New generation live vaccines against human respiratory syncytial virus designed by reverse genetics

Respiratory Syncytial Virus Vaccine Design Using Structure-Based Machine-Learning Models

When designing live-attenuated respiratory syncytial virus (RSV) vaccine candidates, attenuating mutations can be developed through biologic selection or reverse-genetic manipulation and may include point mutations, codon and gene deletions, and genome rearrangements. Attenuation typically involves the reduction in virus replication, due to direct effects on viral structural and replicative machinery or viral factors that antagonize host defense or cause disease. However, attenuation must balance reduced replication and immunogenic antigen expression. In the present study, we explored a new approach in order to discover attenuating mutations. Specifically, we used protein structure modeling and computational methods to identify amino acid substitutions in the RSV nonstructural protein 1 (NS1) predicted to cause various levels of structural perturbation. Twelve different mutations predicted to alter the NS1 protein structure were introduced into infectious virus and analyzed in cell culture for effects on viral mRNA and protein expression, interferon and cytokine expression, and caspase activation. We found the use of structure-based machine learning to predict amino acid substitutions that reduce the thermodynamic stability of NS1 resulted in various levels of loss of NS1 function, exemplified by effects including reduced multi-cycle viral replication in cells competent for type I interferon, reduced expression of viral mRNAs and proteins, and increased interferon and apoptosis responses.

Prevention and Treatment Strategies for Respiratory Syncytial Virus (RSV)

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease, especially in young children. Despite its global impact on healthcare, related to its high prevalence and its association with significant morbidity, the current therapy is still mostly supportive. Moreover, while more than 50 years have passed since the first trial of an RSV vaccine (which unfortunately caused enhanced RSV disease), no vaccine has been approved for RSV prevention. In the last two decades, our understanding of the pathogenesis and immunopathology of RSV have continued to evolve, leading to significant advancements in RSV prevention strategies. These include both the development of new potential vaccines and the successful implementation of passive immunization, which, together, will provide coverage from infancy to old age. In this review, we provide an update of the current treatment options for acute disease (RSV-specific and -non-specific) and different therapeutic approaches focusing on RSV prevention.

Reprogramming viral immune evasion for a rational design of next-generation vaccines for RNA viruses

Type I interferons (IFNs-α/β) are antiviral cytokines that constitute the innate immunity of hosts to fight against viral infections. Recent studies, however, have revealed the pleiotropic functions of IFNs, in addition to their antiviral activities, for the priming of activation and maturation of adaptive immunity. In turn, many viruses have developed various strategies to counteract the IFN response and to evade the host immune system for their benefits. The inefficient innate immunity and delayed adaptive response fail to clear of invading viruses and negatively affect the efficacy of vaccines. A better understanding of evasion strategies will provide opportunities to revert the viral IFN antagonism. Furthermore, IFN antagonism-deficient viruses can be generated by reverse genetics technology. Such viruses can potentially serve as next-generation vaccines that can induce effective and broad-spectrum responses for both innate and adaptive immunities for various pathogens. This review describes the recent advances in developing IFN antagonism-deficient viruses, their immune evasion and attenuated phenotypes in natural host animal species, and future potential as veterinary vaccines.

Predicted effectiveness of vaccines and extended half-life monoclonal antibodies against RSV hospitalizations in children

Several vaccines and extended half-life monoclonal antibodies (mAbs) against respiratory syncytial virus (RSV) have shown promise in clinical trials. We used age-structured transmission models to predict the possible impact of various RSV prevention strategies including maternal immunization, live-attenuated vaccines, and long-lasting mAbs. Our results suggest that maternal immunization and long-lasting mAbs are likely to be highly effective in preventing RSV hospitalizations in infants under 6 months of age, averting more than half of RSV hospitalizations in neonates. Live-attenuated vaccines could reduce RSV hospitalizations in vaccinated age groups and are also predicted to have a modest effect in unvaccinated age groups because of disruptions to transmission. Compared to year-round vaccination, a seasonal vaccination program at the country level provides at most a minor advantage regarding efficiency. Our findings highlight the substantial public health impact that upcoming RSV prevention strategies may provide.

Preventive Strategies for Respiratory Syncytial Virus Infection in Young Infants

Respiratory syncytial virus (RSV) is the leading cause of acute viral lower respiratory tract infections in young children, with the peak of severe disease occurring in infants younger than 6 months of age. Most infants who develop severe RSV infection are born full-term and previously healthy; however, premature infants represent an especially vulnerable population at high risk of developing serious sequelae because of RSV. Despite the high disease burden, the pathogenesis of the disease is not completely understood, treatment options are limited to supportive care, and no licensed vaccines are available.The young age of children affected by severe disease and incomplete understanding of the disease pathogenesis, along with prior vaccine failures, have represented major obstacles to RSV vaccine development. Nevertheless, the increasingly recognized burden associated with RSV in low-middle income countries, where RSV represents the second cause of infant mortality, has made the development of preventive strategies for RSV a global health priority. Increased awareness, together with a better understanding of the viral structure and identification of new viral targets, has led to the development of newer RSV vaccines and monoclonal antibodies to confer protection to both preterm and term infants who represent the most vulnerable population for severe RSV disease.

Host Components Contributing to Respiratory Syncytial Virus Pathogenesis

Respiratory syncytial virus (RSV) is the most prevalent viral etiological agent of acute respiratory tract infection. Although RSV affects people of all ages, the disease is more severe in infants and causes significant morbidity and hospitalization in young children and in the elderly. Host factors, including an immature immune system in infants, low lymphocyte levels in patients under 5 years old, and low levels of RSV-specific neutralizing antibodies in the blood of adults over 65 years of age, can explain the high susceptibility to RSV infection in these populations. Other host factors that correlate with severe RSV disease include high concentrations of proinflammatory cytokines such as interleukins (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and thymic stromal lymphopoitein (TSLP), which are produced in the respiratory tract of RSV-infected individuals, accompanied by a strong neutrophil response. In addition, data from studies of RSV infections in humans and in animal models revealed that this virus suppresses adaptive immune responses that could eliminate it from the respiratory tract. Here, we examine host factors that contribute to RSV pathogenesis based on an exhaustive review of in vitro infection in humans and in animal models to provide insights into the design of vaccines and therapeutic tools that could prevent diseases caused by RSV.

Biology of Infection and Disease Pathogenesis to Guide RSV Vaccine Development

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease in young children and a substantial contributor to respiratory tract disease throughout life and as such a high priority for vaccine development. However, after nearly 60 years of research no vaccine is yet available. The challenges to developing an RSV vaccine include the young age, 2-4 months of age, for the peak of disease, the enhanced RSV disease associated with the first RSV vaccine, formalin-inactivated RSV with an alum adjuvant (FI-RSV), and difficulty achieving protection as illustrated by repeat infections with disease that occur throughout life. Understanding the biology of infection and disease pathogenesis has and will continue to guide vaccine development. In this paper, we review the roles that RSV proteins play in the biology of infection and disease pathogenesis and the corresponding contribution to live attenuated and subunit RSV vaccines. Each of RSV's 11 proteins are in the design of one or more vaccines. The G protein's contribution to disease pathogenesis through altering host immune responses as well as its role in the biology of infection suggest it can make a unique contribution to an RSV vaccine, both live attenuated and subunit vaccines. One of G's potential unique contributions to a vaccine is the potential for anti-G immunity to have an anti-inflammatory effect independent of virus replication. Though an anti-viral effect is essential to an effective RSV vaccine, it is important to remember that the goal of a vaccine is to prevent disease. Thus, other effects of the infection, such as G's alteration of the host immune response may provide opportunities to induce responses that block this effect and improve an RSV vaccine. Keeping in mind the goal of a vaccine is to prevent disease and not virus replication may help identify new strategies for other vaccine challenges, such as improving influenza vaccines and developing HIV vaccines.

