Respiratory syncytial virus (RSV) vaccines—Two steps back for one leap forward

Coexpression of respiratory syncytial virus (RSV) fusion (F) protein and attachment glycoprotein (G) in a vesicular stomatitis virus (VSV) vector system provides synergistic effects against RSV infection in a cotton rat model

Respiratory syncytial virus (RSV) is one of the most important causes of respiratory disease in infants, immunocompromised individuals, and the elderly. Natural infection does not result in long-term immunity, and there is no licensed vaccine. Vesicular stomatitis virus (VSV) is a commonly used vaccine vector platform against infectious diseases, and has been used as a vector for a licensed Ebola vaccine. In this study, we expressed the RSV fusion (F) protein, the RSV F protein stabilized in either a pre-fusion or a post-fusion configuration, the attachment glycoprotein (G), or the G and F proteins of RSV in combination in a VSV vector. Cotton rats were immunized with these recombinants intranasally or subcutaneously to test immunogenicity. RSV F stabilized in either a pre-fusion or a post-fusion configuration proved to be poorly immunogenic and protective when compared to unmodified F. RSV G provided partial protection and moderate levels of neutralizing antibody production, both of which improved with intranasal administration compared to subcutaneous inoculation. The most successful vaccine vector was VSV expressing both the G and F proteins after intranasal inoculation. Immunization with this recombinant induced neutralizing antibodies and provided protection from RSV challenge in the upper and lower respiratory tract for at least 80 days. Our results demonstrate that co-expression of F and G proteins in a VSV vector provides synergistic effects in inducing RSV-specific neutralizing antibodies and protection against RSV infection.

Effect of Previous Respiratory Syncytial Virus Infection on Murine Immune Responses to F and G Protein-Containing Virus-Like Particles

Most individuals are infected with respiratory syncytial virus (RSV) by age two, but infection does not result in long-term protective immunity to subsequent infections. Previous RSV infection may, however, impact responses to an RSV vaccine. The goal of these studies was to explore the effect of previous RSV infection on murine antibody responses to RSV F and G protein-containing virus-like particles (VLP), comparing responses to those resulting from VLP immunization of RSV-naive animals. These studies showed that after RSV infection, immunization with a single dose of VLPs containing a conformation-stabilized prefusion F protein stimulated high titers of neutralizing antibodies (NA), while an immunization with post-F-containing VLPs or a second RSV infection only weakly stimulated NA, even though total anti-F protein IgG antibody levels in both VLP-immunized animals were similar. Furthermore, single pre-F or post-F VLP immunization of animals previously infected (primed) with RSV resulted in total anti-F antibody titers that were 10- to 12-fold higher than titers after a VLP prime and boost of RSV-naive animals or after two consecutive RSV infections. The avidities of serum antibodies as well as numbers of splenic B cells and bone marrow cells after different immunization protocols were also assessed. The combined results show that RSV infection can quite effectively prime animals for the production of protective antibodies that can be efficiently activated by a pre-F VLP boost but not by a post-F VLP boost or a second RSV infection.IMPORTANCE Humans may experience repeated infections caused by the same serotype of respiratory syncytial virus (RSV), in contrast to infections with most other viruses, indicating that immune memory responses to RSV are defective. However, the effects of any residual but nonprotective immunity on responses to RSV vaccines are not clear. This study demonstrates that a VLP vaccine candidate containing a stabilized prefusion F protein can robustly stimulate protective immunity in animals previously infected with RSV, while a second RSV infection or a postfusion F-containing VLP cannot. This result shows that a properly constructed immunogen can be an effective vaccine in animals previously infected with RSV. The results also suggest that the defect in RSV memory is not in the induction of that memory but rather in its activation by a subsequent RSV infection.

Respiratory Syncytial Virus Nonstructural Protein 1 Blocks Glucocorticoid Receptor Nuclear Translocation by Targeting IPO13 and May Account for Glucocorticoid Insensitivity

Despite their powerful antiinflammatory effect, glucocorticoids have shown no significant clinical benefit in respiratory syncytial virus (RSV)-induced bronchiolitis, the reason for which remains unclear. Upon glucocorticoid binding, the cytoplasmic glucocorticoid receptor (GR) translocates to the nucleus with the help of importin 13 (IPO13). Here, we report that RSV infection reduced GR nuclear translocation in nasopharyngeal aspirates from RSV-infected infants, lungs of infected mice, and A549 cells, which coincided with decreased IPO13 expression. This led to repression of GR-induced antiinflammatory genes, such that dexamethasone failed to suppress airway inflammation and airway hyperresponsiveness in the infected mice. The anti-GR effect of RSV was mediated by viral nonstructural protein 1 , which likely functioned by competing with IPO13 for GR binding. Our findings provide a mechanism for the ineffectiveness of glucocorticoids in RSV-related disease and highlight the potential to target the IPO13-GR axis as a treatment for multiple glucocorticoid-related diseases.

Intranasal immunization with a single dose of the fusion protein formulated with a combination adjuvant induces long-term protective immunity against respiratory syncytial virus

Respiratory syncytial virus (RSV) is the most common cause of respiratory tract infections in both children and elderly people. In this study we evaluated the short- and long-term protective efficacy of a single intranasal (IN) immunization with a RSV vaccine formulation consisting of a codon-optimized fusion (F) protein formulated with poly(I:C), an innate defense regulator peptide and a polyphosphazene (ΔF/TriAdj). This vaccine induced strong systemic and local immune responses, including RSV F-specific IgG1 and IgG2a, SIgA and virus neutralizing antibodies in mice. Furthermore, ΔF/TriAdj promoted production of IFN-γ-secreting T cells and RSV F85-93-specific CD8+ effector T cells. After RSV challenge, no virus was recovered from the lungs of the vaccinated mice. To evaluate the duration of immunity induced by a single IN vaccination, mice were again immunized once with ΔF/TriAdj and challenged with RSV five months later. High levels of IgG1, IgG2a and virus neutralizing antibodies were detected in the ΔF/TriAdj-vaccinated animals. Moreover, this vaccine formulation induced robust local SIgA production and IgA-secreting memory B cell development, and conferred complete protection against subsequent RSV challenge. In conclusion, a single IN vaccination with RSV ΔF protein formulated with TriAdj induced robust, long-term protective immune responses against RSV infection.

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.

