Prefusion F, Postfusion F, G Antibodies, and Disease Severity in Infants and Young Children With Acute Respiratory Syncytial Virus Infection

Antibody levels against respiratory syncytial virus fusion protein conformations and lack of association with life-threatening infection in previously healthy infants

BACKGROUND

Humoral immune response against the pre-fusion (pre-F) conformation of respiratory syncytial virus (RSV) F protein has been proposed to play a protective role against infection. An RSV pre-F maternal vaccine has been recently approved in several countries to protect young infants against RSV. We aimed to assess serum IgG titers against the pre-F and post-F conformations of RSV F protein and their association with life-threatening RSV disease (LTD) in previously healthy infants.

METHODS

A prospective cohort study including hospitalized infants <12 months with a first RSV infection was conducted during 2017-2019. Patients with LTD required intensive care and mechanical respiratory assistance. RSV pre-F exclusive and post-F antibody responses were determined by post-F competition and non-competition immunoassays, respectively, and neutralizing activity was measured by plaque reduction neutralization test.

RESULTS

Fifty-eight patients were included; the median age was 3.5 months and 41 % were females. Fifteen patients developed LTD. RSV F-specific antibody titers positively correlated with neutralizing antibody titers in acute and convalescent phases but, importantly, they did not associate with LTD. Acute RSV pre-F exclusive and post-F IgG titers negatively correlated with patient age (P = 0.0007 and P < 0.0001), while a positive correlation was observed between the fold changes in RSV F-specific antibody titers between convalescent and acute phase and patient age (P = 0.0014 and P < 0.0001). Infants ≤2 months exhibited significantly lower fold-changes in RSV F-specific and neutralizing antibody titers between convalescence and acute phase than older infants. Additionally, acute RSV antibody titers showed no correlation with nasal RSV load and, furthermore, nasal viral load was not associated with the development of LTD.

CONCLUSIONS

This study highlights that protection against life-threatening RSV disease is not necessarily antibody-dependent. Further characterization of the immune response against RSV and its role in protection against severe disease is important for the development of the safest possible preventive strategies.

RSV Neutralizing Antibodies Following Nirsevimab and Palivizumab Dosing

BACKGROUND

Data describing respiratory syncytial virus (RSV) neutralizing antibody (nAb) levels for nirsevimab, a recently approved, extended half-life, anti-RSV fusion protein (F protein) monoclonal antibody, relative to the previous standard of care, palivizumab, have not been reported.

METHODS

MEDLEY was a randomized, palivizumab-controlled, phase 2/3 study of nirsevimab during 2 RSV seasons (season 1 and 2) in infants born preterm (≤35 weeks' gestational age; dosed season 1 only) or with congenital heart disease or chronic lung disease of prematurity (dosed seasons 1 and 2). Participants were randomly assigned to receive a single dose of nirsevimab followed by 4 monthly placebo doses, or 5 once-monthly doses of palivizumab. Anti-RSV F protein serology (ie, levels of prefusion [pre-F]/postfusion [post-F] conformation antibodies), nirsevimab and palivizumab concentrations, and RSV nAbs were measured in participant serum collected at baseline (pre-dose) and days 31, 151, and 361.

RESULTS

Serologic data were similar in seasons 1 and 2. Nirsevimab predominately conferred pre-F antibodies, whereas palivizumab conferred pre-F and post-F antibodies. Nirsevimab and palivizumab serum concentrations highly correlated with nAb levels in both seasons. In season 1, nAb levels in nirsevimab recipients were highest in day 31 samples and gradually declined but remained 17-fold above baseline at day 361. nAb levels in palivizumab recipients increased incrementally with monthly doses to day 151. nAb levels followed similar patterns in season 2. nAb levels were ∼10-fold higher with nirsevimab compared with palivizumab across both seasons.

CONCLUSIONS

Nirsevimab prophylaxis confers ∼10-fold higher and more sustained RSV nAb levels relative to palivizumab.

Serum and mucosal antibody-mediated protection and identification of asymptomatic respiratory syncytial virus infection in community-dwelling older adults in Europe

Introduction

Respiratory syncytial virus (RSV) causes acute respiratory tract infection (ARTI) and reinfects adults throughout life, posing a risk for hospitalization in older adults (>60 years) with frailty and comorbidities.

Methods

To investigate serum and mucosal antibodies for protection against RSV infections, baseline serum samples were compared for RSV-pre- and -post-fusion (F) binding, and RSV-A2 neutralizing IgG antibodies between symptomatic RSV-ARTI (N = 30), non-RSV (RSV negative) ARTI (N = 386), and no ARTI (N = 338). Mucosal RSV-pre-F IgA and IgG levels, as well as serum RSV-G IgG antibodies, were analyzed to determine their association with protection from symptomatic RSV-ARTI in a subset study.

Results

Using a receiver operating characteristic (ROC) analysis, we established thresholds of 1.4- to 1.6-fold change (FC) for RSV-pre-F and -post-F, and RSV-A2 neutralizing IgG antibodies, respectively, enabling the identification of asymptomatic RSV cases with high sensitivity and specificity (>80% and >90%, respectively). As a result, serum RSV-pre-F, RSV-G IgG, and mucosal pre-F binding IgA antibodies showed correlations with protection against symptomatic RSV infection. RSV-pre-F IgG antibodies were correlated with protection from RSV infections irrespective of the symptoms.

Discussion

This study provides insights into antibody-mediated protection for symptomatic RSV infection in a community-dwelling older-adult population and establishes a threshold to identify asymptomatic RSV infection using a data-driven approach.

Respiratory Syncytial Virus in Pregnancy: An Obstetrics View

Respiratory syncytial virus (RSV) represents one of the most prevalent causes of lower respiratory tract infection in newborns and children by the time they are two years old, with a peak rate of hospitalization in those between two and three months of age and a high risk of morbidity and mortality, especially under the age of six months of life [...].

Bovine Respiratory Syncytial Virus Nanovaccine Induces Long-Lasting Humoral Immunity in Mice

With limited therapies and vaccines available, human respiratory syncytial virus (HRSV) has a significant negative health impact on all age groups but particularly on infants, young children, and older adults. Bovine respiratory syncytial virus (BRSV) is pathogenically and antigenically similar to HRSV. Building upon previous studies using a BRSV nanovaccine coencapsulating multiple proteins, this work demonstrates the development and comparative evaluation of a coencapsulated nanovaccine to a cocktail nanovaccine formulation composed of polyanhydride nanoparticles encapsulating BRSV postfusion (F) glycoprotein and CpG ODN 1668 coadjuvant delivered simultaneously with nanoparticles encapsulating BRSV attachment glycoprotein (G) and CpG ODN 1668. These nanovaccine formulations were administered to C57BL/6 mice by one of two prime-boost regimens (i.e., intranasal/intranasal or intranasal/subcutaneous) followed by assessment of humoral immunity. The cocktail nanovaccine induced sustained anti-F and anti-G serum IgG antibody responses for 12 weeks postprimary immunization. Using polyanhydride particles to deliver G protein in a prime-boost regime also significantly induced serum anti-G antibodies compared to protein and coadjuvant alone. Serum IgG induced by the nanovaccine demonstrated virus-neutralizing capability from 42 to 119 days postprimary immunization. Further, anti-F IgG antibodies were detected in the bronchoalveolar lavage fluid of vaccinated animals. Finally, the nanovaccine induced long-lived anti-F antibody secreting plasma cells that were detectable in the bone marrow 205 days postprimary immunization. Overall, the BRSV nanovaccine(s) successfully induced long-lived humoral immune responses capable of virus neutralization, making this a promising vaccine candidate for further evaluation in other relevant animal models.