Genetic variability human respiratory syncytial virus subgroups A and B in Turkey during six successive epidemic seasons, 2009-2015

Human respiratory syncytial virus (HRSV) is most important viral respiratory pathogen of acute lower respiratory tract infections in infants and young children worldwide. The circulating pattern and genetic characteristics in the HRSV attachment glycoprotein gene were investigated in Turkey during six consecutive seasons from 2009 to 2015. HRSVA was dominant in the all epidemic seasons except 2011‐2012 season. Partial sequences of the HVR2 region of the G gene of 479 HRSVA and 135 HRSVB were obtained. Most Turkish strains belonged to NA1, ON1, and BA9, which were the predominant genotypes circulating worldwide. Although three novel genotypes, TR‐A, TR‐BA1, and TR‐BA2, were identified, they were not predominant. Clinical data were available for 69 HRSV‐positive patients who were monitored due to acute lower respiratory tract illness. There were no significant differences in the clinical diagnosis, hospitalization rates, laboratory findings and treatment observed between the HRSVA and HRSVB groups, and co‐infections in this study. The major population afflicted by HRSV infections included infants and children between 13 and 24 months of age. We detected that the CB1, GB5, and THB strains clustered in the same branch with a bootstrap value of 100%. CB‐B and BA12 strains clustered in the same branch with a bootstrap value of 65%. The BA11 genotype was clustered in the BA9 genotype in our study. The present study may contribute on the molecular epidemiology of HRSV in Turkey and provide data for HRSV strains circulating in local communities and other regions worldwide.

The Central Conserved Region (CCR) of Respiratory Syncytial Virus (RSV) G Protein Modulates Host miRNA Expression and Alters the Cellular Response to Infection

Respiratory Syncytial Virus (RSV) infects respiratory epithelial cells and deregulates host gene expression by many mechanisms including expression of RSV G protein (RSV G). RSV G protein encodes a central conserved region (CCR) containing a CX3C motif that functions as a fractalkine mimic. Disruption of the CX3C motif (a.a. 182-186) located in the CCR of the G protein has been shown to affect G protein function in vitro and the severity of RSV disease pathogenesis in vivo. We show that infection of polarized Calu3 respiratory cells with recombinant RSV having point mutations in Cys173 and 176 (C173/176S) (rA2-GC12), or Cys186 (C186S) (rA2-GC4) is associated with a decline in the integrity of polarized Calu-3 cultures and decreased virus production. This is accompanied with downregulation of miRNAs let-7f and miR-24 and upregulation of interferon lambda (IFNλ), a primary antiviral cytokine for RSV in rA2-GC12/rA2-GC4 infected cells. These results suggest that residues in the cysteine noose region of RSV G protein can modulate IFN λ expression accompanied by downregulation of miRNAs, and are important for RSV G protein function and targeting.

A Respiratory Syncytial Virus Vaccine Vectored by a Stable Chimeric and Replication-Deficient Sendai Virus Protects Mice without Inducing Enhanced Disease

Respiratory syncytial virus (RSV) is a major cause of severe respiratory infections in children and elderly people, and no marketed vaccine exists. In this study, we generated and analyzed a subunit vaccine against RSV based on a novel genome replication-deficient Sendai virus (SeV) vector. We inserted the RSV F protein, known to be a genetically stable antigen, into our vector in a specific way to optimize the vaccine features. By exchanging the ectodomain of the SeV F protein for its counterpart from RSV, we created a chimeric vectored vaccine that contains the RSV F protein as an essential structural component. In this way, the antigen is actively expressed on the surfaces of vaccine particles in its prefusion conformation, and as recently reported for other vectored vaccines, the occurrence of silencing mutations of the transgene in the vaccine genome can be prevented. In addition, its active gene expression contributes to further stimulation of the immune response. In order to understand the best route of immunization, we compared vaccine efficacies after intranasal (i.n.) or intramuscular (i.m.) immunization of BALB/c mice. Via both routes, substantial RSV-specific immune responses were induced, consisting of serum IgG and neutralizing antibodies, as well as cytotoxic T cells. Moreover, i.n. immunization was also able to stimulate specific mucosal IgA in the upper and lower respiratory tract. In virus challenge experiments, animals were protected against RSV infection after both i.n. and i.m. immunization without inducing vaccine-enhanced disease. Above all, the replication-deficient SeV appeared to be safe and well tolerated.IMPORTANCE Respiratory syncytial virus (RSV) is a major cause of respiratory diseases in young children and elderly people worldwide. There is a great demand for a licensed vaccine. Promising existing vaccine approaches based on live-attenuated vaccines or viral vectors have suffered from unforeseen drawbacks related to immunogenicity and attenuation. We provide a novel RSV vaccine concept based on a genome replication-deficient Sendai vector that has many favorable vaccine characteristics. The specific vaccine design guarantees genetic stability of the transgene; furthermore, it supports a favorable presentation of the antigen, activating the adaptive response, features that other vectored vaccine approaches have often had difficulties with. Wide immunological and pathological analyses in mice confirmed the validity and efficacy of this approach after both parenteral and mucosal administration. Above all, this concept is suitable for initiating clinical studies, and it could also be applied to other infectious diseases.

Animal models of respiratory syncytial virus infection

Human respiratory syncytial virus (hRSV) is a major cause of respiratory disease and hospitalisation of infants, worldwide, and is also responsible for significant morbidity in adults and excess deaths in the elderly. There is no licensed hRSV vaccine or effective therapeutic agent. However, there are a growing number of hRSV vaccine candidates that have been developed targeting different populations at risk of hRSV infection. Animal models of hRSV play an important role in the preclinical testing of hRSV vaccine candidates and although many have shown efficacy in preclinical studies, few have progressed to clinical trials or they have had only limited success. This is, at least in part, due to the lack of animal models that fully recapitulate the pathogenesis of hRSV infection in humans. This review summarises the strengths and limitations of animal models of hRSV, which include those in which hRSV is used to infect non-human mammalian hosts, and those in which non-human pneumoviruses, such as bovine (b)RSV and pneumonia virus of mice (PVM) are studied in their natural host. Apart from chimpanzees, other non-human primates (NHP) are only semi-permissive for hRSV replication and experimental infection with large doses of virus result in little or no clinical signs of disease, and generally only mild pulmonary pathology. Other animal models such as cotton rats, mice, ferrets, guinea pigs, hamsters, chinchillas, and neonatal lambs are also only semi-permissive for hRSV. Nevertheless, mice and cotton rats have been of value in the development of monoclonal antibody prophylaxis for infants at high risk of severe hRSV infection and have provided insights into mechanisms of immunity to and pathogenesis of hRSV. However, the extent to which they predict hRSV vaccine efficacy and safety is unclear and several hRSV vaccine candidates that are completely protective in rodent models are poorly effective in chimpanzees and other NHP, such as African Green monkeys. Furthermore, interpretation of findings from many rodent and NHP models of vaccine-enhanced hRSV disease has been confounded by sensitisation to non-viral antigens present in the vaccine and challenge virus. Studies of non-human pneumoviruses in their native hosts are more likely to reflect the pathogenesis of natural hRSV infection, and experimental infection of calves with bRSV and of mice with PVM result in clinical disease and extensive pulmonary pathology. These animal models have not only been of value in studies on mechanisms of immunity to and the pathogenesis of pneumovirus infections but have also been used to evaluate hRSV vaccine concepts. Furthermore, the similarities between the epidemiology of bRSV in calves and hRSV in infants and the high level of genetic and antigenic similarity between bRSV and hRSV, make the calf model of bRSV infection a relevant model for preclinical evaluation of hRSV vaccine candidates which contain proteins that are conserved between hRSV and bRSV.

