Both immunisation with a formalin-inactivated respiratory syncytial virus (RSV) vaccine and a mock antigen vaccine induce severe lung pathology and a Th2 cytokine profile in RSV-challenged mice

Adjuvant-dependent impact of inactivated SARS-CoV-2 vaccines during heterologous infection by a SARS-related coronavirus

Whole virus-based inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide have been critical to the COVID-19 pandemic response. Although these vaccines are protective against homologous coronavirus infection, the emergence of novel variants and the presence of large zoonotic reservoirs harboring novel heterologous coronaviruses provide significant opportunities for vaccine breakthrough, which raises the risk of adverse outcomes like vaccine-associated enhanced respiratory disease. Here, we use a female mouse model of coronavirus disease to evaluate inactivated vaccine performance against either homologous challenge with SARS-CoV-2 or heterologous challenge with a bat-derived coronavirus that represents a potential emerging disease threat. We show that inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide can cause enhanced respiratory disease during heterologous infection, while use of an alternative adjuvant does not drive disease and promotes heterologous viral clearance. In this work, we highlight the impact of adjuvant selection on inactivated vaccine safety and efficacy against heterologous coronavirus infection.

Adjuvant-dependent effects on the safety and efficacy of inactivated SARS-CoV-2 vaccines during heterologous infection by a SARS-related coronavirus

Inactivated whole virus SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide (Alum) are among the most widely used COVID-19 vaccines globally and have been critical to the COVID-19 pandemic response. Although these vaccines are protective against homologous virus infection in healthy recipients, the emergence of novel SARS-CoV-2 variants and the presence of large zoonotic reservoirs provide significant opportunities for vaccine breakthrough, which raises the risk of adverse outcomes including vaccine-associated enhanced respiratory disease (VAERD). To evaluate this possibility, we tested the performance of an inactivated SARS-CoV-2 vaccine (iCoV2) in combination with Alum against either homologous or heterologous coronavirus challenge in a mouse model of coronavirus-induced pulmonary disease. Consistent with human results, iCoV2 + Alum protected against homologous challenge. However, challenge with a heterologous SARS-related coronavirus, Rs-SHC014-CoV (SHC014), up to at least 10 months post-vaccination, resulted in VAERD in iCoV2 + Alum-vaccinated animals, characterized by pulmonary eosinophilic infiltrates, enhanced pulmonary pathology, delayed viral clearance, and decreased pulmonary function. In contrast, vaccination with iCoV2 in combination with an alternative adjuvant (RIBI) did not induce VAERD and promoted enhanced SHC014 clearance. Further characterization of iCoV2 + Alum-induced immunity suggested that CD4+ T cells were a major driver of VAERD, and these responses were partially reversed by re-boosting with recombinant Spike protein + RIBI adjuvant. These results highlight potential risks associated with vaccine breakthrough in recipients of Alum-adjuvanted inactivated vaccines and provide important insights into factors affecting both the safety and efficacy of coronavirus vaccines in the face of heterologous virus infections.

Development of Respiratory Syncytial Virus Vaccine Candidates for the Elderly

Respiratory syncytial virus (RSV) is a significant threat to elderly populations and repeated infections that occur throughout life are poorly protective. To assess the role of prior RSV infections as well as elderly immune senescence on vaccine efficacy, we compared immune responses after virus-like particle (VLP) immunization of elderly cotton rats and young cotton rats, both previously RSV infected, in order to mimic the human population. We show that immunization of RSV-experienced young or elderly animals resulted in the same levels of anti-pre-F IgG, anti-G IgG, neutralizing antibody titers, and protection from challenge indicating that the delivery of F and G proteins in a VLP is equally effective in activation of protective responses in both elderly and young populations. Our results suggest that F and G protein-containing VLPs induce anti-RSV memory established in prior RSV infections equally well in both young and elderly animals and thus can be an effective vaccine for the elderly.

From animal studies into clinical trials: the relevance of animal models to develop vaccines and therapies to reduce disease severity and prevent hRSV infection

INTRODUCTION

Human respiratory syncytial virus (hRSV) is an important cause of lower respiratory tract infections in the pediatric and the geriatric population worldwide. There is a substantial economic burden resulting from hRSV disease during winter. Although no vaccines have been approved for human use, prophylactic therapies are available for high-risk populations. Choosing the proper animal models to evaluate different vaccine prototypes or pharmacological treatments is essential for developing efficient therapies against hRSV.

AREAS COVERED

This article describes the relevance of using different animal models to evaluate the effect of antiviral drugs, pharmacological molecules, vaccine prototypes, and antibodies in the protection against hRSV. The animal models covered are rodents, mustelids, bovines, and nonhuman primates. Animals included were chosen based on the available literature and their role in the development of the drugs discussed in this manuscript.

EXPERT OPINION

Choosing the correct animal model is critical for exploring and testing treatments that could decrease the impact of hRSV in high-risk populations. Mice will continue to be the most used preclinical model to evaluate this. However, researchers must also explore the use of other models such as nonhuman primates, as they are more similar to humans, prior to escalating into clinical trials.

Mucosal administration of a live attenuated recombinant COVID-19 vaccine protects nonhuman primates from SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the COVID-19 global pandemic. SARS-CoV-2 is an enveloped RNA virus that relies on its trimeric surface glycoprotein spike for entry into host cells. Here we describe the COVID-19 vaccine candidate MV-014-212, a live, attenuated, recombinant human respiratory syncytial virus expressing a chimeric SARS-CoV-2 spike as the only viral envelope protein. MV-014-212 was attenuated and immunogenic in African green monkeys (AGMs). One mucosal administration of MV-014-212 in AGMs protected against SARS-CoV-2 challenge, reducing by more than 200-fold the peak shedding of SARS-CoV-2 in the nose. MV-014-212 elicited mucosal immunoglobulin A in the nose and neutralizing antibodies in serum that exhibited cross-neutralization against virus variants of concern Alpha, Beta, and Delta. Intranasally delivered, live attenuated vaccines such as MV-014-212 entail low-cost manufacturing suitable for global deployment. MV-014-212 is currently in Phase 1 clinical trials as an intranasal COVID-19 vaccine.

Intranasal vaccination with a recombinant protein CTA1-DD-RBF protects mice against hRSV infection

Human respiratory syncytial virus (hRSV) infection is a major pediatric health concern worldwide. Despite more than half a century of efforts, there is still no commercially available vaccine. In this study, we constructed and purified the recombinant protein CTA1-DD-RBF composed of a CTA1-DD mucosal adjuvant and prefusion F protein (RBF) using Escherichia coli BL21 cells. We studied the immunogenicity of CTA1-DD-RBF in mice. Intranasal immunization with CTA1-DD-RBF stimulated hRSV F-specific IgG1, IgG2a, sIgA, and neutralizing antibodies as well as T cell immunity without inducing lung immunopathology upon hRSV challenge. Moreover, the protective immunity of CTA1-DD-RBF was superior to that of the RBF protein, as confirmed by the assessment of serum-neutralizing activity and viral clearance after challenge. Compared to formalin-inactivated hRSV (FI-RSV), intranasal immunization with CTA1-DD-RBF induced a Th1 immune response. In summary, intranasal immunization with CTA1-DD-RBF is safe and effective in mice. Therefore, CTA1-DD-RBF represents a potential mucosal vaccine candidate for the prevention of human infection with hRSV.

