The Reoviridae family

Oncolytic virotherapies for pediatric tumors

INTRODUCTION

Many pediatric patients with malignant tumors continue to suffer poor outcomes. The current standard of care includes maximum safe surgical resection followed by chemotherapy and radiation which may be associated with considerable long-term morbidity. The emergence of oncolytic virotherapy (OVT) may provide an alternative or adjuvant treatment for pediatric oncology patients.

AREAS COVERED

We reviewed seven virus types that have been investigated in past or ongoing pediatric tumor clinical trials: adenovirus (AdV-tk, Celyvir, DNX-2401, VCN-01, Ad-TD-nsIL-12), herpes simplex virus (G207, HSV-1716), vaccinia (JX-594), reovirus (pelareorep), poliovirus (PVSRIPO), measles virus (MV-NIS), and Senecavirus A (SVV-001). For each virus, we discuss the mechanism of tumor-specific replication and cytotoxicity as well as key findings of preclinical and clinical studies.

EXPERT OPINION

Substantial progress has been made in the past 10 years regarding the clinical use of OVT. From our review, OVT has favorable safety profiles compared to chemotherapy and radiation treatment. However, the antitumor effects of OVT remain variable depending on tumor type and viral agent used. Although the widespread adoption of OVT faces many challenges, we are optimistic that OVT will play an important role alongside standard chemotherapy and radiotherapy for the treatment of malignant pediatric solid tumors in the future.

Reovirus uses temporospatial compartmentalization to orchestrate core versus outercapsid assembly

Reoviridae virus family members, such as mammalian orthoreovirus (reovirus), encounter a unique challenge during replication. To hide the dsRNA from host recognition, the genome remains encapsidated in transcriptionally active proteinaceous core capsids that transcribe and release +RNA. De novo +RNAs and core proteins must repeatedly assemble into new progeny cores in order to logarithmically amplify replication. Reoviruses also produce outercapsid (OC) proteins μ1, σ3 and σ1 that assemble onto cores to create highly stable infectious full virions. Current models of reovirus replication position amplification of transcriptionally-active cores and assembly of infectious virions in shared factories, but we hypothesized that since assembly of OC proteins would halt core amplification, OC assembly is somehow regulated. Kinetic analysis of virus +RNA production, core versus OC protein expression, and core particles versus whole virus particle accumulation, indicated that assembly of OC proteins onto core particles was temporally delayed. All viral RNAs and proteins were made simultaneously, eliminating the possibility that delayed OC RNAs or proteins account for delayed OC assembly. High resolution fluorescence and electron microscopy revealed that core amplification occurred early during infection at peripheral core-only factories, while all OC proteins associated with lipid droplets (LDs) that coalesced near the nucleus in a μ1–dependent manner. Core-only factories transitioned towards the nucleus despite cycloheximide-mediated halting of new protein expression, while new core-only factories developed in the periphery. As infection progressed, OC assembly occurred at LD-and nuclear-proximal factories. Silencing of OC μ1 expression with siRNAs led to large factories that remained further from the nucleus, implicating μ1 in the transition to perinuclear factories. Moreover, late during infection, +RNA pools largely contributed to the production of de-novo viral proteins and fully-assembled infectious viruses. Altogether the results suggest an advanced model of reovirus replication with spatiotemporal segregation of core amplification, OC complexes and fully assembled virions.

It is important to understand how viruses replicate and assemble to discover antiviral therapies and to modify viruses for applications like gene therapy or cancer therapy. Reovirus is a harmless virus being tested as a cancer therapy. Reovirus has two coats of proteins, an inner coat and an outer coat. To replicate, reovirus particles need only the inner coat, but to become infectious they require the outer coat. Strangely, inner and outer coat proteins are all made by the virus at once, so it was unknown what determines whether newly made viruses will contain just the inner coat to continue to replicate, or both coats to transmit to new hosts. Our experiments reveal that the inner coat proteins are located in a different area of an infected cell versus the outer coat proteins. The location therefore determines if the newly made viruses contain just the inner coat versus both coats. Reoviruses have evolved extravagant mechanisms to be able to efficiently take on the best composition required for replication and transmission.