In Hot Pursuit of the First Vaccine Against Respiratory Syncytial Virus

Human respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infection, such as bronchiolitis, bronchitis, or pneumonia, in both infants and the elderly. Despite the global burden of diseases attributable to RSV infection, no clinically approved vaccine is available, and a humanized monoclonal antibody for prophylaxis is not readily affordable in developing countries. There are several hurdles to the successful development of RSV vaccines: immune-vulnerable target populations such as premature infants, pregnant women, and immunocompromised people; safety concerns associated with vaccine-enhanced diseases; repeated infection; and waning memory. To develop successful strategies for the prevention of RSV infection, it is necessary to understand the protective and pathologic roles of host immune responses to RSV infection. In this review, we will summarize the positive and negative relationship between RSV infection and host immunity and discuss strategies for the development of the first successful RSV vaccine.

Viral Inhibition of the IFN-Induced JAK/STAT Signalling Pathway: Development of Live Attenuated Vaccines by Mutation of Viral-Encoded IFN-Antagonists

The interferon (IFN) induced anti-viral response is amongst the earliest and most potent of the innate responses to fight viral infection. The induction of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) signalling pathway by IFNs leads to the upregulation of hundreds of interferon stimulated genes (ISGs) for which, many have the ability to rapidly kill viruses within infected cells. During the long course of evolution, viruses have evolved an extraordinary range of strategies to counteract the host immune responses in particular by targeting the JAK/STAT signalling pathway. Understanding how the IFN system is inhibited has provided critical insights into viral virulence and pathogenesis. Moreover, identification of factors encoded by viruses that modulate the JAK/STAT pathway has opened up opportunities to create new anti-viral drugs and rationally attenuated new generation vaccines, particularly for RNA viruses, by reverse genetics.

Immunogenicity and efficacy of alphavirus-derived replicon vaccines for respiratory syncytial virus and human metapneumovirus in nonhuman primates

Human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) are major causes of illness among children, the elderly, and the immunocompromised. No vaccine has been licensed for protection against either of these viruses. We tested the ability of two Venezuelan equine encephalitis virus-based viral replicon particle (VEE-VRP) vaccines that express the hRSV or hMPV fusion (F) protein to confer protection against hRSV or hMPV in African green monkeys. Animals immunized with VEE-VRP vaccines developed RSV or MPV F-specific antibodies and serum neutralizing activity. Compared to control animals, immunized animals were better able to control viral load in the respiratory mucosa following challenge and had lower levels of viral genome in nasopharyngeal and bronchoalveolar lavage fluids. The high level of immunogenicity and protective efficacy induced by these vaccine candidates in nonhuman primates suggest that they hold promise for further development.

Human Respiratory Syncytial Virus: Role of Innate Immunity in Clearance and Disease Progression

Human respiratory syncytial virus (HRSV) infections have worldwide records. The virus is responsible for bronchiolitis, pneumonia, and asthma in humans of different age groups. Premature infants, young children, and immunocompromised individuals are prone to severe HRSV infection that may lead to death. Based on worldwide estimations, millions of cases were reported in both developed and developing countries. In fact, HRSV symptoms develop mainly as a result of host immune response. Due to inability to establish long lasting adaptive immunity, HRSV infection is recurrent and hence impairs vaccine development. Once HRSV attached to the airway epithelia, interaction with the host innate immune components starts. HRSV interaction with pulmonary innate defenses is crucial in determining the disease outcome. Infection of alveolar epithelial cells triggers a cascade of events that lead to recruitment and activation of leukocyte populations. HRSV clearance is mediated by a number of innate leukocytes, including macrophages, natural killer cells, eosinophils, dendritic cells, and neutrophils. Regulation of these cells is mediated by cytokines, chemokines, and other immune mediators. Although the innate immune system helps to clear HRSV infection, it participates in disease progression such as bronchiolitis and asthma. Resolving the mechanisms by which HRSV induces pathogenesis, different possible interactions between the virus and immune components, and immune cells interplay are essential for developing new effective vaccines. Therefore, the current review focuses on how the pulmonary innate defenses mediate HRSV clearance and to what extent they participate in disease progression. In addition, immune responses associated with HRSV vaccines will be discussed.

Modulation of host adaptive immunity by hRSV proteins

Globally, the human respiratory syncytial virus (hRSV) is the major cause of lower respiratory tract infections (LRTIs) in infants and children younger than 2 years old. Furthermore, the number of hospitalizations due to LRTIs has shown a sustained increase every year due to the lack of effective vaccines against hRSV. Thus, this virus remains as a major public health and economic burden worldwide. The lung pathology developed in hRSV-infected humans is characterized by an exacerbated inflammatory and Th2 immune response. In order to rationally design new vaccines and therapies against this virus, several studies have focused in elucidating the interactions between hRSV virulence factors and the host immune system. Here, we discuss the main features of hRSV biology, the processes involved in virus recognition by the immune system and the most relevant mechanisms used by this pathogen to avoid the antiviral host response.

Advances and applications of molecular cloning in clinical microbiology

Molecular cloning is based on isolation of a DNA sequence of interest to obtain multiple copies of it in vitro. Application of this technique has become an increasingly important tool in clinical microbiology due to its simplicity, cost effectiveness, rapidity, and reliability. This review entails the recent advances in molecular cloning and its application in the clinical microbiology in the context of polymicrobial infections, recombinant antigens, recombinant vaccines, diagnostic probes, antimicrobial peptides, and recombinant cytokines. Culture-based methods in polymicrobial infection have many limitation, which has been overcome by cloning techniques and provide gold standard technique. Recombinant antigens produced by cloning technique are now being used for screening of HIV, HCV, HBV, CMV, Treponema pallidum, and other clinical infectious agents. Recombinant vaccines for hepatitis B, cholera, influenza A, and other diseases also use recombinant antigens which have replaced the use of live vaccines and thus reduce the risk for adverse effects. Gene probes developed by gene cloning have many applications including in early diagnosis of hereditary diseases, forensic investigations, and routine diagnosis. Industrial application of this technology produces new antibiotics in the form of antimicrobial peptides and recombinant cytokines that can be used as therapeutic agents.