Structure, Immunogenicity, and Conformation-Dependent Receptor Binding of the Postfusion Human Metapneumovirus F Protein

Human metapneumovirus (hMPV) is an important cause of acute viral respiratory infection. As the only target of neutralizing antibodies, the hMPV fusion (F) protein has been a major focus for vaccine development and targeting by drugs and monoclonal antibodies (MAbs). While X-ray structures of trimeric prefusion and postfusion hMPV F proteins from genotype A, and monomeric prefusion hMPV F protein from genotype B have been determined, structural data for the postfusion conformation for genotype B is lacking. We determined the crystal structure of this protein and compared the structural differences of postfusion hMPV F between hMPV A and B genotypes. We also assessed the receptor binding properties of the hMPV F protein to heparin and heparan sulfate (HS). A library of HS oligomers was used to verify the HS binding activity of hMPV F, and several compounds showed binding to predominantly prefusion hMPV F, but had limited binding to postfusion hMPV F. Furthermore, MAbs to antigenic sites III and the 66-87 intratrimeric epitope block heparin binding. In addition, we evaluated the efficacy of postfusion hMPV B2 F protein as a vaccine candidate in BALB/c mice. Mice immunized with hMPV B2 postfusion F protein showed a balanced Th1/Th2 immune response and generated neutralizing antibodies against both subgroup A2 and B2 hMPV strains, which protected the mice from hMPV challenge. Antibody competition analysis revealed the antibodies generated by immunization target two known antigenic sites (III and IV) on the hMPV F protein. Overall, this study provides new characteristics of the hMPV F protein, which may be informative for vaccine and therapy development. IMPORTANCE Human metapneumovirus (hMPV) is an important cause of viral respiratory disease. In this paper, we report the X-ray crystal structure of the hMPV fusion (F) protein in the postfusion conformation from genotype B. We also assessed binding of the hMPV F protein to heparin and heparan sulfate, a previously reported receptor for the hMPV F protein. Furthermore, we determined the immunogenicity and protective efficacy of postfusion hMPV B2 F protein, which is the first study using a homogenous conformation of the protein. Antibodies generated in response to vaccination give a balanced Th1/Th2 response and target two previously discovered neutralizing epitopes.

Antibody dependent enhancement: Unavoidable problems in vaccine development

In some cases, antibodies can enhance virus entry and replication in cells. This phenomenon is called antibody-dependent infection enhancement (ADE). ADE not only promotes the virus to be recognized by the target cell and enters the target cell, but also affects the signal transmission in the target cell. Early formalin-inactivated virus vaccines such as aluminum adjuvants (RSV and measles) have been shown to induce ADE. Although there is no direct evidence that there is ADE in COVID-19, this potential risk is a huge challenge for prevention and vaccine development. This article focuses on the virus-induced ADE phenomenon and its molecular mechanism. It also summarizes various attempts in vaccine research and development to eliminate the ADE phenomenon, and proposes to avoid ADE in vaccine development from the perspective of antigens and adjuvants.

Respiratory Syncytial Virus Infection Reduces Kynurenic Acid Production and Reverses Th17/Treg Balance by Modulating Indoleamine 2,3-Dioxygenase (IDO) Molecules in Plasmacytoid Dendritic Cells

Background

Respiratory syncytial virus (RSV) infection causes a world-wide medical and economic burden. This study analyzed the effects of RSV infection on plasmacytoid dendritic cells (pDCs) and evaluated the immunopathogenesis of RSV infection by measuring relative numbers of FoxP3+ Treg cells and Th17 cells.

Material/Methods

pDCs were isolated from human blood samples, purified using magnetic microbeads, and treated with RSV, IFN-γ, or vehicle. These cells were mixed with purified CD4+ T cells to yield preparations of pDCs+T cells+vehicle, pDCs+T cells+RSV, and pDCs+T cells+IFN-γ. Preparations of pDCs+T cells+RSV were also incubated with an inducer or an inhibitor of indoleamine 2,3-dioxygenase (IDO). Kynurenic acid concentration was measured by high-pressure liquid chromatography (HPLC). The differentiation of Foxp3+ Treg and Th17 cells from CD4+ T cells was determined by flow cytometry.

Results

pDCs were successfully isolated and purified using the magnetic microbeads. Compared with preparations of pDCs+T cells+vehicle, RSV infection (pDCs+T cells+RSV) significantly reduced and IFN-γ treatment (pDC+T cells+IFN-γ) increased kynurenic acid concentrations and the proportions of Foxp3⁺ Tregs (p<0.05 each). Conversely, RSV infection increased and IFN-γ treatment decreased the proportions of Th17 cells (p<0.05 each). RSV infection reduced kynurenic acid concentrations and inhibited the transformation from Th17 to Foxp3⁺ Tregs by modulating IDO molecules.

Conclusions

RSV infection reduced the production of kynurenic acid and inhibited transformation from Th17 to Foxp3⁺ Tregs (Th17/Treg balance) by modulating IDO molecules in pDCs.

Natural Killer and CD8 T Cells Contribute to Protection by Formalin Inactivated Respiratory Syncytial Virus Vaccination under a CD4-Deficient Condition

Respiratory syncytial virus (RSV) causes severe pulmonary disease in infants, young children, and the elderly. Formalin inactivated RSV (FI-RSV) vaccine trials failed due to vaccine enhanced respiratory disease, but the underlying immune mechanisms remain not fully understood. In this study, we have used wild type C57BL/6 and CD4 knockout (CD4KO) mouse models to better understand the roles of the CD4 T cells and cellular mechanisms responsible for enhanced respiratory disease after FI-RSV vaccination and RSV infection. Less eosinophil infiltration and lower pro-inflammatory cytokine production were observed in FI-RSV vaccinated CD4KO mice after RSV infection compared to FI-RSV vaccinated C57BL/6 mice. NK cells and cytokine-producing CD8 T cells were recruited at high levels in the airways of CD4KO mice, correlating with reduced respiratory disease. Depletion studies provided evidence that virus control was primarily mediated by NK cells whereas CD8 T cells contributed to IFN-γ production and less eosinophilic lung inflammation. This study demonstrated the differential roles of effector CD4 and CD8 T cells as well as NK cells, in networking with other inflammatory infiltrates in RSV disease in immune competent and CD4-deficient condition.

