Assessing Variation in the Cost of Palivizumab for Respiratory Syncytial Virus Prevention in Preterm Infants

Neutralizing activity of anti-respiratory syncytial virus monoclonal antibody produced in Nicotiana benthamiana

Respiratory syncytial virus (RSV) is a highly contagious virus that affects the lungs and respiratory passages of many vulnerable people. It is a leading cause of lower respiratory tract infections and clinical complications, particularly among infants and elderly. It can develop into serious complications such as pneumonia and bronchiolitis. The development of RSV vaccine or immunoprophylaxis remains highly active and a global health priority. Currently, GSK's Arexvy™ vaccine is approved for the prevention of lower respiratory tract disease in older adults (>60 years). Palivizumab and currently nirsevimab are the approved monoclonal antibodies (mAbs) for RSV prevention in high-risk patients. Many studies are ongoing to develop additional therapeutic antibodies for preventing RSV infections among newborns and other susceptible groups. Recently, additional antibodies have been discovered and shown greater potential for development as therapeutic alternatives to palivizumab and nirsevimab. Plant expression platforms have proven successful in producing recombinant proteins, including antibodies, offering a potential cost-effective alternative to mammalian expression platforms. Hence in this study, an attempt was made to use a plant expression platform to produce two anti-RSV fusion (F) mAbs 5C4 and CR9501. The heavy-chain and light-chain sequences of both these antibodies were transiently expressed in Nicotiana benthamiana plants using a geminiviral vector and then purified using single-step protein A affinity column chromatography. Both these plant-produced mAbs showed specific binding to the RSV fusion protein and demonstrate effective viral neutralization activity in vitro. These preliminary findings suggest that plant-produced anti-RSV mAbs are able to neutralize RSV in vitro.

Cost Savings Without Increased Risk of Respiratory Hospitalization for Preterm Children after the 2014 Palivizumab Policy Update

OBJECTIVES

Our objective was to compare rates of hospitalizations for respiratory illnesses in preterm and full-term (FT) children for 4 years before and after the 2014 update to the American Academy of Pediatrics (AAP) respiratory syncytial virus (RSV) immunoprophylaxis guidance, which restricted eligibility among infants born at 29 to 34 weeks in the first winter and all preterm infants in the second winter after neonatal discharge.

STUDY DESIGN

We conducted pre-post and interrupted time series analyses on claims data from a commercial national managed care plan. We compared the number of RSV and all respiratory hospital admissions in the first and second RSV seasons after neonatal discharge among a cohort of preterm children, regardless of palivizumab status, in the 4 years before and after the implementation of the 2014 palivizumab eligibility change. A FT group was included for reference.

RESULTS

The cohort included 821 early preterm (EP, <29 weeks), 4,790 moderate preterm (MP, 29-34 weeks), and 130,782 FT children. Palivizumab use after the policy update decreased among MP children in the first and second RSV seasons after neonatal discharge, without any change in the odds of hospitalization with RSV or respiratory illness. For the EP group, there was no change in the rate of palivizumab or the odds of hospitalization with RSV or respiratory illness after the policy update. For the FT group, there was a slight decrease in odds of hospitalization post-2014 after the policy update. The interrupted time series did not reveal any secular trends over time in hospitalization rates among preterm children. Following the policy change, there were cost savings for MP children in the first and second RSV seasons, when accounting for the cost of hospitalizations and the cost of palivizumab.

CONCLUSION

Hospitalizations for RSV or respiratory illness did not increase, and cost savings were obtained after the implementation of the 2014 AAP palivizumab prophylaxis policy.

KEY POINTS

· Palivizumab use decreased among children born moderate preterm (29 to34 weeks) after the 2014 palivizuamb policy update.. · There was no change in odds of hospitalization with respiratory syncitial virus or respiratory illness among preterm infants after the policy update when compared to before.. · There were cost savings, when accounting for the cost of hospitalizations and the cost of palivizumab, after the policy update among children born moderate preterm..

