Current Animal Models for Understanding the Pathology Caused by the Respiratory Syncytial Virus

Testing pulmonary physiology in ventilated non-human primates

BACKGROUND

Animal models of respiratory viral infections are essential for investigating disease pathogenesis and the efficacy of antivirals and vaccine candidates. A major limitation in the research of respiratory diseases in animal models is correlating clinically relevant changes in pulmonary physiology with cellular and molecular mechanistic studies. Few animal models have captured and correlated physiologic changes in lung function and immune response within same experiment, which is critical given the heterogeneous nature of lung disease due to viral infections. In ventilated human patients, pulmonary physiology testing can be used to not only capture oxygenation, ventilation, but also pulmonary mechanics to yield quantitative measures of lung function and scalar tracings of flow-volume and pressure-volume loops. Application of this protocol during mechanical ventilation in non-human (NHP) models would represent a major advance in respiratory viral disease research.

METHODS

We have applied and optimized a human pulmonary physiology testing protocol to ventilated pigtail macaques (Macaca nemestrina) at baseline and 5 days after influenza A (IAV) viral inoculation.

RESULTS

The NHPs manifested clinical disease with hypothermia and loss of body weight. Declines in lung function were striking with a 66%-81% decline in P/F ratio, a measure of oxygenation reflecting the ratio of partial pressure of oxygen in arterial blood (PaO2 ) to the fraction of inspiratory oxygen concentration (FiO2 ). There was also a 16%-45% decline in lung compliance.

CONCLUSION

We describe a new approach to performing pulmonary physiology testing protocol in non-human primates to better capture quantitative correlates of respiratory disease and demonstrate protection by therapeutics and vaccines.

Modeling Human Respiratory Syncytial Virus (RSV) Infection: Recent Contributions and Future Directions Using the Calf Model of Bovine RSV Disease

The human orthopneumovirus (human respiratory syncytial virus [RSV]) is a leading cause of respiratory disease in children worldwide and a significant cause of infant mortality in low- and middle-income countries. The natural immune response to the virus has a preponderant role in disease progression, with a rapid neutrophil infiltration and dysbalanced T cell response in the lungs associated with severe disease in infants. The development of preventive interventions against human RSV has been difficult partly due to the need to use animal models that only partially recapitulate the immune response as well as the disease progression seen in human infants. In this brief review, we discuss the contributions of the calf model of RSV infection to understanding immunity to RSV and in developing vaccine and drug candidates, focusing on recent research areas. We propose that the bovine model of RSV infection is a valuable alternative for assessing the translational potential of interventions aimed at the human population.

Immunization with a mucosal, post-fusion F/G protein-based polyanhydride nanovaccine protects neonatal calves against BRSV infection

Human respiratory syncytial virus (HRSV) is a leading cause of death in young children and there are no FDA approved vaccines. Bovine RSV (BRSV) is antigenically similar to HRSV, and the neonatal calf model is useful for evaluation of HRSV vaccines. Here, we determined the efficacy of a polyanhydride-based nanovaccine encapsulating the BRSV post-fusion F and G glycoproteins and CpG, delivered prime-boost via heterologous (intranasal/subcutaneous) or homologous (intranasal/intranasal) immunization in the calf model. We compared the performance of the nanovaccine regimens to a modified-live BRSV vaccine, and to non-vaccinated calves. Calves receiving nanovaccine via either prime-boost regimen exhibited clinical and virological protection compared to non-vaccinated calves. The heterologous nanovaccine regimen induced both virus-specific cellular immunity and mucosal IgA, and induced similar clinical, virological and pathological protection as the commercial modified-live vaccine. Principal component analysis identified BRSV-specific humoral and cellular responses as important correlates of protection. The BRSV-F/G CpG nanovaccine is a promising candidate vaccine to reduce RSV disease burden in humans and animals.

The Impact of Coronavirus Disease 2019 on Viral, Bacterial, and Fungal Respiratory Infections

Although coronavirus disease 2019 (COVID-19) remains an ongoing threat, concerns regarding other respiratory infections remain. Throughout the COVID-19 pandemic various epidemiologic trends have been observed in other respiratory viruses including a reduction in influenza and respiratory syncytial virus infections following onset of the COVID-19 pandemic. Observations suggest that infections with other respiratory viruses were reduced with social distancing, mask wearing, eye protection, and hand hygiene practices. Coinfections with COVID-19 exist not only with other respiratory viruses but also with bacterial pneumonias and other nosocomial and opportunistic infections. Coinfections have been associated with increased severity of illness and other adverse outcomes.