Unveiling Integrated Functional Pathways Leading to Enhanced Respiratory Disease Associated With Inactivated Respiratory Syncytial Viral Vaccine

Respiratory syncytial virus (RSV) infection is a severe threat to young children and the elderly. Despite decades of research, no vaccine has been approved. Notably, instead of affording protection, a formalin-inactivated RSV vaccine induced severe respiratory disease including deaths in vaccinated children in a 1960s clinical trial; however, recent studies indicate that other forms of experimental vaccines can also induce pulmonary pathology in pre-clinical studies. These findings suggest that multiple factors/pathways could be involved in the development of enhanced respiratory diseases. Clearly, a better understanding of the mechanisms underlying such adverse reactions is critically important for the development of safe and efficacious vaccines against RSV infection, given the exponential growth of RSV vaccine clinical trials in recent years. By employing an integrated systems biology approach in a pre-clinical cotton rat model, we unraveled a complex network of pulmonary canonical pathways leading to disease development in vaccinated animals upon subsequent RSV infections. Cytokines including IL-1, IL-6 GRO/IL-8, and IL-17 in conjunction with mobilized pulmonary inflammatory cells could play important roles in disease development, which involved a wide range of host responses including exacerbated pulmonary inflammation, oxidative stress, hyperreactivity, and homeostatic imbalance between coagulation and fibrinolysis. Moreover, the observed elevated levels of MyD88 implicate the involvement of this critical signal transduction module as the central node of the inflammatory pathways leading to exacerbated pulmonary pathology. Finally, the immunopathological consequences of inactivated vaccine immunization and subsequent RSV exposure were further substantiated by histological analyses of these key proteins along with inflammatory cytokines, while hypercoagulation was supported by increased pulmonary fibrinogen/fibrin accompanied by reduced levels of plasma D-dimers. Enhanced respiratory disease associated with inactivated RSV vaccine involves a complex network of host responses, resulting in significant pulmonary lesions and clinical manifestations such as tachypnea and airway obstruction. The mechanistic insight into the convergence of different signal pathways and identification of biomarkers could help facilitate the development of safe and effective RSV vaccine and formulation of new targeted interventions.

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.

Monoclonal Antibodies Against the Human Respiratory Syncytial Virus Obtained by Immunization with Epitope Peptides and CpG-DNA-liposome Complex

Respiratory syncytial virus (RSV) is the major cause of pulmonary inflammation in infants, young children, and immunocompromised adults. However, the RSV vaccine is not yet available commercially. The RSV-F glycoprotein mediates virus-host cell fusion, leading to syncytial formation; therefore, the RSV-F glycoprotein has been a treatment target for prevention and therapy of RSV infection. To produce the RSV-F-protein epitope-specific monoclonal antibody (MAb), BALB/c mice were immunized with a complex consisting of epitope peptide and MB-ODN 4531(O), encapsulated in a phosphatidyl-β-oleoyl-γ-palmitoyl ethanolamine (DOPE):cholesterol hemisuccinate (CHEMS) complex (Lipoplex(O)). Using conventional hybridoma technology, we obtained two clones able to produce antibodies reactive to two B-cell epitopes of RSV-F protein. Each anti-RSV-F glycoprotein MAb efficiently binds to each epitope. The F7-1A9D10 clone showed specific binding with RSV-F protein. There was no specific protein detected by Western blot analysis using F9 epitope-specific anti-RSV-F glycoprotein MAb (clone F9-1A6C8). However, based on confocal-image analysis, the antibody from the F9-1A6C8 clone showed specific binding with RSV-F protein. It is important that further study on possible applications for passive immunotherapy against RSV infection, such as therapeutic antibody production, is carried out.

Brief History and Characterization of Enhanced Respiratory Syncytial Virus Disease

In 1967, infants and toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (RSV) experienced an enhanced form of RSV disease characterized by high fever, bronchopneumonia, and wheezing when they became infected with wild-type virus in the community. Hospitalizations were frequent, and two immunized toddlers died upon infection with wild-type RSV. The enhanced disease was initially characterized as a "peribronchiolar monocytic infiltration with some excess in eosinophils." Decades of research defined enhanced RSV disease (ERD) as the result of immunization with antigens not processed in the cytoplasm, resulting in a nonprotective antibody response and CD4(+) T helper priming in the absence of cytotoxic T lymphocytes. This response to vaccination led to a pathogenic Th2 memory response with eosinophil and immune complex deposition in the lungs after RSV infection. In recent years, the field of RSV experienced significant changes. Numerous vaccine candidates with novel designs and formulations are approaching clinical trials, defying our previous understanding of favorable parameters for ERD. This review provides a succinct analysis of these parameters and explores criteria for assessing the risk of ERD in new vaccine candidates.

Virus-Like Particle Vaccine Containing the F Protein of Respiratory Syncytial Virus Confers Protection without Pulmonary Disease by Modulating Specific Subsets of Dendritic Cells and Effector T Cells

There is no licensed vaccine against respiratory syncytial virus (RSV) since the failure of formalin-inactivated RSV (FI-RSV) due to its vaccine-enhanced disease. We investigated immune correlates conferring protection without causing disease after intranasal immunization with virus-like particle vaccine containing the RSV fusion protein (F VLP) in comparison to FI-RSV and live RSV. Upon RSV challenge, FI-RSV immune mice showed severe weight loss, eosinophilia, and histopathology, and RSV reinfection also caused substantial RSV disease despite their viral clearance. In contrast, F VLP immune mice showed least weight loss and no sign of histopathology and eosinophilia. High levels of interleukin-4-positive (IL-4(+)) and tumor necrosis factor alpha-positive (TNF-α(+)) CD4(+) T cells were found in FI-RSV immune mice, whereas gamma interferon-positive (IFN-γ(+)) and TNF-α(+) CD4(+) T cells were predominantly detected in live RSV-infected mice. More importantly, in contrast to FI-RSV and live RSV that induced higher levels of CD11b(+) dendritic cells, F VLP immunization induced CD8α(+) and CD103(+) dendritic cells, as well as F-specific IFN-γ(+) and TNF-α(+) CD8(+) T cells. These results suggest that F VLP can induce protection without causing pulmonary RSV disease by inducing RSV neutralizing antibodies, as well as modulating specific subsets of dendritic cells and CD8 T cell immunity.

IMPORTANCE

It has been a difficult challenge to develop an effective and safe vaccine against respiratory syncytial virus (RSV), a leading cause of respiratory disease. Immune correlates conferring protection but preventing vaccine-enhanced disease remain poorly understood. RSV F virus-like particle (VLP) would be an efficient vaccine platform conferring protection. Here, we investigated the protective immune correlates without causing disease after intranasal immunization with RSV F VLP in comparison to FI-RSV and live RSV. In addition to inducing RSV neutralizing antibodies responsible for clearing lung viral loads, we show that modulation of specific subsets of dendritic cells and CD8 T cells producing T helper type 1 cytokines are important immune correlates conferring protection but not causing vaccine-enhanced disease.

Mucosal vaccines: novel strategies and applications for the control of pathogens and tumors at mucosal sites

The mucosal immune system displays several adaptations reflecting the exposure to the external environment. The efficient induction of mucosal immune responses also requires specific approaches, such as the use of appropriate administration routes and specific adjuvants and/or delivery systems. In contrast to vaccines delivered via parenteral routes, experimental, and clinical evidences demonstrated that mucosal vaccines can efficiently induce local immune responses to pathogens or tumors located at mucosal sites as well as systemic response. At least in part, such features can be explained by the compartmentalization of mucosal B and T cell populations that play important roles in the modulation of local immune responses. In the present review, we discuss molecular and cellular features of the mucosal immune system as well as novel immunization approaches that may lead to the development of innovative and efficient vaccines targeting pathogens and tumors at different mucosal sites.

