Epstein-Barr virus BNRF1 destabilizes SMC5/6 cohesin complexes to evade its restriction of replication compartments

Germinal center cytokine driven epigenetic control of Epstein-Barr virus latency gene expression

Epstein-Barr virus (EBV) persistently infects 95% of adults worldwide and is associated with multiple human lymphomas that express characteristic EBV latency programs used by the virus to navigate the B-cell compartment. Upon primary infection, the EBV latency III program, comprised of six Epstein-Barr Nuclear Antigens (EBNA) and two Latent Membrane Protein (LMP) antigens, drives infected B-cells into germinal center (GC). By incompletely understood mechanisms, GC microenvironmental cues trigger the EBV genome to switch to the latency II program, comprised of EBNA1, LMP1 and LMP2A and observed in GC-derived Hodgkin lymphoma. To gain insights into pathways and epigenetic mechanisms that control EBV latency reprogramming as EBV-infected B-cells encounter microenvironmental cues, we characterized GC cytokine effects on EBV latency protein expression and on the EBV epigenome. We confirmed and extended prior studies highlighting GC cytokine effects in support of the latency II transition. The T-follicular helper cytokine interleukin 21 (IL-21), which is a major regulator of GC responses, and to a lesser extent IL-4 and IL-10, hyper-induced LMP1 expression, while repressing EBNA expression. However, follicular dendritic cell cytokines including IL-15 and IL-27 downmodulate EBNA but not LMP1 expression. CRISPR editing highlighted that STAT3 and STAT5 were necessary for cytokine mediated EBNA silencing via epigenetic effects at the EBV genomic C promoter. By contrast, STAT3 was instead necessary for LMP1 promoter epigenetic remodeling, including gain of activating histone chromatin marks and loss of repressive polycomb repressive complex silencing marks. Thus, EBV has evolved to coopt STAT signaling to oppositely regulate the epigenetic status of key viral genomic promoters in response to GC cytokine cues.

The SMC5/6 complex: folding chromosomes back into shape when genomes take a break

High-level folding of chromatin is a key determinant of the shape and functional state of chromosomes. During cell division, structural maintenance of chromosome (SMC) complexes such as condensin and cohesin ensure large-scale folding of chromatin into visible chromosomes. In contrast, the SMC5/6 complex plays more local and context-specific roles in the structural organization of interphase chromosomes with important implications for health and disease. Recent advances in single-molecule biophysics and cryo-electron microscopy revealed key insights into the architecture of the SMC5/6 complex and how interactions connecting the complex to chromatin components give rise to its unique repertoire of interphase functions. In this review, we provide an integrative view of the features that differentiates the SMC5/6 complex from other SMC enzymes and how these enable dramatic reorganization of DNA folding in space during DNA repair reactions and other genome transactions. Finally, we explore the mechanistic basis for the dynamic targeting of the SMC5/6 complex to damaged chromatin and its crucial role in human health.

