Pre-existing neutralizing antibodies prevent CD8 T cell-mediated immunopathology following respiratory syncytial virus infection

Self-Assembled Multiepitope Nanovaccine Provides Long-Lasting Cross-Protection against Influenza Virus

Seasonal influenza vaccines typically provide strain-specific protection and are reformulated annually, which is a complex and time-consuming process. Multiepitope vaccines, combining multiple conserved antigenic epitopes from a pathogen, can trigger more robust, diverse, and effective immune responses, providing a potential solution. However, their practical application is hindered by low immunogenicity and short-term effectiveness. In this study, multiple linear epitopes from the conserved stem domain of hemagglutinin and the ectodomain of matrix protein 2 are combined with the Helicobacter pylori ferritin, a stable self-assembled nanoplatform, to develop an influenza multiepitope nanovaccine, named MHF. MHF is prokaryotically expressed in a soluble form and self-assembles into uniform nanoparticles. The subcutaneous immunization of mice with adjuvanted MHF induces cross-reactive neutralizing antibodies, antibody-dependent cell-mediated cytotoxicity, and cellular immunity, offering complete protection against H3N2 as well as partial protection against H1N1. Importantly, the vaccine cargo delivered by ferritin triggers epitope-specific memory B-cell responses, with antibody level persisting for over 6 months post-immunization. These findings indicate that self-assembled multiepitope nanovaccines elicit potent and long-lasting immune responses while significantly reducing the risk of vaccine escape mutants, and offer greater practicality in terms of scalable manufacturing and genetic manipulability, presenting a promising and effective strategy for future vaccine development.

Distinct roles for type I and type III interferons in virulent human metapneumovirus pathogenesis

Human metapneumovirus (HMPV) is an important cause of acute lower respiratory infection in children and adults worldwide. There are four genetic subgroups of HMPV and both neutralizing antibodies and T cells contribute to protection. However, little is known about mechanisms of pathogenesis and most published work is based on a few extensively passaged, laboratory-adapted strains of HMPV. In this study, we isolated and characterized a panel of low passage HMPV clinical isolates representing all four genetic subgroups. The clinical isolates exhibited lower levels of in vitro replication compared to a lab-adapted strain. We compared disease phenotypes using a well-established mouse model. Several virulent isolates caused severe weight loss, lung pathology, airway dysfunction, and fatal disease in mice, which was confirmed in three inbred mouse strains. Disease severity did not correlate with lung viral titer, as virulent strains exhibited restricted replication in the lower airway. Virulent HMPV isolates were associated with markedly increased proinflammatory cytokine production and neutrophil influx; however, depletion of neutrophils or genetic ablation of inflammasome components did not reverse disease. Virulent clinical isolates induced markedly increased type I and type III interferon (IFN) secretion in vitro and in vivo. STAT1/2-deficient mice lacking both type I and type III IFN signaling showed reduced disease severity and increased lung viral replication. Inhibition of type I IFN signaling using a blocking antibody or genetic ablation of the type I IFN receptor reduced pathology with minimal effect on viral replication. Conversely, blockade of type III IFN signaling with a neutralizing antibody or genetic ablation of the IFN-lambda receptor had no effect on pathogenesis but restored viral replication. Collectively, these results demonstrate distinct roles for type I and type III IFN in HMPV pathogenesis and immunity.

Host Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) infections are a constant public health problem, especially in infants and older adults. Virtually all children will have been infected with RSV by the age of two, and reinfections are common throughout life. Since antigenic variation, which is frequently observed among other respiratory viruses such as SARS-CoV-2 or influenza viruses, can only be observed for RSV to a limited extent, reinfections may result from short-term or incomplete immunity. After decades of research, two RSV vaccines were approved to prevent lower respiratory tract infections in older adults. Recently, the FDA approved a vaccine for active vaccination of pregnant women to prevent severe RSV disease in infants during their first RSV season. This review focuses on the host response to RSV infections mediated by epithelial cells as the first physical barrier, followed by responses of the innate and adaptive immune systems. We address possible RSV-mediated immunomodulatory and pathogenic mechanisms during infections and discuss the current vaccine candidates and alternative treatment options.

