Immune responses and disease enhancement during respiratory syncytial virus infection

Host immune response to respiratory syncytial virus infection and its contribution to protection and susceptibility in adults: a systematic literature review

INTRODUCTION

Respiratory syncytial virus (RSV) is an important pathogen in infants, children, older adults, and those with comorbidities. Mechanisms involving viral proteins appear to underlie the ability of RSV to evade and modulate host immunity. We aimed to understand virus- and host-dependent factors regulating the development and severity of RSV infection, as related to the prevention and treatment of RSV-associated disease in adults, through a systematic literature review (SLR).

METHODS

An SLR was conducted to identify immune mechanisms involved in the protective response to RSV infection in adults, and responses that may contribute to the development of severe disease. Concurrent searches (MEDLINE/Embase) using embase.com identified relevant papers published between 1990 and 19 April 2023.

RESULTS

Of 1813 records identified, 113 were selected for review. Inclusion criteria were based on relevant patient populations, outcomes, and study methodologies. RSV is common, recurrent, and associated with high morbidity and mortality in older adults and people with underlying chronic diseases. Immune responses differ between younger and older adults. The approval of effective vaccines may protect older individuals from symptomatic RSV infection.

CONCLUSIONS

We established the complexities of RSV immune response, but further research is required to fully understand anti-RSV immunology.

On the Ocean of Biomarkers for the Precise Diagnosis and Prognosis of Lung Diseases

Bronchoalveolar lavage fluid (BALF) has long been used for diagnosing various lung diseases through its cellular components. However, the clinical utility of biomolecules in the BALF remains largely unexplored. Recently, mass spectrometry-based proteomics has been applied to profile the BALF proteomes to identify novel biomarkers for lung diseases. This review discusses the current progress in the field of BALF proteomics and highlights its potential as a valuable source of biomarkers for different lung diseases. Additionally, we explored the latest advancements and findings from BALF studies. Finally, we address the current limitations and propose future directions and research opportunities to advance the study of BALF.

Enhanced construction of a bivalent adenovirus-based vaccine for preventing childhood pathogens: Human respiratory syncytial virus and norovirus

To impede the spread of respiratory syncytial virus (RSV) and norovirus (NoV) in children, we developed novel recombinant adenoviruses expressing RSV fusion (F) and NoV VP1 proteins driven by different promoter elements (EF1α, SV40, and CMV), resulting in Ad-F/E/NoV, Ad-F/S/NoV, and Ad-F/C/NoV, respectively. The expressed F can be recognized by postfusion-specific antibody targeting to site II and prefusion-specific antibodies targeting to sites V and Ø in the Ad-F-infected cells. However, NoV VP1 is only expressed in Ad-F/E/NoV and Ad-F/C/NoV-infected cells. Intraperitoneal two-dose with monovalent Ad-F and all three bicistronic Ads individually in rodents induced anti-F neutralizing antibodies similarly. Ad-F/C/NoV and Ad-F/E/NoV but not Ad-F/S/NoV significantly induced NoV VP1-specific IgG. The serum from Ad-F/C/NoV-immunized subjects elicited superior anti-NoV activity, as evidenced by reduced binding of NoV VLPs to histo-blood group antigens. Ad-F/C/NoV and Ad-F/E/NoV-immunized mice exhibited elevated cellular immune-mediated splenic IFN-γ and IL-4 secretions. In the RSV challenge study, pulmonary virions were significantly decreased during the vaccination with each of the three bicistronic Ads, confirming their efficacy in preventing RSV infection. Finally, the mucosal (intranasal) immunization in mice with Ad-F/C/NoV induced superior anti-RSV and NoV IgA in both serum and vaginal washes specific to RSV and NoV were highly induced. These findings highlight the optimization of an Ad vaccine targeting two pathogens prevalent in childhood. Additionally, the results underscore the utility of mucosal delivery of Ad vaccines as a valuable strategy for public vaccination efforts.

Enhanced Pathogenic Consequences Induced by a Seven-Amino-Acid Extension in the G Protein of the HRSV BA9 Genotype

In a previous outbreak of the human respiratory syncytial virus (HRSV), we identified a variant strain of genotype BA9 with a seven-amino-acid extension (Q-R-L-Q-S-Y-A) at the C-terminus of the attachment protein (G). To assess the impact of this extension on the virulence of HRSV, two full-length infectious clones using the wild strain of genotype BA9 as a backbone, one containing the seven-amino-acid extension (rRSV BA9 WT), and the other deleting this extension (rRSV BA9 Δ7AA), were successfully rescued using a reverse genetics system. The biological properties and virulence of the two rescued viruses were then compared and analyzed in vitro and in vivo. Compared to the rRSV BA9 Δ7AA, the rRSV BA9 WT exhibited a larger plaque size and a more pronounced suppression of the host cell innate immune response in vitro (IFN-β levels: 154.33 pg/mL vs. 11.27 pg/mL). The rRSV BA9 WT demonstrated increased adaptability in mice, with a 10-fold higher lung viral load and a stronger inflammatory response following intranasal exposure. Our study primarily demonstrated that the C-terminal extension of the G protein of the HRSV can enhance viral virulence, underscoring the importance of virological surveillance in the prevention and treatment of severe HRSV-related disease.

Mucosal Immunization with an Influenza Vector Carrying SARS-CoV-2 N Protein Protects Naïve Mice and Prevents Disease Enhancement in Seropositive Th2-Prone Mice

Background/Objectives: Intranasal vaccination enhances protection against respiratory viruses by providing stimuli to the immune system at the primary site of infection, promoting a balanced and effective response. Influenza vectors with truncated NS1 are a promising vaccine approach that ensures a pronounced local CD8+ T-cellular immune response. Here, we describe the protective and immunomodulating properties of an influenza vector FluVec-N carrying the C-terminal fragment of the SARS-CoV-2 nucleoprotein within a truncated NS1 open reading frame. Methods: We generated several FluVec-N recombinant vectors by reverse genetics and confirmed the vector's genetic stability, antigen expression in vitro, attenuation, and immunogenicity in a mouse model. We tested the protective potential of FluVec-N intranasal immunization in naïve mice and seropositive Th2-prone mice, primed with aluminium-adjuvanted inactivated SARS-CoV-2. Immune response in immunized and challenged mice was analyzed through serological methods and flow cytometry. Results: Double intranasal immunization of naïve mice with FluVec-N reduced weight loss and viral load in the lungs following infection with the SARS-CoV-2 beta variant. Mice primed with alum-adjuvanted inactivated coronavirus experienced substantial early weight loss and eosinophilia in the lungs during infection, demonstrating signs of enhanced disease. A single intranasal boost immunization with FluVec-N prevented the disease enhancement in primed mice by modulating the local immune response. Protection was associated with the formation of specific IgA and the early activation of virus-specific effector and resident CD8+ lymphocytes in mouse lungs. Conclusions: Our study supports the potential of immunization with influenza vector vaccines to prevent respiratory diseases and associated immunopathology.

What have we learned from animal studies of immune responses to respiratory syncytial virus infection?