Genome Sequence of a Yunnan Orbivirus Isolated from a Dead Florida White-Tailed Deer (Odocoileus virginianus)

We report the complete coding sequences of a Yunnan orbivirus isolated from a dead white-tailed deer (Odocoileus virginianus) in Florida in 2019. The prevalence of Yunnan orbivirus and its role in disease among farmed white-tailed deer remains to be determined.

We report the complete coding sequences of a Yunnan orbivirus isolated from a dead white-tailed deer (Odocoileus virginianus) in Florida in 2019. The prevalence of Yunnan orbivirus and its role in disease among farmed white-tailed deer remain to be determined.

The genomic constellation of a novel duck reovirus strain associated with hemorrhagic necrotizing hepatitis and splenitis in Muscovy ducklings in Fujian, China

The complete sequence of a reovirus, strain NP03 associated with necrotic focus formation in the liver and spleen of Muscovy ducklings in Fujian Province, China in 2009, was determined and compared with sequences of other waterfowl and chicken-origin avian reoviruses (ARVs). Sequencing of the complete genomes of strain NP03 showed that they consisted of 23,418 bp and were divided into 10 segments, ranging from 1191 bp (S4) to 3959 bp (L1) in length, and all segments contained conserved sequences in the 5' non-coding region (GCUUUU) and 3' non-coding region (UCAUC). Pairwise sequence comparisons demonstrated that NP03 strain showed the highest similarity with novel waterfowl origin reoviruses (WRVs). The genome analysis revealed that the S1 segment of novel WRV is a tricistronic gene, encoding the overlapping open reading frames (ORFs) for p10, p18, and σC, similar to the ARV S1 gene, but distinct from classical WRV S4 genome segment, which contained two overlapping ORFs encoding p10 and σC. Phylogenetic analyses of the nucleotide sequences of all 10 segments revealed that NP03 strain was clustered together with other novel WRVs and were distinct from classical WRVs and chicken-origin ARVs. The analyses also showed possible intra-segmental reassortment events in the segments encoding λA, λB, μB, μNS, σA, and σNS between novel and classical WRVs. Potential recombination events detection in segment L1 suggests that NP03 strain may be recombinants of novel WRVs. Based on our genetic analyses, multiple reassortment events, intra-segmental recombination, and accumulation of point mutations have possibly contributed to the emergence of this novel genotype of WRV, identified in China.

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.

Structure and function of S9 segment of grass carp reovirus Anhui strain

A highly virulent grass carp reovirus (GCRV) strain, named GCRV-AH528, was recently purified from a diseased grass carp with hemorrhage disease in Anhui, China. GCRV-AH528 S9 segment was 1320 nucleotides in length and encoded a 418 amino acid VP6 protein. BLAST search showed that the VP6 protein owned a conserved domain belonging to the reoviral σ2 family. Phylogenetic analysis of VP6 presented that GCRV-AH528 belonged to GCRV genotype II, which was more closely related to Orthoreovirus than GCRV genotype I and genotype III. Further analysis revealed that GCRV-AH528 S9 and mammalian orthoreovirus S8 might have evolved from a common ancestral precursor and have identical mechanism in virus assembly. The expression level of vp6 gene was detected by quantitative real-time PCR (qRT-PCR). Over time, the expression level of vp6 gradually increased in Ctenopharyngodon idellus kidney cells. However, the level of vp6 expression in blood sharply increased at 4-6 days, and then decreased to a low level after GCRV-AH528 challenge (P < 0.05). The vp6 gene was detected in all tissues examined, whereas at relatively higher levels in blood, kidney, and liver (P < 0.05). The yeast two-hybrid (Y2H) system was used to identify VP6 self-interaction, while no interaction was detected in VP6-VP6. This study not only revealed the S9 segment structure and expression pattern but also analyzed the VP6 mechanism by yeast hybridization method. The present study provides valuable informations for further experimental design and investigation of VP6 functions.

