Venezuelan equine encephalitis virus replicon particles encoding respiratory syncytial virus surface glycoproteins induce protective mucosal responses in mice and cotton rats

Unmasking the potential of secretory IgA and its pivotal role in protection from respiratory viruses

Mucosal immunity has regained its spotlight amidst the ongoing Coronavirus disease 19 (COVID-19) pandemic, with numerous studies highlighting the crucial role of mucosal secretory IgA (SIgA) in protection against Severe acute respiratory syndrome coronavirus-2 or SARS-CoV-2 infections. The observed limitations in the efficacy of currently authorized COVID-19 vaccines in inducing effective mucosal immune responses remind us of the limitations of systemic vaccination in promoting protective mucosal immunity. This resurgence of interest has motivated the development of vaccine platforms capable of enhancing mucosal responses, specifically the SIgA response, and the development of IgA-based therapeutics. Recognizing viral respiratory infections as a global threat, we would like to comprehensively review the existing knowledge on mucosal immunity, with a particular emphasis on SIgA, in the context of SARS-CoV-2, influenza, and Respiratory Syncytial Virus (RSV) infections. This review aims to describe the structural and functional specificities of SIgA, along with its nuanced role in combating influenza, RSV, and SARS-CoV-2 infections. Subsequent sections further elaborate promising vaccine strategies, including mucosal vaccines against Influenza, RSV, and SARS-CoV-2 respiratory viruses, currently undergoing preclinical and clinical development. Additionally, we address the challenges associated with mucosal vaccine development, concluding with a discussion on IgA-based therapeutics as a promising platform for the treatment of viral respiratory infections. This comprehensive review not only synthesizes current insights into mucosal immunity but also identifies critical knowledge gaps, strengthening the way for further advancements in our current understanding and approaches to combat respiratory viral threats.

Fc-mediated pan-sarbecovirus protection after alphavirus vector vaccination

Group 2B β-coronaviruses (sarbecoviruses) have caused regional and global epidemics in modern history. Here, we evaluate the mechanisms of cross-sarbecovirus protective immunity, currently less clear yet important for pan-sarbecovirus vaccine development, using a panel of alphavirus-vectored vaccines covering bat to human strains. While vaccination does not prevent virus replication, it protects against lethal heterologous disease outcomes in both severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and clade 2 bat sarbecovirus challenge models. The spike vaccines tested primarily elicit a highly S1-specific homologous neutralizing antibody response with no detectable cross-virus neutralization. Rather, non-neutralizing antibody functions, mechanistically linked to FcgR4 and spike S2, mediate cross-protection in wild-type mice. Protection is lost in FcR knockout mice, further supporting a model for non-neutralizing, protective antibodies. These data highlight the importance of FcR-mediated cross-protective immune responses in universal pan-sarbecovirus vaccine designs.

Virus-like particles containing a prefusion-stabilized F protein induce a balanced immune response and confer protection against respiratory syncytial virus infection in mice

Respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children worldwide. Currently, no licensed RSV vaccines are available. In this study, we explored stable prefusion conformation virus-like particles (Pre-F VLPs) as RSV vaccine candidates. RSV fusion (F) protein mutants were constructed to form stabilized Pre-F or postfusion (Post-F) configurations. VLPs containing Pre-F or Post-F protein were generated using a recombinant baculovirus (rBV)-insect cell expression system. The assembly and immunological properties of Pre-F or Post-F VLPs were investigated. Pre-F and Post-F VLPs contained antigenic sites Ø and I of pre- and postfusion conformations, respectively. Compared with Post-F VLPs, immunization with Pre-F VLPs elicited upregulation of IFN-γ, IL-2 and IL-10 and downregulation of IL-4 and IL-5 cytokine production in mice. A high percentage of CD25⁺ Foxp3⁺ cells or a low percentage of IL-17A-producing cells among CD4⁺ T cells was observed in the lungs of mice vaccinated with Pre-F VLPs. Importantly, immunization with Pre-F VLPs induced a high level of RSV neutralizing antibody and a balanced immune response, which protected mice against RSV infection without evidence of immunopathology. Our results suggested that Pre-F VLPs generated from rBV-insect cells represent promising RSV vaccine candidates.

Proline metabolism reprogramming of trained macrophages induced by early respiratory infection combined with allergen sensitization contributes to development of allergic asthma in childhood of mice

Background

Infants with respiratory syncytial virus (RSV)-associated bronchiolitis are at increased risk of childhood asthma. Recent studies demonstrated that certain infections induce innate immune memory (also termed trained immunity), especially in macrophages, to respond more strongly to future stimuli with broad specificity, involving in human inflammatory diseases. Metabolic reprogramming increases the capacity of the innate immune cells to respond to a secondary stimulation, is a crucial step for the induction of trained immunity. We hypothesize that specific metabolic reprogramming of lung trained macrophages induced by neonatal respiratory infection is crucial for childhood allergic asthma.

Objective

To address the role of metabolic reprogramming in lung trained macrophages induced by respiratory virus infection in allergic asthma.

Methods

Neonatal mice were infected and sensitized by the natural rodent pathogen Pneumonia virus of mice (PVM), a mouse equivalent strain of human RSV, combined with ovalbumin (OVA). Lung CD11b⁺ macrophages in the memory phase were re-stimulated to investigate trained immunity and metabonomics. Adoptive transfer, metabolic inhibitor and restore experiments were used to explore the role of specific metabolic reprogramming in childhood allergic asthma.

Results

PVM infection combined with OVA sensitization in neonatal mice resulted in non-Th2 (Th1/Th17) type allergic asthma following OVA challenge in childhood of mice. Lung CD11b⁺ macrophages in the memory phage increased, and showed enhanced inflammatory responses following re-stimulation, suggesting trained macrophages. Adoptive transfer of the trained macrophages mediated the allergic asthma in childhood. The trained macrophages showed metabolic reprogramming after re-stimulation. Notably, proline biosynthesis remarkably increased. Inhibition of proline biosynthesis suppressed the development of the trained macrophages as well as the Th1/Th17 type allergic asthma, while supplement of proline recovered the trained macrophages as well as the allergic asthma.

