A Recombinant G Protein Plus Cyclosporine A-Based Respiratory Syncytial Virus Vaccine Elicits Humoral and Regulatory T Cell Responses against Infection without Vaccine-Enhanced Disease

Vaccine and therapeutic agents against the respiratory syncytial virus: resolved and unresolved issue

Respiratory syncytial virus (RSV) is a predominant pathogen responsible for respiratory tract infections among infants, the elderly, and immunocompromised individuals. In recent years, significant progress has been made in innovative vaccines and therapeutic agents targeting RSV. Nevertheless, numerous challenges and bottlenecks persist in the prevention and treatment of RSV infections. This review will provide an overview of the resolved and unresolved issues surrounding the development of vaccines and therapeutic agents against RSV. As of September 2024, three RSV vaccines against acute lower respiratory infections (ALRI) have been approved globally. Additionally, there have been notable progress in the realm of passive immunoprophylactic antibodies, with the monoclonal antibody nirsevimab receiving regulatory approval for the prevention of RSV infections in infants. Furthermore, a variety of RSV therapeutic agents are currently under clinical investigation, with the potential to yield breakthrough advancements in the foreseeable future. This review delineates the advancements and challenges faced in vaccines and therapeutic agents targeting RSV. It aims to provide insights that will guide the development of effective preventive and control measures for RSV.

Recombinant RSV G protein vaccine induces enhanced respiratory disease via IL-13 and mucin overproduction

The G protein expressed on the surface of respiratory syncytial virus (RSV) is important for adhesion to host cells and as a vaccine target antigen. The corresponding vaccines can effectively eliminate RSV. However, they exacerbate pulmonary immunopathology including eosinophilic infiltration in the lungs after an RSV challenge in animal models, raising concerns about enhanced respiratory disease (ERD); thus, approaches that mitigate these effects are urgently needed. Herein, we aimed to examine the mechanisms of G protein vaccine-induced ERD in mice, using recombinant G protein as a vaccine antigen. After the RSV challenge, G protein-vaccinated mice exhibited lung weight gain, lung tissue damage, and increased infiltration of eosinophils, neutrophils, and CD4+ T cells into the lungs. We set lung weight gain as the endpoint for ERD and examined the impact of each infiltrating cell on lung weight gain. We observed that CD4+ T cells, but not eosinophils or neutrophils, that infiltrate the lungs are responsible for lung weight gain. In addition, T helper 2 cell-mediated IL-13 induced mucin hypersecretion and lung weight gain. Mucin hypersecretion may contribute to weight gain in the lungs. In conclusion, our results indicate a novel mechanism of G protein vaccine-induced ERD via IL-13 and mucin hypersecretion, which could lead to the development of safe G protein vaccines and the elucidation of the causes of ERD associated with other vaccines.

Immune Responses and Protection Profiles in Mice Induced by Subunit Vaccine Candidates Based on the Extracellular Domain Antigen of Respiratory Syncytial Virus G Protein Combined with Different Adjuvants

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease of infants and older people. There is an urgent need for safe and effective vaccines against RSV infection. In this study, we analyzed the effects of the immune response and protection with the RSV recombinant G protein extracellular domain (Gecto) combined with various adjuvants as novel subunit vaccines in mice. All groups receiving RSV Gecto combined with adjuvants exhibited robust humoral and cellular immunity compared to those receiving an adjuvant alone or inactivated RSV vaccine. The greatest effect was observed in mice receiving Gecto combined with a CpG ODN + Alum salt adjuvant, resulting in the highest production of neutralizing antibodies against both RSV A and B subtypes, G-specific IgG and IFN-γ production in splenocytes, and interleukin-2 and interferon-γ expression in CD4+ T cells. Significant humoral and cellular immune responses were observed in mice immunized with Gecto combined with AddaS03™ or cyclosporin A adjuvants. The vaccine containing the AddaS03™ adjuvant showed significantly high expression of interleukin-4 in CD4+ T cells. Cross-protection against a challenge with either RSV A or B subtypes was observed in the Gecto plus adjuvant groups, resulting in a significant decrease in viral load and reduced pathological damage in the mouse lungs. These findings offer valuable insights into the development and application of recombinant RSV G-subunit vaccines with adjuvants.

