Relation of serum antibody to glycoproteins of respiratory syncytial virus with immunity to infection in children

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

Palivizumab Prophylaxis among Infants at Increased Risk of Hospitalization due to Respiratory Syncytial Virus Infection in UAE: A Hospital-Based Study

Background

Respiratory syncytial virus (RSV) represents a significant public health burden and the leading cause of lower respiratory tract infections globally, and it is the major cause of hospitalization during the winter. We aimed to evaluate the effectiveness of palivizumab prophylaxis to reduce the hospitalization in children at high risk of RSV infection.

Methods

We performed a retrospective observational single-arm hospital-based study including five RSV seasons (September to March) from 2012 to 2017. We retrospectively included premature infants born at less than 35 weeks of gestation with chronic lungs disease or hemodynamic significant congenital heart disease for palivizumab prophylaxis against RSV infection according to the criteria presented.

Results

A total of 925 children were enrolled in the study over the five RSV seasons. Of them, 410 (44.3%) infants born at <32 weeks of gestation and 515 (55.6%) infants born at 32-35 weeks of gestation with mean (±SD) birth weight of 1104.8 ± 402.85 and 1842.5 ± 377.5, respectively. The compliance with the course of palivizumab was reported in 841 (90.9%) children. Of them, about 75 (8.9%) hospitalized children were reported, and 17 (2.02%) RSV positive children were detected. Hospitalization due to RSV infection was decreased from 9.23% in the 2012-2013 season to 0.67% in the 2016-2017 season.

Conclusion

This study demonstrated that palivizumab prophylaxis in children at high risk of developing RSV infection was effective in reducing the risk of hospitalization with a high compliance rate over the five RSV seasons.

Group B streptococcus and respiratory syncytial virus immunisation during pregnancy: a landscape analysis

Group B streptococcus and respiratory syncytial virus are leading causes of infant morbidity and mortality worldwide. No licensed vaccines are available for either disease, but vaccines for both are under development. Severe respiratory syncytial virus disease can be prevented by passively administered antibody. The presence of maternal IgG antibody specific to respiratory syncytial virus is associated with reduced prevalence and severity of respiratory syncytial virus disease in the first few weeks of life, whereas maternal serotype-specific anticapsular antibody is associated with protection against both early-onset and late-onset group B streptococcus disease. Therefore, vaccination in pregnancy might protect infants against both diseases. This report describes what is known about immune protection against group B streptococcus and respiratory syncytial virus, identifies knowledge gaps regarding the immunobiology of both diseases, and aims to prioritise research directions in maternal immunisation.

Prevention of Respiratory Syncytial Virus Infection: From Vaccine to Antibody

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in infants and young children. Initial efforts to develop a vaccine to prevent RSV lower respiratory tract disease in children were halted because of serious adverse events that occurred when children were infected with RSV following vaccination, including vaccine-related deaths. Subsequently, a major focus for researchers was to understand what led to these adverse events. Investment in a vaccine for RSV continues, and new strategies are under development. Success to prevent RSV disease was met by the development of immunoprophylaxis, first with intravenous immunoglobulin and then with recombinant monoclonal antibody. The story of immunoprophylaxis for RSV includes the first-in-class use of antibody technology for infectious disease, and palivizumab currently remains the only way to prevent serious lower respiratory tract disease due to RSV infection.

Risk of respiratory syncytial virus infection in preterm infants: reviewing the need for prevention

Premature infants are at substantial risk for a spectrum of morbidities that are gestational age dependent. Respiratory syncytial virus (RSV) infection is most common in the first two years of life with the highest burden in children aged <6 months. Preterm infants ≤35 weeks' gestation are handicapped by incomplete immunological and pulmonary maturation and immature premorbid lung function with the added risk of bronchopulmonary dysplasia. Superimposed RSV infection incites marked neutrophilic airway inflammation and innate immunological responses that further compromise normal airway modeling. This review addresses the epidemiology and burden of RSV disease, focusing on the preterm population. Risk factors that determine RSV-disease severity and hospitalization and the impact on healthcare resource utilization and potential long-term respiratory sequelae are discussed. The importance of disease prevention and the evidence-based rationale for prophylaxis with palivizumab is explored, while awaiting the development of a universal vaccine.

