Kinetics of antibodies and risk of respiratory syncytial virus infection: a longitudinal cohort in Taizhou City, eastern China.

Respiratory syncytial virus (RSV) is a major cause of serious acute lower respiratory tract infection in infants and the elderly. The lack of a licensed RSV vaccine calls for the development of vaccines with other targets and vaccination strategies. Here, we construct a recombinant protein, designated P-KFD1, comprising RSV phosphoprotein (P) and the E.-coli-K12-strain-derived flagellin variant KFD1. Intranasal immunization with P-KFD1 inhibits RSV replication in the upper and lower respiratory tract and protects mice against lung disease without vaccine-enhanced disease (VED). The P-specific CD4+ Tcells provoked by P-KFD1 intranasal (i.n.) immunization either reside in or migrate to the respiratory tract and mediate protection against RSV infection. Single-cell RNA sequencing (scRNA-seq) and carboxyfluorescein succinimidyl ester (CFSE)-labeled cell transfer further characterize the Th1 and Th17 responses induced by P-KFD1. Finally, we find that anti-viral protection depends on either interferon-γ (IFN-γ) or interleukin-17A (IL-17A). Collectively, P-KFD1 is a promising safe and effective mucosal vaccine candidate for the prevention of RSV infection.

Differential Immune Responses and Pulmonary Pathophysiology Are Induced by Two Different Strains of Respiratory Syncytial Virus

Respiratory Syncytial Virus (RSV) is the major cause of acute lower tract infection in early childhood. Annual epidemics occur which are well documented in developed countries during winter months, placing considerable pressure on the provision of health care. Little is known about the epidemiology of RSV infection in the Middle East and other desert climate regions of the world. The aim of this project was to study the specificity of the immune response to RSV B in children, and to relate this to the infecting RSV strain, with particular emphasis on antibody response to RSV attachment (G) protein. RSV is an important cause of hospital admission in children (54%) during winter months in Qatar. 63% of these infections are due to RSV A. A case study involving analysis of RSV strains from hospitalized children was carried out in Qatar over 2 winter seasons (1999-2000 and 2000-2(01). RSV incidence was found to correlate with high relative humidity and low temperature. A comparison of enzyme immuno assay (EIA) and polymerase chain reaction (peR) for the detection of RSV in clinical samples demonstrated that peR was more sensitive than EIA. All positive RSV samples obtained during the study period were classified as belonging to RSV A and B subtypes using Multiplex peR. In this project, primer sets were designed and optimized to amplify the whole of the G gene of RSV A and B strains. Derived sequence analysis allowed deduction of the molecular epidemiology of RSV G gene for RSV A and B strains in Qatar and elsewhere. Sequence data of the G gene from Qatar RSV A&B isolates confirmed the variability of this protein and showed that variability occurs among group B RSV viruses isolated in Qatar (0.8%), although to a lesser extent than among the group A viruses (5%) from same location. However, the group B viruses isolated in Qatar were highly variable in G gene sequences compared to the prototype strain RSVB N2 (13%) and to strain world-wide (10%) at the nucleotide level. In order to produce an epitope map of the RSVB G protein, synthetic peptides representing linear B-cell epitopes of a representative Qatar RSV B isolate (B/Q/28/00) were used. The reactivity of human sera with the synthetic peptides was studied using sera from young children from whom RSV had been isolated. The sera from these children had variable peptide binding responses against different regions of the G protein of RSV B and the responses were focused on the conserved region. The results indicated that peptide 14 (a. a 150-165) of the G protein, in the conserved region of the protein, is a major antigenic site. This peptide sequence was recognized by a majority of the tested sera (93% sera). To examine the relationship between neutralization antibody titre and reactivity to the synthetic peptides in children's sera, a modified micro-neutralization method was used. There was no significant correlation between the peptide binding activity in the sera and the neutralization titre of these sera. Sera from children infected with RSV A bound to peptides from the G protein of RSV B strain. However, children infected with RSV B had greater neutralizing antibody titre to RSV B strain than to the two RSV A strains. There was no difference in the neutralization antibody titre in sera to RSV A when assessed with prototype strains isolated many years ago (RSV A2), and with the recently-isolated strain AlQ/IO/OO.