Respiratory Syncytial Virus Vaccines: A Review of the Candidates and the Approved Vaccines

Respiratory syncytial virus (RSV) is responsible for a significant proportion of global morbidity and mortality affecting young children and older adults. In the aftermath of formalin-inactivated RSV vaccine development, the effort to develop an immunizing agent was carefully guided by epidemiologic and pathophysiological evidence of the virus, including various vaccine technologies. The pipeline of RSV vaccine development includes messenger ribonucleic acid (mRNA), live-attenuated (LAV), subunit, and recombinant vector-based vaccine candidates targeting different virus proteins. The availability of vaccine candidates of various technologies enables adjustment to the individualized needs of each vulnerable age group. Arexvy® (GSK), followed by Abrysvo® (Pfizer), is the first vaccine available for market use as an immunizing agent to prevent lower respiratory tract disease in older adults. Abrysvo is additionally indicated for the passive immunization of infants by maternal administration during pregnancy. This review presents the RSV vaccine pipeline, analyzing the results of clinical trials. The key features of each vaccine technology are also mentioned. Currently, 24 vaccines are in the clinical stage of development, including the 2 licensed vaccines. Research in the field of RSV vaccination, including the pharmacovigilance methods of already approved vaccines, promotes the achievement of successful prevention.

IgGκ Signal Peptide Enhances the Efficacy of an Influenza Vector Vaccine against Respiratory Syncytial Virus Infection in Mice

Intranasal vaccination using influenza vectors is a promising approach to developing vaccines against respiratory pathogens due to the activation of the mucosa-associated immune response. However, there is no clear evidence of a vector design that could be considered preferable. To find the optimal structure of an influenza vector with a modified NS genomic segment, we constructed four vector expressing identical transgene sequences inherited from the F protein of the respiratory syncytial virus (RSV). Two vectors were designed aiming at transgene accumulation in the cytosol. Another two were supplemented with an IgGκ signal peptide prior to the transgene for its extracellular delivery. Surprisingly, adding the IgGκ substantially enhanced the T-cell immune response to the CD8 epitope of the transgene. Moreover, this strategy allowed us to obtain a better protection of mice from the RSV challenge after a single intranasal immunization. Protection was achieved without antibodies, mediated by a balanced T-cell immune response including the formation of the RSV specific effector CD8+ IFNγ+/IL10+-producing cells and the accumulation of Treg cells preventing immunopathology in the lungs of infected mice. In addition to the presented method for optimizing the influenza vector, our results highlight the possibility of achieving protection against RSV through a respiratory-associated T-cell immune response alone.

A First-in-Human Trial to Evaluate the Safety and Immunogenicity of a G Protein-Based Recombinant Respiratory Syncytial Virus Vaccine in Healthy Adults 18-45 Years of Age

BACKGROUND

With the enormous morbidity and mortality caused by respiratory syncytial virus (RSV) infections among infants and the elderly, vaccines against RSV infections are in large market demand.

METHODS

We conducted a first-in-human (FIH), randomized, double-blind, placebo-controlled dose escalation study to evaluate the safety and immunogenicity response of the rRSV vaccine (BARS13) in healthy adults aged 18-45. A total of 60 eligible participants were randomly assigned to receive one of four dose levels or vaccination regimens of BARS13 or placebo at a 4:1 ratio.

RESULTS

The mean age was 27.40, and 23.3% (14/60) were men. No treatment-emergent adverse events (TEAEs) led to study withdrawal within 30 days after each vaccination. No serious adverse event (SAE) was reported. Most of the treatment-emergent adverse events (TEAEs) recorded were classified as mild. The high-dose repeat group had a serum-specific antibody GMC of 885.74 IU/mL (95% CI: 406.25-1931.17) 30 days after the first dose and 1482.12 IU/mL (706.56-3108.99) 30 days after the second dose, both higher than the GMC in the low-dose repeat group (885.74 IU/mL [406.25-1931.17] and 1187.10 IU/ mL [610.01-2310.13]).

CONCLUSIONS

BARS13 had a generally good safety and tolerability profile, and no significant difference in terms of adverse reaction severity or frequency was observed between different dose groups. The immune response in repeat-dose recipients shows more potential in further study and has guiding significance for the dose selection of subsequent studies.