The protective immunity induced by intranasally inoculated serotype 63 chimpanzee adenovirus vector expressing human respiratory syncytial virus prefusion fusion glycoprotein in BALB/c mice

Human respiratory syncytial virus (RSV) is a ubiquitous pediatric pathogen causing serious lower respiratory tract disease worldwide. No licensed vaccine is currently available. In this work, the coding gene for mDS-Dav1, the full-length and prefusion conformation RSV fusion glycoprotein (F), was designed by introducing the stabilized prefusion F (preF) mutations from DS-Cav1 into the encoding gene of wild-type RSV (wtRSV) F protein. The recombinant adenovirus encoding mDS-Cav1, rChAd63-mDS-Cav1, was constructed based on serotype 63 chimpanzee adenovirus vector and characterized in vitro. After immunizing mice via intranasal route, the rChAd63-mDS-Cav1 induced enhanced neutralizing antibody and F-specific CD8+ T cell responses as well as good immune protection against RSV challenge with the absence of enhanced RSV disease (ERD) in BALB/c mice. The results indicate that rChAd63-mDS-Cav1 is a promising mucosal vaccine candidate against RSV infection and warrants further development.

Spike-specific T-cell responses in COVID-19 patients successfully treated with neutralizing monoclonal antibodies against SARS-CoV-2

Objectives

Neutralizing monoclonal antibodies (moAbs) improves clinical outcomes in patients with COVID-19 when administered during the initial days of infection. The action of moAbs may impair the generation or maintenance of effective immune memory, similar to that demonstrated in other viral diseases. We aimed to evaluate short-term memory T-cell responses in patients effectively treated with bamlanivimab/etesevimab, casirivimab/imdevimab, or sotrovimab (SOT).

Methods

Spike (S)-specific T-cell responses were analyzed in 23 patients with COVID-19 (vaccinated or unvaccinated) before and after a median of 50 (range: 28-93) days from moAb treatment, compared with 11 vaccinated healthy controls. T-cell responses were measured by interferon-γ-enzyme-linked immunospot and flow cytometric activation-induced marker assay.

Results

No statistically significant difference in S-specific T-cell responses was observed between patients treated with moAb and vaccinated healthy controls. Bamlanivimab/etesevimab and casirivimab/imdevimab groups showed significant increases in cellular responses in paired baseline/postrecovery series, as well as vaccinated patients receiving SOT. In contrast, unvaccinated patients prescribed SOT presented no statistically significant increases in T-cell-responses, suggesting diverse impacts of different moAbs on the evolution of S-specific T-cell responses in vaccinated and unvaccinated patients.

Conclusion

The moAbs did not hinder short-term memory S-specific T-cell responses in the overall group of patients; however, differences among moAbs must be further investigated both in vaccinated and unvaccinated individuals.

Mucosal immunization with an adenoviral vector vaccine confers superior protection against RSV compared to natural immunity

Respiratory syncytial virus (RSV) infections are the leading cause of severe respiratory illness in early infancy. Although the majority of children and adults mount immune responses against RSV, recurrent infections are frequent throughout life. Humoral and cellular responses contribute to an effective immunity but also their localization at respiratory mucosae is increasingly recognized as an important factor. In the present study, we evaluate a mucosal vaccine based on an adenoviral vector encoding for the RSV fusion protein (Ad-F), and we investigate two genetic adjuvant candidates that encode for Interleukin (IL)-1β and IFN-β promoter stimulator I (IPS-1), respectively. While vaccination with Ad-F alone was immunogenic, the inclusion of Ad-IL-1β increased F-specific mucosal immunoglobulin A (IgA) and tissue-resident memory T cells (T_RM). Consequently, immunization with Ad-F led to some control of virus replication upon RSV infection, but Ad-F+Ad-IL-1β was the most effective vaccine strategy in limiting viral load and weight loss. Subsequently, we compared the Ad-F+Ad-IL-1β-induced immunity with that provoked by a primary RSV infection. Systemic F-specific antibody responses were higher in immunized than in previously infected mice. However, the primary infection provoked glycoprotein G-specific antibodies as well eventually leading to similar neutralization titers in both groups. In contrast, mucosal antibody levels were low after infection, whereas mucosal immunization raised robust F-specific responses including IgA. Similarly, vaccination generated F-specific T_RM more efficiently compared to a primary RSV infection. Although the primary infection resulted in matrix protein 2 (M2)-specific T cells as well, they did not reach levels of F-specific immunity in the vaccinated group. Moreover, the infection-induced T cell response was less biased towards T_RM compared to vaccine-induced immunity. Finally, our vaccine candidate provided superior protection against RSV infection compared to a primary infection as indicated by reduced weight loss, virus replication, and tissue damage. In conclusion, our mucosal vaccine candidate Ad-F+Ad-IL-1β elicits stronger mucosal immune responses and a more effective protection against RSV infection than natural immunity generated by a previous infection. Harnessing mucosal immune responses by next-generation vaccines is therefore a promising option to establish effective RSV immunity and thereby tackle a major cause of infant hospitalization.