Approaches to the Prevention and Treatment of Respiratory Syncytial Virus Infection in Children: Rationale and Progress to Date

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection (LRTI) in children, and is associated with long-term pulmonary sequelae for up to 30 years after infection. The mainstay of RSV management is supportive therapy such as supplemental oxygen. Palivizumab (Synagis™-AstraZeneca), a monoclonal antibody targeting the RSV F protein site II, has been licensed for the prevention of RSV in high-risk groups since 1998. There has been recent promising progress in preventative strategies that include vaccines and long-acting, high-potency monoclonal antibodies. Nirsevimab (Beyfortus™-AstraZeneca/Sanofi), a monoclonal antibody with an extended half-life, has recently been registered in the European Union and granted licensure by the US Food and Drug Administration. Furthermore, a pre-fusion sub-unit protein vaccine has been granted licensure for pregnant women, aimed at protecting their young infants, following established safety and efficacy in clinical trials (Abrysvo™-Pfizer). Also, multiple novel antiviral therapeutic options are in early phase clinical trials. The next few years have the potential to change the landscape of LRTI through improvements in the prevention and management of RSV LRTI. Here, we discuss these new approaches, current research, and clinical trials in novel therapeutics, monoclonal antibodies, and vaccines against RSV infection in infants and children.

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.

Review and Update of Active and Passive Immunization Against Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection (LRTI) in children, causing approximately 3.6 million hospitalizations per year, and has been associated with long-term pulmonary sequelae for up to 30 years after infection, yet preventative strategies and active treatment options remain elusive. The associated morbidity and healthcare related costs could be decreased substantially with the development of these much-needed medications. After an initial false start in the development of an RSV vaccine, gradual progress is now being made with the development of multiple vaccine candidates using numerous different mechanisms of action. Furthermore, nirsevimab, a new monoclonal antibody for the prevention of RSV, has recently been registered in the European Union. New novel treatments for RSV infection are also in the pipeline, which would provide the clinician with much needed ammunition in the management of the acute disease. The next few years have the potential to change the landscape of LRTI forever through the prevention and management of RSV LRTI and thereby decrease the mortality and morbidity associated with it. In this review, we discuss these new approaches, current research, and clinical trials in monoclonal antibody and vaccine development against RSV.

Variation in clinical practice guidelines for use of palivizumab in preventing severe respiratory syncytial viral (RSV) disease in high-risk infants

BACKGROUND

Uniformity and compliance with clinical practice guidelines (CPGs) for use of palivizumab in preventing severe respiratory syncytial viral infection in Australian high-risk infants remain unclear.

METHODS

An online survey was conducted across the Australian and New Zealand Neonatal Network (ANZNN) to determine clinical practices around palivizumab. A literature search was also performed to identify and compare national and international guidelines.

RESULTS

A total of 65 of 422 ANZNN members completed the survey. Respondents included 61 senior medical staff of consultants/staff specialists (78%) and four nursing staff (6%). According to the survey, infants most likely to be recommended palivizumab included preterm infants born <29 weeks gestational age (GA) (30%), children with chronic lung diseases (CLDs) born <32 weeks GA (40%), and with hemodynamically significant heart disease (35%). Many of the respondents (53%) stated that CPGs for palivizumab were developed locally. Literature search identified 20 guidelines (10 international and 10 domestic); 16 (80%) recommended palivizumab use in preterm infants, 16 (80%) recommended use in infants with CLD, 17 (85%) in congenital heart disease and 6 (30%) in bronchopulmonary dysplasia (BPD). Eight (40%) guidelines provided specific recommendations for immunocompromised infants. Canada, Western Australia, and American Academy of Paediatrics provided recommendations for Indigenous children. Frequency and dosage of palivizumab was universal across all CPGs. None of the international guidelines obtained were from low- or middle-income countries.

CONCLUSIONS

Standardization of CPGs may improve clinical decision making around use of palivizumab in high-risk infants.

Bronchiolitis versus bronchopneumonia: navigating antibiotic use within the LRTI spectrum

Bronchiolitis, a common reason for infant hospitalisation in South Africa (SA), is caused by viral pathogens. Bronchiolitis is typically an illness of mild to moderate severity that occurs in well-nourished children. Hospitalised SA infants frequently have severe disease and/or coexisting medical conditions, and these cases of bronchiolitis may have bacterial co-infection that requires antibiotic therapy. However, the existence of widespread antimicrobial resistance in SA warrants the judicious use of antibiotics. This commentary describes: (i) common clinical pitfalls leading to an incorrect diagnosis of bronchopneumonia; and (ii) considerations for antibiotic therapy in hospitalised infants with bronchiolitis. If antibiotics are prescribed, the indication for their use should be clearly stated, and antibiotic therapy must be stopped promptly if investigations indicate that bacterial co-infection is unlikely. Until more robust data emerge, we recommend a pragmatic management strategy to inform antibiotic use in hospitalised SA infants with bronchiolitis in whom bacterial co-infection is suspected.

