Multiplication of a myxovirus (SV5) with minimal cytopathic effects and without interference

Isolation, genome analysis and comparison of a novel parainfluenza virus 5 from a Siberian tiger (Panthera tigris)

Paramyxoviruses are important pathogens affecting various animals, including mammals and humans. Parainfluenza virus 5 (PIV5)-a member of the family Paramyxoviridae-is a major threat to the health of mammals and humans. However, studies on terrestrial wild animals infected with PIV5 are scanty. In this study, we utilized reverse transcription PCR to detect PIV5 infection in the visceral organ tissues of a Siberian tiger (Panthera tigris ssp. altaica) with vomiting, diarrhea, and dyspnea before its death. A novel PIV5 (named SR strain) with a slowly progressive cytopathic effect was isolated in Vero cells and validated using a transmission electron microscope. Full-length sequencing and analysis revealed that the whole genome of the PIV5 SR strain contained 15,246 nucleotides (nt) and seven non-overlapping genes (3'-N-V/P-M-F-SH-HN-L-5') encoding eight proteins. Phylogenetic analysis of three PIV5 strains identified in the same zoo confirmed that PIV5 strains SR and ZJQ-221 shared the closest genetic relationship as they were clustered in the same branch, while the recently found Siberian tiger strain SZ2 kept a certain distance and formed a relatively unique branch. Furthermore, mutations of nt and amino acids (aa) between strains ZJQ-221, SR, and SZ2 were identified. In summary, we report the identification and genomic characterization of a novel PIV5 strain SR isolated in a Siberian tiger, which may help future research on interspecific transmission mechanisms.

Persistent paramyxovirus infections: in co-infections the parainfluenza virus type 5 persistent phenotype is dominant over the lytic phenotype

Parainfluenza virus type 5 (PIV5) can either have a persistent or a lytic phenotype in cultured cells. We have previously shown that the phenotype is determined by the phosphorylation status of the phosphoprotein (P). Single amino acid substitutions at critical residues, including a serine-to-phenylalanine substitution at position 157 on P, result in a switch between persistent and lytic phenotypes. Here, using PIV5 vectors expressing either mCherry or GFP with persistent or lytic phenotypes, we show that in co-infections the persistent phenotype is dominant. Thus, in contrast to the cell death observed with cells infected solely with the lytic variant, in co-infected cells persistence is immediately established and both lytic and persistent genotypes persist. Furthermore, 10-20 % of virus released from dually infected cells contains both genotypes, indicating that PIV5 particles can package more than one genome. Co-infected cells continue to maintain both genotypes/phenotypes during cell passage, as do individual colonies of cells derived from a culture of persistently infected cells. A refinement of our model on how the dynamics of virus selection may occur in vivo is presented.

Rescue of dual reporter-tagged parainfluenza virus 5 as tool for rapid screening of antivirals in vitro

Parainfluenza virus 5 (PIV5) belongs to the genus Orthorubulavirus in the family Paramyxoviridae. PIV5 can infect a range of mammals, but induce mild or even unobservable clinical signs in some animals, except kennel cough in dogs. It is also able to infect a variety of cell lines, but causes minimal or even invisible cytopathic effects on many cells. Sometimes, owing to neither observable cytopathic effects in vitro nor typical clinical signs in vivo, the PIV5 is not easily usable for screening antiviral drugs. To solve this issue, we used reverse genetics to recover a dual reporter-tagged recombinant PIV5 that could simultaneously express enhanced green fluorescence protein (eGFP) and NanoLuc® luciferase (NLuc) in virus-infected cells. Both reporters were genetically stable during twenty serial passages of virus in MDBK cells. The eGFP allowed us to observe virus-infected MDBK cells in real time, and moreover the NLuc made it possible to quantify the degree of viral replication for determining antiviral activity of a given drug. Subsequently, the recombinant PIV5 was used for antiviral assays on five common drugs, i.e., ribavirin, apigenin, 1-adamantylamine hydrochloride, moroxydine hydrochloride and tea polyphenol. The results showed that only the ribavirin had an anti-PIV5 effect in MDBK cells. This study proposed a novel method for rapid screening (or prescreening) of anti-PIV5 drugs.

Direct Antiviral Activity of IFN-Stimulated Genes Is Responsible for Resistance to Paramyxoviruses in ISG15-Deficient Cells

Cell culture model of ISG15 deficiency replicates findings in ISG15^−/− patient cells.

Cause of resistance in ISG15^−/− cells differs depending on duration of IFN treatment.

ISG15^−/− patients without serious viral disease do not prove ISGylation is unimportant.

IFNs, produced during viral infections, induce the expression of hundreds of IFN-stimulated genes (ISGs). Some ISGs have specific antiviral activity, whereas others regulate the cellular response. Besides functioning as an antiviral effector, ISG15 is a negative regulator of IFN signaling, and inherited ISG15 deficiency leads to autoinflammatory IFNopathies, in which individuals exhibit elevated ISG expression in the absence of pathogenic infection. We have recapitulated these effects in cultured human A549-ISG15^−/− cells and (using A549-UBA7^−/− cells) confirmed that posttranslational modification by ISG15 (ISGylation) is not required for regulation of the type I IFN response. ISG15-deficient cells pretreated with IFN-α were resistant to paramyxovirus infection. We also showed that IFN-α treatment of ISG15-deficient cells led to significant inhibition of global protein synthesis, leading us to ask whether resistance was due to the direct antiviral activity of ISGs or whether cells were nonpermissive because of translation defects. We took advantage of the knowledge that IFN-induced protein with tetratricopeptide repeats 1 (IFIT1) is the principal antiviral ISG for parainfluenza virus 5. Knockdown of IFIT1 restored parainfluenza virus 5 infection in IFN-α–pretreated, ISG15-deficient cells, confirming that resistance was due to the direct antiviral activity of the IFN response. However, resistance could be induced if cells were pretreated with IFN-α for longer times, presumably because of inhibition of protein synthesis. These data show that the cause of virus resistance is 2-fold; ISG15 deficiency leads to the early overexpression of specific antiviral ISGs, but the later response is dominated by an unanticipated, ISG15-dependent loss of translational control.

Analysis of Paramyxovirus Transcription and Replication by High-Throughput Sequencing

High-throughput sequencing (HTS) of virus-infected cells can be used to study in great detail the patterns of virus transcription and replication. For paramyxoviruses, and by analogy for all other negative-strand RNA viruses, we show that directional sequencing must be used to distinguish between genomic RNA and mRNA/antigenomic RNA because significant amounts of genomic RNA copurify with poly(A)-selected mRNA. We found that the best method is directional sequencing of total cell RNA, after the physical removal of rRNA (and mitochondrial RNA), because quantitative information on the abundance of both genomic RNA and mRNA/antigenomes can be simultaneously derived. Using this approach, we revealed new details of the kinetics of virus transcription and replication for parainfluenza virus (PIV) type 2, PIV3, PIV5, and mumps virus, as well as on the relative abundance of the individual viral mRNAs.

We have developed a high-throughput sequencing (HTS) workflow for investigating paramyxovirus transcription and replication. We show that sequencing of oligo(dT)-selected polyadenylated mRNAs, without considering the orientation of the RNAs from which they had been generated, cannot accurately be used to analyze the abundance of viral mRNAs because genomic RNA copurifies with the viral mRNAs. The best method is directional sequencing of infected cell RNA that has physically been depleted of ribosomal and mitochondrial RNA followed by bioinformatic steps to differentiate data originating from genomes from viral mRNAs and antigenomes. This approach has the advantage that the abundance of viral mRNA (and antigenomes) and genomes can be analyzed and quantified from the same data. We investigated the kinetics of viral transcription and replication during infection of A549 cells with parainfluenza virus type 2 (PIV2), PIV3, PIV5, or mumps virus and determined the abundances of individual viral mRNAs and readthrough mRNAs. We found that the mRNA abundance gradients differed significantly between all four viruses but that for each virus the pattern remained relatively stable throughout infection. We suggest that rapid degradation of non-poly(A) mRNAs may be primarily responsible for the shape of the mRNA abundance gradient in parainfluenza virus 3, whereas a combination of this factor and disengagement of RNA polymerase at intergenic sequences, particularly those at the NP:P and P:M gene boundaries, may be responsible in the other viruses.

IMPORTANCE High-throughput sequencing (HTS) of virus-infected cells can be used to study in great detail the patterns of virus transcription and replication. For paramyxoviruses, and by analogy for all other negative-strand RNA viruses, we show that directional sequencing must be used to distinguish between genomic RNA and mRNA/antigenomic RNA because significant amounts of genomic RNA copurify with poly(A)-selected mRNA. We found that the best method is directional sequencing of total cell RNA, after the physical removal of rRNA (and mitochondrial RNA), because quantitative information on the abundance of both genomic RNA and mRNA/antigenomes can be simultaneously derived. Using this approach, we revealed new details of the kinetics of virus transcription and replication for parainfluenza virus (PIV) type 2, PIV3, PIV5, and mumps virus, as well as on the relative abundance of the individual viral mRNAs.