Challenges and opportunities in developing respiratory syncytial virus therapeutics

Two meetings, one sponsored by the Wellcome Trust in 2012 and the other by the Global Virology Foundation in 2013, assembled academic, public health and pharmaceutical industry experts to assess the challenges and opportunities for developing antivirals for the treatment of respiratory syncytial virus (RSV) infections. The practicalities of clinical trials and establishing reliable outcome measures in different target groups were discussed in the context of the regulatory pathways that could accelerate the translation of promising compounds into licensed agents. RSV drug development is hampered by the perceptions of a relatively small and fragmented market that may discourage major pharmaceutical company investment. Conversely, the public health need is far too large for RSV to be designated an orphan or neglected disease. Recent advances in understanding RSV epidemiology, improved point-of-care diagnostics, and identification of candidate antiviral drugs argue that the major obstacles to drug development can and will be overcome. Further progress will depend on studies of disease pathogenesis and knowledge provided from controlled clinical trials of these new therapeutic agents. The use of combinations of inhibitors that have different mechanisms of action may be necessary to increase antiviral potency and reduce the risk of resistance emergence.

Host proteome correlates of vaccine-mediated enhanced disease in a mouse model of respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants. Despite over 50 years of research, to date no safe and efficacious RSV vaccine has been licensed. Many experimental vaccination strategies failed to induce balanced T-helper (Th) responses and were associated with adverse effects such as hypersensitivity and immunopathology upon challenge. In this study, we explored the well-established recombinant vaccinia virus (rVV) RSV-F/RSV-G vaccination-challenge mouse model to study phenotypically distinct vaccine-mediated host immune responses at the proteome level. In this model, rVV-G priming and not rVV-F priming results in the induction of Th2 skewed host responses upon RSV challenge. Mass spectrometry-based spectral count comparisons enabled us to identify seven host proteins for which expression in lung tissue is associated with an aberrant Th2 skewed response characterized by the influx of eosinophils and neutrophils. These proteins are involved in processes related to the direct influx of eosinophils (eosinophil peroxidase [Epx]) and to chemotaxis and extravasation processes (Chil3 [chitinase-like-protein 3]) as well as to eosinophil and neutrophil homing signals to the lung (Itgam). In addition, the increased levels of Arg1 and Chil3 proteins point to a functional and regulatory role for alternatively activated macrophages and type 2 innate lymphoid cells in Th2 cytokine-driven RSV vaccine-mediated enhanced disease.

IMPORTANCE

RSV alone is responsible for 80% of acute bronchiolitis cases in infants worldwide and causes substantial mortality in developing countries. Clinical trials performed with formalin-inactivated RSV vaccine preparations in the 1960s failed to induce protection upon natural RSV infection and even predisposed patients for enhanced disease. Despite the clinical need, to date no safe and efficacious RSV vaccine has been licensed. Since RSV vaccines have a tendency to prime for unbalanced responses associated with an exuberant influx of inflammatory cells and enhanced disease, detailed characterization of primed host responses has become a crucial element in RSV vaccine research. We investigated the lung proteome of mice challenged with RSV upon priming with vaccine preparations known to induce phenotypically distinct host responses. Seven host proteins whose expression levels are associated with vaccine-mediated enhanced disease have been identified. The identified protein biomarkers support the development as well as detailed evaluation of next-generation RSV vaccines.

Recent vaccine development for human metapneumovirus

Human metapneumovirus (hMPV) and respiratory syncytial virus, its close family member, are two major causes of lower respiratory tract infection in the paediatric population. hMPV is also a common cause of worldwide morbidity and mortality in immunocompromised patients and older adults. Repeated infections occur often, demonstrating a heavy medical burden. However, there is currently no hMPV-specific prevention treatment. This review focuses on the current literature on hMPV vaccine development. We believe that a better understanding of the role(s) of viral proteins in host responses might lead to efficient prophylactic vaccine development.

Immunology of bovine respiratory syncytial virus in calves

Bovine respiratory syncytial virus (BRSV) is an important cause of respiratory disease in young calves. The virus is genetically and antigenically closely related to human (H)RSV, which is a major cause of respiratory disease in young infants. As a natural pathogen of calves, BRSV infection recapitulates the pathogenesis of respiratory disease in man more faithfully than semi-permissive, animal models of HRSV infection. With the increasing availability of immunological reagents, the calf can be used to dissect the pathogenesis of and mechanisms of immunity to RSV infection, to analyse the ways in which the virus proteins interact with components of the innate response, and to evaluate RSV vaccine strategies. Passively transferred, neutralising bovine monoclonal antibodies, which recognise the same epitopes in the HRSV and BRSV fusion (F) protein, can protect calves against BRSV infection, and depletion of different T cells subsets in calves has highlighted the importance of CD8(+) T cells in viral clearance. Calves can be used to model maternal-antibody mediated suppression of RSV vaccine efficacy, and to increase understanding of the mechanisms responsible for RSV vaccine-enhanced respiratory disease.

Ginseng diminishes lung disease in mice immunized with formalin-inactivated respiratory syncytial virus after challenge by modulating host immune responses

Formalin-inactivated respiratory syncytial virus (FI-RSV) immunization is known to cause severe pulmonary inflammatory disease after subsequent RSV infection. Ginseng has been used in humans for thousands of years due to its potential health benefits. We investigated whether ginseng would have immune modulating effects on RSV infection in mice previously immunized with FI-RSV. Oral administration of mice with ginseng increased IgG2a isotype antibody responses to FI-RSV immunization, indicating T-helper type 1 (Th1) immune responses. Ginseng-treated mice that were nonimmunized or previously immunized with FI-RSV showed improved protection against RSV challenge compared with control mice without ginseng treatment. Ginseng-mediated improved clinical outcomes after live RSV infection were evidenced by diminished weight losses, decreased interleukin-4 cytokine production but increased interferon-γ production, modulation of CD3 T-cell populations toward a Th1 response, and reduced inflammatory response. Ginseng-mediated protective host immune modulation against RSV pulmonary inflammation was observed in different strains of wild-type and mutant mice. These results indicate that ginseng can modulate host immune responses to FI-RSV immunization and RSV infection, resulting in protective effects against pulmonary inflammatory disease.

Virus-like nanoparticle and DNA vaccination confers protection against respiratory syncytial virus by modulating innate and adaptive immune cells

Respiratory syncytial virus (RSV) is an important human pathogen. Expression of virus structural proteins produces self-assembled virus-like nanoparticles (VLP). We investigated immune phenotypes after RSV challenge of immunized mice with VLP containing RSV F and G glycoproteins mixed with F-DNA (FdFG VLP). In contrast to formalin-inactivated RSV (FI-RSV) causing vaccination-associated eosinophilia, FdFG VLP immunization induced low bronchoalveolar cellularity, higher ratios of CD11c(+) versus CD11b(+) phenotypic cells and CD8(+) T versus CD4(+) T cells secreting interferon (IFN)-γ, T helper type-1 immune responses, and no sign of eosinophilia upon RSV challenge. Furthermore, RSV neutralizing activity, lung viral clearance, and histology results suggest that FdFG VLP can be comparable to live RSV in conferring protection against RSV and in preventing RSV disease. This study provides evidence that a combination of recombinant RSV VLP and plasmid DNA may have a potential anti-RSV prophylactic vaccine inducing balanced innate and adaptive immune responses.