Conclusion

Proline metabolism reprogramming of trained macrophages induced by early respiratory infection combined with allergen sensitization contributes to development of allergic asthma in childhood. Proline metabolism could be a well target for prevention of allergic asthma in childhood.

Construction and immunological evaluation of hepatitis B virus core virus-like particles containing multiple antigenic peptides of respiratory syncytial virus

Respiratory syncytial virus (RSV) infection causes severe disease in the lower respiratory tract of infants and young children. Currently, no licensed vaccine is available. In this study, we generated the chimeric virus-like particles (tHBc/F_E1E2, tHBc/F_E1E2/M2_82-90 and tHBc/F_E1E2/M2_82-90/tG VLPs) containing multiple antigenic peptides of RSV proteins based on a truncated hepatitis B virus core carrier (tHBc). We investigated the immune protection against RSV infection induced by these VLPs in a mouse model. Immunization with the VLPs elicited RSV-specific IgG and neutralizing antibody production and conferred protection against RSV infection in vivo. Compared with UV-RSV or tHBc/F_E1E2/M2_82-90/tG VLPs, the tHBc/F_E1E2 and tHBc/F_E1E2/M2_82-90 VLPs induced significantly decreased Th2 cytokines (IL-4, IL-5) and increased Th1 cytokines (IFN-γ, TNF-α, IL-2) as well as increased IgG2a/IgG1 ratios. tHBc/F_E1E2 and tHBc/F_E1E2/M2_82-90 VLPs also elicited an increased regulatory T (Treg) cell frequency and IL-10 secretion in the lungs of vaccinated mice, thereby relieving pulmonary pathology upon subsequent RSV infection. Our results demonstrate that the VLPs containing antigenic peptides of F protein combined with a CTL epitope of M2 may represent a promising RSV subunit vaccine candidate.

Lipopolysaccharide Inhibits FI-RSV Vaccine-enhanced Inflammation Through Regulating Th Responses

Respiratory syncytial virus (RSV) infection is the primary cause of respiratory disease in infants. The formalin-inactivated RSV (FI-RSV) vaccine resulted in an enhanced respiratory disease (ERD) in infants upon natural RSV infection, which is a major obstacle for development of safe and efficacious vaccines. Excessive and uncontrolled Th immune responses could be involved in the ERD. Agonists of TLRs are used as adjuvants to guide the type of immune response induced by vaccines. We evaluated the impact of lipopolysaccharide (LPS), the agonist of TLR4, on ERD as the adjuvant of FI-RSV. The results showed that LPS remarkably inhibited FI-RSV-enhanced lung inflammation, mucus production, airway inflammatory cell infiltration, and inflammatory cytokines following RSV challenge. Interestingly, LPS inhibited both Th2 and Th17 type cytokines in lungs of FI-RSV-immunized mice following RSV challenge, without an increase in the Th1 type cytokines, suggesting a controlled immune response. In contrast, Pam3Cys and Poly(I:C), the agonist of TLR1/2 or TLR3, partly inhibited FI-RSV-enhanced lung inflammation. Pam3Cys inhibited Th17 type cytokine IL-17, but promoted both Th1 and Th2 type cytokines. Poly(I:C) inhibited Th2 and Th17 type cytokines, but promoted Th1 type cytokines. In addition, LPS promoted IgG and IgG2a antibody production, which might provide protection from RSV challenge. These results suggest that LPS inhibits ERD without impairment in antibody production and protection, and the mechanism appears to be related with regulation of Th responses induced by FI-RSV.

RSV recombinant candidate vaccine G1F/M2 with CpG as an adjuvant prevents vaccine-associated lung inflammation, which may be associated with the appropriate types of immune memory in spleens and lungs

Respiratory syncytial virus (RSV) is a major respiratory pathogen in infants. The early formalin-inactivated RSV not only failed to protect infants against infection, but also was associated with enhanced pulmonary inflammatory disease upon natural infection. A safe and effective vaccine should prevent the inflammatory disease and provide protection. Immune memory is the cornerstone of vaccines. In this study, we evaluated three types of immune memory T cells, antibodies, and lung inflammation of a vaccine candidate G1F/M2, which includes a neutralizing epitope fragment of RSV G protein and a cytotoxic T lymphocyte epitope of M2 protein, with toll-like receptor 9 agonist CpG2006 as an adjuvant by intranasal (i.n.) and intraperitoneal (i.p.) immunization protocols. The results indicated that immunization of mice with G1F/M2 + CpG i.p. induced significantly higher level of CD4⁺ or CD8⁺ central memory (TCM), Th1-type effector memory (TEM), and balanced ratio of IgG1/IgG2a, but lower level of lung tissue-resident memory (TRM), compared with immunization with G1F/M2 + CpG i.n., G1F/M2 i.n., or G1F/M2 i.p. Following RSV challenge, the mice immunized with G1F/M2 + CpG i.p. showed higher level of Th1-type responses, remarkably suppressed inflammatory cytokines and histopathology in lungs, compared with mice immunized with G1F/M2 + CpG i.n., G1F/M2 i.n., or G1F/M2 i.p. These results suggested that high level of TCM and Th1 type of TEM in spleens may contribute to inhibition of lung inflammation, while high level of TRM in lungs and lack of or weak Th1-type immune memory in spleens may promote lung inflammation following RSV challenge.

Will Attention by Vaccine Developers to the Host's Nuclear Hormone Levels and Immunocompetence Improve Vaccine Success?