3D engineered tissue models for studying human-specific infectious viral diseases

Viral infections cause damage to various organ systems by inducing organ-specific symptoms or systemic multi-organ damage. Depending on the infection route and virus type, infectious diseases are classified as respiratory, nervous, immune, digestive, or skin infections. Since these infectious diseases can widely spread in the community and their catastrophic effects are severe, identification of their causative agent and mechanisms underlying their pathogenesis is an urgent necessity. Although infection-associated mechanisms have been studied in two-dimensional (2D) cell culture models and animal models, they have shown limitations in organ-specific or human-associated pathogenesis, and the development of a human-organ-mimetic system is required. Recently, three-dimensional (3D) engineered tissue models, which can present human organ-like physiology in terms of the 3D structure, utilization of human-originated cells, recapitulation of physiological stimuli, and tight cell–cell interactions, were developed. Furthermore, recent studies have shown that these models can recapitulate infection-associated pathologies. In this review, we summarized the recent advances in 3D engineered tissue models that mimic organ-specific viral infections. First, we briefly described the limitations of the current 2D and animal models in recapitulating human-specific viral infection pathology. Next, we provided an overview of recently reported viral infection models, focusing particularly on organ-specific infection pathologies. Finally, a future perspective that must be pursued to reconstitute more human-specific infectious diseases is presented.

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3D in vitro models are different from the traditional model in the infection process.

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Human-specific infection research requires a 3D microenvironment and human cells.

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3D in vitro infectious models can be useful for basic research on infectious disease.

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3D in vitro infectious models recapitulate the complex cell-virus-immune interaction.

Species-agnostic polymeric formulations for inhalable messenger RNA delivery to the lung

Messenger RNA has now been used to vaccinate millions of people. However, the diversity of pulmonary pathologies, including infections, genetic disorders, asthma and others, reveals the lung as an important organ to directly target for future RNA therapeutics and preventatives. Here we report the screening of 166 polymeric nanoparticle formulations for functional delivery to the lungs, obtained from a combinatorial synthesis approach combined with a low-dead-volume nose-only inhalation system for mice. We identify P76, a poly-β-amino-thio-ester polymer, that exhibits increased expression over formulations lacking the thiol component, delivery to different animal species with varying RNA cargos and low toxicity. P76 allows for dose sparing when delivering an mRNA-expressed Cas13a-mediated treatment in a SARS-CoV-2 challenge model, resulting in similar efficacy to a 20-fold higher dose of a neutralizing antibody. Overall, the combinatorial synthesis approach allowed for the discovery of promising polymeric formulations for future RNA pharmaceutical development for the lungs.

Anti-G protein antibodies targeting the RSV G protein CX3C chemokine region improve the interferon response

Background

Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) responses which result in incomplete immunity and RSV disease. Several RSV proteins alter antiviral responses, including the non-structural proteins (NS1, NS2) and the major viral surface proteins, that is, fusion (F) and attachment (G) proteins. The G protein modifies the host immune response to infection linked in part through a CX3 C chemokine motif. Anti-G protein monoclonal antibodies (mAbs), that is, clones 3D3 and 2D10 that target the G protein CX3C chemokine motif can neutralize RSV and inhibit G protein-CX3CR1 mediated chemotaxis.

Objectives

Determine how monoclonal antibodies against the RSV F and G proteins modify the type I and III IFN responses to RSV infection.

Design

As the G protein CX3 C motif is implicated in IFN antagonism, we evaluated two mAbs that block G protein CX3C-CX3CR1 interaction and compared responses to isotype mAb control using a functional cellular assay and mouse model.

Methods

Mouse lung epithelial cells (MLE-15 cells) and BALB/c mice were infected with RSV Line19 F following prophylactic mAb treatment. Cell supernatant or bronchoalveolar lavage fluid (BALF) were assayed for types I and III IFNs. Cells were interrogated for changes in IFN-related gene expression.

Results

Treatment with an anti-G protein mAb (3D3) resulted in improved IFN responses compared with isotype control following infection with RSV, partially independently of neutralization, and this was linked to upregulated SOCS1 expression.