Airway Epithelial Cell Junctions as Targets for Pathogens and Antimicrobial Therapy

Intercellular contacts between epithelial cells are established and maintained by the apical junctional complexes (AJCs). AJCs conserve cell polarity and build epithelial barriers to pathogens, inhaled allergens, and environmental particles in the respiratory tract. AJCs consist of tight junctions (TJs) and adherens junctions (AJs), which play a key role in maintaining the integrity of the airway barrier. Emerging evidence has shown that different microorganisms cause airway barrier dysfunction by targeting TJ and AJ proteins. This review discusses the pathophysiologic mechanisms by which several microorganisms (bacteria and viruses) lead to the disruption of AJCs in airway epithelial cells. We present recent progress in understanding signaling pathways involved in the formation and regulation of cell junctions. We also summarize the potential chemical inhibitors and pharmacological approaches to restore the integrity of the airway epithelial barrier. Understanding the AJCs-pathogen interactions and mechanisms by which microorganisms target the AJC and impair barrier function may further help design therapeutic innovations to treat these infections.

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.

WHO preferred product characteristics for monoclonal antibodies for passive immunization against respiratory syncytial virus (RSV) disease in infants - Key considerations for global use

World Health Organization (WHO) preferred product characteristics describe preferences for product attributes that would help optimize value and use to address global public health needs, with a particular focus on low- and middle-income countries. Having previously published preferred product characteristics for both maternal and paediatric respiratory syncytial virus (RSV) vaccines, WHO recently published preferred product characteristics for monoclonal antibodies to prevent severe RSV disease in infants. This article summarizes the key attributes from the preferred product characteristics and discusses key considerations for future access and use of preventive RSV monoclonal antibodies.

Prefusion F Protein-Based Respiratory Syncytial Virus Immunization in Pregnancy

BACKGROUND

Respiratory syncytial virus (RSV), a major cause of illness and death in infants worldwide, could be prevented by vaccination during pregnancy. The efficacy, immunogenicity, and safety of a bivalent RSV prefusion F protein-based (RSVpreF) vaccine in pregnant women and their infants are uncertain.

METHODS

In a phase 2b trial, we randomly assigned pregnant women, at 24 through 36 weeks' gestation, to receive either 120 or 240 μg of RSVpreF vaccine (with or without aluminum hydroxide) or placebo. The trial included safety end points and immunogenicity end points that, in this interim analysis, included 50% titers of RSV A, B, and combined A/B neutralizing antibodies in maternal serum at delivery and in umbilical-cord blood, as well as maternal-to-infant transplacental transfer ratios.

RESULTS

This planned interim analysis included 406 women and 403 infants; 327 women (80.5%) received RSVpreF vaccine. Most postvaccination reactions were mild to moderate; the incidence of local reactions was higher among women who received RSVpreF vaccine containing aluminum hydroxide than among those who received RSVpreF vaccine without aluminum hydroxide. The incidences of adverse events in the women and infants were similar in the vaccine and placebo groups; the type and frequency of these events were consistent with the background incidences among pregnant women and infants. The geometric mean ratios of 50% neutralizing titers between the infants of vaccine recipients and those of placebo recipients ranged from 9.7 to 11.7 among those with RSV A neutralizing antibodies and from 13.6 to 16.8 among those with RSV B neutralizing antibodies. Transplacental neutralizing antibody transfer ratios ranged from 1.41 to 2.10 and were higher with nonaluminum formulations than with aluminum formulations. Across the range of assessed gestational ages, infants of women who were immunized had similar titers in umbilical-cord blood and similar transplacental transfer ratios.

CONCLUSIONS

RSVpreF vaccine elicited neutralizing antibody responses with efficient transplacental transfer and without evident safety concerns. (Funded by Pfizer; ClinicalTrials.gov number, NCT04032093.).