Antibody-mediated protection against respiratory syncytial virus in children

Respiratory syncytial virus (RSV) is a major global pathogen, causing lower respiratory tract disease in at-risk populations including young children. Antibodies form a crucial layer of protection from RSV disease, particularly in immunologically naïve infants. Such antibodies are derived from the mother via transplacental transfer and breast milk, but may be particularly low in high-risk infants such as those born preterm. Maternally derived antibodies can now be supplemented by the administration of anti-RSV monoclonal antibodies, while a rising wave of maternal and paediatric vaccine strategies are approaching. The implementation of these prophylactics may profoundly decrease the healthcare burden of RSV. In this article, we review the role of antibody-mediated immunity in protecting children from RSV. We focus on maternally derived antibodies as the main source of protection against RSV and study factors that influence the scale of this transfer. The role of passive and active prophylactic approaches in protecting infants against RSV are discussed and knowledge gaps in our understanding of antibody-mediated protection against RSV are identified.

Respiratory Syncytial Virus among People Living with HIV: Is There a Case for Rolling Out Prophylaxis? A Viewpoint Based on a Systematic Review

Respiratory Syncytial Virus (RSV) is responsible for a considerable burden of respiratory disease among children and older adults. Several prophylactic strategies have recently been introduced. We review the available evidence on the interplay between RSV infection and HIV, looking at the specific role of RSV prophylactic strategies in individuals affected by or exposed to HIV. We conducted a systematic review on the association between HIV infection and RSV incidence and severity. We searched in PubMed/MEDLINE for clinical epidemiological studies covering outcomes such as RSV-associated illness, severity, and mortality in individuals affected by or exposed to HIV. A total of 36 studies met the inclusion criteria and were included, the majority conducted in sub-Saharan Africa. There was no compelling evidence suggesting a higher incidence of RSV illness among HIV-infected people. A higher risk of severe disease was consistent among both HIV-positive and HIV-exposed but uninfected (HEU) children. Case fatality rates were also higher for these groups. Evidence on a differing risk among adults was scarce. HIV-positive pregnant women should be given priority for recently approved RSV vaccination, for protection of their newborns. HIV-infected and HEU infants should be considered risk groups for nirsevimab prophylaxis in their first year of life and possibly beyond.

Antibody responses to respiratory syncytial virus: a population-based cross-sectional serological study in Southern China, 2021

OBJECTIVES

With remarkable progress in the field of respiratory syncytial virus (RSV) prophylaxis, it is critical to understand population immunity against RSV. We aim to describe the RSV pre-F IgG antibodies across all age groups in Southern China and to evaluate the risk factors associated with lower antibody levels.

METHODS

We performed a community-based cross-sectional sero-epidemiological study in Anhua County, Hunan Province, Southern China, from July 15, 2021, to November 5, 2021. Serum samples were tested for IgG antibodies against the RSV prefusion F (pre-F) protein using an enzyme-linked immunosorbent assay. We estimated the geometric mean titres (GMTs) and seropositivity rates across all age groups. The generalized linear models were built to identify factors associated with antibody levels.

RESULTS

A total of 890 participants aged 4 months to older than 89 years were enrolled. The lowest RSV pre-F IgG GMTs were observed in infants and toddlers aged 4 months to younger than 2 years (3.0; 95% CI, 2.6-3.5). With increasing age, the RSV pre-F IgG GMT increased to 4.3 (95% CI, 4.1-4.4) between the ages of 2 and younger than 5 years and then stabilized at high levels throughout life. All the children had serological evidence of RSV infection by the age of 5 years. Age was associated with RSV pre-F antibody levels in children, with an estimated 1.9-fold (95% CI, 0.8-3.6) increase in titre per year before 5 years of age, although it was not significantly associated with antibody levels in adults aged older than 60 years.

DISCUSSION

Our findings could provide a comprehensive understanding of the gaps in RSV immunity at the population level and inform the prioritization of immunization platforms.

Passive Immunization Strategies to Prevent Severe Respiratory Syncytial Virus Infection Among Newborns and Young Infants

Newborns and young infants are at risk for severe respiratory syncytial virus (RSV) lower respiratory tract infection. Passive immunity is the mainstay of infection prevention in this cohort. Transplacental transfer of maternal antibodies provides the newborn with immediate protection from life-threatening infections, however, is dependent upon gestational age, birth weight, mother's age, recent maternal vaccination, maternal nutritional status, maternal immunocompetence and medical conditions, and placental integrity. Efficient transplacental transfer of RSV-neutralizing antibodies have led to the development and approval of maternal RSV immunization for the protection of the newborn. Additionally, administration of RSV-specific antibodies to infants leads to high serum titers of RSV-neutralizing antibodies and further protection from severe disease.

RSV Prevention Within Reach for Older Infants and Toddlers: The Role of Active Immunization

This review article will summarize the vaccines and monoclonal antibodies currently under evaluation for the prevention of RSV disease in older infants, toddlers and young children. We will review the rationale for passive protection during the first months of life, and the role of active immunization afterwards, either with live attenuated, protein-based or mRNA vaccines.

ATP-P2X7R pathway activation limits the Tfh cell compartment during pediatric RSV infection

Background

Follicular helper T cells (Tfh) are pivotal in B cell responses. Activation of the purinergic receptor P2X7 on Tfh cells regulates their activity. We investigated the ATP-P2X7R axis in circulating Tfh (cTfh) cells during Respiratory Syncytial Virus (RSV) infection.

Methods

We analyzed two cohorts: children with RSV infection (moderate, n=30; severe, n=21) and healthy children (n=23). We utilized ELISA to quantify the levels of PreF RSV protein-specific IgG antibodies, IL-21 cytokine, and soluble P2X7R (sP2X7R) in both plasma and nasopharyngeal aspirates (NPA). Additionally, luminometry was employed to determine ATP levels in plasma, NPA and supernatant culture. The frequency of cTfh cells, P2X7R expression, and plasmablasts were assessed by flow cytometry. To evaluate apoptosis, proliferation, and IL-21 production by cTfh cells, we cultured PBMCs in the presence of Bz-ATP and/or P2X7R antagonist (KN-62) and a flow cytometry analysis was performed.

Results

In children with severe RSV disease, we observed diminished titers of neutralizing anti-PreF IgG antibodies. Additionally, severe infections, compared to moderate cases, were associated with fewer cTfh cells and reduced plasma levels of IL-21. Our investigation revealed dysregulation in the ATP-P2X7R pathway during RSV infection. This was characterized by elevated ATP levels in both plasma and NPA samples, increased expression of P2X7R on cTfh cells, lower levels of sP2X7R, and heightened ATP release from PBMCs upon stimulation, particularly evident in severe cases. Importantly, ATP exposure decreased cTfh proliferative response and IL-21 production, while promoting their apoptosis. The P2X7R antagonist KN-62 mitigated these effects. Furthermore, disease severity positively correlated with ATP levels in plasma and NPA samples and inversely correlated with cTfh frequency.

Conclusion

Our findings indicate that activation of the ATP-P2X7R pathway during RSV infection may contribute to limiting the cTfh cell compartment by promoting cell death and dysfunction, ultimately leading to increased disease severity.

