Vaccine development for respiratory syncytial virus

Utility of the Neonatal Calf Model for Testing Vaccines and Intervention Strategies for Use against Human RSV Infection

Respiratory syncytial virus (RSV) is a significant cause of pediatric respiratory tract infections. It is estimated that two-thirds of infants are infected with RSV during the first year of life and it is one of the leading causes of death in this age group worldwide. Similarly, bovine RSV is a primary viral pathogen in cases of pneumonia in young calves and plays a significant role in bovine respiratory disease complex. Importantly, naturally occurring infection of calves with bovine RSV shares many features in common with human RSV infection. Herein, we update our current understanding of RSV infection in cattle, with particular focus on similarities between the calf and human infection, and the recent reports in which the neonatal calf has been employed for the development and testing of vaccines and therapeutics which may be applied to hRSV infection in humans.

Respiratory Viral Infections in Transplant Recipients

Respiratory viral infections (RVIs) are common among the general population; however, these often mild viral illnesses can lead to serious morbidity and mortality among recipients of hematopoietic stem cell and solid organ transplantation. The disease spectrum ranges from asymptomatic or mild infections to life-threatening lower respiratory tract infection or long-term airflow obstruction syndromes. Progression to lower respiratory tract infection or to respiratory failure is determined by the intrinsic virulence of the specific viral pathogen as well as various host factors, including the type of transplantation, status of the host’s immune dysfunction, the underlying disease, and other comorbidities. This chapter focuses on the epidemiology, clinical manifestations, diagnosis, and management of RVIs in this susceptible population and includes respiratory syncytial virus, parainfluenza virus, human metapneumovirus, influenza virus, human coronavirus, and human rhinovirus. The optimal management of these infections is limited by the overall paucity of available treatment, highlighting the need for new antiviral drug or immunotherapies.

Innate Immune Cell Suppression and the Link With Secondary Lung Bacterial Pneumonia

Secondary infections arise as a consequence of previous or concurrent conditions and occur in the community or in the hospital setting. The events allowing secondary infections to gain a foothold have been studied for many years and include poor nutrition, anxiety, mental health issues, underlying chronic diseases, resolution of acute inflammation, primary immune deficiencies, and immune suppression by infection or medication. Children, the elderly and the ill are particularly susceptible. This review is concerned with secondary bacterial infections of the lung that occur following viral infection. Using influenza virus infection as an example, with comparisons to rhinovirus and respiratory syncytial virus infection, we will update and review defective bacterial innate immunity and also highlight areas for potential new investigation. It is currently estimated that one in 16 National Health Service (NHS) hospital patients develop an infection, the most common being pneumonia, lower respiratory tract infections, urinary tract infections and infection of surgical sites. The continued drive to understand the mechanisms of why secondary infections arise is therefore of key importance.

The respiratory syncytial virus vaccine landscape: lessons from the graveyard and promising candidates

The global burden of disease caused by respiratory syncytial virus (RSV) is increasingly recognised, not only in infants, but also in older adults (aged ≥65 years). Advances in knowledge of the structural biology of the RSV surface fusion glycoprotein have revolutionised RSV vaccine development by providing a new target for preventive interventions. The RSV vaccine landscape has rapidly expanded to include 19 vaccine candidates and monoclonal antibodies (mAbs) in clinical trials, reflecting the urgency of reducing this global health problem and hence the prioritisation of RSV vaccine development. The candidates include mAbs and vaccines using four approaches: (1) particle-based, (2) live-attenuated or chimeric, (3) subunit, (4) vector-based. Late-phase RSV vaccine trial failures highlight gaps in knowledge regarding immunological protection and provide lessons for future development. In this Review, we highlight promising new approaches for RSV vaccine design and provide a comprehensive overview of RSV vaccine candidates and mAbs in clinical development to prevent one of the most common and severe infectious diseases in young children and older adults worldwide.

Infants Harness the Germline against RSV

In this issue of Immunity, Goodwin et al. (2018) offer hope for an RSV vaccine for young infants by demonstrating that RSV infection in very young infants induces neutralizing antibodies that are close to the germline and have unusual epitope specificity.