Co-immunization with virus-like particle and DNA vaccines induces protection against respiratory syncytial virus infection and bronchiolitis

This study demonstrates that immunization with non-replicating virus-like particle (FFG VLP) containing RSV F and G glycoproteins together with RSV F DNA induced T helper type 1 antibody responses to RSV F similar to live RSV infection. Upon RSV challenge 21weeks after immunization, FFG VLP vaccination induced protection against RSV infection as shown by clearance of lung viral loads, and the absence of eosinophil infiltrates, and did not cause lung pathology. In contrast, formalin-inactivated RSV (FI-RSV) vaccination showed significant pulmonary eosinophilia, severe mucus production, and extensive histopathology resulting in a hallmark of pulmonary pathology. Substantial lung pathology was also observed in mice with RSV re-infections. High levels of systemic and local inflammatory cytokine-secreting cells were induced in mice with FI-RSV but not with FFG VLP immunization after RSV challenge. Therefore, the results provide evidence that recombinant RSV FFG VLP vaccine can confer long-term protection against RSV without causing lung pathology.

Maternal antibodies by passive immunization with formalin inactivated respiratory syncytial virus confer protection without vaccine-enhanced disease

Maternal immunization of mice with formalin inactivated respiratory syncytial virus (FI-RSV) resulted in the passive transfer of RSV antibodies but not cellular components to the offspring. The offspring born to FI-RSV immunized mothers showed serum RSV neutralizing activity, effectively controlled lung viral loads without vaccine-enhanced disease, did not induce pulmonary eosinophilia, and cytokine producing cells after live RSV infection. Therefore, this study provides evidence that maternal immunization provides an in vivo model in investigating the roles of antibodies independent of cellular components.

A recombinant influenza virus vaccine expressing the F protein of respiratory syncytial virus

Infections with influenza and respiratory syncytial virus (RSV) rank high among the most common human respiratory diseases worldwide. Previously, we developed a replication-incompetent influenza virus by replacing the coding sequence of the PB2 gene, which encodes one of the viral RNA polymerase subunits, with that of a reporter gene. Here, we generated a PB2-knockout recombinant influenza virus expressing the F protein of RSV (PB2-RSVF virus) and tested its potential as a bivalent vaccine. In mice intranasally immunized with the PB2-RSVF virus, we detected high levels of antibodies against influenza virus, but not RSV. PB2-RSVF virus-immunized mice were protected from a lethal challenge with influenza virus but experienced severe body weight loss when challenged with RSV, indicating that PB2-RSVF vaccination enhanced RSV-associated disease. These results highlight one of the difficulties of developing an effective bivalent vaccine against influenza virus and RSV infections.

The path to an RSV vaccine

Respiratory syncytial virus (RSV) is the greatest remaining unmet infant vaccine need in developed countries and an important unmet infant vaccine need worldwide. More than 40 years of effort have yet to result in a licensed RSV vaccine for humans. Key challenges to RSV vaccine development include a peak of severe disease at 2-3 months of age, problematic biochemical behavior of key vaccine antigens, a history of vaccine-mediated disease enhancement, and reliance on animal models that may not accurately reflect human disease processes. Potential paths to overcome these challenges include maternal immunization, structure-based engineering of vaccine antigens, the design of a novel platform for safe infant immunization, and the development of improved animal models for vaccine-enhanced disease.

Defective immunoregulation in RSV vaccine-augmented viral lung disease restored by selective chemoattraction of regulatory T cells

Human trials of formaldehyde-inactivated respiratory syncytial virus (FI-RSV) vaccine in 1966-1967 caused disastrous worsening of disease and death in infants during subsequent natural respiratory syncytial virus (RSV) infection. The reasons behind vaccine-induced augmentation are only partially understood, and fear of augmentation continues to hold back vaccine development. We now show that mice vaccinated with FI-RSV show enhanced local recruitment of conventional CD4(+) T cells accompanied by a profound loss of regulatory T cells (Tregs) in the airways. This loss of Tregs was so complete that additional depletion of Tregs (in transgenic depletion of regulatory T-cell mice) produced no additional disease enhancement. Transfer of conventional CD4(+) T cells from FI-RSV-vaccinated mice into naive RSV-infected recipients also caused a reduction in airway Treg responses; boosting Tregs with IL-2 immune complexes failed to restore normal levels of Tregs or to ameliorate disease. However, delivery of chemokine ligands (CCL) 17/22 via the airway selectively recruited airway Tregs and attenuated vaccine-augmented disease, reducing weight loss and inhibiting local recruitment of pathogenic CD4(+) T cells. These findings reveal an unexpected mechanism of vaccine-induced disease augmentation and indicate that selective chemoattraction of Tregs into diseased sites may offer a novel approach to the modulation of tissue-specific inflammation.

DP2 (CRTh2) antagonism reduces ocular inflammation induced by allergen challenge and respiratory syncytial virus

BACKGROUND

Allergic conjunctivitis is characterized by itchy, watery and swollen eyes which occur in response to exposure to seasonal or environmental allergens. The early phase reaction of allergic conjunctivitis is primarily mediated by mast cell degranulation while the late phase reaction is driven by Th2 cells and eosinophils. Prostaglandin D(2) (PGD(2)), released from mast cells, is present in allergic conjunctival tears and may elicit classical allergic responses via interaction with the high-affinity DP2 receptor (chemoattractant receptor-homologous molecule expressed on Th2 cells, CRTh2). Furthermore, antagonism of this receptor is well known to inhibit eosinophil chemotaxis, basophil activation and Th2 cytokine production. PGD(2), therefore, may be involved in both early and late phase reactions in response to allergen challenge.

METHODS

Thus, we explored whether our novel and selective DP2 antagonist AM156 would be efficacious in animal models of allergic conjunctivitis. Furthermore, as respiratory syncytial virus (RSV) has been implicated in the pathogenesis of allergic conjunctivitis, we examined the effects of DP2 antagonism in a murine model of RSV ocular infection.

RESULTS

Utilizing a guinea pig ovalbumin model and a murine ragweed model we demonstrated that AM156 reduces redness, discharge and swelling in response to allergen challenge. These effects were equal to or greater than those of current clinical treatment options for allergic conjunctivitis including topical corticosteroids and a dual-mechanism antihistamine and decongestant. AM156 significantly reduced RSV-induced ocular inflammation and IL-4 production.

CONCLUSION

These results suggest that a topical DP2 antagonist such as AM156 may represent a novel therapeutic for allergic conjunctivitis.

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.