Antibodies enhance CXCL10 production during RSV infection of infant and adult immune cells

Respiratory syncytial virus (RSV) bronchiolitis is a major burden in infants below three months of age, when the primary immune response is mainly dependent on innate immunity and maternal antibodies. We investigated the influence of antibodies on innate immunity during RSV infection. PBMCs from infants and adults were stimulated with live RSV and inactivated RSV in combination with antibody-containing and antibody-depleted serum. The immune response was determined by transcriptome analysis and chemokine levels were measured using ELISA and flow cytometry. Microarray data showed that CXCL10 gene transcription was RSV dependent, whereas CXCL11 and IFNα were upregulated in an antibody-dependent manner. Although the presence of antibodies reduces RSV infection rate, it enhances the innate immune response. In adult immune cells, antibodies enhance CXCL10, CXCL11, IFNα and IFNγ production in response to RSV infection. Contrary, in infant immune cells only CXCL10 was enhanced in an antibody-dependent manner. Monocytes are the main source of CXCL10 and they produce CXCL10 in both an antibody- and virus-dependent manner. This study shows that antibodies enhance CXCL10 production in infant immune cells. CXCL10 has been implicated in exuberating the inflammatory response during viral infections and antibodies could therefore play a role in the pathogenesis of RSV infections.

Co-immunization with virus-like particle and DNA vaccines induces protection against respiratory syncytial virus infection and bronchiolitis

This study demonstrates that immunization with non-replicating virus-like particle (FFG VLP) containing RSV F and G glycoproteins together with RSV F DNA induced T helper type 1 antibody responses to RSV F similar to live RSV infection. Upon RSV challenge 21weeks after immunization, FFG VLP vaccination induced protection against RSV infection as shown by clearance of lung viral loads, and the absence of eosinophil infiltrates, and did not cause lung pathology. In contrast, formalin-inactivated RSV (FI-RSV) vaccination showed significant pulmonary eosinophilia, severe mucus production, and extensive histopathology resulting in a hallmark of pulmonary pathology. Substantial lung pathology was also observed in mice with RSV re-infections. High levels of systemic and local inflammatory cytokine-secreting cells were induced in mice with FI-RSV but not with FFG VLP immunization after RSV challenge. Therefore, the results provide evidence that recombinant RSV FFG VLP vaccine can confer long-term protection against RSV without causing lung pathology.

Serum palivizumab level is associated with decreased severity of respiratory syncytial virus disease in high-risk infants

Monthly doses of palivizumab, an RSV-specific monoclonal antibody, reduce RSV-related hospitalizations (RSVH) in high-risk children; however, no specific palivizumab level has been correlated with disease severity in humans. A post hoc analysis of a previous randomized, placebo-controlled trial evaluated the relationship between serum palivizumab level at the time of RSVH and disease severity. Pediatric intensive care unit (PICU) admission was the primary severity marker. Relationships were evaluated between disease severity and gestational age, age at enrollment, age at RSVH, presence of bronchopulmonary dysplasia, sex, race, multiple birth, household smoking, daycare attendance, sibling(s), family history of atopy, duration between most recent palivizumab dose and RSVH, and palivizumab level at RSVH. Forty-two (87.5%) of 48 palivizumab recipients with RSVH had palivizumab levels drawn; 11 were admitted to the PICU. Mean palivizumab levels were lower in PICU-admitted subjects (47.2 μg/mL) vs. non-PICU subjects (98.7 μg/mL; P < 0.0001); there were no statistically significant differences in other variables examined. The probability of PICU admission declined with higher palivizumab levels; there were no PICU admissions with levels ≥ 92 μg/mL. In multivariate analyses, palivizumab level was the only independent predictor of PICU admission (P = 0.009). Palivizumab level also correlated with duration of RSVH and PICU stay, supplemental oxygen use and duration, and mechanical ventilation use and duration (P < 0.05). Higher palivizumab level was associated with decreased disease severity in high-risk infants with RSVH. Findings suggest that palivizumab level has clinical relevance, and adherence to timely monthly dosing may confer additional protection among high-risk children receiving palivizumab.