Globally, it is estimated that respiratory syncytial virus (RSV) causes 33 million new episodes of acute lower respiratory tract infection (LRTI) in children <5 years of age and ≈120,000 deaths annually. In infants, RSV represents the leading cause of hospitalization worldwide and the second commonest cause of mortality in low- and middle-income countries.1,2 RSV also causes significant disease in immunocompromised hosts and the elderly and has been associated with the development of asthma.3 The increasingly recognized burden of RSV disease has made the development of a vaccine(s) a global health priority. The World Health Organization recently released a roadmap to facilitate the development and implementation of vaccines and monoclonal antibodies (mAbs) and estimated that RSV vaccination will be available in the next 5–10 years.4 This review summarizes the strategies and challenges associated with RSV vaccine development and the vaccine candidates undergoing clinical evaluation, with a focus on those geared toward the pediatric population. THE STRUCTURE OF RSV RSV has a negative sense nonsegmented RNA genome that encodes 11 proteins: 3 are nonstructural (NS1/NS2—that counteract interferon responses—and M2-2), and 8 are structural proteins. Of those 8 proteins, 5 are internal [N, P, M, M2-1, L]), and 3 are embedded in the virion membrane: the small hydrophobic (SH), fusion (F) and attachment (G) glycoproteins. RSV G and F carry antigenic determinants that elicit neutralizing antibodies. However, F is the preferred target for vaccine, mAb and antiviral development because it plays an essential role in host cell viral entry, is highly conserved within and among RSV A and B subtypes and because of its 6 antigenic sites that elicit the production of high-potency neutralizing antibodies (≥90% of neutralizing antibodies are directed against this protein).5 Most of the G protein is covered in glycans, leaving the central conserved domain available for neutralizing antibody binding. Except for this domain, G is not well conserved and it is recognized by few neutralizing antibodies, which has reduced enthusiasm for it as a vaccine target. Our understanding of the F protein in its 2 conformations, prefusion (pre-F) and postfusion (post-F), has revolutionized the field of RSV biology. Pre-F, the active form of F on the virion, is metastable and switches unpredictably to the stable post-F conformation that once it is folded cannot return to the pre-F form. Antibodies that bind to pre-F are more efficient at neutralizing RSV than those against post-F. As examples, antibodies against site ϕ, a pre-F-specific epitope, are 150 times more potent than palivizumab that binds to site-II, present in both F conformations, while antibodies against site I, exclusively present in post-F, show weak or no neutralization.5 In addition, non-neutralizing antibodies to F, G and also SH, may inhibit infection by complement-mediated neutralization or antibody-dependent cell-mediated cytotoxicity. Furthermore, all viral antigens have the potential to induce protection by T-cell-mediated immunity. CHALLENGES FOR RSV VACCINE DEVELOPMENT Despite the burden associated with RSV, and after 60 years of active research, there is no licensed vaccine due in part of our incomplete understanding of the pathogenesis of the disease. In general, primary RSV infections are more severe; however, reinfections are common throughout life as immunity is neither complete nor long-lasting. The ideal vaccine should induce a more durable and improved immune response than natural infection. Legacy of the Formalin-inactivated Vaccine RSV vaccine development has been hindered after the safety concerns of the first RSV vaccine that was developed in the 1960s. The formalin-inactivated-whole virus alum-precipitated vaccine, which recent evidence indicating that it was directed against post-F, was associated in naive infants, but not older children, with enhanced RSV disease (ERD) and 2 deaths upon subsequent exposure to natural RSV. The mechanisms of ERD are not well understood, but it appears that an excess of non-neutralizing antibodies coupled with a skewed T-helper 2 (Th2) immune response, and complement deposition in the lungs contributed to its development. This is a critical aspect that is being considered for the development of inactivated vaccines, and strategies to assess safety risks according to the different vaccine platforms in the infant population are required. Target Populations There are different age groups that will benefit from RSV vaccines, and these might require different approaches: young RSV-naive infants (<4–6 months), children >6 months and the elderly. Vaccination of older children (2–5 years of age) may also limit transmission, as older siblings frequently introduce RSV into the household. Infants <4–6 Months This age group has an immature/developing immune system characterized by low expression of interferon, abundance of regulatory T cells with tolerogenic reactivity and a limited B-cell repertoire because of inefficient generation of somatic hypermutations. All these factors are associated with a poor response to foreign antigens and the generation of high-affinity matured antibodies. In addition, the presence of maternal antibodies may interfere with vaccine immunogenicity. Young infants represent the main target population because the peak of severe RSV disease occurs in the first 2–3 months of life. This age group would likely benefit from maternal vaccination or neutralizing mAbs administered at birth. The main goal of maternal vaccination is to boost neutralizing RSV titers and thereby transplacental antibody transfer. However, the optimal timing for vaccination (2nd or 3rd trimester) and the durability of protection in the infant need to be defined. This coupled with the high prevalence of hypergammaglobulinemia in low- and middle-income countries, associated with HIV or malaria, which impairs transplacental antibody transfer, suggest the need for high maternal antibody titers to compete for transfer. Nevertheless, RSV antibody transfer through breast-feeding (IgG > IgA) may complement the maternal vaccination strategy.6 Vaccinating pregnant women could be questioned if it exclusively benefits the infant and not the mother. The limited data available in pregnant women are mostly derived from influenza surveillance studies with rates of RSV infection varying from 0.2% to 13%, which likely underestimates the real incidence of RSV during pregnancy. The concerns regarding adverse fetal outcomes are relatively low, because this would not be the first time the mother's immune system encounters RSV antigens and the safety profile of other vaccines used in pregnancy, such as tetanus, diptheria and acellular pertussis (Tdap) or influenza, is excellent. A number of RSV maternal vaccines are currently in clinical development (Table 1).TABLE 1.: Landscape of RSV Vaccines Undergoing Clinical TrialsOlder Infants and Children Based on the experience of the formalin-inactivated-RSV vaccine, within this age group those who are naive at the time of vaccination might be at risk of ERD with protein vaccines. This target population would likely benefit most from live-attenuated or vectored vaccines. The Elderly On the