A porcine xenograft-derived bone scaffold is a biocompatible bone graft substitute: An assessment of cytocompatibility and the alpha-Gal epitope

BACKGROUND

Xenografts are an attractive alternative to traditional bone grafts because of the large supply from donors with predictable morphology and biology as well as minimal risk of human disease transmission. Clinical series involving xenograft bone transplantation, most commonly from bovine sources, have reported poor results with frequent graft rejection and failure to integrate with host tissue. Failures have been attributed to residual alpha-Gal epitope in the xenograft which humans produce natural antibody against. To the authors' knowledge, there is currently no xenograft-derived bone graft substitute that has been adopted by orthopedic surgeons for routine clinical use.

METHODS

In the current study, a bone scaffold intended to serve as a bone graft substitute was derived from porcine cancellous bone using a tissue decellularization and chemical oxidation protocol. In vitro cytocompatibility, pathogen clearance, and alpha-Gal quantification tests were used to assess the safety of the bone scaffold intended for human use.

RESULTS

In vitro studies showed the scaffold was free of processing chemicals and biocompatible with mouse and human cell lines. When bacterial and viral pathogens were purposefully added to porcine donor tissue, processing successfully removed these pathogens to comply with sterility assurance levels established by allograft tissue providers. Critically, 98.5% of the alpha-Gal epitope was removed from donor tissue after decellularization as shown by ELISA inhibition assay and immunohistochemical staining.

CONCLUSIONS

The current investigation supports the biologic safety of bone scaffolds derived from porcine donors using a decellularization protocol that meets current sterility assurance standards. The majority of the highly immunogenic xenograft carbohydrate was removed from donor tissue, and these findings support further in vivo investigation of xenograft-derived bone tissue for orthopedic clinical application.

Histone Deacetylase Inhibitors Enhance Cell Killing and Block Interferon-Beta Synthesis Elicited by Infection with an Oncolytic Parainfluenza Virus

Previous results have shown that infection with the cytoplasmic-replicating parainfluenza virus 5 mutant P/V-CPI- sensitizes cells to DNA damaging agents, resulting in the enhanced killing of airway cancer cells. Here, we have tested the hypothesis that histone deacetylase (HDAC) inhibitors can also act with P/V-CPI- infection to enhance cancer cell killing. Using human small cell lung cancer and laryngeal cancer cell lines, 10 HDAC inhibitors were tested for their effect on viability of P/V-CPI- infected cells. HDAC inhibitors such as scriptaid enhanced caspase-3/7, -8 and -9 activity induced by P/V-CPI- and overall cell toxicity. Scriptaid-mediated enhanced killing was eliminated in lung cancer cells that were engineered to express a protein which sequesters double stranded RNA. Scriptaid also enhanced cancer cell killing by two other negative strand RNA viruses - the La Crosse virus and vesicular stomatitis virus. Scriptaid treatment enhanced the spread of the P/V-CPI- virus through a population of cancer cells, and suppressed interferon-beta induction through blocking phosphorylation and nuclear translocation of Interferon Regulatory Factor 3 (IRF-3). Taken together, these data support a role for combinations of a cytoplasmic-replicating RNA virus such as the P/V-CPI- mutant along with chemotherapeutic agents.

The autotransporter protein BatA is a protective antigen against lethal aerosol infection with Burkholderia mallei and Burkholderia pseudomallei

BACKGROUND

Burkholderia mallei and Burkholderia pseudomallei are the causative agents of glanders and melioidosis, respectively. There is no vaccine to protect against these highly-pathogenic and intrinsically antibiotic-resistant bacteria, and there is concern regarding their use as biological warfare agents. For these reasons, B. mallei and B. pseudomallei are classified as Tier 1 organisms by the U.S. Federal Select Agent Program and the availability of effective countermeasures represents a critical unmet need.

METHODS

Vaccines (subunit and vectored) containing the surface-exposed passenger domain of the conserved Burkholderia autotransporter protein BatA were administered to BALB/c mice and the vaccinated animals were challenged with lethal doses of wild-type B. mallei and B. pseudomallei strains via the aerosol route. Mice were monitored for signs of illness for a period of up to 40 days post-challenge and tissues from surviving animals were analyzed for bacterial burden at study end-points.

RESULTS

A single dose of recombinant Parainfluenza Virus 5 (PIV5) expressing BatA provided 74% and 60% survival in mice infected with B. mallei and B. pseudomallei, respectively. Vaccination with PIV5-BatA also resulted in complete bacterial clearance from the lungs and spleen of 78% and 44% of animals surviving lethal challenge with B. pseudomallei, respectively. In contrast, all control animals vaccinated with a PIV5 construct expressing an irrelevant antigen and infected with B. pseudomallei were colonized in those tissues.

CONCLUSION

Our study indicates that the autotransporter BatA is a valuable target for developing countermeasures against B. mallei and B. pseudomallei and demonstrates the utility of the PIV5 viral vaccine delivery platform to elicit cross-protective immunity against the organisms.

Parainfluenza Virus Infection Sensitizes Cancer Cells to DNA-Damaging Agents: Implications for Oncolytic Virus Therapy

A parainfluenza virus 5 (PIV5) with mutations in the P/V gene (P/V-CPI^-) is restricted for spread in normal cells but not in cancer cells in vitro and is effective at reducing tumor burdens in mouse model systems. Here we show that P/V-CPI^- infection of HEp-2 human laryngeal cancer cells results in the majority of the cells dying, but unexpectedly, over time, there is an emergence of a population of cells that survive as P/V-CPI^- persistently infected (PI) cells. P/V-CPI^- PI cells had elevated levels of basal caspase activation, and viability was highly dependent on the activity of cellular inhibitor-of-apoptosis proteins (IAPs) such as Survivin and XIAP. In challenge experiments with external inducers of apoptosis, PI cells were more sensitive to cisplatin-induced DNA damage and cell death. This increased cisplatin sensitivity correlated with defects in DNA damage signaling pathways such as phosphorylation of Chk1 and translocation of damage-specific DNA binding protein 1 (DDB1) to the nucleus. Cisplatin-induced killing of PI cells was sensitive to the inhibition of wild-type (WT) p53-inducible protein 1 (WIP1), a phosphatase which acts to terminate DNA damage signaling pathways. A similar sensitivity to cisplatin was seen with cells during acute infection with P/V-CPI^- as well as during acute infections with WT PIV5 and the related virus human parainfluenza virus type 2 (hPIV2). Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish PI as well as the potential for combining chemotherapy with oncolytic RNA virus vectors.IMPORTANCE There is intense interest in developing oncolytic viral vectors with increased potency against cancer cells, particularly those cancer cells that have gained resistance to chemotherapies. We have found that infection with cytoplasmically replicating parainfluenza virus can result in increases in the killing of cancer cells by agents that induce DNA damage, and this is linked to alterations to DNA damage signaling pathways that balance cell survival versus death. Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish persistent infection, the repurposing of drugs that target cellular IAPs as antivirals, and the combined use of DNA-damaging chemotherapy agents in conjunction with oncolytic RNA virus vectors.

Parainfluenza virus 5-vectored vaccines against human and animal infectious diseases

Parainfluenza virus 5 (PIV5), known as canine parainfluenza virus in the veterinary field, is a negative‐sense, nonsegmented, single‐stranded RNA virus belonging to the Paramyxoviridae family. Parainfluenza virus 5 is an excellent viral vector and has been used as a live vaccine for kennel cough for many years in dogs without any safety concern. It can grow to high titers in many cell types, and its genome is stable even in the presence of foreign gene insertions. So far, PIV5 has been used to develop vaccines against influenza virus, respiratory syncytial virus, rabies virus, and Mycobacterium tuberculosis, demonstrating its ability to elicit robust and protective immune responses in preclinical animal models. Parainfluenza virus 5–based vaccines can be administered intranasally, intramuscularly, or orally. Interestingly, prior exposure of PIV5 does not prevent a PIV5‐vectored vaccine from generating robust immunity, indicating that the vector can be used more than once. Here, these encouraging results are reviewed together along with discussion of the desirable advantages of the PIV5 vaccine vector to aid future vaccine design and to accelerate progression of PIV5‐based vaccines into clinical trials.

First complete genome sequence of parainfluenza virus 5 isolated from lesser panda

Parainfluenza virus 5 (PIV5) is widespread in mammals and humans. Up to now, there is little information about PIV5 infection in lesser pandas. In this study, a PIV5 variant (named ZJQ-221) was isolated from a lesser panda with respiratory disease in Guangzhou zoo in Guangdong province, southern China. The full-length genome of ZJQ-221 was found to be 15,246 nucleotides and consisted of seven non-overlapping genes encoding eight proteins (i.e., NP, V, P, M, F, SH, HN and L). Sequence alignment and genetic analysis revealed that ZJQ-221 shared a close relationship with a PIV5 strain of canine-origin (1168-1) from South Korea. The findings of this study confirm the presence of PIV5 in lesser panda and indicate this mammal as a possible natural reservoir. Furthermore they highlight the urgent need to strengthen viral surveillance and control of PIV5 in zoo animals.