Despite extraordinary advances in fields of immunology and infectious diseases, vaccine development remains a challenge. The development of a respiratory syncytial virus vaccine, for example, has spanned more than 50 years of research with studies of more than 100 vaccine candidates. Dozens of attractive vaccine products have entered clinical trials, but none have completed the path to licensing. Human immunodeficiency virus vaccine development has proven equally difficult, as there is no licensed product after more than 30 years of pre-clinical and clinical research. Here, we examine vaccine development with attention to the host. We discuss how nuclear hormones, including vitamins and sex hormones, can influence responses to vaccines. We show how nuclear hormones interact with regulatory elements of immunoglobulin gene loci and how the deletion of estrogen response elements from gene enhancers will alter patterns of antibody isotype expression. Based on these findings, and findings that nuclear hormone levels are often insufficient or deficient among individuals in both developed and developing countries, we suggest that failed vaccine studies may in some cases reflect weaknesses of the host rather than the product. We encourage analyses of nuclear hormone levels and immunocompetence among study participants in clinical trials to ensure the success of future vaccine programs.

Soluble F proteins exacerbate pulmonary histopathology after vaccination upon respiratory syncytial virus challenge but not when presented on virus-like particles

Respiratory syncytial virus (RSV) fusion (F) protein is suggested to be a protective vaccine target although its efficacy and safety concerns remain not well understood. We investigated immunogenicity, efficacy, and safety of F proteins in a soluble form or on virus-like particle (F-VLP). F VLP preferentially elicited IgG2a antibody and T helper type 1 (Th1) immune responses whereas F protein induced IgG1 isotype and Th2 responses. Despite lung viral clearance after prime or prime-boost and then RSV challenge, F protein immune mice displayed weight loss and lung histopathology and high mucus production and eosinophils. In contrast, prime or prime-boost vaccination of F VLP induced effective protection, prevented infiltration of eosinophils and vaccine- enhanced disease after challenge. This study provides insight into developing an effective and safe RSV vaccine candidate.

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.

Respiratory syncytial virus: an overview of infection biology and vaccination strategies

Respiratory syncytial virus (RSV) is the foremost cause of lower respiratory tract infections, especially in infants and young children. To date, there is no licensed vaccine available for RSV. Only option to restrain RSV is a prophylactic treatment in the form of monoclonal antibody (palivizumab). However, it is quite expensive and used in few patients with co-morbidities. In ongoing research, virologists contemplate about various vaccine candidates to control RSV infection. This review will help in understating the RSV pathobiology and encompass the advancement on various vaccine candidates that would lead to reduce the incidence, mortality and morbidity. Furthermore, it will lighten up the different avenues which might be useful for the development of novel vaccination approaches.

CpG in Combination with an Inhibitor of Notch Signaling Suppresses Formalin-Inactivated Respiratory Syncytial Virus-Enhanced Airway Hyperresponsiveness and Inflammation by Inhibiting Th17 Memory Responses and Promoting Tissue-Resident Memory Cells in Lungs

Respiratory syncytial virus (RSV) is the leading cause of childhood hospitalizations. The formalin-inactivated RSV (FI-RSV) vaccine-enhanced respiratory disease (ERD) has been an obstacle to the development of a safe and effective killed RSV vaccine. Agonists of Toll-like receptor (TLR) have been shown to regulate immune responses induced by FI-RSV. Notch signaling plays critical roles during the differentiation and effector function phases of innate and adaptive immune responses. Cross talk between TLR and Notch signaling pathways results in fine-tuning of TLR-triggered innate inflammatory responses. We evaluated the impact of TLR and Notch signaling on ERD in a murine model by administering CpG, an agonist of TLR9, in combination with L685,458, an inhibitor of Notch signaling during FI-RSV immunization. Activation with CpG or deficiency of MyD88-dependent TLR signaling did not alleviate airway inflammation in FI-RSV-immunized mice. Activation or inhibition of Notch signaling with Dll4, one of the Notch ligands, or L685,458 did not suppress FI-RSV-enhanced airway inflammation either. However, the CpG together with L685,458 markedly inhibited FI-RSV-enhanced airway hyperresponsiveness, weight loss, and lung inflammation. Interestingly, CpG plus L685,458 completely inhibited FI-RSV-associated Th17 and Th17-associated proinflammatory chemokine responses in lungs following RSV challenge but not Th1 or Th2, memory responses. In addition, FI-RSV plus CpG plus L685,458 promoted protective CD8⁺ lung tissue-resident memory (TRM) cells. These results indicate that activation of TLR signaling combined with inhibition of Notch signaling prevent FI-RSV ERD, and the mechanism appears to involve suppressing proinflammatory Th17 memory responses and promoting protective TRM in lungs.IMPORTANCE RSV is the most important cause of lower respiratory tract infections in infants. The FI-RSV-enhanced respiratory disease (ERD) is a major impediment to the development of a safe and effective killed RSV vaccine. Using adjuvants to regulate innate and adaptive immune responses could be an effective method to prevent ERD. We evaluated the impact of TLR and Notch signaling on ERD by administering CpG, an agonist of TLR9, in combination with L685,458, an inhibitor of Notch signaling, during FI-RSV immunization. The data showed that treatment of TLR or Notch signaling alone did not suppress FI-RSV-enhanced airway inflammation, while CpG plus L685,458 markedly inhibited ERD. The mechanism appears to involve suppressing Th17 memory responses and promoting tissue-resident memory cells. Moreover, these results suggest that regulation of lung immune memory with adjuvant compounds containing more than one immune-stimulatory molecule may be a good strategy to prevent FI-RSV ERD.