An alpha-herpesvirus employs host HEXIM1 to promote viral transcription

Although it is widely accepted that herpesviruses utilize host RNA polymerase II (RNAPII) to transcribe viral genes, the mechanism of utilization varies significantly among herpesviruses. With the exception of herpes simplex virus 1 (HSV-1) in alpha-herpesviruses, the mechanism by which RNAPII transcribes viral genes in the remaining alpha-herpesviruses has not been reported. In this study, we investigated the transcriptional mechanism of an avian alpha-herpesvirus, Anatid herpesvirus 1 (AnHV-1). We discovered for the first time that hexamethylene-bis-acetamide-inducing protein 1 (HEXIM1), a major inhibitor of positive elongation factor B (P-TEFb), was significantly upregulated during AnHV-1 infection, and its expression was dynamically regulated throughout the progression of the disease. However, the expression level of HEXIM1 remained stable before and after HSV-1 infection. Excessive HEXIM1 assists AnHV-1 in progeny virus production, gene expression, and RNA polymerase II recruitment by promoting the formation of more inactive P-TEFb and the loss of RNAPII S2 phosphorylation. Conversely, the expression of some host survival-related genes, such as SOX8, CDK1, MYC, and ID2, was suppressed by HEXIM1 overexpression. Further investigation revealed that the C-terminus of the AnHV-1 US1 gene is responsible for the upregulation of HEXIM1 by activating its promoter but not by interacting with P-TEFb, which is the mechanism adopted by its homologs, HSV-1 ICP22. Additionally, the virus proliferation deficiency caused by US1 deletion during the early infection stage could be partially rescued by HEXIM1 overexpression, suggesting that HEXIM1 is responsible for AnHV-1 gaining transcription advantages when competing with cells. Taken together, this study revealed a novel HEXIM1-dependent AnHV-1 transcription mechanism, which has not been previously reported in herpesvirus or even DNA virus studies.IMPORTANCEHexamethylene-bis-acetamide-inducing protein 1 (HEXIM1) has been identified as an inhibitor of positive transcriptional elongation factor b associated with cancer, AIDS, myocardial hypertrophy, and inflammation. Surprisingly, no previous reports have explored the role of HEXIM1 in herpesvirus transcription. This study reveals a mechanism distinct from the currently known herpesvirus utilization of RNA polymerase II, highlighting the dependence on high HEXIM1 expression, which may be a previously unrecognized facet of the host shutoff manifested by many DNA viruses. Moreover, this discovery expands the significance of HEXIM1 in pathogen infection. It raises intriguing questions about whether other herpesviruses employ similar mechanisms to manipulate HEXIM1 and if this molecular target can be exploited to limit productive replication. Thus, this discovery not only contributes to our understanding of herpesvirus infection regulation but also holds implications for broader research on other herpesviruses, even DNA viruses.

Loop extrusion-mediated plasmid DNA cleavage by the bacterial SMC Wadjet complex

Structural maintenance of chromosomes (SMC) protein complexes play pivotal roles in genome organization and maintenance across all domains of life. In prokaryotes, SMC family Wadjet complexes structurally resemble the widespread MukBEF genome-organizing complexes but serve a defensive role by inhibiting plasmid transformation. We previously showed that Wadjet specifically cleaves circular DNA; however, the molecular mechanism underlying DNA substrate recognition remains unclear. Here, we use in vitro single-molecule imaging to directly visualize DNA loop extrusion and plasmid cleavage by Wadjet. We find that Wadjet is a symmetric DNA loop extruder that simultaneously reels in DNA from both sides of a growing loop and that this activity requires a dimeric JetABC supercomplex containing two dimers of the JetC motor subunit. On surface-anchored plasmid DNAs, Wadjet extrudes the full length of a 44 kilobase pair plasmid, stalls, and then cleaves DNA. Our findings reveal the role of loop extrusion in the specific recognition and elimination of plasmids by Wadjet, and establish loop extrusion as an evolutionarily conserved mechanism among SMC complexes across kingdoms of life.

SMC5/6 Promotes Replication Fork Stability via Negative Regulation of the COP9 Signalosome

It is widely accepted that DNA replication fork stalling is a common occurrence during cell proliferation, but there are robust mechanisms to alleviate this and ensure DNA replication is completed prior to chromosome segregation. The SMC5/6 complex has consistently been implicated in the maintenance of replication fork integrity. However, the essential role of the SMC5/6 complex during DNA replication in mammalian cells has not been elucidated. In this study, we investigate the molecular consequences of SMC5/6 loss at the replication fork in mouse embryonic stem cells (mESCs), employing the auxin-inducible degron (AID) system to deplete SMC5 acutely and reversibly in the defined cellular contexts of replication fork stall and restart. In SMC5-depleted cells, we identify a defect in the restart of stalled replication forks, underpinned by excess MRE11-mediated fork resection and a perturbed localization of fork protection factors to the stalled fork. Previously, we demonstrated a physical and functional interaction of SMC5/6 with the COP9 signalosome (CSN), a cullin deneddylase that enzymatically regulates cullin ring ligase (CRL) activity. Employing a combination of DNA fiber techniques, the AID system, small-molecule inhibition assays, and immunofluorescence microscopy analyses, we show that SMC5/6 promotes the localization of fork protection factors to stalled replication forks by negatively modulating the COP9 signalosome (CSN). We propose that the SMC5/6-mediated modulation of the CSN ensures that CRL activity and their roles in DNA replication fork stabilization are maintained to allow for efficient replication fork restart when a replication fork stall is alleviated.