Clinical severity of RSV bronchiolitis

Background

Studies comparing the severity of respiratory syncytial virus (RSV) bronchiolitis to other viruses are inconclusive. Our study aimed to compare the severity of bronchiolitis according to the virus.

Methods

Data were collected from 1152 infants under one year of age admitted to Children's hospital for Wales, over the winter months of 2014-2020. The cohort was divided based on the virus detected: RSV, RSV with another virus, or other virus. Using t tests and Fisher exact statistical test, the groups were compared based on length of hospital stay, admissions PICU/HDU, intubations, and need of nasogastric (NG) nutritional support.

Results

Fifty-six percent throat swabs were RSV positive, 15% had RSV with another virus, and 29% had only another virus. Children positive for RSV had statistically longer hospital admissions and were more likely to need NG nutrition; however, there was no difference between number of PICU/HDU admissions or intubations. The RSV group and RSV with another virus group had no statistical differences.

Hospitalizations for Respiratory Syncytial Virus and Vaccine Preventable Infections following Pediatric Heart Transplantation

OBJECTIVE

To determine the risk factors for acquiring a respiratory syncytial virus (RSV) and vaccine-preventable infections (R/VPI) in pediatric heart transplant recipients and the associated morbidity and hospital resource use.

STUDY DESIGN

Patients <18 years who underwent heart transplantation from September 2003 to December 2018 at hospitals using the Pediatric Health Information System database were identified. Their transplant hospitalization and subsequent hospitalizations for R/VPI through December 2018 were analyzed. Risk factors for R/VPI hospitalizations were evaluated using negative regression binomial models adjusted for demographic and clinical confounders. Total hospital costs were adjusted for 2018 US$.

RESULTS

Of 3815 transplant recipients, 681 (17.9%) had an R/VPI hospitalization during 23 746 available person-years of follow-up. There were 984 R/VPIs diagnosed during 951 hospitalizations, and 440 (44.7%) occurred the first year after transplantation. The most common causes were RSV (n = 380; 38.6%), influenza (n = 265; 26.9%), and pneumococcus (n = 105; 10.7%). In adjusted analyses, there was an increased risk of R/VPI hospitalization in patients requiring mechanical circulatory support before transplantation, patients receiving induction with ≥2 immunosuppressive agents, and patients <2 years in the first year after transplantation. The median length of stay for an R/VPI hospitalization was 4 days (IQR, 2-8 days) with a median total cost of $11 081 (IQR, $6215-$24 322).

CONCLUSIONS

Hospitalization for R/VPIs occurred frequently after heart transplantation and were associated with significant costs. Potential strategies to minimize R/VPI include expanding vaccine use through accelerated immunization schedules, further studies of use of palivizumab beyond 2 years of age, and immunogenicity monitoring after vaccination with re-immunization based on guidelines.

The methyltransferase domain of the Respiratory Syncytial Virus L protein catalyzes cap N7 and 2'-O-methylation

Respiratory syncytial virus (RSV) is a negative sense single-stranded RNA virus and one of the main causes of severe lower respiratory tract infections in infants and young children. RSV RNA replication/transcription and capping are ensured by the viral Large (L) protein. The L protein contains a polymerase domain associated with a polyribonucleotidyl transferase domain in its N-terminus, and a methyltransferase (MTase) domain followed by the C-terminal domain (CTD) enriched in basic amino acids at its C-terminus. The MTase-CTD of Mononegavirales forms a clamp to accommodate RNA that is subsequently methylated on the cap structure and depending on the virus, on internal positions. These enzymatic activities are essential for efficient viral mRNA translation into proteins, and to prevent the recognition of uncapped viral RNA by innate immunity sensors. In this work, we demonstrated that the MTase-CTD of RSV, as well as the full-length L protein in complex with phosphoprotein (P), catalyzes the N7- and 2’-O-methylation of the cap structure of a short RNA sequence that corresponds to the 5’ end of viral mRNA. Using different experimental systems, we showed that the RSV MTase-CTD methylates the cap structure with a preference for N7-methylation as first reaction. However, we did not observe cap-independent internal methylation, as recently evidenced for the Ebola virus MTase. We also found that at μM concentrations, sinefungin, a S-adenosylmethionine analogue, inhibits the MTase activity of the RSV L protein and of the MTase-CTD domain. Altogether, these results suggest that the RSV MTase domain specifically recognizes viral RNA decorated by a cap structure and catalyzes its methylation, which is required for translation and innate immune system subversion.