A comprehensive proteomic view of responses of A549 type II alveolar epithelial cells to human respiratory syncytial virus infection

Human respiratory syncytial virus is a major respiratory pathogen for which there are no suitable antivirals or vaccines. A better understanding of the host cell response to this virus may redress this problem. The present report concerns analysis of multiple independent biological replicates of control and 24 h infected lysates of A549 cells by two different proteomic workflows. One workflow involved fractionation of lysates by in-solution protein IEF and individual fractions were digested using trypsin prior to capillary HPLC-LTQ-OrbitrapXL-MS/MS. A second workflow involved digestion of whole cell lysates and analysis by nanoUltraHPLC-LTQ-OrbitrapElite-MS/MS. Both workflows resulted in the quantification of viral proteins exclusively in lysates of infected cells in the relative abundances anticipated from previous studies. Unprecedented numbers (3247 - 5010) of host cell protein groups were also quantified and the infection-specific regulation of a large number (191) of these protein groups was evident based on a stringent false discovery rate cut-off (<1%). Bioinformatic analyses revealed that most of the regulated proteins were potentially regulated by type I, II, and III interferon, TNF-α and noncanonical NF-κB2 mediated antiviral response pathways. Regulation of specific protein groups by infection was validated by quantitative Western blotting and the cytokine-/key regulator-specific nature of their regulation was confirmed by comparable analyses of cytokine treated A549 cells. Overall, it is evident that the workflows described herein have produced the most comprehensive proteomic characterization of host cell responses to human respiratory syncytial virus published to date. These workflows will form the basis for analysis of the impacts of specific genes of human respiratory syncytial virus responses of A549 and other cell lines using a gene-deleted version of the virus. They should also prove valuable for the analysis of the impact of other infectious agents on host cells.

Development of a reverse genetics system for respiratory syncytial virus long strain and an immunogenicity study of the recombinant virus

Background

Respiratory Syncytial Virus (RSV) is an important human respiratory pathogen, particularly of infants and older adults, and despite several decades of research and development, no licensed vaccine is available. Studies have confirmed that enhancement of RSV disease does not occur after inoculation with RSV live-attenuated vaccine candidates, making such vaccines preferable. In this paper, reverse genetics was used to construct two recombinant viruses, a recombinant Long strain (rLong) and rLong-∆G-EGFP; rLong-∆G-EGFP is a recombinant mutant in which G was replaced with the EGFP gene, based on the Long strain of RSV.

Results

Both rLong and rLong-∆G-EGFP were constructed successfully and recovered in Hep-2 cells, and autofluorescence was observed in rLong-∆G-EGFP-infected cells during consecutive passages. Titers of rLong and rLong-∆G-EGFP were ~100-fold lower than the parental strain. Although virulence was attenuated, high titers of neutralizing antibodies were induced in BALB/c mice after being inoculated with recombinant viruses in a three-dose schedule. Unexpectedly, the neutralizing antibody titer in rLong-∆G-EGFP-immunized recipients did not decline significantly compared with the rLong strain. Protective efficacy of recombinant viruses in lung tissue was up to 100%, and the serum neutralizing antibody levels could stabilize at 21 days with no significant fall post-challenge. Enzyme-linked immunospot (ELISPOT) assays showed that both recombinant viruses were capable of inducing CD8⁺ T cell immune responses, which are crucial for virus clearance, and that rLong stimulated a higher level of IFN-γ production by comparison. In terms of inducing a balanced immune response, rLong-∆G-EGFP elicited slightly higher levels of IgG2a antibodies and lower levels of IgG1/IgG2a than the rLong virus.

Conclusions

This study suggested that immunization with rLong and rLong-∆G-EGFP were immunogenic and protected against RSV infection in the lower respiratory tract of BALB/c mice better than in the nose. Because of a relative low IgG1/IgG2a ratio, rLong-∆G-EGFP was more inclined to make CD4⁺ T cells, shifting toward a Th1-type response, indicating that the generation of a more balanced Th1/Th2 response was desirable. This explorative study on the recombinant Long viruses also contributed to obtaining more RSV attenuated candidates by a reverse genetics approach.

RNA virus reverse genetics and vaccine design

RNA viruses are capable of rapid spread and severe or potentially lethal disease in both animals and humans. The development of reverse genetics systems for manipulation and study of RNA virus genomes has provided platforms for designing and optimizing viral mutants for vaccine development. Here, we review the impact of RNA virus reverse genetics systems on past and current efforts to design effective and safe viral therapeutics and vaccines.

Development of a chimeric strain of porcine reproductive and respiratory syndrome virus with an infectious clone and a Korean dominant field strain

The K418 chimeric virus of porcine reproductive and respiratory syndrome virus (PRRSV) was engineered by replacing the genomic region containing structure protein genes of an infectious clone of PRRSV, FL12, with the same region obtained from a Korean dominant field strain, LMY. The K418 reached 10⁶ TCID₅₀/ml of viral titer with similar growth kinetics to those of parental strains and had a cross-reactive neutralizing antibody response to field serum from the entire country. The chimeric clone pK418 can be used as a practical tool for further studying the molecular characteristics of PRRSV proteins through genetic manipulation. Furthermore, successful construction of the K418 will allow for the development of customized vaccine candidates against PRRSV, which has evolved rapidly in Korea.

Decrease in formalin-inactivated respiratory syncytial virus (FI-RSV) enhanced disease with RSV G glycoprotein peptide immunization in BALB/c mice

Respiratory syncytial virus (RSV) is a high priority target for vaccine development. One concern in RSV vaccine development is that a non-live virus vaccine would predispose for enhanced disease similar to that seen with the formalin inactivated RSV (FI-RSV) vaccine. Since a mAb specific to RSV G protein can reduce pulmonary inflammation and eosinophilia seen after RSV infection of FI-RSV vaccinated mice, we hypothesized that RSV G peptides that induce antibodies with similar reactivity may limit enhanced disease after subunit or other non-live RSV vaccines. In support of this hypothesis, we show that FI-RSV vaccinated mice administered RSV G peptide vaccines had a significant reduction in enhanced disease after RSV challenge. These data support the importance of RSV G during infection to RSV disease pathogenesis and suggest that use of appropriately designed G peptide vaccines to reduce the risk of enhanced disease with non-live RSV vaccines merits further study.

Development and verification of real-time PCR assay for identification of viral agents causing acute respiratory infections in human beings

A multiplex polymerase chain reaction (PCR) for identification of four viruses causing acute respiratory diseases in human beings was developed. The analytical sensitivity of developed RT-PCR for identification of adenovirus, respiratory-syncytial virus, flu viruses types A and B, and actual subtypes of type A flu virus (seasonal and pandemic variants H1N1, seasonal H3N2, and viruses of bird flu that are pathogenic to human beings H5 and H7) was 1 × 10³ genome equivalents per milliliter. Diagnostic sensitivity for flu virus type A and B, and also subtypes H1 (seasonal H1N1, pandemic variant of H1N1 of year 2009), H3, H5 was 1 × 10³–10⁴ viral particles per milliliter. The method developed has high specificity and does not have positive signal in experiments with DNA/cDNA of human beings and viral DNA. We have studied 50 samples using the developed set. Etiology was defined in 33 samples.