Evolution of Human Respiratory Syncytial Virus (RSV) over Multiple Seasons in New South Wales, Australia

There is an ongoing global pandemic of human respiratory syncytial virus (RSV) infection that results in substantial annual morbidity and mortality. In Australia, RSV is a major cause of acute lower respiratory tract infections (ALRI). Nevertheless, little is known about the extent and origins of the genetic diversity of RSV in Australia, nor the factors that shape this diversity. We have conducted a genome-scale analysis of RSV infections in New South Wales (NSW). RSV genomes were successfully sequenced for 144 specimens collected between 2010⁻2016. Of these, 64 belonged to the RSVA and 80 to the RSVB subtype. Phylogenetic analysis revealed a wide diversity of RSV lineages within NSW and that both subtypes evolved rapidly in a strongly clock-like manner, with mean rates of approximately 6⁻8 × 10^-4 nucleotide substitutions per site per year. There was only weak evidence for geographic clustering of sequences, indicative of fluid patterns of transmission within the infected population and no evidence of any clustering by patient age such that viruses in the same lineages circulate through the entire host population. Importantly, we show that both subtypes circulated concurrently in NSW with multiple introductions into the Australian population in each year and only limited evidence for multi-year persistence.

Characterization of circulating RSV strains among subjects in the OUTSMART-RSV surveillance program during the 2016-17 winter viral season in the United States

Background

Respiratory syncytial virus (RSV) is an established cause of serious lower respiratory disease in infants, elderly and high-risk populations. The OUTSMART surveillance program aims to characterize patient populations and currently circulating RSV strains, and monitor temporal and geographic evolution of RSV F and G proteins in the U.S.

Methods

The OUTSMART 2016–17 study collected RSV-positive samples from 25 RSVAlert^® laboratories from 4 U.S. regions and Puerto Rico during November 2016 through March 2017. Frequencies of A and B subtypes and genotypes were determined for several demographic and geographic variables. To gauge the representativeness of the OUTSMART patients, results were compared to discharge data from the NEDS and NIS databases.

Results

A total of 1,041 RSV-positive samples with associated demographic data were obtained and the RSV F gene and second variable region of the G gene were sequenced. The majority of samples (76.0%) came from children under 2 years old: <1 year (48.4%), 1–2 years (27.6%). The OUTSMART patient sample was similar to NEDS and NIS for age, gender, and geographic location. Both OUTSMART and national RSV cases peaked in January. Of OUTSMART samples, 45.3% were subtype A, 53.7% were subtype B and 1.0% were mixed A and B. The percentage of RSV B cases increased with increasing age. Hospitalization (length of hospital stay, LOS, >24 hrs) occurred in 29.0% of patients of which 52.0% had RSV B. Outpatients (LOS <24 hrs) were 64.4% of total of which 73.3% were diagnosed in the ER and discharged, while only 6% were diagnosed in other outpatient settings.

Conclusions

The OUTSMART 2016–17 study was representative of the U.S. RSV experience. Geographic and temporal information from the RSV surveillance program will be used to establish a molecular baseline of RSV F and G sequence variability and to help inform development of novel agents for RSV prophylaxis and treatment.

A Respiratory Syncytial Virus Vaccine Based on the Small Hydrophobic Protein Ectodomain Presented With a Novel Lipid-Based Formulation Is Highly Immunogenic and Safe in Adults: A First-in-Humans Study

Background

Respiratory syncytial virus infection can cause lower respiratory tract infection in older adults comparable to influenza, but no vaccines are available.

Methods

This was a randomized, observer-blinded, first-in-humans study of a novel synthetic RSV antigen based on the ectodomain of the small hydrophobic glycoprotein (SHe) of RSV subgroup A, formulated with either the lipid and oil-based vaccine platform DepoVax (DPX-RSV[A]) or alum (RSV[A]-Alum), in healthy, 50-64-year-old individuals. Two dose levels (10 or 25 µg) of SHe with each formulation were compared to placebo. A booster dose was administered on day 56.

Results

There was no indication that the vaccine was unsafe. Mild pain, drowsiness, and muscles aches were the most common solicited adverse events (AEs), and the frequencies of the AEs did not increase after dose 2. Robust anti-SHe-specific immune responses were demonstrated in the DPX-RSV(A) 10-μg and 25-μg groups (geometric mean titer, approximately 10-fold and 100-fold greater than that of placebo at days 56 and 236, respectively), and responses were sustained in the DPX-RSV(A) 25-μg group at day 421. Responses to the RSV(A)-Alum vaccines were very low.

Conclusions

A novel antigen from the SH protein of RSV, formulated in a lipid and oil-based vaccine platform, was highly immunogenic, with sustained antigen-specific antibody responses, and had an acceptable safety profile.