The importance of RSV F protein conformation in VLPs in stimulation of neutralizing antibody titers in mice previously infected with RSV

Respiratory syncytial virus (RSV) is a significant respiratory pathogen but no vaccine is available. RSV infections present 2 major, unique problems. First, humans can experience repeated infections caused by the same virus sero-group indicating that protective memory responses to RSV infection are defective. Second, most people have been infected with RSV by age 5. Immune responses to these infections, while poorly protective, could impact the effectiveness of a vaccine. The goal of this study was to assess the generation of protective immune responses in mice previously infected with RSV by virus-like particle (VLP) vaccine candidates containing a stabilized pre-fusion form of the RSV F protein or a stabilized post-fusion F protein. We report that a single immunization of RSV-experienced animals with a stabilized pre-fusion F protein VLP stimulated high titers of neutralizing antibody while a single injection of a post-fusion F protein VLP or a second RSV infection only weakly stimulated neutralizing antibody titers. These results suggest that prior RSV infection can induce neutralizing antibody memory responses, which can be activated by pre-F protein VLPs but not by post-F protein VLPs or a subsequent infection. Thus the F protein conformation has a major impact on enhancing production of neutralizing antibodies in RSV-experienced animals. Furthermore, although both VLPs contained the same RSV G protein, the pre-F VLP stimulated significantly higher titers of total anti-G protein IgG than the post-F VLP in both naïve and RSV-experienced animals. Thus the F protein conformation also influences anti-G protein responses.

A single intranasal administration of virus-like particle vaccine induces an efficient protection for mice against human respiratory syncytial virus

Human respiratory syncytial virus (RSV) is an important pediatric pathogen causing acute viral respiratory disease in infants and young children. However, no licensed vaccines are currently available. Virus-like particles (VLPs) may bring new hope to producing RSV VLP vaccine with high immunogenicity and safety. Here, we constructed the recombinants of matrix protein (M) and fusion glycoprotein (F) of RSV, respectively into a replication-deficient first-generation adenoviral vector (FGAd), which were used to co-infect Vero cells to assemble RSV VLPs successfully. The resulting VLPs showed similar immunoreactivity and function to RSV virion in vitro. Moreover, Th1 polarized response, and effective mucosal virus-neutralizing antibody and CD8⁺ T-cell responses were induced by a single intranasal (i.n.) administration of RSV VLPs rather than intramuscular (i.m.) inoculation, although the comparable RSV F-specific serum IgG and long-lasting RSV-specific neutralizing antibody were detected in the mice immunized by both routes. Upon RSV challenge, VLP-immunized mice showed increased viral clearance but decreased signs of enhanced lung pathology and fewer eosinophils compared to mice immunized with formalin-inactivated RSV (FI-RSV). In addition, a single i.n. RSV VLP vaccine has the capability to induce RSV-specific long-lasting neutralizing antibody responses observable up to 15 months. Our results demonstrate that the long-term and memory immune responses in mice against RSV were induced by a single i.n. administration of RSV VLP vaccine, suggesting a successful approach of RSV VLPs as an effective and safe mucosal vaccine against RSV infection, and an applicable and qualified platform of FGAd-infected Vero cells for VLP production.

Direct whole-genome deep-sequencing of human respiratory syncytial virus A and B from Vietnamese children identifies distinct patterns of inter- and intra-host evolution

Human respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infections in children ,2 years of age. Little is known about RSV intra-host genetic diversity over the course of infection or about the immune pressures that drive RSV molecular evolution. We performed whole-genome deep-sequencing on 53 RSV-positive samples (37 RSV subgroup A and 16 RSV subgroup B) collected from the upper airways of hospitalized children in southern Vietnam over two consecutive seasons. RSV A NA1 and RSV B BA9 were the predominant genotypes found in our samples, consistent with other reports on global RSV circulation during the same period. For both RSV A and B, the M gene was the most conserved, confirming its potential as a target for novel therapeutics. The G gene was the most variable and was the only gene under detectable positive selection. Further, positively selected sites inG were found in close proximity to and in some cases overlapped with predicted glycosylation motifs, suggesting that selection on amino acid glycosylation may drive viral genetic diversity. We further identified hotspots and coldspots of intra-host genetic diversity in the RSV genome, some of which may highlight previously unknown regions of functional importance.

Respiratory syncytial virus, an ongoing medical dilemma: an expert commentary on respiratory syncytial virus prophylactic and therapeutic pharmaceuticals currently in clinical trials

As the most important viral cause of severe respiratory disease in infants and increasing recognition as important in the elderly and immunocompromised, respiratory syncytial virus (RSV) is responsible for a massive health burden worldwide. Prophylactic antibodies were successfully developed against RSV. However, their use is restricted to a small group of infants considered at high risk of severe RSV disease. There is still no specific therapeutics or vaccines to combat RSV. As such, it remains a major unmet medical need for most individuals. The World Health Organisations International Clinical Trials Registry Platform (WHO ICTRP) and PubMed were used to identify and review all RSV vaccine, prophylactic and therapeutic candidates currently in clinical trials. This review presents an expert commentary on all RSV-specific prophylactic and therapeutic candidates that have entered clinical trials since 2008.

Cotton rat immune responses to virus-like particles containing the pre-fusion form of respiratory syncytial virus fusion protein

BACKGROUND

Virus-like particles (VLPs) based on Newcastle disease virus (NDV) core proteins, M and NP, and containing two chimera proteins, F/F and H/G, composed of the respiratory syncytial virus (RSV) fusion protein (F) and glycoprotein (G) ectodomains fused to the transmembrane and cytoplasmic domains of the NDV F and HN proteins, respectively, stimulate durable, protective anti-RSV neutralizing antibodies in mice. Furthermore, immunization of mice with a VLP containing a F/F chimera protein with modifications previously reported to stabilize the pre-fusion form of the RSV F protein resulted in significantly improved neutralizing antibody titers over VLPs containing the wild type F protein. The goal of this study was to determine if VLPs containing the pre-fusion form of the RSV F protein stimulated protective immune responses in cotton rats, a more RSV permissive animal model than mice.

METHODS

Cotton rats were immunized intramuscularly with VLPs containing stabilized pre-fusion F/F chimera protein as well as the H/G chimera protein. The anti-RSV F and RSV G antibody responses were determined by ELISA. Neutralizing antibody titers in sera of immunized animals were determined in plaque reduction assays. Protection of the animals from RSV challenge was assessed. The safety of the VLP vaccine was determined by monitoring lung pathology upon RSV challenge of immunized animals.

