Efficient lung recruitment of respiratory syncytial virus-specific Th1 cells induced by recombinant bacillus Calmette-Guérin promotes virus clearance and protects from infection

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.

All Eyes on the Prefusion-Stabilized F Construct, but Are We Missing the Potential of Alternative Targets for Respiratory Syncytial Virus Vaccine Design?

Respiratory Syncytial Virus (RSV) poses a significant global health concern as a major cause of lower respiratory tract infections (LRTIs). Over the last few years, substantial efforts have been directed towards developing vaccines and therapeutics to combat RSV, leading to a diverse landscape of vaccine candidates. Notably, two vaccines targeting the elderly and the first maternal vaccine have recently been approved. The majority of the vaccines and vaccine candidates rely solely on a prefusion-stabilized conformation known for its highly neutralizing epitopes. Although, so far, this antigen design appears to be successful for the elderly, our current understanding remains incomplete, requiring further improvement and refinement in this field. Pediatric vaccines still have a long journey ahead, and we must ensure that vaccines currently entering the market do not lose efficacy due to the emergence of mutations in RSV's circulating strains. This review will provide an overview of the current status of vaccine designs and what to focus on in the future. Further research into antigen design is essential, including the exploration of the potential of alternative RSV proteins to address these challenges and pave the way for the development of novel and effective vaccines, especially in the pediatric population.

Respiratory Syncytial Virus Vaccines: A Review of the Candidates and the Approved Vaccines

Respiratory syncytial virus (RSV) is responsible for a significant proportion of global morbidity and mortality affecting young children and older adults. In the aftermath of formalin-inactivated RSV vaccine development, the effort to develop an immunizing agent was carefully guided by epidemiologic and pathophysiological evidence of the virus, including various vaccine technologies. The pipeline of RSV vaccine development includes messenger ribonucleic acid (mRNA), live-attenuated (LAV), subunit, and recombinant vector-based vaccine candidates targeting different virus proteins. The availability of vaccine candidates of various technologies enables adjustment to the individualized needs of each vulnerable age group. Arexvy® (GSK), followed by Abrysvo® (Pfizer), is the first vaccine available for market use as an immunizing agent to prevent lower respiratory tract disease in older adults. Abrysvo is additionally indicated for the passive immunization of infants by maternal administration during pregnancy. This review presents the RSV vaccine pipeline, analyzing the results of clinical trials. The key features of each vaccine technology are also mentioned. Currently, 24 vaccines are in the clinical stage of development, including the 2 licensed vaccines. Research in the field of RSV vaccination, including the pharmacovigilance methods of already approved vaccines, promotes the achievement of successful prevention.

Characterization of the humoral and cellular immunity induced by a recombinant BCG vaccine for the respiratory syncytial virus in healthy adults

Introduction

The human respiratory syncytial virus (hRSV) is responsible for most respiratory tract infections in infants. Even though currently there are no approved hRSV vaccines for newborns or infants, several candidates are being developed. rBCG-N-hRSV is a vaccine candidate previously shown to be safe in a phase I clinical trial in adults (clinicaltrials.gov identifier #NCT03213405). Here, secondary immunogenicity analyses were performed on these samples.

Methods

PBMCs isolated from immunized volunteers were stimulated with hRSV or mycobacterial antigens to evaluate cytokines and cytotoxic T cell-derived molecules and the expansion of memory T cell subsets. Complement C1q binding and IgG subclass composition of serum antibodies were assessed.

Results

Compared to levels detected prior to vaccination, perforin-, granzyme B-, and IFN-γ-producing PBMCs responding to stimulus increased after immunization, along with their effector memory response. N-hRSV- and mycobacterial-specific antibodies from rBCG-N-hRSV-immunized subjects bound C1q.

Conclusion

Immunization with rBCG-N-hRSV induces cellular and humoral immune responses, supporting that rBCG-N-hRSV is immunogenic and safe in healthy individuals.

Clinical trial registration

https://classic.clinicaltrials.gov/ct2/show/, identifier NCT03213405.

Current GMP standards for the production of vaccines and antibodies: An overview

The manufacture of pharmaceutical products made under good manufacturing practices (GMP) must comply with the guidelines of national regulatory bodies based on international or regional compendia. The existence of this type of regulation allows pharmaceutical laboratories to count on the standardization of high-quality production processes, obtaining a safe product for human use, with a positive impact on public health. In addition, the COVID-19 pandemic highlights the importance of having more and better-distributed manufacturing plants, emphasizing regions such as Latin America. This review shows the most important GMP standards in the world and, in particular, their relevance in the production of vaccines and antibodies.

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.

Female offspring gestated in hypothyroxinemia and infected with human Metapneumovirus (hMPV) suffer a more severe infection and have a higher number of activated CD8+ T lymphocytes

Maternal thyroid hormones (THs) are essential for the appropriate development of the fetus and especially for the brain. Recently, some studies have shown that THs deficiency can also alter the immune system development of the progeny and their ability to mount an appropriate response against infectious agents. In this study, we evaluated whether adult mice gestated under hypothyroxinemia (Hpx) showed an altered immune response against infection with human metapneumovirus (hMPV). We observed that female mice gestated under Hpx showed higher clinical scores after seven days of hMPV infection. Besides, males gestated under Hpx have higher lung viral loads at day seven post-infection. Furthermore, the female offspring gestated in Hpx have already reduced the viral load at day seven and accordingly showed an increased proportion of activated (CD71⁺ and FasL⁺) CD8⁺ T cells in the lungs, which correlated with a trend for a higher histopathological clinical score. These results support that T₄ deficiency during gestation might condition the offspring differently in males and females, enhancing their ability to respond to hMPV.

