Respiratory syncytial virus: reverse genetics and vaccine strategies

Micro-Players of Great Significance-Host microRNA Signature in Viral Infections in Humans and Animals

Over time, more and more is becoming known about micro-players of great significance. This is particularly the case for microRNAs (miRNAs; miR), which have been found to participate in the regulation of many physiological and pathological processes in both humans and animals. One such process is viral infection in humans and animals, in which the host miRNAs—alone or in conjunction with the virus—interact on two levels: viruses may regulate the host’s miRNAs to evade its immune system, while the host miRNAs can play anti- or pro-viral roles. The purpose of this comprehensive review is to present the key miRNAs involved in viral infections in humans and animals. We summarize the data in the available literature, indicating that the signature miRNAs in human viral infections mainly include 12 miRNAs (i.e., miR-155, miR-223, miR-146a, miR-122, miR-125b, miR-132, miR-34a, miR -21, miR-16, miR-181 family, let-7 family, and miR-10a), while 10 miRNAs are commonly found in animals (i.e., miR-155, miR-223, miR-146a, miR-145, miR-21, miR-15a/miR-16 cluster, miR-181 family, let-7 family, and miR-122) in this context. Knowledge of which miRNAs are involved in different viral infections and the biological functions that they play can help in understanding the pathogenesis of viral diseases, facilitating the future development of therapeutic agents for both humans and animals.

Nasal-spraying Bacillus spores as an effective symptomatic treatment for children with acute respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a leading cause of Acute Respiratory Tract Infections (ARTIs) in young children. However, there is currently no vaccine or treatment available for children. Here, we demonstrated that nasal-spraying probiotics containing 5 billion of Bacillus spores (LiveSpo Navax) is an effective symptomatic treatment in a 6-day randomized controlled clinical study for RSV-infected children (n = 40–46/group). Navax treatment resulted in 1-day faster recovery-time and 10–50% better efficacy in relieving ARTI symptoms. At day 3, RSV load and level of pro-inflammatory cytokines in nasopharyngeal samples was reduced by 630 folds and 2.7–12.7 folds respectively. This showed 53-fold and 1.8–3.6-fold more effective than those in the control-standard of care-group. In summary, nasal-spraying Bacillus spores can rapidly and effectively relieve symptoms of RSV-induced ARTIs while exhibit strong impacts in reducing viral load and inflammation. Our nasal-spraying probiotics may provide a basis for simple-to-use, low-cost, and effective treatment against viral infection in general.

Avian Orthoavulavirus Type-1 as Vaccine Vector against Respiratory Viral Pathogens in Animal and Human

Avian orthoavulaviruses type-1 (AOaV-1) have recently transitioned from animal vaccine vector to a bona fide vaccine delivery vehicle in human. Owing to induction of robust innate and adaptive immune responses in mucus membranes in both birds and mammals, AOaVs offer an attractive vaccine against respiratory pathogens. The unique features of AOaVs include over 50 years of safety profile, stable expression of foreign genes, high infectivity rates in avian and mammalian hosts, broad host spectrum, limited possibility of recombination and lack of pre-existing immunity in humans. Additionally, AOaVs vectors allow the production of economical and high quantities of vaccine antigen in chicken embryonated eggs and several GMP-grade mammalian cell lines. In this review, we describe the biology of AOaVs and define protocols to manipulate AOaVs genomes in effectively designing vaccine vectors. We highlighted the potential and established portfolio of AOaV-based vaccines for multiple respiratory and non-respiratory viruses of veterinary and medical importance. We comment on the limitations of AOaV-based vaccines and propose mitigations strategies. The exploitation of AOaVs vectors is expanding at an exciting pace; thus, we have limited the scope to their use as vaccines against viral pathogens in both animals and humans.

New Insights into the Role of the Complement System in Human Viral Diseases

The complement system (CS) is part of the human immune system, consisting of more than 30 proteins that play a vital role in the protection against various pathogens and diseases, including viral diseases. Activated via three pathways, the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP), the complement system leads to the formation of a membrane attack complex (MAC) that disrupts the membrane of target cells, leading to cell lysis and death. Due to the increasing number of reports on its role in viral diseases, which may have implications for research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this review aims to highlight significant progress in understanding and defining the role of the complement system in four groups of diseases of viral etiology: (1) respiratory diseases; (2) acute liver failure (ALF); (3) disseminated intravascular coagulation (DIC); and (4) vector-borne diseases (VBDs). Some of these diseases already present a serious global health problem, while others are a matter of concern and require the collaboration of relevant national services and scientists with the World Health Organization (WHO) to avoid their spread.

Reversion mutations in phosphoprotein P of a codon-pair-deoptimized human respiratory syncytial virus confer increased transcription, immunogenicity, and genetic stability without loss of attenuation

Recoding viral genomes by introducing numerous synonymous nucleotide substitutions that create suboptimal codon pairs provides new live-attenuated vaccine candidates. Because recoding typically involves a large number of nucleotide substitutions, the risk of de-attenuation is presumed to be low. However, this has not been thoroughly studied. We previously generated human respiratory syncytial virus (RSV) in which the NS1, NS2, N, P, M and SH ORFs were codon-pair deoptimized (CPD) by 695 synonymous nucleotide changes (Min A virus). Min A exhibited a global reduction in transcription and protein synthesis, was restricted for replication in vitro and in vivo, and exhibited moderate temperature sensitivity. Here, we show that under selective pressure by serial passage at progressively increasing temperatures, Min A regained replication fitness and lost its temperature sensitivity. Whole-genome deep sequencing identified numerous missense mutations in several genes, in particular ones accumulating between codons 25 and 34 of the phosphoprotein (P), a polymerase cofactor and chaperone. When re-introduced into Min A, these P mutations restored viral transcription to wt level, resulting in increased protein expression and RNA replication. Molecular dynamic simulations suggested that these P mutations increased the flexibility of the N-terminal domain of P, which might facilitate its interaction with the nucleoprotein N, and increase the functional efficiency of the RSV transcription/replication complex. Finally, we evaluated the effect of the P mutations on Min A replication and immunogenicity in hamsters. Mutation P[F28V] paradoxically reduced Min A replication but not its immunogenicity. The further addition of one missense mutation each in M and L generated a version of Min A with increased genetic stability. Thus, this study provides further insight into the adaptability of large-scale recoded RNA viruses under selective pressure and identified an improved CPD RSV vaccine candidate.

Synonymous recoding of viral genomes by codon-pair deoptimization (CPD) generates live-attenuated vaccines presumed to be genetically stable due to the high number of nucleotide substitutions. However, their actual genetic stability under selective pressure was largely unknown. In a recoded human respiratory syncytial virus (RSV) mutant called Min A, six of 11 ORFs were CPD, reducing protein expression and inducing moderate temperature sensitivity and attenuation. When passaged in vitro under selective pressure, Min A lost its temperature-sensitive phenotype and regained fitness by the acquisition of numerous mutations, in particular missense mutations in the viral phosphoprotein (P), a polymerase cofactor and a chaperone for soluble nucleoprotein. These P mutations increased RSV gene transcription globally, thereby increasing RSV protein expression, RNA replication, and virus particle production. Thus, the P mutations increased the efficiency of the RSV transcription/replication complex, compensating for the reduced protein expression due to CPD. In addition, introduction of the P mutations into Min A generated a live-attenuated vaccine candidate with increased genetic stability. Surprisingly, this vaccine candidate exhibited increased attenuation and, paradoxically, exhibited increased immunogenicity per plaque-forming unit in hamsters. This study provides insights into the adaptability of large-scale recoded RNA viruses and identified an improved CPD RSV vaccine candidate.