RESULTS

The Pre-F/F VLP induced neutralizing titers that were well above minimum levels previously proposed to be required for a successful vaccine and titers significantly higher than those stimulated by RSV infection. In addition, Pre-F/F VLP immunization stimulated higher IgG titers to the soluble pre-fusion F protein than RSV infection. Cotton rats immunized with Pre-F/F VLPs were protected from RSV challenge, and, importantly, the VLP immunization did not result in enhanced respiratory disease upon RSV challenge.

CONCLUSIONS

VLPs containing the pre-fusion RSV F protein have characteristics required for a safe, effective RSV vaccine.

Murine immune responses to virus-like particle-associated pre- and postfusion forms of the respiratory syncytial virus F protein

Virus-like particles (VLPs) built on the Newcastle disease virus (NDV) core proteins, NP and M, and containing two chimeric proteins, F/F and H/G, composed of respiratory syncytial virus (RSV) fusion protein (F) and glycoprotein (G) ectodomains fused to the transmembrane and cytoplasmic domains of the NDV F and HN proteins, respectively, stimulate durable, protective RSV neutralizing antibodies in mice. Here, we report the properties of VLPs constructed to contain mutant RSV F protein ectodomains stabilized in prefusion (pre-F/F) or postfusion (post-F/F) configurations. The structures of the chimeric proteins assembled into VLPs were verified immunologically by their reactivities with a conformationally restricted anti-F protein monoclonal antibody. Following immunization of mice, without adjuvant, pre-F/F-containing VLPs induced significantly higher neutralizing antibody titers than the post-F/F-containing VLPs or the wild-type F/F-containing VLPs after a single immunization but not after prime and boost immunization. The specificities of anti-F IgG induced by the two mutant VLPs were assessed by enzyme-linked immunosorbent assay (ELISA) using soluble forms of the prefusion and postfusion forms of the F protein as targets. While both types of VLPs stimulated similar levels of IgG specific for the soluble postfusion F protein, titers of IgG specific for prefusion F induced by the pre-F/F-containing VLPs were higher than those induced by post-F/F-containing VLPs. Thus, VLPs containing a stabilized prefusion form of the RSV F protein represent a promising RSV vaccine candidate.

IMPORTANCE

The development of vaccines for respiratory syncytial virus has been hampered by a lack of understanding of the requirements for eliciting high titers of neutralizing antibodies. The results of this study suggest that particle-associated RSV F protein containing mutations that stabilize the structure in a prefusion conformation may stimulate higher titers of protective antibodies than particles containing F protein in a wild-type or postfusion conformation. These findings indicate that the prefusion F protein assembled into VLPs has the potential to produce a successful RSV vaccine candidate.

Modification of the respiratory syncytial virus f protein in virus-like particles impacts generation of B cell memory

Immunization with virus-like particles (VLPs) containing the Newcastle disease virus (NDV) core proteins, NP and M, and two chimera proteins (F/F and H/G) containing the respiratory syncytial virus (RSV) F- and G-protein ectodomains fused to the transmembrane and cytoplasmic domains of NDV F and HN proteins, respectively, stimulated durable RSV-neutralizing antibodies, F-protein-specific long-lived, bone marrow-associated plasma cells (LLPCs), and B cell memory, in striking contrast to RSV infection, which did not (M. R. Schmidt, L. W. McGinnes, S. A. Kenward, K. N. Willems, R. T. Woodland, and T. G. Morrison, J. Virol. 86:11654-11662, 2012). Here we report the characterization of a VLP with an RSV F-protein ectodomain fused to the NDV F-protein heptad repeat 2 (HR2), transmembrane, and cytoplasmic domain sequences, creating a chimera with two tandem HR2 domains, one from the RSV F protein and the other from the NDV F-protein ectodomain (F/HR2F). The F/HR2F chimera protein was efficiently assembled into VLPs along with the H/G chimera protein. This VLP (VLP-H/G+F/HR2F) stimulated anti-F-protein and anti-G-protein IgG, durable RSV-neutralizing antibodies, and anti-RSV F-protein-secreting LLPCs. However, the subtypes of anti-F-protein IgG induced were different from those elicited by VLPs containing the F/F chimera (VLP-H/G+F/F). Most importantly, VLP-H/G+F/HR2F did not induce RSV F-protein-specific B cell memory, as shown by the adoptive transfer of B cells from immunized animals to immunodeficient animals. The VLP did, however, induce B cell memory specific to the RSV G protein. Thus, the form of the F protein has a direct role in inducing anti-F-protein B cell memory.

IMPORTANCE

The development of vaccines for respiratory syncytial virus (RSV) is hampered by a lack of a clear understanding of the requirements for eliciting protective as well as durable human immune responses to virus antigens. The results of this study indicate that the form of the RSV F protein has a direct and significant impact on the type of anti-F-protein IgG antibodies induced and the generation of F-protein-specific memory. Identification of the conformation of the RSV F protein that most effectively stimulates not only LLPCs and but also memory B cells will be important in the future development of RSV vaccines.

Subunit and virus-like particle vaccine approaches for respiratory syncytial virus

Despite its impact on global health, there is no vaccine available for the prevention of respiratory syncytial virus (RSV) infection. Failure to develop a licensed vaccine is not due to lack of effort, as numerous vaccine candidates have been characterized in preclinical and clinical studies spanning five decades. The vaccine candidates thus far explored can be generally divided into four categories: (1) whole inactivated virus, (2) replication competent, attenuated virus including recombinant viruses, (3) gene-based vectors, and (4) subunit and particulate forms of RSV antigens. The first clinically tested RSV vaccine candidate was a formalin-inactivated purified virus preparation administered to infants and children in the late 1960s. Due to the disastrous outcome of these trials and results of animal models investigating the mechanisms involved, there have been no further studies with inactivated RSV vaccines. Rather, efforts have focused on development of other approaches. In this chapter, we review the history and status of purified proteins, peptides, virus-like particles, virosomes, and nanoparticles and discuss their future potential.