BCG-Based Vaccines Elicit Antigen-Specific Adaptive and Trained Immunity against SARS-CoV-2 and Andes orthohantavirus

Background:Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is a live attenuated vaccine mainly administered to newborns and used for over 100 years to prevent the disease caused by Mycobacterium tuberculosis (M. tb). This vaccine can induce immune response polarization towards a Th1 profile, which is desired for counteracting M. tb, other mycobacteria, and unrelated intracellular pathogens. The vaccine BCG has been used as a vector to express recombinant proteins and has been shown to protect against several diseases, particularly respiratory viruses. Methods: BCG was used to develop recombinant vaccines expressing either the Nucleoprotein from SARS-CoV-2 or Andes orthohantavirus. Mice were immunized with these vaccines with the aim of evaluating the safety and immunogenicity parameters. Results: Immunization with two doses of 1 × 10⁸ CFU or one dose of 1 × 10⁵ CFU of these BCGs was safe in mice. A statistically significant cellular immune response was induced by both formulations, characterized as the activation of CD4⁺ and CD8⁺ T cells. Stimulation with unrelated antigens resulted in increased expression of activation markers by T cells and secretion of IL-2 and IFN-γ, while increased secretion of IL-6 was found for both recombinant vaccines; all of these parameters related to a trained immunity profile. The humoral immune response elicited by both vaccines was modest, but further exposure to antigens could increase this response. Conclusions: The BCG vaccine is a promising platform for developing vaccines against different pathogens, inducing a marked antigen-specific immune response.

Punicalagin Alleviates Aged Bronchial Asthma by Inhibiting Th2 Differentiation through IL-4/STAT6 and Jagged1/Notch Pathways

OBJECTIVE

To explore the therapeutic effect and mechanism of punicalagin on bronchial asthma in the elderly.

METHODS

Peripheral venous blood was collected from healthy people and elderly patients with bronchial asthma. Peripheral blood mononuclear cells (PBMCs) were isolated and cultured. PBMCs in the patient group were treated with different concentrations (0, 50, 100, and 200 mg/L) of punicalagin (PUN). MTT assay was used to detect cell activity, ELISA was used to detect the levels of IFN-γ, IL-2, IL-4, and IL-5, and Western blotting was used to detect the protein levels of p-STAT6, Jagged1, and GATA3.

RESULT

MTT results showed that 50-200 mg/L PUN had no cytotoxicity to PBMCs within 24 h. ELISA results showed that the levels of IFN-γ and IL-2 in the serum of the patients were significantly lower than those of healthy people, and the levels of IL-4 and IL-5 were significantly higher than those of the healthy people. PUN treatment significantly increased the levels of IFN-γ and IL-2 in the supernatant of PBMCs culture, while significantly decreased the levels of IL-4 and IL-5, and the change was proportional to the concentration of PUN. Western blotting results showed that the levels of p-STAT6, Jagged1, and GATA3 protein in PBMCs of patients were significantly higher than those of the healthy people. PUN treatment could significantly reduce the expression of p-STAT6, Jagged1, and GATA3 protein in PBMCs of patients, and the reduction level was proportional to PUN concentration.

CONCLUSION

PUN can inhibit Th2 differentiation and regulate Th1/Th2 balance by regulating IL-4/STAT6 and Jagged1/Notch pathways to alleviate the progress of bronchial asthma in the elderly.

A safe and effective mucosal RSV vaccine in mice consisting of RSV phosphoprotein and flagellin variant

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+ T cells 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.

A Recombinant BCG Vaccine Is Safe and Immunogenic in Neonatal Calves and Reduces the Clinical Disease Caused by the Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) constitutes a major health burden, causing millions of hospitalizations in children under five years old worldwide due to acute lower respiratory tract infections. Despite decades of research, licensed vaccines to prevent hRSV are not available. Development of vaccines against hRSV targeting young infants requires ruling out potential vaccine-enhanced disease presentations. To achieve this goal, vaccine testing in proper animal models is essential. A recombinant BCG vaccine that expresses the Nucleoprotein of hRSV (rBCG-N-hRSV) protects mice against hRSV infection, eliciting humoral and cellular immune protection. Further, this vaccine was shown to be safe and immunogenic in human adult volunteers. Here, we evaluated the safety, immunogenicity, and protective efficacy of the rBCG-N-hRSV vaccine in a neonatal bovine RSV calf infection model. Newborn, colostrum-replete Holstein calves were either vaccinated with rBCG-N-hRSV, WT-BCG, or left unvaccinated, and then inoculated via aerosol challenge with bRSV strain 375. Vaccination with rBCG-N-hRSV was safe and well-tolerated, with no systemic adverse effects. There was no evidence of vaccine-enhanced disease following bRSV challenge of rBCG-N-hRSV vaccinated animals, suggesting that the vaccine is safe for use in neonates. Vaccination increased virus-specific IgA and virus-neutralization activity in nasal fluid and increased the proliferation of virus- and BCG-specific CD4+ and CD8+ T cells in PBMCs and lymph nodes at 7dpi. Furthermore, rBCG-N-hRSV vaccinated calves developed reduced clinical disease as compared to unvaccinated control calves, although neither pathology nor viral burden were significantly reduced in the lungs. These results suggest that the rBCG-N-hRSV vaccine is safe in neonatal calves and induces protective humoral and cellular immunity against this respiratory virus. These data from a newborn animal model provide further support to the notion that this vaccine approach could be considered as a candidate for infant immunization against RSV.

