The structure and function of the reovirus genome

Oncolytic Viruses and Immune Checkpoint Inhibition: The Best of Both Worlds

Cancer immunotherapy and the emergence of immune checkpoint inhibitors have markedly changed the treatment paradigm for many cancers. They function to disrupt cancer cell evasion of the immune response and activate sustained anti-tumor immunity. Oncolytic viruses have also emerged as an additional therapeutic agent for cancer treatment. These viruses are designed to target and kill tumor cells while leaving the normal cells unharmed. As part of this process, oncolytic virus infection stimulates anti-cancer immune responses that augment the efficacy of checkpoint inhibition. These viruses have the capability of transforming a “cold” tumor microenvironment with few immune effector cells into a “hot” environment with increased immune cell and cytokine infiltration. For this reason, there are multiple ongoing clinical trials that combine oncolytic virotherapy and immune checkpoint inhibitors. This review will detail the key oncolytic viruses in preclinical and clinical studies and highlight the results of their testing with checkpoint inhibitors.

Isolation and genomic characterization of a novel chicken-orign orthoreovirus causing goslings hepatitis

A severe infectious disease characterized by nephritis, hepatitis and splenitis has attacked goslings around Shandong province in China since 2016. A novel chicken-origin avian orthoreovirus (ARV) was isolated with LMH cells from affected goslings named Reo/Goose/SDPY/1116/17 (SDPY-ARV) strain, and the infection was successfully reproduced experimentally. The ARV-SDPY full genome sequencing was conducted using Next-Generation Sequencing (NGS) technique on Illumina HiSeq platform. The complete genome of SDPY-ARV was 23,427 bp in length and consist of 10 dsRNA segments ranged from 1192 bp (S4) to 3958 bp (L1) which encoding 12 viral proteins. Genomic sequence analysis showed that the SDPY-ARV strain is in the same branch with broiler, pheasant-origin ARV isolates, and shares 51.8-96.2% of nucleotide identity of σC gene with them; while only 49.3-50.3% with waterfowl isolates. In addition, the occurrence of 10 segments genetic reassortment of SDPY strain is confirmed among the PA15511, the 1733 and the PA13649 strains from America. In conclusion, the causative agent of gosling hemorrhagic necrotic hepatitis and nephritis occurring in China is a novel chicken-origin goose orthoreovirus.

Chapter 9 Infections caused by rubella, reoviridae, retro, Norwalk and ronaviruses

This chapter focuses on infections caused by rubella, reoviridae, retro, Norwalk and coronaviruses. High incidence of acute gastroenteritis caused by rotaviruses calls for prophylactic and therapeutic measures. Although no vaccine is presently available, it seems likely that vaccines will be developed in the next few years. There are also several rotavirus enzymes useful as targets for antiviral drugs. However, no antiviral drugs have shown therapeutic effects against rotavirus infections. The newly discovered human retrovirus (HTLV) has not yet been investigated in such detail as to predict the usefulness of vaccine or antiviral drugs. Several compounds are known to inhibit other retrovirus enzymes but the implication of this for chemotherapy of HTLV infection is unknown at present. The possibility and need for vaccination or chemotherapy against Norwalk virus and related agents is unclear. Very little work has been carried out to date with human coronaviruses, either from the point of view of vaccine development or specific antivirals. Both approaches may be usefully investigated in the future. Genetic cloning may be particularly useful for development of inactivated vaccines because the virus itself would be difficult to replicate and purify in large quantities for conventional vaccines.