Fc gamma receptors in respiratory syncytial virus infections: implications for innate immunity

RSV infections are a major burden in infants less than 3 months of age. Newborns and infants express a distinct immune system that is largely dependent on innate immunity and passive immunity from maternal antibodies. Antibodies can regulate immune responses against viruses through interaction with Fc gamma receptors leading to enhancement or neutralization of viral infections. The mechanisms underlying the immunomodulatory effect of Fc gamma receptors on viral infections have yet to be elucidated in infants. Herein, we will discuss current knowledge of the effects of antibodies and Fc gamma receptors on infant innate immunity to RSV. A better understanding of the pathogenesis of RSV infections in young infants may provide insight into novel therapeutic strategies such as vaccination.

The adaptive immune response to respiratory syncytial virus

Respiratory syncytial virus (RSV) causes severe respiratory disease in children, the elderly and immunocompromised individuals. The combined actions of CD4 and CD8 T cells play a critical role in terminating an acute RSV infection whereas antibodies can provide protection from re-infection. Despite eliciting an immune response that mediates clearance of the virus, immunity to the virus appears to wane over time and individuals remain susceptible to reinfection with RSV throughout their lifetime. The ineffectiveness of the natural infection to induce long-term immunity has hampered vaccine efforts and there is currently no licensed RSV vaccine. In this review, we summarize our current understanding of the adaptive immune response to RSV and its contribution to disease.

Influenza and respiratory syncytial virus (RSV) vaccines for infants: safety, immunogenicity, and efficacy

Respiratory viral infections in infants and young children frequently cause illness that can easily progress to hospitalization and death. There are currently no licensed vaccines to prevent respiratory viral disease in children younger than 6 months, reflecting safety concerns and the difficulty in inducing effective immune responses in infants. This review discusses vaccines that have been developed, or are currently being developed, against influenza and respiratory syncytial virus, with a focus on studies performed to demonstrate their safety and efficacy, and the impact of immunologic immaturity and maternal antibodies on the infant response to vaccines.

Targeting RSV with vaccines and small molecule drugs

Respiratory syncytial virus (RSV) is the most significant cause of pediatric respiratory infections. Palivizumab (Synagis®), a humanized monoclonal antibody, has been used successfully for a number of years to prevent severe RSV disease in at-risk infants. However, despite intense efforts, there is no approved vaccine or small molecule drug for RSV. As an enveloped virus, RSV must fuse its envelope with the host cell membrane, which is accomplished through the actions of the fusion (F) glycoprotein, with attachment help from the G glycoprotein. Because of their integral role in initiation of infection and their accessibility outside the lipid bilayer, these proteins have been popular targets in the discovery and development of antiviral compounds and vaccines against RSV. This review examines advances in the development of antiviral compounds and vaccine candidates.

Prevention of serious respiratory syncytial virus-related illness. II: Immunoprophylaxis

Respiratory syncytial virus (RSV) causes significant morbidity in very young children, preterm infants with and without chronic lung disease, and children with hemodynamically significant congenital heart disease. In the absence of a safe and effective vaccine, alternative means of protecting high-risk infants and young children from serious RSV illness have been studied. Clinical observations and animal model data over the past 30 years suggested that RSV immunoglobulin G (IgG) neutralizing antibodies might offer protection from severe RSV lower respiratory tract disease. Transfer of adequate amounts of IgG to the fetus does not occur efficiently until the third trimester of pregnancy, which helps to explain why premature infants are at high risk of serious RSV illness. Efforts shifted toward the prophylactic monthly administration of standard immunoglobulins and, later, of RSV-enriched immunoglobulin in selected high-risk infants and young children. Although this approach proved effective, RSV-enriched immune globulin was not suitable for all patients and administration was labor intensive. The development of palivizumab, a monoclonal antibody that can bind to a specific antigenic site on the virus and prevent cell-to-cell spread of infection has since become the mainstay of RSV illness prevention in preterm infants and those with significant congenital heart disease. Palivizumab, the only monoclonal antibody approved for the prevention of RSV lower respiratory tract disease must be administered monthly throughout the RSV season and does not always prevent serious RSV illness. Further research to develop more effective and less labor-intensive immunoprophylactic agents is ongoing.