Nasal delivery of an immunotherapeutic vaccine in thermosensitive hydrogel against allergic asthma

Asthma poses a significant threat to public health, with an estimated burden of over 334 million people worldwide. Available treatments are often inadequate. We developed a thermo-sensitive hydrogel vaccine containing allergen and FK506 that induced immune tolerance via intranasal administration to treat experimental allergic asthma. The hydrogel delivery system was formulated based on Poloxamer 407 (P407), Carbopol 974P NF, and Polyoxyl 15 hydroxystearate (Kolliphor HS15, HS15). It flowed freely at room temperature and rapidly formed a hydrogel in the nasal cavity once the temperature rose over 33 °C. Ovalbumin and FK506 were slowly released from the hydrogel form and their mucosal residence time was significantly prolonged compared to the liquid formulation. In both an OVA-induced asthma model and an HDM-induced asthma model, the vaccines formulated in hydrogel gave lower levels of eosinophilic inflammation, and airway remodeling. The reduction of lung function was ameliorated, and Foxp3-expressing CD4 + Treg cells were significantly higher. The frequency of Foxp3 + Tregs in lung-draining lymph nodes (dLNs) was correlated with the amelioration. Depletion of Foxp3 + Treg cells abolished the beneficial effects of the allergen/FK506 hydrogel vaccinations. Thus, the allergen/FK506 hydrogel formulation has the potential to be a delivery system for therapeutic allergy vaccines to induce immune tolerance.

A human antibody potently neutralizes RSV by targeting the conserved hydrophobic region of prefusion F

Respiratory syncytial virus (RSV) continues to pose serious threats to pediatric populations due to the lack of a vaccine and effective antiviral drugs. RSV fusion (F) glycoprotein mediates viral-host membrane fusion and is a key target for neutralizing antibodies. We generated 23 full-human monoclonal antibodies (hmAbs) against prefusion F protein (pre-F) from a healthy adult with natural RSV infection by single B cell cloning technique. A highly potent RSV-neutralizing hmAb, named as 25-20, is selected, which targets a new site Ø-specific epitope. Site-directed mutagenesis and structural modelling analysis demonstrated that 25-20 mainly targets a highly conserved hydrophobic region located at the a4 helix and a1 helix of pre-F, indicating a site of vulnerability for drug and vaccine design. It is worth noting that 25-20 uses an unreported inferred germline (iGL) that binds very poorly to pre-F, thus high levels of somatic mutations are needed to gain high binding affinity with pre-F. Our observation helps to understand the evolution of RSV antibody during natural infection. Furthermore, by in silico prediction and experimental verification, we optimized 25-20 with KD values as low as picomolar range. Therefore, the optimized 25-20 represents an excellent candidate for passive protection against RSV infection.

RSV pre-fusion F protein enhances the G protein antibody and anti-infectious responses

Respiratory syncytial virus (RSV) infection in children is the most common viral respiratory infection and can cause severe lung damage or death. There is no licensed vaccine for preventing RSV infection. Previously we demonstrated that an RSV vaccine, BARS13, consisting of recombinant G protein from E. coli plus cyclosporine A (CsA) as an immune-modulator, can protect animals from RSV challenge without inducing vaccine-enhanced disease (VED). To maximize the efficacy of such a vaccine, we introduced RSV pre-fusion F protein (pre-F) to form a new vaccine comprised of the pre-F and G proteins with the CsA. Two intramuscular immunizations with the vaccine induced a higher level of neutralizing antibodies against RSV and protected mice from RSV challenge without incurring VED. Interestingly, the addition of the pre-F to the vaccine facilitated anti-G antibody production and protection from RSV infection mainly via induction of antibodies against the central conserved domain (CCD) of the G protein which correlated with blocking the CX3C-CX3CR1 interaction. A 15 amino acid sequence (FP4) within the F2 region of pre-F served as a CD4⁺ Th epitope to facilitate the anti-G antibody response. Collectively, such a combination of the FP4 peptide with the G protein and CsA provides a novel strategy for developing a safe and maximally effective recombinant G protein-containing RSV vaccine.

Structure-Based Design and Antigenic Validation of Respiratory Syncytial Virus G Immunogens