G. Germinal Center Cytokines Driven Epigenetic Control of Epstein-Barr Virus Latency Gene Expression

Epstein-Barr virus (EBV) persistently infects 95% of adults worldwide and is associated with multiple human lymphomas that express characteristic EBV latency programs used by the virus to navigate the B-cell compartment. Upon primary infection, the EBV latency III program, comprised of six Epstein-Barr Nuclear Antigens (EBNA) and two Latent Membrane Protein (LMP) antigens, drives infected B-cells into germinal center (GC). By incompletely understood mechanisms, GC microenvironmental cues trigger the EBV genome to switch to the latency II program, comprised of EBNA1, LMP1 and LMP2A and observed in GC-derived Hodgkin lymphoma. To gain insights into pathways and epigenetic mechanisms that control EBV latency reprogramming as EBV-infected B-cells encounter microenvironmental cues, we characterized GC cytokine effects on EBV latency protein expression and on the EBV epigenome. We confirmed and extended prior studies highlighting GC cytokine effects in support of the latency II transition. The T-follicular helper cytokine interleukin 21 (IL-21), which is a major regulator of GC responses, and to a lesser extent IL-4 and IL-10, hyper-induced LMP1 expression, while repressing EBNA expression. However, follicular dendritic cell cytokines including IL-15 and IL-27 downmodulate EBNA but not LMP1 expression. CRISPR editing highlighted that STAT3 and STAT5 were necessary for cytokine mediated EBNA silencing via epigenetic effects at the EBV genomic C promoter. By contrast, STAT3 was instead necessary for LMP1 promoter epigenetic remodeling, including gain of activating histone chromatin marks and loss of repressive polycomb repressive complex silencing marks. Thus, EBV has evolved to coopt STAT signaling to oppositely regulate the epigenetic status of key viral genomic promoters in response to GC cytokine cues.

ATM, KAP1 and the Epstein-Barr virus polymerase processivity factor direct traffic at the intersection of transcription and replication

The timing of transcription and replication must be carefully regulated for heavily-transcribed genomes of double-stranded DNA viruses: transcription of immediate early/early genes must decline as replication ramps up from the same genome-ensuring efficient and timely replication of viral genomes followed by their packaging by structural proteins. To understand how the prototypic DNA virus Epstein-Barr virus tackles the logistical challenge of switching from transcription to DNA replication, we examined the proteome at viral replication forks. Specifically, to transition from transcription, the viral DNA polymerase-processivity factor EA-D is SUMOylated by the epigenetic regulator and E3 SUMO-ligase KAP1/TRIM28. KAP1's SUMO2-ligase function is triggered by phosphorylation via the PI3K-related kinase ATM and the RNA polymerase II-associated helicase RECQ5 at the transcription machinery. SUMO2-EA-D then recruits the histone loader CAF1 and the methyltransferase SETDB1 to silence the parental genome via H3K9 methylation, prioritizing replication. Thus, a key viral protein and host DNA repair, epigenetic and transcription-replication interference pathways orchestrate the handover from transcription-to-replication, a fundamental feature of DNA viruses.

Epstein-Barr virus infectious particles initiate B cell transformation and modulate cytokine response

IMPORTANCE

The Epstein-Barr virus efficiently infects and transforms B lymphocytes. During this process, infectious viral particles transport the viral genome to the nucleus of target cells. We show here that these complex viral structures serve additional crucial roles by activating transcription of the transforming genes encoded by the virus. We show that components of the infectious particle sequentially activate proinflammatory B lymphocyte signaling pathways that, in turn, activate viral gene expression but also cause cytokine release. However, virus infection activates expression of ZFP36L1, an RNA-binding stress protein that limits the length and the intensity of the cytokine response. Thus, the infectious particles can activate viral gene expression and initiate cellular transformation at the price of a limited immune response.