Axl Mediates Resistance to Respiratory Syncytial Virus Infection Independent of Cell Attachment

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract infections in infants and young children. Axl, a TAM family receptor tyrosine kinase (RTK), has been demonstrated as a receptor mediating enveloped virus infection. Here we show that Axl functions as a suppressor of antiviral response during RSV infection. Knockdown of Axl expression in human cells resulted in cell resistance to RSV infection although the treatment did not significantly affect RSV binding or cell entry. Mice deficiency of Axl showed resistance to RSV infection including reduction in viral load and in pulmonary injury. Although T lymphocyte and macrophage infiltration was reduced, more IFN-γ producing cells were present in BALF in Axl-/- mice. Less alternatively activated alveolar macrophages were found in the lungs of Axl-/- mice. Axl-/- MEF cells and siRNA-treated human cells had more robust IFN-β and ISG induction of antiviral genes. Furthermore, re-expression of Axl using Ad-mediated Axl delivery repressed ISG induction in Axl-null MEF cells by RSV infection. The results suggest that Axl, independent of being a virus entry receptor of RSV infection, negatively regulates interferon signaling to modulate host antiviral response against RSV infection.

HRSV prefusion-F protein with Adju-Phos adjuvant induces long-lasting Th2-biased immunity in mice

The development of human respiratory syncytial virus (hRSV) vaccine has been hampered by the risk of enhanced respiratory disease (ERD) which was induced by highly skewed toward Th2 immune response. In our previous study, we expressed the recombinant pre-F protein using Escherichia coli BL21, called RBF. To verify if the RBF protein could cause ERD, we tested the immunogenicity and safety of RBF with a commercial alum adjuvant (GMP-grade Adju-Phos). RBF alone and RBF/Adju-Phos elicited long-lasting protective antibodies and a cellular immune response in mice after three immunizations. Unfortunately, compared with the mice in RBF group, mice in RBF/Adju-Phos generated a serious Th2 humoral immune response that elicited Th2-mediated lung pathology. From the IL-4+:IFNγ+ ratio, there was also a robust Th2 cellullar immunologic response in the RBF/Adju-Phos group. This study demonstrates that it may not be enough for RBF to increase the titer of neutralizing antibodies. A balanced immune response must be induced for hRSV vaccine safety.

A Recombinant BCG Vaccine Is Safe and Immunogenic in Neonatal Calves and Reduces the Clinical Disease Caused by the Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) constitutes a major health burden, causing millions of hospitalizations in children under five years old worldwide due to acute lower respiratory tract infections. Despite decades of research, licensed vaccines to prevent hRSV are not available. Development of vaccines against hRSV targeting young infants requires ruling out potential vaccine-enhanced disease presentations. To achieve this goal, vaccine testing in proper animal models is essential. A recombinant BCG vaccine that expresses the Nucleoprotein of hRSV (rBCG-N-hRSV) protects mice against hRSV infection, eliciting humoral and cellular immune protection. Further, this vaccine was shown to be safe and immunogenic in human adult volunteers. Here, we evaluated the safety, immunogenicity, and protective efficacy of the rBCG-N-hRSV vaccine in a neonatal bovine RSV calf infection model. Newborn, colostrum-replete Holstein calves were either vaccinated with rBCG-N-hRSV, WT-BCG, or left unvaccinated, and then inoculated via aerosol challenge with bRSV strain 375. Vaccination with rBCG-N-hRSV was safe and well-tolerated, with no systemic adverse effects. There was no evidence of vaccine-enhanced disease following bRSV challenge of rBCG-N-hRSV vaccinated animals, suggesting that the vaccine is safe for use in neonates. Vaccination increased virus-specific IgA and virus-neutralization activity in nasal fluid and increased the proliferation of virus- and BCG-specific CD4+ and CD8+ T cells in PBMCs and lymph nodes at 7dpi. Furthermore, rBCG-N-hRSV vaccinated calves developed reduced clinical disease as compared to unvaccinated control calves, although neither pathology nor viral burden were significantly reduced in the lungs. These results suggest that the rBCG-N-hRSV vaccine is safe in neonatal calves and induces protective humoral and cellular immunity against this respiratory virus. These data from a newborn animal model provide further support to the notion that this vaccine approach could be considered as a candidate for infant immunization against RSV.