Longitudinal humoral analysis in RSV-infected infants identifies pre-existing RSV strain-specific G and evolving cross-reactive F antibodies

Respiratory syncytial virus (RSV) is among the most common causes of lower respiratory tract infection (LRTI) and hospitalization in infants. However, the mechanisms of immune control in infants remain incompletely understood. Antibody profiling against attachment (G) and fusion (F) proteins in children less than 2 years of age, with mild (outpatients) or severe (inpatients) RSV disease, indicated substantial age-dependent differences in RSV-specific immunity. Maternal antibodies were detectable for the first 3 months of life, followed by a long window of immune vulnerability between 3 and 6 months and a rapid evolution of FcγR-recruiting immunity after 6 months of age. Acutely ill hospitalized children exhibited lower G-specific antibodies compared with healthy controls. With disease resolution, RSV-infected infants generated broad functional RSV strain-specific G-responses and evolved cross-reactive F-responses, with minimal maternal imprinting. These data suggest an age-independent RSV G-specific functional humoral correlate of protection, and the evolution of RSV F-specific functional immunity with disease resolution.

Exacerbated lung inflammation in offspring with high maternal antibody levels following secondary RSV exposure

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis-related hospitalizations among children under 5 years of age, with reinfection being common throughout life. Maternal vaccination has emerged as a promising strategy, delivering elevated antibody levels to newborns for immediate protection. However, limited research has explored the protective efficacy of maternal antibodies (matAbs) against secondary RSV infections in offspring. To address this gap, we employed a mouse model of maternal RSV vaccination and secondary infection of offspring to evaluate lung pathology following RSV reinfection in mice with varying levels of maternal antibody (matAb). Additionally, we aimed to investigate the potential causes of exacerbated lung inflammation in offspring with high matAb levels following secondary RSV exposure. Our findings revealed that offspring with elevated levels of maternal pre-F antibody demonstrated effective protection against lung pathology following the initial RSV infection. However, this protection was compromised upon reinfection, manifesting as heightened weight loss, exacerbated lung pathology, increased expression of RSV-A N genes, eosinophilia, enhanced IL-5, IL-13, MUC5AC, and eosinophils Major Basic Protein (MBP) production in lung tissue compared to offspring lacking matAbs. Importantly, these unexpected outcomes were not attributed to antibody-dependent enhancement (ADE) resulting from declining matAb levels over time. Notably, our findings showed a decline in secretory IgA (sIgA), mucosal IgA, and mucosal IgG levels in offspring with high matAb levels post-primary RSV challenge. We propose that this decline may be a critical factor contributing to the ineffective protection observed during secondary RSV exposure. Overall, these findings offer valuable insights into maternal vaccination against RSV, contributing to a comprehensive understanding and mitigation of potential risks associated with maternal RSV vaccination.

Understanding New Recommendations for Respiratory Syncytial Virus Prevention in Pregnancy

Respiratory syncytial virus (RSV) is a significant cause of infant morbidity and mortality worldwide with peak hospitalization rates for RSV-mediated illnesses between 2 and 3 months of life. Until very recently, prevention strategies for RSV involved primarily passive immunization of neonates at high risk with monoclonal antibodies and promotion of breastfeeding. The Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices now recommends passive immunization of all neonates with monoclonal antibodies during RSV season, and the American Association of Pediatrics has endorsed this practice. The U.S. Food and Drug Administration (FDA) recently approved a vaccination for RSV in pregnancy. The CDC's Advisory Committee on Immunization Practices has recently recommended RSV vaccination for all pregnant patients between 32 and 36 weeks of gestation who are anticipated to deliver during RSV season if they are not planning nirsevimab for their infants. This recommendation has been endorsed by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine. In this clinical perspective, we review the scientific evidence, potential concerns, challenges, and future considerations for RSV vaccination in pregnancy.

Engineered dityrosine-bonding of the RSV prefusion F protein imparts stability and potency advantages

Viral fusion proteins facilitate cellular infection by fusing viral and cellular membranes, which involves dramatic transitions from their pre- to postfusion conformations. These proteins are among the most protective viral immunogens, but they are metastable which often makes them intractable as subunit vaccine targets. Adapting a natural enzymatic reaction, we harness the structural rigidity that targeted dityrosine crosslinks impart to covalently stabilize fusion proteins in their native conformations. We show that the prefusion conformation of respiratory syncytial virus fusion protein can be stabilized with two engineered dityrosine crosslinks (DT-preF), markedly improving its stability and shelf-life. Furthermore, it has 11X greater potency as compared with the DS-Cav1 stabilized prefusion F protein in immunogenicity studies and overcomes immunosenescence in mice with simply a high-dose formulation on alum.

A tale of two fusion proteins: understanding the metastability of human respiratory syncytial virus and metapneumovirus and implications for rational design of uncleaved prefusion-closed trimers

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) cause human respiratory diseases and are major targets for vaccine development. In this study, we designed uncleaved prefusion-closed (UFC) trimers for the fusion (F) proteins of both viruses by examining mutations critical to F metastability. For RSV, we assessed four previous prefusion F designs, including the first and second generations of DS-Cav1, SC-TM, and 847A. We then identified key mutations that can maintain prefusion F in a native-like, closed trimeric form (up to 76%) without introducing any interprotomer disulfide bond. For hMPV, we developed a stable UFC trimer with a truncated F2-F1 linkage and an interprotomer disulfide bond. Tens of UFC constructs were characterized by negative-stain electron microscopy (nsEM), x-ray crystallography (11 RSV-F and one hMPV-F structures), and antigenic profiling. Using an optimized RSV-F UFC trimer as bait, we identified three potent RSV neutralizing antibodies (NAbs) from a phage-displayed human antibody library, with a public NAb lineage targeting sites Ø and V and two cross-pneumovirus NAbs recognizing site III. In mouse immunization, rationally designed RSV-F and hMPV-F UFC trimers induced robust antibody responses with high neutralizing titers. Our study provides a foundation for future prefusion F-based RSV and hMPV vaccine development.

Development and comparison of immunologic assays to detect primary RSV infections in infants

Effective respiratory syncytial virus (RSV) vaccines have been developed and licensed for elderly adults and pregnant women but not yet for infants and young children. The RSV immune state of the young child, i.e., previously RSV infected or not, is important to the conduct and interpretation of epidemiology studies and vaccine clinical trials. To address the need for sensitive assays to detect immunologic evidence of past infection, we developed, characterized, and evaluated 7 assays including 4 IgG antibody enzyme immunoassays (EIAs), two neutralizing antibody assays, and an IFN-γ EliSpot (EliSpot) assay. The four IgG EIAs used a subgroup A plus subgroup B RSV-infected Hep-2 cell lysate antigen (Lysate), an expressed RSV F protein antigen (F), an expressed subgroup A G protein antigen (Ga), or an expressed subgroup B G protein (Gb) antigen. The two neutralizing antibody assays used either a subgroup A or a subgroup B RSV strain. The EliSpot assay used a sucrose cushion purified combination of subgroup A and subgroup B infected cell lysate. All seven assays had acceptable repeatability, signal against control antigen, lower limit of detection, and, for the antibody assays, effect of red cell lysis, lipemia and anticoagulation of sample on results. In 44 sera collected from children >6 months after an RSV positive illness, the lysate, F, Ga and Gb IgG EIAs, and the subgroup A and B neutralizing antibody assays, and the EliSpot assays were positive in 100%, 100%, 86%, 95%, 43%, and 57%, respectively. The Lysate and F EIAs were most sensitive for detecting RSV antibody in young children with a documented RSV infection. Unexpectedly, the EliSpot assay was positive in 9/15 (60%) of PBMC specimens from infants not exposed to an RSV season, possibly from maternal microchimerism. The Lysate and F EIAs provide good options to reliably detect RSV antibodies in young children for epidemiologic studies and vaccine trials.