The BCG Vaccine for COVID-19: First Verdict and Future Directions

Despite of the rapid development of the vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it will take several months to have enough doses and the proper infrastructure to vaccinate a good proportion of the world population. In this interim, the accessibility to the Bacille Calmette-Guerin (BCG) may mitigate the pandemic impact in some countries and the BCG vaccine offers significant advantages and flexibility in the way clinical vaccines are administered. BCG vaccination is a highly cost-effective intervention against tuberculosis (TB) and many low-and lower-middle-income countries would likely have the infrastructure, and health care personnel sufficiently familiar with the conventional TB vaccine to mount full-scale efforts to administer novel BCG-based vaccine for COVID-19. This suggests the potential for BCG to overcome future barriers to vaccine roll-out in the countries where health systems are fragile and where the effects of this new coronavirus could be catastrophic. Many studies have reported cross-protective effects of the BCG vaccine toward non-tuberculosis related diseases. Mechanistically, this cross-protective effect of the BCG vaccine can be explained, in part, by trained immunity, a recently discovered program of innate immune memory, which is characterized by non-permanent epigenetic reprogramming of macrophages that leads to increased inflammatory cytokine production and consequently potent immune responses. In this review, we summarize recent work highlighting the potential use of BCG for the treatment respiratory infectious diseases and ongoing SARS-CoV-2 clinical trials. In situations where no other specific prophylactic tools are available, the BCG vaccine could be used as a potential adjuvant, to decrease sickness of SARS-CoV-2 infection and/or to mitigate the effects of concurrent respiratory infections.

Induction of Trained Immunity by Recombinant Vaccines

Vaccines represent an important strategy to protect humans against a wide variety of pathogens and have even led to eradicating some diseases. Although every vaccine is developed to induce specific protection for a particular pathogen, some vaccine formulations can also promote trained immunity, which is a non-specific memory-like feature developed by the innate immune system. It is thought that trained immunity can protect against a wide variety of pathogens other than those contained in the vaccine formulation. The non-specific memory of the trained immunity-based vaccines (TIbV) seems beneficial for the immunized individual, as it may represent a powerful strategy that contributes to the control of pathogen outbreaks, reducing morbidity and mortality. A wide variety of respiratory viruses, including respiratory syncytial virus (hRSV) and metapneumovirus (hMPV), cause serious illness in children under 5 years old and the elderly. To address this public health problem, we have developed recombinant BCG vaccines that have shown to be safe and immunogenic against hRSV or hMPV. Besides the induction of specific adaptive immunity against the viral antigens, these vaccines could generate trained immunity against other respiratory pathogens. Here, we discuss some of the features of trained immunity induced by BCG and put forward the notion that recombinant BCGs expressing hRSV or hMPV antigens have the capacity to simultaneously induce specific adaptive immunity and non-specific trained immunity. These recombinant BCG vaccines could be considered as TIbV capable of inducing simultaneously the development of specific protection against hRSV or hMPV, as well as non-specific trained-immunity-based protection against other pathogenic viruses.

Safety and immunogenicity evaluation of recombinant BCG vaccine against respiratory syncytial virus in a randomized, double-blind, placebo-controlled phase I clinical trial

BACKGROUND

Respiratory syncytial virus (RSV) is responsible for most respiratory tract infections and hospitalizations in infants and represents a significant economic burden for public health. The development of a safe, effective, and affordable vaccine is a priority for the WHO.

METHODS

We conducted a double-blinded, escalating-dose phase 1 clinical trial in healthy males aged 18-50 years to evaluate safety, tolerability, and immunogenicity of a recombinant Mycobacterium bovis BCG vaccine expressing the nucleoprotein of RSV (rBCG-N-hRSV). Once inclusion criteria were met, volunteers were enrolled in three cohorts in an open and successive design. Each cohort included six volunteers vaccinated with 5 × 10³, 5 × 10⁴, or 1 × 10⁵ CFU, as well as two volunteers vaccinated with the full dose of the standard BCG vaccine. This clinical trial (clinicaltrials.gov NCT03213405) was conducted in Santiago, Chile.

FINDINGS

The rBCG-N-RSV vaccine was safe, well-tolerated, and no serious adverse events related to the vaccine were recorded. Serum IgG-antibodies directed against Mycobacterium and the N-protein of RSV increased after vaccination, which were capable of neutralizing RSV in vitro. Additionally, all volunteers displayed increased cellular response consisting of IFN-γ and IL-2 production against PPD and the N-protein, starting at day 14 and 30 post-vaccination respectively.

INTERPRETATION

The rBCG-N-hRSV vaccine had a good safety profile and induced specific cellular and humoral responses.

FUNDING

This work was supported by Millennium Institute on Immunology and Immunotherapy from Chile (P09/016), FONDECYT 1190830, and FONDEF D11E1098.

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.

Could BCG Vaccination Induce Protective Trained Immunity for SARS-CoV-2?