Respiratory syncytial virus (RSV) is a common cause of severe respiratory tract infection at the extremes of age and in vulnerable populations. However, it is difficult to predict the clinical course and most infants who develop severe disease have no pre-existing risk factors. With the recent licencing of RSV vaccines and monoclonal antibodies, it is important to identify high-risk individuals in order to prioritise those who will most benefit from prophylaxis. The immune response to RSV and the mechanisms by which the virus prevents the establishment of immunological memory have been extensively investigated but remain incompletely characterised. In animal models, beneficial and harmful immune responses have both been demonstrated. While only chimpanzees are fully permissive for human RSV replication, most research has been conducted in rodents, or in calves infected with bovine RSV. Based on these studies, components of innate and adaptive immune systems, cytokines, chemokines and metabolites, and specific genetic and transcriptomic signatures are identified as potential predictive indicators of RSV disease severity. These findings may inform the development of future human studies and contribute to the early identification of patients at high risk of severe infection. This narrative review summarises the factors involved in the immune response to RSV infection in these models and highlights the relationship between potential biomarkers and disease severity.

Exposure to bacterial PAMPs before RSV infection exacerbates innate inflammation and disease via IL-1α and TNF-α

Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infections. Understanding why some individuals get more serious disease may help with diagnosis and treatment. One possible risk factor underlying severe disease is bacterial exposure before RSV infection. Bacterial exposure has been associated with increased respiratory viral-induced disease severity but the mechanism remains unknown. Respiratory bacterial infections or exposure to their pathogen associated molecular patterns (PAMPs) trigger innate immune inflammation, characterised by neutrophil and inflammatory monocyte recruitment and the production of inflammatory cytokines. We hypothesise that these changes to the lung environment alter the immune response and disease severity during subsequent RSV infection. To test this, we intranasally exposed mice to LPS, LTA or Acinetobacter baumannii (an airway bacterial pathogen) before RSV infection and observed an early induction of disease, measured by weight loss, at days 1-3 after infection. Neutrophils or inflammatory monocytes were not responsible for driving this exacerbated weight loss. Instead, exacerbated disease was associated with increased IL-1α and TNF-α, which orchestrated the recruitment of innate immune cells into the lung. This study shows that exposure to bacterial PAMPs prior to RSV infection increases the expression of IL-1α and TNF-α, which dysregulate the immune response resulting in exacerbated disease.

From Pancytopenia to Hyperleukocytosis, an Unexpected Presentation of Immune Reconstitution Inflammatory Syndrome in an Infant with Methylmalonic Acidemia

A 2.5-month-old girl admitted for failure to thrive and severe pancytopenia was diagnosed with methylmalonic acidemia (MMA) secondary to transcobalamin II deficiency, an inborn error of vitamin B12 metabolism. Opportunistic Cytomegalovirus and Pneumocystis jirovecii pneumonia led to severe acute respiratory distress syndrome (ARDS) and immune reconstitution inflammatory syndrome (IRIS) after treatment initiation with vitamin B12 supplementation. In children with interstitial pneumonia-related ARDS, normal lymphocyte count should not delay invasive procedures required to document opportunistic infections. MMA can be associated with underlying lymphocyte dysfunction and vitamin B12 supplementation can fully reverse the associated immunodeficiency. IRIS may appear in highly treatment-responsive forms of pancytopenia in children and prompt treatment of dysregulated inflammation with high-dose corticosteroids should be initiated.

p53 suppresses the inflammatory response following respiratory syncytial virus infection by inhibiting TLR2

-Respiratory syncytial virus (RSV) is a pivotal virus leading to acute lower respiratory tract infections in children under 5 years old. This study aimed to explore the correlation between p53 and Toll-like receptors (TLRs) post RSV infection. p53 levels exhibited a substantial decrease in nasopharyngeal aspirates (NPAs) from infants with RSV infection compared to control group. Manipulating p53 expression had no significant impact on RSV replication or interferon signaling pathway. Suppression of p53 expression led to heightened inflammation following RSV infection in A549 cells or airways of BALB/c mice. while stabilizing p53 expression using Nutlin-3a mitigated the inflammatory response in A549 cells. Additionally, Inhibiting p53 expression significantly increased Toll-like receptor 2 (TLR2) expression in RSV-infected epithelial cells and BALB/c mice. Furthermore, the TLR2 inhibitor, C29, effectively reduced inflammation mediated by p53 in A549 cells. Collectively, our results indicate that p53 modulates the inflammatory response after RSV infection through TLR2.

Early-life pulmonary viral infection leads to long-term functional and lower airway structural changes in the lungs

Early-life respiratory virus infections have been correlated with enhanced development of childhood asthma. In particular, significant numbers of respiratory syncytial virus (RSV)-hospitalized infants go on to develop lung disease. It has been suggested that early-life viral infections may lead to altered lung development or repair that negatively impacts lung function later in life. Our data demonstrate that early-life RSV infection modifies lung structure, leading to decreased lung function. At 5 wk postneonatal RSV infection, significant defects are observed in baseline pulmonary function test (PFT) parameters consistent with decreased lung function as well as enlarged alveolar spaces. Lung function changes in the early-life RSV-infected group continue at 3 mo of age. The altered PFT and structural changes induced by early-life RSV were mitigated in TSLPR-/- mice that have previously been shown to have reduced immune cell accumulation associated with a persistent Th2 environment. Importantly, long-term effects were demonstrated using a secondary RSV infection 3 mo following the initial early-life RSV infection and led to significant additional defects in lung function, with severe mucus deposition within the airways, and consolidation of the alveolar spaces. These studies suggest that early-life respiratory viral infection leads to alterations in lung structure/repair that predispose to diminished lung function later in life.NEW & NOTEWORTHY These studies outline a novel finding that early-life respiratory virus infection can alter lung structure and function long-term. Importantly, the data also indicate that there are critical links between inflammatory responses and subsequent events that produce a more severe pathogenic response later in life. The findings provide additional data to support that early-life infections during lung development can alter the trajectory of airway function.

Difference in respiratory syncytial virus-specific Fc-mediated antibody effector functions between children and adults

Respiratory syncytial virus (RSV) infections are a major cause of bronchiolitis and pneumonia in infants and older adults, for which there is no known correlate of protection. Increasing evidence suggests that Fc-mediated antibody effector functions have an important role, but little is known about the development, heterogeneity, and durability of these functional responses. In light of future vaccine strategies, a clear view of the immunological background and differences between various target populations is of crucial importance. In this study, we have assessed both quantitative and qualitative aspects of RSV-specific serum antibodies, including IgG/IgA levels, IgG subclasses, antibody-dependent complement deposition, cellular phagocytosis, and NK cell activation (ADNKA). Samples were collected cross-sectionally in different age groups (11-, 24-, and 46-month-old children, adults, and older adults; n = 31-35 per group) and longitudinally following natural RSV infection in (older) adults (2-36 months post-infection; n = 10). We found that serum of 24-month-old children induces significantly lower ADNKA than the serum of adults (P < 0.01), which is not explained by antibody levels. Furthermore, in (older) adults we observed boosting of antibody levels and functionality at 2-3 months after RSV infection, except for ADNKA. The strongest decrease was subsequently observed within the first 9 months, after which levels remained relatively stable up to three years post-infection. Together, these data provide a comprehensive overview of the functional landscape of RSV-specific serum antibodies in the human population, highlighting that while antibodies reach adult levels already at a young age, ADNKA requires more time to fully develop.