Immunogenicity of RSV F DNA Vaccine in BALB/c Mice

Respiratory syncytial virus (RSV) causes severe acute lower respiratory tract disease leading to numerous hospitalizations and deaths among the infant and elderly populations worldwide. There is no vaccine or a less effective drug available against RSV infections. Natural RSV infection stimulates the Th1 immune response and activates the production of neutralizing antibodies, while earlier vaccine trials that used UV-inactivated RSV exacerbated the disease due to the activation of the allergic Th2 response. With a focus on Th1 immunity, we developed a DNA vaccine containing the native RSV fusion (RSV F) protein and studied its immune response in BALB/c mice. High levels of RSV specific antibodies were induced during subsequent immunizations. The serum antibodies were able to neutralize RSV in vitro. The RSV inhibition by sera was also shown by immunofluorescence analyses. Antibody response of the RSV F DNA vaccine showed a strong Th1 response. Also, sera from RSV F immunized and RSV infected mice reduced the RSV infection by 50% and 80%, respectively. Our data evidently showed that the RSV F DNA vaccine activated the Th1 biased immune response and led to the production of neutralizing antibodies, which is the desired immune response required for protection from RSV infections.

Chimeric virus-like particles containing a conserved region of the G protein in combination with a single peptide of the M2 protein confer protection against respiratory syncytial virus infection

To investigate the feasibility and efficacy of a virus-like particle (VLP) vaccine composed of the conserved antigenic epitopes of respiratory syncytial virus (RSV), the chimeric RSV VLPs HBcΔ-tG and HBcΔ-tG/M282-90 were generated based on the truncated hepatitis B virus core protein (HBcΔ). HBcΔ-tG consisted of HBcΔ, the conserved region (aa 144-204) of the RSV G protein. HBcΔ-tG was combined with a single peptide (aa 82-90) of the M2 protein to generate HBcΔ-tG/M282-90. Immunization of mice with the HBcΔ-tG or HBcΔ-tG/M282-90 VLPs elicited RSV-specific IgG and neutralizing antibody production and conferred protection against RSV infection. Compared with HBcΔ-tG, HBcΔ-tG/M282-90 induced decreased Th2 cytokine production (IL-4 and IL-5), increased Th1 cytokine response (IFN-γ, TNF-α, and IL-2), and increased ratios of IgG2a/IgG1 antibodies, thereby relieving pulmonary pathology upon subsequent RSV infection. Our results demonstrated that chimeric HBcΔ-tG/M282-90 VLPs represented an effective RSV subunit vaccine candidate.

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

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

Sendai virus as a backbone for vaccines against RSV and other human paramyxoviruses

Human paramyxoviruses are the etiological agents for life-threatening respiratory virus infections of infants and young children. These viruses, including respiratory syncytial virus (RSV), the human parainfluenza viruses (hPIV1-4) and human metapneumovirus (hMPV), are responsible for millions of serious lower respiratory tract infections each year worldwide. There are currently no standard treatments and no licensed vaccines for any of these pathogens. Here we review research with which Sendai virus, a mouse parainfluenza virus type 1, is being advanced as a Jennerian vaccine for hPIV1 and as a backbone for RSV, hMPV and other hPIV vaccines for children.

Protection against respiratory syncytial virus by inactivated influenza virus carrying a fusion protein neutralizing epitope in a chimeric hemagglutinin

A desirable vaccine against respiratory syncytial virus (RSV) should induce neutralizing antibodies without eliciting abnormal T cell responses to avoid vaccine-enhanced pathology. In an approach to deliver RSV neutralizing epitopes without RSV-specific T cell antigens, we genetically engineered chimeric influenza virus expressing RSV F262-276 neutralizing epitopes in the globular head domain as a chimeric hemagglutinin (HA) protein. Immunization of mice with formalin-inactivated recombinant chimeric influenza/RSV F262-276 was able to induce RSV protective neutralizing antibodies and lower lung viral loads after challenge. Formalin-inactivated RSV immune mice showed high levels of pulmonary inflammatory cytokines, macrophages, IL-4-producing T cells, and extensive histopathology. However, RSV-specific T cell responses and enhancement of pulmonary histopathology were not observed after RSV infection of inactivated chimeric influenza/RSV F262-276. This study provides evidence that an inactivated vaccine platform of chimeric influenza/RSV virus can be developed into a safe RSV vaccine candidate without priming RSV-specific T cells and immunopathology.

FROM THE CLINICAL EDITOR

Respiratory syncytial virus (RSV) is a major cause of respiratory tract illness and morbidity in children. Hence, there is a need to develop an effective vaccine against this virus. In this article, the authors engineered chimeric influenza virus to express RSV neutralizing epitopes. The positive findings in in-vivo experiments provide a beginning for future clinical trials and perhaps eventual product realization.

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.

Self-replicating alphavirus RNA vaccines

Recombinant nucleic acids are considered as promising next-generation vaccines. These vaccines express the native antigen upon delivery into tissue, thus mimicking live attenuated vaccines without having the risk of reversion to pathogenicity. They also stimulate the innate immune system, thus potentiating responses. Nucleic acid vaccines are easy to produce at reasonable cost and are stable. During the past years, focus has been on the use of plasmid DNA for vaccination. Now mRNA and replicon vaccines have come into focus as promising technology platforms for vaccine development. This review discusses self-replicating RNA vaccines developed from alphavirus expression vectors. These replicon vaccines can be delivered as RNA, DNA or as recombinant virus particles. All three platforms have been pre-clinically evaluated as vaccines against a number of infectious diseases and cancer. Results have been very encouraging and propelled the first human clinical trials, the results of which have been promising.

Induction of protective effector immunity to prevent pathogenesis caused by the respiratory syncytial virus. Implications on therapy and vaccine design

Human respiratory syncytial virus (hRSV) is the leading cause of respiratory illness in infants and young children around the globe. This pathogen, which was discovered in 1956, continues to cause a huge number of hospitalizations due to respiratory disease and it is considered a health and economic burden worldwide, especially in developing countries. The immune response elicited by hRSV infection leads to lung and systemic inflammation, which results in lung damage but is not efficient at preventing viral replication. Indeed, natural hRSV infection induces a poor immune memory that allows recurrent infections. Here, we review the most recent knowledge about the lifecycle of hRSV, the immune response elicited by this virus and the subsequent pathology induced in response to infection in the airways. Novel findings about the alterations that this virus causes in the central nervous system and potential therapies and vaccines designed to treat or prevent hRSV infection are discussed.