The effect of glycosylation on cytotoxicity of Ibaraki virus nonstructural protein NS3

The cytotoxicity of Ibaraki virus nonstructural protein NS3 was confirmed, and the contribution of glycosylation to this activity was examined by using glycosylation mutants of NS3 generated by site-directed mutagenesis. The expression of NS3 resulted in leakage of lactate dehydrogenase to the culture supernatant, suggesting the cytotoxicity of this protein. The lack of glycosylation impaired the transport of NS3 to the plasma membrane and resulted in reduced cytotoxicity. Combined with the previous observation that NS3 glycosylation was specifically observed in mammalian cells (Urata et al., Virus Research 2014), it was suggested that the alteration of NS3 cytotoxicity through modulating glycosylation is one of the strategies to achieve host specific pathogenisity of Ibaraki virus between mammals and vector arthropods.

Genomic characterization of a turkey reovirus field strain by Next-Generation Sequencing

The genome of a turkey arthritis reovirus (TARV) field strain (Reo/PA/Turkey/22342/13), isolated from a turkey flock in Pennsylvania (PA) in 2013, has been sequenced using Next-Generation Sequencing (NGS) on the Illumina MiSeq platform. The genome of the PA TARV field strain was 23,496bp in length with 10 dsRNA segments encoding 12 viral proteins. The lengths of the genomic segments ranged from 1192bp (S4) to 3959bp (L1). The 5' and 3' conserved terminal sequences of the PA TARV field strain were similar to the two Minnesota (MN) TARVs (MN9 and MN10) published recently and avian orthoreovirus (ARV) reference strains. Phylogenetic analysis of the nucleotide sequences of all 10 genome segments revealed that there was a low to significant nucleotide sequence divergence between the PA TARV field strain and reference TARV and ARV strains. Analysis of the PA TARV sequence indicates that this PA TARV field strain is a unique strain and is different from the TARV MN9 or MN10 in M2 segment genes and ARV S1133 vaccine strain.

Isolation and characterization of three mammalian orthoreoviruses from European bats

In recent years novel human respiratory disease agents have been described in South East Asia and Australia. The causative pathogens were classified as pteropine orthoreoviruses with strong phylogenetic relationship to orthoreoviruses of flying foxes inhabiting these regions. Subsequently, a zoonotic bat-to-human transmission has been assumed. We report the isolation of three novel mammalian orthoreoviruses (MRVs) from European bats, comprising bat-borne orthoreovirus outside of South East Asia and Australia and moreover detected in insectivorous bats (Microchiroptera). MRVs are well known to infect a broad range of mammals including man. Although they are associated with rather mild and clinically unapparent infections in their hosts, there is growing evidence of their ability to also induce more severe illness in dogs and man. In this study, eight out of 120 vespertilionid bats proved to be infected with one out of three novel MRV isolates, with a distinct organ tropism for the intestine. One isolate was analyzed by 454 genome sequencing. The obtained strain T3/Bat/Germany/342/08 had closest phylogenetic relationship to MRV strain T3D/04, isolated from a dog. These novel reoviruses provide a rare chance of gaining insight into possible transmission events and of tracing the evolution of bat viruses.

dsRNA and the innate antiviral immune response

Innate immunity is the first line of defense against viral infections. It is based on a mechanism of sensing pathogen-associated molecular patterns through host germline-encoded pattern recognition receptors. dsRNA is arguably the most important viral pathogen-associated molecular pattern due to its expression by almost all viruses at some point during their replicative cycle. Viral dsRNA has been studied for over 55 years, first as a toxin, then as a type I interferon inducer, a viral mimetic and an immunomodulator for therapeutic purposes. This article will focus on dsRNA, its structure, generation (both endogenous and viral), host sensing mechanisms and induction of type I interferons. The possible therapeutic applications of these findings will also be discussed. The goal of this article is to give an overview of these mechanisms, highlighting novel findings, while providing a historical perspective.