Respiratory syncytial virus (RSV) is responsible of infant bronchiolitis and severe lower respiratory tract infections in infants and young children, and the leading cause of hospitalization in children under one year of age. However, we still lack a vaccine and therapeutics against this important pathogen. The main enzymatic activities involved in RSV propagation are embedded in the Large (L) protein that contains the polymerase domain and also all the activities required for RNA cap structure synthesis and methylation. These post-transcriptional RNA modifications play a key role in virus replication because cap N7-methylation is required for viral RNA translation into proteins, and 2’-O-methylation hides viral RNA from innate immunity detection. Viral methyltransferase (MTase) activities are now considered potential antiviral targets because their inhibition might limit the virus production and strengthen early virus detection by innate immunity sensors. In this work, we compared the enzymatic activities of the MTase expressed as a single domain or in the context of the full-length L protein. We demonstrated that the MTase protein catalyzes the specific methylation of the cap structure at both N7- and 2’-O-positions, and we obtained the proof of concept that a S-adenosylmethionine analogue can inhibit the MTase activity of the L protein.

Current State of Respiratory Syncytial Virus Disease and Management

Respiratory syncytial virus (RSV) is a major cause of hospitalizations due to pneumonia and bronchiolitis. Substantial morbidity and socioeconomic burden are associated with RSV infection worldwide. Populations with higher susceptibility to developing severe RSV include premature infants, children with chronic lung disease of prematurity (CLDP) or congenital heart disease (CHD), elderly individuals aged > 65 years, and immunocompromised individuals. In the pediatric population, RSV can lead to long-term sequelae such as wheezing and asthma, which are associated with increased health care costs and reduced quality of life. Treatment for RSV is mainly supportive, and general preventive measures such as good hygiene and isolation are highly recommended. Although vaccine development for RSV has been a global priority, attempts to date have failed to yield a safe and effective product for clinical use. Currently, palivizumab is the only immunoprophylaxis (IP) available to prevent severe RSV in specific high-risk pediatric populations. Well-controlled, randomized clinical trials have established the efficacy of palivizumab in reducing RSV hospitalization (RSVH) in high-risk infants including moderate- to late-preterm infants. However, the American Academy of Pediatrics (AAP), in its 2014 policy, stopped recommending RSV IP use for ≥ 29 weeks' gestational age infants. Revisions to the AAP policy for RSV IP have largely narrowed the proportion of pediatric patients eligible to receive RSV IP and have been associated with an increase in RSVH and morbidity. On the other hand, after reviewing the recent evidence on RSV burden, the National Perinatal Association, in its 2018 clinical practice guidelines, recommended RSV IP use for a wider pediatric population. As the AAP recommendations drive insurance reimbursements for RSV IP, they should be revised to help further mitigate RSV disease burden.

Molecular epidemiology of human respiratory syncytial virus (HRSV) in Iranian military trainees with acute respiratory symptoms in 2017

Background and Objectives

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection in many populations, including military recruits receiving basic training. Therefore, this study was set out to determine the molecular epidemiology, genotype and phylogenetic features of RSVs in patients with respiratory infection as a case study.

Materials and Methods

In this study, military barracks of Tehran, Iran, between January to March 2017 exposed to respiratory diseases were used for sampling. Throat swabs were taken, a reverse transcriptase-polymerase chain reaction (RTPCR) assay was performed to identify RSV and then the genotyping and phylogenetic analyses of RSVs in patients with a respiratory infection.

Results

Among 400 Iranian military trainees with respiratory symptoms, RSV infection was identified in 2.75% (11/400) using RT-PCR. Sequencing showed the incidence of type A (2.5%, n=10) to be much higher than type B (0.25%, n=1); Sore throat was the most common symptom among RSV patients. Phylogenetic analysis revealed that the majority of strains from the studied samples were more consistent with those from the Philippines and the US strains.