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease of children, the elderly, and immunocompromised individuals. Currently, there are no FDA-approved RSV vaccines. The RSV G glycoprotein is used for viral attachment to host cells and impairment of host immunity by interacting with the human chemokine receptor CX3CR1. Antibodies that disrupt this interaction are protective against infection and disease. Nevertheless, development of an RSV G vaccine antigen has been hindered by its low immunogenicity and safety concerns. A previous study described three engineered RSV G proteins containing single-point mutations that induce higher levels of IgG antibodies and have improved safety profiles compared to wild-type RSV G (H. C. Bergeron, J. Murray, A. M. Nuñez Castrejon, et al., Viruses 13:352, 2021, https://doi.org/10.3390/v13020352). However, it is unclear if the mutations affect RSV G protein folding and display of its conformational epitopes. In this study, we show that the RSV G S177Q protein retains high-affinity binding to protective human and mouse monoclonal antibodies and has equal reactivity as wild-type RSV G protein to human reference immunoglobulin to RSV. Additionally, we determined the high-resolution crystal structure of RSV G S177Q protein in complex with the anti-RSV G antibody 3G12, further validating its antigenic structure. These studies show for the first time that an engineered RSV G protein with increased immunogenicity and safety retains conformational epitopes to high-affinity protective antibodies, supporting its further development as an RSV vaccine immunogen. IMPORTANCE Respiratory syncytial virus (RSV) causes severe lower respiratory diseases of children, the elderly, and immunocompromised populations. There currently are no FDA-approved RSV vaccines. Most vaccine development efforts have focused on the RSV F protein, and the field has generally overlooked the receptor-binding antigen RSV G due to its poor immunogenicity and safety concerns. However, single-point mutant RSV G proteins have been previously identified that have increased immunogenicity and safety. In this study, we investigate the antibody reactivities of three known RSV G mutant proteins. We show that one mutant RSV G protein retains high-affinity binding to protective monoclonal antibodies, is equally recognized by anti-RSV antibodies in human sera, and forms the same three-dimensional structure as the wild-type RSV G protein. Our study validates the structure-guided design of the RSV G protein as an RSV vaccine antigen.

Dynamic Host Immune and Transcriptomic Responses to Respiratory Syncytial Virus Infection in a Vaccination-Challenge Mouse Model

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infections in children. Inactivated RSV vaccine was developed in the late 1960's, but the vaccine-enhanced disease (VED) occurred to vaccinated infants upon subsequent natural RSV infection. The excessive inflammatory immunopathology in the lungs might be involved in the VED, but the underlying mechanisms remain not fully understood. In this study, we utilized UV-inactivated RSV in the prime/boost approach followed by RSV challenge in BALB/c mice to mimic RSV VED. The dynamic virus load, cytokines, histology and transcriptome profiles in lung tissues of mice were investigated from day 1 to day 6 post-infection. Compared to PBS-treated mice, UV-RSV vaccination leads to a Th2 type inflammatory response characterized by enhanced histopathology, reduced Treg cells and increased IL4+CD4 T cells in the lung. Enhanced production of several Th2 type cytokines (IL-4, IL-5, IL-10) and TGF-β,  reduction of IL-6 and IL-17 were observed in UV-RSV vaccinated mice. A total of 5582 differentially expressed (DE) genes between PBS-treated or vaccinated mice and naïve mice were identified by RNA-Seq. Eleven conserved high-influential modules (HMs) were recognized, majorly grouped into regulatory networks related to cell cycle and cell metabolism, signal transduction, immune and inflammatory responses. At an early time post-infection, the vaccinated mice showed obvious decreased expression patterns of DE genes in 11 HMs compared to PBS-treated mice. The extracellular matrix (HM5) and immune responses (HM8) revealed tremendous differences in expression and regulation characteristics of transcripts between PBS-treated and vaccinated mice at both early and late time points. The highly connected genes in HM5 and HM8 networks were further validated by RT-qPCR. These findings reveal the relationship between RSV VED and immune responses, which could benefit the development of novel RSV vaccines.

Respiratory syntycial virus: Current treatment strategies and vaccine approaches

Respiratory Syncytial Virus is a yearly respiratory virus that causes significant frequencies of morbidities, particularly in the young and elderly populations. However, preventive vaccines and/or treatment therapies are generally lacking, although much attention is now being placed on this virus. Moreover, there are now multiple strategies currently being explored in a race to the first licensed vaccine. While vaccines are being developed, multiple treatment strategies are being explored to attenuate the severity of infection and thus reduce hospitalization rates in vulnerable populations. This review outlines current strategies to prevent or treat this virus in the hopes of reducing significant human morbidity and mortality that occurs yearly with this seasonal virus.

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.