Vaccination with the RSV fusion protein formulated with a combination adjuvant induces long-lasting protective immunity

Respiratory syncytial virus (RSV) is one of the primary causative agents of upper and lower respiratory tract infections in young children, in particular infants. Recently, we reported the protective efficacy of a RSV vaccine formulation consisting of a truncated version of the fusion (F) protein formulated with a Toll-like receptor (TLR) agonist and an immunostimulatory peptide in a carrier system (ΔF/TriAdj). To evaluate the duration of immunity induced by this vaccine candidate, we carried out long-term trials. The ΔF was formulated with triple adjuvant (TriAdj) containing either polyinosinic : polycytidylic acid (polyI : C) or cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODNs) and administered intranasally to mice. One year after the second vaccination all mice were challenged with RSV. Both ΔF/TriAdj formulations mediated the induction of high levels of IgG1, IgG2a and virus-neutralizing antibodies, and IgA in the lungs. Based on the numbers of IFN-γ- and IL-5-secreting cells in the spleen, the immune response was slightly T-helper cell type 1 (Th1)-biased. This was confirmed by the presence of F85-93-specific CD8(+) effector T cells in the lungs of both ΔF/TriAdj(polyI : C)- and ΔF/TriAdj(CpG)-immunized mice. Both ΔF/TriAdj formulations induced RSV-specific CD8(+) T cells. However, ΔF/TriAdj(polyI : C) generated significantly higher IgG affinity maturation and higher numbers of RSV-specific CD8(+) effector memory T cells in lungs and CD8(+) central memory T cells in spleen and lymph nodes than ΔF/TriAdj(CpG). After RSV challenge, no virus replication and no evidence of vaccine-induced pathology were detected in mice immunized with either of the ΔF/TriAdj formulations, demonstrating that the duration of immunity induced with these vaccines is at least one year.

Sublingual administration of a helper-dependent adenoviral vector expressing the codon-optimized soluble fusion glycoprotein of human respiratory syncytial virus elicits protective immunity in mice

Sublingual (s.l.) immunization has been described as a convenient and safe way to induce mucosal immune responses in the respiratory and genital tracts. We constructed a helper-dependent adenoviral (HDAd) vector expressing a condon-optimized soluble fusion glycoprotein (sFsyn) of respiratory syncytial virus (HDAd-sFsyn) and explored the potential of s.l. immunization with HDAd-sFsyn to stimulate immune responses in the respiratory mucosa. The RSV specific systemic and mucosal immune responses were generated in BALB/c mice, and the serum IgG with neutralizing activity was significantly elevated after homologous boost with s.l. application of HDAd-sFsyn. Humoral immune responses could be measured even 14weeks after a single immunization. Upon challenge, s.l. immunization with HDAd-sFsyn displayed an effective protection against RSV infection. These findings suggest that s.l. administration of HDAd-sFsyn acts as an effective and safe mucosal vaccine against RSV infection, and may be a useful tool in the prevention of RSV infection.

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.

Recent advances in diagnosis, prevention, and treatment of human respiratory syncytial virus

Human respiratory syncytial virus (RSV) is a common cause of respiratory infection in infants and the elderly, leading to significant morbidity and mortality. The interdisciplinary fields, especially biotechnology and nanotechnology, have facilitated the development of modern detection systems for RSV. Many anti-RSV compounds like fusion inhibitors and RNAi molecules have been successful in laboratory and clinical trials. But, currently, there are no effective drugs for RSV infection even after decades of research. Effective diagnosis can result in effective treatment, but the progress in both of these facets must be concurrent. The development in prevention and treatment measures for RSV is at appreciable pace, but the implementation into clinical practice still seems a challenge. This review attempts to present the promising diverse research approaches and advancements in the area of diagnosis, prevention, and treatment that contribute to RSV management.

Nanoparticle vaccines encompassing the respiratory syncytial virus (RSV) G protein CX3C chemokine motif induce robust immunity protecting from challenge and disease

Nanoparticle vaccines were produced using layer-by-layer fabrication and incorporating respiratory syncytial virus (RSV) G protein polypeptides comprising the CX3C chemokine motif. BALB/c mice immunized with G protein nanoparticle vaccines produced a neutralizing antibody response that inhibited RSV replication in the lungs following RSV challenge. ELISPOT analysis showed that G nanoparticle vaccinated mice had increased levels of RSV G protein-specific IL-4 and IFN-γ secreting cells compared to controls following RSV challenge. Remarkably, RSV challenge of G protein nanoparticle vaccinated mice resulted in increased RSV M2-specific IL-4 and IFN-γ secreting T cells, and increased M2-specific H-2Kd-tetramer positive CD8⁺ T cells in the lungs compared to controls. Cell type analysis showed vaccination was not associated with increased pulmonary eosinophilia following RSV challenge. These results demonstrate that vaccination of mice with the RSV G protein nanoparticle vaccines induces a potent neutralizing antibody response, increased G protein- and M2- specific T cell responses, and a reduction in RSV disease pathogenesis.

Infection-enhancing lipopeptides do not improve intranasal immunization of cotton rats with a delta-G candidate live-attenuated human respiratory syncytial virus vaccine

Development of live-attenuated human respiratory syncytial virus (HRSV) vaccines has proven to be difficult. Several vaccine candidates were found to be over-attenuated and displayed limited immunogenicity. Recently, we identified three synthetic cationic lipopeptides that enhanced paramyxovirus infections in vitro. The infection enhancement proved to be mediated by enhanced virus binding to target cells. We hypothesized that these lipopeptides can be used as adjuvants to promote immune responses induced by live-attenuated paramyxovirus vaccines. This hypothesis was tested in a vaccination and challenge model in cotton rats, using a previously described recombinant live-attenuated candidate HRSV vaccine lacking the gene encoding the G glycoprotein (rHRSVΔG). Surprisingly, intranasal vaccination of cotton rats with rHRSVΔG formulated in infection-enhancing lipopeptides resulted in reduced virus loads in nasopharyngeal lavages, reduced seroconversion levels and reduced protection from wild-type HRSV challenge. In conclusion, we were unable to demonstrate the feasibility of lipopeptides as adjuvants for a candidate live-attenuated HRSV vaccine in the cotton rat model.

