and rabbits were anesthetized once weekly for blood collection. When compared with the control group, anti-CD4-treated rabbits had fewer clinical signs and displayed higher levels of viral DNA via qPCR in splenocytes; however, flow cytometry results showed only a partial depletion of CD4 T-cells. Treatment with anti-pan-T-cell antibody did not result in noticeable T-cell depletion. These data suggest the EBV-infected rabbit is a promising model for testing antiviral medications and prophylactic vaccines for EBV.

Isolation and identification of two new strains of mammalian orthoreovirus from Chinese tree shrews

Chinese tree shrews have been used extensively in studies of different types of cancer and for the modeling of viral infections. In the present study, we report the isolation and characterization of two strains of mammalian orthoreovirus (MRV), MRV1/TS/2011 and MRV3/TS/2012, which were isolated from the feces of tree shrews in Yunnan, China. These two strains of MRV were isolated and cultured in both primary tree shrew intestinal epithelial cells (pTIECs) and primary tree shrew alveolar epithelial cells (pTAECs). A neutralization test using immunofluorescence was employed to determine the subtype of each isolate. Viral RNA was extracted and analyzed by polyacrylamide gel electrophoresis (PAGE), and the sequence was determined by next-generation sequencing for construction of a phylogenetic tree and analysis of gene polymorphism. Electron microscopy examination revealed the presence of virus particles with the typical morphological characteristics of MRV. Serotype analysis showed that strain MRV1/TS/2011 was of type I and strain MRV3/TS/2012 was of type III. A sequence comparison showed that the isolates were 25.4% identical in the S1 gene.

Pathogenesis and Immune Response Caused by Vector-Borne and Other Viral Infections in a Tupaia Model

The Tupaia or tree shrew (Tupaia belangeri), a small mammal of the Tupaiidae family, is an increasingly used and promising infection model for virological and immunological research. Recently, sequencing of the Tupaia whole genome revealed that it is more homologous to the genome of humans than of rodents. Viral infections are a global threat to human health, and a complex series of events are involved in the interactions between a virus and the host immune system, which play important roles in the activation of an immune response and the outcome of an infection. Majority of immune response data in viral infections are obtained from studies using animal models that enhance the understanding of host-virus interactions; a proper understanding of these interactions is very important for the development of effective antivirals and prophylactics. Therefore, animal models that are permissive to infection and that recapitulate human disease pathogenesis and immune responses to viral infections are essential. Several studies have shown the permissiveness of Tupaia to a number of important human viral infections in vitro and in vivo without prior adaptation of the viruses; the immune responses and clinical manifestations were comparable to those observed in human infections. Thus, the Tupaia is being utilized and developed as a promising immunocompetent small animal model for viral infection studies. In this review, we focused on the immune responses, mostly innate, during viral infection and pathogenesis in the Tupaia model; we evaluated the interaction between the virus and the components of host resistance, the usefulness of this model for immunopathogenesis studies, and the vaccines and antivirals available.

The characteristics of gut microbiota and commensal Enterobacteriaceae isolates in tree shrew (Tupaia belangeri)

BACKGROUND

Tree shrew is a novel laboratory animal with specific characters for human disease researches in recent years. However, little is known about its characteristics of gut microbial community and intestinal commensal bacteria. In this study, 16S rRNA sequencing method was used to illustrate the gut microbiota structure and commensal Enterobacteriaceae bacteria were isolated to demonstrate their features.

RESULTS

The results showed Epsilonbacteraeota (30%), Proteobacteria (25%), Firmicutes (19%), Fusobacteria (13%), and Bacteroidetes (8%) were the most abundant phyla in the gut of tree shrew. Campylobacteria, Campylobacterales, Helicobacteraceae and Helicobacter were the predominant abundance for class, order, family and genus levels respectively. The alpha diversity analysis showed statistical significance (P < 0.05) for operational taxonomic units (OTUs), the richness estimates, and diversity indices for age groups of tree shrew. Beta diversity revealed the significant difference (P < 0.05) between age groups, which showed high abundance of Epsilonbacteraeota and Spirochaetes in infant group, Proteobacteria in young group, Fusobacteria in middle group, and Firmicutes in senile group. The diversity of microbial community was increased followed by the aging process of this animal. 16S rRNA gene functional prediction indicated that highly hot spots for infectious diseases, and neurodegenerative diseases in low age group of tree shrew (infant and young). The most isolated commensal Enterobacteriaceae bacteria from tree shrew were Proteus spp. (67%) and Escherichia coli (25%). Among these strains, the antibiotic resistant isolates were commonly found, and pulsed-field gel electrophoresis (PFGE) results of Proteus spp. indicated a high degree of similarity between isolates in the same age group, which was not observed for other bacteria.

CONCLUSIONS

In general, this study made understandings of the gut community structure and diversity of tree shrew.

Zika Virus Infection in Tupaia belangeri Causes Dermatological Manifestations and Confers Protection against Secondary Infection

Animal models of Zika virus (ZIKV) infection have recently been established in mice, guinea pigs, and nonhuman primates. Tree shrews (Tupaia belangeri) are an emerging experimental animal in biomedical applications, but their susceptibility to ZIKV infection has not been explored. In the present study, we show that subcutaneous inoculation of ZIKV led to rapid viremia and viral secretion in saliva, as well as to typical dermatological manifestations characterized by massive diffuse skin rash on the trunk. Global transcriptomic sequencing of peripheral blood mononuclear cells isolated from ZIKV-infected animals revealed systematic gene expression changes related to the inflammatory response and dermatological manifestations. Importantly, ZIKV infection readily triggered the production of high-titer neutralizing antibodies, thus preventing secondary homologous infection in tree shrews. However, neonatal tree shrews succumbed to ZIKV challenge upon intracerebral infection. The tree shrew model described here recapitulates the most common dermatological manifestations observed in ZIKV-infected patients and may greatly facilitate the elucidation of ZIKV pathogenesis and the development of novel vaccines and therapeutics.IMPORTANCE The reemergence of Zika virus (ZIKV) has caused a global public health crisis since 2016, and there are currently no vaccines or antiviral drugs to prevent or treat ZIKV infection. However, considerable advances have been made in understanding the biology and pathogenesis of ZIKV infection. In particular, various animal models have been successfully established to mimic ZIKV infection and its associated neurological diseases and to evaluate potential countermeasures. However, the clinical symptoms in these mouse and nonhuman primate models are different from the common clinical manifestations seen in human ZIKV patients; in particular, dermatological manifestations are rarely recapitulated in these animal models. Here, we developed a new animal model of ZIKV infection in tree shrews, a rat-sized, primate-related mammal. In vitro and in vivo characterization of ZIKV infection in tree shrews established a direct link between ZIKV infection and the immune responses and dermatological manifestations. The tree shrew model described here, as well as other available animal models, provides a valuable platform to study ZIKV pathogenesis and to evaluate vaccines and therapeutics.