Development of antibody against drug-resistant respiratory syncytial virus: Rapid detection of mutant virus using split superfolder green fluorescent protein-antibody system

Respiratory syncytial virus (RSV) infections are associated with severe bronchiolitis or pneumonia. Although palivizumab is used to prevent RSV infections, the occurrence of palivizumab-resistant RSV strains is increasing, and these strains pose a threat to public health. Herein, we report an antibody with affinity to the S275F RSV antigen, enabling the specific detection of palivizumab-resistant RSV strains. Experimental and simulation results confirmed the affinity of the antibody to the S275F RSV antigen. Furthermore, we developed a rapid S275F RSV antigen detection method using a split superfolder green fluorescent protein (ssGFP) that can interact with the antibody. In the presence of the mutant virus antigen, ssGFP emitted fluorescence within 1 min, allowing the rapid identification of S275F RSV. We anticipate that the developed antibody would be useful for the precise diagnosis of antiviral drug-resistant RSV strains and help treat patients with RSV infections.

Antiviral iridoid glycosides from Clerodendrum myricoides

The methanol root extract of Clerodendrum myricoides (Hochst.) Vatke afforded two new (1, 2) and two known (3, 4) iridoid glycosides. The structures of the isolated compounds were established based on NMR, IR, UV and MS data analyses. The crude extract and the isolated constituents were assayed for antiviral activity against the human respiratory syncytial virus (RSV) in human laryngeal epidermoid carcinoma (HEp-2) cells. The crude extract inhibited RSV infectivity at EC₅₀ = 0.21 μg/ml, while it showed cytotoxicity against HEp-2 cells with CC₅₀ = 9 μg/ml. Compound 2 showed 43.2% virus inhibition at 100 μM, while compounds 1 as well as 3 and 4 had only weak antiviral and cytotoxic activities.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

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.

Zinc binding activity of human metapneumovirus M2-1 protein is indispensable for viral replication and pathogenesis in vivo

Human metapneumovirus (hMPV) is a member of the Pneumovirinae subfamily in the Paramyxoviridae family that causes respiratory tract infections in humans. Unlike members of the Paramyxovirinae subfamily, the polymerase complex of pneumoviruses requires an additional cofactor, the M2-1 protein, which functions as a transcriptional antitermination factor. The M2-1 protein was found to incorporate zinc ions, although the specific role(s) of the zinc binding activity in viral replication and pathogenesis remains unknown. In this study, we found that the third cysteine (C21) and the last histidine (H25) in the zinc binding motif (CCCH) of hMPV M2-1 were essential for zinc binding activity, whereas the first two cysteines (C7 and C15) play only minor or redundant roles in zinc binding. In addition, the zinc binding motif is essential for the oligomerization of M2-1. Subsequently, recombinant hMPVs (rhMPVs) carrying mutations in the zinc binding motif were recovered. Interestingly, rhMPV-C21S and -H25L mutants, which lacked zinc binding activity, had delayed replication in cell culture and were highly attenuated in cotton rats. In contrast, rhMPV-C7S and -C15S strains, which retained 60% of the zinc binding activity, replicated as efficiently as rhMPV in cotton rats. Importantly, rhMPVs that lacked zinc binding activity triggered high levels of neutralizing antibody and provided complete protection against challenge with rhMPV. Taken together, these results demonstrate that zinc binding activity is indispensable for viral replication and pathogenesis in vivo. These results also suggest that inhibition of zinc binding activity may serve as a novel approach to rationally attenuate hMPV and perhaps other pneumoviruses for vaccine purposes.

IMPORTANCE

The pneumoviruses include many important human and animal pathogens, such as human respiratory syncytial virus (hRSV), hMPV, bovine RSV, and avian metapneumovirus (aMPV). Among these viruses, hRSV and hMPV are the leading causes of acute respiratory tract infection in infants and children. Despite major efforts, there is no antiviral or vaccine to combat these diseases. All known pneumoviruses encode a zinc binding protein, M2-1, which is a transcriptional antitermination factor. In this work, we found that the zinc binding activity of M2-1 is essential for virus replication and pathogenesis in vivo. Recombinant hMPVs that lacked zinc binding activity were not only defective in replication in the upper and lower respiratory tract but also triggered a strong protective immunity in cotton rats. Thus, inhibition of M2-1 zinc binding activity can lead to the development of novel, live attenuated vaccines, as well as antiviral drugs for pneumoviruses.

Rational design of human metapneumovirus live attenuated vaccine candidates by inhibiting viral mRNA cap methyltransferase

The paramyxoviruses human respiratory syncytial virus (hRSV), human metapneumovirus (hMPV), and human parainfluenza virus type 3 (hPIV3) are responsible for the majority of pediatric respiratory diseases and inflict significant economic loss, health care costs, and emotional burdens. Despite major efforts, there are no vaccines available for these viruses. The conserved region VI (CR VI) of the large (L) polymerase proteins of paramyxoviruses catalyzes methyltransferase (MTase) activities that typically methylate viral mRNAs at positions guanine N-7 (G-N-7) and ribose 2'-O. In this study, we generated a panel of recombinant hMPVs carrying mutations in the S-adenosylmethionine (SAM) binding site in CR VI of L protein. These recombinant viruses were specifically defective in ribose 2'-O methylation but not G-N-7 methylation and were genetically stable and highly attenuated in cell culture and viral replication in the upper and lower respiratory tracts of cotton rats. Importantly, vaccination of cotton rats with these recombinant hMPVs (rhMPVs) with defective MTases triggered a high level of neutralizing antibody, and the rats were completely protected from challenge with wild-type rhMPV. Collectively, our results indicate that (i) amino acid residues in the SAM binding site in the hMPV L protein are essential for 2'-O methylation and (ii) inhibition of mRNA cap MTase can serve as a novel target to rationally design live attenuated vaccines for hMPV and perhaps other paramyxoviruses, such as hRSV and hPIV3.

IMPORTANCE

Human paramyxoviruses, including hRSV, hMPV, and hPIV3, cause the majority of acute upper and lower respiratory tract infections in humans, particularly in infants, children, the elderly, and immunocompromised individuals. Currently, there is no licensed vaccine available. A formalin-inactivated vaccine is not suitable for these viruses because it causes enhanced lung damage upon reinfection with the same virus. A live attenuated vaccine is the most promising vaccine strategy for human paramyxoviruses. However, it remains a challenge to identify an attenuated virus strain that has an optimal balance between attenuation and immunogenicity. Using reverse genetics, we generated a panel of recombinant hMPVs that were specifically defective in ribose 2'-O methyltransferase (MTase) but not G-N-7 MTase. These MTase-defective hMPVs were genetically stable and sufficiently attenuated but retained high immunogenicity. This work highlights a critical role of 2'-O MTase in paramyxovirus replication and pathogenesis and a new avenue for the development of safe and efficacious live attenuated vaccines for hMPV and other human paramyxoviruses.

The interactome of the human respiratory syncytial virus NS1 protein highlights multiple effects on host cell biology

Viral proteins can have multiple effects on host cell biology. Human respiratory syncytial virus (HRSV) nonstructural protein 1 (NS1) is a good example of this. During the virus life cycle, NS1 can act as an antagonist of host type I and III interferon production and signaling, inhibit apoptosis, suppress dendritic cell maturation, control protein stability, and regulate transcription of host cell mRNAs, among other functions. It is likely that NS1 performs these different roles through interactions with multiple host cell proteins. To investigate this and identify cellular proteins that could interact with NS1, we used quantitative proteomics in combination with green fluorescent protein (GFP)-trap immunoprecipitation and bioinformatic analysis. This analysis identified 221 proteins that were potentially part of complexes that could interact with NS1, with many of these associated with transcriptional regulation as part of the mediator complex, cell cycle regulation, and other functions previously assigned to NS1. Specific immunoprecipitation using the GFP trap was used to confirm the ability of selected cellular proteins to interact individually with NS1. Infection of A549 cells with recombinant viruses deficient in the expression of NS1 and overexpression analysis both demonstrated that NS1 was necessary and sufficient for the enrichment of cells in the G(1) phase of the cell cycle.