Neonatal immunization with respiratory syncytial virus glycoprotein fragment induces protective immunity in the presence of maternal antibodies in mice

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections in infants and the elderly worldwide. The significant morbidity and mortality associated with this infection underscores the urgent need for development of RSV vaccine. In this study, we first show that intranasal administration of RSV glycoprotein core fragment (Gcf) to neonatal mice can induce systemic humoral immune responses and protective immunity against RSV without causing lung eosinophilia, although antibody response was shifted to a Th2 response. Next, we examined whether the presence of maternal anti-RSV antibodies would affect the responsiveness and protection efficacy of Gcf in newborn mice, since infants can possess RSV-specific maternal antibodies due to frequent RSV re-infections to adults. Intranasal administration of Gcf induced antibody response and increased IFNγ secretion and protected mice against RSV challenge without severe lung eosinophilia, even in the presence of high levels of RSV-specific maternal antibodies. Thus, our findings suggest that Gcf may be an effective and safe RSV vaccine during the neonatal period.

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.

Intranasal immunization with a helper-dependent adenoviral vector expressing the codon-optimized fusion glycoprotein of human respiratory syncytial virus elicits protective immunity in BALB/c mice

Background

Human respiratory syncytial virus (RSV) is a serious pediatric pathogen of the lower respiratory tract. Currently, there is no clinically approved vaccine against RSV infection. Recent studies have shown that helper-dependent adenoviral (HDAd) vectors may represent effective and safe vaccine vectors. However, viral challenge has not been investigated following mucosal vaccination with HDAd vector vaccines.

Methods

To explore the role played by HDAd as an intranasally administered RSV vaccine vector, we constructed a HDAd vector encoding the codon optimized fusion glycoprotein (Fsyn) of RSV, designated HDAd-Fsyn, and delivered intranasally HDAd-Fsyn to mice.

Results

RSV-specific humoral and cellular immune responses were generated in BALB/c mice, and serum IgG with neutralizing activity was significantly elevated after a homologous boost with intranasal (i.n.) application of HDAd-Fsyn. Humoral immune responses could be measured even 14 weeks after a single immunization. Immunization with i.n. HDAd-Fsyn led to effective protection against RSV infection on challenge.

Conclusion

The results indicate that HDAd-Fsyn can induce powerful systemic immunity against subsequent i.n. RSV challenge in a mouse model and is a promising candidate vaccine against RSV infection.

Respiratory syncytial virus infection in children with severe motor and intellectual disabilities

Children with severe motor intellectual disabilities (SMID) are at high risk of death from acute viral lower respiratory tract infections (LRTI). Although respiratory syncytial virus (RSV) is the most common cause of viral LRTI in children, there have been a few reports on the relationship between SMID and the severity of RSV-LRTI. The aim of the present study is to assess the influence of RSV-LRTI in children with SMID. A case-control study composed of children with SMID (n = 18) and previously healthy children (n = 43) less than 16 years old hospitalized for RSV-LRTI was performed during five consecutive RSV seasons. The clinical presentation and the laboratory data in the SMID group were compared with those in the non-SMID group. In the bivariate analysis, the median age of the SMID group was higher than that of the non-SMID group (p = 0.002). Children with SMID had an increased risk for ventilation support (p = 0.057). The count of neutrophils in the SMID group was significantly increased (p = 0.012), whereas the proportion of bacterial co-infection was lower than that in the non-SMID group (p = 0.005). Multivariate logistic analysis showed that SMID was associated with longer oxygen usage [>7 days: odds ratio (OR) 5.309, p = 0.033]. The present study revealed that children with SMID were prone to developing hypoxia by RSV-LRTI. The strategies for the treatment and prevention of RSV infection need to be improved in SMID children.

A nonviral pHEMA+chitosan nanosphere-mediated high-efficiency gene delivery system

The transport of DNA into eukaryotic cells is minimal because of the cell membrane barrier, and this limits the application of DNA vaccines, gene silencing, and gene therapy. Several available transfection reagents and techniques have been used to circumvent this problem. Alternatively, nonviral nanoscale vectors have been shown to bypass the eukaryotic cell membrane. In the present work, we developed a unique nanomaterial, pHEMA+chitosan nanospheres (PCNSs), which consisted of poly(2-hydroxyethyl methacrylate) nanospheres surrounded by a chitosan cationic shell, and we used this for encapsulation of a respiratory syncytial virus (RSV)-F gene construct (a model for a DNA vaccine). The new nanomaterial was capable of transfecting various eukaryotic cell lines without the use of a commercial transfection reagent. Using transmission electron microscopy, (TEM), fluorescence activated cell sorting (FACS), and immunofluorescence, we clearly demonstrated that the positively charged PCNSs were able to bind to the negatively charged cell membrane and were taken up by endocytosis, in Cos-7 cells. Using quantitative polymerase chain reaction (qPCR), we also evaluated the efficiency of transfection achieved with PCNSs and without the use of a liposomal-based transfection mediator, in Cos-7, HEp-2, and Vero cells. To assess the transfection efficiency of the PCNSs in vivo, these novel nanomaterials containing RSV-F gene were injected intramuscularly into BALB/c mice, resulting in high copy number of the transgene. In this study, we report, for the first time, the application of the PCNSs as a nanovehicle for gene delivery in vitro and in vivo.

Respiratory viruses from hospitalized children with severe pneumonia in the Philippines

BACKGROUND

Pneumonia remains a leading cause of child death in developing countries. The viruses in severe pneumonia remain poorly defined.

METHODS

The study was conducted at the Eastern Visayas Regional Medical Center in Tacloban City, Philippines from May 2008 to May 2009. Patients aged 8 days to 13 years old who were admitted to the Department of Pediatrics with severe pneumonia were enrolled for the study. Upon admission, polymerase chain reaction was performed using nasopharyngeal swabs and blood cultures to detect respiratory viruses and bacteria, respectively.

RESULT

Among the 819 patients enrolled, at least one virus was detected in 501 cases (61.2%). In addition, 423 cases were positive for a single virus while bacteria were detected in the blood culture sample of 31 cases. The most commonly detected viruses were human rhinoviruses (n = 189), including types A (n = 103), B (n = 17), and C (n = 69), and respiratory syncytial virus (RSV) (n = 165). Novel viruses such as human metapneumovirus, human coronavirus NL63, human bocavirus, and human polyomaviruses WU and KI were also detected. There were 70 deaths, and one or more viruses were detected in 35 (50%) of these cases. Positivity only for influenza A virus (OR = 4.3, 95% CI = 1.3-14.6) was significantly associated with fatal outcome. From the blood culture, Burkholderia cepacia group (n = 9), Streptococcus pneumoniae (n = 4), Staphylococcus aureus (n = 4), Haemophilus influenzae (n = 1), and Salmonella C1 (n = 1) were also isolated.