A CRISPR-based system to investigate HBV cccDNA biology

IMPORTANCE

Hepatitis B virus cccDNA is the key target for the necessary development of antiviral therapies aimed at curing chronic hepatitis B. The CRISPR-based system to produce covalently closed circular (cccDNA)-like extrachromosomal DNAs described in this report enables large-scale screens of chemical libraries to identify drug candidates with the potential to permanently inactivate cccDNA. Moreover, this approach permits investigations on unresolved problems as described in this report concerning cccDNA biology including mechanisms of SMC5/6-dependent transcriptional silencing and the contributions of the SMC5/6 complex to cccDNA stability in resting and dividing hepatocytes.

A R-loop sensing pathway mediates the relocation of transcribed genes to nuclear pore complexes

Nuclear pore complexes (NPCs) have increasingly recognized interactions with the genome, as exemplified in yeast, where they bind transcribed or damaged chromatin. By combining genome-wide approaches with live imaging of model loci, we uncover a correlation between NPC association and the accumulation of R-loops, which are genotoxic structures formed through hybridization of nascent RNAs with their DNA templates. Manipulating hybrid formation demonstrates that R-loop accumulation per se, rather than transcription or R-loop-dependent damages, is the primary trigger for relocation to NPCs. Mechanistically, R-loop-dependent repositioning involves their recognition by the ssDNA-binding protein RPA, and SUMO-dependent interactions with NPC-associated factors. Preventing R-loop-dependent relocation leads to lethality in hybrid-accumulating conditions, while NPC tethering of a model hybrid-prone locus attenuates R-loop-dependent genetic instability. Remarkably, this relocation pathway involves molecular factors similar to those required for the association of stalled replication forks with NPCs, supporting the existence of convergent mechanisms for sensing transcriptional and genotoxic stresses.

Genome control by SMC complexes

Many cellular processes require large-scale rearrangements of chromatin structure. Structural maintenance of chromosomes (SMC) protein complexes are molecular machines that can provide structure to chromatin. These complexes can connect DNA elements in cis, walk along DNA, build and processively enlarge DNA loops and connect DNA molecules in trans to hold together the sister chromatids. These DNA-shaping abilities place SMC complexes at the heart of many DNA-based processes, including chromosome segregation in mitosis, transcription control and DNA replication, repair and recombination. In this Review, we discuss the latest insights into how SMC complexes such as cohesin, condensin and the SMC5-SMC6 complex shape DNA to direct these fundamental chromosomal processes. We also consider how SMC complexes, by building chromatin loops, can counteract the natural tendency of alike chromatin regions to cluster. SMC complexes thus control nuclear organization by participating in a molecular tug of war that determines the architecture of our genome.

SMC-based immunity against extrachromosomal DNA elements

SMC and SMC-like complexes promote chromosome folding and genome maintenance in all domains of life. Recently, they were also recognized as factors in cellular immunity against foreign DNA. In bacteria and archaea, Wadjet and Lamassu are anti-plasmid/phage defence systems, while Smc5/6 and Rad50 complexes play a role in anti-viral immunity in humans. This raises an intriguing paradox - how can the same, or closely related, complexes on one hand secure the integrity and maintenance of chromosomal DNA, while on the other recognize and restrict extrachromosomal DNA? In this minireview, we will briefly describe the latest understanding of each of these complexes in immunity including speculations on how principles of SMC(-like) function may explain how the systems recognize linear or circular forms of invading DNA.