Respiratory syncytial virus vaccine development

The importance of RSV as a respiratory pathogen in young children made it a priority for vaccine development shortly after it was discovered. Unfortunately, after over 50 years of vaccine development no vaccine has yet been licensed and it is not certain which if any vaccines being developed will be successful. The first candidate vaccine, a formalin inactivated RSV vaccine (FI-RSV), was tested in children in the 1960s and predisposed young recipients to more serious disease with later natural infection. The ongoing challenges in developing RSV vaccines are balanced by advances in our understanding of the virus, the host immune response to vaccines and infection, and pathogenesis of disease. It seems likely that with efficient and appropriately focused effort a safe and effective vaccine is within reach. There are at least 4 different target populations for an RSV vaccine, i.e. the RSV naïve young infant, the RSV naïve infant >4-6 months of age, pregnant women, and elderly adults. Each target population has different issues related to vaccine development. Numerous vaccines from live attenuated RSV to virus like particle vaccines have been developed and evaluated in animals. Very few vaccines have been studied in humans and studies in humans are needed to determine which vaccines are worth moving toward licensure. Some changes in the approach may improve the efficiency of evaluating candidate vaccines. The complexity of the challenges for developing RSV vaccines suggests that collaboration among academic, government, and funding institutions and industry is needed to most efficiently achieve an RSV vaccine.

Attenuation of live respiratory syncytial virus vaccines is associated with reductions in levels of nasal cytokines

BACKGROUND

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract illness (LRTI) in children. Several promising live-attenuated RSV vaccines are in development. Defining additional markers of attenuation could enhance clinical trials.

METHODS

We used clinical data, virologic data, and nasal wash (NW) specimens from 20 RSV-naive children enrolled in studies of 4 live-attenuated RSV vaccines. Seven received minimally attenuated cpts248/955 or cpts530/1009 (group 1), 6 received moderately attenuated cpts248/404 (group 2), and 7 received highly attenuated rA2cp248/404/1030/ΔSH (group 3). NW specimens were tested for cytokines and chemokines via an electrochemiluminescence biosensor assay.

RESULTS

Group 1 exhibited 1 instance of LRTI and significantly higher rates of fever than groups 2 or 3; there were no significant differences in peak titers of vaccine virus in NW specimens. In contrast, levels of interferon γ, interleukin 1β, interleukin 2, interleukin 6, and interleukin 13 were significantly greater in NW specimens from group 1, compared with those from group 3. Maximum increases in levels of most cytokines occurred after peak viral replication but coincided with clinical illness.

CONCLUSIONS

Substantial increases in proinflammatory, antiinflammatory, T-helper 1, T-helper 2, and regulatory cytokines were detected in children who received minimally attenuated live RSV vaccines but not in children who received highly attenuated vaccines. Levels of cytokines in NW specimens may be useful biomarkers of attenuation for live RSV vaccines.

Live-attenuated respiratory syncytial virus vaccines

Live-attenuated respiratory syncytial virus (RSV) vaccines offer several advantages for immunization of infants and young children: (1) they do not cause vaccine-associated enhanced RSV disease; (2) they broadly stimulate innate, humoral, and cellular immunity, both systemically and locally in the respiratory tract; (3) they are delivered intranasally; and (4) they replicate in the upper respiratory tract of young infants despite the presence of passively acquired maternally derived RSV neutralizing antibody. This chapter describes early efforts to develop vaccines through the classic methods of serial cold-passage and chemical mutagenesis, and recent efforts using reverse genetics to derive attenuated derivatives of wild-type (WT) RSV and to develop parainfluenza vaccine vectors that express RSV surface glycoproteins.

Respiratory syncytial virus modified by deletions of the NS2 gene and amino acid S1313 of the L polymerase protein is a temperature-sensitive, live-attenuated vaccine candidate that is phenotypically stable at physiological temperature

Human respiratory syncytial virus (RSV) is the leading viral cause of lower respiratory tract disease in infants and children worldwide. In previous work to develop point mutations in RSV with improved genetic stability, we observed that an attenuating mutation at amino acid position 1321 in the L polymerase protein was subject to deattenuation by a spontaneous second-site compensatory mutation at position 1313 (C. Luongo, C. C. Winter, P. L. Collins, and U. J. Buchholz, J. Virol. 86:10792-10804, 2012). In the present study, we found that deletion of position 1313 (Δ1313), irrespective of the presence of an attenuating mutation at position 1321, provided a new attenuating mutation. RSV bearing Δ1313 replicated in cell culture as efficiently as wild-type virus at 32°C, was restricted for replication at 37°C, and was restricted 50-fold and 150-fold in the upper and lower respiratory tracts, respectively, of mice. We combined the Δ1313 deletion with the previously described, attenuating NS2 gene deletion (ΔNS2) to produce the recombinant live-attenuated RSV vaccine candidate ΔNS2/Δ1313. During in vitro stress tests involving serial passage at incrementally increasing temperatures, a second-site compensatory mutation was detected in close proximity of Δ1313, namely, I1314T. This site was genetically and phenotypically stabilized by an I1314L substitution. Combination of I1314L with ΔNS2/Δ1313 yielded a virus, ΔNS2/Δ1313/1314L, with genetic stability at physiological temperature. This stabilized vaccine candidate was moderately temperature sensitive and had a level of restriction in chimpanzees comparable to that of MEDI-559, a promising RSV vaccine candidate that presently is in clinical trials but lacks stabilized attenuating mutations. The level of attenuation and genetic stability identify ΔNS2/Δ1313/1314L as a promising candidate for evaluation in pediatric phase I studies.

RSV--a substantial slice of the airway disease burden and the way to a vaccine

BACKGROUND

The impact of an active RSV vaccine in the future will depend on the true fraction of airway diseases attributable to RSV as the causal pathogen, since many pathogens contribute to the airway disease burden at the same time. This attributable slice of the airway disease burden can vary between populations, regions and seasons, and by the incidence of co-infections. Furthermore, potential future vaccine effectiveness will depend on several characteristics such as prevention of vaccine escape mutants and earliest possible time of vaccination.

AIMS AND METHODS

To analyse the disease burden attributable to RSV and review recently published, high-quality epidemiological data from all parts of the world. The development of an active RSV vaccine is illustrated and hurdles in delivery are described.

RESULTS

RSV is estimated to be responsible for up to 22% of severe lower respiratory tract infections in children under 5 years of age. First lifetime RSV infections occur at a very early age, mainly in infants and toddlers, in a seasonal pattern, and lead to bacterial co-infections in about one-third of patients. The development of an active RSV vaccine faces several hurdles such as incomplete natural immunity, high variability of RS viruses, selection of the best antigens, choosing the proper vaccine technology platform, and lack of an immune correlate of protection. Added to this is the long way a clinical development programme has to go before it is possible from a regulatory point of view to test a vaccine candidate in a considerable number of RSV-naive children.

CONCLUSION

An active RSV vaccine is urgently needed, but, given experience in the 1960s with the formalin-inactivated vaccines, and the long and complicated process involved in development, considerable support and flexibility by regulatory bodies and substantial funds are needed. The slice of up to 22% of the ARI disease burden in the first 5 years of life, which is potentially preventable by an active vaccine, is substantial, and the endeavour worthwhile.