Human IFIT1 Inhibits mRNA Translation of Rubulaviruses but Not Other Members of the Paramyxoviridae Family

We have previously shown that IFIT1 is primarily responsible for the antiviral action of interferon (IFN) alpha/beta against parainfluenza virus type 5 (PIV5), selectively inhibiting the translation of PIV5 mRNAs. Here we report that while PIV2, PIV5, and mumps virus (MuV) are sensitive to IFIT1, nonrubulavirus members of the paramyxoviridae such as PIV3, Sendai virus (SeV), and canine distemper virus (CDV) are resistant. The IFIT1 sensitivity of PIV5 was not rescued by coinfection with an IFIT1-resistant virus (PIV3), demonstrating that PIV3 does not specifically inhibit the antiviral activity of IFIT1 and that the inhibition of PIV5 mRNAs is regulated by cis-acting elements. We developed an in vitro translation system using purified human IFIT1 to further investigate the mechanism of action of IFIT1. While the translations of PIV2, PIV5, and MuV mRNAs were directly inhibited by IFIT1, the translations of PIV3, SeV, and CDV mRNAs were not. Using purified human mRNA-capping enzymes, we show biochemically that efficient inhibition by IFIT1 is dependent upon a 5' guanosine nucleoside cap (which need not be N7 methylated) and that this sensitivity is partly abrogated by 2'O methylation of the cap 1 ribose. Intriguingly, PIV5 M mRNA, in contrast to NP mRNA, remained sensitive to inhibition by IFIT1 following in vitro 2'O methylation, suggesting that other structural features of mRNAs may influence their sensitivity to IFIT1. Thus, surprisingly, the viral polymerases (which have 2'-O-methyltransferase activity) of rubulaviruses do not protect these viruses from inhibition by IFIT1. Possible biological consequences of this are discussed.

IMPORTANCE

Paramyxoviruses cause a wide variety of diseases, and yet most of their genes encode structural proteins and proteins involved in their replication cycle. Thus, the amount of genetic information that determines the type of disease that paramyxoviruses cause is relatively small. One factor that will influence disease outcomes is how they interact with innate host cell defenses, including the interferon (IFN) system. Here we show that different paramyxoviruses interact in distinct ways with cells in a preexisting IFN-induced antiviral state. Strikingly, all the rubulaviruses tested were sensitive to the antiviral action of ISG56/IFIT1, while all the other paramyxoviruses tested were resistant. We developed novel in vitro biochemical assays to investigate the mechanism of action of IFIT1, demonstrating that the mRNAs of rubulaviruses can be directly inhibited by IFIT1 and that this is at least partially because their mRNAs are not correctly methylated.

Stability of the parainfluenza virus 5 genome revealed by deep sequencing of strains isolated from different hosts and following passage in cell culture

The strain diversity of a rubulavirus, parainfluenza virus 5 (PIV5), was investigated by comparing 11 newly determined and 6 previously published genome sequences. These sequences represent 15 PIV5 strains, of which 6 were isolated from humans, 1 was from monkeys, 2 were from pigs, and 6 were from dogs. Strain diversity is remarkably low, regardless of host, year of isolation, or geographical origin; a total of 7.8% of nucleotides are variable, and the average pairwise difference between strains is 2.1%. Variation is distributed unevenly across the PIV5 genome, but no convincing evidence of selection for antibody-mediated evasion in hemagglutinin-neuraminidase was found. The finding that some canine and porcine, but not primate, strains are mutated in the SH gene, and do not produce SH, raised the possibility that dogs (or pigs) may not be the natural host of PIV5. The genetic stability of PIV5 was also demonstrated during serial passage of one strain (W3) in Vero cells at a high multiplicity of infection, under conditions of competition with large proportions of defective interfering genomes. A similar observation was made for a strain W3 mutant (PIV5VΔC) lacking V gene function, in which the dominant changes were related to pseudoreversion in this gene. The mutations detected in PIV5VΔC during pseudoreversion, and also those characterizing the SH gene in canine and porcine strains, predominantly involved U-to-C transitions. This suggests an important role for biased hypermutation via an adenosine deaminase, RNA-specific (ADAR)-like activity.

IMPORTANCE

Here we report the sequence variation of 16 different isolates of parainfluenza virus 5 (PIV5) that were isolated from a number of species, including humans, monkeys, dogs, and pigs, over 4 decades. Surprisingly, strain diversity was remarkably low, regardless of host, year of isolation, or geographical origin. Variation was distributed unevenly across the PIV5 genome, but no convincing evidence of immune or host selection was found. This overall genome stability of PIV5 was also observed when the virus was grown in the laboratory, and the genome stayed remarkably constant even during the selection of virus mutants. Some of the canine isolates had lost their ability to encode one of the viral proteins, termed SH, suggesting that although PIV5 commonly infects dogs, dogs may not be the natural host for PIV5.

Characterization in vitro and in vivo of a novel porcine parainfluenza virus 5 isolate in Korea

A novel porcine parainfluenza 5 (pPIV5), KNU-11, in the genus Rubulavirus of the subfamily Paramyxovirinae, was isolated from the lung of a piglet in Korea in 2011. To understand the importance of this virus as an infectious agent, in vitro and in vivo characteristics of KNU-11 virus was investigated. KNU-11 was remarkably cytopathogenic, showing distinct cell rounding and clumping evident in porcine alveolar macrophage (PAM), porcine kidney (PK-15), and swine testicle (ST) cells within 12h postinfection and capable of hemagglutinating guinea pig red blood cells. Interestingly, this cytopathology was found to be absent in cell lines from other mammalian species. To evaluate the in vitro immunity of the pPIV5 isolate, we sought to explore alteration of inflammatory cytokine and chemokine expression in PAM cells infected with KNU-11 by using quantitative real-time RT-PCR. Most cytokine and chemokine genes including type 1 interferons (IFN-α/β) and IFN-related antiviral genes were found to be significantly elevated in KNU-11 virus-infected PAM cells. A serum neutralization test-based serosurvey demonstrated that neutralizing antibodies against KNU-11 are readily detected in domestic swine populations, suggesting high prevalence of pPIV5 in Korean pig farms. Animal studies showed that KNU-11 fails to establish an acute respiratory illness, indicating that pPIV5 is non- or very mildly pathogenic to pigs.

Deep sequencing analysis of defective genomes of parainfluenza virus 5 and their role in interferon induction

Preparations of parainfluenza virus 5 (PIV5) that are potent activators of the interferon (IFN) induction cascade were generated by high-multiplicity passage in order to accumulate defective interfering virus genomes (DIs). Nucleocapsid RNA from these virus preparations was extracted and subjected to deep sequencing. Sequencing data were analyzed using methods designed to detect internal deletion and "copyback" DIs in order to identify and characterize the different DIs present and to approximately quantify the ratio of defective to nondefective genomes. Trailer copybacks dominated the DI populations in IFN-inducing preparations of both the PIV5 wild type (wt) and PIV5-VΔC (a recombinant virus that does not encode a functional V protein). Although the PIV5 V protein is an efficient inhibitor of the IFN induction cascade, we show that nondefective PIV5 wt is unable to prevent activation of the IFN response by coinfecting copyback DIs due to the interfering effects of copyback DIs on nondefective virus protein expression. As a result, copyback DIs are able to very rapidly activate the IFN induction cascade prior to the expression of detectable levels of V protein by coinfecting nondefective virus.

Experimental vaccines against potentially pandemic and highly pathogenic avian influenza viruses

Influenza A viruses continue to emerge and re-emerge, causing outbreaks, epidemics and occasionally pandemics. While the influenza vaccines licensed for public use are generally effective against seasonal influenza, issues arise with production, immunogenicity, and efficacy in the case of vaccines against pandemic and emerging influenza viruses, and highly pathogenic avian influenza virus in particular. Thus, there is need of improved influenza vaccines and vaccination strategies. This review discusses advances in alternative influenza vaccines, touching briefly on licensed vaccines and vaccine antigens; then reviewing recombinant subunit vaccines, virus-like particle vaccines and DNA vaccines, with the main focus on virus-vectored vaccine approaches.

Evaluating a parainfluenza virus 5-based vaccine in a host with pre-existing immunity against parainfluenza virus 5

Parainfluenza virus 5 (PIV5), formerly known as simian virus 5 (SV5), is a paramyxovirus often referred to as canine parainfluenza virus (CPI) in the veterinary field. PIV5 is thought to be a contributing factor to kennel cough. Kennel cough vaccines containing live PIV5 have been used in dogs for many decades. PIV5 is not known to cause any diseases in humans or other animals. PIV5 has been used as a vector for vaccine development for humans and animals. One critical question concerning the use of PIV5 as a vector is whether prior exposure to PIV5 would prevent the use of PIV5-based vaccines. In this work, we have examined immunogenicity of a recombinant PIV5 expressing hemagglutinin (HA) of influenza A virus subtype 3 (rPIV5-H3) in dogs that were immunized against PIV5. We found that vaccination of the dogs containing neutralizing antibodies against PIV5 with rPIV5-H3 generated immunity against influenza A virus, indicting that PIV5-based vaccine is immunogenic in dogs with prior exposure. Furthermore, we have examined exposure of PIV5 in human populations. We have detected neutralizing antibody (nAb) against PIV5 in 13 out of 45 human serum samples (about 29 percent). The nAb titers in humans were lower than that in vaccinated dogs, suggesting that nAb in humans is unlikely to prevent PIV5 from being an efficacious vector in humans.

