New Insights Contributing to the Development of Effective Vaccines and Therapies to Reduce the Pathology Caused by hRSV

A molecular perspective for the development of antibodies against the human respiratory syncytial virus

The human respiratory syncytial virus (hRSV) is the leading etiologic agent causing respiratory infections in infants, children, older adults, and patients with comorbidities. Sixty-seven years have passed since the discovery of hRSV, and only a few successful mitigation or treatment tools have been developed against this virus. One of these is immunotherapy with monoclonal antibodies against structural proteins of the virus, such as Palivizumab, the first prophylactic approach approved by the Food and Drug Administration (FDA) of the USA. In this article, we discuss different strategies for the prevention and treatment of hRSV infection, focusing on the molecular mechanisms against each target that underly the rational design of antibodies against hRSV. At the same time, we describe the latest results regarding currently approved therapies against hRSV and the challenges associated with developing new candidates.

From animal studies into clinical trials: the relevance of animal models to develop vaccines and therapies to reduce disease severity and prevent hRSV infection

INTRODUCTION

Human respiratory syncytial virus (hRSV) is an important cause of lower respiratory tract infections in the pediatric and the geriatric population worldwide. There is a substantial economic burden resulting from hRSV disease during winter. Although no vaccines have been approved for human use, prophylactic therapies are available for high-risk populations. Choosing the proper animal models to evaluate different vaccine prototypes or pharmacological treatments is essential for developing efficient therapies against hRSV.

AREAS COVERED

This article describes the relevance of using different animal models to evaluate the effect of antiviral drugs, pharmacological molecules, vaccine prototypes, and antibodies in the protection against hRSV. The animal models covered are rodents, mustelids, bovines, and nonhuman primates. Animals included were chosen based on the available literature and their role in the development of the drugs discussed in this manuscript.

EXPERT OPINION

Choosing the correct animal model is critical for exploring and testing treatments that could decrease the impact of hRSV in high-risk populations. Mice will continue to be the most used preclinical model to evaluate this. However, researchers must also explore the use of other models such as nonhuman primates, as they are more similar to humans, prior to escalating into clinical trials.

The Causes and Long-Term Consequences of Viral Encephalitis

Reports regarding brain inflammation, known as encephalitis, have shown an increasing frequency during the past years. Encephalitis is a relevant concern to public health due to its high morbidity and mortality. Infectious or autoimmune diseases are the most common cause of encephalitis. The clinical symptoms of this pathology can vary depending on the brain zone affected, with mild ones such as fever, headache, confusion, and stiff neck, or severe ones, such as seizures, weakness, hallucinations, and coma, among others. Encephalitis can affect individuals of all ages, but it is frequently observed in pediatric and elderly populations, and the most common causes are viral infections. Several viral agents have been described to induce encephalitis, such as arboviruses, rhabdoviruses, enteroviruses, herpesviruses, retroviruses, orthomyxoviruses, orthopneumovirus, and coronaviruses, among others. Once a neurotropic virus reaches the brain parenchyma, the resident cells such as neurons, astrocytes, and microglia, can be infected, promoting the secretion of pro-inflammatory molecules and the subsequent immune cell infiltration that leads to brain damage. After resolving the viral infection, the local immune response can remain active, contributing to long-term neuropsychiatric disorders, neurocognitive impairment, and degenerative diseases. In this article, we will discuss how viruses can reach the brain, the impact of viral encephalitis on brain function, and we will focus especially on the neurocognitive sequelae reported even after viral clearance.

Palivizumab for preventing severe respiratory syncytial virus (RSV) infection in children

BACKGROUND

Respiratory viruses are the leading cause of lower respiratory tract infection (LRTI) and hospitalisation in infants and young children. Respiratory syncytial virus (RSV) is the main infectious agent in this population. Palivizumab is administered intramuscularly every month during five months in the first RSV season to prevent serious RSV LRTI in children. Given its high cost, it is essential to know if palivizumab continues to be effective in preventing severe RSV disease in children.

OBJECTIVES

To assess the effects of palivizumab for preventing severe RSV infection in children.

SEARCH METHODS

We searched CENTRAL, MEDLINE, three other databases and two trials registers to 14 October 2021, together with reference checking, citation searching and contact with study authors to identify additional studies. We searched Embase to October 2020, as we did not have access to this database for 2021.