Features of the mammalian orthoreovirus 3 Dearing l1 single-stranded RNA that direct packaging and serotype restriction

A series of recombinant mammalian orthoreoviruses (mammalian orthoreovirus 3 Dearing, MRV-3De) were generated that express an MRV-3De lambda3-CAT fusion protein. Individual viruses contain L1CAT double-stranded (ds) RNAs that range in length from a minimum of 1020 bp to 4616 bp. The engineered dsRNAs were generated from in vitro-transcribed single-stranded (ss) RNAs and incorporated into infectious virus particles by using reverse genetics. In addition to defining the sequences required for these ssRNAs to be 'identified' as l1 ssRNAs, the individual nucleotides in these regions that 'mark' each ssRNA as originating from mammalian orthoreovirus 1 Lang (MRV-1La), mammalian orthoreovirus 2 D5/Jones (MRV-2Jo) or MRV-3De have been identified. A C at position 81 in the MRV-1La 5' 129 nt sequence was able to be replaced with a U, as normally present in MRV-3De; this toggled the activity of the MRV-1La ssRNA to that of an MRV-3De 5' l1. RNA secondary-structure predictions for the 5' 129 nt of both the biologically active MRV-3De l1 ssRNA and the U81-MRV-3De-restored MRV-1La 5' ssRNA predicted a common structure.

Localizing the reovirus packaging signals using an engineered m1 and s2 ssRNA

Using in vitro engineered and transcribed reovirus m1 and s2 ssRNAs, we demonstrate that the nucleotides used to identify these ssRNAs are localized to the 5' and not the 3' termini. To demonstrate this, we used our previously reported S2-CAT reovirus and we report the creation of an engineered M1-CAT reovirus. The M1 gene of this virus retains 124 nucleotides from the wild type M1 gene preceding the CAT gene and 172 nucleotides from the wild type gene following the CAT gene. The engineered M1-CAT ssRNA is 1048 nucleotides in length, much shorter than the wild type M1 at 2304 nucleotides. We have used a set of chimeric s2.m1 ssRNAs to localize the packaging signals within these RNAs. By packaging signals we mean that the presence of these signals in engineered ssRNAs results in these ssRNAs being replicated to dsRNA and packaged into progeny virus. An engineered ssRNA with a 5' sequence identical with the wild type s2 ssRNA, supported by a 3' sequence from either the m1 or s2 ssRNA, is incorporated into a virus as an S2 dsRNA. Likewise, an ssRNA with an m1 5' end is incorporated as an M1 dsRNA.

Molecular Cloning, DNA Sequence Analysis, and Expression of cDNA Sequence of RNA Genomic Segment 6 (S6) that Encodes a Viral Outer Capsid Protein of Threadfin Aquareovirus (TFV)

The genome segment 6 (S6) of threadfin reovirus (TFV) was cloned and sequenced. The entire S6 nucleotide sequence is 2056 bp long with an open reading frame that encodes a protein of 653 amino acids. Sequence analysis of the TFV S6 genome revealed that the 5'-terminal sequence, GTTTTA and the 3'-terminal sequence, ATTCATC of the plus strand is common to other genome segments of TFV. The pentanucleotide, TCATC, at the 3'-terminal of the plus strand was also conserved in other reported isolates of Aquareovirus such as chum salmon reovirus (CSV), striped bass reovirus (SBR), grass carp reovirus (GCRV) and golden shiner reovirus (GSV) as well as to the 10 genome segments of mammalian reovirus (MRV). Blast results indicated that the TFV S6 gene segment sequence had high identity towards the CSV S6 gene sequence, which codes for the CSV outer coat protein. This implied that the TFV S6 gene segment codes for an outer capsid protein (OCP) of the virus. Amino acid sequence analysis of this TFV OCP sequence revealed the presence of a putative conserved asparagine-proline (Asn-Pro) protease cleavage site, which was found in all reported isolates of Aquareovirus as well as in the MRV mu1 protein. N-terminal sequencing of the corresponding S6 native protein obtained from purified TFV particles verified the presence of this cleavage site. Phylogenetic analysis of the TFV S6 protein revealed that TFV was closely related to CSV, from Aquareovirus species, ARV-A. Cloning of the TFV S6 gene sequence into an Escherichia coli expression host produced a recombinant protein that corresponded to the predicated size of the OCP of TFV. Immunization of mice using this recombinant outer capsid protein (rOCP) revealed that the protein was able to elicit an antibody response, thus indicating that the rOCP of TFV was immunogenic.