Trained immunity is a type of non-specific memory-like immune response induced by some pathogens and vaccines, such as BCG, which can confer antigen-independent protection against a wide variety of pathogens. The BCG vaccine has been extensively used to protect against tuberculosis for almost a 100 years. Interestingly, this vaccine reduces children's mortality caused by infections unrelated to Mycobacterium tuberculosis infection, a phenomenon thought to be due to the induction of trained immunity. The SARS-CoV-2 pandemic has infected, as of April 22, 2020, 2,623,231 people globally, causing a major public health problem worldwide. Currently, no vaccine or treatment is available to control this pandemic. We analyzed the number of positive cases and deaths in different countries and correlated them with the inclusion of BCG vaccination at birth in their national vaccination programs. Interestingly, those countries where BCG vaccination is given at birth have shown a lower contagion rate and fewer COVID-19-related deaths, suggesting that this vaccine may induce trained immunity that could confer some protection for SARS-CoV-2.

TCR Repertoire Characterization for T Cells Expanded in Response to hRSV Infection in Mice Immunized with a Recombinant BCG Vaccine

T cells play an essential role in the immune response against the human respiratory syncytial virus (hRSV). It has been described that both CD4⁺ and CD8⁺ T cells can contribute to the clearance of the virus during an infection. However, for some individuals, such an immune response can lead to an exacerbated and detrimental inflammatory response with high recruitment of neutrophils to the lungs. The receptor of most T cells is a heterodimer consisting of α and β chains (αβTCR) that upon antigen engagement induces the activation of these cells. The αβTCR molecule displays a broad sequence diversity that defines the T cell repertoire of an individual. In our laboratory, a recombinant Bacille Calmette–Guérin (BCG) vaccine expressing the nucleoprotein (N) of hRSV (rBCG-N-hRSV) was developed. Such a vaccine induces T cells with a Th1 polarized phenotype that promote the clearance of hRSV infection without causing inflammatory lung damage. Importantly, as part of this work, the T cell receptor (TCR) repertoire of T cells expanded after hRSV infection in naïve and rBCG-N-hRSV-immunized mice was characterized. A more diverse TCR repertoire was observed in the lungs from rBCG-N-hRSV-immunized as compared to unimmunized hRSV-infected mice, suggesting that vaccination with the recombinant rBCG-N-hRSV vaccine triggers the expansion of T cell populations that recognize more viral epitopes. Furthermore, differential expansion of certain TCRVβ chains was found for hRSV infection (TCRVβ⁺8.3 and TCRVβ⁺5.1,5.2) as compared to rBCG-N-hRSV vaccination (TCRVβ⁺11 and TCRVβ⁺12). Our findings contribute to better understanding the T cell response during hRSV infection, as well as the functioning of a vaccine that induces a protective T cell immunity against this virus.

Neonatal priming and infancy boosting with a novel respiratory syncytial virus vaccine induces protective immune responses without concomitant respiratory disease upon RSV challenge

Although respiratory syncytial virus (RSV) infection in infants and young children is a global public health issue, development of a safe RSV vaccine has been impeded by formalin-inactivated RSV-enhanced respiratory disease (ERD). In developing a safer yet effective RSV vaccine for children, a strategy to decrease over-reactive T cells and increase neutralizing anti-RSV antibodies should be considered. We previously demonstrated that adult mice immunized with RSV recombinant G protein plus low-dose Cyclosporine A (G+ CsA) could, upon subsequent RSV challenge, produce increased levels of antigen-specific T regulatory cells in lungs that overcame the ERD. Neutralizing anti-RSV antibodies that prevented viral infection were also elicited. In this study, we investigated if such a G+ CsA vaccine could provide infant mice with the same protection from RSV infection without ERD. The results showed that the G+ CsA vaccine could prevent RSV infection with only a mild loss of body weight. Importantly, there was nearly normal morphology and no mucus appearance in lung tissues after RSV challenge. These results demonstrate that the G+ CsA vaccine strategy achieved similar benefits in the neonatal prime and infancy boost model as in the adult mouse model. The G+ CsA immunization strategy is potentially safe and effective in neonates and infants because it suppresses the devastating ERD.

Contribution of Resident Memory CD8+ T Cells to Protective Immunity Against Respiratory Syncytial Virus and Their Impact on Vaccine Design

Worldwide, human respiratory syncytial virus (RSV) is the most common etiological agent for acute lower respiratory tract infections (ALRI). RSV-ALRI is the major cause of hospital admissions in young children, and it can cause in-hospital deaths in children younger than six months old. Therefore, RSV remains one of the pathogens deemed most important for the generation of a vaccine. On the other hand, the effectiveness of a vaccine depends on the development of immunological memory against the pathogenic agent of interest. This memory is achieved by long-lived memory T cells, based on the establishment of an effective immune response to viral infections when subsequent exposures to the pathogen take place. Memory T cells can be classified into three subsets according to their expression of lymphoid homing receptors: central memory cells (T_CM), effector memory cells (T_EM) and resident memory T cells (T_RM). The latter subset consists of cells that are permanently found in non-lymphoid tissues and are capable of recognizing antigens and mounting an effective immune response at those sites. T_RM cells activate both innate and adaptive immune responses, thus establishing a robust and rapid response characterized by the production of large amounts of effector molecules. T_RM cells can also recognize antigenically unrelated pathogens and trigger an innate-like alarm with the recruitment of other immune cells. It is noteworthy that this rapid and effective immune response induced by T_RM cells make these cells an interesting aim in the design of vaccination strategies in order to establish T_RM cell populations to prevent respiratory infectious diseases. Here, we discuss the biogenesis of T_RM cells, their contribution to the resolution of respiratory viral infections and the induction of T_RM cells, which should be considered for the rational design of new vaccines against RSV.

