Deletion of immune evasion genes provides an effective vaccine design for tumor-associated herpesviruses

Replication-dead gammaherpesvirus vaccine protects against acute replication, reactivation from latency, and lethal challenge in mice

Gammaherpesviruses (GHVs) are oncogenic viruses that establish lifelong infections and are significant causes of human morbidity and mortality. While several vaccine strategies to limit GHV infection and disease are in development, there are no FDA-approved vaccines for human GHVs. As a new approach to gammaherpesvirus vaccination, we developed and tested a replication-dead virus (RDV) platform, using murine gammaherpesvirus 68 (MHV68), a well-established mouse model for gammaherpesvirus pathogenesis studies and preclinical therapeutic evaluations. We employed codon-shuffling-based complementation to generate revertant-free RDV lacking expression of the essential replication and transactivator protein (RTA) encoded by ORF50 to arrest viral gene expression early after de novo infection. Inoculation with RDV-50.stop exposes the host to intact virion particles and leads to limited lytic gene expression in infected cells. Prime-boost vaccination of mice with RDV-50.stop elicited virus-specific neutralizing antibody and effector T cell responses in the lung and spleen. Vaccination with RDV-50.stop resulted in a near complete abolishment of virus replication in the lung 7 days post-challenge and virus reactivation from spleen 16 days post-challenge with WT MHV68. Ifnar1-/- mice, which lack the type I interferon receptor, exhibit severe disease upon infection with WT MHV68. RDV-50.stop vaccination of Ifnar1-/- mice prevented wasting and mortality upon challenge with WT MHV68. These results demonstrate that prime-boost vaccination with a GHV that is unable to undergo lytic replication offers protection against acute replication, reactivation, and severe disease upon WT virus challenge.

Microorganisms-derived antigens for preventive anti-cancer vaccines

Cancer prevention is one of the aim with the highest priority in order to reduce the burden of cancer diagnosis and treatment on individuals as well as on healthcare systems. To this aim, vaccines represent the most efficient primary cancer prevention strategy. Indeed, anti-cancer immunological memory elicited by preventive vaccines might promptly expand and prevent tumor from progressing. Antigens derived from microorganisms (MoAs), represent the obvious target for developing highly effective preventive vaccines for virus-induced cancers. In this respect, the drastic reduction in cancer incidence following HBV and HPV preventive vaccines are the paradigmatic example of such evidence. More recently, experimental evidences suggest that MoAs may represent a "natural" anti-cancer preventive vaccination or can be exploited for developing vaccines to prevent cancers presenting highly homologous tumor-associated antigens (TAAs) (e.g. molecular mimicry). The present review describes the different preventive anti-cancer vaccines based on antigens derived from pathogens at the different stages of development.

Singapore grouper iridovirus infection counteracts poly I:C induced antiviral immune response in vitro

Groupers are important mariculture fish in South China and Southeast Asian countries. However, the increasing frequency of infectious disease outbreaks has caused great economic losses in the grouper industry. Among these pathogens, Singapore grouper iridovirus (SGIV) infection causes high mortality in larval and juvenile stages of grouper. However, the mechanism underlying the action of viral manipulation on cellular immune response still remained largely uncertain. Here, using RNA-seq technology, we investigated the regulatory roles of SGIV infection on synthetic RNA duplex poly I:C induced immune response in vitro. Using reporter gene assays, we found that SGIV infection decreased poly I:C induced interferon promoter activation. Transcriptomic analysis showed that the mRNA expression levels of 2238 genes were up-regulated, while 1247 genes were down-regulated in poly I:C transfected grouper spleen (GS) cells. Interestingly, SGIV infection decreased the expression of 1479 up-regulated genes and increased the expression of 297 down-regulated genes in poly I:C transfected cells. The differentially expressed genes (DEGs) down-regulated by SGIV were directly related to immune, inflammation and viral infection, and JUN, STAT1, NFKB1, MAPK14A, TGFB1 and MX were the 6 top hub genes in the down-regulated DEGs' protein-protein interaction (PPI) network. Furthermore, quantitative real-time PCR (qPCR) analysis confirmed that the interferon signaling and inflammatory-related genes, including cGAS, STING, TBK1, MAVS, TNF, IRAK4 and NOD2 were up-regulated by poly I:C stimulation, but all significantly down-regulated after SGIV infection. Thus, we speculated that SGIV infection counteracted poly I:C induced antiviral immune response and this ability helped itself to escape host immune surveillance. Together, our data will contribute greatly to understanding the potential immune evasion mechanism of iridovirus infection in vitro.