Recombinant parainfluenza virus 5 expressing hemagglutinin of influenza A virus H5N1 protected mice against lethal highly pathogenic avian influenza virus H5N1 challenge

A safe and effective vaccine is the best way to prevent large-scale highly pathogenic avian influenza virus (HPAI) H5N1 outbreaks in the human population. The current FDA-approved H5N1 vaccine has serious limitations. A more efficacious H5N1 vaccine is urgently needed. Parainfluenza virus 5 (PIV5), a paramyxovirus, is not known to cause any illness in humans. PIV5 is an attractive vaccine vector. In our studies, a single dose of a live recombinant PIV5 expressing a hemagglutinin (HA) gene of H5N1 (rPIV5-H5) from the H5N1 subtype provided sterilizing immunity against lethal doses of HPAI H5N1 infection in mice. Furthermore, we have examined the effect of insertion of H5N1 HA at different locations within the PIV5 genome on the efficacy of a PIV5-based vaccine. Interestingly, insertion of H5N1 HA between the leader sequence, the de facto promoter of PIV5, and the first viral gene, nucleoprotein (NP), did not lead to a viable virus. Insertion of H5N1 HA between NP and the next gene, V/phosphorprotein (V/P), led to a virus that was defective in growth. We have found that insertion of H5N1 HA at the junction between the small hydrophobic (SH) gene and the hemagglutinin-neuraminidase (HN) gene gave the best immunity against HPAI H5N1 challenge: a dose as low as 1,000 PFU was sufficient to protect against lethal HPAI H5N1 challenge in mice. The work suggests that recombinant PIV5 expressing H5N1 HA has great potential as an HPAI H5N1 vaccine.

Comparison of differing cytopathic effects in human airway epithelium of parainfluenza virus 5 (W3A), parainfluenza virus type 3, and respiratory syncytial virus

Parainfluenza virus 5 (PIV5) infects a wide range of animals including dogs, pigs, cats, and humans; however, its association with disease in humans remains controversial. In contrast to parainfluenza virus 3 (PIV3) or respiratory syncytial virus (RSV), PIV5 is remarkably non-cytopathic in monolayer cultures of immortalized epithelial cells. To compare the cytopathology produced by these viruses in a relevant human tissue, we infected an in vitro model of human ciliated airway epithelium and measured outcomes of cytopathology. PIV5, PIV3 and, RSV all infected ciliated cells, and PIV5 and PIV3 infection was dependent on sialic acid residues. Only PIV5-infected cells formed syncytia. PIV5 infection resulted in a more rapid loss of infected cells by shedding of infected cells into the lumen. These studies revealed striking differences in cytopathology of PIV5 versus PIV3 or RSV and indicate the extent of cytopathology determined in cell-lines does not predict events in differentiated airway cells.

Parainfluenza virus 5-based vaccine vectors expressing vaccinia virus (VACV) antigens provide long-term protection in mice from lethal intranasal VACV challenge

To test the potential for parainfluenza virus 5 (PIV5)-based vectors to provide protection from vaccinia virus (VACV) infection, PIV5 was engineered to express secreted VACV L1R and B5R proteins, two important antigens for neutralization of intracellular mature (IMV) and extracellular enveloped (EEV) virions, respectively. Protection of mice from lethal intranasal VACV challenge required intranasal immunization with PIV5-L1R/B5R in a prime-boost protocol, and correlated with low VACV-induced pathology in the respiratory tract and anti-VACV neutralizing antibody. Mice immunized with PIV5-L1R/B5R showed some disease symptoms following VACV challenge such as loss of weight and hunching, but these symptoms were delayed and less severe than with unimmunized control mice. While immunization with PIV5 expressing B5R alone conferred at least some protection, the most effective immunization included the PIV5 vector expressing L1R alone or in combination with PIV5-B5R. PIV5-L1R/B5R vectors elicited protection from VACV challenge even when CD8+ cells were depleted, but not in the case of mice that were defective in B cell production. Mice were protected from VACV challenge out to at least 1.5 years after immunization with PIV5-L1R/B5R vectors, and showed significant levels of anti-VACV neutralizing antibodies. These results demonstrate the potential for PIV5-based vectors to provide long lasting protection against complex human respiratory pathogens such as VACV, but also highlight the need to understand mechanisms for the generation of strong immune responses against poorly immunogenic viral proteins.

Failure to activate the IFN-β promoter by a paramyxovirus lacking an interferon antagonist

It is generally thought that pathogen-associated molecular patterns (PAMPs) responsible for triggering interferon (IFN) induction are produced during virus replication and, to limit the activation of the IFN response by these PAMPs, viruses encode antagonists of IFN induction. Here we have studied the induction of IFN by parainfluenza virus type 5 (PIV5) at the single-cell level, using a cell line expressing GFP under the control of the IFN-β promoter. We demonstrate that a recombinant PIV5 (termed PIV5-VΔC) that lacks a functional V protein (the viral IFN antagonist) does not activate the IFN-β promoter in the majority of infected cells. We conclude that viral PAMPs capable of activating the IFN induction cascade are not produced or exposed during the normal replication cycle of PIV5, and suggest instead that defective viruses are primarily responsible for inducing IFN during PIV5 infection in this system.

Heterocellular induction of interferon by negative-sense RNA viruses

The infection of cells by RNA viruses is associated with the recognition of virus PAMPs (pathogen-associated molecular patterns) and the production of type I interferon (IFN). To counter this, most, if not all, RNA viruses encode antagonists of the IFN system. Here we present data on the dynamics of IFN production and response during developing infections by paramyxoviruses, influenza A virus and bunyamwera virus. We show that only a limited number of infected cells are responsible for the production of IFN, and that this heterocellular production is a feature of the infecting virus as opposed to an intrinsic property of the cells.

Analysis of parainfluenza virus-5 hemagglutinin-neuraminidase protein mutants that are blocked in internalization and degradation

The PIV-5 hemagglutinin-neuraminidase (HN) protein is a multifunctional protein with sialic acid binding, neuraminidase and fusion promotion activity. HN is internalized by clathrin-mediated endocytosis and degraded. HN lacks internalization signals in its cytoplasmic tail but a single glutamic acid present at residue 37 at the putative transmembrane/ectodomain boundary is critical. We rescued rPIV-5 with mutations E37D or E37K, which have been shown to impair or abolish HN internalization, respectively. These viruses exhibited growth properties similar to wild-type (wt) virus but are impaired for fitness in tissue culture. Biochemical analysis of HN activities showed differences between HN E37D and HN E37K in fusion promotion and incorporation of HN and F into virions. Furthermore, oligomeric analyses indicate that HN E37 mutants perturb the tetrameric organization of HN, probably by destabilizing the dimer-of-dimers interface.

Replication-independent activation of human plasmacytoid dendritic cells by the paramyxovirus SV5 Requires TLR7 and autophagy pathways

The paramyxovirus Simian Virus 5 (SV5) is a poor inducer of interferon (IFN) secretion in all cell types tested so far, including primary epithelial cells and primary human myeloid dendritic cells. SV5 is hypothesized to limit induction of antiviral responses through control of viral gene expression and production of the V protein antagonist. Plasmacytoid dendritic cells (pDCs) are known to uniquely express toll-like receptor (TLR)-7 and are a main producer of IFN-alpha among peripheral blood mononuclear cells in response to many viruses. Here, we tested whether SV5 would remain a poor inducer of IFN in primary human pDCs. The efficiency of SV5 infection of pDCs could be increased by an increasing multiplicity of infection. pDCs infected by both live and UV-inactivated SV5 induced large amounts of IFN-alpha secretion and resulted in upregulation of maturation markers CD80 and CD86. However, IL-6 secretion was not induced by SV5 infection. When TLR7 signaling was inhibited, SV5 induced less IFN secretion and CD80 expression, and there was a corresponding increase in number of infected cells. Similar effects were seen with inhibitors of cellular autophagy pathways, suggesting that the SV5 activation of pDC requires access to the cytoplasm and autophagic sampling of cytoplasmic contents. These results have implications for control of SV5 infections in vivo and for development of SV5 as a vaccine vector.

TLR3-dependent upregulation of RIG-I leads to enhanced cytokine production from cells infected with the parainfluenza virus SV5

Here we address the role of RIG-I and TLR3 in differential cytokine responses against Simian Virus 5 (SV5) and two distinct cytokine inducing SV5 mutants. IFN-beta and IL-6 secretion was induced by infection with P/V-CPI-, an SV5 mutant with P/V substitutions, and were reduced by either siRNA-mediated knockdown of RIG-I expression or by expression of a dsRNA-binding protein. TLR3 overexpression did not alter cytokine secretion induced by P/V-CPI- or by Le-(U5C, A14G), an SV5 promoter mutant. TLR3 signaling by addition of exogenously added dsRNA was not blocked by WT SV5 or either SV5 mutant. Unexpectedly, TLR3 activation in infected cells led to enhanced IL-8 secretion, which correlated with increased RIG-I expression. Dominant negative RIG-I and TRIF supported a model whereby TLR3 activation upregulates RIG-I expression and in turn hypersensitizes cells to RIG-I-mediated cytokine secretion. Implications for crosstalk between different innate immunity pathways in mounting antiviral responses to paramyxoviruses are discussed.