Progress in the development of human parainfluenza virus vaccines

In children under 5 years of age, human parainfluenza viruses (HPIVs) as a group are the second most common etiology of acute respiratory illness leading to hospitalization, surpassed only by respiratory syncytial virus but ahead of influenza viruses. Using reverse genetics systems for HPIV serotypes 1, 2 and 3 (HPIV1, 2 and 3), several live-attenuated HPIVs have been generated and evaluated as intranasal vaccines in adults and in children. Two vaccines against HPIV3 were found to be well tolerated, infectious and immunogenic in Phase I trials in HPIV3-seronegative infants and children and should progress to proof-of-concept trials. Vaccines against HPIV1 and HPIV2 are less advanced and have just entered pediatric trials.

Multiple functional domains and complexes of the two nonstructural proteins of human respiratory syncytial virus contribute to interferon suppression and cellular location

Human respiratory syncytial virus (RSV), a major cause of severe respiratory diseases, efficiently suppresses cellular innate immunity, represented by type I interferon (IFN), using its two unique nonstructural proteins, NS1 and NS2. In a search for their mechanism, NS1 was previously shown to decrease levels of TRAF3 and IKKε, whereas NS2 interacted with RIG-I and decreased TRAF3 and STAT2. Here, we report on the interaction, cellular localization, and functional domains of these two proteins. We show that recombinant NS1 and NS2, expressed in lung epithelial A549 cells, can form homo- as well as heteromers. Interestingly, when expressed alone, substantial amounts of NS1 and NS2 localized to the nuclei and to the mitochondria, respectively. However, when coexpressed with NS2, as in RSV infection, NS1 could be detected in the mitochondria as well, suggesting that the NS1-NS2 heteromer localizes to the mitochondria. The C-terminal tetrapeptide sequence, DLNP, common to both NS1 and NS2, was required for some functions, but not all, whereas only the NS1 N-terminal region was important for IKKε reduction. Finally, NS1 and NS2 both interacted specifically with host microtubule-associated protein 1B (MAP1B). The contribution of MAP1B in NS1 function was not tested, but in NS2 it was essential for STAT2 destruction, suggesting a role of the novel DLNP motif in protein-protein interaction and IFN suppression.

Replacement of previously circulating respiratory syncytial virus subtype B strains with the BA genotype in South Africa

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and pneumonia in infants, the immunocompromised, and the elderly in both developed and developing countries. Reinfections are common, and G protein variability is one mechanism to overcome herd immunity. This is illustrated by the appearance of the BA genotype with a 60-nucleotide duplication dominating the subtype B genotypes in epidemics worldwide. To investigate the evolution of subtype B in South Africa since 2002, the genetic variability of the G protein was analyzed in all recent strains isolated over 4 years (2006 to 2009) in South African hospitals. Bayesian analysis revealed a replacement of all subtype B genotypes previously identified in South Africa with the BA genotype since 2006, while subtype A genotypes identified in previous years are still circulating. Compared to BA strains from other countries, the evolutionary rate of the South African BA genotype was shown to be 2.305 × 10(-3) nucleotide substitutions/site/year and drift was evident. The most recent common ancestor (MRCA) of the South African BA viruses was determined to date back to 1996. All South African BA isolates clustered with the BA-IV subgenotype, and the appearance of new subgenotypes within this branch may occur if drift continues. Sequencing of the complete G protein of selected South African strains revealed an additional 6-nucleotide deletion. Acquisition of the 60-nucleotide duplication appeared to have improved the fitness of this virus, and more recent subtype B strains may need to be included in experimental vaccines to evaluate their efficacy in the current setting of evolved circulating strains.

Identification of deletion mutant respiratory syncytial virus strains lacking most of the G protein in immunocompromised children with pneumonia in South Africa

Respiratory syncytial virus (RSV) G protein deletion mutants replicate effectively in vitro but have not been detected in nature. Subtyping of RSV strains in hospitalized children in South Africa identified G protein PCR amplicons significantly reduced in size in 2 out of 209 clinical specimens screened over 4 years. Sequence analysis revealed subtype B strains lacking nearly the entire G protein ectodomain in one HIV-positive and one HIV-exposed child hospitalized with pneumonia. The association of clinical strains lacking most of the G protein with lower respiratory tract infection in immunocompromised children may have implications for RSV vaccine development.

T Cell receptor clonotype influences epitope hierarchy in the CD8+ T cell response to respiratory syncytial virus infection

CD8+ T cell responses are important for recognizing and resolving viral infections. To better understand the selection and hierarchy of virus-specific T cell responses, we compared the T cell receptor (TCR) clonotype in parent and hybrid strains of respiratory syncytial virus-infected mice. K(d)M2(82-90) (SYIGSINNI) in BALB/c and D(b)M(187-195) (NAITNAKII) in C57Bl/6 are both dominant epitopes in parent strains but assume a distinct hierarchy, with K(d)M2(82-90) dominant to D(b)M(187-195) in hybrid CB6F1/J mice. The dominant K(d)M2(82-90) response is relatively public and is restricted primarily to the highly prevalent Vβ13.2 in BALB/c and hybrid mice, whereas D(b)M(187-195) responses in C57BL/6 mice are relatively private and involve multiple Vβ subtypes, some of which are lost in hybrids. A significant frequency of TCR CDR3 sequences in the D(b)M(187-195) response have a distinct "(D/E)WG" motif formed by a limited number of recombination strategies. Modeling of the dominant epitope suggested a flat, featureless structure, but D(b)M(187-195) showed a distinctive structure formed by Lys(7). The data suggest that common recombination events in prevalent Vβ genes may provide a numerical advantage in the T cell response and that distinct epitope structures may impose more limited options for successful TCR selection. Defining how epitope structure is interpreted to inform T cell function will improve the design of future gene-based vaccines.

The synthetic bacterial lipopeptide Pam3CSK4 modulates respiratory syncytial virus infection independent of TLR activation

Respiratory syncytial virus (RSV) is an important cause of acute respiratory disease in infants, immunocompromised subjects and the elderly. However, it is unclear why most primary RSV infections are associated with relatively mild symptoms, whereas some result in severe lower respiratory tract infections and bronchiolitis. Since RSV hospitalization has been associated with respiratory bacterial co-infections, we have tested if bacterial Toll-like receptor (TLR) agonists influence RSV-A2-GFP infection in human primary cells or cell lines. The synthetic bacterial lipopeptide Pam3-Cys-Ser-Lys4 (Pam3CSK4), the prototype ligand for the heterodimeric TLR1/TLR2 complex, enhanced RSV infection in primary epithelial, myeloid and lymphoid cells. Surprisingly, enhancement was optimal when lipopeptides and virus were added simultaneously, whereas addition of Pam3CSK4 immediately after infection had no effect. We have identified two structurally related lipopeptides without TLR-signaling capacity that also modulate RSV infection, whereas Pam3CSK4-reminiscent TLR1/2 agonists did not, and conclude that modulation of infection is independent of TLR activation. A similar TLR-independent enhancement of infection could also be demonstrated for wild-type RSV strains, and for HIV-1, measles virus and human metapneumovirus. We show that the effect of Pam3CSK4 is primarily mediated by enhanced binding of RSV to its target cells. The N-palmitoylated cysteine and the cationic lysines were identified as pivotal for enhanced virus binding. Surprisingly, we observed inhibition of RSV infection in immortalized epithelial cell lines, which was shown to be related to interactions between Pam3CSK4 and negatively charged glycosaminoglycans on these cells, which are known targets for binding of laboratory-adapted but not wild-type RSV. These data suggest a potential role for bacterial lipopeptides in enhanced binding of RSV and other viruses to their target cells, thus affecting viral entry or spread independent of TLR signaling. Moreover, our results also suggest a potential application for these synthetic lipopeptides as adjuvants for live-attenuated viral vaccines.