Hepatitis B Virus Core Particles Containing a Conserved Region of the G Protein Combined with Interleukin-35 Protected Mice against Respiratory Syncytial Virus Infection without Vaccine-Enhanced Immunopathology

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infection in infants and young children. The vaccine-enhanced disease (VED) has greatly hindered the development of an RSV vaccine. Currently, there are no licensed vaccines for RSV. In this study, immunization of mice with hepatitis B virus core particles containing a conserved region of the G protein (HBc-tG) combined with interleukin-35 (IL-35) elicited a Th1-biased response and a high frequency of regulatory T (Treg) cells and increased the levels of IL-10, transforming growth factor β, and IL-35 production. Importantly, immunization with HBc-tG together with IL-35 protected mice against RSV infection without vaccine-enhanced immunopathology. To explore the mechanism of how IL-35 reduces lung inflammation at the gene expression level, transcription profiles were obtained from lung tissues of immunized mice after RSV infection by the Illumina sequencing technique and further analyzed by a systems biology method. In total, 2,644 differentially expressed genes (DEGs) were identified. Twelve high-influence modules (HIMs) were selected from these DEGs on the basis of the protein-protein interaction network. A detailed analysis of HIM10, involved in the immune response network, revealed that Il10 plays a key role in regulating the host response. The selected DEGs were consistently confirmed by quantitative real-time PCR (qRT-PCR). Our results demonstrate that IL-35 inhibits vaccine-enhanced immunopathology after RSV infection and has potential for development in novel therapeutic and prophylactic strategies.IMPORTANCE In the past few decades, respiratory syncytial virus (RSV) has still been a major health concern worldwide. The vaccine-enhance disease (VED) has hindered RSV vaccine development. A truncated hepatitis B virus core protein vaccine containing the conserved region (amino acids 144 to 204) of the RSV G protein (HBc-tG) had previously been shown to induce effective immune responses and confer protection against RSV infection in mice but to also lead to VED. In this study, we investigated the effect of IL-35 on the host response and immunopathology following RSV infection in vaccinated mice. Our results indicate that HBc-tG together with IL-35 elicited a balanced immune response and protected mice against RSV infection without vaccine-enhanced immunopathology. Applying a systems biology method, we identified Il10 to be the key regulator in reducing the excessive lung inflammation. Our study provides new insight into the function of IL-35 and its regulatory mechanism of VED at the network level.

Engineering of Live Chimeric Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is an important human pathogen that, along with respiratory syncytial virus (RSV), is a major cause of respiratory tract infections in young infants. Development of an effective vaccine against Pneumoviruses has proven to be particularly difficult; despite over 50 years of research in this field, no vaccine against HMPV or RSV is currently available. Recombinant chimeric viruses expressing antigens of other viruses can be generated by reverse genetics and used for simultaneous immunization against more than one pathogen. This approach can result in the development of promising vaccine candidates against HMPV, and several studies have indeed validated viral vectors expressing HMPV antigens. In this review, we summarize current efforts in generating recombinant chimeric vaccines against HMPV, and we discuss their potential optimization based on the correspondence with RSV studies.

Safety and immunogenicity of novel modified vaccinia Ankara-vectored RSV vaccine: A randomized phase I clinical trial

Respiratory disease caused by RSV infection is recognized as a severe public health issue in infants, young children and elderly with no specific treatment option. Vaccination may be the most effective strategy to combat this highly infectious virus although no vaccine has been approved. The novel vaccine candidate MVA-BN-RSV encodes RSV surface proteins F and G (subtypes A, B) as well as internal proteins N and M2 in the MVA-BN viral vector backbone to provide broad protection against RSV. This was a first in human study to investigate safety, reactogenicity and immunogenicity of MVA-BN-RSV. Sixty-three participants were allocated to 3 groups: adult (18-49 years) low (1 × 10⁷ TCID₅₀) or high (1 × 10⁸ TCID₅₀) dose and older adult (50-65 years) high dose. Participants in each group were randomized in a 6:1 ratio to receive 2 doses of MVA-BN-RSV or placebo 4 weeks apart and were monitored for 30 weeks. All participants completed the study, receiving both doses. No serious AEs or AEs of special interest were reported. The most common AEs were injection site pain (56% in the combined high dose groups, 17% in the low dose group). MVA-BN-RSV induced robust T cell responses covering all 5 inserts with fold increases ranging from 1.8 to 3.8. Higher and broader responses were observed in the high dose groups (83% responders to at least 3 peptide pools in the combined high dose groups compared to 63% in the low dose group). Moderate but consistent humoral responses were observed against A and B RSV subtypes (up to approximately 2-fold increases in the high dose groups). No differences were observed between the adult and the older adult groups in safety, reactogenicity or immunogenicity. The study demonstrated that the well tolerated MVA-BN-RSV vaccine candidate induces broad cellular and humoral immune responses, warranting further development.