Conclusion

This study is the first to document RSV as a major cause of acute respiratory illness among military trainees in Iran. The prevalence of RSV is substantial in the cold season and the prevalence of genotype A is dominant in the country, leading to take essential steps in preparing a preventive vaccine against this viral infection.

Convergent structural features of respiratory syncytial virus neutralizing antibodies and plasticity of the site V epitope on prefusion F

Respiratory syncytial virus (RSV) is a global public health burden for which no licensed vaccine exists. To aid vaccine development via increased understanding of the protective antibody response to RSV prefusion glycoprotein F (PreF), we performed structural and functional studies using the human neutralizing antibody (nAb) RSB1. The crystal structure of PreF complexed with RSB1 reveals a conformational, pre-fusion specific site V epitope with a unique cross-protomer binding mechanism. We identify shared structural features between nAbs RSB1 and CR9501, elucidating for the first time how diverse germlines obtained from different subjects can develop convergent molecular mechanisms for recognition of the same PreF site of vulnerability. Importantly, RSB1-like nAbs were induced upon immunization with PreF in naturally-primed cattle. Together, this work reveals new details underlying the immunogenicity of site V and further supports PreF-based vaccine development efforts.

Respiratory syncytial virus (RSV) is a persistent, contagious seasonal pathogen and a serious public health threat. While infants are the most at-risk population, with infections potentially leading to bronchiolitis, adults, especially the elderly, are also burdened by RSV-induced respiratory infections. The only treatment currently available for RSV is passive immunization for high-risk infants. Thus, there is a critical need to develop a vaccine for the vast majority of the vulnerable population for which there is no preventative treatment. The RSV fusion protein in its prefusion form (PreF) is the target of the majority of naturally-induced neutralizing antibodies, and several clinical trials are currently evaluating PreF as a promising vaccine candidate. In this study, we solved the X-ray structure of PreF bound to the Fab fragment of a human neutralizing antibody. The structure reveals plasticity of the epitope, as well as a unique molecular signature for antibodies elicited towards this region of PreF. We also find that similar antibodies are induced upon immunization of naturally-primed cattle with a PreF vaccine antigen, suggesting that this epitope is highly immunogenic. These results will help us better understand the human immune response to RSV infection and vaccination, and guide future vaccine-design efforts.

Innate Type 2 Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a common and contagious virus that results in acute respiratory tract infections in infants. In many cases, the symptoms of RSV remain mild, however, a subset of individuals develop severe RSV-associated bronchiolitis. As such, RSV is the chief cause of infant hospitalization within the United States. Typically, the immune response to RSV is a type 1 response that involves both the innate and adaptive immune systems. However, type 2 cytokines may also be produced as a result of infection of RSV and there is increasing evidence that children who develop severe RSV-associated bronchiolitis are at a greater risk of developing asthma later in life. This review summarizes the contribution of a newly described cell type, group 2 innate lymphoid cells (ILC2), and epithelial-derived alarmin proteins that activate ILC2, including IL-33, IL-25, thymic stromal lymphopoietin (TSLP), and high mobility group box 1 (HMGB1). ILC2 activation leads to the production of type 2 cytokines and the induction of a type 2 response during RSV infection. Intervening in this innate type 2 inflammatory pathway may have therapeutic implications for severe RSV-induced disease.

Structure of the Respiratory Syncytial Virus Polymerase Complex

Numerous interventions are in clinical development for respiratory syncytial virus (RSV) infection, including small molecules that target viral transcription and replication. These processes are catalyzed by a complex comprising the RNA-dependent RNA polymerase (L) and the tetrameric phosphoprotein (P). RSV P recruits multiple proteins to the polymerase complex and, with the exception of its oligomerization domain, is thought to be intrinsically disordered. Despite their critical roles in RSV transcription and replication, structures of L and P have remained elusive. Here, we describe the 3.2-Å cryo-EM structure of RSV L bound to tetrameric P. The structure reveals a striking tentacular arrangement of P, with each of the four monomers adopting a distinct conformation. The structure also rationalizes inhibitor escape mutants and mutations observed in live-attenuated vaccine candidates. These results provide a framework for determining the molecular underpinnings of RSV replication and transcription and should facilitate the design of effective RSV inhibitors.