Conclusions

These findings show that anti-G protein antibodies improve the protective early antiviral response, which has important implications for vaccine and therapeutic design.

Plain Language Summary

RSV is a leading cause of respiratory disease in infants and the elderly. The only Food and Drug Administration-approved prophylactic treatment is limited to an anti-F protein monoclonal antibody (mAb), that is, palivizumab which has modest efficacy against RSV disease. Accumulating evidence suggests that targeting the RSV attachment (G) protein may provide improved protection from RSV disease. It is known that the G protein is an IFN antagonist, and IFN has been shown to be protective against RSV disease. In this study, we compared IFN responses in mouse lung epithelial (MLE-15) cells and in mice infected with RSV Line19 F treated with anti-G protein or anti-F protein mAbs. The levels of type I and III IFNs were determined. Anti-G protein mAbs improved the levels of IFNs compared with isotype-treated controls. These findings support the concept that anti-G protein mAbs mediate improved IFN responses against RSV disease, which may enable improved treatment of RSV infections.

Intranasal immunization with HRSV prefusion F protein and CpG adjuvant elicits robust protective effects in mice

Human respiratory syncytial virus (HRSV) is a leading cause of lower respiratory tract infections in elderly individuals and young children/infants and can cause bronchiolitis and even death. There is no licensed HRSV vaccine. An ideal vaccine should induce high titers of neutralizing antibodies and a Th1-biased immune response. In this study, we used EXPI293 cells to express the fusion (F) protein with a prefusion conformation (PrF) and compared the safety and efficacy of intranasal immunization with PrF in combination with two mucosal adjuvants (CpG ODN and liposomes) in mice. After two intranasal administrations, mice in the PrF + CpG group produced high titers of neutralizing antibodies (4961) and a Th1-biased immune response compared with the PrF + Lipo group. The lung viral load of mice in the PrF + CpG group was significantly reduced (3.5 log) compared with that in the adjuvant control group, and the survival rate was 100 %, while the survival rate of mice in the PrF + Lipo group was only 67 %. At the same time, this immunization strategy reduced the pathological damage to the lungs in mice. In conclusion, the combination of PrF and CpG adjuvant is immunogenic, elicits a Th1 type immune response, and completely protects mice from a lethal HRSV challenge. It is worthy of further evaluation as an HRSV vaccine in clinical trials. Clinical trial registration. This study was not related to human participation or experimentation.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Mucosal 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.

Factors Limiting the Translatability of Rodent Model-Based Intranasal Vaccine Research to Humans

The intranasal route of vaccination presents an attractive alternative to parenteral routes and offers numerous advantages, such as the induction of both mucosal and systemic immunity, needle-free delivery, and increased patient compliance. Despite demonstrating promising results in preclinical studies, however, few intranasal vaccine candidates progress beyond early clinical trials. This discrepancy likely stems in part from the limited predictive value of rodent models, which are used frequently in intranasal vaccine research. In this review, we explored the factors that limit the translatability of rodent-based intranasal vaccine research to humans, focusing on the differences in anatomy, immunology, and disease pathology between rodents and humans. We also discussed approaches that minimize these differences and examined alternative animal models that would produce more clinically relevant research.

Controlled Human Infection Challenge Studies with RSV

Despite considerable momentum in the development of RSV vaccines and therapeutics, there remain substantial barriers to the development and licensing of effective agents, particularly in high-risk populations. The unique immunobiology of RSV and lack of clear protective immunological correlates has held back RSV vaccine development, which, therefore, depends on large and costly clinical trials to demonstrate efficacy. Studies involving the deliberate infection of human volunteers offer an intermediate step between pre-clinical and large-scale studies of natural infection. Human challenge has been used to demonstrate the potential efficacy of vaccines and antivirals while improving our understanding of the protective immunity against RSV infection. Early RSV human infection challenge studies determined the role of routes of administration and size of inoculum on the disease. However, inherent limitations, the use of highly attenuated/laboratory-adapted RSV strains and the continued evolutionary adaptation of RSV limits extrapolation of results to present-day vaccine testing. With advances in technology, it is now possible to perform more detailed investigations of human mucosal immunity against RSV in experimentally infected adults and, more recently, older adults to optimise the design of vaccines and novel therapies. These studies identified defects in RSV-induced humoral and CD8+ T cell immunity that may partly explain susceptibility to recurrent RSV infection. We discuss the insights from human infection challenge models, ethical and logistical considerations, potential benefits, and role in streamlining and accelerating novel antivirals and vaccines against RSV. Finally, we consider how human challenges might be extended to include relevant at-risk populations.