other side of the spectrum, the immunosenescence of adults >65 years of age and the presence of additional comorbidities may compromise vaccine responses and the ability to assess efficacy. This population might benefit most from adjuvanted vaccines. Clinical Endpoints The ideal vaccine should be able to prevent severe disease and limit transmission, but the lack of a standard definition of severe disease or precise markers to assess severity in infants has been a barrier for vaccine development. Clinical endpoints that define a successful vaccine might be different depending on the target population. Hospitalization and other endpoints that capture the inpatient/outpatient burden of the disease, such as a reduction in medically significant visits for RSV infection, should be considered.7 Developing composite endpoints that include a combination of viral (and possibly bacterial) factors, clinical parameters, and fast turn-around point of care biomarkers could help with patient classification and to standardize definitions.8 Also, long-term follow-up is recommended, as studies suggest that interventions reducing the acute burden of RSV disease may also impact the development of recurrent wheezing/asthma.9 Immune Correlates of Protection Serum neutralizing antibodies (IgG against pre-F > post-F and G) represent the main surrogate of protection, as shown by the effectiveness of immunoprophylaxis with anti-F mAb (palivizumab) in high risk infants. However, a standardized protective threshold has not been defined yet. Newer systems biology approaches are helping to define the optimal correlates of protection, which are complex and depend on multiple factors, rather than a single cutoff value in antibody assays, and will need to be adjusted to each target population. Other cocorrelates of protection may include, F-specific epitope antibodies, mucosal IgA, interferon responses, antibody-dependent cell-mediated cytotoxicity and cell-mediated immunity. In addition, a balanced Th1/Th2 immune response, indicated by a high IgG2a/IgG1 ratio, is desirable. Other Factors The lack of an ideal animal model has also slowed down RSV vaccine development. Human challenge models mostly reproduce upper but not LRTI, limiting the generalizability of the results or the ability to assess the impact of vaccines on disease severity. There are also gaps in RSV epidemiology with lack of accurate information defining the temporal and geographic patterns of RSV circulation in inpatients/outpatients, across different age groups or RSV-associated mortality. Implementing robust multiplex polymerase chain reaction-based surveillance platforms could help to assess the impact of interventions on the burden of RSV disease, to identify possible escape mutants, or the contribution of other respiratory viruses causing RSV-like illnesses. VACCINE STRATEGIES The most effective approach to protect young infants and children from severe RSV infection may be a combined strategy using passive and active immunization: either maternal vaccination with stabilized pre-F or virus-like particles containing the F protein or mAb against pre-F at birth; followed by pediatric active immunization with a live vaccine, either attenuated RSV or the pre-F protein expressed from a virus vector. There are 39 vaccines candidates under development (http://www.path.org); of those 19 are undergoing clinical trials (Table 1).10 Protein Vaccines Particle Based The recombinant adjuvanted RSV post-F nanoparticle vaccine is the most advanced vaccine in clinical development. Results from a phase-3 clinical trial that enrolled 4636 pregnant women on the third trimester demonstrated a decrease in RSV hospitalizations in the offspring; however, the study did not meet the primary endpoint defined as prevention of medically significant RSV LRTI. The potential approval of this vaccine is being evaluated. It also aims to target elderly individuals and children >6 months to 5 years of age. Subunit Vaccines These vaccines consist of purified, adjuvanted proteins and use stabilized pre-F as the main antigen with promising results. They are mainly directed at pregnant women or the elderly because of the risk of ERD in RSV-naive infants. Other subunit vaccines in clinical or preclinical stages are using SH or G as main vaccine antigens. Live Vaccines Vector Based There are 5 vector-based vaccines in clinical development. The first 4 use adenovirus as a vector, while the other uses a modified vaccinia Ankara virus. Two of them are intended for use in pediatric seronegative patients. All of these vaccines express RSV F (pre-F > post-F depending on the vaccine) and 2 of them also express other viral antigens (N, M2 or G proteins). Live-attenuated vaccines (LAVs) represent an attractive alternative for older infants and young children. LAVs are administered intranasally and are able to elicit broad innate, humoral and cellular responses and replicate in the respiratory tract despite the presence of maternal antibodies. Importantly, these vaccines have not been associated with ERD and are considered safer in infants. The use of reverse genetics has made possible to incorporate different mutations in the viral genome, making LAV sufficiently immunogenic and, except for rhinorrhea, not associated with adverse events. There are 6 intranasal LAVs undergoing phase-1 clinical trials; 4 are using attenuated RSV, one Sendai virus as a backbone expressing RSV F and the last one is a chimeric vaccine using bacille Calmette-Guerin (BCG). The BCG/RSV vaccine is the only LAV intended to be administered systemically (subdermal) and in newborns. MONOCLONAL ANTIBODIES mAbs are also being evaluated for the prevention of RSV LRTI in young infants. Of those, suptavumab (REGN-2222), that targeted the pre-F-specific site V, has been discontinued from the market after it failed to prevent serious RSV LRTI in premature infants (primary endpoint). During the study, RSV type B was the predominant circulating strain and developed escape mutations that conferred resistance to this mAb. MK-1654 is an extended half-life mAb currently undergoing phase-I clinical trials and it is directed against antigenic site-IV (present the pre-F and post-F forms). Nirsevimab (MEDI8897) is a highly potent human neutralizing IgG1Κ targeting the pre-F-specific antigenic site ϕ. It also has an extended half-life because of modifications in the FC region using YTE technology. MEDI8897 is entering phase-3 clinical trials with the intent to provide passive immunization for prevention of severe RSV LRTI to all infants (preterm and full term), using a fixed, once per season intramuscular dose. SUMMARY Over the past decade, there have been significant advances in our knowledge of RSV molecular and structural biology and in the understanding of the human immune response to RSV. Despite the barriers, there are several opportunities for RSV vaccine development to protect the most vulnerable populations. The increasing interest of academic, industry and international bodies, such as the World Health Organization or Bill & Melinda Gates Foundation, is helping to move the field forward, promoting the implementation of surveillance platforms and standardization of clinical definitions, assays and surrogate markers of protection.