Prevention of serious respiratory syncytial virus-related illness. I: Disease pathogenesis and early attempts at prevention

Respiratory syncytial virus (RSV) was first described 160 years ago but was not officially recognized as a cause of serious illness in children until the late 1950s. It has been estimated that virtually all children have had at least one RSV infection by their second birthday. RSV is responsible for annual disease outbreaks, usually during a defined winter seasonal period that can vary by community and year. RSV is recognized as the leading cause of hospitalization among young children worldwide. Infants of young chronologic age and children with predisposing factors, such as premature birth, pulmonary disease, or congenital heart disease, are most susceptible to serious illness. Unlike other viruses, immunity to RSV infection is incomplete and short lived, and reinfection is common throughout life. Initial attempts to develop a vaccine in the 1960s met with unexpected and tragic results; many children vaccinated with a formalin-inactivated wild-type virus developed serious pulmonary disease upon subsequent natural infection. Numerous other vaccine technologies have since been studied, including vectored approaches, virus-like particles, DNA vaccines, and live attenuated virus vaccine. As of early 2010, only two companies or institutions had RSV vaccine candidates in early clinical trials, and no vaccine is likely to be licensed for marketing in the immediate future.

Immunoprophylaxis of RSV infection: advancing from RSV-IGIV to palivizumab and motavizumab

Antibodies mediate humoral immune responses and play key roles in the defense of viral infection by the recognition, neutralization, and elimination of viruses from the circulation. For the prevention of respiratory syncytial virus (RSV) infection, the natural immune response to RSV from pooled human plasma has been harvested and successfully developed as a prophylactic polyclonal RSV hyperimmune globulin, RespiGam (RSV-IGIV; MedImmune, Gaithersburg, MD). The success of RSV-IGIV validated the immunoprophylaxis approach for RSV prevention and led to the development of Synagis (palivizumab; MedImmune, Gaithersburg, MD), a humanized monoclonal antibody (mAb) that binds to the RSV F protein. Palivizumab is a potent anti-RSV mAb that is about 50-fold more potent than RSV-IGIV, and since obtaining regulatory approval in 1998 it has been used extensively to help prevent severe RSV disease in high-risk infants and children. However, a very small number of patients receiving the drug do not appear to be adequately protected. To further improve protection against RSV, we have applied a directed evolution approach to enhance the binding of palivizumab to F protein by manipulation of both the on and off rates. These efforts have yielded a more potent second-generation mAb, motavizumab, which is currently under study in phase III clinical trials. Most recently, a third generation mAb, Numax-YTE, has been generated with the intent to extend the serum half-life of the mAb in humans. If successfully developed, this drug may offer the opportunity for less frequent dosing, obviating the need for the monthly treatments that are required with palivizumab. The development of these anti-RSV approaches exemplifies the accelerated pace of drug development made possible with cutting-edge antibody engineering technologies.

Respiratory syncytial virus and innate immunity: a complex interplay of exploitation and subversion

Respiratory syncytial virus causes significant disease in infants, the elderly and select groups of immunocompromised patients. Healthy individuals are also naturally infected with respiratory syncytial virus repeatedly throughout life. Therefore, safe and effective vaccines and therapies are needed. However, a number of factors have prevented development of such antiviral interventions to date. These include a failed vaccine trial, the very young age of the primary target population (neonates), the inability of natural infection to induce long-term protective immunity, and an incomplete understanding of virus-host interactions. The identification of pattern recognition receptors has led to significant increases in our understanding of induction and regulation of innate immune responses. This review will address the impact of these findings on respiratory syncytial virus research.