Probenecid Inhibits Respiratory Syncytial Virus (RSV) Replication

RNA viruses like SARS-CoV-2, influenza virus, and respiratory syncytial virus (RSV) are dependent on host genes for replication. We investigated if probenecid, an FDA-approved and safe urate-lowering drug that inhibits organic anion transporters (OATs) has prophylactic or therapeutic efficacy to inhibit RSV replication in three epithelial cell lines used in RSV studies, i.e., Vero E6 cells, HEp-2 cells, and in primary normal human bronchoepithelial (NHBE) cells, and in BALB/c mice. The studies showed that nanomolar concentrations of all probenecid regimens prevent RSV strain A and B replication in vitro and RSV strain A in vivo, representing a potential prophylactic and chemotherapeutic for RSV.

Replacement Strategies for Animal Studies in Inhalation Testing

Animal testing is mandatory in drug testing and is the gold standard for toxicity and efficacy evaluations. This situation is expected to change in the future as the 3Rs principle, which stands for the replacement, reduction, and refinement of the use of animals in science, is reinforced by many countries. On the other hand, technologies for alternatives to animal testing have increased. The need to develop and use alternatives depends on the complexity of the research topic and also on the extent to which the currently used animal models can mimic human physiology and/or exposure. The lung morphology and physiology of commonly used animal species differs from that of human lungs, and the realistic inhalation exposure of animals is challenging. In vitro and in silico methods can assess important aspects of the in vivo effects, namely particle deposition, dissolution, action at, and permeation through, the respiratory barrier, and pharmacokinetics. This review discusses the limitations of animal models and exposure systems and proposes in vitro and in silico techniques that could, when used together, reduce or even replace animal testing in inhalation testing in the future.

miRNA-34b/c regulates mucus secretion in RSV-infected airway epithelial cells by targeting FGFR1

Respiratory syncytial virus (RSV) infection in airway epithelial cells is the main cause of bronchiolitis in children. Excessive mucus secretion is one of the primary symbols in RSV related lower respiratory tract infections (RSV-related LRTI). However, the pathological processes of mucus hypersecretion in RSV-infected airway epithelial cells remains unclear. The current study explores the involvement of miR-34b/miR-34c in mucus hypersecretion in RSV-infected airway epithelial cells by targeting FGFR1. First, miR-34b/miR-34c and FGFR1 mRNA were quantified by qPCR in throat swab samples and cell lines, respectively. Then, the luciferase reporters' assay was designed to verify the direct binding between FGFR1 and miR-34b/miR-34c. Finally, the involvement of AP-1 signalling was assessed by western blot. This study identified that miR-34b/miR-34c was involved in c-Jun-regulated MUC5AC production by targeting FGFR1 in RSV-infected airway epithelial cells. These results provide some useful insights into the molecular mechanisms of mucus hypersecretion which may also bring new potential strategies to improve mucus hypersecretion in RSV disease.

In Vitro Modelling of Respiratory Virus Infections in Human Airway Epithelial Cells - A Systematic Review

Respiratory tract infections (RTI) are a major cause of morbidity and mortality in humans. A large number of RTIs is caused by viruses, often resulting in more severe disease in infants, elderly and the immunocompromised. Upon viral infection, most individuals experience common cold-like symptoms associated with an upper RTI. However, in some cases a severe and sometimes life-threatening lower RTI may develop. Reproducible and scalable in vitro culture models that accurately reflect the human respiratory tract are needed to study interactions between respiratory viruses and the host, and to test novel therapeutic interventions. Multiple in vitro respiratory cell culture systems have been described, but the majority of these are based on immortalized cell lines. Although useful for studying certain aspects of viral infections, such monomorphic, unicellular systems fall short in creating an understanding of the processes that occur at an integrated tissue level. Novel in vitro models involving primary human airway epithelial cells and, more recently, human airway organoids, are now in use. In this review, we describe the evolution of in vitro cell culture systems and their characteristics in the context of viral RTIs, starting from advances after immortalized cell cultures to more recently developed organoid systems. Furthermore, we describe how these models are used in studying virus-host interactions, e.g. tropism and receptor studies as well as interactions with the innate immune system. Finally, we provide an outlook for future developments in this field, including co-factors that mimic the microenvironment in the respiratory tract.