Mumps virus Enders strain is sensitive to interferon (IFN) despite encoding a functional IFN antagonist

Although the Enders strain of mumps virus (MuV) encodes a functional V protein that acts as an interferon (IFN) antagonist, in multi-cycle growth assays MuV Enders grew poorly in naïve ('IFN-competent' Hep2) cells but grew to high titres in 'IFN-compromised' Hep2 cells. Even so, the growth rate of MuV Enders was significantly slower in 'IFN-compromised' Hep2 cells when compared with its replication rate in Vero cells and with the replication rate of parainfluenza virus type 5 (a closely related paramyxovirus) in both naïve and 'IFN-compromised' Hep2 cells. This suggests that a consequence of slower growth is that the IFN system of naïve Hep2 cells can respond quickly enough to control the growth of MuV Enders. This is supported by the finding that rapidly growing variants of MuV Enders that were selected on 'IFN-compromised' Hep2 cells (i.e. in the absence of any selection pressure exerted by the IFN response) also grew to high titres on naïve Hep2 cells. Sequencing of the complete genome of one of these variants identified a single point mutation that resulted in a substitution of a conserved asparagine by histidine at position 498 of the haemagglutinin-neuraminidase protein, although this mutation was not present in all rapidly growing variants. These results support the concept that there is a race between the ability of a cell to detect and respond to virus infection and the ability of a virus to block the IFN response. Importantly, this emphasizes that factors other than viral IFN antagonists influence the sensitivity of viruses to IFN.

Role for the paramyxovirus genomic promoter in limiting host cell antiviral responses and cell killing

The parainfluenza virus simian virus 5 (SV5) is a poor inducer of innate immune responses. In contrast, the naturally occurring SV5 variant Wake Forest parainfluenza virus (WF-PIV) activates the synthesis of proinflammatory cytokines and beta interferon (IFN-beta). Comparison of SV5 and WF-PIV genome sequences revealed nine nucleotide differences within the viral genomic promoter, including two substitutions (U5C and A14G) in the most highly conserved 3'-end promoter element. To test the consequences of these promoter variations, a recombinant SV5 mutant [Le-(U5C, A14G)] was engineered to harbor the two WF-PIV genomic promoter substitutions in an otherwise wild-type (WT) SV5 background. Human lung epithelial cells infected with the Le-(U5C, A14G) mutant had higher rates of viral protein synthesis and levels of mRNA than cells infected with WT SV5, but levels of genomic RNA were not changed. Unlike WT SV5, the Le-(U5C, A14G) mutant was a potent inducer of interleukin-6 and IFN-beta synthesis, despite expressing a functional V protein antagonist. Cytokine responses to Le-(U5C, A14G) infection were reduced either by small interfering RNA-mediated knockdown of retinoic acid-inducible gene I (RIG-I) or after infection of cells that were engineered to express the reovirus sigma3 double-stranded RNA-binding protein. Le-(U5C, A14G) induced cytopathic effects not seen with WT SV5, and the extent of cell killing correlated with elevated levels of viral F protein and cell-cell fusion. Our results support a model whereby the SV5 promoter has evolved to function at an attenuated level in order to limit (i) synthesis of aberrant RNAs which induce RIG-I-mediated responses and (ii) overproduction of mRNA for potentially toxic gene products, such as the F protein. Control of genomic promoter activity may be particularly important for viruses such as SV5, that express a V protein targeting mda-5 but do not encode antagonists such as the paramyxovirus C proteins, that specifically target RIG-I.

Parainfluenza virus 5 genomes are located in viral cytoplasmic bodies whilst the virus dismantles the interferon-induced antiviral state of cells

Although the replication cycle of parainfluenza virus type 5 (PIV5) is initially severely impaired in cells in an interferon (IFN)-induced antiviral state, the virus still targets STAT1 for degradation. As a consequence, the cells can no longer respond to IFN and after 24−48 h, they go out of the antiviral state and normal virus replication is established. Following infection of cells in an IFN-induced antiviral state, viral nucleocapsid proteins are initially localized within small cytoplasmic bodies, and appearance of these cytoplasmic bodies correlates with the loss of STAT1 from infected cells. In situ hybridization, using probes specific for the NP and L genes, demonstrated the presence of virus genomes within these cytoplasmic bodies. These viral cytoplasmic bodies do not co-localize with cellular markers for stress granules, cytoplasmic P-bodies or autophagosomes. Furthermore, they are not large insoluble aggregates of viral proteins and/or nucleocapsids, as they can simply and easily be dispersed by ‘cold-shocking’ live cells, a process that disrupts the cytoskeleton. Given that during in vivo infections, PIV5 will inevitably infect cells in an IFN-induced antiviral state, we suggest that these cytoplasmic bodies are areas in which PIV5 genomes reside whilst the virus dismantles the antiviral state of the cells. Consequently, viral cytoplasmic bodies may play an important part in the strategy that PIV5 uses to circumvent the IFN system.

The paramyxoviruses simian virus 5 and mumps virus recruit host cell CD46 to evade complement-mediated neutralization

The complement system is a critical component of the innate immune response that all animal viruses must face during natural infections. Our previous results have shown that treatment of the paramyxovirus simian virus 5 (SV5) with human serum results in deposition of complement C3-derived polypeptides on virion particles. Here, we show that the virion-associated C3 component includes the inactive form iC3b, suggesting that SV5 may have mechanisms to evade the host complement system. Electron microscopy, gradient centrifugation, and Western blot analysis indicated that purified SV5 virions derived from human A549 cells contained CD46, a plasma membrane-expressed regulator of complement that acts as a cofactor for cleavage and inactivation of C3b into iC3b. In vitro cleavage assays with purified complement components showed that SV5 virions had C3b cofactor activity, resulting in specific factor I-mediated cleavage of C3b into inactive iC3b. SV5 particles generated in CHO cells, which do not express CD46, did not have cofactor activity. Conversely, virions derived from a CHO cell line that was engineered to overexpress human CD46 contained elevated levels of virion-associated CD46 and displayed enhanced C3b cofactor activity. In comparison with C3b, purified SV5 virions had very low cofactor activity against C4b, consistent with the known preference of CD46 for C3b versus C4b. Similar results were obtained for the closely related mumps virus (MuV), except that MuV particles derived from CHO-CD46 cells had higher C4b cofactor activity than SV5 virions. In neutralization assays with human serum, SV5 and MuV containing CD46 showed slower kinetics and more resistance to neutralization than SV5 and MuV that lacked CD46. Our results support a model in which the rubulaviruses SV5 and MuV incorporate cell surface complement inhibitors into progeny virions as a mechanism to limit complement-mediated neutralization.

Engineered expression of the TLR5 ligand flagellin enhances paramyxovirus activation of human dendritic cell function

The paramyxovirus simian virus 5 (SV5) is a poor activator of human dendritic cell (DC) maturation pathways in vitro, and infected DC do not upregulate cell surface costimulatory proteins or secretion of immunomodulatory cytokines. We evaluated the hypothesis that activation of SV5-infected DC would be enhanced by engineering SV5 to express a Toll-like-receptor (TLR) ligand. To test this hypothesis, a novel virus was engineered such that the gene encoding an intracellular form of the TLR5 ligand flagellin was expressed from the genome of wild-type (WT) SV5 (SV5-flagellin). Cells infected in vitro with the flagellin-expressing virus released low levels of biologically active flagellin, which was capable of stimulating TLR5 signaling. Infection of human peripheral blood mononuclear cell-derived immature DC with SV5-flagellin resulted in enhanced levels of interleukin-6 (IL-6) and IL-12 compared to infection with DC with the parental virus, WT SV5. In contrast to cytokine induction, the flagellin-expressing virus did not appreciably increase DC surface expression of the costimulatory molecule CD80 or CD86 above the level seen with WT SV5 alone. In mixed-culture assays, DC infected with the flagellin-expressing virus were more effective at activating gamma interferon secretion from both CD8(+) and CD4(+) allogeneic T cells than DC infected with WT SV5. Our results with SV5-directed intracellular expression of flagellin may be applicable to other vectors or pathogenic viruses where overcoming impairment of DC activation could contribute to the development of safer and more effective vaccines.