SELECTION CRITERIA

We included randomised controlled trials (RCTs), including cluster-RCTs, comparing palivizumab given at a dose of 15 mg/kg once a month (maximum five doses) with placebo, no intervention or standard care in children 0 to 24 months of age from both genders, regardless of RSV infection history.  DATA COLLECTION AND ANALYSIS: We used Cochrane's Screen4Me workflow to help assess the search results. Two review authors screened studies for selection, assessed risk of bias and extracted data. We used standard Cochrane methods. We used GRADE to assess the certainty of the evidence. The primary outcomes were hospitalisation due to RSV infection, all-cause mortality and adverse events. Secondary outcomes were hospitalisation due to respiratory-related illness, length of hospital stay, RSV infection, number of wheezing days, days of supplemental oxygen, intensive care unit length of stay and mechanical ventilation days.

MAIN RESULTS

We included five studies with  a total of 3343 participants. All studies were parallel RCTs, assessing the effects of 15 mg/kg of palivizumab every month up to five months compared to placebo or no intervention in an outpatient setting, although one study also included hospitalised infants. Most of the included studies were conducted in children with a high risk of RSV infection due to comorbidities like bronchopulmonary dysplasia and congenital heart disease. The risk of bias of outcomes across all studies was similar and predominately low.  Palivizumab reduces hospitalisation due to RSV infection at two years' follow-up (risk ratio (RR) 0.44, 95% confidence interval (CI) 0.30 to 0.64; 5 studies, 3343 participants; high certainty evidence). Based on 98 hospitalisations per 1000 participants in the placebo group, this corresponds to 43 (29 to 62) per 1000 participants in the palivizumab group. Palivizumab probably results in little to no difference in mortality at two years' follow-up (RR 0.69, 95% CI 0.42 to 1.15; 5 studies, 3343 participants; moderate certainty evidence). Based on 23 deaths per 1000 participants in the placebo group, this corresponds to 16 (10 to 27) per 1000 participants in the palivizumab group. Palivizumab probably results in little to no difference in adverse events at 150 days' follow-up (RR 1.09, 95% CI 0.85 to 1.39; 3 studies, 2831 participants; moderate certainty evidence). Based on 84 cases per 1000 participants in the placebo group, this corresponds to 91 (71 to 117) per 1000 participants in the palivizumab group. Palivizumab probably results in a slight reduction in hospitalisation due to respiratory-related illness at two years' follow-up (RR 0.78, 95% CI 0.62 to 0.97; 5 studies, 3343 participants; moderate certainty evidence). Palivizumab may result in a large reduction in RSV infection at two years' follow-up (RR 0.33, 95% CI 0.20 to 0.55; 3 studies, 554 participants; low certainty evidence). Based on 195 cases of RSV infection per 1000 participants in the placebo group, this corresponds to 64 (39 to 107) per 1000 participants in the palivizumab group. Palivizumab also reduces the number of wheezing days at one year's follow-up (RR 0.39, 95% CI 0.35 to 0.44; 1 study, 429 participants; high certainty evidence).

AUTHORS' CONCLUSIONS

The available evidence suggests that prophylaxis with palivizumab reduces hospitalisation due to RSV infection and results in little to no difference in mortality or adverse events. Moreover, palivizumab results in a slight reduction in hospitalisation due to respiratory-related illness and may result in a large reduction in RSV infections. Palivizumab also reduces the number of wheezing days. These results may be applicable to children with a high risk of RSV infection due to comorbidities. Further research is needed to establish the effect of palivizumab on children with other comorbidities known as risk factors for severe RSV disease (e.g. immune deficiencies) and other social determinants of the disease, including children living in low- and middle-income countries, tropical regions, children lacking breastfeeding, living in poverty, or members of families in overcrowded situations.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

First-in-Human Randomized Study to Assess the Safety and Immunogenicity of an Investigational Respiratory Syncytial Virus (RSV) Vaccine Based on Chimpanzee-Adenovirus-155 Viral Vector-Expressing RSV Fusion, Nucleocapsid, and Antitermination Viral Proteins in Healthy Adults

Background

Respiratory syncytial virus (RSV) disease is a major cause of infant morbidity and mortality. This Phase I, randomized, observer-blind, placebo- and active-controlled study evaluated an investigational vaccine against RSV (ChAd155-RSV) using the viral vector chimpanzee-adenovirus-155, encoding RSV fusion (F), nucleocapsid, and transcription antitermination proteins.

Methods

Healthy 18–45-year-old adults received ChAd155-RSV, a placebo, or an active control (Bexsero) at Days (D) 0 and 30. An escalation from a low dose (5 × 10⁹ viral particles) to a high dose (5 × 10¹⁰ viral particles) occurred after the first 16 participants. Endpoints were solicited/unsolicited and serious adverse events (SAEs), biochemical/hematological parameters, cell-mediated immunogenicity by enzyme-linked immunospot, functional neutralizing antibodies, anti RSV-F immunoglobin (Ig) G, and ChAd155 neutralizing antibodies.