Respiratory syncytial virus infection and novel interventions

The large global burden of respiratory syncytial virus (RSV) respiratory tract infections in young children and older adults has gained increased recognition in recent years. Recent discoveries regarding the neutralization-specific viral epitopes of the pre-fusion RSV glycoprotein have led to a shift from empirical to structure-based design of RSV therapeutics, and controlled human infection model studies have provided early-stage proof of concept for novel RSV monoclonal antibodies, vaccines and antiviral drugs. The world's first vaccines and first monoclonal antibody to prevent RSV among older adults and all infants, respectively, have recently been approved. Large-scale introduction of RSV prophylactics emphasizes the need for active surveillance to understand the global impact of these interventions over time and to timely identify viral mutants that are able to escape novel prophylactics. In this Review, we provide an overview of RSV interventions in clinical development, highlighting global disease burden, seasonality, pathogenesis, and host and viral factors related to RSV immunity.

Binding of respiratory syncytial virus particles to platelets does not result in their degranulation in vitro

Respiratory syncytial virus (RSV) is a major cause of severe respiratory infection in infants and the elderly. The mechanisms behind severe RSV disease are incompletely understood, but a dysregulated immune response probably plays an important role. Platelets are increasingly being recognized as immune cells and are involved in the pathology of several viruses. The release of chemokines from platelets upon activation may attract, for example, neutrophils to the site of infection, which is a hallmark of RSV pathology. In addition, since RSV infections are sometimes associated with cardiovascular events and platelets express several known RSV receptors, we investigated the effect of RSV exposure on platelet degranulation. Washed human platelets were incubated with sucrose-purified RSV particles. P-selectin and CD63 surface expression and CCL5 secretion were measured to assess platelet degranulation. We found that platelets bind and internalize RSV particles, but this does not result in degranulation. Our results suggest that platelets do not play a direct role in RSV pathology by releasing chemokines to attract inflammatory cells.

Respiratory Syncytial Virus-An Update for Prenatal and Primary Health Providers

Respiratory syncytial virus (RSV) infection is a significant cause of morbidity and mortality among infants aged younger than 1 year, adults aged 65 years or older, and immunocompromised persons. Limited data exist on RSV infection in pregnancy and further research is needed. Strides are being made to develop vaccines, including vaccines for maternal immunization, as well as monoclonal antibodies for disease prevention.

A Multimodal Imaging-Supported Down Syndrome Mouse Model of RSV Infection

Individuals with Down syndrome (DS) are more prone to develop severe respiratory tract infections. Although a RSV infection has a high clinical impact and severe outcome in individuals with DS, no vaccine nor effective therapeutics are available. Any research into infection pathophysiology or prophylactic and therapeutic antiviral strategies in the specific context of DS would greatly benefit this patient population, but currently such relevant animal models are lacking. This study aimed to develop and characterize the first mouse model of RSV infection in a DS-specific context. Ts65Dn mice and wild type littermates were inoculated with a bioluminescence imaging-enabled recombinant human RSV to longitudinally track viral replication in host cells throughout infection progression. This resulted in an active infection in the upper airways and lungs with similar viral load in Ts65Dn mice and euploid mice. Flow cytometric analysis of leukocytes in lungs and spleen demonstrated immune alterations with lower CD8+ T cells and B-cells in Ts65Dn mice. Overall, our study presents a novel DS-specific mouse model of hRSV infection and shows that potential in using the Ts65Dn preclinical model to study immune-specific responses of RSV in the context of DS and supports the need for models representing the pathological development.

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.

Early-life respiratory tract infections and the risk of school-age lower lung function and asthma: a meta-analysis of 150 000 European children

BACKGROUND

Early-life respiratory tract infections might affect chronic obstructive respiratory diseases, but conclusive studies from general populations are lacking. Our objective was to examine if children with early-life respiratory tract infections had increased risks of lower lung function and asthma at school age.

METHODS

We used individual participant data of 150 090 children primarily from the EU Child Cohort Network to examine the associations of upper and lower respiratory tract infections from age 6 months to 5 years with forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC, forced expiratory flow at 75% of FVC (FEF75%) and asthma at a median (range) age of 7 (4-15) years.

RESULTS

Children with early-life lower, not upper, respiratory tract infections had a lower school-age FEV1, FEV1/FVC and FEF75% (z-score range: -0.09 (95% CI -0.14- -0.04) to -0.30 (95% CI -0.36- -0.24)). Children with early-life lower respiratory tract infections had a higher increased risk of school-age asthma than those with upper respiratory tract infections (OR range: 2.10 (95% CI 1.98-2.22) to 6.30 (95% CI 5.64-7.04) and 1.25 (95% CI 1.18-1.32) to 1.55 (95% CI 1.47-1.65), respectively). Adjustment for preceding respiratory tract infections slightly decreased the strength of the effects. Observed associations were similar for those with and without early-life wheezing as a proxy for early-life asthma.

CONCLUSIONS

Our findings suggest that early-life respiratory tract infections affect development of chronic obstructive respiratory diseases in later life, with the strongest effects for lower respiratory tract infections.

A single local delivery of paclitaxel and nucleic acids via an immunoactive polymer eliminates tumors and induces antitumor immunity

SignificanceThe rationale of local cancer immunotherapy is that the treated tumor cells can serve as a depot of tumor antigens and activate/mobilize the patient's immune system to address systemic diseases. However, the challenge is to coordinate several events involved in the activation of antitumor immune responses, colocalize and retain multiple therapies in tumors, and support the functions of immune cells. Our carrier polyethyleneimine-lithocholic acid conjugate (2E') addresses these challenges based on the amphiphilic structure and inherent immunostimulatory activity. 2E' codelivers hydrophobic drugs and nucleic acids and leverages their effects to eliminate primary tumors and protect the hosts from distant and recurrent diseases. The versatility of 2E' will enable the use of therapeutic combinations to improve clinical outcomes of cancer immunotherapy.

Anti-inflammatory effects of curcumin-loaded niosomes on respiratory syncytial virus infection in a mice model

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in paediatrics. While antivirals are apparent candidates to treat RSV-induced diseases, they have not yet met expectations and have remained in infancy. There is growing evidence to suggest that modulating the exacerbated inflammation during RSV infection can improve disease outcome. Curcumin-loaded niosomes have anti-inflammatory effects against RSV-induced respiratory disease by reducing immune cells' infiltration and inflammatory cytokines' production. This study evaluated the effects of curcumin-loaded niosomes on RSV-induced immunopathology in a mice model. Curcumin-loaded niosomes were prepared using the thin-film hydration method and characterized in vitro. Female Balb/c mice were infected by RSV-A2 and treated daily with curcumin-loaded niosomes. The potential anti-inflammatory effects of curcumin-loaded niosomes were evaluated on day 5 after infection. Using curcumin-loaded niosomes decreased immune cell influx and the inflammatory mediators (MIP-1α, TNF-α and IFN-γ) production in the lung, resulting in alleviated lung pathology following RSV infection. These findings indicate that curcumin-loaded niosomes have anti-inflammatory potential and could be a promising candidate to alleviate RSV-associated immunopathology.

Neonatal Immune Responses to Respiratory Viruses

Respiratory tract infections are a leading cause of morbidity and mortality in newborns, infants, and young children. These early life infections present a formidable immunologic challenge with a number of possibly conflicting goals: simultaneously eliminate the acute pathogen, preserve the primary gas-exchange function of the lung parenchyma in a developing lung, and limit long-term sequelae of both the infection and the inflammatory response. The latter has been most well studied in the context of childhood asthma, where multiple epidemiologic studies have linked early life viral infection with subsequent bronchospasm. This review will focus on the clinical relevance of respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and rhinovirus (RV) and examine the protective and pathogenic host responses within the neonate.