CONCLUSION

Viruses were commonly detected in children with severe pneumonia in the Philippines. Hence, viral etiologies should be considered while developing better effective strategies to reduce child pneumonia-related deaths in developing countries.

Long-term and memory immune responses in mice against Newcastle disease virus-like particles containing respiratory syncytial virus glycoprotein ectodomains

Although respiratory syncytial virus (RSV) is a significant human pathogen, no RSV vaccines are available. We have reported that a virus-like particle (VLP) RSV vaccine candidate stimulated, in mice, robust, protective anti-RSV glycoprotein T(H)1 biased immune responses without enhanced respiratory disease upon RSV challenge. We report here an analysis of long-term responses to these VLPs. BALB/c mice immunized, without adjuvant, with VLPs or with infectious RSV generated anti-F and anti-G protein serum antibody responses that were stable over 14 months. Neutralizing antibody titers stimulated by VLPs were robust and durable for 14 months, whereas those of RSV-immunized animals declined significantly by 3 months. F protein-specific antibody-secreting cells were detected in the bone marrows of VLP-immunized mice but not in the marrows of RSV-immunized mice. Adoptive transfer of enriched splenic B cells from VLP-immunized mice into immunodeficient rag(-/-) mice resulted in anti-F and anti-G protein serum IgG antibody responses, in recipient mice, that were protective upon RSV challenge. In contrast, transfer of splenic B cells from RSV-immunized mice produced no detectable serum antibody in the recipients, nor could these mice inhibit RSV replication upon virus challenge. Immunization with VLPs stimulated the formation of germinal center GL7(+) B cells in normal mice. VLP immunization of TCR βδ(-/-) T-cell-deficient mice did not induce anti-RSV IgG antibodies, results consistent with T-cell-dependent immune responses. These results demonstrate that VLPs are effective in stimulating long-lived RSV-specific, T-cell-dependent neutralizing antibody-secreting cells and RSV-specific memory responses.

Antibodies to the central conserved region of respiratory syncytial virus (RSV) G protein block RSV G protein CX3C-CX3CR1 binding and cross-neutralize RSV A and B strains

Respiratory syncytial virus (RSV) is a primary cause of severe lower respiratory tract disease in infants, young children, and the elderly worldwide, and despite decades of effort, there remains no safe and effective vaccine. RSV modifies the host immune response during infection by CX3C chemokine mimicry adversely affecting pulmonary leukocyte chemotaxis and CX3CR1+ RSV-specific T-cell responses. In this study we investigated whether immunization of mice with RSV G protein polypeptides from strain A2 could induce antibodies that block G protein-CX3CR1 interactions of both RSV A and B strains. The results show that mice immunized with RSV A2 G polypeptides generate antibodies that block binding of RSV A2 and B1 native G proteins to CX3CR1, and that these antibodies effectively cross-neutralize both A and B strains of RSV. These findings suggest that vaccines that induce RSV G protein-CX3CR1 blocking antibodies may provide a disease intervention strategy in the efforts to develop safe and efficacious RSV vaccines.

The respiratory syncytial virus G protein conserved domain induces a persistent and protective antibody response in rodents

Respiratory syncytial virus (RSV) is an important cause of severe upper and lower respiratory disease in infants and in the elderly. There are 2 main RSV subtypes A and B. A recombinant vaccine was designed based on the central domain of the RSV-A attachment G protein which we had previously named G2Na (aa130-230). Here we evaluated immunogenicity, persistence of antibody (Ab) response and protective efficacy induced in rodents by: (i) G2Na fused to DT (Diphtheria toxin) fragments in cotton rats. DT fusion did not potentiate neutralizing Ab responses against RSV-A or cross-reactivity to RSV-B. (ii) G2Nb (aa130-230 of the RSV-B G protein) either fused to, or admixed with G2Na. G2Nb did not induce RSV-B-reactive Ab responses. (iii) G2Na at low doses. Two injections of 3 µg G2Na in Alum were sufficient to induce protective immune responses in mouse lungs, preventing RSV-A and greatly reducing RSV-B infections. In cotton rats, G2Na-induced RSV-reactive Ab and protective immunity against RSV-A challenge that persisted for at least 24 weeks. (iv) injecting RSV primed mice with a single dose of G2Na/Alum or G2Na/PLGA [poly(D,L-lactide-co-glycolide]. Despite the presence of pre-existing RSV-specific Abs, these formulations effectively boosted anti-RSV Ab titres and increased Ab titres persisted for at least 21 weeks. Affinity maturation of these Abs increased from day 28 to day 148. These data indicate that G2Na has potential as a component of an RSV vaccine formulation.

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.

Respiratory syncytial virus disease: update on treatment and prevention

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in infants and young children, accounting for more than 100,000 hospitalizations per year in the USA. The majority of hospitalizations occur in infants less than 1 year of age. Worldwide, RSV is associated with an annual mortality rate of 160,000-600,000 deaths. Premature infants, and infants with congenital heart disease, neuromuscular disease, structural airway abnormalities and immunodeficiencies are at increased risk for severe RSV disease. Despite the magnitude of RSV disease, treatment remains primarily supportive. Trials of bronchodilators, corticosteroids and montelukast have not demonstrated conclusive clinical benefit. The antiviral drug ribavirin has demonstrated only marginal clinical benefit and is not routinely indicated in treatment of RSV disease. Palivizumab is beneficial in prophylaxis for infants at high-risk for severe RSV infection although optimal indications based on cost-effectiveness considerations have not been defined. Future directions in treatment and prevention of RSV infections likely include the second-generation monoclonal antibody motavizumab, more potent antiviral compounds and more unique anti-inflammatory agents. Vaccination against RSV is in development but not eminent.

Reduced Dicer expression in the cord blood of infants admitted with severe respiratory syncytial virus disease

Background

Respiratory syncytial virus (RSV) is one of the most important causes of pediatric hospital admissions in the developed world. The ribonuclease Dicer is an important regulator of gene expression and cellular function via RNA interference, and may also have anti-viral functions. A previous microarray analysis of the cord blood of 5 patients with RSV disease suggested downregulation of Dicer. In order to further investigate whether reduced Dicer expression can predispose newborns to RSV disease, we have analyzed the gene expression of Dicer in the cord blood of 37 infants with confirmed RSV disease.