A novel inactivated intranasal respiratory syncytial virus vaccine promotes viral clearance without Th2 associated vaccine-enhanced disease

BACKGROUND

Respiratory syncytial virus (RSV) is a leading cause of bronchiolitis and pneumonia in young children worldwide, and no vaccine is currently available. Inactivated RSV vaccines tested in the 1960's led to vaccine-enhanced disease upon viral challenge, which has undermined RSV vaccine development. RSV infection is increasingly being recognized as an important pathogen in the elderly, as well as other individuals with compromised pulmonary immunity. A safe and effective inactivated RSV vaccine would be of tremendous therapeutic benefit to many of these populations.

PRINCIPAL FINDINGS

In these preclinical studies, a mouse model was utilized to assess the efficacy of a novel, nanoemulsion-adjuvanted, inactivated mucosal RSV vaccine. Our results demonstrate that NE-RSV immunization induced durable, RSV-specific humoral responses, both systemically and in the lungs. Vaccinated mice exhibited increased protection against subsequent live viral challenge, which was associated with an enhanced Th1/Th17 response. In these studies, NE-RSV vaccinated mice displayed no evidence of Th2 mediated immunopotentiation, as has been previously described for other inactivated RSV vaccines.

CONCLUSIONS

These studies indicate that nanoemulsion-based inactivated RSV vaccination can augment viral-specific immunity, decrease mucus production and increase viral clearance, without evidence of Th2 immune mediated pathology.

Exercise Training and Immunosenescence

During the aging process, a decrease in the ability of the immune system to control infection, known as immunosenescence, takes place. Paradoxically, aging also results in chronic low-level inflammation and exaggerated inflammatory responses. A number of studies have investigated the effects of a variety of exercise training interventions on the immune system both in humans and using animal models of aging. Cross-sectional studies that compared masters athletes to untrained, age-matched controls found that the athletes had significantly better immune function, but these studies suffered because of the difficulty in generalizing results from highly trained athletes to a general population of physically active older adults. Prospective studies in humans have attempted to address this, but these studies have resulted in sometimes equivocal findings, possibly as a result of the differences in exercise training programs used. Finally, animal studies, both observational and mechanistic, have almost universally supported the exercise effect on enhancing immune status in the aged. More research is needed to determine the mechanism by which exercise influences immunity in the aged and to identify exercise training programs for use in this population. It is clear, however, that exercise is likely to be effective at boosting immunity in the older people when undertaken regularly.

The use of a neonatal mouse model to study respiratory syncytial virus infections

Respiratory syncytial virus (RSV) infection is the most significant cause of viral death in infants worldwide. The significant morbidity and mortality associated with this disease underscores the urgent need for the development of an RSV vaccine. The development of an RSV vaccine has been hampered by our limited understanding of the human host immune system, which plays a significant role in RSV pathogenesis, susceptibility and vaccine efficacy. As a result, animal models have been developed to better understand the mechanisms by which RSV causes disease. Within the past few years, a revolutionary variation on these animal models has emerged--age at time of initial infection--and early studies in neonatal mice (aged <7 days at time of initial infection) indicate the validity of this model to understand RSV infection in infants. This article reviews available information on current murine and emerging neonatal mouse RSV models.

Local innate and adaptive immune responses regulate inflammatory cell influx into the lungs after vaccination with formalin inactivated RSV

Inactivated respiratory syncytial virus (RSV) vaccines tend to predispose for immune mediated enhanced disease, characterized by Th2 responses and airway hypersensitivity reactions. We show in a C57BL/6 mouse model that the early innate response elicited by the challenge virus (RSV versus influenza virus) influences the outcome of the Th1/Th2 balance in the lung after intramuscular priming with inactivated vaccine. Priming of CD4(+)/IFN-γ(+) T cells by mature dendritic cells administered intravenously and/or priming of a virus specific CD8(+) T cell response ameliorated the Th2-mediated inflammatory response in the lung, suggesting that vaccination procedures are feasible that prevent vaccine induced immune pathology.

Efficient lung recruitment of respiratory syncytial virus-specific Th1 cells induced by recombinant bacillus Calmette-Guérin promotes virus clearance and protects from infection

Infection by the respiratory syncytial virus (RSV) can cause extensive inflammation and lung damage in susceptible hosts due to a Th2-biased immune response. Such a deleterious inflammatory response can be enhanced by immunization with formalin- or UV-inactivated RSV, as well as with vaccinia virus expressing the RSV-G protein. Recently, we have shown that vaccination with rBCG-expressing RSV Ags can prevent the disease in the mouse. To further understand the immunological mechanisms responsible for protection against RSV, we have characterized the T cell populations contributing to virus clearance in mice immunized with this BCG-based vaccine. We found that both CD4(+) and CD8(+) T cells were recruited significantly earlier to the lungs of infected mice that were previously vaccinated. Furthermore, we observed that simultaneous adoptive transfer of CD8(+) and CD4(+) RSV-specific T cells from vaccinated mice was required to confer protection against virus infection in naive recipients. In addition, CD4(+) T cells induced by vaccination released IFN-γ after RSV challenge, indicating that protection is mediated by a Th1 immune response. These data suggest that vaccination with rBCG-expressing RSV Ags can induce a specific effector/memory Th1 immune response consisting on CD4(+) and CD8(+) T cells, both necessary for a fully protective response against RSV. These results support the notion that an effective induction of Th1 T cell immunity against RSV during childhood could counteract the unbalanced Th2-like immune response triggered by the natural RSV infection.

Gene expression differences in lungs of mice during secondary immune responses to respiratory syncytial virus infection

Vaccine-induced immunity has been shown to alter the course of a respiratory syncytial virus (RSV) infection both in murine models and in humans. To elucidate which mechanisms underlie the effect of vaccine-induced immunity on the course of RSV infection, transcription profiles in the lungs of RSV-infected mice were examined by microarray analysis. Three models were used: RSV reinfection as a model for natural immunity, RSV challenge after formalin-inactivated RSV vaccination as a model for vaccine-enhanced disease, and RSV challenge following vaccination with recombinant RSV virus lacking the G gene (DeltaG-RSV) as a model for vaccine-induced immunity. Gene transcription profiles, histopathology, and viral loads were analyzed at 1, 2, and 5 days after RSV challenge. On the first 2 days after challenge, all mice displayed an expression pattern in the lung similar of that found in primary infection, showing a strong innate immune response. On day 5 after RSV reinfection or after challenge following DeltaG-RSV vaccination, the innate immune response was waning. In contrast, in mice with vaccine-enhanced disease, the innate immune response 5 days after RSV challenge was still present even though viral replication was diminished. In addition, only in this group was Th2 gene expression induced. These findings support a hypothesis that vaccine-enhanced disease is mediated by prolonged innate immune responses and Th2 polarization in the absence of viral replication.