Respiratory syncytial virus (RSV) infections are an important cause of hospitalization of infants during the winter season. However, RSV is often not the only detectable pathogen, but co-infections with respiratory bacteria are common. It has been hypothesized that this results from epithelial damage caused by the virus, facilitating colonization by pathogenic bacteria such as Streptococcus pneumoniae. However, an inverse order of events is not impossible: bacterial infections may activate respiratory epithelial cells through TLR signaling, resulting in increased susceptibility to virus infections. We tested this hypothesis by screening bacterial TLR agonists for their capacity to modulate RSV infection in different cell types, and identified the lipopeptide and prototype TLR1/2 agonist Pam3CSK4 as an enhancer of RSV infections. However, to our surprise this proved independent of TLR activation, but was mediated by enhancement of binding between virus and target cell. Two structurally related lipopeptides unable to stimulate TLR responses were identified that enhanced infections with RSV, but also with other enveloped viruses including HIV-1, human metapneumovirus, and measles virus. We speculate that bacterial infections may influence the pathogenesis of virus infections by facilitating binding to target cells.

Quantitative proteomic analysis of A549 cells infected with human respiratory syncytial virus

Human respiratory syncytial virus (HRSV) is a major cause of pediatric lower respiratory tract disease to which there is no vaccine or efficacious chemotherapeutic strategy. Although RNA synthesis and virus assembly occur in the cytoplasm, HRSV is known to induce nuclear responses in the host cell as replication alters global gene expression. Quantitative proteomics was used to take an unbiased overview of the protein changes in transformed human alveolar basal epithelial cells infected with HRSV. Underpinning this was the use of stable isotope labeling with amino acids in cell culture coupled to LC-MS/MS, which allowed the direct and simultaneous identification and quantification of both cellular and viral proteins. To reduce sample complexity and increase data return on potential protein localization, cells were fractionated into nuclear and cytoplasmic extracts. This resulted in the identification of 1,140 cellular proteins and six viral proteins. The proteomics data were analyzed using Ingenuity Pathways Analysis to identify defined canonical pathways and functional groupings. Selected data were validated using Western blot, direct and indirect immunofluorescence confocal microscopy, and functional assays. The study served to validate and expand upon known HRSV-host cell interactions, including those associated with the antiviral response and alterations in subnuclear structures such as the nucleolus and ND10 (promyelocytic leukemia bodies). In addition, novel changes were observed in mitochondrial proteins and functions, cell cycle regulatory molecules, nuclear pore complex proteins and nucleocytoplasmic trafficking proteins. These data shed light into how the cell is potentially altered to create conditions more favorable for infection. Additionally, the study highlights the application and advantage of stable isotope labeling with amino acids in cell culture coupled to LC-MS/MS for the analysis of virus-host interactions.

Respiratory syncytial virus grown in Vero cells contains a truncated attachment protein that alters its infectivity and dependence on glycosaminoglycans

Human respiratory syncytial virus (RSV) contains a heavily glycosylated 90-kDa attachment glycoprotein (G). Infection of HEp-2 and Vero cells in culture depends largely on virion G protein binding to cell surface glycosaminoglycans (GAGs). This GAG-dependent phenotype has been described for RSV grown in HEp-2 cells, but we have found that it is greatly reduced by a single passage in Vero cells. Virions produced from Vero cells primarily display a 55-kDa G glycoprotein. This smaller G protein represents a post-Golgi compartment form that is lacking its C terminus, indicating that the C terminus is required for GAG dependency. Vero cell-grown virus infected primary well-differentiated human airway epithelial (HAE) cell cultures 600-fold less efficiently than did HEp-2 cell-grown virus, indicating that the C terminus of the G protein is also required for virus attachment to this model of the in vivo target cells. This reduced infectivity for HAE cell cultures is not likely to be due to the loss of GAG attachment since heparan sulfate, the primary GAG used by RSV for attachment to HEp-2 cells, is not detectable at the apical surface of HAE cell cultures where RSV enters. Growing RSV stocks in Vero cells could dramatically reduce the initial infection of the respiratory tract in animal models or in volunteers receiving attenuated virus vaccines, thereby reducing the efficiency of infection or the efficacy of the vaccine.

Recombinant simian varicella viruses expressing respiratory syncytial virus antigens are immunogenic

Recombinant simian varicella viruses (rSVVs) were engineered to express respiratory syncytial virus (RSV) antigens. The RSV surface glycoprotein G and second matrix protein M2 (22k) genes were cloned into the SVV genome, and recombinant viruses were characterized in vitro and in vivo. rSVVs were also engineered to express the membrane-anchored or secreted forms of the RSV-G protein as well as an RSV G lacking its chemokine mimicry motif (CX3C), which may have different effects on priming the host immune response. The RSV genes were efficiently expressed in rSVV/RSV-infected Vero cells as RSV-G and -M2 transcripts were detected by RT-PCR, and RSV antigens were detected by immunofluorescence and immunoblot assays. The rSVVs replicated efficiently in Vero cell culture. Rhesus macaques immunized with rSVV/RSV-G and rSVV/RSV-M2 vaccines produced antibody responses to SVV and RSV antigens. The results demonstrate that recombinant varicella viruses are suitable vectors for the expression of RSV antigens and may represent a novel vaccine strategy for immunization against both pathogens.

Alphavirus replicon particles encoding the fusion or attachment glycoproteins of respiratory syncytial virus elicit protective immune responses in BALB/c mice and functional serum antibodies in rhesus macaques

Respiratory syncytial virus (RSV) is a major cause of acute respiratory tract disease in humans. Towards development of a prophylactic vaccine, we genetically engineered Venezuelan equine encephalitis virus (VEEV) replicons encoding the fusion (Fa) or attachment (Ga or Gb) proteins of the A or B subgroups of RSV. Intramuscular immunization with a formulation composed of equal amounts of each replicon particle (3vRSV replicon vaccine) generated serum neutralizing antibodies against A and B strains of RSV in BALB/c mice and rhesus macaques. When contrasted with purified natural protein or formalin-inactivated RSV formulated with alum, the 3vRSV replicon vaccine induced balanced Th1/Th2 T cell responses in mice. This was evident in the increased number of RSV-specific IFN-gamma(+) splenocytes following F or G peptide stimulation, diminished quantity of eosinophils and type 2 T cell cytokines in the lungs after challenge, and increased in vivo lysis of RSV peptide-loaded target cells. The immune responses in mice were also protective against intranasal challenge with RSV. Thus, the replicon-based platform represents a promising new strategy for vaccines against RSV.

Expression of RNA virus proteins by RNA polymerase II dependent expression plasmids is hindered at multiple steps

Background

Proteins of human and animal viruses are frequently expressed from RNA polymerase II dependent expression cassettes to study protein function and to develop gene-based vaccines. Initial attempts to express the G protein of vesicular stomatitis virus (VSV) and the F protein of respiratory syncytial virus (RSV) by eukaryotic promoters revealed restrictions at several steps of gene expression.

Results

Insertion of an intron flanked by exonic sequences 5'-terminal to the open reading frames (ORF) of VSV-G and RSV-F led to detectable cytoplasmic mRNA levels of both genes. While the exonic sequences were sufficient to stabilise the VSV-G mRNA, cytoplasmic mRNA levels of RSV-F were dependent on the presence of a functional intron. Cytoplasmic VSV-G mRNA levels led to readily detectable levels of VSV-G protein, whereas RSV-F protein expression remained undetectable. However, RSV-F expression was observed after mutating two of four consensus sites for polyadenylation present in the RSV-F ORF. Expression levels could be further enhanced by codon optimisation.