Investigating the Interaction between Negative Strand RNA Viruses and Their Hosts for Enhanced Vaccine Development and Production

The current pandemic has highlighted the ever-increasing risk of human to human spread of zoonotic pathogens. A number of medically-relevant zoonotic pathogens are negative-strand RNA viruses (NSVs). NSVs are derived from different virus families. Examples like Ebola are known for causing severe symptoms and high mortality rates. Some, like influenza, are known for their ease of person-to-person transmission and lack of pre-existing immunity, enabling rapid spread across many countries around the globe. Containment of outbreaks of NSVs can be difficult owing to their unpredictability and the absence of effective control measures, such as vaccines and antiviral therapeutics. In addition, there remains a lack of essential knowledge of the host–pathogen response that are induced by NSVs, particularly of the immune responses that provide protection. Vaccines are the most effective method for preventing infectious diseases. In fact, in the event of a pandemic, appropriate vaccine design and speed of vaccine supply is the most critical factor in protecting the population, as vaccination is the only sustainable defense. Vaccines need to be safe, efficient, and cost-effective, which is influenced by our understanding of the host–pathogen interface. Additionally, some of the major challenges of vaccines are the establishment of a long-lasting immunity offering cross protection to emerging strains. Although many NSVs are controlled through immunisations, for some, vaccine design has failed or efficacy has proven unreliable. The key behind designing a successful vaccine is understanding the host–pathogen interaction and the host immune response towards NSVs. In this paper, we review the recent research in vaccine design against NSVs and explore the immune responses induced by these viruses. The generation of a robust and integrated approach to development capability and vaccine manufacture can collaboratively support the management of outbreaking NSV disease health risks.

Prefusion RSV F Immunization Elicits Th2-Mediated Lung Pathology in Mice When Formulated With a Th2 (but Not a Th1/Th2-Balanced) Adjuvant Despite Complete Viral Protection

Respiratory syncytial virus (RSV) remains the most common cause of lower respiratory tract infections in children worldwide. Development of a vaccine has been hindered by the risk of developing enhanced respiratory disease (ERD) upon natural exposure to the virus. Generation of higher quality neutralizing antibodies with stabilized pre-fusion F protein antigens has been proposed as a strategy to prevent ERD. We sought to test whether there was evidence of ERD in naïve BALB/c mice immunized with an unadjuvanted, stabilized pre-fusion F protein, and challenged with RSV line 19. We further sought to determine the extent to which formulation with a Th2-biased (alum) or a more Th1/Th2-balanced (Advax-SM) adjuvant influenced cellular responses and lung pathology. When exposed to RSV, mice immunized with pre-fusion F protein alone (PreF) exhibited increased airway eosinophilia and mucus accumulation. This was further exacerbated by formulation of PreF with Alum (aluminum hydroxide). Conversely, formulation of PreF with a Th1/Th2-balanced adjuvant, Advax-SM, not only suppressed RSV viral replication, but also inhibited airway eosinophilia and mucus accumulation. This was associated with lower numbers of lung innate lymphocyte cells (ILC2s) and CD4+ T cells producing IL-5+ or IL-13+ and increased IFNγ+ CD4+ and CD8+ T cells, in addition to RSV F-specific CD8+ T cells. These data suggest that in the absence of preimmunity, stabilized PreF antigens may still be associated with aberrant Th2 responses that induce lung pathology in response to RSV infection, and can be prevented by formulation with more Th1/Th2-balanced adjuvants that enhance CD4+ and CD8+ IFNγ+ T cell responses. This may support the use of stabilized PreF antigens with Th1/Th2-balanced adjuvants like, Advax-SM, as safer alternatives to alum in RSV vaccine candidates.