Baculovirus-expressed virus-like particle vaccine in combination with DNA encoding the fusion protein confers protection against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major viral agent causing significant morbidity and mortality in young infants and the elderly. There is no licensed vaccine against RSV and it is a high priority to develop a safe RSV vaccine. We determined the immunogenicity and protective efficacy of combined virus-like particle and DNA vaccines presenting RSV glycoproteins (Fd.VLP) in comparison with formalin inactivated RSV (FI-RSV). Immunization of mice with Fd.VLP induced higher ratios of IgG2a/IgG1 antibody responses compared to those with FI-RSV. Upon live RSV challenge, Fd.VLP and FI-RSV vaccines were similarly effective in clearing lung viral loads. However, FI-RSV immunized mice showed a substantial weight loss and high levels of T helper type 2 (Th2) cytokines as well as extensive lung histopathology and eosinophil infiltration. In contrast, Fd.VLP immunized mice did not exhibit Th2 type cytokines locally and systemically, which might contribute to preventing vaccine-associated RSV lung disease. These results indicate that virus-like particles in combination with DNA vaccines represent a potential approach for developing a safe and effective RSV vaccine.

Enhancement of protein expression by alphavirus replicons by designing self-replicating subgenomic RNAs

Since the development of infectious cDNA clones of viral RNA genomes and the means of delivery of the in vitro-synthesized RNA into cells, alphaviruses have become an attractive system for expression of heterologous genetic information. Alphaviruses replicate exclusively in the cytoplasm, and their genetic material cannot recombine with cellular DNA. Alphavirus genome-based, self-replicating RNAs (replicons) are widely used vectors for expression of heterologous proteins. Their current design relies on replacement of structural genes, encoded by subgenomic RNAs (SG RNA), with heterologous sequences of interest. The SG RNA is transcribed from a promoter located in the alphavirus-specific RNA replication intermediate and is not further amplified. In this study, we have applied the accumulated knowledge of the mechanism of alphavirus replication and promoter structures, in particular, to increase the expression level of heterologous proteins from Venezuelan equine encephalitis virus (VEEV)-based replicons. During VEEV infection, replication enzymes are produced in excess to RNA replication intermediates, and a large fraction of them are not involved in RNA synthesis. The newly designed constructs encode SG RNAs, which are not only transcribed from the SG promoter, but are additionally amplified by the previously underused VEEV replication enzymes. These replicons produce SG RNAs and encoded proteins of interest 10- to 50-fold more efficiently than those using a traditional design. A modified replicon encoding West Nile virus (WNV) premembrane and envelope proteins efficiently produced subviral particles and, after a single immunization, elicited high titers of neutralizing antibodies, which protected mice from lethal challenge with WNV.

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.

Mucosal vaccines against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory disease in infants, young children, immune-compromised and elderly populations worldwide. Natural RSV infection in young children does not elicit long-lasting immunity and individuals remain susceptible to repeated RSV infections throughout life. Because RSV infection is restricted to the respiratory tract, an RSV vaccine should elicit mucosal immunity at upper and lower respiratory tracts in order to most effectively prevent RSV reinfection. Although there is no safe and effective RSV vaccine available, significant progress has been recently made in basic RSV research and vaccine development. This review will discuss recent advances in the identification of a new neutralizing antigenic site within the RSV fusion (F) protein, understanding the importance of mucosal immune responses against RSV infection, and the development of novel mucosal vaccination strategies.

Advances in and the potential of vaccines for respiratory syncytial virus

Respiratory syncytial virus (RSV) is the leading cause of serious lower respiratory track illness causing bronchiolitis and some mortality in infants and the elderly. Despite decades of research there is no licensed RSV vaccine. To enable the development of RSV vaccines, several major obstacles must be overcome including immature and waning immunity to RSV infection, the capacity of RSV to evade immunity and the failure of RSV infection to induce robust enduring immunity. Since the failure of the formalin-inactivated RSV vaccine trial, more cautious and deliberate progress has been made toward RSV vaccine development using a variety of experimental approaches. The scientific rational and the state of development of these approaches are reviewed in this article.

Immunomodulatory activity of red ginseng against influenza A virus infection

Ginseng herbal medicine has been known to have beneficial effects on improving human health. We investigated whether red ginseng extract (RGE) has preventive effects on influenza A virus infection in vivo and in vitro. RGE was found to improve survival of human lung epithelial cells upon influenza virus infection. Also, RGE treatment reduced the expression of pro-inflammatory genes (IL-6, IL-8) probably in part through interference with the formation of reactive oxygen species by influenza A virus infection. Long-term oral administration of mice with RGE showed multiple immunomodulatory effects such as stimulating antiviral cytokine IFN-γ production after influenza A virus infection. In addition, RGE administration in mice inhibited the infiltration of inflammatory cells into the bronchial lumens. Therefore, RGE might have the potential beneficial effects on preventing influenza A virus infections via its multiple immunomodulatory functions.

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.