The effects of maternal employment on child injuries and infectious disease

This article presents estimates of effects of maternal paid work and nonmaternal child care on injuries and infectious disease for children aged 12 to 36 months. Mother-child fixed-effects estimates are obtained by using data from the NICHD Study of Early Child Care. Estimates indicate that maternal employment itself has no statistically significant adverse effects on the incidence of infectious disease and injury. However, greater time spent by children in center-based care is associated with increased rates of respiratory problems for children aged 12 to 36 months and increased rates of ear infections for children aged 12 to 24 months.

Increased susceptibility of human respiratory syncytial virus to neutralization by anti-fusion protein antibodies on adaptation to replication in cell culture

Subgroup A respiratory syncytial viruses present in respiratory secretions and low passage level cell culture isolates were found to be markedly less susceptible to neutralization with monoclonal antibodies (MAbs) to the F glycoprotein than the cell culture adapted A2 virus strain. Low passage virus isolates collected over a 20 year period and belonging to several sub-group A lineages were refractory to neutralization with antibodies recognizing two major neutralizing antigenic sites located sub-terminally at opposite ends of the F(1) glycoprotein sub-unit. On further passage in cell culture, virus isolates exhibited both increased infectivity titers and increased susceptibility to neutralization by antibodies to both antigenic sites. The consensus nucleotide sequence of the membrane associated proteins M and of the SH, G and F glycoprotein genes, and their intergenic regions were compared for neutralization resistant and susceptible stocks of one virus strain, R17532. No changes were observed in the known monoclonal antibody epitopes on the F glycoprotein. In line with this, the increase in susceptibility was not found to be associated with any increased binding of monoclonal antibody to isolated F glycoprotein in a BIAcore assay, thus excluding the possibility that passage in cell culture selected for viruses with mutations in the antibody binding sites. M and SH genes were conserved but a number of sites in the G and F glycoprotein genes were found to vary on adaptation to cell culture suggesting that change in susceptibility to neutralization was associated with a change in the prevalent quasispecies present in the virus population. The genetic basis of phenotypic change in susceptibility remains to be determined.

Recombinant Sendai virus as a novel vaccine candidate for respiratory syncytial virus

Respiratory syncytial virus (RSV) is among the most important and serious pediatric respiratory diseases, and yet after more than four decades of research an effective vaccine is still unavailable. This review examines the role of the immune response in reducing disease severity; considers the history of RSV vaccine development; and advocates the potential utility of Sendai virus (a murine paramyxovirus) as a xenogenic vaccine vector for the delivery of RSV antigens. The immunogenicity and protective efficacy of RSV-recombinant Sendai virus vectors constructed using reverse genetics is examined. RSV-recombinant Sendai virus is easy to grow (i.e., achieves extremely high titers in eggs), is easy to administer (intranasal drops), and elicits both B- and T-cell responses leading to protection from RSV challenge in a small-animal model. Unmodified Sendai virus is currently being studied in clinical trials as a vaccine for its closely related human cognate (human parainfluenza virus type 1). Sendai virus may prove an enormously valuable vaccine platform, permitting the delivery of recombinants targeting important pediatric respiratory pathogens, RSV chief among them.

Maternal vaccines

Acute lower respiratory illness (LRI) is the leading cause of disease worldwide as measured by disability-adjusted life years. New strategies are necessary to decrease the disease burden that is largely borne by infants. Respiratory syncytial virus is the most important cause of LRI in infants. Lower respiratory illness can be prevented by endowing infants with high levels of neutralizing antibodies from mothers whose antibodies are boosted during pregnancy with a potent subunit vaccine. Another important cause of infant mortality is group B streptococcus sepsis in the neonatal period; maternal immunization with a group B conjugate vaccine could prevent this devastating infection.

Respiratory syncytial virus vaccine development

Development of an RSV vaccine for infants has been hindered by the lack of an ideal animal model that exhibits disease, and the challenge of effectively immunizing very young infants who are immunologically immature. Nevertheless, significant progress has been made recently in developing live attenuated viruses and protein subunit vaccine candidates. Numerous vaccine candidates are currently in early clinical trials. This paper reviews the significant obstacles to development of RSV vaccines, and the progress made to date.