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

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

Increased innate immune activation induces protective RSV-specific lung-resident memory T cells in neonatal mice

Young infants frequently experience respiratory tract infections, yet vaccines designed to provide mucosal protection are lacking. Localizing pathogen-specific cellular and humoral immune responses to the lung could provide improved immune protection. We used a well-characterized murine model of respiratory syncytial virus (RSV) to study the development of lung-resident memory T cells (TRM) in neonatal compared to adult mice. We demonstrated that priming with RSV during the neonatal period failed to retain RSV-specific clusters of differentiation (CD8) TRM 6 weeks post infection, in contrast to priming during adulthood. The reduced development of RSV-specific TRM was associated with poor acquisition of two key markers of tissue residence: CD69 and CD103. However, by augmenting both innate immune activation and antigen exposure, neonatal RSV-specific CD8 T cells increased expression of tissue-residence markers and were maintained in the lung at memory time points. Establishment of TRM correlated with more rapid control of the virus in the lungs upon reinfection. This is the first strategy to effectively establish RSV-specific TRM in neonates providing new insight into neonatal memory T cell development and vaccine strategies.

Prenatal exposure to RSV season influences first-year risk of RSV lower respiratory illness and RSV-specific immune responses assessed at birth

Maternal-to-fetal transmission of respiratory syncytial virus (RSV) has been shown to occur but whether late prenatal exposure to RSV season influences offspring postnatal RSV-lower respiratory illness (LRI) risk in early life or RSV immune status at birth is unclear. In this study, the duration of third trimester RSV season exposure was determined for 1,094 newborns of the Tucson Children's Respiratory Study (TCRS) and found to show an inverse relation to risk for first RSV-LRI in the first year. Cord blood anti-RSV antibody is related to third trimester RSV season exposure but not to first year RSV-LRI risk. In a separate birth cohort (the Infant Immune Study), supernatants from cord blood mononuclear cells stimulated with the recall antigen, UV-inactivated RSV, were assayed for IFN-γ and IL-4. The frequency of detectable IFN-γ (but not IL-4) was increased for those with at least 2 mo of third trimester RSV season exposure, suggestive of a fetal immune response to RSV. IMPORTANCE Our study found that duration of third trimester exposure to RSV season related inversely to subsequent risk of postnatal RSV-LRI in the first year, thus implicating this exposure as an important factor in reducing risk of postnatal RSV-LRIs, a risk reduction that appears to be independent of maternally transferred anti-RSV antibody level. The increase in frequency of detectable IFN-γ and not IL-4 in response to UV-inactivated RSV in cord blood immune cells for infants with greater third trimester exposure to RSV season is suggestive of a Type-1 immune response to RSV occurring in utero.

Respiratory Syncytial Virus Infection Among Hospitalized Infants in Four Middle-Income Countries

BACKGROUND

Understanding respiratory syncytial virus (RSV) global epidemiology is important to inform future prevention strategies.

METHODS

Hospitalized infants <1-year-old with acute illness were enrolled prospectively in Albania, Jordan, Nicaragua, and Philippines during respiratory seasons in 2015-2017. Medical chart review, parental interview, and post-discharge follow up were conducted. Respiratory specimens were tested using real-time RT-PCR for RSV. Infant characteristics associated with very severe illness (intensive care unit [ICU] admission or receipt of supplemental oxygen) were assessed using logistic regression to adjust for potential confounders (age, sex, study site, and preterm birth).

RESULTS

Of 3634 enrolled hospitalized infants, 1129 (31%) tested positive for RSV. The median age of RSV-positive infants was 2.7 (IQR: 1.4-6.1) months and 665 (59%) were male. Very severe illness in 583 (52%) RSV-positive infants was associated with younger age (aOR 4.1, 95% CI: 2.6-6.5 for 0-2 compared to 9-11-months; P < .01), low weight-for-age z-score (aOR 1.9, 95% CI: 1.2-2.8; P < .01), ICU care after birth (aOR 1.6, 95% CI: 1.0-2.5; P = .048), and cesarean delivery (aOR 1.4, 95% CI: 1.0-1.8; P = .03). RSV subgroups A and B co-circulated at all sites with alternating predominance by year; subgroup was not associated with severity (aOR 1.0, 95% CI: 0.8-1.4). Nine (0.8%) RSV-positive infants died during admission or within ≤30 days of discharge, of which 7 (78%) were <6-months-old.

CONCLUSIONS

RSV was associated with nearly a third of infant acute illness hospitalizations in four middle-income countries during the respiratory season, where, in addition to young age, factors including low weight-for-age might be important predictors of severity. RSV prevention strategies targeting young infants could substantially reduce RSV-associated hospitalizations in middle-income countries.

A Pseudovirus-Based Entry Assay to Evaluate Neutralizing Activity against Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) infection can cause life-threatening pneumonia and bronchiolitis, posing a significant threat to human health worldwide, especially to children and the elderly. Currently, there is no specific treatment for RSV infection. The most effective measures for preventing RSV infection are vaccines and prophylactic medications. However, not all population groups are eligible for the approved vaccines or antibody-based preventive medications. Therefore, there is an urgent need to develop novel vaccines and prophylactic drugs available for people of all ages. High-throughput assays that evaluate the efficacy of viral entry inhibitors or vaccine-induced neutralizing antibodies in blocking RSV entry are crucial for evaluating vaccine and prophylactic drug candidates. We developed an efficient entry assay using a lentiviral pseudovirus carrying the fusion (F) protein of type A or B RSV. In addition, the essential parameters were systematically optimized, including the number of transfected plasmids, storage conditions of the pseudovirus, cell types, cell numbers, virus inoculum, and time point of detection. Furthermore, the convalescent sera exhibited comparable inhibitory activity in this assay as in the authentic RSV virus neutralization assay. We established a robust pseudovirus-based entry assay for RSV, which holds excellent promise for studying entry mechanisms, evaluating viral entry inhibitors, and assessing vaccine-elicited neutralizing antibodies against RSV.

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

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

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.

Structural interrogation of a trimeric prefusion RSV fusion protein vaccine candidate by a camelid nanobody

In the past decade, camelid nanobodies have been developed for multiple applications, including immuno-imaging, cancer immunotherapy, and antiviral therapeutics. Despite the prevalence of these approaches, nanobodies have rarely been used to assess the potency of vaccine antigen candidates, which are primarily based on mAb binding approaches. In this work, we demonstrate that a nanobody-based ELISA method is suitable for characterization of a leading respiratory syncytial virus (RSV) vaccine candidate, RSVPreF3. This nanobody, F-VHH-L66, compares similarly with AM14, an antibody well-known to be specific for the prefusion form of the RSV surface fusion glycoprotein, RSV F. ELISA assays based on F-VHH-L66 were specific for the trimeric, prefusion form of RSV F, the antigen conformation that best generates neutralizing antibodies. Additionally, the F-VHH-L66-based ELISA proved accurate, linear, and stability-indicating. Statistical analysis of 65 independent F-VHH-L66-based ELISA experiments indicated assay performance similar to that of ELISA assays based on AM14. Moreover, the binding kinetics of F-VHH-L66 to RSVPreF3 are comparable to those of AM14 when measured by surface plasmon resonance (SPR). Finally, F-VHH-L66 neutralized RSV(A) with similar efficacy as AM14; this bioactivity data further supports its use as an alternative to AM14 for pre-fusion specific structural characterization of RSVPreF3.