Respiratory virus prophylaxis in congenital heart disease

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections and causes up to 200,000 infant deaths a year worldwide. The average rate of hospitalization for severe RSV infection is 5 per 1000 children, and the rate is three-times higher in those with congenital heart disease (CHD). Palivizumab, a monoclonal antibody, reduces hospitalization rates and intensive care admissions. It is used prophylactically and is administered as monthly doses during the RSV season. Hemodynamically unstable CHD is the most susceptible CHD to a severe episode of RSV infection. This review explores current evidence surrounding therapies, patterns of infection and identifies groups which may still be vulnerable to severe RSV infection.

Human respiratory syncytial virus: pathogenesis, immune responses, and current vaccine approaches

Respiratory syncytial virus continues to pose a serious threat to the pediatric populations worldwide. With a genomic makeup of 15,200 nucleotides, the virus encodes for 11 proteins serving as envelope spikes, inner envelope proteins, and non-structural and ribonucleocapsid complexes. The fusion (F) and attachment (G) surface glycoproteins are the key targets for neutralizing antibodies. The highly variable G with altered glycosylations and the conformational alternations of F create challenges for vaccine development. The metastable F protein is responsible for RSV-host cell fusion and thus infectivity. Novel antigenic sites were identified on this form following its stabilization and solving its crystal structure. Importantly, site ø displays neutralizing activity exceeding those of post-F-specific and shared antigenic sites, such as site II which is the target for Palivizumab therapeutic antibody. Induction of high neutralizing antibody responses by pre-F immunization in animal models promoted it as a major vaccine candidate. Since RSV infection is more serious at age extremities and in individuals with undermining health conditions, vaccines are being developed to target these populations. Infants below three months of age have a suppressive immune system, making vaccines' immunogenicity weak. Therefore, a suggested strategy to protect newborns from RSV infection would be through passive immunity of maternal antibodies. Hence, pregnant women at their third trimester have been selected as an ideal target for vaccination with RSV pre-F vaccine. This review summarizes the different modes of RSV pathogenesis and host's immune response to the infection, and illustrates on the latest updates of vaccine development and vaccination approaches.

Neonatal Immunization: Rationale, Current State, and Future Prospects

Infections take their greatest toll in early life necessitating robust approaches to protect the very young. Here, we review the rationale, current state, and future research directions for one such approach: neonatal immunization. Challenges to neonatal immunization include natural concern about safety as well as a distinct neonatal immune system that is generally polarized against Th1 responses to many stimuli such that some vaccines that are effective in adults are not in newborns. Nevertheless, neonatal immunization could result in high-population penetration as birth is a reliable point of healthcare contact, and offers an opportunity for early protection of the young, including preterm newborns who are deficient in maternal antibodies. Despite distinct immunity and reduced responses to some vaccines, several vaccines have proven safe and effective at birth. While some vaccines such as polysaccharide vaccines have little effectiveness at birth, hepatitis B vaccine can prime at birth and requires multiple doses to achieve protection, whereas the live-attenuated Bacille Calmette-Guérin (BCG), may offer single shot protection, potentially in part via heterologous ("non-specific") beneficial effects. Additional vaccines have been studied at birth including those directed against pertussis, pneumococcus, Haemophilus influenza type B and rotavirus providing important lessons. Current areas of research in neonatal vaccinology include characterization of early life immune ontogeny, heterogeneity in and heterologous effects of BCG vaccine formulations, applying systems biology and systems serology, in vitro platforms that model age-specific human immunity and discovery and development of novel age-specific adjuvantation systems. These approaches may inform, de-risk, and accelerate development of novel vaccines for use in early life. Key stakeholders, including the general public, should be engaged in assessing the opportunities and challenges inherent to neonatal immunization.

Infants Infected with Respiratory Syncytial Virus Generate Potent Neutralizing Antibodies that Lack Somatic Hypermutation

Respiratory syncytial virus (RSV) is a leading cause of infant mortality, and there are currently no licensed vaccines to protect this vulnerable population. A comprehensive understanding of infant antibody responses to natural RSV infection would facilitate vaccine development. Here, we isolated more than 450 RSV fusion glycoprotein (F)-specific antibodies from 7 RSV-infected infants and found that half of the antibodies recognized only two antigenic sites. Antibodies targeting both sites showed convergent sequence features, and structural studies revealed the molecular basis for their recognition of RSV F. A subset of antibodies targeting one of these sites displayed potent neutralizing activity despite lacking somatic mutations, and similar antibodies were detected in RSV-naive B cell repertoires, suggesting that expansion of these B cells in infants may be possible with suitably designed vaccine antigens. Collectively, our results provide fundamental insights into infant antibody responses and a framework for the rational design of age-specific RSV vaccines.