Vaccines in pregnancy

The concept of maternal immunization to prevent infectious diseases during a period of increased vulnerability in the infant is supported by historical experience and carefully conducted studies of various viral and bacterial vaccines. Candidate vaccines should be minimally reactogenic, immunogenic, and safe. Health education and access to immunization should be a priority if maternal immunization is to succeed as a disease prevention strategy. The potential effect on the incidence of disease in the newborn and young infant can only increase as more candidate vaccines that could be administered during pregnancy become available. In the future, common infections and other, more dreaded diseases, such as herpes simplex virus infection, cytomegalovirus, and human immunodeficiency virus infection, could be prevented with this intervention. Further research on the safety and efficacy of maternal immunization must continue if the occurrence of serious infectious diseases in neonates and young infants is to be reduced.

Respiratory syncytial virus infection in adults

Respiratory syncytial virus (RSV) is now recognized as a significant problem in certain adult populations. These include the elderly, persons with cardiopulmonary diseases, and immunocompromised hosts. Epidemiological evidence indicates that the impact of RSV in older adults may be similar to that of nonpandemic influenza. In addition, RSV has been found to cause 2 to 5% of adult community-acquired pneumonias. Attack rates in nursing homes are approximately 5 to 10% per year, with significant rates of pneumonia (10 to 20%) and death (2 to 5%). Clinical features may be difficult to distinguish from those of influenza but include nasal congestion, cough, wheezing, and low-grade fever. Bone marrow transplant patients prior to marrow engraftment are at highest risk for pneumonia and death. Diagnosis of RSV infection in adults is difficult because viral culture and antigen detection are insensitive, presumably due to low viral titers in nasal secretions, but early bronchoscopy is valuable in immunosuppressed patients. Treatment of RSV in the elderly is largely supportive, whereas early therapy with ribavirin and intravenous gamma globulin is associated with improved survival in immunocompromised persons. An effective RSV vaccine has not yet been developed, and thus prevention of RSV infection is limited to standard infection control practices such as hand washing and the use of gowns and gloves.

Respiratory syncytial virus infection in adults

Respiratory syncytial virus (RSV) is now recognized as a significant problem in certain adult populations. These include the elderly, persons with cardiopulmonary diseases, and immunocompromised hosts. Epidemiological evidence indicates that the impact of RSV in older adults may be similar to that of nonpandemic influenza. In addition, RSV has been found to cause 2 to 5% of adult community-acquired pneumonias. Attack rates in nursing homes are approximately 5 to 10% per year, with significant rates of pneumonia (10 to 20%) and death (2 to 5%). Clinical features may be difficult to distinguish from those of influenza but include nasal congestion, cough, wheezing, and low-grade fever. Bone marrow transplant patients prior to marrow engraftment are at highest risk for pneumonia and death. Diagnosis of RSV infection in adults is difficult because viral culture and antigen detection are insensitive, presumably due to low viral titers in nasal secretions, but early bronchoscopy is valuable in immunosuppressed patients. Treatment of RSV in the elderly is largely supportive, whereas early therapy with ribavirin and intravenous gamma globulin is associated with improved survival in immunocompromised persons. An effective RSV vaccine has not yet been developed, and thus prevention of RSV infection is limited to standard infection control practices such as hand washing and the use of gowns and gloves.

A step ahead. Infant protection through maternal immunization

The concept of maternal immunization to prevent infectious diseases during a period of increased vulnerability in infants is not new and is supported by historical experience and carefully conducted studies of various viral and bacterial vaccines. Candidate vaccines should be minimally reactogenic, immunogenic, and safe for maternal immunization to be considered as a disease prevention strategy. The possibilities increase as more potential candidate vaccines for use during pregnancy become available, including conjugate meningococcal vaccines, parainfluenza virus type 3 purified subunit vaccines, herpes simplex virus, cytomegalovirus, and HIV vaccines. Additional research on the safety and efficacy of maternal immunization must continue to effect the development of infectious diseases in neonates and infants.