Contribution of IDO to human respiratory syncytial virus infection

IDO is an enzyme that participates in the degradation of tryptophan (Trp), which is an essential amino acid necessary for vital cellular processes. The degradation of Trp and the metabolites generated by the enzymatic activity of IDO can have immunomodulating effects, notably over T cells, which are particularly sensitive to the absence of Trp and leads to the inhibition of T cell activation, cell death, and the suppression of T cell effector functions. Noteworthy, T cells participate in the cellular immune response against the human respiratory syncytial virus (hRSV) and are essential for viral clearance, as well as the total recovery of the host. Furthermore, inadequate or non‐optimal polarization of T cells is often seen during the acute phase of the disease caused by this pathogen. Here, we discuss the capacity of hRSV to exploit the immunosuppressive features of IDO to reduce T cell function, thus acquiring relevant aspects during the biology of the virus. Additionally, we review studies on the influence of IDO over T cell activation and its relationship with hRSV infection.

Current Animal Models for Understanding the Pathology Caused by the Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) is the main etiologic agent of severe lower respiratory tract infections that affect young children throughout the world, associated with significant morbidity and mortality, becoming a serious public health problem globally. Up to date, no licensed vaccines are available to prevent severe hRSV-induced disease, and the generation of safe-effective vaccines has been a challenging task, requiring constant biomedical research aimed to overcome this ailment. Among the difficulties presented by the study of this pathogen, it arises the fact that there is no single animal model that resembles all aspects of the human pathology, which is due to the specificity that this pathogen has for the human host. Thus, for the study of hRSV, different animal models might be employed, depending on the goal of the study. Of all the existing models, the murine model has been the most frequent model of choice for biomedical studies worldwide and has been of great importance at contributing to the development and understanding of vaccines and therapies against hRSV. The most notable use of the murine model is that it is very useful as a first approach in the development of vaccines or therapies such as monoclonal antibodies, suggesting in this way the direction that research could have in other preclinical models that have higher maintenance costs and more complex requirements in its management. However, several additional different models for studying hRSV, such as other rodents, mustelids, ruminants, and non-human primates, have been explored, offering advantages over the murine model. In this review, we discuss the various applications of animal models to the study of hRSV-induced disease and the advantages and disadvantages of each model, highlighting the potential of each model to elucidate different features of the pathology caused by the hRSV infection.

Contribution of Fcγ Receptor-Mediated Immunity to the Pathogenesis Caused by the Human Respiratory Syncytial Virus

The human Respiratory Syncytial Virus (hRSV) is the leading cause of severe acute lower respiratory tract infections (ALRTIs) in humans at all ages and is the main cause of hospitalization due to pneumonia, asthma, and bronchiolitis in infants. hRSV symptoms mainly develop due to an excessive host immune and inflammatory response in the respiratory tissue. hRSV infection during life is frequent and likely because of non-optimal immunological memory is developed against this virus. Vaccine development against this pathogen has been delayed after the detrimental effects produced in children by vaccination with a formalin-inactivated hRSV preparation (FI-hRSV), which caused enhanced disease upon natural viral infection. Since then, several studies have focused on understanding the mechanisms underlying such disease exacerbation. Along these lines, several studies have suggested that antibodies elicited by immunization with FI-hRSV show low neutralizing capacity and promote the formation of immune complexes containing hRSV (hRSV-ICs), which contribute to hRSV pathogenesis through the engagement of Fc gamma receptors (FcγRs) expressed on the surface of immune cells. Furthermore, a role for FcγRs is supported by studies evaluating the contribution of these molecules to hRSV-induced disease. These studies have shown that FcγRs can modulate viral clearance by the host and the inflammatory response triggered by hRSV infection. In addition, ICs can facilitate viral entry into host cells expressing FcγRs, thus extending hRSV infectivity. In this article, we discuss current knowledge relative to the contribution of hRSV-ICs and FcγRs to the pathogenesis caused by hRSV and their putative role in the exacerbation of the disease caused by this virus after FI-hRSV vaccination. A better understanding FcγRs involvement in the immune response against hRSV will contribute to the development of new prophylactic or therapeutic tools to promote virus clearance with limited inflammatory damage to the airways.

Will Attention by Vaccine Developers to the Host's Nuclear Hormone Levels and Immunocompetence Improve Vaccine Success?

Despite extraordinary advances in fields of immunology and infectious diseases, vaccine development remains a challenge. The development of a respiratory syncytial virus vaccine, for example, has spanned more than 50 years of research with studies of more than 100 vaccine candidates. Dozens of attractive vaccine products have entered clinical trials, but none have completed the path to licensing. Human immunodeficiency virus vaccine development has proven equally difficult, as there is no licensed product after more than 30 years of pre-clinical and clinical research. Here, we examine vaccine development with attention to the host. We discuss how nuclear hormones, including vitamins and sex hormones, can influence responses to vaccines. We show how nuclear hormones interact with regulatory elements of immunoglobulin gene loci and how the deletion of estrogen response elements from gene enhancers will alter patterns of antibody isotype expression. Based on these findings, and findings that nuclear hormone levels are often insufficient or deficient among individuals in both developed and developing countries, we suggest that failed vaccine studies may in some cases reflect weaknesses of the host rather than the product. We encourage analyses of nuclear hormone levels and immunocompetence among study participants in clinical trials to ensure the success of future vaccine programs.