Results

There were 7 participants who received the ChAd155-RSV low dose, 31 who received the ChAd155-RSV high dose, 19 who received the placebo, and 15 who received the active control. No dose-related toxicity or attributable SAEs at the 1-year follow-up were observed. The RSV-A neutralizing antibodies geometric mean titer ratios (post/pre-immunization) following a high dose were 2.6 (D30) and 2.3 (D60). The ratio of the fold-rise (D0 to D30) in anti-F IgG over the fold-rise in RSV-A–neutralizing antibodies was 1.01. At D7 after the high dose of the study vaccine, the median frequencies of circulating B-cells secreting anti-F antibodies were 133.3/10⁶ (IgG) and 16.7/10⁶ (IgA) in peripheral blood mononuclear cells (PBMCs). The median frequency of RSV-F–specific interferon γ–secreting T-cells after a ChAd155-RSV high dose was 108.3/10⁶ PBMCs at D30, with no increase after the second dose.

Conclusions

In adults previously naturally exposed to RSV, ChAd155-RSV generated increases in specific humoral and cellular immune responses without raising significant safety concerns.

Clinical Trials Registration

NCT02491463.

Seasonality of Respiratory Syncytial Virus Hospitalization

Seasonality of respiratory syncytial virus (RSV) infection is an area of limited knowledge. In this study, we set out to get insight into the epidemic characteristics of RSV. We retrospectively evaluated medical files of 512 hospitalizations in children due to RSV infection from January 2010 to July 2017. In this cohort of patients, there were 96.3% of children below 1 year of age; the median age was 2.8 months. The influence of weather condition during the week of hospitalization (WH) and also the preceding week (WP) on the rate of hospitalizations was also assessed. An overview of morbidity data demonstrates that the epidemic RSV season started from Week 50 of a year and lasts until Week 15 of the following year, with a peak between Week 4 and Week 10. The average monthly percentage rate of morbidity per year was as follows: December, 12.3%; January, 24.5%; February, 29%; and March, 21.7%. Hospitalizations were positively associated with the minimum and maximum outside air temperature during the WH (62.5% and 59.7%, respectively) and the WP (64.3% and 63.4%, respectively) and with relative humidity (WH 23% and WP 29.8%). A weak association with the wind speed was also noticed (WH 22% and WP 21%), while there was no influence of the level of atmospheric pressure on RSV morbidity. We conclude that seasonality of RSV is present between December and April each year, and morbidity is mostly influenced by minimum-maximum outside air temperature changes. Further epidemiological exploration is required to get a better knowledge on both active and passive immunization against RSV.

Pharmacological management of human respiratory syncytial virus infection

INTRODUCTION

Human respiratory syncytial virus (hRSV) is the primary viral cause of respiratory diseases, leading to bronchiolitis and pneumonia in vulnerable populations. The only current treatment against this virus is palliative, and no efficient and specific vaccine against this pathogen is available.

AREAS COVERED

The authors describe the disease symptoms caused by hRSV, the economic and social impact of this infection worldwide, and how this infection can be modulated using pharmacological treatments, preventing and limiting its dissemination. The authors discuss the use of antibodies as prophylactic tools -such as palivizumab- and the use of nonspecific drugs to decrease the symptoms associated with the infection -such as bronchodilators, corticoids, and antivirals. They also discuss current vaccine candidates, new prophylactic treatments, and new antivirals options, which are currently being tested.

EXPERT OPINION

Today, many researchers are focused on developing different strategies to modulate the symptoms induced by hRSV. However, to achieve this, understanding how current treatments are working and their shortcomings needs to be further elucidated.

Antibody development for preventing the human respiratory syncytial virus pathology