Targeting RSV with vaccines and small molecule drugs

Respiratory syncytial virus (RSV) is the most significant cause of pediatric respiratory infections. Palivizumab (Synagis®), a humanized monoclonal antibody, has been used successfully for a number of years to prevent severe RSV disease in at-risk infants. However, despite intense efforts, there is no approved vaccine or small molecule drug for RSV. As an enveloped virus, RSV must fuse its envelope with the host cell membrane, which is accomplished through the actions of the fusion (F) glycoprotein, with attachment help from the G glycoprotein. Because of their integral role in initiation of infection and their accessibility outside the lipid bilayer, these proteins have been popular targets in the discovery and development of antiviral compounds and vaccines against RSV. This review examines advances in the development of antiviral compounds and vaccine candidates.

Specific temperature-induced perturbations of secondary mRNA structures are associated with the cold-adapted temperature-sensitive phenotype of influenza A virus

For decades, cold-adapted, temperature-sensitive (ca/ts) strains of influenza A virus have been used as live attenuated vaccines. Due to their great public health importance it is crucial to understand the molecular mechanism(s) of cold adaptation and temperature sensitivity that are currently unknown. For instance, secondary RNA structures play important roles in influenza biology. Thus, we hypothesized that a relatively minor change in temperature (32-39°C) can lead to perturbations in influenza RNA structures and, that these structural perturbations may be different for mRNAs of the wild type (wt) and ca/ts strains. To test this hypothesis, we developed a novel in silico method that enables assessing whether two related RNA molecules would undergo (dis)similar structural perturbations upon temperature change. The proposed method allows identifying those areas within an RNA chain where dissimilarities of RNA secondary structures at two different temperatures are particularly pronounced, without knowing particular RNA shapes at either temperature. We identified such areas in the NS2, PA, PB2 and NP mRNAs. However, these areas are not identical for the wt and ca/ts mutants. Differences in temperature-induced structural changes of wt and ca/ts mRNA structures may constitute a yet unappreciated molecular mechanism of the cold adaptation/temperature sensitivity phenomena.

Increased genetic and phenotypic stability of a promising live-attenuated respiratory syncytial virus vaccine candidate by reverse genetics

Human respiratory syncytial virus (RSV) is the most important viral cause of serious pediatric respiratory illness worldwide. Currently, the most promising live-attenuated vaccine candidate is a temperature-sensitive (ts) cDNA-derived virus named rA2cp248/404/1030ΔSH, in reference to its set of attenuating mutations. In a previous clinical study, more than one-third of postvaccination nasal wash isolates exhibited partial loss of the ts phenotype. Most of this instability appeared to be due to reversion at a missense point mutation called 1030. This 1030 mutation is a single-nucleotide tyrosine-to-asparagine substitution at position 1321 (Y1321N) of the polymerase L protein that contributes to the ts and attenuation phenotypes of the vaccine candidate. The goals of the present study were to identify a reversion-resistant codon at position 1321 conferring a comparable level of attenuation and to use this to develop a genetically stable version of the vaccine virus. We modified wild-type (wt) RSV to insert each of the 20 possible amino acids at position 1321; 19 viruses were recoverable. We also investigated small deletions at or near this position, but these viruses were not recoverable. Phenotypic analysis identified alternative attenuating amino acids for position 1321. Several of these amino acids were predicted, based on the genetic code, to be refractory to deattenuation. Classical genetics, using temperature stress tests in vitro combined with nucleotide sequencing, confirmed this stability but identified a second site with a compensatory mutation at position 1313. It was possible to stabilize the 1313 site as well, providing a stable 1030 mutation. Further stress tests identified additional incidental mutations, but these did not reverse the ts/attenuation phenotype. An improved version of the vaccine candidate virus was constructed and validated in vitro by temperature stress tests and in vivo by evaluation of attenuation in seronegative chimpanzees. In addition to developing an improved version of this promising live-attenuated RSV vaccine candidate, this study demonstrated the propensity of an RNA virus to escape from attenuation but also showed that, through systematic analysis, genetics can be used to cut off the routes of escape.

The human respiratory syncytial virus nonstructural protein 1 regulates type I and type II interferon pathways

Respiratory syncytial viruses encode a nonstructural protein (NS1) that interferes with type I and III interferon and other antiviral responses. Proteomic studies were conducted on human A549 type II alveolar epithelial cells and type I interferon-deficient Vero cells (African green monkey kidney cells) infected with wild-type and NS1-deficient clones of human respiratory syncytial virus to identify other potential pathway and molecular targets of NS1 interference. These analyses included two-dimensional differential gel electrophoresis and quantitative Western blotting. Surprisingly, NS1 was found to suppress the induction of manganese superoxide dismutase (SOD2) expression in A549 cells and to a much lesser degree Vero cells in response to infection. Because SOD2 is not directly inducible by type I interferons, it served as a marker to probe the impact of NS1 on signaling of other cytokines known to induce SOD2 expression and/or indirect effects of type I interferon signaling. Deductive analysis of results obtained from cell infection and cytokine stimulation studies indicated that interferon-γ signaling was a potential target of NS1, possibly as a result of modulation of STAT1 levels. However, this was not sufficient to explain the magnitude of the impact of NS1 on SOD2 induction in A549 cells. Vero cell infection experiments indicated that NS1 targeted a component of the type I interferon response that does not directly induce SOD2 expression but is required to induce another initiator of SOD2 expression. STAT2 was ruled out as a target of NS1 interference using quantitative Western blot analysis of infected A549 cells, but data were obtained to indicate that STAT1 was one of a number of potential targets of NS1. A label-free mass spectrometry-based quantitative approach is proposed as a means of more definitive identification of NS1 targets.

Progress in understanding and controlling respiratory syncytial virus: still crazy after all these years

Human respiratory syncytial virus (RSV) is a ubiquitous pathogen that infects everyone worldwide early in life and is a leading cause of severe lower respiratory tract disease in the pediatric population as well as in the elderly and in profoundly immunosuppressed individuals. RSV is an enveloped, nonsegmented negative-sense RNA virus that is classified in Family Paramyxoviridae and is one of its more complex members. Although the replicative cycle of RSV follows the general pattern of the Paramyxoviridae, it encodes additional proteins. Two of these (NS1 and NS2) inhibit the host type I and type III interferon (IFN) responses, among other functions, and another gene encodes two novel RNA synthesis factors (M2-1 and M2-2). The attachment (G) glycoprotein also exhibits unusual features, such as high sequence variability, extensive glycosylation, cytokine mimicry, and a shed form that helps the virus evade neutralizing antibodies. RSV is notable for being able to efficiently infect early in life, with the peak of hospitalization at 2-3 months of age. It also is notable for the ability to reinfect symptomatically throughout life without need for significant antigenic change, although immunity from prior infection reduces disease. It is widely thought that re-infection is due to an ability of RSV to inhibit or subvert the host immune response. Mechanisms of viral pathogenesis remain controversial. RSV is notable for a historic, tragic pediatric vaccine failure involving a formalin-inactivated virus preparation that was evaluated in the 1960s and that was poorly protective and paradoxically primed for enhanced RSV disease. RSV also is notable for the development of a successful strategy for passive immunoprophylaxis of high-risk infants using RSV-neutralizing antibodies. Vaccines and new antiviral drugs are in pre-clinical and clinical development, but controlling RSV remains a formidable challenge.