Recent advances in human respiratory epithelium models for drug discovery

The respiratory epithelium is intimately associated with the pathophysiologies of highly infectious viral contagions and chronic illnesses such as chronic obstructive pulmonary disorder, presently the third leading cause of death worldwide with a projected economic burden of £1.7 trillion by 2030. Preclinical studies of respiratory physiology have almost exclusively utilised non-humanised animal models, alongside reductionistic cell line-based models, and primary epithelial cell models cultured at an air-liquid interface (ALI). Despite their utility, these model systems have been limited by their poor correlation to the human condition. This has undermined the ability to identify novel therapeutics, evidenced by a 15% chance of success for medicinal respiratory compounds entering clinical trials in 2018. Consequently, preclinical studies require new translational efficacy models to address the problem of respiratory drug attrition. This review describes the utility of the current in vivo (rodent), ex vivo (isolated perfused lungs and precision cut lung slices), two-dimensional in vitro cell-line (A549, BEAS-2B, Calu-3) and three-dimensional in vitro ALI (gold-standard and co-culture) and organoid respiratory epithelium models. The limitations to the application of these model systems in drug discovery research are discussed, in addition to perspectives of the future innovations required to facilitate the next generation of human-relevant respiratory models.

Viral and Bacterial Co-Infections in the Lungs: Dangerous Liaisons

Respiratory tract infections constitute a significant public health problem, with a therapeutic arsenal that remains relatively limited and that is threatened by the emergence of antiviral and/or antibiotic resistance. Viral–bacterial co-infections are very often associated with the severity of these respiratory infections and have been explored mainly in the context of bacterial superinfections following primary influenza infection. This review summarizes our current knowledge of the mechanisms underlying these co-infections between respiratory viruses (influenza viruses, RSV, and SARS-CoV-2) and bacteria, at both the physiological and immunological levels. This review also explores the importance of the microbiome and the pathological context in the evolution of these respiratory tract co-infections and presents the different in vitro and in vivo experimental models available. A better understanding of the complex functional interactions between viruses/bacteria and host cells will allow the development of new, specific, and more effective diagnostic and therapeutic approaches.

A study of the effects of age on the dynamics of RSV in animal models

Respiratory syncytial virus can cause severe illness and even death, particularly in infants. The increased severity of disease in young children is thought to be due to a lack of previous exposure to the virus as well as the limited immune response in infants. While studies have examined the clinical differences in disease between infants and adults, there has been limited examination of how the viral dynamics differ as infants develop. In this study, we apply a mathematical model to data from cotton rats and ferrets of different ages to assess how viral kinetics parameters change as the animals age. We find no clear trend in the viral decay rate, infecting time, and basic reproduction number as the animals age. We discuss possible reasons for the null result including the limited data, lack of detail of the mathematical model, and the limitations of animal models.

Non-human primate models of human respiratory infections

Respiratory pathogens represent a great burden for humanity and a potential source of new pandemics, as illustrated by the recent emergence of coronavirus disease 2019 (COVID-19). In recent decades, biotechnological advances have led to the development of numerous innovative therapeutic molecules and vaccine immunogens. However, we still lack effective treatments and vaccines against many respiratory pathogens. More than ever, there is a need for a fast, predictive, preclinical pipeline, to keep pace with emerging diseases. Animal models are key for the preclinical development of disease management strategies. The predictive value of these models depends on their ability to reproduce the features of the human disease, the mode of transmission of the infectious agent and the availability of technologies for monitoring infection. This review focuses on the use of non-human primates as relevant preclinical models for the development of prevention and treatment for human respiratory infections.