Overview of Current Therapeutics and Novel Candidates Against Influenza, Respiratory Syncytial Virus, and Middle East Respiratory Syndrome Coronavirus Infections

Emergence and re-emergence of respiratory virus infections represent a significant threat to global public health, as they occur seasonally and less frequently (such as in the case of influenza virus) as pandemic infections. Some of these viruses have been in the human population for centuries and others had recently emerged as a public health problem. Influenza viruses have been affecting the human population for a long time now; however, their ability to rapidly evolve through antigenic drift and antigenic shift causes the emergence of new strains. A recent example of these events is the avian-origin H7N9 influenza virus outbreak currently undergoing in China. Human H7N9 influenza viruses are resistant to amantadines and some strains are also resistant to neuraminidase inhibitors greatly limiting the options for treatment. Respiratory syncytial virus (RSV) may cause a lower respiratory tract infection characterized by bronchiolitis and pneumonia mainly in children and the elderly. Infection with RSV can cause severe disease and even death, imposing a severe burden for pediatric and geriatric health systems worldwide. Treatment for RSV is mainly supportive since the only approved therapy, a monoclonal antibody, is recommended for prophylactic use in high-risk patients. The Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly emerging respiratory virus. The virus was first recognized in 2012 and it is associated with a lower respiratory tract disease that is more severe in patients with comorbidities. No licensed vaccines or antivirals have been yet approved for the treatment of MERS-CoV in humans. It is clear that the discovery and development of novel antivirals that can be used alone or in combination with existing therapies to treat these important respiratory viral infections are critical. In this review, we will describe some of the novel therapeutics currently under development for the treatment of these infections.

Transient opening of trimeric prefusion RSV F proteins

The respiratory syncytial virus (RSV) F glycoprotein is a class I fusion protein that mediates viral entry and is a major target of neutralizing antibodies. Structures of prefusion forms of RSV F, as well as other class I fusion proteins, have revealed compact trimeric arrangements, yet whether these trimeric forms can transiently open remains unknown. Here, we perform structural and biochemical studies on a recently isolated antibody, CR9501, and demonstrate that it enhances the opening of prefusion-stabilized RSV F trimers. The 3.3 Å crystal structure of monomeric RSV F bound to CR9501, combined with analysis of over 25 previously determined RSV F structures, reveals a breathing motion of the prefusion conformation. We also demonstrate that full-length RSV F trimers transiently open and dissociate on the cell surface. Collectively, these findings have implications for the function of class I fusion proteins, as well as antibody prophylaxis and vaccine development for RSV.

Palivizumab Prophylaxis for Respiratory Syncytial Virus: Examining the Evidence Around Value

Respiratory syncytial virus (RSV) infection is the most common cause of lower respiratory tract infection and the leading cause of hospitalization among young children, incurring high annual costs among US children under the age of 5 years. Palivizumab has been found to be effective in reducing hospitalization and preventing serious lower respiratory tract infections in high-risk infants. This paper presents a systematic review of the cost-effectiveness studies of palivizumab and describes the main highlights of a round table discussion with clinical, payer, economic, research method, and other experts. The objectives of the discussion were to (1) review the current state of clinical, epidemiology, and economic data related to severe RSV disease; (2) review new cost-effectiveness estimates of RSV immunoprophylaxis in US preterm infants, including a review of the field’s areas of agreement and disagreement; and (3) identify needs for further research.

Respiratory syncytial virus seasonality and its implications on prevention strategies

With maternal and infant vaccines against respiratory syncytial virus (RSV) in development, it is timely to consider how the deployment of these vaccines might vary according to local RSV disease seasonality. In temperate regions RSV infection is predictably limited to a period of 3 to 5 months, while in tropical regions disease seasonality is often both more variable and more prolonged. Accordingly, in tropical regions a year-round immunisation schedule for both maternal and infant immunisation might be appropriate. In contrast, in temperate regions the benefit of year-round maternal immunisation would be heavily dependent on the duration of protection this provided, potentially necessitating a strategy directed at children due to be born in the months immediately prior to the RSV season. This review will consider the impact of seasonality on maternal and infant immunisation strategies against RSV, and the potential of an alternative approach of passive immunisation for all infants immediately prior to the RSV season.