Lactobacillus plantarum DK119 as a probiotic confers protection against influenza virus by modulating innate immunity

Lactobacillus plantarum DK119 (DK119) isolated from the fermented Korean cabbage food was used as a probiotic to determine its antiviral effects on influenza virus. DK119 intranasal or oral administration conferred 100% protection against subsequent lethal infection with influenza A viruses, prevented significant weight loss, and lowered lung viral loads in a mouse model. The antiviral protective efficacy was observed in a dose and route dependent manner of DK119 administration. Mice that were treated with DK119 showed high levels of cytokines IL-12 and IFN-γ in bronchoalveolar lavage fluids, and a low degree of inflammation upon infection with influenza virus. Depletion of alveolar macrophage cells in lungs and bronchoalveolar lavages completely abrogated the DK119-mediated protection. Modulating host innate immunity of dendritic and macrophage cells, and cytokine production pattern appeared to be possible mechanisms by which DK119 exhibited antiviral effects on influenza virus infection. These results indicate that DK119 can be developed as a beneficial antiviral probiotic microorganism.

Viral vectors for vaccine applications

Traditional approach of inactivated or live-attenuated vaccine immunization has resulted in impressive success in the reduction and control of infectious disease outbreaks. However, many pathogens remain less amenable to deal with the traditional vaccine strategies, and more appropriate vaccine strategy is in need. Recent discoveries that led to increased understanding of viral molecular biology and genetics has rendered the used of viruses as vaccine platforms and as potential anti-cancer agents. Due to their ability to effectively induce both humoral and cell-mediated immune responses, viral vectors are deemed as an attractive alternative to the traditional platforms to deliver vaccine antigens as well as to specifically target and kill tumor cells. With potential targets ranging from cancers to a vast number of infectious diseases, the benefits resulting from successful application of viral vectors to prevent and treat human diseases can be immense.

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.

The role of dendritic cells in innate and adaptive immunity to respiratory syncytial virus, and implications for vaccine development

Respiratory syncytial virus (RSV) is a common human pathogen that causes cold-like symptoms in most healthy adults and children. However, RSV often moves into the lower respiratory tract in infants and young children predisposed to respiratory illness, making it the most common cause of pediatric broncheolitis and pneumonia. The development of an appropriate balanced immune response is critical for recovery from RSV, while an unbalanced and/or excessively vigorous response may lead to immunopathogenesis. Different dendritic cell (DC) subsets influence the magnitude and quality of the host response to RSV infection, with myeloid DCs mediating and plasmacytoid DCs modulating immunopathology. Furthermore, stimulation of DCs through Toll-like receptors is essential for induction of protective immunity to RSV. These characteristics have implications for the rational design of a RSV vaccine.

NADPH oxidase limits lipopolysaccharide-induced lung inflammation and injury in mice through reduction-oxidation regulation of NF-κB activity

Although reactive oxygen species (ROS) produced by NADPH oxidase are known to regulate inflammatory responses, the impact of ROS on intracellular signaling pathways is incompletely understood. In these studies, we treated wild-type (WT) and p47(phox)-deficient mice with LPS to investigate mechanisms by which NADPH oxidase regulates signaling through the NF-κB pathway. After intratracheal instillation of LPS, ROS generation was impaired in p47(phox)(-/-) mice, whereas these mice had increased neutrophilic alveolitis and greater lung injury compared with WT controls. In mice interbred with transgenic NF-κB reporters (HIV-long terminal repeat/luciferase [HLL]), we found exaggerated LPS-induced NF-κB activation and increased expression of proinflammatory cytokines in lungs of p47(phox)(-/-)/HLL mice compared with controls. Both lung macrophages and bone marrow-derived macrophages (BMDMs) isolated from p47(phox)(-/-)/HLL mice showed enhanced LPS-stimulated NF-κB activity compared with controls. Although nuclear translocation of NF-κB proteins was similar between genotypes, EMSAs under nonreducing conditions showed increased DNA binding in p47(phox)(-/-)/HLL BMDMs, suggesting that ROS production reduces NF-κB binding to DNA without affecting nuclear translocation. Increased intracellular reduced glutathione/glutathione disulfide ratio and greater nuclear redox factor 1 (Ref-1) levels were present in p47(phox)(-/-)/HLL compared with WT BMDMs, pointing to NADPH oxidase modulating intracellular redox status in macrophages. Treatment with the Ref-1-specific inhibitor E3330 or hydrogen peroxide inhibited LPS-induced NF-κB activation in p47(phox)(-/-)/HLL BMDMs but not in WT/HLL cells. Consistent with these findings, small interfering RNA against Ref-1 selectively reduced NF-κB activity in LPS-treated p47(phox)(-/-)/HLL BMDMs. Together, these results indicate that NADPH oxidase limits LPS-induced NF-κB transcriptional activity through regulation of intracellular redox state.

Respiratory syncytial virus: current progress in vaccine development

Respiratory syncytial virus (RSV) is the etiological agent for a serious lower respiratory tract disease responsible for close to 200,000 annual deaths worldwide. The first infection is generally most severe, while re-infections usually associate with a milder disease. This observation and the finding that re-infection risks are inversely associated with neutralizing antibody titers suggest that immune responses generated toward a first RSV exposure can significantly reduce morbidity and mortality throughout life. For more than half a century, researchers have endeavored to design a vaccine for RSV that can mimic or improve upon natural protective immunity without adverse events. The virus is herein described together with the hurdles that must be overcome to develop a vaccine and some current vaccine development approaches.

Gene-based vaccine approaches for respiratory syncytial virus

A respiratory syncytial virus (RSV) vaccine has remained elusive for decades, largely due to the failure of a formalin-inactivated RSV vaccine in the 1960s that resulted in enhanced disease upon RSV exposure in the immunized individuals. Vaccine development has also been hindered by the incomplete immunity conferred by natural infection allowing for re-infection at any time, and the immature immune system and circulating maternal antibodies present in the neonate, the primary target for a vaccine. This chapter will review the use of gene delivery, both nonviral and viral, as a potential vaccine approach for human RSV. Many of these gene-based vaccines vectors elicit protective immune responses in animal models. None of the RSV gene-based platforms have progressed into clinical trials, mostly due to uncertainty regarding the direct translation of animal model results to humans and the hesitancy to invest in costly clinical trials with the potential for unclear and complicated immune responses. The continued development of RSV vaccine gene-based approaches is warranted because of their inherent flexibility with regard to composition and administration. It is likely that multiple candidate vaccines will reach human testing in the next few years.