Decreased replication of human respiratory syncytial virus treated with the proteasome inhibitor MG-132

Many enveloped viruses require components of the host protein ubiquitin system including members of the Paramyxoviridae family of viruses (PIV5, SeV). Until recently, little has been known about the requirements of the subfamily Pneumovirinae. We report here that treatment of Vero cells with the proteasome inhibitor MG-132 results in the reduction of human respiratory syncytial virus (HRSV) titers by as much as 2.2log(10). Inhibition of HRSV by MG-132 was only observed early in infection (4-14h post-infection). Although Western blots indicated a possible decrease of 52% in virion production, we show by fluorescence microscopy and treatment with cyclohexamide that any apparent inhibition in HRSV budding is the result of decreased viral protein levels and not an inhibition of virus budding. Further, we demonstrate that inhibition of HRSV in Vero cells by MG-132 corresponds with an increase in eIF2alpha phosphorylation. Phosphorylation of eIF2alpha during MG-132 treatment only occurred in HRSV infected Vero cells, and not in GFP transfected controls. A combination of HRSV infection and MG-132 treatment may therefore provide sufficient signaling cues to induce inhibition of protein synthesis.

Pulmonary eosinophils and their role in immunopathologic responses to formalin-inactivated pneumonia virus of mice

Enhanced disease is the term used to describe the aberrant Th2-skewed responses to naturally acquired human respiratory syncytial virus (hRSV) infection observed in individuals vaccinated with formalin-inactivated viral Ags. Here we explore this paradigm with pneumonia virus of mice (PVM), a pathogen that faithfully reproduces features of severe hRSV infection in a rodent host. We demonstrate that PVM infection in mice vaccinated with formalin-inactivated Ags from PVM-infected cells (PVM Ags) yields Th2-skewed hypersensitivity, analogous to that observed in response to hRSV. Specifically, we detect elevated levels of IL-4, IL-5, IL-13, and eosinophils in bronchoalveolar lavage fluid of PVM-infected mice that were vaccinated with PVM Ags, but not among mice vaccinated with formalin-inactivated Ags from uninfected cells (control Ags). Interestingly, infection in PVM Ag-vaccinated mice was associated with a approximately 10-fold reduction in lung virus titer and protection against weight loss when compared with infected mice vaccinated with control Ags, despite the absence of serum-neutralizing Abs. Given recent findings documenting a role for eosinophils in promoting clearance of hRSV in vivo, we explored the role of eosinophils in altering the pathogenesis of disease with eosinophil-deficient mice. We found that eosinophil deficiency had no impact on virus titer in PVM Ag-vaccinated mice, nor on weight loss or levels of CCL11 (eotaxin-1), IFN-gamma, IL-5, or IL-13 in bronchoalveolar lavage fluid. However, levels of both IL-4 and CCL3 (macrophage inflammatory protein-1alpha) in bronchoalveolar lavage fluid were markedly diminished in PVM Ag-vaccinated, PVM-infected eosinophil-deficient mice when compared with wild-type controls.

Prior immunization with severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) nucleocapsid protein causes severe pneumonia in mice infected with SARS-CoV

The details of the mechanism by which severe acute respiratory syndrome-associated coronavirus (SARS-CoV) causes severe pneumonia are unclear. We investigated the immune responses and pathologies of SARS-CoV-infected BALB/c mice that were immunized intradermally with recombinant vaccinia virus (VV) that expressed either the SARS-CoV spike (S) protein (LC16m8rVV-S) or simultaneously all the structural proteins, including the nucleocapsid (N), membrane (M), envelope (E), and S proteins (LC16m8rVV-NMES) 7-8 wk before intranasal SARS-CoV infection. The LC16m8rVV-NMES-immunized group exhibited as severe pneumonia as the control groups, although LC16m8rVV-NMES significantly decreased the pulmonary SARS-CoV titer to the same extent as LC16m8rVV-S. To identify the cause of the exacerbated pneumonia, BALB/c mice were immunized with recombinant VV that expressed the individual structural proteins of SARS-CoV (LC16mOrVV-N, -M, -E, -S) with or without LC16mOrVV-S (i.e., LC16mOrVV-N, LC16mOrVV-M, LC16mOrVV-E, or LC16mOrVV-S alone or LC16mOrVV-N + LC16mOrVV-S, LC16mOrVV-M + LC16mOrVV-S, or LC16mOrVV-E + LC16mOrVV-S), and infected with SARS-CoV more than 4 wk later. Both LC16mOrVV-N-immunized mice and LC16mOrVV-N + LC16mOrVV-S-immunized mice exhibited severe pneumonia. Furthermore, LC16mOrVV-N-immunized mice upon infection exhibited significant up-regulation of both Th1 (IFN-gamma, IL-2) and Th2 (IL-4, IL-5) cytokines and down-regulation of anti-inflammatory cytokines (IL-10, TGF-beta), resulting in robust infiltration of neutrophils, eosinophils, and lymphocytes into the lung, as well as thickening of the alveolar epithelium. These results suggest that an excessive host immune response against the nucleocapsid protein of SARS-CoV is involved in severe pneumonia caused by SARS-CoV infection. These findings increase our understanding of the pathogenesis of SARS.

Pulmonary immunity and immunopathology: lessons from respiratory syncytial virus

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants and is an important source of morbidity and mortality in the elderly and immunocompromised. This review will discuss the humoral and cellular adaptive immune responses to RSV infection and how these responses are shaped in the immature immune system of the infant and the aged environment of the elderly. Furthermore, we will provide an overview of our current understanding of the role the various arms of the adaptive immune response play in mediating the delicate balance between the successful elimination of the virus from the host and the induction of immunopathology. Efficacious immunization against RSV remains a high priority within the field and we will highlight recent advances made in vaccine design.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

Asthma is a common and debilitating disease that has substantially increased in prevalence in Western Societies in the last 2 decades. Respiratory tract infections by respiratory syncytial virus (RSV) and rhinovirus (RV) are widely implicated as common causes of the induction and exacerbation of asthma. These infections in early life are associated with the induction of wheeze that may progress to the development of asthma. Infections may also promote airway inflammation and enhance T helper type 2 lymphocyte (Th2 cell) responses that result in exacerbations of established asthma. The mechanisms of how RSV and RV induce and exacerbate asthma are currently being elucidated by clinical studies, in vitro work with human cells and animal models of disease. This research has led to many potential therapeutic strategies and, although none are yet part of clinical practise, they show much promise for the prevention and treatment of viral disease and subsequent asthma.

Immunization of macaques with formalin-inactivated human metapneumovirus induces hypersensitivity to hMPV infection

Human metapneumovirus (hMPV), a member of the family Paramyxoviridae, is an important cause of acute respiratory tract disease. In the 1960s, vaccination with formalin-inactivated paramyxovirus preparations--respiratory syncytial virus (RSV) and measles virus (MV)--resulted in predisposition for enhanced disease upon natural infection. We have produced a formalin-inactivated hMPV preparation (FI-hMPV), which was used to immunize young cynomolgus macaques. Six days after challenge FI-hMPV-primed monkeys had developed eosinophilic bronchitis and bronchiolitis, indicative of a hypersensitivity response. This study indicates that formalin-inactivated hMPV vaccines have the same propensity to predispose for immune-mediated disease as inactivated RSV and MV vaccines.