Conclusion

Insufficient cytoplasmic mRNA levels and premature polyadenylation prevent expression of RSV-F by RNA polymerase II dependent expression plasmids. Since RSV replicates in the cytoplasm, the presence of premature polyadenylation sites and elements leading to nuclear instability should not interfere with RSV-F expression during virus replication. The molecular mechanisms responsible for the destabilisation of the RSV-F and VSV-G mRNAs and the different requirements for their rescue by insertion of an intron remain to be defined.

Vaccination with recombinant modified vaccinia virus Ankara expressing bovine respiratory syncytial virus (bRSV) proteins protects calves against RSV challenge

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and calves. Bovine RSV (bRSV) is a natural pathogen for cattle, and bRSV infection in calves shares many features with the human infection. Thus, bRSV infection in cattle provides the ideal setting to evaluate the safety and efficacy of novel RSV vaccine strategies. Here, we have evaluated the efficacy and safety of modified vaccinia virus Ankara (rMVA)-based vaccine candidates, expressing the bovine RSV-F protein, either or not in combination with the G protein, in colostrums-deprived SPF calves born by caesarean section. Vaccination induced bRSV-specific IgG and CD8 T cell responses. Importantly, no IgE responses were detected. After bRSV challenge, rMVA vaccinated calves experienced less severe symptoms of lower respiratory tract disease compared to the mock-immunized control group. Immunized animals showed reduced pulmonary virus loads, and no eosinophilic infiltration or enhanced respiratory distress. In conclusion, candidate rMVA/bRSV vaccines induced protective and safe immune responses in calves.

Live vaccines for human metapneumovirus designed by reverse genetics

Human metapneumovirus (HMPV) was first described in 2001 and has quickly become recognized as an important cause of respiratory tract disease worldwide, especially in the pediatric population. A vaccine against HMPV is required to prevent severe disease associated with infection in infancy. The primary strategy is to develop a live-attenuated virus for intranasal immunization, which is particularly well suited against a respiratory virus. Reverse genetics provides a means of developing highly characterized 'designer' attenuated vaccine candidates. To date, several promising vaccine candidates have been developed, each using a different mode of attenuation. One candidate involves deletion of the G glycoprotein, providing attenuation that is probably based on reduced efficiency of attachment. A second candidate involves deletion of the M2-2 protein, which participates in regulating RNA synthesis and whose deletion has the advantageous property of upregulating transcription and increasing antigen synthesis. A third candidate involves replacing the P protein gene of HMPV with its counterpart from the related avian metapneumovirus, thereby introducing attenuation owing to its chimeric nature and host range restriction. Another live vaccine strategy involves using an attenuated parainfluenza virus as a vector to express HMPV protective antigens, providing a bivalent pediatric vaccine. Additional modifications to provide improved vaccines will also be discussed.

Viral infection of the lungs through the eye

Respiratory syncytial virus (RSV) is the foremost respiratory pathogen in newborns and claims millions of lives annually. However, there has been no methodical study of the pathway(s) of entry of RSV or its interaction with nonrespiratory tissues. We and others have recently established a significant association between allergic conjunctivitis and the presence of RSV in the eye. Here we adopt a BALB/c mouse model and demonstrate that when instilled in the live murine eye, RSV not only replicated robustly in the eye but also migrated to the lung and produced a respiratory disease that is indistinguishable from the standard, nasally acquired RSV disease. Ocularly applied synthetic anti-RSV small interfering RNA prevented infection of the eye as well as the lung. RSV infection of the eye activated a plethora of ocular cytokines and chemokines with profound relevance to inflammation of the eye. Anticytokine treatments in the eye reduced ocular inflammation but had no effect on viral growth in both eye and lung, demonstrating a role of the cytokine response in ocular pathology. These results establish the eye as a major gateway of respiratory infection and a respiratory virus as a bona fide eye pathogen, thus offering novel intervention and treatment options.

Unravelling the complexities of respiratory syncytial virus RNA synthesis

Human respiratory syncytial virus (RSV) is the leading cause of paediatric respiratory disease and is the focus of antiviral- and vaccine-development programmes. These goals have been aided by an understanding of the virus genome architecture and the mechanisms by which it is expressed and replicated. RSV is a member of the order Mononegavirales and, as such, has a genome consisting of a single strand of negative-sense RNA. At first glance, transcription and genome replication appear straightforward, requiring self-contained promoter regions at the 3' ends of the genome and antigenome RNAs, short cis-acting elements flanking each of the genes and one polymerase. However, from these minimal elements, the virus is able to generate an array of capped, methylated and polyadenylated mRNAs and encapsidated antigenome and genome RNAs, all in the appropriate ratios to facilitate virus replication. The apparent simplicity of genome expression and replication is a consequence of considerable complexity in the polymerase structure and its cognate cis-acting sequences; here, our understanding of mechanisms by which the RSV polymerase proteins interact with signals in the RNA template to produce different RNA products is reviewed.

Formulation with CpG oligodeoxynucleotides increases cellular immunity and protection induced by vaccination of calves with formalin-inactivated bovine respiratory syncytial virus

Vaccination of calves with formalin-inactivated bovine respiratory syncytial virus (FI-BRSV) induces low levels of cellular immunity that may not be protective. Since inactivated and subunit vaccines formulated with CpG oligodeoxynucleotides (ODNs) have been shown to induce cellular immune responses, we studied the ability of a FI-BRSV vaccine formulated with CpG ODN to elicit cellular immunity against BRSV. Neonatal calves were immunized with FI-BRSV, FI-BRSV formulated with CpG ODN or medium and challenged with BRSV after two immunizations. Calves vaccinated with FI-BRSV formulated with CpG ODN developed increased numbers of IFN-gamma secreting cells in the peripheral blood and broncho-tracheal lymph nodes and enhanced BRSV-specific serum IgG2 in comparison to FI-BRSV immunized animals. Calves that received the FI-BRSV vaccine formulated with CpG ODN also experienced a reduction in the amount of BRSV in the lung tissue. Based on these observations, CpG ODN appears to be a suitable candidate adjuvant for inactivated BRSV vaccines.

Bovine respiratory syncytial virus lacking the virokinin or with a mutation in furin cleavage site RA(R/K)R109 induces less pulmonary inflammation without impeding the induction of protective immunity in calves

The BRSV fusion (F) protein is cleaved at two furin consensus sequence sites, resulting in the generation of disulphide-linked F1 and F2 subunits and the release of an intervening peptide of 27 amino acids (pep27), which is converted into a biologically active tachykinin (virokinin). The role of the virokinin and the importance of one of the furin cleavage sites, FCS-2 [RA(R/K)R109], in the pathogenesis of BRSV infection and in the subsequent development of immunity was studied in gnotobiotic calves infected with a recombinant BRSV (rBRSV) lacking pep27 (rBRSVdelta p27) or with rBRSV108/109, which contains two amino acid substitutions in FCS-2 (RANN109). Although replication of the mutant viruses and the parental wild-type (WT) rBRSV in the lungs was similar, the extent of gross and microscopic lesions induced by the mutant viruses was less than that induced by WT rBRSV. Furthermore, the numbers of eosinophils in the lungs of calves infected with the mutant viruses were significantly less than that in calves infected with WT virus. These observations suggest a role for the virokinin in the pathogenesis of BRSV infection. Following mucosal immunization with rBRSVdelta p27, the levels of BRSV-specific serum antibodies were similar to those induced by WT virus. In contrast, the level of neutralizing antibodies induced by rBRSV108/109 was 10-fold lower than that induced by WT virus. Nevertheless, resistance to BRSV challenge induced by the mutant and WT viruses was similar, suggesting that neither pep27 nor FCS-2 plays a major role in the induction of protective immunity.