Pulmonary mesenchymal stem cells are engaged in distinct steps of host response to respiratory syncytial virus infection

Lung-resident (LR) mesenchymal stem and stromal cells (MSCs) are key elements of the alveolar niche and fundamental regulators of homeostasis and regeneration. We interrogated their function during virus-induced lung injury using the highly prevalent respiratory syncytial virus (RSV) which causes severe outcomes in infants. We applied complementary approaches with primary pediatric LR-MSCs and a state-of-the-art model of human RSV infection in lamb. Remarkably, RSV-infection of pediatric LR-MSCs led to a robust activation, characterized by a strong antiviral and pro-inflammatory phenotype combined with mediators related to T cell function. In line with this, following in vivo infection, RSV invades and activates LR-MSCs, resulting in the expansion of the pulmonary MSC pool. Moreover, the global transcriptional response of LR-MSCs appears to follow RSV disease, switching from an early antiviral signature to repair mechanisms including differentiation, tissue remodeling, and angiogenesis. These findings demonstrate the involvement of LR-MSCs during virus-mediated acute lung injury and may have therapeutic implications.

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.

Reverse genetics systems for contemporary isolates of respiratory syncytial virus enable rapid evaluation of antibody escape mutants

Human respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infection in children under 5 y of age. In the absence of a safe and effective vaccine and with limited options for therapeutic interventions, uncontrolled epidemics of RSV occur annually worldwide. Existing RSV reverse genetics systems have been predominantly based on older laboratory-adapted strains such as A2 or Long. These strains are not representative of currently circulating genotypes and have a convoluted passage history, complicating their use in studies on molecular determinants of viral pathogenesis and intervention strategies. In this study, we have generated reverse genetics systems for clinical isolates of RSV-A (ON1, 0594 strain) and RSV-B (BA9, 9671 strain) in which the full-length complementary DNA (cDNA) copy of the viral antigenome is cloned into a bacterial artificial chromosome (BAC). Additional recombinant (r) RSVs were rescued expressing enhanced green fluorescent protein (EGFP), mScarlet, or NanoLuc luciferase from an additional transcription unit inserted between the P and M genes. Mutations in antigenic site II of the F protein conferring escape from palivizumab neutralization (K272E, K272Q, S275L) were investigated using quantitative cell-fusion assays and rRSVs via the use of BAC recombineering protocols. These mutations enabled RSV-A and -B to escape palivizumab neutralization but had differential impacts on cell-to-cell fusion, as the S275L mutation resulted in an almost-complete ablation of syncytium formation. These reverse genetics systems will facilitate future cross-validation efficacy studies of novel RSV therapeutic intervention strategies and investigations into viral and host factors necessary for virus entry and cell-to-cell spread.

Streptococcus pneumoniae serotype 22F infection in respiratory syncytial virus infected neonatal lambs enhances morbidity

Respiratory syncytial virus (RSV) is the primary cause of viral bronchiolitis resulting in hospitalization and a frequent cause of secondary respiratory bacterial infection, especially by Streptococcus pneumoniae (Spn) in infants. While murine studies have demonstrated enhanced morbidity during a viral/bacterial co-infection, human meta-studies have conflicting results. Moreover, little knowledge about the pathogenesis of emerging Spn serotype 22F, especially the co-pathologies between RSV and Spn, is known. Here, colostrum-deprived neonate lambs were divided into four groups. Two of the groups were nebulized with RSV M37, and the other two groups were mock nebulized. At day three post-RSV infection, one RSV group (RSV/Spn) and one mock-nebulized group (Spn only) were inoculated with Spn intratracheally. At day six post-RSV infection, bacterial/viral loads were assessed along with histopathology and correlated with clinical symptoms. Lambs dually infected with RSV/Spn trended with higher RSV titers, but lower Spn. Additionally, lung lesions were observed to be more frequent in the RSV/Spn group characterized by increased interalveolar wall thickness accompanied by neutrophil and lymphocyte infiltration and higher myeloperoxidase. Despite lower Spn in lungs, co-infected lambs had more significant morbidity and histopathology, which correlated with a different cytokine response. Thus, enhanced disease severity during dual infection may be due to lesion development and altered immune responses rather than bacterial counts.