Intranasal proteosome-based respiratory syncytial virus (RSV) vaccines protect BALB/c mice against challenge without eosinophilia or enhanced pathology

A safe and effective vaccine against respiratory syncytial virus (RSV) is still unavailable. Proteosome-based adjuvants are derived from the outer membrane proteins (OMP) of Neisseria species and are potent inducers of both mucosal and systemic immunity in humans and animals. Candidate RSV subunit vaccines comprising enriched RSV proteins (eRSV) formulated with proteosomes alone or with LPS (Protollin) were produced. Administered intranasally in BALB/c mice, both vaccines elicited long-lasting systemic and mucosal RSV-specific antibodies and fully protected against challenge. In vitro restimulation of lymphocytes from the Protollin-eRSV immunized mice with F (MHC-I) and G (MHC-II) peptides elicited F peptide-specific CD8(+) T cells and supernatant IFNgamma, TNFalpha, IL-2 and IL-10 while the formalin-inactivated RSV (FI-RSV) vaccine elicited predominantly IL-5. Pulmonary eosinophilia did not develop following immunization with either proteosome-based vaccine following challenge compared to mice immunized with FI-RSV. Proteosome-based eRSV vaccines can therefore protect against RSV challenge in mice without increasing the risk of pulmonary immunopathologic responses.

Respiratory syncytial virus differentially activates murine myeloid and plasmacytoid dendritic cells

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis in young children. Upon infection both T helper 1 (Th1) and Th2 cytokines are produced. Because RSV-induced Th2 responses have been associated with severe immunopathology and aggravation of allergic reactions, the regulation of the immune response following RSV infection is crucial. In this study we examined the influence of RSV on the activation and function of murine bone marrow-derived dendritic cells (DCs). RSV induced the expression of maturation markers on myeloid DCs (mDCs) in vitro. The mDCs stimulated with RSV and ovalbumin (OVA) enhanced proliferation of OVA-specific T cells, which produced both Th1 and Th2 cytokines. In contrast to mDCs, RSV did not induce the expression of maturation markers on plasmacytoid DCs (pDCs), not did it enhance the proliferation of OVA-specific T cells that were cocultured with pDCs. However, RSV stimulated the production of interferon-alpha (IFN-alpha) by pDCs. Our findings indicate a clear difference in the functional activation of DC subsets. RSV-stimulated mDCs may have immunostimulatory effects on both Th1 and Th2 responses, while RSV-stimulated pDCs have direct antiviral activity through the release of IFN-alpha.

Host transcription profiles upon primary respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a common cause of severe lower respiratory tract infection in children. Severe RSV disease is related to an inappropriate immune response to RSV resulting in enhanced lung pathology which is influenced by host genetic factors. To gain insight into the early pathways of the pathogenesis of and immune response to RSV infection, we determined the transcription profiles of lungs and lymph nodes on days 1 and 3 after infection of mice. Primary RSV infection resulted in a rapid but transient innate, proinflammatory response, as exemplified by the induction of a large number of type I interferon-regulated genes and chemokine genes, genes involved in inflammation, and genes involved in antigen processing. Interestingly, this response is much stronger on day 1 than on day 3 after infection, indicating that the strong transcriptional response in the lung precedes the peak of viral replication. Surprisingly, the set of down-regulated genes was small and none of these genes displayed strong down-regulation. Responses in the lung-draining lymph nodes were much less prominent than lung responses and are suggestive of NK cell activation. Our data indicate that at time points prior to the peak of viral replication and influx of inflammatory cells, the local lung response, measured at the transcriptional level, has already dampened down. The processes and pathways induced shortly after RSV infection can now be used for the selection of candidate genes for human genetic studies of children with severe RSV infection.

Respiratory syncytial virus (RSV) evades the human adaptive immune system by skewing the Th1/Th2 cytokine balance toward increased levels of Th2 cytokines and IgE, markers of allergy--a review

Infection of infants in their first year of life, children and elderly people with the respiratory syncytial virus (RSV) endangers the life of the patient. An attempt to develop a formalin-inactivated RSV (FI-RSV) vaccine during the 1960s resulted in an aggravated infection in immunized children, leading to hospitalization, while infection of non-immunized children produced much milder symptoms. The reason for this remained an enigma, one which was gradually solved over the last decade by many researchers who studied the molecular biology of RSV infection of respiratory ciliary cells. Clinical studies of RSV-infected patients indicated increased levels of Th2 cytokines and IgE in the patients' sera, suggesting that an allergy-like condition developed during infection. The biomarkers of allergy caused by endogenous or environmental allergens include a marked increase of the Th2 cytokine IL-4 and IgE non-neutralizing antibodies to the allergen. The way allergens trigger allergy was deciphered recently, and will be discussed later. Studies of RSV infection led to the suggestion that RSV patients suffer from allergy prior to RSV infection, a concept that was later abandoned. Studies on HIV-1 [Y. Becker, Virus Genes 28, 319-331 (2005)] research led me to the hypothesis that since HIV-1 infection induces a marked increase of IL-4 and IgE in serum, an allergy-like condition, the AIDS stage is the result of an allergen motif that is embedded in the shed viral gp120 molecules. It is hypothesized that the viral-soluble G glycoprotein (sG) contains a T cell superantigen (Tsag) that is capable of binding to the V(H)3 domain of IgE/FcepsilonRI(+) hematopoietic cells, basophils, mast cells and monocytes, similar to the case of allergens, and that this aggregation causes these innate system cells to degranulate and release large amounts of Th2 cytokines (IL-4, IL-5, IL-10, IL-13) into the blood. The way these Th2 cytokines skew the Th1/Th2 balance toward Th2 > Th1 will be discussed. The aim of the present review is to base RSV pathogenicity on the numerous very good analyses of the virus genes and to suggest a therapeutic approach to treatment that is directed at preventing the inhibitory effects of Th2 cytokines on the adaptive immune system of the patients, instead of inhibiting RSV replication by antivirals. The review of the molecular research on the role of the viral fusion (F) and attachment (G) glycoproteins of RSV provided information on their role in the virus infection: early in infection the F glycoprotein induces Th1 cells to release the Th1 cytokines IL-2, IL-12 and IFN-gamma to activate precursors CTLs (pCTLs) to become anti-RSV CTLs. The G and sG glycoproteins attach to FKNR1(+) ciliary respiratory epithelial cells as well as directly to eosinophils to the lungs. The sG T cell antigen can also induce the release of large amounts of Th2 cytokines from CD4(+) T cells and from FCepsilonRI(+) mast cells, basophils and monocytes. By comparison to HIV-1 gp120 it is possible to show that in the G and sG proteins the T cell antigen resembles the CD4(+) T cell superantigen (=allergen) domain of HIV-1 gp120 which aggregates with IgE/FCepsilonRI(+) hematopoietic cells. The increased IL-4 level in the serum inhibits the adaptive immune response: IL-4Ralpha(+) Th1 cells stop Th1 cytokine synthesis and IL-4Ralpha(+) B cells stop the synthesis of antiviral IgG and IgA and switch to IgE synthesis. In addition, the hematopoietic cells release histamine and prostaglandin which induce wheezing. The gradual increase of sG molecules creates a gradient of fractalkine (FKN) which directs IL-5-activated eosinophils to the lungs of the patient.