The role of reverse genetics in the development of vaccines against respiratory viruses

Despite their significance, the only available vaccines against respiratory viruses are those for the prevention of influenza. Attempts have been made to produce vaccines against other respiratory viruses using traditional techniques, but have met with little success. Reverse genetics, although still a r-elatively new tool for the manipulation of negative-strand RNA viruses, has great potential for the preparation of vaccines against many of the common respiratory viruses. In the preparation of live vaccines, reverse genetics s-ystems allow the direct modification of the specific regions in the genomes of negative-stranded RNA viruses concerned with attenuation; the ultimate goal is the introduction of site-specific mutations through a cDNA intermediate in order to develop strains with the requisite attenuation, antigenic and growth properties needed in a vaccine. These techniques can also be used to disarm potentially highly pathogenic viruses, such as emerging H5N1 avian influenza viruses, in order to facilitate large-scale preparation of viruses for use in inactivated vaccines under conditions of manufacturing safety. Before these vaccines become available, residual issues concerned with intellectual property rights to the technology and its application will need to be resolved.

Protection against respiratory syncytial virus by a recombinant Newcastle disease virus vector

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract disease in infants and the elderly, but no safe and effective RSV vaccine is yet available. For reasons that are not well understood, RSV is only weakly immunogenic, and reinfection occurs throughout life. This has complicated the search for an effective live attenuated viral vaccine, and past trials with inactivated virus preparations have led to enhanced immunopathology following natural infection. We have tested the hypothesis that weak stimulation of innate immunity by RSV correlates with ineffective adaptive responses by asking whether expression of the fusion glycoprotein of RSV by Newcastle disease virus (NDV) would stimulate a more robust immune response to RSV than primary RSV infection. NDV is a potent inducer of both alpha/beta interferon (IFN-alpha/beta) production and dendritic cell maturation, while RSV is not. When a recombinant NDV expressing the RSV fusion glycoprotein was administered to BALB/c mice, they were protected from RSV challenge, and this protection correlated with a robust anti-F CD8+ T-cell response. The effectiveness of this vaccine construct reflects the differential abilities of NDV and RSV to promote dendritic cell maturation and is retained even in the absence of a functional IFN-alpha/beta receptor.

Overexpression of the M2-2 protein of respiratory syncytial virus inhibits viral replication

The M2-2 protein of respiratory syncytial virus (RSV) is involved in regulation of viral RNA transcription and replication. Encoded by the next-to-last gene of RSV, the M2-2 open reading frame (ORF) overlaps with the upstream M2-1 ORF, suggesting that the production of the M2-2 protein might be tightly regulated during virus replication. To evaluate the effect of M2-2 overexpression on RSV replication, the M2-2 gene was separated from M2-1 by leaving it at the position prior to the M2-1 or moving it to the promoter proximal position as an independent transcriptional unit in the RSV A2 genome. Although recombinant viruses bearing the shuffled M2-2 gene were recovered and expressed higher levels of M2-2, most of these viruses grew poorly in HEp-2 cells. Sequence analysis revealed that various mutations (substitution, insertion, and deletion) occurred in the M2-2 gene, resulting in reduced M2-2 activity as measured by the RSV minigenome system. Further examination of the M2-2 sequence and its function showed that either one of the first two AUG codons located at the 5' end of M2-2 could be used to produce a functional M2-2 protein and that deletion of the first six amino acids from its N terminus or four amino acids from its C terminus greatly reduced its function. The effect of M2-2 protein on RSV replication was also studied by examining RSV replication in cells transiently expressing M2-2. The M2-2 protein expressed at a high level completely inhibited RSV replication. These results strongly suggested that the level of the M2-2 protein produced in the infected cells is critical to RSV replication.

Human parainfluenza virus 3 neuraminidase activity contributes to dendritic cell maturation

Mechanisms of dendritic cells (DCs) immunomodulation by parainfluenza viruses have not been characterized. We analyzed whether the human parainfluenza 3 (HPF3) virus hemagglutinin-neuraminidase glycoprotein (HN) might influence DC maturation. HN possesses a receptor binding function and a neuraminidase or desialidating activity. To assess whether the neuraminidase activity of HN affects DC maturation, human myeloid DCs were exposed to either live or UV-inactivated HPF3 viruses containing wild type or a mutated form of HN with decreased neuraminidase activity. Exposure of human DCs to either UV-inactivated or live virus induced up-regulation of CD83 and CD86 surface markers, morphological changes, and a cytokine expression pattern consistent with maturation. However, the level of maturation was found to be lower in DCs infected with the neuraminidase deficient variant as compared to the wild type. These results suggest that during the course of viral infection, HN's neuraminidase activity may play an important role contributing to maturation and activation of DCs.

Carriers for the delivery of a vaccine against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and pneumonia in young children and the elderly. Despite its clinical importance, there is no licensed vaccine available at present. Vaccine development has been hampered by observations of increased pathology after RSV infection in infants vaccinated with formalin-inactivated RSV; incomplete immunity following natural infection; and the need to be effective during the neonatal period when levels of maternal antibody are high. Four categories of RSV vaccine carriers--live-attenuated RSVs, recombinant vectors expressing the protective antigens of RSV, DNA vaccines and subunit vaccines--have been evaluated in animal models and/or clinical trials. So far, studies with live-attenuated virus vaccines highlight the need to improve immunogenicity whilst maintaining a suitable level of attenuation. Studies with recombinant vectors, DNA and subunit vaccines illustrate the pivotal nature of the vaccine carrier in determining the balance between immune-mediated protection against infection and the induction of immune-mediated pulmonary pathology.

Live-attenuated intranasal parainfluenza virus type 2 vaccine candidates developed by reverse genetics containing L polymerase protein mutations imported from heterologous paramyxoviruses

Live-attenuated recombinant human parainfluenza virus type 2 (rHPIV2) vaccine candidates were created using reverse genetics by importing known attenuating mutations in the L polymerase protein from heterologous paramyxoviruses into the homologous sites of the HPIV2 L protein. Four recombinants (rF460L, rY948H, rL1566I, and rS1724I) were recovered and three were attenuated for replication in hamsters. The genetic stability of the imported mutations at three of the four sites was enhanced by use of alternative codons or by deletion of a pair of amino acids. rHPIV2s bearing these modified mutations exhibited enhanced attenuation. The genetically stabilized mutations conferring a high level of attenuation will be useful in generating a live-attenuated virus vaccine for HPIV2.

Human parainfluenza virus type I (HPIV1) vaccine candidates designed by reverse genetics are attenuated and efficacious in African green monkeys

A set of recombinant, live attenuated human parainfluenza virus type 1 (rHPIV1) vaccine candidates was evaluated for attenuation, immunogenicity, and protective efficacy in African green monkeys (AGMs). Temperature sensitive (ts) and non-ts attenuating (att) mutations in the P/C and L genes were introduced individually or in various combinations into rHPIV1, including the C(R84G) and HN(T553A) mutations identified in the present work and the C(F170S), L(Y942A), and L(L992C) mutations identified previously. The rHPIV1 vaccine candidates exhibited a spectrum of attenuation in AGMs. One genetically and phenotypically stable vaccine candidate, rC(R84G/F170S)L(Y942A/L992C), was attenuated and efficacious in AGMs and is a promising live attenuated intranasal HPIV1 vaccine candidate suitable for clinical evaluation.