Molecular and Cellular Mechanisms of Respiratory Syncytial Viral Infection: Using Murine Models to Understand Human Pathology

Respiratory syncytial virus (RSV) causes severe pathology of the lower respiratory tract in infants, immunocompromised people, and elderly. Despite decades of research, there is no licensed vaccine against RSV, and many therapeutic drugs are still under development. Detailed understanding of molecular and cellular mechanisms of the RSV infection pathology can accelerate the development of efficacious treatment. Current studies on the RSV pathogenesis are based on the analysis of biopsies from the infected patients; however deeper understanding of molecular and cellular mechanisms of the RSV pathology could be achieved using animal models. Mice are the most often used model for RSV infection because they exhibit manifestations similar to those observed in humans (bronchial obstruction, mucous hypersecretion, and pulmonary inflammation mediated by lymphocytes, macrophages, and neutrophils). Additionally, the use of mice is economically feasible, and many molecular tools are available for studying RSV infection pathogenesis at the molecular and cellular levels. This review summarizes new data on the pathogenesis of RSV infection obtained in mouse models, which demonstrated the role of T cells in both the antiviral defense and the development of lung immunopathology. T cells not only eliminate the infected cells, but also produce significant amounts of the proinflammatory cytokines TNFα and IFNγ. Recently, a new subset of tissue-resident memory T cells (TRM) was identified that provide a strong antiviral defense without induction of lung immunopathology. These cells accumulate in the lungs after local rather than systemic administration of RSV antigens, which suggests new approaches to vaccination. The studies in mouse models have revealed a minor role of interferons in the anti-RSV protection, as RSV possesses mechanisms to escape the antiviral action of type I and III interferons, which may explain the low efficacy of interferon-containing drugs. Using knockout mice, a significant breakthrough has been achieved in understanding the role of many pro-inflammatory cytokines in lung immunopathology. It was found that in addition to TNFα and IFNγ, the cytokines IL-4, IL-5, IL-13, IL-17A, IL-33, and TSLP mediate the major manifestations of the RSV pathogenesis, such as bronchial obstruction, mucus hyperproduction, and lung infiltration by pro-inflammatory cells, while IL-6, IL-10, and IL-27 exhibit the anti-inflammatory effect. Despite significant differences between the mouse and human immune systems, mouse models have made a significant contribution to the understanding of molecular and cellular mechanisms of the pathology of human RSV infection.

Contribution of NKT cells to the immune response and pathogenesis triggered by respiratory viruses

Human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) cause acute respiratory tract infections in children worldwide. Natural killer T (NKT) cells are unconventional T lymphocytes, and their TCRs recognize glycolipids bound to the MHC-I-like molecule, CD1d. These cells modulate the inflammatory response in viral infections. Here, we evaluated the contribution of NKT cells in both hRSV and hMPV infections. A significant decrease in the number of neutrophils, eosinophils, and CD103⁺DCs infiltrating to the lungs, as well as an increased production of IFN-γ, were observed upon hRSV-infection in CD1d-deficient BALB/c mice, as compared to wild-type control mice. However, this effect was not observed in the CD1d-deficient BALB/c group, upon infection with hMPV. Importantly, reduced expression of CD1d in CD11b⁺ DCs and epithelial cells was found in hRSV -but not hMPV-infected mice. Besides, a reduction in the expression of CD1d in alveolar macrophages of lungs from hRSV- and hMPV-infected mice was found. Such reduction of CD1d expression interfered with NKT cells activation, and consequently IL-2 secretion, as characterized by in vitro experiments for both hRSV and hMPV infections. Furthermore, increased numbers of NKT cells recruited to the lungs in response to hRSV- but not hMPV-infection was detected, resulting in a reduction in the expression of IFN-γ and IL-2 by these cells. In conclusion, both hRSV and hMPV might be differently impairing NKT cells function and contributing to the immune response triggered by these viruses.

The role of biomaterials and three dimensional (3D) in vitro tissue models in fighting against COVID-19

Over the past century, viral respiratory pandemics have been a leading cause of infectious disease worldwide. A deep understanding of the underlying mechanisms of the viral interactions with host cells at the target sites is necessary for a rapid response to such pandemics. To meet this aim, various testing platforms are required to recapitulate the pathophysiological behavior of the virus within the respiratory tract. These bioengineered platforms can effectively be used for the development of different therapeutics and vaccines. This paper briefly reviews the progress in the areas of biomaterial use for pulmonary tissue regeneration and integration with current bioengineered platforms including engineered tissues, organoids, and organs-on-a-chip platforms for viral respiratory disease studies. Finally, a brief overview of the opportunities presented by organ-on-a-chip systems for studying COVID-19 and subsequent drug development is introduced.