An Epstein-Barr virus protein interaction map reveals NLRP3 inflammasome evasion via MAVS UFMylation

Epstein-Barr virus (EBV) causes infectious mononucleosis, triggers multiple sclerosis, and is associated with 200,000 cancers/year. EBV colonizes the human B cell compartment and periodically reactivates, inducing expression of 80 viral proteins. However, much remains unknown about how EBV remodels host cells and dismantles key antiviral responses. We therefore created a map of EBV-host and EBV-EBV interactions in B cells undergoing EBV replication, uncovering conserved herpesvirus versus EBV-specific host cell targets. The EBV-encoded G-protein-coupled receptor BILF1 associated with MAVS and the UFM1 E3 ligase UFL1. Although UFMylation of 14-3-3 proteins drives RIG-I/MAVS signaling, BILF1-directed MAVS UFMylation instead triggered MAVS packaging into mitochondrial-derived vesicles and lysosomal proteolysis. In the absence of BILF1, EBV replication activated the NLRP3 inflammasome, which impaired viral replication and triggered pyroptosis. Our results provide a viral protein interaction network resource, reveal a UFM1-dependent pathway for selective degradation of mitochondrial cargo, and highlight BILF1 as a novel therapeutic target.

The multi-functional Smc5/6 complex in genome protection and disease

Structural maintenance of chromosomes (SMC) complexes are ubiquitous genome regulators with a wide range of functions. Among the three types of SMC complexes in eukaryotes, cohesin and condensin fold the genome into different domains and structures, while Smc5/6 plays direct roles in promoting chromosomal replication and repair and in restraining pathogenic viral extra-chromosomal DNA. The importance of Smc5/6 for growth, genotoxin resistance and host defense across species is highlighted by its involvement in disease prevention in plants and animals. Accelerated progress in recent years, including structural and single-molecule studies, has begun to provide greater insights into the mechanisms underlying Smc5/6 functions. Here we integrate a broad range of recent studies on Smc5/6 to identify emerging features of this unique SMC complex and to explain its diverse cellular functions and roles in disease pathogenesis. We also highlight many key areas requiring further investigation for achieving coherent views of Smc5/6-driven mechanisms.

Advancing therapeutic strategies for Epstein-Barr virus-associated malignancies through lytic reactivation

Epstein-Barr virus (EBV) is a widespread human herpes virus associated with lymphomas and epithelial cell cancers. It establishes two separate infection phases, latent and lytic, in the host. Upon infection of a new host cell, the virus activates several pathways, to induce the expression of lytic EBV antigens and the production of infectious virus particles. Although the carcinogenic role of latent EBV infection has been established, recent research suggests that lytic reactivation also plays a significant role in carcinogenesis. In this review, we summarize the mechanism of EBV reactivation and recent findings about the role of viral lytic antigens in tumor formation. In addition, we discuss the treatment of EBV-associated tumors with lytic activators and the targets that may be therapeutically effective in the future.

Tegument proteins of Epstein-Barr virus: Diverse functions, complex networks, and oncogenesis

The tegument is the structure between the envelope and nucleocapsid of herpesvirus particles. Viral (and cellular) proteins accumulate to create the layers of the tegument. Some Epstein-Barr virus (EBV) tegument proteins are conserved widely in Herpesviridae, but others are shared only by members of the gamma-herpesvirus subfamily. As the interface to envelope and nucleocapsid, the tegument functions in virion morphogenesis and budding of the nucleocapsid during progeny production. When a virus particle enters a cell, enzymes such as kinase and deubiquitinase, and transcriptional activators are released from the virion to promote virus infection. Moreover, some EBV tegument proteins are involved in oncogenesis. Here, we summarize the roles of EBV tegument proteins, in comparison to those of other herpesviruses.