Paramyxovirus-induced shutoff of host and viral protein synthesis: role of the P and V proteins in limiting PKR activation

The paramyxovirus simian virus 5 (SV5) establishes highly productive persistent infections of epithelial cells without inducing a global inhibition of translation. Here we show that an SV5 mutant (the P/V-CPI(-) mutant) with substitutions in the P subunit of the viral polymerase and the accessory V protein also establishes highly productive infections like wild-type (WT) SV5 but that cells infected with the P/V-CPI(-) mutant show an overall shutdown of both host and viral translation at late times postinfection. Reduced host and viral protein synthesis with the P/V-CPI(-) virus was not due to lower levels of mRNA or caspase-dependent apoptosis and correlated with phosphorylation of the translation initiation factor eIF-2alpha. WT SV5 was a poor activator of the eIF-2alpha kinase protein kinase R (PKR). By contrast, the P/V-CPI(-) mutant induced PKR phosphorylation, which correlated with the time course of translation inhibition but was independent of interferon signaling. In HeLa cells that expressed the PKR inhibitor influenza A virus NS1 or reovirus sigma3, the rate of host protein synthesis at late times after infection with the P/V-CPI(-) mutant was restored to approximately 50% that of control HeLa cells. By contrast, the rates of P/V-CPI(-) viral protein synthesis in HeLa cells expressing NS1 or sigma3 were dramatically enhanced, between 5- and 20-fold, while levels of viral mRNA were increased only slightly (NS1-expressing cells) or remained constant (sigma3-expressing cells). Similar results were found using HeLa cells where PKR levels were reduced due to knockdown by small interfering RNA. Expression of either the WT P or the WT V protein from the genome of the P/V-CPI(-) mutant resulted in lower levels of PKR activation and rates of host and viral protein synthesis that closely matched those seen with WT SV5. Despite higher rates of translation, cells infected with the V- or P-complemented virus accumulated viral mRNAs to lower levels than that seen with the parental P/V-CPI(-) mutant. We present a model in which the paramyxovirus P/V gene products limit induction of PKR by limiting the synthesis of aberrant viral mRNAs and double-stranded RNA and thus prevent the shutdown of translation by a mechanism that differs from that of other PKR inhibitors such as NS1 and sigma3.

Role for the phosphoprotein P subunit of the paramyxovirus polymerase in limiting induction of host cell antiviral responses

Six amino acid substitutions in the shared N-terminal region of the P subunit of the viral polymerase and the accessory V protein convert the noncytopathic paramyxovirus simian virus 5 (SV5), which is a poor inducer of host cell responses, into a P/V mutant (P/V-CPI-) that induces high levels of apoptosis, interferon-beta (IFN-beta), and proinflammatory cytokines. In this study, we addressed the question of whether these new mutant phenotypes are due to the presence of an altered P protein or of an altered V protein or of both proteins. By the use of the P/V-CPI- mutant as a backbone, new mutant viruses were engineered to express the wild-type (WT) V protein (+V-wt) or WT P protein (+P-wt) from an additional gene inserted between the HN and L genes. In human epithelial cell lines, the +V-wt virus showed reduced activation of apoptosis and lower secretion of IFN-beta and proinflammatory cytokines compared to the parental P/V-CPI- virus. The presence of a V protein lacking the C-terminal cysteine-rich domain (corresponding to the SV5 I protein) did not reduce these host cell responses to P/V-CPI- infection. Unexpectedly, the +P-wt virus, which expressed a WT P subunit of the viral polymerase, also induced much lower levels of host cell responses than the parental P/V-CPI- mutant. For both +V-wt and +P-wt viruses, reduced levels of IFN-beta synthesis correlated with reduced IRF-3 dimerization and nuclear localization of IRF-3 and NF-kappaB, suggesting that the WT P and V proteins acted at an early stage in antiviral pathways. Host cell responses induced by the various P/V mutants directly correlated with levels of viral mRNA accumulation but not with steady-state levels of genomic RNA. Our results support the hypothesis that WT P and V proteins limit induction of antiviral responses by controlling the production of key viral inducers. A model is presented for the mechanism by which both the P subunit of the viral polymerase and the V accessory protein contribute to the ability of a paramyxovirus to limit activation of antiviral responses.

TLR-4 and -6 agonists reverse apoptosis and promote maturation of simian virus 5-infected human dendritic cells through NFkB-dependent pathways

Infection of primary cultures of human immature monocyte-derived dendritic cells (moDC) with the paramyxovirus Simian Virus 5 (SV5) results in extensive cytopathic effect (CPE) and induction of apoptosis, but DC maturation pathways are not activated. In this study, we investigated the relationship between SV5-induced apoptosis and the lack of DC maturation. Reducing CPE and apoptosis in SV5-infected immature DC by the addition of a pancaspase inhibitor resulted in only low level expression of maturation markers CD40, CD80 and CD86, suggesting that SV5 infection either actively blocked maturation pathways or failed to provide sufficient signals to activate maturation. To distinguish between these hypotheses, SV5-infected immature DC were challenged with agonists that stimulate toll-like receptors (TLRs). Treatment with the TLR-4 agonist LPS or TLR-6 agonist FSL1 enhanced cell surface expression of CD40, CD80 and CD86 on SV5-infected cells to levels approaching that of mock-infected TLR-treated moDC, but treatment with agonists for TLR-2, -3, -5 or -8 had little effect. Addition of TLR-4 or -6 agonists to SV5-infected DC also dramatically reduced CPE and apoptosis, but the levels of viral protein and virus yield were not affected. Similarly, SV5-infected immature moDC were matured by treatment with IL-1beta, and these mature infected cells also showed reduced CPE and apoptosis. In the presence of NFkB inhibitors, TLR-4 and -6 agonists did not promote maturation or reduce apoptosis of SV5-infected DC, indicating that maturation and cell survival were both dependent on signaling through NFkB-dependent pathways. Our results suggest a model whereby SV5 replication induces apoptosis in immature DC but fails to provide strong maturation signals, while activation of NFkB-dependent pathways by exogenous ligands can lead to moDC maturation and override SV5-induced cell death.

Mapuera virus, a rubulavirus that inhibits interferon signalling in a wide variety of mammalian cells without degrading STATs

Mapuera virus (MPRV) is a paramyxovirus that was originally isolated from bats, but its host range remains unknown. It was classified as a member of the genus Rubulavirus on the basis of structural and genetic features. Like other rubulaviruses it encodes a V protein (MPRV/V) that functions as an interferon (IFN) antagonist. Here we show that MPRV/V differs from the IFN antagonists of other rubulaviruses in that it does not induce the proteasomal degradation of STAT proteins, key factors in the IFN signalling cascade. Rather, MPRV/V prevents the nuclear translocation of STATs in response to IFN stimulation and inhibits the formation of the transcription factor complex ISGF3. We also show that MPRV/V blocks IFN signalling in cells from diverse mammalian species and discuss the IFN response as a barrier to cross-species infections.

Recombinant parainfluenza virus 5 (PIV5) expressing the influenza A virus hemagglutinin provides immunity in mice to influenza A virus challenge

Parainfluenza virus type 5 (PIV5), formerly known as simian virus 5 (SV5), is a non-segmented negative strand RNA virus that offers several advantages as a vaccine vector. PIV5 infects many cell types causing little cytopathic effect, it replicates in the cytoplasm of infected cells, and does not have a DNA phase in its life cycle thus avoiding the possibility of introducing foreign genes into the host DNA genome. Importantly, PIV5 can infect humans but it is not associated with any known human illness. PIV5 grows well in tissue culture cells, including Vero cells, which have been approved for vaccine production, and the virus can be obtained easily from the media. To test the feasibility of using PIV5 as a live vaccine vector, the hemagglutinin (HA) gene from influenza A virus strain A/Udorn/72 (H3N2) was inserted into the PIV5 genome as an extra gene between the hemagglutinin-neuraminidase (HN) gene and the large (L) polymerase gene. Recombinant PIV5 containing the HA gene of Udorn (rPIV5-H3) was recovered and it replicated similarly to wild type PIV5, both in vitro and in vivo. The HA protein expressed by rPIV5-H3-infected cells was incorporated into the virions and addition of the HA gene did not increase virus virulence in mice. The efficacy of rPIV5-H3 as a live vaccine was examined in 6-week-old BALB/c mice. The results show that a single dose inoculation provides broad and considerable immunity against influenza A virus infection.

Exchange of P/V genes between two non-cytopathic simian virus 5 variants results in a recombinant virus that kills cells through death pathways that are sensitive to caspase inhibitors

The paramyxovirus Simian virus 5 (SV5) is largely non-cytopathic in human epithelial and fibroblast cells. WF-PIV has been described previously as a naturally occurring SV5 variant that encodes P and V proteins differing from the wild-type (WT) SV5 proteins in eight and five amino acid positions, respectively. In this study, it is shown that WF-PIV is like WT SV5 by being largely non-cytopathic in A549 lung epithelial cells. However, substitution of the WF-PIV P/V gene into the background of WT SV5 resulted in a hybrid virus (P/V-WF) that induced apoptotic cell death not seen with either of the parental viruses. The kinetics of HeLa cell killing and induction of apoptosis by the P/V-WF chimera differed from those of the previously described P/V-CPI- chimera by being slower and less extensive. HeLa cell killing by the P/V-WF chimera was effectively reduced by inhibitors of caspase-9, but not of caspase-8. These results demonstrate that an exchange of P/V genes from two non-cytopathic SV5 variants can produce apoptosis-inducing chimeras, and that the role of the SV5 P/V gene products in limiting apoptosis can be dependent on expression in the context of a native viral genome.

