Mammalian orthoreovirus can exit cells in extracellular vesicles

Several egress pathways have been defined for many viruses. Among these pathways, extracellular vesicles (EVs) have been shown to function as vehicles of non-lytic viral egress. EVs are heterogenous populations of membrane-bound structures released from cells as a form of intercellular communication. EV-mediated viral egress may enable immune evasion and collective viral transport. Strains of nonenveloped mammalian orthoreovirus (reovirus) differ in cell lysis phenotypes, with T3D disrupting cell membranes more efficiently than T1L. However, mechanisms of reovirus egress and the influence of transport strategy on infection are only partially understood. To elucidate reovirus egress mechanisms, we infected murine fibroblasts (L cells) and non-polarized human colon epithelial (Caco-2) cells with T1L or T3D reovirus and enriched cell culture supernatants for large EVs, medium EVs, small EVs, and free reovirus. We found that both reovirus strains exit cells in association with large and medium EVs and as free virus particles, and that EV-enriched fractions are infectious. While reovirus visually associates with large and medium EVs, only medium EVs offer protection from antibody-mediated neutralization. EV-mediated protection from neutralization is virus strain- and cell type-specific, as medium EVs enriched from L cell supernatants protect T1L and T3D, while medium EVs enriched from Caco-2 cell supernatants largely fail to protect T3D and only protect T1L efficiently. Using genetically barcoded reovirus, we provide evidence that large and medium EVs can convey multiple particles to recipient cells. Finally, T1L or T3D infection increases the release of all EV sizes from L cells. Together, these findings suggest that in addition to exiting cells as free particles, reovirus promotes egress from distinct cell types in association with large and medium EVs during lytic or non-lytic infection, a mode of exit that can mediate multiparticle infection and, in some cases, protection from antibody neutralization.

Cross-Hemispheric Genetic Diversity and Spatial Genetic Structure of Callinectes sapidus Reovirus 1 (CsRV1)

The movement of viruses in aquatic systems is rarely studied over large geographic scales. Oceanic currents, host migration, latitude-based variation in climate, and resulting changes in host life history are all potential drivers of virus connectivity, adaptation, and genetic structure. To expand our understanding of the genetic diversity of Callinectes sapidus reovirus 1 (CsRV1) across a broad spatial and host life history range of its blue crab host (Callinectes sapidus), we obtained 22 complete and 96 partial genomic sequences for CsRV1 strains from the US Atlantic coast, Gulf of Mexico, Caribbean Sea, and the Atlantic coast of South America. Phylogenetic analyses of CsRV1 genomes revealed that virus genotypes were divided into four major genogroups consistent with their host geographic origins. However, some CsRV1 sequences from the US mid-Atlantic shared high genetic similarity with the Gulf of Mexico genotypes, suggesting potential human-mediated movement of CsRV1 between the US mid-Atlantic and Gulf coasts. This study advances our understanding of how climate, coastal geography, host life history, and human activity drive patterns of genetic structure and diversity of viruses in marine animals and contributes to the capacity to infer broadscale host population connectivity in marine ecosystems from virus population genetic data.

[Orthoreoviruses]

Members of the genus Orthoreovirus in the family Reoviridae are nonenveloped, icosahedral viruses. Their genomes contain 10 segments of double-stranded RNA (dsRNA). The orthoreoviruses are divided into two subgroups, the fusogenic and nonfusogenic reoviruses, based on the ability of the virus to induce cell-to-cell fusion. The fusogenic subgroup consists of the avian reovirus, baboon reovirus, pteropine reovirus, and reptilian reovirus, whereas the nonfusogenic subgroup consists of the prototypical mammalian reovirus (MRV) species. MRVs are highly tractable experimental models for studies of segmented dsRNA virus replication and pathogenesis. Moreover, MRVs can selectively kill tumor cells and have been evaluated as oncolytic agents in clinical trials. This review provides a brief overview of current knowledge on the virological features of MRVs.

A NOVEL INTRAVESICAL THERAPY FOR SUPERFICIAL BLADDER CANCER IN AN ORTHOTOPIC MODEL: ONCOLYTIC REOVIRUS THERAPY

PURPOSE

To our knowledge this is the first report of intravesical oncolytic reovirus for therapy of superficial bladder cancer in an orthotopic bladder tumor model. Superficial bladder carcinomas are often multifocal and have high recurrences after surgical resection. In 20% of cases intravesical immunotherapy fails to prevent recurrence and complications from bacillus Calmette-Guerin (BCG) are common. Human reovirus is an oncolytic virus that selectively destroys cancer cells with an activated Ras pathway. We examined the ability of this virus to kill bladder cancer cells in vitro and inhibit tumor growth in vivo.

MATERIALS AND METHODS

Following cytotoxicity assays in vitro dose escalation of intravesical reovirus was tested for tumor control and toxicity in a rat model. Treatments were done twice weekly for 3 weeks. In parallel intravesical BCG was studied. Animals were monitored on a daily basis for health status and by routine urine cytology. Animals underwent necropsy at study end point and appropriate tissues were taken for histology.

RESULTS

Side effects in reovirus groups were minor compared with BCG complications. Tumor response (animal survival) was 90% 100 days after tumor implantation in reovirus treated animals, whereas the highest survival in BCG treated groups was 50%. Animals treated with reovirus had significantly higher tumor-free survival than those treated with immunotherapy or normal saline (log rank test p = 0.0002 and 0.04, respectively).

CONCLUSIONS

Intravesical reovirus is safe and effective in this animal model and it may have clinical applications for bladder cancer treatment.