Nuclear-localized human respiratory syncytial virus NS1 protein modulates host gene transcription.

Respiratory syncytial virus (RSV) remains one of the most important infectious causes of hospitalization in infants and children. This enveloped, RNA virus produces predictable yearly outbreaks of disease that typically peak between January and February in countries in the northern hemisphere.1 The outcome of RSV infection varies from mild upper respiratory tract infection in approximately 75% of infected infants and young children to severe life-threatening disease in a small percent of infected patients.2 In the United States, RSV lower respiratory tract infection accounts for nearly 50% of hospitalizations due to bronchiolitis and 25% of hospitalizations due to pneumonia.1 Serologic surveys suggest that by 2 years of age, more than 90% of all children have been infected by RSV.3 Whether RSV infection early in life predisposes to subsequent reactive airway disease remains an unanswered question. Reinfection is common, indicating that immunity to RSV following natural infection is less than complete.4-6RSV lower respiratory tract disease occurs primarily in infants under 2 years of age; most infants who require hospitalization are previously healthy infants less than 6 months of age. Premature infants, infants born with congenital heart disease, and those with chronic lung disease (such as bronchopulmonary dysplasia [BPD]) constitute additional high-risk groups with high rates of hospitalization due to RSV infection.7-13 A recent report describes RSV mortality rates among such hospitalized infants of 4% to 5%.14Pre-engraftment bone marrow transplant recipients, solid organ transplant recipients, and lymphopenic children receiving chemotherapy appear to suffer even higher mortality rates, although prospective data are not available.15 Morbidity in these groups is also great; the average hospital stay and intensity of care for such children may be several times that of previously healthy infants.Despite the importance of RSV as a pathogen in the pediatric age group, options for treatment and prevention of RSV disease are limited. Aerosolized ribavirin was licensed in 1986 for treatment of children hospitalized with severe RSV lower respiratory tract infection. The efficacy of ribavirin therapy remains controversial despite the growing number of carefully conducted trials.16 Factors that complicate evaluation of antiviral therapy include the self-limited nature of most viral respiratory tract illness, and variation in the natural history of RSV disease from patient to patient. These variables make it difficult to select and define distinct endpoints that can be used to evaluate differences between treatment and control groups.Active immunization to prevent severe RSV disease has not yet been successful. Persistent concern regarding vaccine safety in the young infant is the result of an unanticipated reaction to a formalin inactivated RSV vaccine used in trials conducted in the early 1960s.17-19 Recipients (less than 12 months of age) of the inactivated RSV vaccine experienced higher mortality and morbidity rates upon subsequent RSV infection than did infants who received the control vaccine. The immunologic mechanism for this reaction remains unclear although there appears to have been an aberration in both the cellular and humoral response to the vaccine. Vaccine development is also complicated by the limited ability of infants to mount an immune response to RSV glycoprotein antigens. Furthermore, the presence of maternal neutralizing antibodies may attenuate an active immune response in a vaccinated infant. Despite current efforts to develop subunit vaccines, peptide vaccines, or live attenuated RSV vaccines, it is unlikely that active immunization for infants will be available in the near future.20As an alternative to active immunization against RSV, several approaches to passive immunization in high-risk infants have been evaluated. Clinical trials were first conducted using standard intravenous immune globulin (IGIV). Two randomized controlled trials involving monthly infusions of standard IGIV to high-risk infants failed to demonstrate a reduction in hospitalization rates due to RSV.2122 This lack of efficacy was most likely due to a failure to attain adequate peak and trough RSV neutralizing antibody titers. With the development of an RSV-enriched immune globulin in the late 1980s (RSV-IGIV), it became possible to achieve sufficiently high neutralizing antibody levels in the outpatient setting with infusion of a reasonable fluid volume (15 mL/kg). The first RSV-IGIV prophylaxis trial (National Institute of Allergy and Infectious Disease [NIAID] trial) published in 1993 was conducted over three respiratory virus seasons and included 249 children with prematurity, chronic lung disease or congenital heart disease.23 Children who received 750 mg/kg/dose of RSV-IGIV had a 63% reduction in RSV hospitalizations and a 63% reduction in RSV hospital days relative to control patients receiving no RSV-IGIV. A second prophylaxis trial using RSV-IGIV (PREVENT trial), was conducted over one respiratory virus season and included 510 premature infants with and without BPD.24 This trial demonstrated a 41% reduction in RSV hospitalizations and a 53% reduction in RSV hospital days. A third multicenter RSV-IGIV prophylaxis trial involving 416 infants and children (Cardiac trial) failed to show an overall reduction in RSV disease severity in children with congenital heart disease (unpublished data). A meta-analysis of children less than 6 months of age from all three prophylaxis trials demonstrated a 47% reduction in RSV-induced hospitalization (95% confidence interval of .28–.82) (P = .006) (Table). However, caution must be observed in interpreting these data. Although there is considerable interest in the evaluation of hospitalization rates in subgroups of infants, none of the three trials were prospectively designed for subgroup analysis.Two additional clinical benefits of polyclonal immune globulin administration were observed in recipients of RSV-IGIV prophylaxis. The PREVENT trial demonstrated a 38% reduction in hospitalization due to respiratory tract infection by any respiratory virus and a 46% reduction in total hospital days due to all respiratory