Human respiratory syncytial virus (hRSV) is the most important etiological agent causing hospitalizations associated with respiratory diseases in children under 5 years of age as well as the elderly, newborns and premature children are the most affected populations. This viral infection can be associated with various symptoms, such as fever, coughing, wheezing, and even pneumonia and bronchiolitis. Due to its severe symptoms, the need for mechanical ventilation is not uncommon in clinical practice. Additionally, alterations in the central nervous system -such as seizures, encephalopathy and encephalitis- have been associated with cases of hRSV-infections. Furthermore, the absence of effective vaccines or therapies against hRSV leads to elevated expenditures by the public health system and increased mortality rates for the high-risk population. Along these lines, vaccines and therapies can elicit different responses to this virus. While hRSV vaccine candidates seek to promote an active immune response associated with the achievement of immunological memory, other therapies -such as the administration of antibodies- provide a protective environment, although they do not trigger the activation of the immune system and therefore do not promote an immunological memory. An interesting approach to vaccination is the use of virus-neutralizing antibodies, which inhibit the entry of the pathogen into the host cells, therefore impairing the capacity of the virus to replicate. Currently, the most common molecule targeted for antibody design against hRSV is the F protein of this virus. However, other molecular components of the virus -such as the G or the N hRSV proteins- have also been explored as potential targets for the control of this disease. Currently, palivizumab is the only monoclonal antibody approved for human use. However, studies in humans have shown a protective effect only after the administration of at least 3 to 5 doses, due to the stability of this vaccine. Furthermore, other studies suggest that palivizumab only has an effectiveness close to 50% in high-risk infants. In this work, we will review different strategies addressed for the use of antibodies in a prophylactic or therapeutic context and their ability to prevent the symptoms caused by hRSV infection of the airways, as well as in other tissues such as the CNS.

Up-to-date role of biologics in the management of respiratory syncytial virus

INTRODUCTION

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease in young children and a substantial contributor to respiratory tract disease throughout life. Despite RSV being a high priority for vaccine development, there is currently no safe and effective vaccine available. There are many challenges to developing an RSV vaccine and there are limited antiviral drugs or biologics available for the management of infection. In this article, we review the antiviral treatments, vaccination strategies along with alternative therapies for RSV.

AREAS COVERED

This review is a summary of the current antiviral and RSV vaccination approaches noting strategies and alternative therapies that may prevent or decrease the disease severity in RSV susceptible populations.

EXPERT OPINION

This review discusses anti-RSV strategies given that no safe and efficacious vaccines are available, and therapeutic treatments are limited. Various biologicals that target for RSV are considered for disease intervention, as it is likely that it may be necessary to develop separate vaccines or therapeutics for each at-risk population.

Molecular characterization of the glycoprotein and fusion protein in human respiratory syncytial virus subgroup A: Emergence of ON-1 genotype in Iran

HRSV is a principle cause of infant hospitalization, childhood wheezing and a common pathogen in the elderly. Limited information exists regarding HRSV genotypes in Iran. In order to better understand HRSV strain diversity, we performed an in-depth evaluation of the genetic variability of the HRSV F protein detected in children under two years of age that, presented with acute respiratory symptoms during 2015-2016 in Tehran. A total of 180 nasopharyngeal swabs were evaluated. The HRSV positive samples were genotyped for G and F gene sequences using RT-PCR and sequencing methods. Phylogenetic analysis was performed using the neighbor-joining and maximum likelihood methods. Genetic and antigenic characteristics of the F gene, nucleotide and amino acids in significant positions and immune system binding regions, as well as the p-distance, positive/negative selection site, linear epitopes and glycosylation sites were investigated in all selected sequences. Among the 83 HRSV positive samples, the Fifty-five cases were successfully sequenced. All of them were classified as subgroup A and belonged to the ON-1 genotype, which possessed 72-nt duplication in the G gene. This study is the first report on the emergence of ON-1 in Iran. ON-1 Iranian sequences clustered in three lineages according to virus fusion (F) gene variations. F gene sequence analysis showed that all genetic changes in the isolates from Iran were base substitutions and no deletion/insertions were identified. The low dN/dS ratio and lack of positively selected sites showed that the fusion genes found in the strains from Iran are not under host selective pressure. Continuing and long-term molecular epidemiological surveys for early detection of circulating and newly emerging genotypes are necessary to gain a better understanding of their epidemic potential.

Active prophylaxis for respiratory syncytial virus: current knowledge and future perspectives

Respiratory syncytial virus (RSV) is the most common respiratory pathogen in infants and young children but represents also an important cause of morbidity in adults, particularly in the elderly and immunocompromised persons. Despite its global impact on human health, no effective treatment is available except for supportive care and no safe vaccine has been licensed yet. Vaccine development has been hindered by several factors including vaccine enhanced disease associated with formalin-inactivated RSV vaccine, ethical concerns and lack of consensus concerning the most appropriate target antigen. In this review, we analyze history of RSV vaccine and current approaches for preventing RSV including live-attenuated, vector-based, subunit, nucleic acid-based, particle-based vaccines and we debate about concerns on target population, correlates of protection and obstacles that are slowing the progress toward a successful RSV vaccination strategy.