A simian virus 5 (SV5) P/V mutant is less cytopathic than wild-type SV5 in human dendritic cells and is a more effective activator of dendritic cell maturation and function

Human epithelial cells infected with the parainfluenza virus simian virus 5 (SV5) show minimal activation of host cell interferon (IFN), cytokine, and cell death pathways. In contrast, a recombinant SV5 P/V gene mutant (rSV5-P/V-CPI-) overexpresses viral gene products and is a potent inducer of IFN, proinflammatory cytokines, and apoptosis in these cells. In this study, we have compared the outcomes of wild-type (WT) SV5 and rSV5-P/V-CPI- infections of primary human dendritic cells (DC), important antigen-presenting cells for initiating adaptive immune responses. We have tested the hypothesis that a P/V mutant which activates host antiviral responses will be a more potent inducer of DC maturation and function than WT rSV5, which suppresses host cell responses. Infection of peripheral blood mononuclear cell-derived immature DC with WT rSV5 resulted in high levels of viral protein and progeny virus but very little increase in cell surface costimulatory molecules or secretion of IFN and proinflammatory cytokines. In contrast, immature DC infected with the rSV5-P/V-CPI- mutant produced only low levels of viral protein and progeny virus, but these infected cells were induced to secrete IFN-alpha and other cytokines and showed elevated levels of maturation markers. Unexpectedly, DC infected with WT rSV5 showed extensive cytopathic effects and increased levels of active caspase-3, while infection of DC with the P/V mutant was largely noncytopathic. In mixed-culture assays, WT rSV5-infected DC were impaired in the ability to stimulate proliferation of autologous CD4+ T cells, whereas DC infected with the P/V mutant were very effective at activating T-cell proliferation. The addition of a pancaspase inhibitor to DC infected with WT rSV5 reduced cytopathic effects and resulted in higher surface expression levels of maturation markers. Our finding that the SV5 P/V mutant has both a reduced cytopathic effect in human DC compared to WT SV5 and an enhanced ability to induce DC function has implications for the rational design of novel recombinant paramyxovirus vectors based on engineered mutations in the viral P/V gene.

Function of small hydrophobic proteins of paramyxovirus

Mumps virus (MuV), a rubulavirus of the paramyxovirus family, causes acute infections in humans. MuV has seven genes including a small hydrophobic (SH) gene, which encodes a type I membrane protein of 57 amino acid residues. The function of the SH protein is not clear, although its expression is not necessary for growth of MuV in tissue culture cells. It is speculated that MuV SH plays a role in viral pathogenesis. Simian virus 5 (SV5), a closely related rubulavirus, encodes a 44-amino-acid-residue SH protein. Recombinant SV5 lacking the SH gene (rSV5DeltaSH) is viable and has no growth defect in tissue culture cells. However, rSV5DeltaSH induces apoptosis in tissue culture cells and is attenuated in vivo. Neutralizing antibodies against tumor necrosis factor alpha (TNF-alpha) and TNF-alpha receptor 1 block rSV5DeltaSH-induced apoptosis, suggesting that SV5 SH plays an essential role in blocking the TNF-alpha-mediated apoptosis pathway. Because MuV is closely related to SV5, we hypothesize that the SH protein of MuV has a function similar to that of SV5, even though there is no sequence homology between them. To test this hypothesis and to study the function of MuV SH, we have replaced the open reading frame (ORF) of SV5 SH with the ORF of MuV SH in a SV5 genome background. The recombinant SV5 (rSV5DeltaSH+MuV-SH) was analyzed in comparison with SV5. It was found that rSV5DeltaSH+MuV-SH was viable and behaved like wild-type SV5, suggesting that MuV SH has a function similar to that of SV5 SH. Furthermore, both ectopically expressed SV5 SH and MuV SH blocked activation of NF-kappaB by TNF-alpha in a reporter gene assay, suggesting that both SH proteins can inhibit TNF-alpha signaling.

The properties of recombinant Sendai virus having the P gene of Sendai virus pi strain derived from BHK cells persistently infected with Sendai virus

We prepared the chimeric recombinant Sendai virus [rSeV(Ppi)] by replacing the P gene of the Z strain with that of pi strain for analyzing the function of Ppi, Vpi and Cpi proteins. Intriguingly, HA production by rSeV(Ppi) is significantly lower at 38 degrees C than at 32 degrees C, showing that virus growth of rSeV(Ppi) is slightly suppressed at 38 degrees C. However, the main phenotypes of SeVpi, a marked temperature sensitivity as viral replication and an ability of establishing persistent infection, are not explained by the Ppi, Vpi and Cpi proteins. The V and C proteins form inclusion bodies in L929 cells infected with rSeV(Ppi) and incubated at 38 degrees C. L929 cells infected with rSeV(Ppi) and L929 cells stably expressing the Cpi protein show resistance to interferon-beta at 32 and 38 degrees C, indicating that the Cpi protein per se is not temperature-sensitive to inhibition of IFN signaling. The complete genome sequences of Sendai virus (SeV) pi and parent Nagoya strains were determined. Fifty nucleic acid substitutions are found in the genome sequence of SeV pi strain in comparison with Nagoya strain. There are three nucleic acid substitutions in the leader sequence, while the trailer, intergenic, gene-end and gene-start sequences of both strains are completely identical. Deletions and insertions of nucleotide are not found. There are 32 amino acid substitutions in Sendai virus pi strain. The specific amino acid substitutions unique to the SeVpi are 18. Information about the complete genome sequences of SeVpi strain is important to totally understand the persistent infection and lower pathogenicity of SeV.

Growth sensitivity of a recombinant simian virus 5 P/V mutant to type I interferon differs between tumor cell lines and normal primary cells

A paramyxovirus SV5 mutant (rSV5-P/V-CPI-) that encodes 6 naturally-occurring P/V gene substitutions is a potent inducer of type I interferon (IFN) and is restricted for low moi growth, two phenotypes not seen with WT SV5. In this study, we have compared the IFN sensitivity of WT SV5 and the rSV5-P/V-CPI- mutant in tumor cell lines and in cultures of normal primary cells. We have tested the hypothesis that differences in IFN induction elicited by WT rSV5 and rSV5-P/V-CPI- are responsible for differences in low moi growth and spread. In contrast to WT SV5, low moi infection of A549 lung carcinoma cells with rSV5-P/V-CPI- resulted in a plateau of virus production by 24-48 h pi when secreted IFN levels were between approximately 100 and 1000 U/ml. Gene microarray and RT-PCR analyses identified IFN genes and IFN-stimulated genes whose expression were increased by infection of A549 cells with WT and P/V mutant viruses. Restricted low moi growth and spread of rSV5-P/V-CPI- in A549 cells was relieved in the presence of neutralizing antibodies to IFN-beta but not TNF-alpha. When A549 or MDA-MB-435 breast tumor cells were pretreated with IFN, both WT and P/V mutant viruses showed delayed spread and approximately 10-fold reduction in virus yield, but infections were not eliminated. Using normal primary human epithelial cells that have undergone limited passage in culture, WT rSV5 and rSV5-P/V-CPI- displayed high moi growth properties that were similar to that seen in A549 cells. However, IFN pretreatment of these primary cells as well as normal human lung cells eliminated low moi spread of both mutant and WT rSV5 infections. Together, these data demonstrate that SV5 growth in normal primary human cells is highly sensitive to IFN compared to growth in some tumor cell lines, regardless of whether the P/V gene is WT or mutant. These results suggest a model in which spread of WT SV5 in normal human cells is dependent on the ability of the virus to prevent IFN synthesis. The implications of these results for the use of recombinant paramyxoviruses as vectors are discussed.

Early stage of establishment of persistent Sendai virus infection: unstable dynamic phase and then selection of viruses which are tightly cell associated, temperature sensitive, and capable of establishing persistent infection

We obtained 157 cloned cell lines persistently infected with Sendai virus; these cell lines were generated independently of each other. Infectious viruses could be isolated from 123 of these cloned cell lines by inoculation of culture fluids or infected cells into embryonated eggs. The majority of the viruses carried by cells persistently infected with viruses showed high cytotoxicity and did not have the ability to establish persistent infection. The association of carried virus with cells became stronger and virus isolation correspondingly became more difficult as cells persistently infected with virus were subcultured. Viruses derived from virus-infected cells eventually acquired the ability to establish persistent infection, although the ways in which the viruses acquired this ability varied. The viruses also acquired temperature sensitivity as persistently infected cells were subcultured. First, the hemagglutinin-neuraminidase and M proteins acquired temperature sensitivity, and then the polymerase(s) did so. The M proteins were localized in the nuclei of cells infected with cloned viruses that had the ability to establish persistent infection. Cells infected with viruses capable of establishing persistent infection showed no or slight staining by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling. Specific amino acid substitutions accumulated in the M protein and the L protein as virus-infected cells were subcultured. This study shows that there is an unstable dynamic phase at an early stage of the establishment of persistent Sendai virus infection (steady state), and then viruses capable of establishing persistent infection are selected.

Relationships and host range of human, canine, simian and porcine isolates of simian virus 5 (parainfluenza virus 5)

Sequence comparison of the V/P and F genes of 13 human, canine, porcine and simian isolates of simian virus 5 (SV5) revealed a surprising lack of sequence variation at both the nucleotide and amino acid levels (0–3 %), even though the viruses were isolated over 30 years and originated from countries around the world. Furthermore, there were no clear distinguishing amino acid or nucleotide differences among the isolates that correlated completely with the species from which they were isolated. In addition, there was no evidence that the ability of the viruses to block interferon signalling by targeting STAT1 for degradation was confined to the species from which they were isolated. All isolates had an extended cytoplasmic tail in the F protein, compared with the original W3A and WR monkey isolates. Sequence analysis of viruses that were derived from human bone-marrow cells isolated in London in the 1980s revealed that, whilst they were related more closely to one another than to the other isolates, they all had identifying differences, suggesting that they were independent isolates. These results therefore support previous data suggesting that SV5 can infect humans persistently, although the relationship of SV5 to any human disease remains highly contentious. Given that SV5 has been isolated on multiple occasions from different species, it is proposed that the term simian virus 5 is inappropriate and suggested that the virus should be renamed parainfluenza virus 5.