illnesses.24 Further, both the NIAID trial and the PREVENT trial demonstrated a reduction in the incidence of acute otitis media in high-dose RSV-IGIV recipients (750 mg/kg/dose) relative to low-dose or control patients.2425RSV-IGIV use in patients with congenital heart disease has been evaluated in two trials (the NIAID trial and the Cardiac trial) and has involved a total of 516 children. The safety of RSV-IGIV, particularly in children with cyanotic heart disease, is uncertain. There appeared to be an increased incidence in both morbidity and mortality, particularly in association with cardiac surgery in RSV-IGIV recipients with cyanotic heart disease as compared with placebo recipients. The deaths occurred at variable times, up to 3 months following an RSV-IGIV infusion. No explanation has yet been found. At the present time, use of RSV-IGIV should be avoided in children with cyanotic heart disease. Among children with left to right shunts who received RSV-IGIV there was not a statistically significant reduction in the overall incidence of RSV hospitalization relative to the control group. Therefore, based on the currently available data, RSV-IGIV does not appear to be indicated for most children with noncyanotic congenital heart disease. It may be that immunoprophylaxis will be beneficial in those infants with noncyanotic heart disease who also satisfy immunoprophylaxis criteria based on prematurity or the presence of BPD. The role of RSV-IGIV in infants with large left to right shunts with pulmonary hypertension remains uncertain.RSV-neutralizing antibodies are directed mainly against two surface glycoproteins. The G glycoprotein mediates RSV attachment to a cell that will support RSV replication by binding with cellular receptors containing sialic acid. The F glycoprotein mediates fusion of the viral lipid envelope with the plasma membrane of the cell. Although there may be considerable sequence divergence in the G glycoprotein between RSV subgroups, the important neutralizing epitopes of the F glycoprotein appear to be faithfully conserved between RSV strains and over time. There has been interest in the use of monoclonal antibodies for prophylaxis against RSV disease because of the possibility of intramuscular (rather than intravenous) administration. One immunoprophylaxis trial using a humanized immunoglobulin G (IgG) monoclonal antibody was conducted during the 1995–1996 respiratory season. In this large, multicenter, double-blind, randomized, placebo-controlled trial, monoclonal antibody or placebo was administered intramuscularly once a month to preterm infants during the respiratory virus season. The results proved disappointing (unpublished data). Although safe, this monoclonal antibody preparation did not reduce RSV hospitalization rates at the dose administered. A second multicenter prophylaxis trial using a higher dose of a somewhat different humanized murine IgG monoclonal antibody and involving over 1500 patients is currently underway.RSV transmission occurs primarily by direct introduction of virus contaminated secretions onto mucous membranes of the upper airway. Bronchiolitis and pneumonia develop when RSV from the upper airway is aspirated into the lungs. The presence of RSV immunoglobulin A (IgA) nasal antibody may protect infants against the low titer of RSV that initiates infection. Studies in experimental animals demonstrate that intranasal administration of a murine monoclonal IgA directed against the RSV F glycoprotein significantly reduced viral replication in the nasal turbinates and the lungs.2627 Phase III prophylaxis trials to evaluate topical daily instillation of IgA antibody as nose drops are currently in progress in high-risk infants.The severity of RSV infection appears to be a function of both a direct viral cytopathic effect and the immune response of the host. Evidence supporting the concept that antiviral activity alone may not be sufficient to attenuate RSV disease expression comes from the unpublished trial demonstrating little if any benefit from prophylaxis with monoclonal IgG antibody, and from the clinical trials that show little beneficial effect from RSV-IGIV in the treatment of established RSV disease in infants.28 The beneficial effect on RSV disease severity that is derived from immunoprophylaxis with a hyperimmune polyclonal product may not be due to RSV neutralizing antibody alone.29 What other critical functions might be present in RSV-IGIV that are not present in a preparation of monoclonal antibodies? Recognized immunomodulatory functions of standard IGIV include: alteration of cytokine production,30 inhibition of T-cell proliferation in vitro,31 increase in natural killer cell activity,32 increase in antibody dependent cell cytotoxicity,32 and neutralization of superantigen activity.33 How important these or other as yet unrecognized immunomodulatory functions are in the attenuation of RSV disease expression remains to be determined.The cost of immunoprophylaxis with RSV-IGIV (licensed in 1996 by the Food and Drug Administration and sold under the trade name RespiGam) over one respiratory season is approximately $5000.34Therefore, it is important that prophylaxis be reserved for carefully selected infants. A recently published consensus statement reviewed the existing literature on RSV disease in various high-risk groups and offered the following guidelines for selection of RSV-IGIV eligible patients15:It must be remembered that the majority of children hospitalized due to RSV disease are previously healthy, young infants. During the 1995–1996 respiratory virus season, 69% of 95 children hospitalized at the New England Medical Center with RSV infection were full-term infants with normal cardiac and pulmonary status. Therefore, use of RSV-IGIV in appropriately selected, high-risk infants is unlikely to dramatically reduce the overall number of RSV induced admissions. However, high-risk children have a disproportionately high economic impact on RSV-associated health care costs because of the greater disease severity and the complexity of care required for these groups. In appropriately selected infants for whom the risk of hospitalization due to RSV and other respiratory viruses is greatest, passive immunoprophylaxis should have an important medical impact and improve their quality of life.