Genome-Scale Analysis of Cellular Restriction Factors That Inhibit Transgene Expression from Adeno-Associated Virus Vectors

Adeno-associated virus (AAV) vectors are one of the leading platforms for gene delivery for the treatment of human genetic diseases, but the antiviral cellular mechanisms that interfere with optimal transgene expression are incompletely understood. Here, we performed two genome-scale CRISPR screens to identify cellular factors that restrict transgene expression from recombinant AAV vectors. Our screens revealed several components linked to DNA damage response, chromatin remodeling, and transcriptional regulation. Inactivation of the Fanconi anemia gene FANCA; the human silencing hub (HUSH)-associated methyltransferase SETDB1; and the gyrase, Hsp90, histidine kinase, and MutL (GHKL)-type ATPase MORC3 led to increased transgene expression. Moreover, SETDB1 and MORC3 knockout improved transgene levels of several AAV serotypes as well as other viral vectors, such as lentivirus and adenovirus. Finally, we demonstrated that the inhibition of FANCA, SETDB1, or MORC3 also enhanced transgene expression in human primary cells, suggesting that they could be physiologically relevant pathways that restrict AAV transgene levels in therapeutic settings. IMPORTANCE Recombinant AAV (rAAV) vectors have been successfully developed for the treatment of genetic diseases. The therapeutic strategy often involves the replacement of a defective gene by the expression of a functional copy from the rAAV vector genome. However, cells possess antiviral mechanisms that recognize and silence foreign DNA elements thereby limiting transgene expression and its therapeutic effect. Here, we utilize a functional genomics approach to uncover a comprehensive set of cellular restriction factors that inhibit rAAV-based transgene expression. Genetic inactivation of selected restriction factors increased rAAV transgene expression. Hence, modulation of identified restriction factors has the potential to enhance AAV gene replacement therapies.

Contribution of Epstein–Barr Virus Lytic Proteins to Cancer Hallmarks and Implications from Other Oncoviruses

Epstein–Barr virus (EBV) is a prevalent human gamma-herpesvirus that infects the majority of the adult population worldwide and is associated with several lymphoid and epithelial malignancies. EBV displays a biphasic life cycle, namely, latent and lytic replication cycles, expressing a diversity of viral proteins. Among the EBV proteins being expressed during both latent and lytic cycles, the oncogenic roles of EBV lytic proteins are largely uncharacterized. In this review, the established contributions of EBV lytic proteins in tumorigenesis are summarized according to the cancer hallmarks displayed. We further postulate the oncogenic properties of several EBV lytic proteins by comparing the evolutionary conserved oncogenic mechanisms in other herpesviruses and oncoviruses.

Identification of dynamic gene expression profiles during sequential vaccination with ChAdOx1/BNT162b2 using machine learning methods

To date, COVID-19 remains a serious global public health problem. Vaccination against SARS-CoV-2 has been adopted by many countries as an effective coping strategy. The strength of the body’s immune response in the face of viral infection correlates with the number of vaccinations and the duration of vaccination. In this study, we aimed to identify specific genes that may trigger and control the immune response to COVID-19 under different vaccination scenarios. A machine learning-based approach was designed to analyze the blood transcriptomes of 161 individuals who were classified into six groups according to the dose and timing of inoculations, including I-D0, I-D2-4, I-D7 (day 0, days 2–4, and day 7 after the first dose of ChAdOx1, respectively) and II-D0, II-D1-4, II-D7-10 (day 0, days 1–4, and days 7–10 after the second dose of BNT162b2, respectively). Each sample was represented by the expression levels of 26,364 genes. The first dose was ChAdOx1, whereas the second dose was mainly BNT162b2 (Only four individuals received a second dose of ChAdOx1). The groups were deemed as labels and genes were considered as features. Several machine learning algorithms were employed to analyze such classification problem. In detail, five feature ranking algorithms (Lasso, LightGBM, MCFS, mRMR, and PFI) were first applied to evaluate the importance of each gene feature, resulting in five feature lists. Then, the lists were put into incremental feature selection method with four classification algorithms to extract essential genes, classification rules and build optimal classifiers. The essential genes, namely, NRF2, RPRD1B, NEU3, SMC5, and TPX2, have been previously associated with immune response. This study also summarized expression rules that describe different vaccination scenarios to help determine the molecular mechanism of vaccine-induced antiviral immunity.