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

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

Recombinant subtype A and B human respiratory syncytial virus clinical isolates co-infect the respiratory tract of cotton rats

Human respiratory syncytial virus (HRSV) is an important respiratory pathogen causing a spectrum of illness, from common cold-like symptoms, to bronchiolitis and pneumonia requiring hospitalization in infants, the immunocompromised and the elderly. HRSV exists as two antigenic subtypes, A and B, which typically cycle biannually in separate seasons. There are many unresolved questions in HRSV biology regarding the interactions and interplay of the two subtypes. Therefore, we generated a reverse genetics system for a subtype A HRSV from the 2011 season (A11) to complement our existing subtype B reverse genetics system. We obtained the sequence (HRSVA11) directly from an unpassaged clinical sample and generated the recombinant (r) HRSVA11. A version of the virus expressing enhanced green fluorescent protein (EGFP) from an additional transcription unit in the fifth (5) position of the genome, rHRSVA11EGFP(5), was also generated. rHRSVA11 and rHRSVA11EGFP(5) grew comparably in cell culture. To facilitate animal co-infection studies, we derivatized our subtype B clinical isolate using reverse genetics toexpress the red fluorescent protein (dTom)-expressing rHRSVB05dTom(5). These viruses were then used to study simultaneous in vivo co-infection of the respiratory tract. Following intranasal infection, both rHRSVA11EGFP(5) and rHRSVB05dTom(5) infected cotton rats targeting the same cell populations and demonstrating that co-infection occurs in vivo. The implications of this finding on viral evolution are important since it shows that inter-subtype cooperativity and/or competition is feasible in vivo during the natural course of the infection.

In vivo comparison of a laboratory-adapted and clinical-isolate-based recombinant human respiratory syncytial virus

Human respiratory syncytial virus (HRSV) is the leading cause of severe respiratory tract disease in infants. Most HRSV infections remain restricted to the upper respiratory tract (URT), but in a small percentage of patients the infection spreads to the lower respiratory tract, resulting in bronchiolitis or pneumonia. We have a limited understanding of HRSV pathogenesis and what factors determine disease severity, partly due to the widespread use of tissue-culture-adapted viruses. Here, we studied early viral dissemination and tropism of HRSV in cotton rats, BALB/cJ mice and C57BL/6 mice. We used a novel recombinant (r) strain based on a subgroup A clinical isolate (A11) expressing EGFP [rHRSV^A11EGFP(5)]. A recombinant laboratory-adapted HRSV strain [rHRSV^A2EGFP(5)] was used as a direct comparison. Our results show that rHRSV^A11EGFP(5) replicated to higher viral titres than laboratory-adapted rHRSV^A2EGFP(5) in the URT of cotton rats and mice. HRSV-infected cells were detected as early as 2 days post-inoculation in both species in the nasal septa and lungs. Infection was predominantly present in ciliated epithelial cells in cotton rats and in the olfactory mucosa of mice. In our opinion, this study highlights that the choice of virus strain is important when studying HRSV pathogenesis in vivo and demonstrates that A11 is a representative clinical-based virus. Additionally, we show critical differences in tropism and inflammation when comparing HRSV infection of cotton rats and mice.

A Single Shot Pre-fusion-Stabilized Bovine RSV F Vaccine is Safe and Effective in Newborn Calves with Maternally Derived Antibodies

Achieving safe and protective vaccination against respiratory syncytial virus (RSV) in infants and in calves has proven a challenging task. The design of recombinant antigens with a conformation close to their native form in virus particles is a major breakthrough. We compared two subunit vaccines, the bovine RSV (BRSV) pre-fusion F (preF) alone or with nanorings formed by the RSV nucleoprotein (preF+N). PreF and N proteins are potent antigenic targets for neutralizing antibodies and T cell responses, respectively. To tackle the challenges of neonatal immunization, three groups of six one-month-old calves with maternally derived serum antibodies (MDA) to BRSV received a single intramuscular injection of PreF, preF+N with Montanide^TM ISA61 VG (ISA61) as adjuvant or only ISA61 (control). One month later, all calves were challenged with BRSV and monitored for virus replication in the upper respiratory tract and for clinical signs of disease over one week, and then post-mortem examinations of their lungs were performed. Both preF and preF+N vaccines afforded safe, clinical, and virological protection against BRSV, with little difference between the two subunit vaccines. Analysis of immune parameters pointed to neutralizing antibodies and antibodies to preF as being significant correlates of protection. Thus, a single shot vaccination with preF appears sufficient to reduce the burden of BRSV disease in calves with MDA.