The rate of decay and the subsequent antibody responses to RSV are poorly defined in young infants and children who possess maternally derived respiratory syncytial virus (RSV) antibodies. A birth cohort from rural Kenya was studied intensively to monitor infections from whom blood samples were collected at regular intervals to describe the age-related serological characteristics. A simple linear regression model was used to calculate the rate of RSV-specific maternal antibody decline. In addition, the effect of risk factors on cord blood titres was investigated. Using the random effects model, the half-life of RSV maternal antibodies was calculated to be 79 days. Although 97% of infants were bom with RSV-specific maternal antibodies, it was noted that infants who went on to experience an infection in early life, had lower starting titres of RSV maternal antibodies in comparison to infants who did not have any clinically confirmed infection in the first 6 months. Additionally, clinically confirmed infections within the first 6 months of life had no effect on the rate of decay of maternal antibodies. Both RSV group A and B were seen to circulate in the community in varying amounts, with RSV A seen to be the most dominant strain in the 4 epidemics experienced by the cohort. The same RSV strain was observed to cause both RSV-associated upper respiratory tract and lower respiratory tract infections. It was observed that there existed patterns of antibody decay and acquisition of RSV-specific immune responses that groups of children appeared to follow. A group of infants were seen to undergo clinical infection that was subsequently confirmed by the ELISA, or were observed to seroconvert in the absence of clinical symptoms, or infants did not experience any infection at all despite experiencing at least 2 epidemics. Post-infection dynamics showed classical boosting of RSV antibodies, which either quickly waned or remained elevated over time. Furthermore, the risk of re-infection with clinically identified RSV illness decreased with age, from an initial infection rate of 252 to 41/1000 child years observation. In conclusion, the evidence shows that RSV maternal antibodies provide some protection against severe disease during the first 6-7 months. Since there is efficient transfer of antibodies from mother to child, maternal vaccination against RSV may be a useful strategy to consider. However, our observations show that these antibodies decline quickly, hence childhood vaccines should also be taken into consideration to augment the immune responses.