Neonatal priming and infancy boosting with a novel respiratory syncytial virus vaccine induces protective immune responses without concomitant respiratory disease upon RSV challenge

Although respiratory syncytial virus (RSV) infection in infants and young children is a global public health issue, development of a safe RSV vaccine has been impeded by formalin-inactivated RSV-enhanced respiratory disease (ERD). In developing a safer yet effective RSV vaccine for children, a strategy to decrease over-reactive T cells and increase neutralizing anti-RSV antibodies should be considered. We previously demonstrated that adult mice immunized with RSV recombinant G protein plus low-dose Cyclosporine A (G+ CsA) could, upon subsequent RSV challenge, produce increased levels of antigen-specific T regulatory cells in lungs that overcame the ERD. Neutralizing anti-RSV antibodies that prevented viral infection were also elicited. In this study, we investigated if such a G+ CsA vaccine could provide infant mice with the same protection from RSV infection without ERD. The results showed that the G+ CsA vaccine could prevent RSV infection with only a mild loss of body weight. Importantly, there was nearly normal morphology and no mucus appearance in lung tissues after RSV challenge. These results demonstrate that the G+ CsA vaccine strategy achieved similar benefits in the neonatal prime and infancy boost model as in the adult mouse model. The G+ CsA immunization strategy is potentially safe and effective in neonates and infants because it suppresses the devastating ERD.

Tolerogenic vaccine composited with islet-derived multipeptides and cyclosporin A induces pTreg and prevents Type 1 diabetes in murine model

Regulatory T cells (Tregs) play a crucial role in the control of the initiation and progression of type 1 diabetes (T1D). Various immunological interventions including those to ex vivo expansion Tregs transfer, in vivo induction of peripherally derived Treg (pTreg) have been considered as promising approaches for T1D therapy. In this study, we developed a novel tolerogenic vaccine using four autoantigenic peptides of islet-derived with cyclosporine A (CsA) as the pTreg inducer, designated as GAD-IN+CsA. This vaccine immunized into prediabetic NOD mice subcutaneously could induce IL-10 and TGF-β expressing pTregs and lead to suppressing autoreactive T cells responses, resulting in the prevention of T1D in these animals. Furthermore, we demonstrated that CsA with autoantigenic peptides modulates dendritic cells (DCs) to become immature IL-10^hiCD40^lo DCs. Such modulated DCs could foster naïve CD4⁺CD25⁻ T cell into Tregs when presenting antigen peptides in vitro. This novel approach offers an alternative strategy to induce pTregs to treat T1D.

Vaccine containing G protein fragment and recombinant baculovirus expressing M2 protein induces protective immunity to respiratory syncytial virus

Purpose

Respiratory syncytial virus (RSV) can cause serious respiratory illnesses such as pneumonia, asthma, and bronchiolitis in infants and elderly or immunocompromised individuals. An RSV vaccine has yet to be developed; only prophylactic anti-RSV antibody is commercially available. So, we investigated whether our vaccine candidate is able to induce type 1 CD4⁺ T helper (Th1), CD8⁺ T-cell responses, and protective immunity without vaccine-enhanced disease (VED) against RSV.

Materials and Methods

We used RSV G protein fragment (Gcf A) with recombinant baculovirus capable of expressing the RSV M2 protein (Bac M2) as a vaccine candidate, and injected this vaccine (Gcf A/Bac M2) intramuscularly, and challenged with RSV intranasally into mice. Enzyme-linked immunosorbent assay, flow cytometry, plaque assay, and weight measurement were performed to confirm humoral immunity, cellular immunity, and protective immunity.

Results

The Gcf A/Bac M2 formulation induced a stronger IgG response to Gcf A than Gcf A inoculation alone, and the ratio of IgG1/IgG2a indicated that the responses shifted predominantly to Th1. In addition, both RSV G-specific Th1 responses and RSV M2-specific CD8⁺ T-cell responses were induced, and G protein-associated eosinophilic infiltration was suppressed compared to the control group. Moreover, the Gcf A/Bac M2 group showed effective protection after an RSV challenge.

Conclusion

Bac M2 could serve as a vaccine with intrinsic adjuvant activity, and the Gcf A/Bac M2 shows promise as a vaccine candidate for inducing protective immunity without inciting VED.