Methods

The cord blood of 2108 newborns was collected. 51 had a positive nasopharyngeal aspirate for RSV <1 year, and were grouped according to disease severity. 37 had sufficient cord blood RNA of good quality. Dicer gene expression was assessed by qPCR analysis of cord blood using a TaqMan low-density array and compared to control infants who did not present with RSV disease using the Mann-Whitney test.

Results

There was significant downregulation of Dicer in the severe disease group: relative quantity 0.69 (95% CI: 0.56 - 0.87), p = 0.002. There was no significant downregulation in the mild disease group.

Conclusions

We demonstrate reduced Dicer expression in the cord blood of infants with severe RSV disease, prior to RSV exposure. We theorize that this may predispose to RSV disease by disruption of leukocyte gene regulation or direct anti-viral RNA interference mechanisms.

Respiratory syncytial virus represses glucocorticoid receptor-mediated gene activation

Respiratory syncytial virus (RSV) is a common cause of bronchiolitis in infants. Although antiinflammatory in nature, glucocorticoids have been shown to be ineffective in the treatment of RSV-induced bronchiolitis and wheezing. In addition, the effectiveness of glucocorticoids at inhibiting RSV-induced proinflammatory cytokine production in cell culture has been questioned. In this study, we have investigated the effect of RSV infection on glucocorticoid-induced gene activation in lung epithelium-derived cells. We show that RSV infection inhibits dexamethasone induction of three glucocorticoid receptor (GR)-regulated genes (glucocorticoid-inducible leucine zipper, FK506 binding protein, and MAPK phosphatase 1) in A549, BEAS-2B cells, and primary small airway epithelial cells. UV irradiation of the virus prevents this repression, suggesting that viral replication is required. RSV is known to activate the nuclear factor κB (NFκB) pathway, which is mutually antagonistic towards the GR pathway. However, specific inhibition of NFκB had no effect on the repression of GR-induced genes by RSV infection, indicating that RSV repression of GR is independent of NFκB. RSV infection of A549 cells does not alter GR protein levels or GR nuclear translocation but does reduce GR binding to the promoters of the glucocorticoid responsive genes analyzed in this study. Repression of GR by RSV infection may account for the apparent clinical ineffectiveness of glucocorticoids in RSV bronchiolitis therapy. In addition, this data adds to our previously published data suggesting that GR may be a general target for infectious agents. Identifying the mechanisms through which this suppression occurs may lead to the development of novel therapeutics.

Prevention of serious respiratory syncytial virus-related illness. I: Disease pathogenesis and early attempts at prevention

Respiratory syncytial virus (RSV) was first described 160 years ago but was not officially recognized as a cause of serious illness in children until the late 1950s. It has been estimated that virtually all children have had at least one RSV infection by their second birthday. RSV is responsible for annual disease outbreaks, usually during a defined winter seasonal period that can vary by community and year. RSV is recognized as the leading cause of hospitalization among young children worldwide. Infants of young chronologic age and children with predisposing factors, such as premature birth, pulmonary disease, or congenital heart disease, are most susceptible to serious illness. Unlike other viruses, immunity to RSV infection is incomplete and short lived, and reinfection is common throughout life. Initial attempts to develop a vaccine in the 1960s met with unexpected and tragic results; many children vaccinated with a formalin-inactivated wild-type virus developed serious pulmonary disease upon subsequent natural infection. Numerous other vaccine technologies have since been studied, including vectored approaches, virus-like particles, DNA vaccines, and live attenuated virus vaccine. As of early 2010, only two companies or institutions had RSV vaccine candidates in early clinical trials, and no vaccine is likely to be licensed for marketing in the immediate future.

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.

Newcastle disease virus-like particles as a platform for the development of vaccines for human and agricultural pathogens

Vaccination is the single most effective way to control viral diseases. However, many currently used vaccines have safety concerns, efficacy issues or production problems. For other viral pathogens, classic approaches to vaccine development have, thus far, been unsuccessful. Virus-like particles (VLPs) are increasingly being considered as vaccine candidates because they offer significant advantages over many currently used vaccines or developing vaccine technologies. VLPs formed with structural proteins of Newcastle disease virus, an avian paramyxovirus, are a potential vaccine candidate for Newcastle disease in poultry. More importantly, these VLPs are a novel, uniquely versatile VLP platform for the rapid construction of effective vaccine candidates for many human pathogens, including genetically complex viruses and viruses for which no vaccines currently exist.

Use of respiratory syncytial virus surveillance data to optimize the timing of immunoprophylaxis

OBJECTIVE

For children in the United States who are at high risk for severe respiratory syncytial virus (RSV) infection, the American Academy of Pediatrics (AAP) recommends administering immunoprophylaxis during the RSV season. We present an approach to using surveillance data to help guide application of AAP recommendations for immunoprophylaxis to local patterns of RSV outbreaks.

METHODS

We analyzed data from laboratories that report consistently to the National Respiratory and Enteric Virus Surveillance System from 1992 to 2007. Local RSV seasons were defined and an immunoprophylaxis schedule was determined by using the median onset dates from each laboratory during 2002-2007. We applied these dates to 10 preceding years of RSV detection data. We compared how well the 5-year median-based method and a fixed date method were able to match the timing of immunoprophylaxis to the RSV season.

RESULTS

Nineteen laboratories met our inclusion criteria and generally experienced only 1 RSV outbreak per season. Five years of data gave similar median onset/offset dates and season duration, as did 10 years and 15 years of data. The 5-year median schedule increased the number of seasons that children were protected at the season onset by 15% compared with a fixed start date of November 1 and identified communities that experienced RSV seasons with extended durations.

CONCLUSIONS

The 5-year median method can be used to characterize timing of RSV seasons and optimally apply the current AAP recommendations for timing of palivizumab prophylaxis to the local community.

Relative impact of influenza and respiratory syncytial virus in young children

OBJECTIVE

We measured the relative impact of influenza and respiratory syncytial virus (RSV) infections in young children in terms of emergency department (ED) visits, clinical care requirements, and overall resource use.

METHODS

Patients who were aged <or=7 years and treated in the ED of a tertiary care pediatric hospital for an acute respiratory infection were enrolled during 2 winter seasons between 2003 and 2005. We quantified health care resource use for children with influenza or RSV infections, and extrapolated results to estimate the national resource use associated with influenza and RSV infections.