To the Editor: Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and elderly persons.RSV strains have been divided into 2 major antigenic groups (A and B), which are further divided into several genotypes.The main genetic and antigenic differences between genotypes are found within the 2 hypervariable regions of the attachment (G) glycoprotein.In 1999, a novel RSV B genotype, which contained a 60-nt duplication in the second hypervariable region of the G protein, was discovered in Buenos Aires, Argentina, and named BA (1).Since then, genotype BA has almost completely replaced other RSV B strains worldwide and has diversified into several subgenotypes (2).In February 2012, as part of routine RSV surveillance, we identified a novel RSV A genotype with a 72-nt duplication in the second hypervariable region of G, thus representing the first RSV A genotype with nucleotide duplications in the G gene.Shortly thereafter, circulation of this genotype

SummaryThe susceptibility of suckling mice of different ages to the neuropathic strain of respiratory syncytial (RS) virus was examined periodically during serial intra-cerebral passage (s) of the virus in newborn mice. By passing the virus serially in mouse brain, beginning with the one-day-old mouse and gradually increasing the age, it became possible to grow the RS virus in 7- and 9-day-old mice. The pathogenesis of the encephalitis produced by neuropathic strain of the RS virus, in intracerebrally inoculated suckling mice, was studied by means of immunofluores-cent and histopathologic techniques. The histological changes were correlated with im-munofluorescen.ee and infectivity titrations. The clinical evidence of encephalitis in the infected mice was found to be associated with extensive necrosis and liquefaction of the brain. This mouse brain adapted strain of RS virus was found to be strictly neuropathic, in that it produced lesions only in the nervous system of the intracerebrally inoculated suckl...