Proteomic analysis of antiviral innate immunity

The capacity of host cells to detect and restrict an infecting virus rests on an array of cell-autonomous antiviral effectors and innate immune receptors that can trigger inflammatory processes at tissue and organismal levels. Dynamic changes in protein abundance, subcellular localisation, post-translational modifications and interactions with other biomolecules govern these processes. Proteomics is therefore an ideal experimental tool to discover novel mechanisms of host antiviral immunity. Additional information can be gleaned both about host and virus by systematic analysis of viral immune evasion strategies. In this review, we summarise recent advances in proteomic technologies and their application to antiviral innate immunity.

DNA-measuring Wadjet SMC ATPases restrict smaller circular plasmids by DNA cleavage

Structural maintenance of chromosome (SMC) complexes fold DNA by loop extrusion to support chromosome segregation and genome maintenance. Wadjet systems (JetABCD/MksBEFG/EptABCD) are derivative SMC complexes with roles in bacterial immunity against selfish DNA. Here, we show that JetABCD restricts circular plasmids with an upper size limit of about 100 kb, whereas a linear plasmid evades restriction. Purified JetABCD complexes cleave circular DNA molecules, regardless of the DNA helical topology; cleavage is DNA sequence nonspecific and depends on the SMC ATPase. A cryo-EM structure reveals a distinct JetABC dimer-of-dimers geometry, with the two SMC dimers facing in opposite direction-rather than the same as observed with MukBEF. We hypothesize that JetABCD is a DNA-shape-specific endonuclease and propose the "total extrusion model" for DNA cleavage exclusively when extrusion of an entire plasmid has been completed by a JetABCD complex. Total extrusion cannot be achieved on the larger chromosome, explaining how self-DNA may evade processing.

Urgency and necessity of Epstein-Barr virus prophylactic vaccines

Epstein-Barr virus (EBV), a γ-herpesvirus, is the first identified oncogenic virus, which establishes permanent infection in humans. EBV causes infectious mononucleosis and is also tightly linked to many malignant diseases. Various vaccine formulations underwent testing in different animals or in humans. However, none of them was able to prevent EBV infection and no vaccine has been approved to date. Current efforts focus on antigen selection, combination, and design to improve the efficacy of vaccines. EBV glycoproteins such as gH/gL, gp42, and gB show excellent immunogenicity in preclinical studies compared to the previously favored gp350 antigen. Combinations of multiple EBV proteins in various vaccine designs become more attractive approaches considering the complex life cycle and complicated infection mechanisms of EBV. Besides, rationally designed vaccines such as virus-like particles (VLPs) and protein scaffold-based vaccines elicited more potent immune responses than soluble antigens. In addition, humanized mice, rabbits, as well as nonhuman primates that can be infected by EBV significantly aid vaccine development. Innovative vaccine design approaches, including polymer-based nanoparticles, the development of effective adjuvants, and antibody-guided vaccine design, will further enhance the immunogenicity of vaccine candidates. In this review, we will summarize (i) the disease burden caused by EBV and the necessity of developing an EBV vaccine; (ii) previous EBV vaccine studies and available animal models; (iii) future trends of EBV vaccines, including activation of cellular immune responses, novel immunogen design, heterologous prime-boost approach, induction of mucosal immunity, application of nanoparticle delivery system, and modern adjuvant development.

Functional Implications of Epstein-Barr Virus Lytic Genes in Carcinogenesis

Epstein-Barr virus (EBV) is associated with a diverse range of tumors of both lymphoid and epithelial origin. Similar to other herpesviruses, EBV displays a bipartite life cycle consisting of latent and lytic phases. Current dogma indicates that the latent genes are key drivers in the pathogenesis of EBV-associated cancers, while the lytic genes are primarily responsible for viral transmission. In recent years, evidence has emerged to show that the EBV lytic phase also plays an important role in EBV tumorigenesis, and the expression of EBV lytic genes is frequently detected in tumor tissues and cell lines. The advent of next generation sequencing has allowed the comprehensive profiling of EBV gene expression, and this has revealed the consistent expression of several lytic genes across various types of EBV-associated cancers. In this review, we provide an overview of the functional implications of EBV lytic gene expression to the oncogenic process and discuss possible avenues for future investigations.