Recombinant BCG Vaccines Reduce Pneumovirus-Caused Airway Pathology by Inducing Protective Humoral Immunity

The Human Respiratory Syncytial Virus (hRSV) and the Human Metapneumovirus (hMPV) are two pneumoviruses that are leading agents causing acute lower respiratory tract infections (ALRTIs) affecting young infants, the elderly, and immunocompromised patients worldwide. Since these pathogens were first discovered, many approaches for the licensing of safe and effective vaccines have been explored being unsuccessful to date. We have previously described that immunization with recombinant strains of Mycobacterium bovis Bacillus Calmette-Guérin (rBCG) expressing the hRSV nucleoprotein (rBCG-N) or the hMPV phosphoprotein (rBCG-P) induced immune protection against each respective virus. These vaccines efficiently promoted viral clearance without significant lung damage, mainly through the induction of a T helper 1 cellular immunity. Here we show that upon viral challenge, rBCG-immunized mice developed a protective humoral immunity, characterized by production of antibodies specific for most hRSV and hMPV proteins. Further, isotype switching from IgG1 to IgG2a was observed in mice immunized with rBCG vaccines and correlated with an increased viral clearance, as compared to unimmunized animals. Finally, sera obtained from animals immunized with rBCG vaccines and infected with their respective viruses exhibited virus neutralizing capacity and protected naïve mice from viral replication and pulmonary disease. These results support the notion that the use of rBCG strains could be considered as an effective vaccination approach against other respiratory viruses with similar biology as hRSV and hMPV.

Human Metapneumovirus: Mechanisms and Molecular Targets Used by the Virus to Avoid the Immune System

Human metapneumovirus (hMPV) is a respiratory virus, first reported the year 2001. Since then, it has been described as one of the main etiological agents that causes acute lower respiratory tract infections (ALRTIs), which is characterized by symptoms such as bronchiolitis, wheezing and coughing. Susceptible population to hMPV-infection includes newborn, children, elderly and immunocompromised individuals. This viral agent is a negative-sense, single-stranded RNA enveloped virus, that belongs to the Pneumoviridae family and Metapneumovirus genus. Early reports—previous to 2001—state several cases of respiratory illness without clear identification of the responsible pathogen, which could be related to hMPV. Despite the similarities of hMPV with several other viruses, such as the human respiratory syncytial virus or influenza virus, mechanisms used by hMPV to avoid the host immune system are still unclear. In fact, evidence indicates that hMPV induces a poor innate immune response, thereby affecting the adaptive immunity. Among these mechanisms, is the promotion of an anergic state in T cells, instead of an effective polarization or activation, which could be induced by low levels of cytokine secretion. Further, the evidences support the notion that hMPV interferes with several pattern recognition receptors (PRRs) and cell signaling pathways triggered by interferon-associated genes. However, these mechanisms reported in hMPV are not like the ones reported for hRSV, as the latter has two non-structural proteins that are able to inhibit these pathways. Several reports suggest that viral glycoproteins, such as G and SH, could play immune-modulator roles during infection. In this work, we discuss the state of the art regarding the mechanisms that underlie the poor immunity elicited by hMPV. Importantly, these mechanisms will be compared with those elicited by other common respiratory viruses.

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

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

Patterns of antibody response during natural hRSV infection: insights for the development of new antibody-based therapies

INTRODUCTION

The human respiratory syncytial virus (hRSV) is the main cause of acute lower respiratory tract infection in susceptible population worldwide, such as young children and the elderly. Although hRSV is a major public health burden, there are no licensed vaccines and the only available therapy is palivizumab. During life, reinfections with hRSV are common, suggesting that the virus can impair the development of an efficient host immune response. This feature has hindered the development of efficient therapies.

AREAS COVERED

This article focuses on research about the natural development of antibodies in humans after the exposure to hRSV. The difficulties of developing anti-hRSV therapies based on monoclonal antibodies have been recently associated to the relationship between the disease outcome and the pattern of antibody response.

EXPERT OPINION

Development of monoclonal antibodies is a potentially successful approach to prevent the population from suffering severe respiratory diseases caused by hRSV infection, for which there are no available vaccines. Although the use of palivizumab is safe, its effectiveness is controversial. Recent data have prompted research to develop therapies targeting alternative viral antigens, rather than focusing only on the F protein, as well as the development of antibodies with a cell-mediated function.

A multifaceted approach to RSV vaccination

Respiratory Syncytial Virus (RSV) is the leading cause of pneumonia and bronchiolitis in infants, resulting in significant morbidity and mortality worldwide. In addition, RSV infections occur throughout different ages, thus, maintaining the virus in circulation, and increasing health risk to more susceptible populations such as infants, the elderly, and the immunocompromised. To date, there is no vaccine approved to prevent RSV infection or minimize symptoms of infection. Current clinical trials for vaccines against RSV are being carried out in four very different populations. There are vaccines that target two different pediatric populations, infants 2 to 6 month of age and seropositive children over 6 months of age, as well as women (non-pregnant or pregnant in their third trimester). There are vaccines that target adult and elderly populations. In this review, we will present and discuss RSV vaccine candidates currently in clinical trials. We will describe the preclinical studies instrumental for their advancement, with the goal of introducing new preclinical models that may more accurately predict the outcome of clinical vaccine studies.