Live bivalent vaccine for parainfluenza and influenza virus infections

Influenza and human parainfluenza virus infections are of both medical and economical importance. Currently, inactivated vaccines provide suboptimal protection against influenza, and vaccines for human parainfluenza virus infection are not available, underscoring the need for new vaccines against these respiratory diseases. Furthermore, to reduce the burden of vaccination, the development of multivalent vaccines is highly desirable. Thus, to devise a single vaccine that would elicit immune responses against both influenza and parainfluenza viruses, we used reverse genetics to generate an influenza A virus that possesses the coding region for the hemagglutinin/neuraminidase ectodomain of parainfluenza virus instead of the influenza virus neuraminidase. The recombinant virus grew efficiently in eggs but was attenuated in mice. When intranasally immunized with the recombinant vaccine, all mice developed antibodies against both influenza and parainfluenza viruses and survived an otherwise lethal challenge with either of these viruses. This live bivalent vaccine has obvious advantages over combination vaccines, and its method of generation could, in principle, be applied in the development of a "cocktail" vaccine with efficacy against several different infectious diseases.

Rotavirus nonstructural protein 1 subverts innate immune response by inducing degradation of IFN regulatory factor 3

IFN regulatory factor 3 (IRF3), a constitutively expressed protein localizing largely to the cytoplasm, is a primary effector of the innate immune response. Infection can trigger the phosphorylation, dimerization, and nuclear translocation of IRF3, where the factor stimulates the expression and release of IFN. In this study, we determined that the rotavirus gene 5 product, nonstructural protein 1 (NSP1), interacts with IRF3 in the infected cell. To understand the importance of the interaction, we compared IRF3 activation by rotaviruses expressing wild-type and C-truncated forms of NSP1. The analysis showed that IRF3 underwent dimerization and nuclear translocation and stimulated IFN promoter activity in infected cells expressing truncated NSP1. In contrast, infected cells expressing wild-type NSP1 were characterized by the rapid degradation of IRF3 during the replication cycle, severe decreases in IRF3 dimerization and nuclear translocation, and lack of IFN promoter activity. The implication of these results, that wild-type NSP1 is an antagonist of the IFN-signaling pathway, was confirmed in transient expression assays, which showed that wild-type NSP1, but not the C-truncated protein, induced the degradation of IRF3 fusion proteins. Related experiments indicated that NSP1 mediates IRF3 degradation through a proteasome-dependent pathway. The critical role of NSP1 in promoting cell-to-cell spread of rotavirus was demonstrated by using gene 5-specific short interfering RNAs in plaque assays. Although several viruses have been described that subvert the innate immune response by preventing IRF3 activation, rotavirus is identified as one that accomplishes this task by inducing the degradation of IRF3.

Parainfluenza virus type 3 expressing the native or soluble fusion (F) Protein of Respiratory Syncytial Virus (RSV) confers protection from RSV infection in African green monkeys

Respiratory syncytial virus (RSV) causes respiratory disease in young children, the elderly, and immunocompromised individuals, often resulting in hospitalization and/or death. After more than 40 years of research, a Food and Drug Administration-approved vaccine for RSV is still not available. In this study, a chimeric bovine/human (b/h) parainfluenza virus type 3 (PIV3) expressing the human PIV3 (hPIV3) fusion (F) and hemagglutinin-neuraminidase (HN) proteins from an otherwise bovine PIV3 (bPIV3) genome was employed as a vector for RSV antigen expression with the aim of generating novel RSV vaccines. b/h PIV3 vaccine candidates expressing native or soluble RSV F proteins were evaluated for efficacy and immunogenicity in a nonhuman primate model. b/h PIV3 is suited for development of pediatric vaccines since bPIV3 had already been evaluated in clinical studies in 1- and 2-month-old infants and was found to be safe, immunogenic, and nontransmissible in a day care setting (Karron et al., Pediatr. Infect. Dis. J. 15:650-654, 1996; Lee et al., J. Infect. Dis. 184:909-913, 2001). African green monkeys immunized with b/h PIV3 expressing either the native or soluble RSV F protein were protected from challenge with wild-type RSV and produced RSV neutralizing and RSV F-protein specific immunoglobulin G serum antibodies. The PIV3-vectored RSV vaccines evaluated here further underscore the utility of this vector system for developing safe and immunogenic pediatric respiratory virus vaccines.

Vaccination of infant macaques with a recombinant modified vaccinia virus Ankara expressing the respiratory syncytial virus F and G genes does not predispose for immunopathology

We have evaluated the safety and immunogenicity of a recombinant modified vaccinia virus Ankara (MVA) vector expressing the respiratory syncytial virus (RSV) fusion (F) and attachment (G) proteins in infant macaques. Animals were vaccinated twice and 4 months later challenged with RSV. Although vaccination did not predispose for immunopathology upon challenge, we were also unable to demonstrate protection. Since vaccination had resulted in priming for secondary immune responses upon challenge, we suggest that vaccination efficacy will have to be improved by using MVA in a prime-boost strategy.

Functional antagonism of chemokine receptor CCR1 reduces mortality in acute pneumovirus infection in vivo

We present an antiviral-immunomodulatory therapeutic strategy involving the chemokine receptor antagonist Met-RANTES, which yields significant survival in the setting of an otherwise fatal respiratory virus infection. In previous work, we demonstrated that infection with the natural rodent pathogen pneumonia virus of mice involves robust virus replication accompanied by cellular inflammation modulated by the CC chemokine macrophage inflammatory protein 1alpha (MIP-1alpha). We found that the antiviral agent ribavirin limited virus replication in vivo but had no impact on morbidity and mortality associated with this disease in the absence of immunomodulatory control. We show here that ribavirin reduces mortality, from 100% to 10 and 30%, respectively, in gene-deleted CCR1(-/-) mice and in wild-type mice treated with the small-molecule chemokine receptor antagonist, Met-RANTES. As MIP-1alpha-mediated inflammation is a common response to several distantly related respiratory virus pathogens, specific antiviral therapy in conjunction with blockade of the MIP-1alpha/CCR1 inflammatory cascade may ultimately prove to be a useful, generalized approach to severe respiratory virus infection and its pathological sequelae in human subjects.

Vaccines for neonatal viral infections: Towards a live respiratory syncytial virus vaccine: a study in risk

There is risk attached to the development of respiratory syncytial virus vaccines, live attenuated or otherwise, but without the acceptance of this risk by manufacturers, health providers and the public, the conclusion of successful Phase III trials may lie in the distant future.

Recombinant respiratory syncytial viruses lacking the C-terminal third of the attachment (G) protein are immunogenic and attenuated in vivo and in vitro

The design of attenuated vaccines for respiratory syncytial virus (RSV) historically focused on viruses made sensitive to physiologic temperature through point mutations in the genome. These prototype vaccines were not suitable for human infants primarily because of insufficient attenuation, genetic instability, and reversion to a less-attenuated phenotype. We therefore sought to construct novel attenuated viruses with less potential for reversion through genetic alteration of the attachment G protein. Complete deletion of G protein was previously shown to result in RSV strains overly attenuated for replication in mice. Using reverse genetics, recombinant RSV (rRSV) strains were engineered with truncations at amino acid 118, 174, 193, or 213 and respectively designated rA2cpDeltaG118, rA2cpDeltaG174, rA2cpDeltaG193, and rA2cpDeltaG213. All rA2cpDeltaG strains were attenuated for growth in vitro and in the respiratory tracts of BALB/c mice but not restricted for growth at 37 degrees C. The mutations did not significantly affect nascent genome synthesis in human lung epithelial (A549) cells, but infectious rA2cpDeltaG virus shed into the culture medium was dramatically diminished. Hence, the data suggested that a site within the C-terminal 85 amino acids of G protein is important for efficient genome packaging or budding of RSV from the infected cell. Vaccination with the rA2cpDeltaG strains also generated efficacious immune responses in mice that were similar to those elicited by the temperature-sensitive cpts248/404 strain previously tested in human infants. Collectively, the data indicate that the rA2cpDeltaG strains are immunogenic, not likely to revert to the less-attenuated phenotype, and thus candidates for further development as vaccines against RSV.