Evolutionary dynamics of group A and B respiratory syncytial virus in China, 2009-2018

Respiratory syncytial virus (RSV) is a major cause of acute respiratory tract infections in children and is a public health threat globally. To investigate the spatiotemporal dynamics of RSV evolution, we performed systematic phylogenetic analysis using all available sequences from the GenBank database, together with sequences from Shanghai, China. Both RSV-A and RSV-B appear to have originated in North America, with an inferred origin time of 1954.0 (1938.7-1967.6) and 1969.7 (1962.6-1975.5), respectively. BA-like strains of RSV-B, with a 60-nt insertion, and the ON1 strain of RSV-A, with a 72-nt insertion, emerged in 1997.6 (1996.2-1998.6) and 2010.1 (2009.1-2010.3), respectively. Since their origin, both genotypes have gradually replaced the former circulating genotypes to become the dominant strain. The population dynamic of RSV-A showed a seasonal epidemic pattern with obvious expansion in the periods of 2006-2007, 2010-2011, 2011-2012, and 2013-2014. Thirty fixed amino acid substitutions were identified during the divergence of NA4 from GA1 genotypes of RSV-A, and 13 were found during the divergence of SAB4 from GB1 of RSV-B. Importantly, ongoing evolution has occurred since the emergence of ON1, including four amino acid substitutions (I208L, E232G, T253K, and P314L). RSV-A genotypes GA5, NA4, NA1, and ON1 and RSV-B genotypes CB1, SAB4, BA-C, BA10, BA7, and BA9 were co-circulating in China from 2005 to 2015. In particular, RSV-A genotype ON1 was first detected in China in 2011, and it completely replaced GA2 to become the predominant strain after 2016. These data provide important insights into the evolution and epidemiology of RSV.

Vaccine-associated enhanced disease: Case definition and guidelines for data collection, analysis, and presentation of immunization safety data

This is a Brighton Collaboration Case Definition of the term "Vaccine Associated Enhanced Disease" to be utilized in the evaluation of adverse events following immunization. The Case Definition was developed by a group of experts convened by the Coalition for Epidemic Preparedness Innovations (CEPI) in the context of active development of vaccines for SARS-CoV-2 vaccines and other emerging pathogens. The case definition format of the Brighton Collaboration was followed to develop a consensus definition and defined levels of certainty, after an exhaustive review of the literature and expert consultation. The document underwent peer review by the Brighton Collaboration Network and by selected Expert Reviewers prior to submission.

Comprehensive at-arrival transcriptomic analysis of post-weaned beef cattle uncovers type I interferon and antiviral mechanisms associated with bovine respiratory disease mortality

BACKGROUND

Despite decades of extensive research, bovine respiratory disease (BRD) remains the most devastating disease in beef cattle production. Establishing a clinical diagnosis often relies upon visual detection of non-specific signs, leading to low diagnostic accuracy. Thus, post-weaned beef cattle are often metaphylactically administered antimicrobials at facility arrival, which poses concerns regarding antimicrobial stewardship and resistance. Additionally, there is a lack of high-quality research that addresses the gene-by-environment interactions that underlie why some cattle that develop BRD die while others survive. Therefore, it is necessary to decipher the underlying host genomic factors associated with BRD mortality versus survival to help determine BRD risk and severity. Using transcriptomic analysis of at-arrival whole blood samples from cattle that died of BRD, as compared to those that developed signs of BRD but lived (n = 3 DEAD, n = 3 ALIVE), we identified differentially expressed genes (DEGs) and associated pathways in cattle that died of BRD. Additionally, we evaluated unmapped reads, which are often overlooked within transcriptomic experiments.

RESULTS

69 DEGs (FDR<0.10) were identified between ALIVE and DEAD cohorts. Several DEGs possess immunological and proinflammatory function and associations with TLR4 and IL6. Biological processes, pathways, and disease phenotype associations related to type-I interferon production and antiviral defense were enriched in DEAD cattle at arrival. Unmapped reads aligned primarily to various ungulate assemblies, but failed to align to viral assemblies.

CONCLUSION

This study further revealed increased proinflammatory immunological mechanisms in cattle that develop BRD. DEGs upregulated in DEAD cattle were predominantly involved in innate immune pathways typically associated with antiviral defense, although no viral genes were identified within unmapped reads. Our findings provide genomic targets for further analysis in cattle at highest risk of BRD, suggesting that mechanisms related to type I interferons and antiviral defense may be indicative of viral respiratory disease at arrival and contribute to eventual BRD mortality.

Immunogenicity and inflammatory properties of respiratory syncytial virus attachment G protein in cotton rats

Human respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection in infants and young children worldwide. The attachment (G) protein of RSV is synthesized by infected cells in both a membrane bound (mG) and secreted form (sG) and uses a CX3C motif for binding to its cellular receptor. Cell culture and mouse studies suggest that the G protein mimics the cytokine CX3CL1 by binding to CX3CR1 on immune cells, which is thought to cause increased pulmonary inflammation in vivo. However, because these studies have used RSV lacking its G protein gene or blockade of the G protein with a G protein specific monoclonal antibody, the observed reduction in inflammation may be due to reduced virus replication and spread, and not to a direct role for G protein as a viral chemokine. In order to more directly determine the influence of the soluble and the membrane-bound forms of G protein on the immune system independent of its attachment function for the virion, we expressed the G protein in cotton rat lungs using adeno-associated virus (AAV), a vector system which does not itself induce inflammation. We found no increase in pulmonary inflammation as determined by histology and bronchoalveolar lavage after inoculation of AAVs expressing the membrane bound G protein, the secreted G protein or the complete G protein gene which expresses both forms. The long-term low-level expression of AAV-G did, however, result in the induction of non-neutralizing antibodies, CD8 T cells and partial protection from challenge with RSV. Complete protection was accomplished through co-immunization with AAV-G and an AAV expressing cotton rat interferon α.

Humoral immune responses and neutralizing antibodies against SARS-CoV-2; implications in pathogenesis and protective immunity

The magnitude and the quality of humoral responses against SARS-CoV-2 have been associated with clinical outcome. Although the elicitation of humoral responses against different viral proteins is rapid and occurs in most infected individuals, its magnitude is highly variable among them and positively correlates with COVID-19 disease severity. This rapid response is characterized by the almost concomitant appearance of virus-specific IgG, IgA and IgM antibodies that contain neutralizing antibodies directed against different epitopes of the Spike glycoprotein. Of particularly interest, the antibodies against domain of the Spike that interacts with the cellular receptor ACE2, known as the receptor binding domain (RBD), are present in most infected individuals and are block viral entry and infectivity. Such neutralizing antibodies protect different animal species when administered before virus exposure; therefore, its elicitation is the main target of current vaccine approaches and their clinical use as recombinant monoclonal antibodies (mAbs) is being explored. Yet, little information exists on the duration of humoral responses during natural infection. This is a key issue that will impact the management of the pandemic and determine the utility of seroconversion studies and the level of herd immunity. Certainly, several cases of reinfection have been reported, suggesting that immunity could be transient, as reported for other coronaviruses. In summary, although the kinetics of the generation of antibodies against SASR-CoV-2 and their protective activity have been clearly defined, their role in COVID-19 pathogenesis and the length of these responses are still open questions.