Immunization with a Mixture of Nucleoprotein from Human Metapneumovirus and AbISCO-100 Adjuvant Reduces Viral Infection in Mice Model

The human metapneumovirus (hMPV) is the second leading cause globally of acute infection of the respiratory tract in children, infecting the upper and lower airways. The hMPV may induce an inappropriate Th2-type immune response, which causes severe pulmonary inflammation, leading to the obstruction of airways. Despite its severe epidemiological relevance, no vaccines are currently available for the prevention of hMPV-induced illness. In this investigation, we demonstrated that immunization of mice with the recombinant hMPV nucleoprotein (hMPV-N) mixed with the AbISCO-100 adjuvant reduced viral replication in lungs following challenge with the virus. We found that immunized mice had reduced weight loss, decreased granulocytes in the lung, an increased level of specific nucleoprotein antibodies of IgG1 and IgG2a-isotypes, and a local profile of Th1/Th17-type cytokines. Our results suggest that immunization with the hMPV-N and the AbISCO-100 adjuvant induces a reduction of viral infection and could be considered for the development of an hMPV vaccine.

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

Human Respiratory Syncytial Virus (hRSV) is one of the major causes of acute lower respiratory tract infections (ALRTI) worldwide, leading to significant levels of immunocompromisation as well as morbidity and mortality in infants. Its main target of infection is the ciliated epithelium of the lungs and the host immune responses elicited is ineffective at achieving viral clearance. It is thought that the lack of effective immunity against hRSV is due in part to the activity of several viral proteins that modulate the host immune response, enhancing a Th2-like pro-inflammatory state, with the secretion of cytokines that promote the infiltration of immune cells to the lungs, with consequent damage. Furthermore, the adaptive immunity triggered by hRSV infection is characterized by weak cytotoxic T cell responses and secretion of low affinity antibodies by B cells. These features of hRSV infection have meant that, to date, no effective and safe vaccines have been licensed. In this article, we will review in detail the information regarding hRSV characteristics, pathology, and host immune response, along with several prophylactic treatments and vaccine prototypes. We will also expose significant data regarding the newly developed BCG-based vaccine that promotes protective cellular and humoral response against hRSV infection, which is currently undergoing clinical evaluation.

A safe and efficient BCG vectored vaccine to prevent the disease caused by the human Respiratory Syncytial Virus

The human Respiratory Syncytial Virus (hRSV) causes lower respiratory tract infections including pneumonia and bronchiolitis. Such infections also cause a large number of hospitalizations and affects mainly newborns, young children and the elderly worldwide. Symptoms associated with hRSV infection are due to an exacerbated immune response characterized by low levels of IFN-γ, recruitment of neutrophils and eosinophils to the site of infection and lung damage. Although hRSV is a major health problem, no vaccines are currently available. Different immunization approaches have been developed to achieve a vaccine that activates the immune system, without triggering an unbalanced inflammation. These approaches include live attenuated vaccine, DNA or proteins technologies, and the use of vectors to express proteins of the virus. In this review, we discuss the host immune response to hRSV and the immunological mechanisms underlying an effective and safe BCG vectored vaccine against hRSV.

Heme Oxygenase-1 Modulates Human Respiratory Syncytial Virus Replication and Lung Pathogenesis during Infection

Human respiratory syncytial virus (hRSV) is the leading cause of severe lower respiratory tract infections in children. The development of novel prophylactic and therapeutic antiviral drugs against hRSV is imperative to control the burden of disease in the susceptible population. In this study, we examined the effects of inducing the activity of the host enzyme heme oxygenase-1 (HO-1) on hRSV replication and pathogenesis on lung inflammation induced by this virus. Our results show that after hRSV infection, HO-1 induction with metalloporphyrin cobalt protoporphyrin IX significantly reduces the loss of body weight due to hRSV-induced disease. Further, HO-1 induction also decreased viral replication and lung inflammation, as evidenced by a reduced neutrophil infiltration into the airways, with diminished cytokine and chemokine production and reduced T cell function. Concomitantly, upon cobalt protoporphyrin IX treatment, there is a significant upregulation in the production of IFN-α/β mRNAs in the lungs. Furthermore, similar antiviral and protective effects occur by inducing the expression of human HO-1 in MHC class II⁺ cells in transgenic mice. Finally, in vitro data suggest that HO-1 induction can modulate the susceptibility of cells, especially the airway epithelial cells, to hRSV infection.

Immunological Features of Respiratory Syncytial Virus-Caused Pneumonia-Implications for Vaccine Design

The human respiratory syncytial virus (hRSV) is the causative agent for high rates of hospitalizations due to viral bronchiolitis and pneumonia worldwide. Such a disease is characterized by an infection of epithelial cells of the distal airways that leads to inflammation and subsequently to respiratory failure. Upon infection, different pattern recognition receptors recognize the virus and trigger the innate immune response against the hRSV. Further, T cell immunity plays an important role for virus clearance. Based on animal studies, it is thought that the host immune response to hRSV is based on a biased T helper (Th)-2 and Th17 T cell responses with the recruitment of T cells, neutrophils and eosinophils to the lung, causing inflammation and tissue damage. In contrast, human immunity against RSV has been shown to be more complex with no definitive T cell polarization profile. Nowadays, only a humanized monoclonal antibody, known as palivizumab, is available to protect against hRSV infection in high-risk infants. However, such treatment involves several injections at a significantly high cost. For these reasons, intense research has been focused on finding novel vaccines or therapies to prevent hRSV infection in the population. Here, we comprehensively review the recent literature relative to the immunological features during hRSV infection, as well as the new insights into preventing the disease caused by this virus.