Recovery of human metapneumovirus from cDNA: optimization of growth in vitro and expression of additional genes

Human metapneumovirus (HMPV) is a recently recognized causative agent of respiratory tract disease in individuals of all ages and especially young infants. HMPV remains poorly characterized and has been reported to replicate inefficiently in vitro. Complete consensus sequences were recently determined for two isolates representing the two proposed HMPV genetic subgroups. We have developed a reverse genetic system to produce one of these isolates, CAN97-83, entirely from cDNA. We also recovered a version, rHMPV-GFP, in which the enhanced green fluorescent protein (GFP) was expressed from a transcription cassette inserted as the first gene, leaving the 41-nt leader region and first 16 nt of the N gene undisturbed. The ability to monitor GFP expression in living cells greatly facilitated the initial recovery of this slow-growing virus. In addition, the ability to express a foreign gene from an engineered transcription cassette confirmed the identification of the HMPV transcription signals and identified the F gene-end signal as being highly efficient for transcription termination. The ability to recover virus containing a foreign insert in this position indicated that the viral promoter is contained within the 3'-terminal 57 nt of the genome. Recombinant HMPV replicated in vitro as efficiently as biologically derived HMPV, whereas the kinetics and final yield of rHMPV-GFP were reduced several-fold. Conditions for trypsin treatment were investigated, providing for improved virus yields. Another version of HMPV, rHMPV+G1F23, was recovered that contained a second copy of the G gene and two extra copies of F in promoter-proximal positions in the order G1-F2-F3. Thus, this recombinant genome would encode 11 mRNAs rather than eight and would be 17.3 kb long, 30% longer than that of the natural virus. Nonetheless, the rHMPV+G1F23 virus replicated in vitro with an efficiency that was only modestly reduced compared to rHMPV and was essentially the same as rHMPV-GFP. Northern blot analysis showed that the increased number and promoter-proximal location of the added copies of the F and G genes resulted in a more than 6- and 14-fold increase in the expression of F and G mRNA, respectively, and sequence analysis confirmed the intactness of the added genes in recovered virus. Thus, it should be feasible to construct an HMPV vaccine virus containing extra copies of the G and F putative protective antigen genes to increase antigen expression or to provide representation of additional antigenic lineages or subgroups of HMPV.

Suppression of the induction of alpha, beta, and lambda interferons by the NS1 and NS2 proteins of human respiratory syncytial virus in human epithelial cells and macrophages [corrected]

Wild-type human respiratory syncytial virus (HRSV) is a poor inducer of alpha/beta interferons (IFN-alpha/beta). However, recombinant HRSV lacking the NS1 and NS2 genes (Delta NS1/2) induced high levels of IFN-alpha and -beta in human pulmonary epithelial cells (A549) as well as in macrophages derived from primary human peripheral blood monocytes. Results with NS1 and NS2 single- and double-gene-deletion viruses indicated that the two proteins function independently as well as coordinately to achieve the full inhibitory effect, with NS1 having a greater independent role. The relative contributions of the individual NS proteins were the converse of that recently described for bovine RSV (J. F. Valarcher, J. Furze, S. Wyld, R. Cook, K. K. Conzelmann, and G. Taylor, J. Virol. 77:8426-8439, 2003). This pattern of inhibition by HRSV NS1 and NS2 also extended to the newly described antiviral cytokines IFN-lambda 1, -2 and -3.

Essential role of the NV protein of Novirhabdovirus for pathogenicity in rainbow trout

Novirhabdovirus, infectious hematopoietic necrosis virus (IHNV), and viral hemorrhagic septicemia virus (VHSV) are fish rhabdoviruses that, in comparison to the other rhabdoviruses, contain an additional gene coding for a small nonvirion (NV) protein of unassigned function. A recombinant IHNV with the NV gene deleted but expressing the green fluorescent protein (rIHNV-Delta NV) has previously been shown to be efficiently recovered by reverse genetics (S. Biacchesi et al., J. Virol. 74:11247-11253, 2000). However, preliminary experiments suggested that the growth in cell culture of rIHNV-Delta NV was affected by the NV deletion. In the present study, we show that the growth in cell culture of rIHNV-Delta NV is indeed severely impaired but that a normal growth of rIHNV-Delta NV can be restored when NV is provided in trans by using fish cell clones constitutively expressing the NV protein. These results indicate that NV is a protein that has a crucial biological role for optimal replication of IHNV in cell culture. Although IHNV and VHSV NV proteins do not share any significant identity, we show here that both NV proteins play a similar role since a recombinant IHNV virus, rIHNV-NV(VHSV), in which the IHNV NV open reading frame has been replaced by that of VHSV, was shown to replicate as well as the wild-type (wt) IHNV into fish cells. Finally, data provided by experimental fish infections with the various recombinant viruses strongly suggest an essential role of the NV protein for the pathogenicity of IHNV. Furthermore, we show that juvenile trout immunized with NV-knockout IHNV were protected against challenge with wt IHNV. That opens a new perspective for the development of IHNV attenuated live vaccines.

Animal pneumoviruses: molecular genetics and pathogenesis

Pneumoviruses are single-stranded, negative-sense, nonsegmented RNA viruses of the family Paramyxoviridae, subfamily Pneumovirinae, and include pathogens that infect humans (respiratory syncytial virus and human metapneumovirus), domestic mammals (bovine, ovine, and caprine respiratory syncytial viruses), rodents (pneumonia virus of mice), and birds (avian metapneumovirus). Among the topics considered in this review are recent studies focused on the roles of the individual virus-encoded components in promoting virus replication as well as in altering and evading innate antiviral host defenses. Advances in the molecular technology of pneumoviruses and the emergence of recombinant pneumoviruses that are leading to improved virus-based vaccine formulations are also discussed. Since pneumovirus infection in natural hosts is associated with a profound inflammatory response that persists despite adequate antiviral therapy, we also review the recent experimental treatment strategies that have focused on combined antiviral, anti-inflammatory, and immunomodulatory approaches.

Codon substitution mutations at two positions in the L polymerase protein of human parainfluenza virus type 1 yield viruses with a spectrum of attenuation in vivo and increased phenotypic stability in vitro

The Y942H and L992F temperature-sensitive (ts) and attenuating amino acid substitution mutations, previously identified in the L polymerase of the HPIV3cp45 vaccine candidate, were introduced into homologous positions of the L polymerase of recombinant human parainfluenza virus type 1 (rHPIV1). In rHPIV1, the Y942H mutation specified the ts phenotype in vitro and the attenuation (att) phenotype in hamsters, whereas the L992F mutation specified neither phenotype. Each of these codon mutations was generated by a single nucleotide substitution and therefore had the potential to readily revert to a codon specifying the wild-type amino acid residue. We introduced alternative amino acid assignments at codon 942 or 992 as a strategy to increase genetic stability and to generate mutants that exhibit a range of attenuation. Twenty-three recombinants with codon substitutions at position 942 or 992 of the L protein were viable. One highly ts and att mutant, the Y942A virus, which had a difference of three nucleotides from the codon encoding a wild-type tyrosine, also possessed a high level of genetic and phenotypic stability upon serial passage in vitro at restrictive temperatures compared to that of the parent Y942H virus, which possessed a single nucleotide substitution. We obtained mutants with substitutions at position 992 that, in contrast to the L992F virus, possessed the ts and att phenotypes. These findings identify the use of alternative codon substitution mutations as a method that can be used to generate candidate vaccine viruses with increased genetic stability and/or a modified level of attenuation.