RESULTS

Nationally, an estimated 10.2 ED visits per 1000 children were attributable to influenza and 21.5 visits per 1000 to RSV. Children who were aged 0 to 23 months and infected with RSV had the highest rate of ED visits with 64.4 visits per 1000 children. Significantly more children required hospitalization as a result of an RSV infection compared with influenza, with national hospitalization rates of 8.5 and 1.4 per 1000 children, respectively. The total number of workdays missed yearly by caregivers of children who required ED care was 246965 days for influenza infections and 716404 days for RSV infections.

CONCLUSION

For young children, RSV is associated with higher rates of ED visits, hospitalization, and caregiver resource use than is influenza. Our results provide data on the large number of children who receive outpatient care for influenza and RSV illnesses and serve to inform analyses of prevention programs and treatments for both influenza and RSV disease.

Vaccination to induce antibodies blocking the CX3C-CX3CR1 interaction of respiratory syncytial virus G protein reduces pulmonary inflammation and virus replication in mice

Respiratory syncytial virus (RSV) infection causes substantial morbidity and some deaths in the young and elderly worldwide. There is no safe and effective vaccine available, although it is possible to reduce the hospitalization rate for high-risk children by anti-RSV antibody prophylaxis. RSV has been shown to modify the immune response to infection, a feature linked in part to RSV G protein CX3C chemokine mimicry. This study determined if vaccination with G protein polypeptides or peptides spanning the central conserved region of the G protein could induce antibodies that blocked G protein CX3C-CX3CR1 interaction and disease pathogenesis mediated by RSV infection. The results show that mice vaccinated with G protein peptides or polypeptides containing the CX3C motif generate antibodies that inhibit G protein CX3C-CX3CR1 binding and chemotaxis, reduce lung virus titers, and prevent body weight loss and pulmonary inflammation. The results suggest that RSV vaccines that induce antibodies that block G protein CX3C-CX3CR1 interaction may offer a new, safe, and efficacious RSV vaccine strategy.

Virus vaccines and children with asthma

PURPOSE OF REVIEW

To describe what is currently known about the role of virus vaccines in the pathogenesis of asthma and atopy and summarize their role in the prevention of morbidity due to childhood asthma.

RECENT FINDINGS

The development of virus vaccines and their incorporation into infant and childhood immunization programmes over the last few decades of the twentieth century have been accompanied by a striking concomitant rise in the incidence of asthma and atopy. However, a causal relationship is not supported by the majority of observational studies. The role of childhood immunization against respiratory viruses in the reduction of morbidity from asthma is another important public health issue. Recent findings suggest that influenza is not strongly associated with exacerbations of asthma in children, despite recommendations that this group should be immunized against it.

SUMMARY

Current evidence suggests that virus vaccination is well tolerated and does not lead to an increased incidence of asthma or atopy in children receiving vaccines. Debate continues regarding the place of respiratory virus vaccination in the therapeutic armamentarium for children with asthma. In the case of influenza, there appears to be an absence of harm, but benefit seems to be limited to younger children.

Primary high-dose murine norovirus 1 infection fails to protect from secondary challenge with homologous virus

Human noroviruses in the Caliciviridae family are the major cause of nonbacterial epidemic gastroenteritis worldwide. Primary human norovirus infection does not elicit lasting protective immunity, a fact that could greatly affect the efficacy of vaccination strategies. Little is known regarding the pathogenesis of human noroviruses or the immune responses that control them because there has previously been no small-animal model or cell culture system of infection. Using the only available small-animal model of norovirus infection, we found that primary high-dose murine norovirus 1 (MNV-1) infection fails to afford protection against a rechallenge with a homologous virus. Thus, MNV-1 represents a valuable model with which to dissect the pathophysiological basis for the lack of lasting protection against human norovirus infection. Interestingly, the magnitude of protection afforded by a primary MNV-1 infection inversely correlates with the inoculum dose. Future studies will elucidate the mechanisms by which noroviruses avoid the induction of protective immunity and the role played by the inoculum dose in this process, ultimately translating this knowledge into successful vaccination approaches.

Genetic diversity of the host and severe respiratory syncytial virus-induced lower respiratory tract infection

Respiratory syncytial virus (RSV)-induced lower respiratory tract disease is a common problem in children and adults in Western societies. The clinical range of RSV infection from asymptomatic to respiratory distress syndrome is believed to be the outcome of viral and host immunity interactions. Genes associated with immune response are of particular interest regarding genetic predisposition to severe RSV infection. Several investigators have sought to identify genetic markers for high-risk patients, and more than 20 independent studies in the medical literature assess the impact of genetic variations-mostly single nucleotide polymorphisms-on the clinical presentation of RSV-induced disease. Several candidate gene loci have been tested in association studies based on the concept that a particular allele is a significant risk factor for a phenotype of interest. Despite the wealth of information available, we are still far from evolving a practical and cost-effective screening tool; certain flaws in association studies first need to be overcome. The development of haplotype-based analysis for candidate loci across the genome, along with advances in biostatistics and bioinformatics, would facilitate the assessment of the relative contribution of genetic markers to disease susceptibility in RSV infection.

RNA interference inhibits respiratory syncytial virus replication and disease pathogenesis without inhibiting priming of the memory immune response

Respiratory syncytial virus (RSV) is a major cause of morbidity in infants, young children, and the elderly worldwide. Currently, there is no effective vaccine, and antiviral drugs to control infection are limited. RNA interference is a powerful tool amenable to development of antiviral drugs. Using small interfering RNA (siRNA) targeting the RSV P gene (siRNA-P), RSV replication can be silenced both in vitro and in a BALB/c model of RSV infection. In this study, we examine the effect of siRNA prophylaxis on the primary and memory immune response to RSV infection in mice. We show that mice prophylactically treated with siRNA-P to decrease but not eliminate RSV replication exhibit reduced pulmonary inflammation and lung pathogenesis and produce a robust anti-RSV memory response when subsequently challenged with RSV. The pulmonary T-cell memory response was characterized by high numbers of CD44(hi) CD62L(lo) CD4(+) and CD8(+) T cells, M2 peptide tetramer(+) CD8(+) T cells expressing gamma interferon, and an RSV-specific antibody response. The results support the hypothesis that siRNAs can be developed as effective antiviral drugs that can be used to reduce the viral load and parameters of pathogenesis without limiting the induction of the memory immune response.