Accessory genes of the paramyxoviridae, a large family of nonsegmented negative-strand RNA viruses, as a focus of active investigation by reverse genetics

The Paramyxoviridae, a large family of nonsegmented negative-strand RNA viruses, comprises several genera each containing important human and animal pathogens. They possess in common six basal genes essential for viral replication and, in addition, a subset of accessory genes that are largely unique to each genus. These accessory genes are either encoded in one or more alternative overlapping frames of a basal gene, which are accessed transcriptionally or translationally, or inserted before or between the basal genes as one or more extra genes. However, the question of how the individual accessory genes contribute to actual viral replication and pathogenesis remained unanswered. It was not even established whether they are dispensable or indispensable for the viral life cycle. The plasmid-based reverse genetics of the full-length viral genome has now come into wide use to demonstrate that most, if not all, of these putative accessory genes can be disrupted without destroying viral infectivity, conclusively defining them as indeed dispensable accessory genes. Studies on the phenotypes of the resulting gene knockout viruses have revealed that the individual accessory genes greatly contribute specifically and additively to the overall viral fitness both in vitro and in vivo.

Apoptosis induction and interferon signaling but not IFN-beta promoter induction by an SV5 P/V mutant are rescued by coinfection with wild-type SV5

Infection of human cells with the paramyxovirus simian virus 5 (SV5) results in minimal cytopathic effect, and host interferon (IFN) and apoptotic pathways are not activated. We have previously shown that an rSV5 containing six naturally occurring P/V gene substitutions (rSV5-P/V-CPI-) displays premature and elevated expression of viral RNA and protein. In addition, cells infected with rSV5-P/V-CPI- show induction of the IFN-beta promoter as well as activation of IFN signaling and apoptotic pathways. In this article, we have tested the hypothesis that rSV5-WT can supply trans-acting factors that prevent host cell antiviral responses induced by rSV5-P/V-CPI-. During coinfection of human A549 cells, rSV5-WT blocked cell rounding, loss of cell volume, and DNA fragmentation induced by rSV5-P/V-CPI-, three later events in the apoptotic pathway, but was not able to block the loss of mitochondrial membrane potential (DeltaPsi(m)), an early event in the cell death process. As expected, IFN signaling was blocked during coinfections, and this was attributed to the loss of STAT1 induced by the rSV5-WT V protein. Surprisingly, simultaneous infection with rSV5-WT could not suppress the activation of the IFN-beta promoter by rSV5-P/V-CPI- infection. However, the IFN-beta promoter was not activated in cells that were first preinfected for 1 h with rSV5-WT and then subsequently infected with rSV5-P/V-CPI-. A model is proposed for activation of host responses to infection with the rSV5-P/V-CPI- mutant and the steps that are blocked by rSV5-WT.

Characterization of Sendai virus persistently infected L929 cells and Sendai virus pi strain: recombinant Sendai viruses having Mpi protein shows lower cytotoxicity and are incapable of establishing persistent infection

It is commonly accepted that the temperature-sensitive phenotype of Sendai virus (SeV) persistently infected cells is caused by the M and/or HN proteins. Expression level of the L, M, HN, and V proteins is extremely low in L929 cells persistently infected with SeVpi (L929/SeVpi cells) incubated at 38 degrees C. The HN protein quickly disappears in L929/SeVpi cells following a temperature shift up to 38 degrees C, and pulse-chase experiments show that the Lpi, HNpi, and Mpi proteins are unstable at 38 degrees C. Following a temperature shift either upward or downward, M protein is translocated into the nucleus and then localizes to the perinuclear region. None of virus-specific polypeptides are detected in the cells primarily infected with SeVpi and incubated at 38 degrees C and virus proteins are not pulse-labeled at 38 degrees C, indicating that temperature-sensitive step is at an early stage of infection. The Mpi protein is transiently located in the nucleus of the SeVpi primarily infected cells. Recombinant SeVs possessing the HNpi or/and Mpi proteins are not temperature-sensitive. The HN protein is expressed at very low levels and the F protein localizes to the perinuclear region in rSeV(Mpi)-infected cells incubated at 38 degrees C for 18 h. rSeVs having the Mpi protein exhibit lower cytotoxicity and are incapable of establishing persistent infection. Amino acid 116 of the Mpi protein is related to the nuclear translocation and lower cytopathogenesis, whereas aa183 is involved in the interaction between M protein and viral glycoproteins.

Isolation and partial characterization of a novel paramyxovirus from the gills of diseased seawater-reared Atlantic salmon (Salmo salar L)

A formerly undescribed virus has been isolated from the gills of farmed Atlantic salmon post-smolts in Norway suffering from gill disease. Cytopathic effects appeared in RTgill-W1 cells 9 weeks post-inoculation with gill tissue material. Virus production continued for an extended period thereafter. Light and electron microscopic examination revealed inclusions and replication in the cytoplasm. The viral nucleocapsid consisted of approximately 17 nm thick filaments in a herringbone pattern. Certain areas of the plasma membrane were thickened by the alignment of nucleocapsids on the internal surface and projections of 10 nm long viral glycoprotein spikes on the external surface. Virus assembly and release was achieved by budding through the modified plasma membrane. Negatively stained virions were spherical and partly pleomorphic with a diameter of 150-300 nm as seen by electron microscopy. The virus was sensitive to chloroform, heat and low and high pH, and replication was not inhibited by Br-dU or IdU indicating an RNA genome. Both haemagglutination and receptor-destroying enzyme activity were associated with the virions and the formation of syncytia in infected cultures indicated fusion activity. The receptor-destroying enzyme was identified as neuraminidase. The virus contained five major structural polypeptides with estimated molecular masses of 70, 62, 60, 48 and 37 kDa. Its buoyant density was 1.18-1.19 g ml(-1) in CsCl gradients. From the observed properties we conclude that this new virus belongs to the Paramyxoviridae and suggest the name Atlantic salmon paramyxovirus (ASPV). Furthermore, replication occurred at 6-21 degrees C, suggesting a host range confined to cold-blooded animals.

Induction of apoptosis by paramyxovirus simian virus 5 lacking a small hydrophobic gene

Simian virus 5 (SV5) is a member of the paramyxovirus family, which includes emerging viruses such as Hendra virus and Nipah virus as well as many important human and animal pathogens that have been known for years. SV5 encodes eight known viral proteins, including a small hydrophobic integral membrane protein (SH) of 44 amino acids. SV5 without the SH gene (rSV5deltaSH) is viable, and growth of rSV5deltaSH in tissue culture cells and viral protein and mRNA production in rSV5deltaSH-infected cells are indistinguishable from those of the wild-type SV5 virus. However, rSV5deltaSH causes increased cytopathic effect (CPE) and apoptosis in MDBK cells and is attenuated in vivo, suggesting the SH protein plays an important role in SV5 pathogenesis. How rSV5deltaSH induces apoptosis in infected cells has been examined in this report. Tumor necrosis factor alpha (TNF-alpha), a proinflammatory cytokine, was detected in culture media of rSV5deltaSH-infected cells. Apoptosis induced by rSV5deltaSH was inhibited by neutralizing antibodies against TNF-alpha and TNF-alpha receptor 1 (TNF-R1), suggesting that TNF-alpha played an essential role in rSV5deltaSH-induced apoptosis in a TNF-R1-dependent manner. Examination of important proteins in the TNF-alpha signaling pathway showed that p65, a major NF-kappaB subunit whose activation can lead to transcription of TNF-alpha, was first translocated to the nucleus and was capable of binding to DNA and then was targeted for degradation in rSV5deltaSH-infected cells while expression levels of TNF-R1 remained relatively constant. Thus, rSV5deltaSH induced cell death by activating TNF-alpha expression, possibly through activation of the NF-kappaB subunit p65 and then targeting p65 for degradation, leading to apoptosis.

The V proteins of simian virus 5 and other paramyxoviruses inhibit induction of interferon-beta

In this article we show that the paramyxovirus SV5 is a poor inducer of interferon-beta (IFN-beta). This inefficient induction is a consequence of the expression of an intact viral V protein. In the absence of the viral V protein cysteine-rich C-terminal domain, IFN-beta mRNA is strongly induced and the transcription factors NF-kappaB and IRF-3 are activated significantly. The V protein can work in isolation from SV5 to block intracellular dsRNA signaling. The mechanism of block to dsRNA signaling is distinct from that previously observed for blocking IFN signaling in that proteolysis of candidate factors cannot be detected, and furthermore, the respective blocks require distinct protein domains. Blocking of the induction of IFN-beta by dsRNA requires the C-terminal cysteine-rich domain, a feature that is highly conserved among paramyxoviruses. We demonstrate that the V proteins from other paramyxoviruses have equivalent functions and speculate that limiting the yield of IFN-beta during infection may be a general property of paramyxoviruses.