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

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

Vaccines We Need But Don't Have

Vaccinations have had tremendous success in the 20th century. However, in the 21st century, we are facing complex immunological issues in relation to controlling underlying infectious diseases. Therefore, new technologies are needed to develop vaccines against infectious diseases like respiratory syncytial virus, human immunodeficiency virus, and cytomegalovirus. In addition, recent emerging infections have taught us that we must prepare preventative measures in advance using our scientific abilities.

Role of viral infections in the development and exacerbation of asthma in children

Viral infections are closely linked to wheezing illnesses in children of all ages. Respiratory syncytial virus (RSV) is the main causative agent of bronchiolitis, whereas rhinovirus (RV) is most commonly detected in wheezing children thereafter. Severe respiratory illness induced by either of these viruses is associated with subsequent development of asthma, and the risk is greatest for young children who wheeze with RV infections. Whether viral illnesses actually cause asthma is the subject of intense debate. RSV-induced wheezing illnesses during infancy influence respiratory health for years. There is definitive evidence that RSV-induced bronchiolitis can damage the airways to promote airway obstruction and recurrent wheezing. RV likely causes less structural damage and yet is a significant contributor to wheezing illnesses in young children and in the context of asthma. For both viruses, interactions between viral virulence factors, personal risk factors (eg, genetics), and environmental exposures (eg, airway microbiome) promote more severe wheezing illnesses and the risk for progression to asthma. In addition, allergy and asthma are major risk factors for more frequent and severe RV-related illnesses. Treatments that inhibit inflammation have efficacy for RV-induced wheezing, whereas the anti-RSV mAb palivizumab decreases the risk of severe RSV-induced illness and subsequent recurrent wheeze. Developing a greater understanding of personal and environmental factors that promote more severe viral illnesses might lead to new strategies for the prevention of viral wheezing illnesses and perhaps reduce the subsequent risk for asthma.

Respiratory syncytial virus (RSV) entry is inhibited by serine protease inhibitor AEBSF when present during an early stage of infection

Background

Host proteases have been shown to play important roles in many viral activities such as entry, uncoating, viral protein production and disease induction. Therefore, these cellular proteases are putative targets for the development of antivirals that inhibit their activity. Host proteases have been described to play essential roles in Ebola, HCV, HIV and influenza, such that specific protease inhibitors are able to reduce infection. RSV utilizes a host protease in its replication cycle but its potential as antiviral target is unknown. Therefore, we evaluated the effect of protease inhibitors on RSV infection.

Methods

To measure the sensitivity of RSV infection to protease inhibitors, cells were infected with RSV and incubated for 18 h in the presence or absence of the inhibitors. Cells were fixed, stained and studied using fluorescence microscopy.

Results

Several protease inhibitors, representing different classes of proteases (AEBSF, Pepstatin A, E-64, TPCK, PMSF and aprotinin), were tested for inhibitory effects on an RSV A2 infection of HEp-2 cells. Different treatment durations, ranging from 1 h prior to inoculation and continuing for 18 h during the assay, were evaluated. Of all the inhibitors tested, AEBSF and TPCK significantly decreased RSV infection. To ascertain that the observed effect of AEBSF was not a specific feature related to HEp-2 cells, A549 and BEAS-2B cells were also used. Similar to HEp-2, an almost complete block in the number of RSV infected cells after 18 h of incubation was observed and the effect was dose-dependent. To gain insight into the mechanism of this inhibition, AEBSF treatment was applied during different phases of an infection cycle (pre-, peri- and post-inoculation treatment). The results from these experiments indicate that AEBSF is mainly active during the early entry phase of RSV. The inhibitory effect was also observed with other RSV isolates A1998/3–2 and A2000/3–4, suggesting that this is a general feature of RSV.

Conclusion

RSV infection can be inhibited by broad serine protease inhibitors, AEBSF and TPCK. We confirmed that AEBSF inhibition is independent of the cell line used or RSV strain. The time point at which treatment with the inhibitor was most potent, was found to coincide with the expected moment of entry of the virion with the host cell.