Reovirus nonstructural protein mu NS recruits viral core surface proteins and entering core particles to factory-like inclusions

Mammalian reoviruses are thought to assemble and replicate within cytoplasmic, nonmembranous structures called viral factories. The viral nonstructural protein mu NS forms factory-like globular inclusions when expressed in the absence of other viral proteins and binds to the surfaces of the viral core particles in vitro. Given these previous observations, we hypothesized that one or more of the core surface proteins may be recruited to viral factories through specific associations with mu NS. We found that all three of these proteins--lambda 1, lambda 2, and sigma 2--localized to factories in infected cells but were diffusely distributed through the cytoplasm and nucleus when each was separately expressed in the absence of other viral proteins. When separately coexpressed with mu NS, on the other hand, each core surface protein colocalized with mu NS in globular inclusions, supporting the initial hypothesis. We also found that lambda 1, lambda 2, and sigma 2 each localized to filamentous inclusions formed upon the coexpression of mu NS and mu 2, a structurally minor core protein that associates with microtubules. The first 40 residues of mu NS, which are required for association with mu 2 and the RNA-binding nonstructural protein sigma NS, were not required for association with any of the three core surface proteins. When coexpressed with mu 2 in the absence of mu NS, each of the core surface proteins was diffusely distributed and displayed only sporadic, weak associations with mu 2 on filaments. Many of the core particles that entered the cytoplasm of cycloheximide-treated cells following entry and partial uncoating were recruited to inclusions of mu NS that had been preformed in those cells, providing evidence that mu NS can bind to the surfaces of cores in vivo. These findings expand a model for how viral and cellular components are recruited to the viral factories in infected cells and provide further evidence for the central but distinct roles of viral proteins mu NS and mu 2 in this process.

Reovirus nonstructural protein muNS binds to core particles but does not inhibit their transcription and capping activities

Previous studies provided evidence that nonstructural protein muNS of mammalian reoviruses is present in particle assembly intermediates isolated from infected cells. Morgan and Zweerink (Virology 68:455-466, 1975) showed that a subset of these intermediates, which can synthesize the viral plus strand RNA transcripts in vitro, comprise core-like particles plus large amounts of muNS. Given the possible role of muNS in particle assembly and/or transcription implied by those findings, we tested whether recombinant muNS can bind to cores in vitro. The muNS protein bound to cores, but not to two particle forms, virions and intermediate subvirion particles, that contain additional outer-capsid proteins. Incubating cores with increasing amounts of muNS resulted in particle complexes of progressively decreasing buoyant density, approaching the density of protein alone when very large amounts of muNS were bound. Thus, the muNS-core interaction did not exhibit saturation or a defined stoichiometry. Negative-stain electron microscopy of the muNS-bound cores revealed that the cores were intact and linked together in large complexes by an amorphous density, which we ascribe to muNS. The muNS-core complexes retained the capacity to synthesize the viral plus strand transcripts as well as the capacity to add methylated caps to the 5' ends of the transcripts. In vitro competition assays showed that mixing muNS with cores greatly reduced the formation of recoated cores by stoichiometric binding of outer-capsid proteins mu1 and sigma3. These findings are consistent with the presence of muNS in transcriptase particles as described previously and suggest that, by binding to cores in the infected cell, muNS may block or delay outer-capsid assembly and allow continued transcription by these particles.

Evidence for secondary structure within the virion RNA of echovirus 22

Phenol-extracted echovirus 22 virion RNA is infectious, but unlike poliovirus virion RNA, it resists digestion with pancreatic RNase and nuclease P-1, a 3' exonuclease selective for single-stranded RNA. These data indicate the presence of an enzyme-resistant portion somewhere in the RNA molecule and suggest that it is a double-stranded or base-paired region distant from the unblocked 3' terminus. Equilibrium density gradient centrifugation of native echovirus 22 virion RNA results in a single peak with a density of 1.63 g/cm3. When sheared before centrifugation, the molecule is resolved into two RNA species: one with an approximate density of 1.70 to 1.71 g/cm3, as is observed also for single-stranded poliovirus virion RNA, and the other with a density of 1.58 to 1.59 g/cm3. Data obtained from rate zonal centrifugation may be used to calculate an approximate sedimentation coefficient corrected to water at 20 degrees C of 34 and a molecular weight of 2.4 X 10(6) for the virion RNA. We propose a model for echovirus 22 RNA composed of a linear RNA molecule with a 5' hairpin.