Progress in respiratory virus vaccine development

Viral respiratory infections cause significant morbidity and mortality in infants and young children as well as in at-risk adults and the elderly. Although many viral pathogens are capable of causing respiratory disease, vaccine development has to focus on a limited number of pathogens, such as those that commonly cause serious lower respiratory illness (LRI). Whereas influenza virus vaccines have been available for some time (see the review by Clark and Lynch in this issue), vaccines against other medically important viruses such as respiratory syncytial virus (RSV), the parainfluenza viruses (PIVs), and metapneumovirus (MPVs) are not available. This review aims to provide a brief update on investigational vaccines against RSV, the PIVs, and MPV that have been evaluated in clinical trials or are currently in clinical development.

A novel mechanism for the inhibition of interferon regulatory factor-3-dependent gene expression by human respiratory syncytial virus NS1 protein

Human respiratory syncytial virus (RSV), a leading cause of respiratory tract infections in infants, inhibits type I interferon (IFN)-dependent signalling, as well as IFN synthesis. RSV non-structural protein NS1 plays a significant role in this inhibition; however, the mechanism(s) responsible is not fully known. The transcription factor interferon regulatory factor (IRF)-3 is essential for viral-induced IFN-β synthesis. In this study, we found that NS1 protein inhibits IRF-3-dependent gene transcription in constitutively active IRF-3 overexpressing cells, demonstrating that NS1 directly targets IRF-3. Our data also demonstrate that NS1 associates with IRF-3 and its transcriptional coactivator CBP, leading to disrupted association of IRF-3 to CBP and subsequent reduced binding of IRF-3 to the IFN-β promoter without blocking viral-induced IRF-3 phosphorylation, nuclear translocation and dimerization, thereby identifying a novel molecular mechanism by which RSV inhibits IFN-β synthesis.

Therapeutic targeting of respiratory syncytial virus G-protein

Respiratory syncytial virus (RSV) is a leading cause of pneumonia and bronchiolitis in infants and young children and an important pathogen of the elderly and immune suppressed. The only intervention currently available is a monoclonal antibody against the RSV fusion protein, which has shown utility as a prophylactic for high-risk premature infants, but which has not shown postinfection therapeutic efficacy in the specific RSV-infected populations studied. Thus, for the major susceptible populations, there remains a great need for effective treatment. Recent results support monoclonal antibody targeting of the RSV G-protein for therapeutic use. This objective encompasses a dual mechanism: reduction in the ability of RSV G-protein to distort the host innate immune response, and direct complement-mediated antiviral activity.

An evaluation of the emerging interventions against Respiratory Syncytial Virus (RSV)-associated acute lower respiratory infections in children

Background

Respiratory Syncytial Virus (RSV) is the leading cause of acute lower respiratory infections (ALRI) in children. It is estimated to cause approximately 33.8 million new episodes of ALRI in children annually, 96% of these occurring in developing countries. It is also estimated to result in about 53,000 to 199,000 deaths annually in young children. Currently there are several vaccine and immunoprophylaxis candidates against RSV in the developmental phase targeting active and passive immunization.

Methods

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In Stage I, we systematically reviewed the literature related to emerging vaccines against RSV relevant to 12 criteria of interest. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies). The policy makers and industry representatives accepted our invitation on the condition of anonymity, due to the sensitive nature of their involvement in such exercises. They answered questions from the CHNRI framework and their “collective optimism” towards each criterion was documented on a scale from 0 to 100%.

Results

In the case of candidate vaccines for active immunization of infants against RSV, the experts expressed very low levels of optimism for low product cost, affordability and low cost of development; moderate levels of optimism regarding the criteria of answerability, likelihood of efficacy, deliverability, sustainability and acceptance to end users for the interventions; and high levels of optimism regarding impact on equity and acceptance to health workers. While considering the candidate vaccines targeting pregnant women, the panel expressed low levels of optimism for low product cost, affordability, answerability and low development cost; moderate levels of optimism for likelihood of efficacy, deliverability, sustainability and impact on equity; high levels of optimism regarding acceptance to end users and health workers. The group also evaluated immunoprophylaxis against RSV using monoclonal antibodies and expressed no optimism towards low product cost; very low levels of optimism regarding deliverability, affordability, sustainability, low implementation cost and impact on equity; moderate levels of optimism against the criteria of answerability, likelihood of efficacy, acceptance to end-users and health workers; and high levels of optimism regarding low development cost. They felt that either of these vaccines would have a high impact on reducing burden of childhood ALRI due to RSV and reduce the overall childhood ALRI burden by a maximum of about 10%.

Conclusion

Although monoclonal antibodies have proven to be effective in providing protection to high-risk infants, their introduction in resource poor settings might be limited by high cost associated with them. Candidate vaccines for active immunization of infants against RSV hold greatest promise. Introduction of a low cost vaccine against RSV would reduce the inequitable distribution of burden due to childhood ALRI and will most likely have a high impact on morbidity and mortality due to severe ALRI.

Assembly and immunological properties of Newcastle disease virus-like particles containing the respiratory syncytial virus F and G proteins

Human respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children as well as elderly and immunocompromised populations. However, no RSV vaccines are available. We have explored the potential of virus-like particles (VLPs) as an RSV vaccine candidate. VLPs composed entirely of RSV proteins were produced at levels inadequate for their preparation as immunogens. However, VLPs composed of the Newcastle disease virus (NDV) nucleocapsid and membrane proteins and chimera proteins containing the ectodomains of RSV F and G proteins fused to the transmembrane and cytoplasmic domains of NDV F and HN proteins, respectively, were quantitatively prepared from avian cells. Immunization of mice with these VLPs, without adjuvant, stimulated robust, anti-RSV F and G protein antibody responses. IgG2a/IgG1 ratios were very high, suggesting predominantly T(H)1 responses. In contrast to infectious RSV immunization, neutralization antibody titers were robust and stable for 4 months. Immunization with a single dose of VLPs resulted in the complete protection of mice from RSV replication in lungs. Upon RSV intranasal challenge of VLP-immunized mice, no enhanced lung pathology was observed, in contrast to the pathology observed in mice immunized with formalin-inactivated RSV. These results suggest that these VLPs are effective RSV vaccines in mice, in contrast to other nonreplicating RSV vaccine candidates.

Toll-like receptor 4 Asp299Gly polymorphism in respiratory syncytial virus epidemics

The respiratory syncytial virus (RSV) antigen serves as ligand for Toll-like receptor (TLR) 4 that is a transmembrane signaling receptor in macrophages and dendritic cells. According to current evidence single nucleotide polymorphism involving amino acid 299 influences the susceptibility to severe RSV infections. The Asp299Gly allele has been shown to influence the TLR4-mediated signaling causing conformational change in the extracellular domain that recognizes pathogen-associated molecular patterns. The aim was to study the association between the TLR4 Asp299Gly polymorphism and the susceptibility to severe RSV bronchiolitis in infants. Altogether 312 cases and 356 controls, selected on the basis place of residence, date of birth, gender, and gestation at birth, were studied. When adjusted for multiple dependent variables, no allele or genotype frequency difference was found between the cases and the controls. Post hoc analysis revealed that during the year 2000 epidemics, the Gly299Gly genotype associated with protection against severe RSV and during 2004 epidemics Gly299Gly genotype and 299Gly allele associated with severe RSV. To conclude, we could not confirm the association of the Gly299 allele with severe RSV. This is consistent with the evidence that the susceptibility to severe RSV infection is principally dependent on environmental and constitutional factors. We propose that the risk of severe RSV infection may additionally depend on the interaction between individual TLR4 genotype and the particular RSV group causing bronchiolitis.