Nasal immunization with RSV F and G protein fragments conjugated to an M cell-targeting ligand induces an enhanced immune response and protection against RSV infection

Human respiratory syncytial virus (RSV) is a major paediatric health concern worldwide. The development of an effective and safe vaccine against RSV is urgently needed. As RSV infects via the mucosal surfaces, developing a nasal vaccine may offer protective benefits over alternative administration routes. In this study, we tested a recombinant protein FG-Gb1 as an intranasal vaccine candidate against RSV. FG-Gb1 consists of the core fragments of the RSV fusion (F) and attachment (G) proteins conjugated to an microfold (M) cell-specific ligand Gb-1. Intranasal immunization with FG-Gb1 induced efficient systemic and mucosal immune responses as measured by the level of antigen-specific antibodies, cytokine-secreting cells and antigen-specific lymphocyte proliferation after exposure to antigen. Moreover, intranasal immunization induced protective immunity against nasal challenge with RSV, which was confirmed by a lack of weight loss and by viral clearance after challenge. Collectively, we confirmed that a ligand capable of targeting the conjugated antigen to nasopharynx-associated lymphoid tissue (NALT) can be used as an effective nasal vaccine adjuvant to induce protective immunity against RSV infection. Moreover, FG-Gb1 may have promise as an RSV vaccine but requires further studies.

Prevention and treatment of respiratory viral infections: Presentations on antivirals, traditional therapies and host-directed interventions at the 5th ISIRV Antiviral Group conference

The International Society for Influenza and other Respiratory Virus Diseases held its 5th Antiviral Group (isirv-AVG) Conference in Shanghai, China, in conjunction with the Shanghai Public Health Center and Fudan University from 14-16 June 2017. The three-day programme encompassed presentations on some of the clinical features, management, immune responses and virology of respiratory infections, including influenza A(H1N1)pdm09 and A(H7N9) viruses, MERS-CoV, SARS-CoV, adenovirus Type 80, enterovirus D68, metapneumovirus and respiratory syncytial virus (RSV). Updates were presented on several therapeutics currently in clinical trials, including influenza polymerase inhibitors pimodivir/JNJ6362387, S033188, favipiravir, monoclonal antibodies MHAA45449A and VIS410, and host directed strategies for influenza including nitazoxanide, and polymerase ALS-008112 and fusion inhibitors AK0529, GS-5806 for RSV. Updates were also given on the use of the currently licensed neuraminidase inhibitors. Given the location in China, there were also presentations on the use of Traditional Chinese Medicines. Following on from the previous conference, there were ongoing discussions on appropriate endpoints for severe influenza in clinical trials from regulators and clinicians, an issue which remains unresolved. The aim of this conference summary is to provide information for not only conference participants, but a detailed referenced review of the current status of clinical trials, and pre-clinical development of therapeutics and vaccines for influenza and other respiratory diseases for a broader audience.

Pre-fusion RSV F strongly boosts pre-fusion specific neutralizing responses in cattle pre-exposed to bovine RSV

Human respiratory syncytial virus (hRSV) is responsible for serious lower respiratory tract disease in infants and in older adults, and remains an important vaccine need. RSV fusion (F) glycoprotein is a key target for neutralizing antibodies. RSV F stabilized in its pre-fusion conformation (DS-Cav1 F) induces high neutralizing antibody titers in naïve animals, but it remains unknown to what extent pre-fusion F can boost pre-existing neutralizing responses in RSV seropositive adults. We here assess DS-Cav1 F immunogenicity in seropositive cattle pre-exposed to bovine RSV, a virus closely related to hRSV. A single immunization with non-adjuvanted DS-Cav1 F strongly boosts RSV neutralizing responses, directed towards pre-fusion F-specific epitopes, whereas a post-fusion F is unable to do so. Vaccination with pre-fusion F thus represents a promising strategy for maternal immunization and for other RSV vaccine target populations such as older adults.

Global epidemiology of non-influenza RNA respiratory viruses: data gaps and a growing need for surveillance

Together with influenza, the non-influenza RNA respiratory viruses (NIRVs), which include respiratory syncytial virus, parainfluenza viruses, coronavirus, rhinovirus, and human metapneumovirus, represent a considerable global health burden, as recognised by WHO's Battle against Respiratory Viruses initiative. By contrast with influenza viruses, little is known about the contemporaneous global diversity of these viruses, and the relevance of such for development of pharmaceutical interventions. Although far less advanced than for influenza, antiviral drugs and vaccines are in different stages of development for several of these viruses, but no interventions have been licensed. This scarcity of global genetic data represents a substantial knowledge gap and impediment to the eventual licensing of new antiviral drugs and vaccines for NIRVs. Enhanced genetic surveillance will assist and boost research and development into new antiviral drugs and vaccines for these viruses. Additionally, understanding the global diversity of respiratory viruses is also part of emerging disease preparedness, because non-human coronaviruses and paramyxoviruses have been listed as priority concerns in a recent WHO research and development blueprint initiative for emerging infectious diseases. In this Personal View, we explain further the rationale for expanding the genetic database of NIRVs and emphasise the need for greater investment in this area of research.