Singapore Grouper Iridovirus VP131 Drives Degradation of STING-TBK1 Pathway Proteins and Negatively Regulates Antiviral Innate Immunity

Iridoviruses are large DNA viruses which cause great economic losses to the aquaculture industry and serious threats to ecological diversity worldwide. Singapore grouper iridovirus (SGIV), a novel member of the genus Ranavirus, causes high mortality in grouper aquaculture. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. Here, we reported that the protein encoded by SGIV ORF131R (VP131) was localized predominantly within the endoplasmic reticulum (ER). Ectopic expression of GFP-VP131 significantly enhanced SGIV replication, while VP131 knockdown decreased viral infection in vitro, suggesting that VP131 functioned as a proviral factor during SGIV infection. Overexpression of GFP-VP131 inhibited the interferon (IFN)-1 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), Epinephelus coioides cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), TANK-binding kinase 1 (EcTBK1), or melanoma differentiation-associated gene 5 (EcMDA5), whereas such activation induced by mitochondrial antiviral signaling protein (EcMAVS) was not affected. Moreover, VP131 interacted with EcSTING and degraded EcSTING through both the autophagy-lysosome pathway and ubiquitin-proteasome pathway, and targeted for the K63-linked ubiquitination. Of note, we also found that EcSTING significantly accelerated the formation of GFP-VP131 aggregates in co-transfected cells. Finally, GFP-VP131 inhibited EcSTING- or EcTBK1-induced antiviral activity upon red-spotted grouper nervous necrosis virus (RGNNV) infection. Together, our results demonstrated that the SGIV VP131 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion. IMPORTANCE STING has been identified as a critical factor participating in the innate immune response which recruits and phosphorylates TBK1 and IFN regulatory factor 3 (IRF3) to induce IFN production and defend against viral infection. However, viruses also distort the STING-TBK1 pathway to negatively regulate the IFN response and facilitate viral replication. Here, we reported that SGIV VP131 interacted with EcSTING within the ER and degraded EcSTING, leading to the suppression of IFN production and the promotion of SGIV infection. These results for the first time demonstrated that fish iridovirus evaded the host antiviral response via abrogating the STING-TBK1 signaling pathway.

KSHV (HHV8) vaccine: promises and potential pitfalls for a new anti-cancer vaccine

Seven viruses cause at least 15% of the total cancer burden. Viral cancers have been described as the "low-hanging fruit" that can be potentially prevented or treated by new vaccines that would alter the course of global human cancer. Kaposi sarcoma herpesvirus (KSHV or HHV8) is the sole cause of Kaposi sarcoma, which primarily afflicts resource-poor and socially marginalized populations. This review summarizes a recent NIH-sponsored workshop's findings on the epidemiology and biology of KSHV as an overlooked but potentially vaccine-preventable infection. The unique epidemiology of this virus provides opportunities to prevent its cancers if an effective, inexpensive, and well-tolerated vaccine can be developed and delivered.

Conquering the Host: Determinants of Pathogenesis Learned from Murine Gammaherpesvirus 68

Gammaherpesviruses are an important class of oncogenic pathogens that are exquisitely evolved to their respective hosts. As such, the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV) do not naturally infect nonhuman primates or rodents. There is a clear need to fully explore mechanisms of gammaherpesvirus pathogenesis, host control, and immune evasion in the host. A gammaherpesvirus pathogen isolated from murid rodents was first reported in 1980; 40 years later, murine gammaherpesvirus 68 (MHV68, MuHV-4, γHV68) infection of laboratory mice is a well-established pathogenesis system recognized for its utility in applying state-of-the-art approaches to investigate virus-host interactions ranging from the whole host to the individual cell. Here, we highlight recent advancements in our understanding of the processes by which MHV68 colonizes the host and drives disease. Lessons that inform KSHV and EBV pathogenesis and provide future avenues for novel interventions against infection and virus-associated cancers are emphasized.

Activation and Evasion of Innate Immunity by Gammaherpesviruses

Gammaherpesviruses are ubiquitous pathogens that establish lifelong infections in the vast majority of adults worldwide. Importantly, these viruses are associated with numerous malignancies and are responsible for significant human cancer burden. These virus-associated cancers are due, in part, to the ability of gammaherpesviruses to successfully evade the innate immune response throughout the course of infection. In this review, we will summarize the current understanding of how gammaherpesviruses are detected by innate immune sensors, how these viruses evade recognition by host cells, and how this knowledge can inform novel therapeutic approaches for these viruses and their associated diseases.