Fcγ Receptor IIa (FCGR2A) Polymorphism Is Associated With Severe Respiratory Syncytial Virus Disease in Argentinian Infants

Background

Most patients with respiratory syncytial virus (RSV) infection requiring hospitalization have no risk factors for severe disease. Genetic variation in the receptor for the Fc portion of IgG (FcγR) determines their affinity for IgG subclasses driving innate and adaptive antiviral immunity. We investigated the relationship between FcγRIIa-H131R polymorphism and RSV disease.

Methods

Blood samples were collected from 182 infants ≤24-month-old (50 uninfected, 114 RSV-infected with moderate course and 18 suffering severe disease). FcγRIIa-H131R SNP genotypic frequencies (HH, HR, RR) and anti-RSV IgG1, IgG2 and IgG3 levels were studied.

Results

Genotypic frequencies for FcγRIIa-H131R SNP were comparable between uninfected and RSV-infected infants. In contrast, we found a significant higher frequency of HH genotype in severe RSV-infected children compared to moderate patients. Among severe group, HH infants presented more factors associated to severity than HR or RR patients did. Furthermore, compared to moderate RSV-infected infants, severe patients showed higher levels of anti-RSV IgG1 and IgG3.

Conclusions

We found an association between an FcγRIIa (H131) polymorphism and severe RSV disease, which points towards a critical role for interactions between FcγRs and immune complexes in RSV pathogenesis. This genetic factor could also predict the worse outcome and identify those infants at risk during hospitalization.

Harnessing Cellular Immunity for Vaccination against Respiratory Viruses

Severe respiratory viral infections, such as influenza, metapneumovirus (HMPV), respiratory syncytial virus (RSV), rhinovirus (RV), and coronaviruses, including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), cause significant mortality and morbidity worldwide. These viruses have been identified as important causative agents of acute respiratory disease in infants, the elderly, and immunocompromised individuals. Clinical signs of infection range from mild upper respiratory illness to more serious lower respiratory illness, including bronchiolitis and pneumonia. Additionally, these illnesses can have long-lasting impact on patient health well beyond resolution of the viral infection. Aside from influenza, there are currently no licensed vaccines against these viruses. However, several research groups have tested various vaccine candidates, including those that utilize attenuated virus, virus-like particles (VLPs), protein subunits, and nanoparticles, as well as recent RNA vaccines, with several of these approaches showing promise. Historically, vaccine candidates have advanced, dependent upon the ability to activate the humoral immune response, specifically leading to strong B cell responses and neutralizing antibody production. More recently, it has been recognized that the cellular immune response is also critical in proper resolution of viral infection and protection against detrimental immunopathology associated with severe disease and therefore, must also be considered when analyzing the efficacy and safety of vaccine candidates. These candidates would ideally result in robust CD4+ and CD8+ T cell responses as well as high-affinity neutralizing antibody. This review will aim to summarize established and new approaches that are being examined to harness the cellular immune response during respiratory viral vaccination.

Harnessing Cellular Immunity for Vaccination against Respiratory Viruses

Severe respiratory viral infections, such as influenza, metapneumovirus (HMPV), respiratory syncytial virus (RSV), rhinovirus (RV), and coronaviruses, including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), cause significant mortality and morbidity worldwide. These viruses have been identified as important causative agents of acute respiratory disease in infants, the elderly, and immunocompromised individuals. Clinical signs of infection range from mild upper respiratory illness to more serious lower respiratory illness, including bronchiolitis and pneumonia. Additionally, these illnesses can have long-lasting impact on patient health well beyond resolution of the viral infection. Aside from influenza, there are currently no licensed vaccines against these viruses. However, several research groups have tested various vaccine candidates, including those that utilize attenuated virus, virus-like particles (VLPs), protein subunits, and nanoparticles, as well as recent RNA vaccines, with several of these approaches showing promise. Historically, vaccine candidates have advanced, dependent upon the ability to activate the humoral immune response, specifically leading to strong B cell responses and neutralizing antibody production. More recently, it has been recognized that the cellular immune response is also critical in proper resolution of viral infection and protection against detrimental immunopathology associated with severe disease and therefore, must also be considered when analyzing the efficacy and safety of vaccine candidates. These candidates would ideally result in robust CD4+ and CD8+ T cell responses as well as high-affinity neutralizing antibody. This review will aim to summarize established and new approaches that are being examined to harness the cellular immune response during respiratory viral vaccination.

Pharmacological Characterization of TP0591816, a Novel Macrocyclic Respiratory Syncytial Virus Fusion Inhibitor with Antiviral Activity against F Protein Mutants

Human respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in early childhood. However, no vaccines have yet been approved for prevention of RSV infection, and the treatment options are limited. Therefore, development of effective and safe anti-RSV drugs is needed. In this study, we evaluated the antiviral activity and mechanism of action of a novel macrocyclic anti-RSV compound, TP0591816. TP0591816 showed significant antiviral activities against both subgroup A and subgroup B RSV, while exerting no cytotoxicity. Notably, the antiviral activity of TP0591816 was maintained against a known fusion inhibitor-resistant RSV strain with a mutation in the cysteine-rich region or in heptad repeat B. Results of a time-of-addition assay and a temperature shift assay indicated that TP0591816 inhibited fusion of RSV with the cell membrane during viral entry. In addition, TP0591816 added after cell infection also inhibited cell-cell fusion. A TP0591816-resistant virus strain selected by serial passage had an L141F mutation, but no mutation in the cysteine-rich region or in heptad repeat B in the fusion (F) protein. Treatment with TP0591816 reduced lung virus titers in a dose-dependent manner in a mouse model of RSV infection. Furthermore, the estimated effective dose of TP0591816 for use against F protein mutants was thought to be clinically realistic and potentially tolerable. Taken together, these findings suggest that TP0591816 is a promising novel candidate for the treatment of resistant RSV infection.

Vaccines for COVID-19

Since the emergence of COVID-19, caused by the SARS-CoV-2 virus at the end of 2019, there has been an explosion of vaccine development. By 24 September 2020, a staggering number of vaccines (more than 200) had started preclinical development, of which 43 had entered clinical trials, including some approaches that have not previously been licensed for human vaccines. Vaccines have been widely considered as part of the exit strategy to enable the return to previous patterns of working, schooling and socializing. Importantly, to effectively control the COVID-19 pandemic, production needs to be scaled-up from a small number of preclinical doses to enough filled vials to immunize the world's population, which requires close engagement with manufacturers and regulators. It will require a global effort to control the virus, necessitating equitable access for all countries to effective vaccines. This review explores the immune responses required to protect against SARS-CoV-2 and the potential for vaccine-induced immunopathology. We describe the profile of the different platforms and the advantages and disadvantages of each approach. The review also addresses the critical steps between promising preclinical leads and manufacturing at scale. The issues faced during this pandemic and the platforms being developed to address it will be invaluable for future outbreak control. Nine months after the outbreak began we are at a point where preclinical and early clinical data are being generated for the vaccines; an overview of this important area will help our understanding of the next phases.

Is Cross-Reactive Immunity Triggering COVID-19 Immunopathogenesis?