RSV A2-Based Prefusion F Vaccine Candidates Induce RSV A and RSV B Cross Binding and Neutralizing Antibodies and Provide Protection against RSV A and RSV B Challenge in Preclinical Models

RSV is divided into two antigenic subtypes, RSV A and RSV B, which is largely based on the variation in the G protein, while the fusion protein F is more conserved and a target for antibody-mediated neutralization. Here we evaluate the breadth of the protective immune responses across RSV A and RSV B subtypes, induced by vaccines based on the RSV A-based fusion protein, stabilized in the prefusion conformation (preF) in preclinical models. Immunization of naïve cotton rats with preF subunit or preF encoded by a replication incompetent Adenoviral 26, induced antibodies capable of neutralizing recent RSV A and RSV B clinical isolates, as well as protective efficacy against a challenge with RSV A and RSV B strains. Similarly, induction of cross-neutralizing antibodies was observed after immunization with Ad26-encoded preF, preF protein or a mix of both (Ad26/preF protein) in RSV pre-exposed mice and African Green Monkeys. Transfer of serum of human subjects immunized with Ad26/preF protein into cotton rats provide protection against challenges with both RSV A and RSV B, with complete protection against both strains observed in the lower respiratory tract. In contrast, almost no protection against RSV A and B infection was observed after the transfer of a human serum pool isolated pre-vaccination. These results collectively show that the RSV A-based monovalent Ad26/preF protein vaccine induced neutralizing antibodies, as well as protection against both RSV A and RSV B subtypes in animals, including by passive transfer of human antibodies alone, suggesting that clinical efficacy against both subtypes can be achieved.

Virus-like Particle Vaccine Expressing the Respiratory Syncytial Virus Pre-Fusion and G Proteins Confers Protection against RSV Challenge Infection

Respiratory syncytial virus (RSV) causes severe lower respiratory tract disease in children and the elderly. However, there are no effective antiviral drugs or licensed vaccines available for RSV infection. Here, RSV virus-like particle (VLP) vaccines expressing Pre-F, G, or Pre-F and G proteins on the surface of influenza virus matrix protein 1 (M1) were produced using the baculovirus expression system, and their protective efficacy was evaluated in mice. The morphology and successful assembly of VLPs were confirmed by transmission electron microscope (TEM) and Western blot. High levels of serum IgG antibody response were detected in VLP-immunized mice, and significantly higher levels of IgG2a and IgG2b were found in the Pre-F+G VLP immunization group compared to the unimmunized control. Serum-neutralizing activity was higher in the VLP immunization groups compared to the naïve group, with Pre-F+G VLPs demonstrating superior neutralizing activity to the single antigen-expressing VLP groups. Pulmonary IgA and IgG responses were generally comparable across the immunization groups, with VLPs expressing the Pre-F antigen eliciting higher IFN-γ in spleens. The frequencies of eosinophils and IL-4-producing CD4+ T cell populations were substantially lower in the lungs of VLP-immunized mice, with the PreF+G vaccine inducing a significant increase in CD4+ and CD8+ T cells. VLP immunization significantly decreased the viral titer and inflammation in the lungs of mice, with Pre-F+G VLPs conferring the best protection. In conclusion, our present study suggests that the Pre-F+G VLPs could be a potential vaccine candidate against RSV infection.

The Quest for a Respiratory Syncytial Virus Vaccine for Older Adults: Thinking beyond the F Protein

Respiratory syncytial virus (RSV) is a common cause of paediatric respiratory tract infection and causes a significant health burden in older adults. Natural immunity to RSV is incomplete, permitting recurrent symptomatic infection over an individual's lifespan. When combined with immunosenescence, this increases older adults' susceptibility to more severe disease symptoms. As RSV prophylaxis is currently limited to infants, older adults represent an important target population for RSV vaccine development. The relationship between RSV and our immune systems is complex, and these interactions require deeper understanding to tailor an effective vaccine candidate towards older adults. To date, vaccine candidates targeting RSV antigens, including pre-F, F, G (A), G (B), M2-1, and N, have shown efficacy against RSV infection in older adults in clinical trial settings. Although vaccine candidates have demonstrated robust neutralising IgG and cellular responses, it is important that research continues to investigate the RSV immune response in order to further understand how the choice of antigenic target site may impact vaccine effectiveness. In this article, we discuss the Phase 3 vaccine candidates being tested in older adults and review the hurdles that must be overcome to achieve effective protection against RSV.

mRNA vaccines: The future of prevention of viral infections?

Messenger RNA (mRNA) vaccines against COVID-19 are the first authorized biological preparations developed using this platform. During the pandemic, their administration has been proven to be a life-saving intervention. Here, we review the main advantages of using mRNA vaccines, identify further technological challenges to be met during the development of the mRNA platform, and provide an update on the clinical progress on leading mRNA vaccine candidates against different viruses that include influenza viruses, human immunodeficiency virus 1, respiratory syncytial virus, Nipah virus, Zika virus, human cytomegalovirus, and Epstein-Barr virus. The prospects and challenges of manufacturing mRNA vaccines in low-income countries are also discussed. The ongoing interest and research in mRNA technology are likely to overcome some existing challenges for this technology (e.g., related to storage conditions and immunogenicity of some components of lipid nanoparticles) and enhance the portfolio of vaccines against diseases for which classical formulations are already authorized. It may also open novel pathways of protection against infections and their consequences for which no safe and efficient immunization methods are currently available.

Antibody Correlates of Protection From Severe Respiratory Syncytial Virus Disease in a Vaccine Efficacy Trial

Background

Respiratory syncytial virus (RSV) can cause serious lung infections in young children and there is currently no available vaccine.

Methods

We used complementary statistical frameworks to analyze 4 RSV serology measurements in mothers and their infants in South Africa who participated in a phase 3 maternal immunization trial of an RSV F protein nanoparticle vaccine as correlates of risk and of protection against different RSV disease endpoints.

Results

We found evidence to support each antibody measurement-encompassing RSV-neutralizing antibodies and F surface glycoprotein-binding antibodies-as an inverse correlate of risk of RSV-associated acute lower respiratory tract infection with severe hypoxia in at least 1 framework, with vaccine-induced fold-rise from the maternal enrollment to day 14 samples of anti-F immunoglobulin G (IgG) binding antibodies having the most consistent evidence. This evidence includes a significant association of fold-rise anti-F IgG with vaccine efficacy (VE); achieving a baseline covariate-adjusted VE of 75% requires a vaccine-induced maternal anti-F IgG fold-rise of around 16. Neither multivariable logistic regression nor superlearning analyses showed benefit to including multiple time points or assays in the same model, suggesting a parsimonious correlate. Post hoc exploratory analyses supported adherence of vaccine-induced maternal anti-F IgG fold-rise to the Prentice criteria for a valid surrogate endpoint.

Conclusions

Our results suggest that the vaccine induced protective anti-F antibody responses. If this finding is confirmed, VE could potentially be augmented by increasing these responses.