Virus-like particles as a highly efficient vaccine platform: diversity of targets and production systems and advances in clinical development

Virus-like particles (VLPs) are a class of subunit vaccines that differentiate themselves from soluble recombinant antigens by stronger protective immunogenicity associated with the VLP structure. Like parental viruses, VLPs can be either non-enveloped or enveloped, and they can form following expression of one or several viral structural proteins in a recombinant heterologous system. Depending on the complexity of the VLP, it can be produced in either a prokaryotic or eukaryotic expression system using target-encoding recombinant vectors, or in some cases can be assembled in cell-free conditions. To date, a wide variety of VLP-based candidate vaccines targeting various viral, bacterial, parasitic and fungal pathogens, as well as non-infectious diseases, have been produced in different expression systems. Some VLPs have entered clinical development and a few have been licensed and commercialized. This article reviews VLP-based vaccines produced in different systems, their immunogenicity in animal models and their status in clinical development.

Targeting RSV with vaccines and small molecule drugs

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

Need for a safe vaccine against respiratory syncytial virus infection

Human respiratory syncytial virus (HRSV) is a major cause of severe respiratory tract illnesses in infants and young children worldwide. Despite its importance as a respiratory pathogen, there is currently no licensed vaccine for HRSV. Following failure of the initial trial of formalin-inactivated virus particle vaccine, continuous efforts have been made for the development of safe and efficacious vaccines against HRSV. However, several obstacles persist that delay the development of HRSV vaccine, such as the immature immune system of newborn infants and the possible Th2-biased immune responses leading to subsequent vaccine-enhanced diseases. Many HRSV vaccine strategies are currently being developed and evaluated, including live-attenuated viruses, subunit-based, and vector-based candidates. In this review, the current HRSV vaccines are overviewed and the safety issues regarding asthma and vaccine-induced pathology are discussed.

Antibody response to the central unglycosylated region of the respiratory syncytial virus attachment protein in mice

We examined the humoral immune response to the unglycosylated central region of the respiratory syncytial virus (RSV) attachment (G) protein in mice following intranasal challenge at day 0 (primary) and day 21 (secondary) with subtype A (A2 strain) or B (B1 strain) RSV preparations. Our serological screening reagents included bacterially derived glutathione S-transferase (GST) fusion proteins, each bearing a portion of the RSV G central core (CC; residues 151-190), proximal central core (PCC; residues 151-172), and the distal central core (DCC; residues 173-190) and purified RSV G proteins from subtype A and B viruses. Convalescent sera collected on day 21 following primary RSV infection bore robust IgG response primarily against the homosubtypic RSV G DCC with relatively modest antigen affinity/avidity as demonstrated by brief incubation with 6M urea. In contrast, sera collected on day 42 following secondary homosubtypic RSV infection bore IgG titers of higher magnitudes and antigen affinity/avidity against the homosubtypic RSV G CC, PCC, and/or the DCC regions and full-length RSV G protein but not against the heterosubtypic RSV G protein or recombinant CC subdomains. In contrast, heterosubtypic secondary RSV infection elicits a broad array of IgG responses with titers of varying magnitudes to homo- and heterosubtypic RSV G CC regions as well as to purified F, Ga, and Gb proteins with the notable exception of minimal response to the RSV G DCC domain associated with the secondary RSV challenge. Our results have implications for RSV G-based serological assays as well as prophylactic immunotherapy and RSV vaccine development.

Lack of interference with immunogenicity of a chimeric alphavirus replicon particle-based influenza vaccine by preexisting antivector immunity

Antivector immunity has been recognized as a potential caveat of using virus-based vaccines. In the present study, an alphavirus-based replicon particle vaccine platform, which has demonstrated robust immunogenicity in animal models, was tested for effects of antivector immunity on immunogenicity against hemagglutinin of influenza virus as a target antigen and efficacy for protection against lethal challenge with the virus. Chimeric alphavirus-based replicon particles, comprising Venezuelan equine encephalitis virus nonstructural and Sindbis virus structural components, induced efficient protective antibody responses, which were not adversely influenced after multiple immunizations with the same vector expressing various antigens.

Infected dendritic cells are sufficient to mediate the adjuvant activity generated by Venezuelan equine encephalitis virus replicon particles

Replicon particles derived from Venezuelan equine encephalitis virus (VEE) are infectious non-propagating particles which act as a safe and potent systemic, mucosal, and cellular adjuvant when delivered with antigen. VEE and VEE replicon particles (VRP) can target multiple cell types including dendritic cells (DCs). The role of these cell types in VRP adjuvant activity has not been previously evaluated, and for these studies we focused on the contribution of DCs to the response to VRP. By analysis of VRP targeting in the draining lymph node, we found that VRP induced rapid recruitment of TNF-secreting monocyte-derived inflammatory dendritic cells. VRP preferentially infected these inflammatory DCs as well as classical DCs and macrophages, with less efficient infection of other cell types. DC depletion suggested that the interaction of VRP with classical DCs was required for recruitment of inflammatory DCs, induction of high levels of many cytokines, and for stable transport of VRP to the draining lymph node. Additionally, in vitro-infected DCs enhanced antigen-specific responses by CD4 and CD8 T cells. By transfer of VRP-infected DCs into mice we showed that these DCs generated an inflammatory state in the draining lymph node similar to that achieved by VRP injection. Most importantly, VRP-infected DCs were sufficient to establish robust adjuvant activity in mice comparable to that produced by VRP injection. These findings indicate that VRP infect, recruit and activate both classical and inflammatory DCs, and those DCs become mediators of the VRP adjuvant activity.