Pharmacologic advances in the treatment and prevention of respiratory syncytial virus

Currently, only 2 drugs have been approved for the treatment of respiratory syncytial virus (RSV). Palivizumab is a monoclonal antibody for the prevention of RSV in high-risk children. Ribavirin is approved for treatment of severe RSV disease; however, its effectiveness in improving outcomes is questionable. During the past 40 years, many obstacles have delayed the development of safe and effective vaccines and treatment regimens. This article reviews these obstacles and presents the novel development strategies used to overcome many of them. Also discussed are promising new antiviral treatment candidates and their associated mechanism of action, the significant advances made in vaccine development, and exciting, new studies directed at improving outcomes through pharmacologic manipulation of the host response to RSV disease.

A highly attenuated recombinant human respiratory syncytial virus lacking the G protein induces long-lasting protection in cotton rats

Background

Respiratory syncytial virus (RSV) is a primary cause of serious lower respiratory tract illness for which there is still no safe and effective vaccine available. Using reverse genetics, recombinant (r)RSV and an rRSV lacking the G gene (ΔG) were constructed based on a clinical RSV isolate (strain 98-25147-X).

Results

Growth of both recombinant viruses was equivalent to that of wild type virus in Vero cells, but was reduced in human epithelial cells like Hep-2. Replication in cotton rat lungs could not be detected for ΔG, while rRSV was 100-fold attenuated compared to wild type virus. Upon single dose intranasal administration in cotton rats, both recombinant viruses developed high levels of neutralizing antibodies and conferred comparable long-lasting protection against RSV challenge; protection against replication in the lungs lasted at least 147 days and protection against pulmonary inflammation lasted at least 75 days.

Conclusion

Collectively, the data indicate that a single dose immunization with the highly attenuated ΔG as well as the attenuated rRSV conferred long term protection in the cotton rat against subsequent RSV challenge, without inducing vaccine enhanced pathology. Since ΔG is not likely to revert to a less attenuated phenotype, we plan to evaluate this deletion mutant further and to investigate its potential as a vaccine candidate against RSV infection.

Prospects for defined epitope vaccines for respiratory syncytial virus

The history of vaccines for respiratory syncytial virus (RSV) illustrates the complex immunity and immunopathology to this ubiquitous virus, starting from the failed formalin-inactivated vaccine trials performed in the 1960s. An attractive alternative to traditional live or killed virus vaccines is a defined vaccine composed of discrete antigenic epitopes for which immunological activities have been characterized as comprehensively as possible. Here we present cumulative data on murine and human CD4, CD8 and neutralization epitopes identified in RSV proteins along with information regarding their associated immune responses and host-dependent variability. Identification and characterization of RSV epitopes is a rapidly expanding topic of research with potential contributions to the tailored design of improved safe and effective vaccines.

Respiratory syncytial virus vaccine development

Respiratory syncytial virus (RSV) is a clinically significant cause of respiratory tract disease, especially among high-risk infants and immunocompromised and elderly adults. Despite the burden of disease, there is no licensed prophylactic RSV vaccine. The initial efforts to develop an RSV vaccine involved formalin-inactivated virus preparations that unexpectedly caused vaccine-enhanced disease in clinical trials in RSV-naive children. Over the last 40 years, cautious and deliberate progress has been made toward RSV vaccine development using various experimental approaches, including live attenuated strains and vector-based and viral protein subunit/DNA-based candidates. The scientific rationale, preclinical testing, and clinical development of each of these approaches are reviewed.

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.

Codon stabilization analysis of the "248" temperature sensitive mutation for increased phenotypic stability of respiratory syncytial virus vaccine candidates

Human respiratory syncytial virus (RSV) is the most important viral agent of serious pediatric respiratory tract illness worldwide. Presently, the most promising vaccine candidate is a live, attenuated, cDNA-derived virus, RSV rA2cp248/404/1030DeltaSH, whose attenuation phenotype is based in large part on a series of point mutations including a glutamine to leucine (Q to L) substitution at amino acid residue 831 of the polymerase protein L, a mutation originally called "248". This mutation specifies both a temperature sensitive (ts) and attenuation phenotype. Reversion of this mutation from leucine back to glutamine was detected in some samples in clinical phase 1 trials. To identify the most genetically stable "attenuating" codon at this position to be included in a more stable RSV vaccine, we sought to create and evaluate recombinant RSVs representing all 20 possible amino acid assignments at this position, as well as small insertions and deletions. The recoverable viruses constituted a panel representing 18 different amino acid assignments, and were evaluated for temperature sensitivity in vitro and attenuation in mice. The original leucine mutation was found to be the most attenuating, followed only by phenylalanine. The paucity of highly attenuating assignments limited the possibility of increasing genetic stability. Indeed, it was not possible to find a leucine or phenylalanine codon requiring more than a single nucleotide change to yield a "non-attenuating" codon, as is necessary for the stabilization strategy. Nonetheless, serial passage of the six possible leucine codons in vitro at increasing temperatures revealed differences, with slower reversion to non-attenuated phenotypes for a subset of codons. Thus, it should be possible to modestly increase the phenotypic stability of the rA2cp248/404/1030DeltaSH vaccine virus by codon modification at the locus of the 248 mutation. In addition to characterizing the phenotypes associated with a particular locus in the RSV L protein, this manuscript provides insight into the problem of the instability of point mutations and the limitations of strategies to stabilize them.

The burden of respiratory syncytial virus infection in young children

BACKGROUND

The primary role of respiratory syncytial virus (RSV) in causing infant hospitalizations is well recognized, but the total burden of RSV infection among young children remains poorly defined.

METHODS

We conducted prospective, population-based surveillance of acute respiratory infections among children under 5 years of age in three U.S. counties. We enrolled hospitalized children from 2000 through 2004 and children presenting as outpatients in emergency departments and pediatric offices from 2002 through 2004. RSV was detected by culture and reverse-transcriptase polymerase chain reaction. Clinical information was obtained from parents and medical records. We calculated population-based rates of hospitalization associated with RSV infection and estimated the rates of RSV-associated outpatient visits.

RESULTS

Among 5067 children enrolled in the study, 919 (18%) had RSV infections. Overall, RSV was associated with 20% of hospitalizations, 18% of emergency department visits, and 15% of office visits for acute respiratory infections from November through April. Average annual hospitalization rates were 17 per 1000 children under 6 months of age and 3 per 1000 children under 5 years of age. Most of the children had no coexisting illnesses. Only prematurity and a young age were independent risk factors for hospitalization. Estimated rates of RSV-associated office visits among children under 5 years of age were three times those in emergency departments. Outpatients had moderately severe RSV-associated illness, but few of the illnesses (3%) were diagnosed as being caused by RSV.

CONCLUSIONS

RSV infection is associated with substantial morbidity in U.S. children in both inpatient and outpatient settings. Most children with RSV infection were previously healthy, suggesting that control strategies targeting only high-risk children will have a limited effect on the total disease burden of RSV infection.