The serological responses to both SARS-CoV-1 and SARS-CoV-2 virus have some unique characteristics that suggest cross-reactive priming by other human coronaviruses (hCoVs). The early kinetics and magnitude of these responses are, in some cases, associated with worse clinical outcomes in SARS and COVID-19. Cross-reactive hCoV antibody responses have been detected in both SARS and COVID-19 patients. There is also evidence that pre-existing T cell immunity to common cold coronaviruses can prime the response to SARS-CoV-2. Studies in non-human primates show that SARS-CoV-1 S-protein vaccine-induced antibodies are associated with acute lung injury in macaques challenged with SARS-CoV-1. Here we discuss the potential of cross-reactive immunity to drive the immunopathogenesis of COVID-19 and its implications for current efforts to develop immune-based therapies and vaccines.

Respiratory syncytial virus infection-induced mucus secretion by down-regulation of miR-34b/c-5p expression in airway epithelial cells

Severe RSV infection is the main cause of hospitalization to children under the age of five. The regulation of miRNAs on the severity of RSV infection is unclear. The aim of the study was to identify the critical differential expression miRNAs (DE miRNAs) that can regulate the pathological response in RSV‐infected airway epithelial cells. In this study, miRNA and mRNA chips of RSV‐infected airway epithelia from Gene Expression Omnibus (GEO) were screened and analysed, separately. DE miRNAs‐targeted genes were performed for further pathway and process enrichment analysis. DE miRNA‐targeted gene functional network was constructed on the basis of miRNA‐mRNA interaction. The screened critical miRNA was also investigated by bioinformatics analysis. Then, RSV‐infected human bronchial epithelial cells (HBECs) were constructed to verify the expression of the DE miRNAs. Finally, specific synthetic DE miRNAs mimics were used to confirm the effect of DE miRNAs on the RSV‐infected HBECs. 45 DE miRNAs were identified from GEO62306 dataset. Our results showed that hsa‐mir‐34b‐5p and hsa‐mir‐34c‐5p decreased significantly in HBECs after RSV infection. Consistent with the biometric analysis, hsa‐mir‐34b/c‐5p is involved in the regulation of mucin expression gene MUC5AC. In RSV‐infected HBECs, the inducement of MUC5AC production by decreased hsa‐mir‐34b/c‐5p was partly mediated through activation of c‐Jun. These findings provide new insights into the mechanism of mucus obstruction after RSV infection and represent valuable targets for RSV infection and airway obstruction treatment.

Antibody and Local Cytokine Response to Respiratory Syncytial Virus Infection in Community-Dwelling Older Adults

Respiratory syncytial virus (RSV) can cause severe morbidity and mortality in certain risk groups, especially infants and older adults. Currently no (prophylactic) treatment is available, except for a partially effective yet highly expensive monoclonal antibody. RSV therefore remains a major public health concern. To allow targeted development of novel vaccines and therapeutics, it is of great importance to understand the immunological mechanisms that underlie (protection from) severe disease in specific risk populations. Since most RSV-related studies focus on infants, there are only very limited data available concerning the response to RSV in the elderly population. Therefore, in this study, RSV-induced antibody responses and local cytokine secretion were assessed in community-dwelling older adults. These data provide novel insights that will benefit ongoing efforts to design safe and effective prevention and treatment strategies for RSV in an understudied risk group.

Respiratory syncytial virus (RSV) is increasingly recognized for causing severe morbidity and mortality in older adults, but there are few studies on the RSV-induced immune response in this population. Information on the immunological processes at play during RSV infection in specific risk groups is essential for the rational and targeted design of novel vaccines and therapeutics. Here, we assessed the antibody and local cytokine response to RSV infection in community-dwelling older adults (≥60 years of age). During three winters, serum and nasopharyngeal swab samples were collected from study participants during acute respiratory infection and recovery. RSV IgG enzyme-linked immunosorbent assays (ELISA) and virus neutralization assays were performed on serum samples from RSV-infected individuals (n = 41) and controls (n = 563 and n = 197, respectively). Nasal RSV IgA and cytokine concentrations were determined using multiplex immunoassays in a subset of participants. An in vitro model of differentiated primary bronchial epithelial cells was used to assess RSV-induced cytokine responses over time. A statistically significant increase in serum neutralization titers and IgG concentrations was observed in RSV-infected participants compared to controls. During acute RSV infection, a statistically significant local upregulation of beta interferon (IFN-β), IFN-λ1, IFN-γ, interleukin 1β (IL-1β), tumor necrosis factor alpha (TNF-α), IL-6, IL-10, CXCL8, and CXCL10 was found. IFN-β, IFN-λ1, CXCL8, and CXCL10 were also upregulated in the epithelial model upon RSV infection. In conclusion, this study provides novel insights into the basic immune response to RSV infection in an important and understudied risk population, providing leads for future studies that are essential for the prevention and treatment of severe RSV disease in older adults.

IMPORTANCE Respiratory syncytial virus (RSV) can cause severe morbidity and mortality in certain risk groups, especially infants and older adults. Currently no (prophylactic) treatment is available, except for a partially effective yet highly expensive monoclonal antibody. RSV therefore remains a major public health concern. To allow targeted development of novel vaccines and therapeutics, it is of great importance to understand the immunological mechanisms that underlie (protection from) severe disease in specific risk populations. Since most RSV-related studies focus on infants, there are only very limited data available concerning the response to RSV in the elderly population. Therefore, in this study, RSV-induced antibody responses and local cytokine secretion were assessed in community-dwelling older adults. These data provide novel insights that will benefit ongoing efforts to design safe and effective prevention and treatment strategies for RSV in an understudied risk group.

A gammaherpesvirus licenses CD8 T cells to protect the host from pneumovirus-induced immunopathologies

Human respiratory syncytial virus (RSV) is a pneumovirus that causes severe infections in infants worldwide. Despite intensive research, safe and effective vaccines against RSV have remained elusive. The main reason is that RSV infection of children previously immunized with formalin-inactivated-RSV vaccines has been associated with exacerbated pathology, a phenomenon called RSV vaccine-enhanced respiratory disease. In parallel, despite the high RSV prevalence, only a minor proportion of children develop severe diseases. Interestingly, variation in the immune responses against RSV or following RSV vaccination could be linked with differences of exposure to microbes during childhood. Gammaherpesviruses (γHVs), such as the Epstein-Barr virus, are persistent viruses that deeply influence the immune system of their host and could therefore affect the development of pneumovirus-induced immunopathologies for the long term. Here, we showed that a previous ɣHV infection protects against both pneumovirus vaccine-enhanced disease and pneumovirus primary infection and that CD8 T cells are essential for this protection. These observations shed a new light on the understanding of pneumovirus-induced diseases and open new perspectives for the development of vaccine strategies.