Immune responses of infants to infection with respiratory viruses and live attenuated respiratory virus candidate vaccines

Respiratory viruses such as respiratory syncytial virus (RSV), the parainfluenza viruses (PIV), and the influenza viruses cause severe lower respiratory tract diseases in infants and children throughout the world. Experimental live attenuated vaccines for each of these viruses are being developed for intranasal administration in the first weeks or months of life. A variety of promising RSV, PIV-3, and influenza virus vaccine strains have been developed by classical biological methods, evaluated extensively in preclinical and clinical studies, and shown to be attenuated and genetically stable. The ongoing clinical evaluation of these vaccine candidates, coupled with recent major advances in the ability to develop genetically engineered viruses with specified mutations, may allow the rapid development of respiratory virus strains that possess ideal levels of replicative capacity and genetic stability in vivo. A major remaining obstacle to successful immunization of infants against respiratory virus associated disease may be the relatively poor immune response of very young infants to primary virus infection. This paper reviews the immune correlates of protection against disease caused by these viruses, immune responses of infants to naturally-acquired infection, and immune responses of infants to experimental infection with candidate vaccine viruses.

Maternal immunization against viral disease

The protective effect of maternal antibody against many viral diseases has been recognized. The use of maternal immunization has been considered as a means to augment this protection in the young infant against disease. Advantages of maternal immunization include the fact that young infants are most susceptible to infections but least responsive to vaccines, that pregnant women are accessible to medical care and respond well to vaccines, that IgG antibodies cross the placenta well during the third trimester, and that immunization of the pregnant woman has the potential to benefit both the mother and the infant. Disadvantages include the potential inhibition of an infant's response to active immunization or natural infection and liability issues with pharmaceutical companies and physicians. Immunization of pregnant women with viral vaccines for poliovirus, influenza viruses, and rubella has been described and maternal vaccination with these vaccines has been found to be safe for both the mother and the fetus. An open-label study of post-partum women immunized with the purified fusion protein of RSV (PFP-2, Wyeth-Lederle Pediatrics and Vaccines, Inc., Pearl River, NY) demonstrated that the vaccine was non-reactogenic and immunogenic; RSV-specific antibody was detected in breast milk. Immunization of pregnant women with purified protein or subunit vaccines could be considered against neonatal viral pathogens, such as respiratory syncytial virus, parainfluenza viruses, herpes group viruses, and human immunodeficiency virus. Further studies are needed to define the safety and efficacy of maternal immunization.

Prevalence of antibodies against HEp-2 cell antigen in infants and children hospitalized with respiratory syncytial virus infection

Infants with respiratory syncytial virus (RSV) infection were shown to have antibodies against HEp-2 cell antigen present in RSV-antigen preparation used for immunoblot analysis. The prevalence of anti HEp-2 cell antibodies was examined in infants hospitalized for RSV infection (n = 49, median age 121 days) compared to rotavirus infected children (n = 30, median age 114 days) and to healthy controls (n = 20, median age 150 days). The immunoblot analysis with RSV-infected and non-infected HEp-2 cells as antigen revealed the expected age-dependent low prevalence of G protein antibodies and clear seroconversion of N and P protein antibodies. HEp-2 antibody prevalence was higher in RSV antigen-positive infants (33/49) than in rotavirus antigen-positive (5/30) and RSV antigen-negative infants (4/20), respectively (p < 0.001). Anti HEp-2 antibodies were mostly directed against 47, 46, 33, 30 kD antigens. A multiple regression analysis found the following correlations (odds ratio; 95% confidence interval): 42 kD RSV antibodies (N protein) with pneumonia (7.58; 1.43-40), 94 kD RSV antibodies (G protein) with bronchiolitis (0.064; 0.006-0.686). This study shows repeated well-known features of humoral immunity in RSV infection. The data on anti HEp-2 antibodies point to a role for these pre-existing autoreactive antibodies in the pathogenesis of RSV infection.

Purified fusion protein vaccine protects against lower respiratory tract illness during respiratory syncytial virus season in children with cystic fibrosis

OBJECTIVE

To test in a double blind, placebo-controlled study a purified fusion protein (PFP-2) vaccine against respiratory syncytial virus (RSV) in RSV-seropositive children with cystic fibrosis (CF).