Evaluation of Measles Vaccine Virus as a Vector to Deliver Respiratory Syncytial Virus Fusion Protein or Epstein-Barr Virus Glycoprotein gp350

Live attenuated recombinant measles vaccine virus (MV) Edmonston-Zagreb (EZ) strain was evaluated as a viral vector to express the ectodomains of fusion protein of respiratory syncytial virus (RSV F) or glycoprotein 350 of Epstein-Barr virus (EBV gp350) as candidate vaccines for prophylaxis of RSV and EBV. The glycoprotein gene was inserted at the 1^st or the 3^rd position of the measles virus genome and the recombinant viruses were generated. Insertion of the foreign gene at the 3^rd position had a minimal impact on viral replication in vitro. RSV F or EBV gp350 protein was secreted from infected cells. In cotton rats, EZ-RSV F and EZ-EBV gp350 induced MV- and insert-specific antibody responses. In addition, both vaccines also induced insert specific interferon gamma (IFN-γ) secreting T cell response. EZ-RSV F protected cotton rats from pulmonary replication of RSV A2 challenge infection. In rhesus macaques, although both EZ-RSV F and EZ-EBV gp350 induced MV specific neutralizing antibody responses, only RSV F specific antibody response was detected. Thus, the immunogenicity of the foreign antigens delivered by measles vaccine virus is dependent on the nature of the insert and the animal models used for vaccine evaluation.

Interleukin-27 inhibits vaccine-enhanced pulmonary disease following respiratory syncytial virus infection by regulating cellular memory responses

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract disease in young children. In the 1960s, infants vaccinated with formalin-inactivated RSV developed a more severe disease characterized by excessive inflammatory immunopathology in lungs upon natural RSV infection. The fear of causing the vaccine-enhanced disease (VED) is an important obstacle for development of safe and effective RSV vaccines. The recombinant vaccine candidate G1F/M2 immunization also led to VED. It has been proved that cellular memory induced by RSV vaccines contributed to VED. Interleukin-27 (IL-27) and IL-23 regulate Th1, Th17, and/or Th2 cellular immune responses. In this study, mice coimmunized with pcDNA3-IL-27 and G1F/M2 were fully protected and, importantly, did not develop vaccine-enhanced inflammatory responses and immunopathology in lungs after RSV challenge, which was correlated with moderate Th1-, suppressed Th2-, and Th17-like memory responses activated by RSV. In contrast, G1F/M2- or pcDNA3-IL-23+G1F/M2-immunized mice, in which robust Th2- and Th17-like memory responses were induced, developed enhanced pulmonary inflammation and severe immunopathology. Mice coimmunized with G1F/M2 and the two cytokine plasmids exhibited mild inflammatory responses as well as remarkable Th1-, suppressed Th2-, and Th17-like memory responses. These results suggested that Th1-, Th2-, and Th17-like memory responses and, in particular, excessive Th2- and Th17-like memory responses were closely associated with VED; IL-27 may inhibit VED following respiratory syncytial virus infection by regulating cellular memory responses.

Respiratory syncytial virus vaccine development

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract viral disease in infants and young children. Presently, there are no explicit recommendations for RSV treatment apart from supportive care. The virus is therefore responsible for an estimated 160,000 deaths per year worldwide. Despite half a century of dedicated research, there remains no licensed vaccine product. Herein are described past and current efforts to harness innate and adaptive immune potentials to combat RSV. A plethora of candidate vaccine products and strategies are reviewed. The development of a successful RSV vaccine may ultimately stem from attention to historical lessons, in concert with an integral partnering of immunology and virology research fields.

Viruslike particle vaccine induces protection against respiratory syncytial virus infection in mice

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral death in infants. Despite decades of research with traditional or subunit vaccine approaches, there are no approved RSV vaccines. New approaches are therefore urgently needed to develop effective RSV vaccines.

METHODS

We developed viruslike particles (VLPs) consisting of an influenza virus matrix (M1) protein core and RSV-F or -G on the surface. We tested the immunogenicity and vaccine efficacy of these VLPs (RSV-F, RSV-G) in a mouse model.

RESULTS

Intramuscular vaccination with RSV-F or RSV-G VLPs elicited IgG2a dominant RSV-specific immunoglobulin G (IgG) antibody responses against RSV-A2 viruses in both serum and lung extract. Mice immunized with VLPs (RSV-F or RSV-G) showed higher viral neutralizing antibodies in vitro and significantly decreased lung virus loads in vivo after live RSV-A2 challenge. RSV-G VLPs showed better protective efficacy than RSV-F VLPs as determined by the levels of lung virus loads and morbidity postchallenge.

CONCLUSIONS

This study demonstrates that VLP vaccination provides effective protection against RSV infection. VLPs containing RSV-F and/or RSV-G are potential vaccine candidates against RSV.

Current progress on development of respiratory syncytial virus vaccine

Human respiratory syncytial virus (HRSV) is a major cause of upper and lower respiratory tract illness in infants and young children worldwide. Despite its importance as a respiratory pathogen, there is currently no licensed vaccine for prophylaxis of HRSV infection. There are several hurdles complicating the development of a RSV vaccine: 1) incomplete immunity to natural RSV infection leading to frequent re-infection, 2) immature immune system and maternal antibodies of newborn infants who are the primary subject population, and 3) imbalanced Th2-biased immune responses to certain vaccine candidates leading to exacerbated pulmonary disease. After the failure of an initial trial featuring formalin-inactivated virus as a RSV vaccine, more careful and deliberate efforts have been made towards the development of safe and effective RSV vaccines without vaccine-enhanced disease. A wide array of RSV vaccine strategies is being developed, including live-attenuated viruses, protein subunit-based, and vector-based candidates. Though licensed vaccines remain to be developed, our great efforts will lead us to reach the goal of attaining safe and effective RSV vaccines in the near future.

Progress in respiratory virus vaccine development

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