Double-edged role of natural killer cells during RSV infection

Natural killer cells play a vital role in the rejection of tumors and pathogen-infected cells. NK cells are indispensable in the early immune response against viral infections by directly targeting infected cells. Furthermore, NK cells influence adaptive immunity by driving virus-specific T-cell responses. Respiratory syncytial virus, a highly contagious virus that causes bronchiolitis, is the main reason for mortality in infants and elderly patients. RSV infection triggers both innate and adaptive immune responses. However, immunity against RSV is ephemeral due to the impaired development of immunological memory. The role of NK cells during RSV infection remains ambiguous. NK cells play a dual role in RSV infection; initially, their role is a protective one as they utilize their intrinsic cytotoxicity, followed by a detrimental one that induces lung injury due to the inhibition of antibody responses and the secretion of pro-inflammatory factors. Noteworthy, IFN-γ released from NK cells play a critical role in promoting a shift to adaptive responses and inhibiting antibody responses in neonates. Indeed, NK cells have a pro-inflammatory and inhibitory role rather than a cytotoxic one that contributes to the severity of the disease. Therapeutic options, including DNA-protein-based vaccines, synthetic peptides, and attenuated strains, are presently under tests. However, there is a need for effective strategies to augment NK cell activity and circumvent the pro-inflammatory activity to benefit the host. In this review, we focused on the role played by NK cells in the immune response and its outcome on the immunopathogenesis of RSV disease.

Respiratory Syncytial Virus-Induced Oxidative Stress Leads to an Increase in Labile Zinc Pools in Lung Epithelial Cells

Zinc supplementation in cell culture has been shown to inhibit various viruses, like herpes simplex virus, rotavirus, severe acute respiratory syndrome (SARS) coronavirus, rhinovirus, and respiratory syncytial virus (RSV). However, whether zinc plays a direct antiviral role in viral infections and whether viruses have adopted strategies to modulate zinc homeostasis have not been investigated. Results from clinical trials of zinc supplementation in infections indicate that zinc supplementation may be beneficial in a pathogen- or disease-specific manner, further underscoring the importance of understanding the interaction between zinc homeostasis and virus infections at the molecular level. We investigated the effect of RSV infection on zinc homeostasis and show that RSV infection in lung epithelial cells leads to modulation of zinc homeostasis. The intracellular labile zinc pool increases upon RSV infection in a multiplicity of infection (MOI)-dependent fashion. Small interfering RNA (siRNA)-mediated knockdown of the ubiquitous zinc uptake transporter ZIP1 suggests that labile zinc levels are increased due to the increased uptake by RSV-infected cells as an antiviral response. Adding zinc to culture medium after RSV infection led to significant inhibition of RSV titers, whereas depletion of zinc by a zinc chelator, N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) led to an increase in RSV titers. The inhibitory effect of zinc was specific, as other divalent cations had no effect on RSV titers. Both RSV infection and zinc chelation by TPEN led to reactive oxygen species (ROS) induction, whereas addition of zinc blocked ROS induction. These results suggest a molecular link between RSV infection, zinc homeostasis, and oxidative-stress pathways and provide new insights for developing strategies to counter RSV infection.IMPORTANCE Zinc deficiency rates in developing countries range from 20 to 30%, and zinc supplementation trials have been shown to correct clinical manifestations attributed to zinc deficiency, but the outcomes in the case of respiratory infections have been inconsistent. We aimed at understanding the role of zinc homeostasis in respiratory syncytial virus (RSV) infection. Infection of lung epithelial cell lines or primary small-airway epithelial cells led to an increase in labile zinc pools, which was due to increased uptake of zinc. Zinc supplementation inhibited RSV replication, whereas zinc chelation had an opposing effect, leading to increases in RSV titers. Increases in labile zinc in RSV-infected cells coincided with induction of reactive oxygen species (ROS). Both zinc depletion and addition of exogenous ROS led to enhanced RSV infection, whereas addition of the antioxidant inhibited RSV, suggesting that zinc is part of an interplay between RSV-induced oxidative stress and the host response to maintain redox balance.

CX3CR1 as a respiratory syncytial virus receptor in pediatric human lung

BACKGROUND

Data on the host factors that contribute to infection of young children by respiratory syncytial virus (RSV) are limited. The human chemokine receptor, CX3CR1, has recently been implicated as an RSV receptor. Here we evaluate a role for CX3CR1 in pediatric lung RSV infections.

METHODS

CX3CR1 transcript levels in the upper and lower pediatric airways were assessed. Tissue localization and cell-specific expression was confirmed using in situ hybridization and immunohistochemistry. The role of CX3CR1 in RSV infection was also investigated using a novel physiological model of pediatric epithelial cells.

RESULTS

Low levels of CX3CR1 transcript were often, but not always, expressed in both upper (62%) and lower airways (36%) of pediatric subjects. CX3CR1 transcript and protein expression was detected in epithelial cells of normal human pediatric lung tissues. CX3CR1 expression was readily detected on primary cultures of differentiated pediatric/infant human lung epithelial cells. RSV demonstrated preferential infection of CX3CR1-positive cells, and blocking CX3CR1/RSV interaction significantly decreased viral load.

CONCLUSION

CX3CR1 is present in the airways of pediatric subjects where it may serve as a receptor for RSV infection. Furthermore, CX3CR1 appears to play a mechanistic role in mediating viral infection of pediatric airway epithelial cells in vitro.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Ethics of Conducting Clinical Research in an Outbreak Setting

The conduct of clinical trials during the West Africa Ebola outbreak in 2014 highlighted many ethical challenges. How these challenges were addressed, what clinical studies were conducted during that outbreak, and the lessons learned for dealing with future outbreaks were the subject of a National Academy of Medicine committee report titled Integrating Clinical Research into Epidemic Response: The Ebola Experience. This report suggested improvements for research during subsequent emerging or re-emerging outbreaks and is summarized in this review. We also discuss the current Ebola outbreak in the Democratic Republic of the Congo and highlight how the dialogue has changed and how successful clinical trials have been implemented. We conclude with a description of productive efforts to include pregnant women and children in therapeutic and vaccine trials during outbreaks that are currently ongoing.

Downregulation of A20 Expression Increases the Immune Response and Apoptosis and Reduces Virus Production in Cells Infected by the Human Respiratory Syncytial Virus

Human respiratory syncytial virus (HRSV) causes severe lower respiratory tract infections in infants, the elderly, and immunocompromised adults. Regulation of the immune response against HRSV is crucial to limiting virus replication and immunopathology. The A20/TNFAIP3 protein is a negative regulator of nuclear factor kappa B (NF-κB) and interferon regulatory factors 3/7 (IRF3/7), which are key transcription factors involved in the inflammatory/antiviral response of epithelial cells to virus infection. Here, we investigated the impact of A20 downregulation or knockout on HRSV growth and the induction of the immune response in those cells. Cellular infections in which the expression of A20 was silenced by siRNAs or eliminated by gene knockout showed increased inflammatory/antiviral response and reduced virus production. Similar results were obtained when the expression of A20-interacting proteins, such as TAX1BP1 and ABIN1, was silenced. Additionally, downregulation of A20, TAX1BP1, and ABIN1 increased cell apoptosis in HRSV-infected cells. These results show that the downregulation of A20 expression might contribute in the control of HRSV infections by potentiating the early innate immune response and increasing apoptosis in infected cells.

Respiratory syncytial virus infection: why does disease severity vary among individuals?

Introduction: Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory tract infections in infancy. While many infants are infected with RSV, the nature and severity of the disease vary among individuals. RSV causes bronchiolitis, pneumonia, and asthma exacerbation. However, most children infected with RSV have only mild upper airways disease and may be asymptomatic.Areas covered: Despite efforts to elucidate mechanisms for the various clinical responses to RSV infection, they remain largely unknown, suggesting that susceptibility and disease are influenced by multiple intrinsic and extrinsic factors. This article reviews the available literature on the field of RSV disease severity and discusses important factors associated to susceptibility and different disease outcome.Expert opinion: The severity of RSV-induced illness is a phenomenon that depends on a variety of graded mechanisms of interaction between the host, virus, and environment. This may lead to differences in the intensity of immune response in the lung and different courses of the disease. By characterizing, classifying, and grading the affecting factors in high-risk patients versus those who do not fall ill by RSV, we may find therapies or point to disease-limiting medications.