A prefusion-stabilized RSV F subunit vaccine elicits B cell responses with greater breadth and potency than a postfusion F vaccine

There is currently no licensed vaccine for respiratory syncytial virus (RSV). Here, we assess the effect of RSV fusion protein (F) conformation on B cell responses in a post hoc comparison of samples from the DS-Cav1 [prefusion (pre-F)] and MEDI7510 [postfusion (post-F)] vaccine clinical trials. We compared the magnitude and quality of the serological and B cell responses across time points and vaccines. We measured RSV A and B neutralization, F-binding immunoglobulin G titers, and competition assays at week 0 (before vaccination) and week 4 (after vaccination) to evaluate antibody specificity and potency. To compare B cell specificity and activation, we used pre-F and post-F probes in tandem with a 17-color immunophenotyping flow cytometry panel at week 0 (before vaccination) and week 1 (after vaccination). Our data demonstrate that both DS-Cav1 and MEDI7510 vaccination robustly elicit F-specific antibodies and B cells, but DS-Cav1 elicited antibodies that more potently neutralized both RSV A and B. The superior potency was mediated by antibodies that bind antigenic sites on the apex of pre-F that are not present on post-F. In the memory (CD27+) B cell compartment, vaccination with DS-Cav1 or MEDI7510 elicited B cells with different epitope specificities. B cells preferentially binding the pre-F probe were activated in DS-Cav1-vaccinated participants but not in MEDI7510-vaccinated participants. Our findings emphasize the importance of using pre-F as an immunogen in humans because of its deterministic role in eliciting highly potent neutralizing antibodies and memory B cells.

Virus-like particles containing a prefusion-stabilized F protein induce a balanced immune response and confer protection against respiratory syncytial virus infection in mice

Respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children worldwide. Currently, no licensed RSV vaccines are available. In this study, we explored stable prefusion conformation virus-like particles (Pre-F VLPs) as RSV vaccine candidates. RSV fusion (F) protein mutants were constructed to form stabilized Pre-F or postfusion (Post-F) configurations. VLPs containing Pre-F or Post-F protein were generated using a recombinant baculovirus (rBV)-insect cell expression system. The assembly and immunological properties of Pre-F or Post-F VLPs were investigated. Pre-F and Post-F VLPs contained antigenic sites Ø and I of pre- and postfusion conformations, respectively. Compared with Post-F VLPs, immunization with Pre-F VLPs elicited upregulation of IFN-γ, IL-2 and IL-10 and downregulation of IL-4 and IL-5 cytokine production in mice. A high percentage of CD25⁺ Foxp3⁺ cells or a low percentage of IL-17A-producing cells among CD4⁺ T cells was observed in the lungs of mice vaccinated with Pre-F VLPs. Importantly, immunization with Pre-F VLPs induced a high level of RSV neutralizing antibody and a balanced immune response, which protected mice against RSV infection without evidence of immunopathology. Our results suggested that Pre-F VLPs generated from rBV-insect cells represent promising RSV vaccine candidates.

Enhancing Anti-G Antibody Induction by a Live Single-Cycle Prefusion F-Expressing RSV Vaccine Improves In Vitro and In Vivo Efficacy

The human respiratory syncytial virus (RSV) is a major cause of severe respiratory tract disease, and a vaccine is not available. We previously reported a novel live vaccine expressing prefusion-stabilized fusion protein (preF) in place of the native F protein (RSV-preFΔCT). As preF is non-functional, RSV-preFΔCT was amplified in a production line expressing a functional substitute, and exhibited a single-cycle replication phenotype, which holds several unique potential advantages. RSV-preFΔCT prevented shedding and lung pathology after viral challenge in mice, but induced low levels of anti-attachment protein (G) antibodies (Abs). Given the significant contributions of anti-G Abs toward disease prevention, we generated modifications to RSV-preFΔCT in an effort to induce higher anti-G Ab levels. The Ab levels were monitored after the prime-boost vaccination of mice with modified vaccines. The most successful modification for enhancing induced anti-G Abs was seen with the placement of G in the first genome position. This vaccine also reduced the pathology after challenge with a high dose of wt RSV, and outperformed the sera from wt RSV-vaccinated mice in in vitro neutralization. Thus, raising the anti-G Ab levels induced by RSV-preFΔCT enhanced efficacy in vitro and in vivo, and constitutes an important next step in developing a live, single-cycle, efficacious vaccine for the human population.

Level of maternal antibodies against respiratory syncytial virus (RSV) nucleoprotein at birth and risk of RSV very severe lower respiratory tract infection

BACKGROUND

The nucleoprotein (N protein) of respiratory syncytial virus (RSV) is a candidate antigen for new RSV vaccine development. The aim of the present study was to investigate the association between maternal antibody titers against the RSV N protein at birth and the newborns' risk of developing very severe lower respiratory tract infection (VS-LRTI).

METHODS

In this single-center prospective cohort study, 578 infants born during the RSV epidemic season in France were included. Among these, 36 were hospitalized for RSV VS-LRTI. A generalized linear model was used to test the occurrence of a VS-LRTI in function of sex, mode of delivery, parity of the mother, type of pregnancy, date of birth in relation to the peak of the epidemic, and antibody titer against N protein.

RESULTS

All cord blood samples had detectable antibodies against N protein. The mean titers were significantly lower in newborns with risk factors for RSV severe LRTI (preterm infants, birth before the peak epidemic, multiparous mother). There was no association between antibody titer against the N protein and a protection against VS-LRTI.

CONCLUSIONS

Further studies are needed to support the hypothesis that transfer of maternal antibodies against the RSV N protein can provide a significant immune protection early in infancy and that N protein candidate vaccine may be a suitable target for maternal vaccine.

Codon-optimization of the respiratory syncytial virus (RSV) G protein expressed in a vesicular stomatitis virus (VSV) vector improves immune responses in a cotton rat model

Respiratory syncytial virus is an important cause of pneumonia in children, the elderly, and immunocompromised individuals. The attachment (G) protein of RSV generates neutralizing antibodies in natural RSV infection which correlate with protection against disease. The immune response to RSV is typically short-lived, which may be related to the heavy glycosylation of RSV-G. In order to improve its immunogenicity, we expressed G protein mutants in a vesicular stomatitis virus (VSV) vector system and tested their ability to protect cotton rats from RSV challenge. We found that the most protective construct was codon-optimized RSV-G, followed by wild-type G and membrane-bound G. Constructs which expressed the G protein with reduced glycosylation or the secreted G protein provided either partial or no protection. Our results demonstrate that modifications to the G protein are not advantageous in a VSV vector system, and that an intact, codon-optimized G is a superior vaccine candidate.

Structure-Based Design and Antigenic Validation of Respiratory Syncytial Virus G Immunogens

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease of children, the elderly, and immunocompromised individuals. Currently, there are no FDA-approved RSV vaccines. The RSV G glycoprotein is used for viral attachment to host cells and impairment of host immunity by interacting with the human chemokine receptor CX3CR1. Antibodies that disrupt this interaction are protective against infection and disease. Nevertheless, development of an RSV G vaccine antigen has been hindered by its low immunogenicity and safety concerns. A previous study described three engineered RSV G proteins containing single-point mutations that induce higher levels of IgG antibodies and have improved safety profiles compared to wild-type RSV G (H. C. Bergeron, J. Murray, A. M. Nuñez Castrejon, et al., Viruses 13:352, 2021, https://doi.org/10.3390/v13020352). However, it is unclear if the mutations affect RSV G protein folding and display of its conformational epitopes. In this study, we show that the RSV G S177Q protein retains high-affinity binding to protective human and mouse monoclonal antibodies and has equal reactivity as wild-type RSV G protein to human reference immunoglobulin to RSV. Additionally, we determined the high-resolution crystal structure of RSV G S177Q protein in complex with the anti-RSV G antibody 3G12, further validating its antigenic structure. These studies show for the first time that an engineered RSV G protein with increased immunogenicity and safety retains conformational epitopes to high-affinity protective antibodies, supporting its further development as an RSV vaccine immunogen. IMPORTANCE Respiratory syncytial virus (RSV) causes severe lower respiratory diseases of children, the elderly, and immunocompromised populations. There currently are no FDA-approved RSV vaccines. Most vaccine development efforts have focused on the RSV F protein, and the field has generally overlooked the receptor-binding antigen RSV G due to its poor immunogenicity and safety concerns. However, single-point mutant RSV G proteins have been previously identified that have increased immunogenicity and safety. In this study, we investigate the antibody reactivities of three known RSV G mutant proteins. We show that one mutant RSV G protein retains high-affinity binding to protective monoclonal antibodies, is equally recognized by anti-RSV antibodies in human sera, and forms the same three-dimensional structure as the wild-type RSV G protein. Our study validates the structure-guided design of the RSV G protein as an RSV vaccine antigen.