The subtype characteristics of 22 strains of respiratory syncytial (RS) virus isolated in Sweden were determined by the use of monoclonal antibodies. Eleven antibodies specific for distinct epitopes on five different structural proteins were used in immunofluorescence and radioimmune precipitation assays. One group of 12 isolates were derived from a three-month epidemic during 1984, whereas the other ten virus isolates were recovered during a time period of 13 years (1971-1983). All isolates could be allocated to the previously defined groups of subtype A and B strains of RS virus. During the single epidemic season, five subtype A and seven subtype B strains were found. During the 13-year period a randomly alternating appearance of six subtype A and four subtype B strains was observed. Thus RS virus strains of different subtype characteristics may occur alternately or concomitantly. The possible significance of consecutive infections with RS virus subtypes for immunopathological events deserves further studies.

BackgroundSevere respiratory syncytial virus (RSV) disease occurs predominantly in children under 6 months of age. There is no licensed RSV vaccine. Protection of young infants could be achieved by a maternal vaccine to boost titres of passively transferred protective antibodies. Data on the level and kinetics of functional RSV-specific antibody at birth and over the early infant period would inform vaccine product design. MethodsFrom a birth cohort study (2002–2007) in Kilifi, Kenya, 100 participants were randomly selected for whom cord blood and 2 subsequent 3-monthly blood samples within the first year of life, were available. RSV antibodies against the A2 strain of RSV were assayed and recorded as the logarithm (base 2) plaque reduction neutralisation test (PRNT) titre. Analysis by linear regression accounted for within-person clustering. ResultsThe geometric mean neutralisation antibody titre was 10.6 (SD: 1.13) at birth with a log-linear decay over the first 6 months of life. The estimated rate of decay was −0.58 (SD: 0.20) log2PRNT titre per month and a half-life of 36 days. There was no significant interaction between cord titre and rate of decay with age. Mean cord titres rose and fell in a pattern temporally tracking community virus transmission. ConclusionsIn this study population, RSV neutralising antibody titres decay approximately two-fold every one month. The rate of decay varies widely by individual but is not related to titre at birth. RSV specific cord titres vary seasonally, presumably due to maternal boosting.

Respiratory syncytial virus (RSV) is the most common cause of serious lower respiratory tract disease in infants and young children. In this study a hybridoma line secreting a chimpanzee monoclonal antibody that neutralizes RSV was isolated. Two chimpanzees were immunized with recombinant vaccinia viruses that express the RSV F or G surface glycoprotein and 1 month later were infected intranasally with the wild-type RSV strain A2. Peripheral blood lymphocytes obtained from the animals were transformed with Epstein-Barr virus, and lymphoblastoid cell lines that secreted anti-RSV antibodies were identified by an RSV antigen-binding enzyme-linked immunosorbent assay. Supernatants from RSV antibody-secreting lymphoblastoid cell lines were tested for in vitro virus neutralization before being fused to the heteromyeloma cell GLI-H7. A chimpanzee antibody [immunoglobulin G3(lambda) subclass] produced from a hybridoma line designated E1.4/2 was shown to bind to the RSV G glycoprotein and neutralize a panel of subgroup A viruses, but not subgroup B viruses, at low (nanomolar) concentrations. Mice passively immunized with this antibody were partially resistant to RSV strain A2 challenge. The usefulness of such antibodies in immunoprophylaxis and immunotherapy of RSV infection is discussed.

Community-acquired respiratory viruses

Asthma and respiratory syncytial virus infection in infancy: is there a link?

Respiratory syncytial virus with ongoing COVID-19: is it an emerging threat?