Sirtuin 1 regulates mitochondrial function and immune homeostasis in respiratory syncytial virus infected dendritic cells

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in children worldwide. Sirtuin 1 (SIRT1), a NAD+ dependent deacetylase, has been associated with induction of autophagy, reprogramming cellular metabolism, and regulating immune mediators. In this study, we investigated the role of SIRT1 in bone marrow dendritic cell (BMDC) function during RSV infection. SIRT1 deficient (SIRT1 -/-) BMDC showed a defect in mitochondrial membrane potential (Δ⍦m) that worsens during RSV infection. This defect in Δ⍦m caused the generation of elevated levels of reactive oxygen species (ROS). Furthermore, the oxygen consumption rate (OCR) was reduced as assessed in Seahorse assays, coupled with lower levels of ATP in SIRT1-/- DC. These altered responses corresponded to altered innate cytokine responses in the SIRT1-/- DC in response to RSV infection. Reverse Phase Protein Array (RPPA) functional proteomics analyses of SIRT1-/- and WT BMDC during RSV infection identified a range of differentially regulated proteins involved in pathways that play a critical role in mitochondrial metabolism, autophagy, oxidative and ER stress, and DNA damage. We identified an essential enzyme, acetyl CoA carboxylase (ACC1), which plays a central role in fatty acid synthesis and had significantly increased expression in SIRT1-/- DC. Blockade of ACC1 resulted in metabolic reprogramming of BMDC that ameliorated mitochondrial dysfunction and reduced pathologic innate immune cytokines in DC. The altered DC responses attenuated Th2 and Th17 immunity allowing the appropriate generation of anti-viral Th1 responses both in vitro and in vivo during RSV infection thus reducing the enhanced pathogenic responses. Together, these studies identify pathways critical for appropriate DC function and innate immunity that depend on SIRT1-mediated regulation of metabolic processes.

Caveolin-2 deficiency induces a rapid anti-tumor immune response prior to regression of implanted murine lung carcinoma tumors

Immunosuppression is critical for tumor growth and metastasis as well as obstacle to effective immunotherapy. Here, we demonstrate that host deficiency in caveolin-2, a member of caveolin protein family, increases M1-polarized tumor-associated macrophage (TAM) and CD8 T cell infiltration into subcutaneously implanted murine lung carcinoma tumors. Importantly, increase in M1 TAM-specific markers and cytokines occurs prior to increased numbers of tumor-infiltrating CD8 T cells and tumor regression in caveolin-2 deficient mice, suggesting that an early increase in M1 TAMs is a novel mechanism, via which host deficiency in caveolin-2 inhibits tumor growth. Consistent with the latter, transfer and co-injection of caveolin-2 deficient bone marrow (origin of TAMs) suppresses tumor growth and increases numbers of M1-polarized TAMs in wild type mice. Collectively, our data suggest that lung cancer cells use caveolin-2 expressed in bone marrow-derived cell types including TAMs to promote tumor growth via suppressing the anti-tumor immune response and that caveolin-2 could be a potential target for cancer immunotherapy.

Respiratory Syncytial Virus Infects Primary Neonatal and Adult Natural Killer Cells and Affects Their Antiviral Effector Function

Background

Respiratory syncytial virus (RSV) is a major cause of severe acute lower respiratory tract infections in infants. Natural killer (NK) cells are important antiviral effector cells that likely encounter RSV in the presence of virus-specific (maternal) antibodies. As NK cells potentially contribute to immunopathology, we investigated whether RSV affects their antiviral effector functions.

Methods

We assessed the phenotype and functionality of primary neonatal and adult NK cells by flow cytometry after stimulation with RSV or RSV-antibody complexes.

Results

We demonstrate for the first time that RSV infects neonatal and adult NK cells in vitro. Preincubation of virus with subneutralizing concentrations of RSV-specific antibodies significantly increased the percentage of infected NK cells. Upon infection, NK cells were significantly more prone to produce interferon-γ, while secretion of the cytotoxicity molecule perforin was not enhanced.

Conclusions

Our findings suggest that (antibody-enhanced) RSV infection of NK cells induces a proinflammatory rather than a cytotoxic response, which may contribute to immunopathology. Considering that most RSV vaccines currently being developed aim at inducing (maternal) antibodies, these results highlight the importance of understanding the interactions between innate effector cells and virus-specific antibodies.

T-Cell Responses in Adults During Natural Respiratory Syncytial Virus Infection

Background

The pathogenesis of respiratory syncytial virus (RSV) in older adults may be due to age-related T-cell immunosenescence. Thus, we evaluated CD4 and CD8 T-cell responses during RSV infection in adults across the age spectrum.

Methods

Peripheral blood mononuclear cells collected during RSV infection in adults, age 26-96 years, were stimulated with live RSV and peptide pools representing F, M, NP, and G proteins and analyzed by flow cytometry.

Results

There were no significant age-related differences in frequency of CD4+ T cells synthesizing interferon (IFN)γ, interleukin (IL)2, IL4, IL10, or tumor necrosis factor (TNF)α or in CD8+IFNγ+ T cells. IL4+CD4+ T-cell numbers were low, as were IL13 and IL17 responses. However, in univariate analysis, CD4 T-cell IFNγ, IL2, IL4, IL10, and TNFα responses and CD8+IFNγ+ T cells were significantly increased with more severe illness requiring hospitalization. In multivariate analysis, viral load was also associated with increased T-cell responses.

Conclusions

We found no evidence of diminished RSV-specific CD4 or CD8 T-cell responses in adults infected with RSV. However, adults with severe disease seemed to have more robust CD4 and CD8 T-cell responses during infection, suggesting that disease severity may have a greater association with T-cell responses than age.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

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

The human respiratory syncytial virus (hRSV) is the main etiologic agent of severe lower respiratory tract infections that affect young children throughout the world, associated with significant morbidity and mortality, becoming a serious public health problem globally. Up to date, no licensed vaccines are available to prevent severe hRSV-induced disease, and the generation of safe-effective vaccines has been a challenging task, requiring constant biomedical research aimed to overcome this ailment. Among the difficulties presented by the study of this pathogen, it arises the fact that there is no single animal model that resembles all aspects of the human pathology, which is due to the specificity that this pathogen has for the human host. Thus, for the study of hRSV, different animal models might be employed, depending on the goal of the study. Of all the existing models, the murine model has been the most frequent model of choice for biomedical studies worldwide and has been of great importance at contributing to the development and understanding of vaccines and therapies against hRSV. The most notable use of the murine model is that it is very useful as a first approach in the development of vaccines or therapies such as monoclonal antibodies, suggesting in this way the direction that research could have in other preclinical models that have higher maintenance costs and more complex requirements in its management. However, several additional different models for studying hRSV, such as other rodents, mustelids, ruminants, and non-human primates, have been explored, offering advantages over the murine model. In this review, we discuss the various applications of animal models to the study of hRSV-induced disease and the advantages and disadvantages of each model, highlighting the potential of each model to elucidate different features of the pathology caused by the hRSV infection.