Maternal vaccination: a review of current evidence and recommendations

Maternal vaccination is an effective means of protecting pregnant women, their fetuses, and infants from vaccine-preventable infections. Despite the availability of sufficient safety data to support the use of vaccines during pregnancy, maternal immunization remains an underutilized method of disease prevention, often because of concerns from both healthcare providers and pregnant women about vaccine safety. Such concerns have been reflected in the low uptake of the COVID-19 vaccine among pregnant women seen in many parts of the world. Here, we present an update of the current recommendations for the use of vaccines during pregnancy, including the evidence supporting the use of novel vaccine platforms. We also provide an overview of the data supporting the use of COVID-19 vaccines in pregnancy and an update of the status of vaccines that are currently under development for use in pregnant women.

Protein and Peptide Substances in the Treatment of Respiratory Syncytial Infection: Current State

Respiratory syncytial virus infection (RSVI) is an acute medical and social problem in many countries globally. Infection is most dangerous for infants under one year old and the elderly. Despite its epidemiological relevance, only two drugs are registered for clinical use against RSVI: ribavirin (approved in a limited number of countries due to side effects) and palivizumab (Synagis), which is intended only for the prevention, but not the treatment, of infection. Currently, various research groups are searching for new drugs against RSV, with three main areas of research: small molecules, polymeric drugs (proteins and peptides), and plant extracts. This review is devoted to currently developed protein and peptide anti-RSV drugs.

A systems genomics approach uncovers molecular associates of RSV severity

Respiratory syncytial virus (RSV) infection results in millions of hospitalizations and thousands of deaths each year. Variations in the adaptive and innate immune response appear to be associated with RSV severity. To investigate the host response to RSV infection in infants, we performed a systems-level study of RSV pathophysiology, incorporating high-throughput measurements of the peripheral innate and adaptive immune systems and the airway epithelium and microbiota. We implemented a novel multi-omic data integration method based on multilayered principal component analysis, penalized regression, and feature weight back-propagation, which enabled us to identify cellular pathways associated with RSV severity. In both airway and immune cells, we found an association between RSV severity and activation of pathways controlling Th17 and acute phase response signaling, as well as inhibition of B cell receptor signaling. Dysregulation of both the humoral and mucosal response to RSV may play a critical role in determining illness severity.

This paper presents a novel approach to understanding the localized molecular responses to respiratory syncytial virus (RSV) and the system-level correlates of clinical outcomes. To do this, we developed a novel statistical method able to integrate high dimensional molecular data characterizing the host airway microbota and immune and nasal gene expression. We show that this integrative approach facilitates superior performance in estimating clinical outcome as opposed to any single data type. Using this approach, we identified both cell type-specific and shared biomarkers and regulatory pathways associated with RSV severity. Specifically, we identified an association between RSV severity, activation of pathways controlling Th17, and inhibition of B cell receptor signaling, which were present in both the site of infection airway and in peripheral immune cells. These results can guide future efforts to identify biomarkers for identifying or predicting illness severity following infant RSV infection. They may also be useful as biomarkers to inform the efficacy of future interventions (e.g., therapies) or preventative measures to suppress the rate of severe disease (e.g., vaccines).

Immunopathology of RSV: An Updated Review

RSV is a leading cause of respiratory tract disease in infants and the elderly. RSV has limited therapeutic interventions and no FDA-approved vaccine. Gaps in our understanding of virus-host interactions and immunity contribute to the lack of biological countermeasures. This review updates the current understanding of RSV immunity and immunopathology with a focus on interferon responses, animal modeling, and correlates of protection.

Risk of Transmission and Viral Shedding From the Time of Infection for Respiratory Syncytial Virus in Households

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection worldwide, but reports of temporal changes in the risk of transmission among close contacts has been scarce. This study aimed to examine an association between the viral load trajectory and transmission risk to develop a better control strategy for the disease spread. We conducted a household-based prospective cohort study in Biliran Province, the Philippines, and enrolled 451 participants to observe the development of acute respiratory infection. Including the cases found at the health-care facility, we analyzed the data of viral loads with symptom records obtained from 172 followed participants who had household member positive for RSV with a rapid test during an RSV outbreak in 2018-2019. We developed a model estimating a temporal change in the viral shedding from the infection and evaluated transmission dynamics. We found that most transmission events occurred within approximately 7 days of the household exposure, including potential presymptomatic transmissions. The inferred risk of infection among those younger than 5 years was 3.5 times higher than that of those older than 5 years. This finding suggested that the initial week after the household exposure is particularly important for preventing RSV spread.

New preventive strategies for respiratory syncytial virus infection in children

Respiratory syncytial virus (RSV) infections result in significant morbidity and mortality for young children worldwide. The development of preventive strategies for RSV has faced different challenges, including the legacy of the first vaccine attempt, and an incomplete understanding of the host immune response to the virus. However, promising preventive strategies against RSV are in the pipeline and their development has advanced rapidly in the past decade due in part to our improved knowledge about the structural conformation of key RSV proteins. These strategies include monoclonal antibodies and different vaccines platforms directed towards the main target populations.

Coexpression of respiratory syncytial virus (RSV) fusion (F) protein and attachment glycoprotein (G) in a vesicular stomatitis virus (VSV) vector system provides synergistic effects against RSV infection in a cotton rat model

Respiratory syncytial virus (RSV) is one of the most important causes of respiratory disease in infants, immunocompromised individuals, and the elderly. Natural infection does not result in long-term immunity, and there is no licensed vaccine. Vesicular stomatitis virus (VSV) is a commonly used vaccine vector platform against infectious diseases, and has been used as a vector for a licensed Ebola vaccine. In this study, we expressed the RSV fusion (F) protein, the RSV F protein stabilized in either a pre-fusion or a post-fusion configuration, the attachment glycoprotein (G), or the G and F proteins of RSV in combination in a VSV vector. Cotton rats were immunized with these recombinants intranasally or subcutaneously to test immunogenicity. RSV F stabilized in either a pre-fusion or a post-fusion configuration proved to be poorly immunogenic and protective when compared to unmodified F. RSV G provided partial protection and moderate levels of neutralizing antibody production, both of which improved with intranasal administration compared to subcutaneous inoculation. The most successful vaccine vector was VSV expressing both the G and F proteins after intranasal inoculation. Immunization with this recombinant induced neutralizing antibodies and provided protection from RSV challenge in the upper and lower respiratory tract for at least 80 days. Our results demonstrate that co-expression of F and G proteins in a VSV vector provides synergistic effects in inducing RSV-specific neutralizing antibodies and protection against RSV infection.