METHODS

Seventeen CF children, mean age 4.5 years, received PFP-2 vaccine and 17 CF children, mean age 5.8 years, received a saline vaccine. At enrollment the Shwachman clinical score, Brasfield radiographic score, oxygen saturation (SpO2), anthropometric indices and other variables were recorded. After vaccination the reactions were assessed daily for 7 days. During the RSV season weekly telephone interviews were performed and children with an acute respiratory illness were evaluated and cultured for RSV. Serum was drawn before vaccination, 1 month after vaccination and at the end of the RSV season and tested for antibodies to RSV.

RESULTS

Other than age the baseline measurements at enrollment were similar between groups. The PFP-2 vaccine produced mild local reactions and induced a significant neutralizing antibody response in two-thirds of the vaccinees and a significant enzyme-linked immunosorbent assay-fusion glycoprotein antibody response in nearly all the PFP-2 vaccinees. Vaccine-enhanced disease was not observed in PFP-2 vaccines infected with RSV. Protection against RSV infection was not observed; however, a significant reduction (t test, P < 0.01) in mean number of lower respiratory tract illnesses (0.8 vs. 2.1), antibiotic courses (2.2 vs 4.5) and days ill (30.5 vs. 67) occurred among RSV-infected PFP-2 vaccinees.

CONCLUSIONS

Efficacy of the PFP-2 vaccine against lower respiratory tract illness during the RSV season was shown in RSV-seropositive children with CF.

Attenuated temperature-sensitive respiratory syncytial virus mutants generated by cold adaptation

Two strains of respiratory syncytial virus (RSV), RSV 2B and RSV 3A (representing subgroup B and A virus respectively) were cold-adapted by passaging in Vero cells for up to 42 weeks at successively lower temperatures down to 20 degrees C. Successful cold adaptation of the virus population was dependent on the amount of time the cultures were maintained at the various low temperatures, as well as on the strain of virus used. Temperature-sensitive (TS) mutants appeared in the cold passaged virus populations; however, the majority of the virus variants remained predominantly non-TS. Four RSV 2B and three RSV 3A TS mutants were selected for further characterization. These seven TS mutants retained their fusion phenotype and two major neutralizing antibody epitopes, and displayed varying levels of temperature sensitivity. Six of the seven mutants had a cold-adapted (CA) phenotype. All of the RSV 2B mutants were highly attenuated in cotton rats and two of the mutants elicited relatively high levels of neutralizing antibody and were able to protect rats against virus challenge. The RSV 3A TS mutants grew well in the nose but poorly in the cotton rat lungs, as did the parental 3A virus. All 3A mutants elicited high titers of neutralizing antibody and provided complete protection against virus challenge. These mutants showed varying levels of temperature sensitivity in vitro and attenuation in vivo and represent potential vaccine candidates.

Immunity to human and bovine respiratory syncytial virus

Human and bovine respiratory syncytial viruses resemble each other closely. During annual winter outbreaks, they cause similar respiratory tract disease in infants and calves. The disease is most severe in children and calves between 1 and 3 months old, when maternal antibodies against the virus are usually present. Reinfections, which are common, are accompanied by progressively milder illnesses in children, but are symptomless in calves. Because maternal antibodies suppress serum and mucosal antibody responses of all isotypes, the development of a vaccine that is effective in young children and calves with high levels of maternal antibodies has been severely hampered. Although virus administered intranasally to young calves with maternal antibodies does not evoke antibody responses, it can prime these calves for a protective memory response upon reinfection. Protection appears to be associated with the capacity to mount a mucosal memory IgA response. There are several indications that one or more immunopathologic mechanisms contribute to the disease. An Arthus reaction (type III) may have a role in the pathogenesis, because activated complement may cause most of the pathologic lesions, including edema and emphysema in uninfected parts of the lung. Lungs from calves with severe or fatal disease have depositions of complement component C3 and a low histamine content. The most immunogenic and protective antigen of the virus is the fusion (F) glycoprotein, which evokes a strong antibody response and is a target for cytotoxic T cells. On the F protein, epitopes that induce neutralizing and non-neutralizing antibodies, both of which may enhance complement activation, were identified. Immunity to the F protein may have beneficial and harmful effects.