A critical role of Gas6/Axl signal in allergic airway responses during RSV vaccine-enhanced disease

Respiratory syncytial virus (RSV) is a common virus that causes lower respiratory infections across a wide range of ages. A licensed RSV vaccine is not available because vaccination with formalin-inactivated RSV (FI-RSV) and the subsequent RSV infection cause not only insufficient induction of neutralizing antibodies but also severe allergic airway responses, termed FI-RSV vaccine-enhanced disease (FI-RSV VED). However, the underlying mechanism has not been identified, although a Th2-biased immune response is known to be a hallmark of this disease. Our previous studies have shown that growth arrest-specific 6 (Gas6)/Axl signaling leads to Th2-biased immune responses during fungus-induced allergic airway inflammation. Here, we show that Gas6/Axl signaling also leads to FI-RSV VED and partially identify the mechanism in mice. Inhibiting Gas6/Axl signaling using Gas6-deficient mice, neutralizing antibodies, and a specific inhibitor of Axl attenuated allergic airway hyperresponsiveness, including airway inflammation, goblet cell hyperplasia, and Th2 cytokine production, in addition to increasing interferon-γ levels and the production of RSV-neutralizing IgG2a in FI-RSV VED. Gas6 was produced in lymph nodes during immunization with FI-RSV. Lymph node cells derived from immunized mice produced high levels of Gas6 and Th2 cytokines, but not IFN-γ, after restimulation with RSV. Finally, we found that dendritic cells stimulated with RSV-glycoprotein (G protein) produced Gas6 and that Axl signaling suppressed DC maturation and the induction of IL-12 production by the toll-like receptor 4 agonist RSV-fusion protein. Taken together, these results indicate that RSV-G protein-induced Gas6/Axl signaling causes allergic airway responses during FI-RSV VED.

Immunological Features of Respiratory Syncytial Virus-Caused Pneumonia-Implications for Vaccine Design

The human respiratory syncytial virus (hRSV) is the causative agent for high rates of hospitalizations due to viral bronchiolitis and pneumonia worldwide. Such a disease is characterized by an infection of epithelial cells of the distal airways that leads to inflammation and subsequently to respiratory failure. Upon infection, different pattern recognition receptors recognize the virus and trigger the innate immune response against the hRSV. Further, T cell immunity plays an important role for virus clearance. Based on animal studies, it is thought that the host immune response to hRSV is based on a biased T helper (Th)-2 and Th17 T cell responses with the recruitment of T cells, neutrophils and eosinophils to the lung, causing inflammation and tissue damage. In contrast, human immunity against RSV has been shown to be more complex with no definitive T cell polarization profile. Nowadays, only a humanized monoclonal antibody, known as palivizumab, is available to protect against hRSV infection in high-risk infants. However, such treatment involves several injections at a significantly high cost. For these reasons, intense research has been focused on finding novel vaccines or therapies to prevent hRSV infection in the population. Here, we comprehensively review the recent literature relative to the immunological features during hRSV infection, as well as the new insights into preventing the disease caused by this virus.

DNA vaccine encoding central conserved region of G protein induces Th1 predominant immune response and protection from RSV infection in mice

Human respiratory syncytial virus (RSV) can cause serious infection in the lower respiratory tract, especially in infants, young children, the elderly and the immunocompromised population worldwide. Previous study demonstrated the polypeptide (amino acids 148-198) of RSV attachment (G) glycoprotein, corresponding to the central conserved region and encompassing CX3C chemokine motif, could induce antibodies and protection from RSV challenge in mice [1,2]. In this study, we evaluated the immune efficacy of the recombinant DNA vaccine of pVAX1/3G_148-198 encoding RSV G protein polypeptide. RSV specific serum IgG antibodies with neutralizing activity were stimulated following prime-boost immunization of pVAX1/3G_148-198 intramuscularly, and the ratio of IgG2a/IgG1 was 4.93, indicating a Th1 biased immune response. After challenged intranasally with RSV Long, the vaccinated mice showed both decreased lung RSV titers, pulmonary inflammation and body weight loss. The results suggest that pVAX1/3G_148-198 DNA vaccine may be an effective RSV vaccine candidate, and deserves further exploration.