A Systematic Review and Meta-analysis of Animal Studies Investigating the Relationship Between Serum Antibody, T Lymphocytes, and Respiratory Syncytial Virus Disease

BACKGROUND

Respiratory syncytial virus (RSV) infections occur in human populations around the globe, causing disease of variable severity, disproportionately affecting infants and older adults (>65 years of age). Immune responses can be protective but also contribute to disease. Experimental studies in animals enable detailed investigation of immune responses, provide insights into clinical questions, and accelerate the development of passive and active vaccination. We aimed to review the role of antibody and T-cell responses in relation to RSV disease severity in animals.

METHODS

Systematic review and meta-analysis of animal studies examining the association between T-cell responses/phenotype or antibody titers and severity of RSV disease. The PubMed, Zoological Record, and Embase databases were screened from January 1980 to May 2018 to identify animal studies of RSV infection that assessed serum antibody titer or T lymphocytes with disease severity as an outcome. Sixty-three studies were included in the final review.

RESULTS

RSV-specific antibody appears to protect from disease in mice, but such an effect was less evident in bovine RSV. Strong T-cell, Th1, Th2, Th17, CD4/CD8 responses, and weak Treg responses accompany severe disease in mice.

CONCLUSIONS

Murine studies suggest that measures of T-lymphocyte activity (particularly CD4 and CD8 T cells) may be predictive biomarkers of severity. Further inquiry is merited to validate these results and assess relevance as biomarkers for human disease.

Immunologic and Virologic Factors Associated With Hospitalization in Human Immunodeficiency Virus-Exposed, Uninfected Infants in the United States

BACKGROUND

Human immunodeficiency virus (HIV)-exposed, uninfected (HEU) infants experience higher rates of morbidity and mortality than HIV-unexposed, uninfected (HUU) infants. Few studies have examined whether particular infections and/or immune responses are associated with hospitalization among HEU infants born in the United States.

METHODS

We evaluated a subset of HEU infants enrolled in the International Maternal Pediatric Adolescent AIDS Clinical Trials Group P1025 and/or Pediatric HIV/AIDS Cohort Study Surveillance Monitoring for ART Toxicities studies. We determined seroconversion to 6 respiratory viruses and measured antibody concentrations to 9 vaccine antigens using quantitative ELISA or electrochemiluminescence. Multivariable modified Poisson regression models were fit to evaluate associations of seroconversion to each respiratory virus/family and antibody concentrations to vaccine antigens with risk of hospitalization in the first year of life. Antibody concentrations to vaccine antigens were compared between HEU infants and HUU infants from a single site using multivariable linear regression models.

RESULTS

Among 556 HEU infants, seroconversion to respiratory syncytial virus (RSV) and parainfluenza was associated with hospitalization (adjusted risk ratio, 1.95 [95% CI, 1.21-3.15] and 2.30 [1.42-3.73], respectively). Antibody concentrations to tetanus toxoid, pertussis, and pneumococcal vaccine antigens were higher among 525 HEU compared with 100 HUU infants. No associations were observed between antibody concentrations with any vaccine and hospitalization among HEU infants.

CONCLUSIONS

RSV and parainfluenza contribute to hospitalization among HEU infants in the first year of life. HEU infants demonstrate robust antibody responses to vaccine antigens; therefore, humoral immune defects likely do not explain the increased susceptibility to infection observed in this population.

RSV Specific Antibodies in Pregnant Women and Subsequent Risk of RSV Hospitalization in Young Infants

Background

The fusion (F) glycoprotein of respiratory syncytial virus (RSV) represents the major neutralizing antigen, and antibodies against the pre-F conformation have the most potent neutralizing activity. This study aimed to assess the correlation between maternal antibody titers against the pre-F, post-F, and G glycoproteins and the child’s risk of developing severe RSV bronchiolitis early in infancy.

Methods

We identified previously healthy term infants <3 months of age hospitalized with RSV bronchiolitis from December 2015 to March 2016. We measured IgG antibody titers to pre-F, post-F, and G proteins in maternal sera obtained at 9–12 weeks of pregnancy of these hospitalized infants’ mothers (n = 94) and compared them with serum antibody titers of control pregnant mothers (n = 130) whose children were not hospitalized.

Results

All maternal samples (n = 224) had detectable pre-F antibodies. Pre-F antibody titers were significantly lower in mothers whose infants were hospitalized with RSV bronchiolitis compared with those mothers whose infants were not hospitalized (23.9 [range (or antibody titer range), 1.4–273.7] µg/L vs 30.6 [XXX, 3.4–220.0] µg/L; P = .0026). There were no significant differences in maternal post-F and G antibody titers between hospitalized and nonhospitalized infants.

Conclusions

Our findings indicate that maternal pre-F antibodies are fundamental for providing immune protection to the infant.

Performance evaluation of antibody tests for detecting infant respiratory syncytial virus infection

Respiratory syncytial virus (RSV) infection is a major cause of respiratory tract disease in young children and throughout life. Infant infection is also associated with later respiratory morbidity including asthma. With a prospective birth cohort study of RSV and asthma, we evaluated the performance of an RSV antibody enzyme-linked immunoassay (EIA) for detecting prior infant RSV infection. Infant RSV infection was determined by biweekly respiratory illness surveillance plus RSV polymerase chain reaction (PCR) testing in their first RSV season and serum RSV antibodies after the season at approximately 1 year of age. RSV antibodies were detected by RSV A and B lysate EIA. Antibody and PCR results on 1707 children included 327 RSV PCR positive (PCR+) and 1380 not RSV+. Of 327 PCR+ children, 314 (96%) were lysate EIA positive and 583 out of 1380 (42%) children not PCR+ were positive. We compared the lysate EIA to RSV F, group A G (Ga), and group B G (Gb) protein antibody EIAs in a subset of 226 sera, 118 PCR+ children (97 group A and 21 group B) and 108 not PCR+. In this subset, 117 out of 118 (99%) RSV PCR+ children were positive by both the F and lysate EIAs and 103 out of 118 (87%) were positive by the Ga and/or Gb EIAs. Comparison of the two G EIAs indicated the infecting group correctly in 100 out of 118 (86%) and incorrectly in 1 out of 118 (1%). The lysate and F EIAs are sensitive for detecting infant infection and the two G EIAs can indicate the group of an earlier primary infection.

Airway Gene Expression Correlates of Respiratory Syncytial Virus Disease Severity and Microbiome Composition in Infants

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants. The causes and correlates of severe illness in the majority of infants are poorly defined.

METHODS

We recruited a cohort of RSV-infected infants and simultaneously assayed the molecular status of their airways and the presence of airway microbiota. We used rigorous statistical approaches to identify gene expression patterns associated with disease severity and microbiota composition, separately and in combination.

RESULTS

We measured comprehensive airway gene expression patterns in 106 infants with primary RSV infection. We identified an airway gene expression signature of severe illness dominated by excessive chemokine expression. We also found an association between Haemophilus influenzae, disease severity, and airway lymphocyte accumulation. Exploring the time of onset of clinical symptoms revealed acute activation of interferon signaling following RSV infection in infants with mild or moderate illness, which was absent in subjects with severe illness.

CONCLUSIONS

Our data reveal that airway gene expression patterns distinguish mild/moderate from severe illness. Furthermore, our data identify biomarkers that may be therapeutic targets or useful for measuring efficacy of intervention responses.