Respiratory reovirus 1/L induction of intraluminal fibrosis, a model of bronchiolitis obliterans organizing pneumonia, is dependent on T lymphocytes

Bronchiolitis obliterans organizing pneumonia (BOOP) is a clinical syndrome characterized by perivascular/peribronchiolar leukocyte infiltration leading to the development of intraalveolar fibrosis. We have developed an animal model of BOOP where CBA/J mice infected with 1 x 10(6) plaque-forming units (PFU) reovirus 1/L develop follicular bronchiolitis and intraalveolar fibrosis similar to human BOOP. In this report, we demonstrate a role for T cells in the development of intraluminal fibrosis associated with BOOP. Corticosteroid treatment of reovirus 1/L-infected mice both inhibited the development of fibrotic lesions when administered early in the time-course and promoted the resolution of fibrotic lesions when corticosteroid administration was delayed. Further, the depletion of either CD4(+) or CD8(+) T cells before reovirus 1/L infection also inhibited fibrotic lesion development. Both corticosteroid treatment and depletion of CD4(+) or CD8(+) T cells also resulted in decreased expression of the proinflammatory and profibrotic cytokines, interferon (IFN)-gamma and monocyte chemoattractant protein-1 (MCP-1). Further, treatment of mice with a neutralizing monoclonal antibody to IFN-gamma also significantly inhibited the development of fibrosis. Taken together, these results suggest a significant role for T cells in the development of reovirus 1/L-induced BOOP fibrotic lesions in CBA/J mice and suggests that T(H)1-derived cytokines, especially IFN-gamma, may play a key role in fibrotic lesion development.

Effect of antibodies to intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 on cytokine mRNA expression in reovirus type-2-triggered autoimmune insulitis in suckling DBA/1 mice

Interleukin (IL)-12 in the presence of IL-18 induces T helper (Th) 1 dominated systemic immune reactions, such as those that occur in autoimmune insulitis in suckling mice infected with reovirus type-2 (Reo-2). The role of intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 on the induction of cytokines responsible for Reo-2-triggered insulitis with impaired glucose tolerance (IGT) was examined. One-day-old DBA/1 mice infected with Reo-2 intraperitoneally (i.p.) were treated i.p. with monoclonal antibodies (mAbs) against ICAM-1 and LFA-1 (ICAM-1/LFA-1) at 5 days post-infection (d.p.i.). At 10 d.p.i., the administration of the mAbs was seen to have prevented the development of insulitis with IGT. This was associated with a decrease in the mRNA expression for IL-12(p40) and IL-18 by splenic cells. The present study suggests that ICAM-1/LFA-1 may be required for the differentiation of Th0 cells to Th1 cells, which mediate insulitis with IGT in Reo-2-infected suckling mice.

Interleukin-4-expressing plasmid DNA inhibits reovirus type-2-triggered autoimmune insulitis in DBA/1 J suckling mice

In this study we have examined the effect of systemic administration of T helper (Th) 2 cytokines on reovirus type-2 (Reo-2)-triggered Th1-mediated autoimmune insulitis with impaired glucose tolerance (IGT) in DBA/1J suckling mice. We have demonstrated clearly that the systemic administration of both interleukin (IL)-4-expressing plasmid DNA (pIL-4) and recombinant IL-4 (rIL-4) inhibited the development of insulitis with IGT in a dose dependent manner as compared to untreated groups in Reo-2-infected DBA/1J suckling mice. The inhibitory effects of IL-4 on the development of insulitis with IGT and the advantages of pIL-4 as compared to rIL-4 in this model are discussed.

CpG oligodeoxynucleotides accelerate reovirus type 2-triggered insulitis in DBA/1 suckling mice

We reported previously that reovirus type-2 (Reo-2) triggers T-helper (Th) 1-mediated autoimmune insulitis resulting in temporal impaired glucose tolerance (IGT) approximately 10 days post infection (d.p.i) in suckling DBA/1 mice. We hypothesized that CpG motifs in bacteria may enhance virus-induced insulitis through its content of unmethylated CpG motifs. In the infected mice, the intraperitoneal treatment of synthetic 20-base oligodeoxynucleotides with CpG motifs (CpG ODN) caused increase in cumulative incidence of insulitis with IGT, increased serum interferon (IFN)-gamma concentration, and high frequency of autoantibody against pancreatic islet cells, compared to the infected mice without CpG ODN at 17 d.p.i. Also CD4+ and CD8+ lymphocytes infiltrated in and/or around pancreatic islets in the CpG ODN-treated mice. This evidence suggests that CpG ODN may contribute to accelerate Reo-2-induced autoimmune reaction against pancreatic islet cells via additional effects of Th1 cytokines especially IFN-gamma.

FINE STRUCTURE OF REOVIRUS TYPE 2

Loh, Philip C. (University of Hawaii, Honolulu), H. R. Hohl, and M. Soergel. Fine structure of reovirus type 2. J. Bacteriol. 89:1140-1144. 1965.-The fine structure reovirus type 2 was studied by electron microscopy with the negative-staining method. The virus has a mean diameter of 772 A and shows evidence of icosahedral shape and 5:3:2 symmetry. The particle is composed of a core, an inner layer, and a capsid composed of 92 elongated hollow capsomeres. These capsomeres have mean dimensions of 116 A x 110 A and a central hole 48 A in diameter. In size and architecture, reovirus type 2 is very similar to the other members (reoviruses types 1 and 3) of this group of animal viruses.