A single, low dose of a cGMP recombinant BCG vaccine elicits protective T cell immunity against the human respiratory syncytial virus infection and prevents lung pathology in mice

Human respiratory syncytial virus (hRSV) is a major health burden worldwide, causing the majority of hospitalizations in children under two years old due to bronchiolitis and pneumonia. HRSV causes year-to-year outbreaks of disease, which also affects the elderly and immunocompromised adults. Furthermore, both hRSV morbidity and epidemics are explained by a consistently high rate of re-infections that take place throughout the patient life. Although significant efforts have been invested worldwide, currently there are no licensed vaccines to prevent hRSV infection. Here, we describe that a recombinant Bacillus Calmette-Guerin (BCG) vaccine expressing the nucleoprotein (N) of hRSV formulated under current good manufacture practices (cGMP rBCG-N-hRSV) confers protective immunity to the virus in mice. Our results show that a single dose of the GMP rBCG-N-hRSV vaccine retains its capacity to protect mice against a challenge with a disease-causing infection of 1×10⁷ plaque-forming units (PFUs) of the hRSV A2 clinical strain 13018-8. Compared to unimmunized infected controls, vaccinated mice displayed reduced weight loss and less infiltration of neutrophils within the airways, as well as reduced viral loads in bronchoalveolar lavages, parameters that are characteristic of hRSV infection in mice. Also, ex vivo re-stimulation of splenic T cells at 28days post-immunization activated a repertoire of T cells secreting IFN-γ and IL-17, which further suggest that the rBCG-N-hRSV vaccine induced a mixed, CD8⁺ and CD4⁺ T cell response capable of both restraining viral spread and preventing damage of the lungs. All these features support the notion that rBCG-N-hRSV is a promising candidate vaccine to be used in humans to prevent the disease caused by hRSV in the susceptible population.

Aberrant T cell immunity triggered by human Respiratory Syncytial Virus and human Metapneumovirus infection

Human Respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) are the two major etiological viral agents of lower respiratory tract diseases, affecting mainly infants, young children and the elderly. Although the infection of both viruses trigger an antiviral immune response that mediate viral clearance and disease resolution in immunocompetent individuals, the promotion of long-term immunity appears to be deficient and reinfection are common throughout life. A possible explanation for this phenomenon is that hRSV and hMPV, can induce aberrant T cell responses, which leads to exacerbated lung inflammation and poor T and B cell memory immunity. The modulation of immune response exerted by both viruses include different strategies such as, impairment of immunological synapse mediated by viral proteins or soluble factors, and the induction of pro-inflammatory cytokines by epithelial cells, among others. All these viral strategies contribute to the alteration of the adaptive immunity in order to increase the susceptibility to reinfections. In this review, we discuss current research related to the mechanisms underlying the impairment of T and B cell immune responses induced by hRSV and hMPV infection. In addition, we described the role each virulence factor involved in immune modulation caused by these viruses.

Human Respiratory Syncytial Virus: Infection and Pathology

The human respiratory syncytial virus (hRSV) is by far the major cause of acute lower respiratory tract infections (ALRTIs) worldwide in infants and children younger than 2 years. The overwhelming number of hospitalizations due to hRSV-induced ALRTI each year is due, at least in part, to the lack of licensed vaccines against this virus. Thus, hRSV infection is considered a major public health problem and economic burden in most countries. The lung pathology developed in hRSV-infected individuals is characterized by an exacerbated proinflammatory and unbalanced Th2-type immune response. In addition to the adverse effects in airway tissues, hRSV infection can also cause neurologic manifestations in the host, such as seizures and encephalopathy. Although the origins of these extrapulmonary symptoms remain unclear, studies with patients suffering from neurological alterations suggest an involvement of the inflammatory response against hRSV. Furthermore, hRSV has evolved numerous mechanisms to modulate and evade the immune response in the host. Several studies have focused on elucidating the interactions between hRSV virulence factors and the host immune system, to rationally design new vaccines and therapies against this virus. Here, we discuss about the infection, pathology, and immune response triggered by hRSV in the host.

A Recombinant G Protein Plus Cyclosporine A-Based Respiratory Syncytial Virus Vaccine Elicits Humoral and Regulatory T Cell Responses against Infection without Vaccine-Enhanced Disease

Respiratory syncytial virus (RSV) infection can cause severe disease in the lower respiratory tract of infants and older people. Vaccination with a formalin-inactivated RSV vaccine (FI-RSV) and subsequent RSV infection has led to mild to severe pneumonia with two deaths among vaccinees. The vaccine-enhanced disease (VED) was recently demonstrated to be due to an elevated level of Th2 cell responses following loss of regulatory T (Treg) cells from the lungs. To induce high levels of neutralizing Abs and minimize pathogenic T cell responses, we developed a novel strategy of immunizing animals with a recombinant RSV G protein together with cyclosporine A. This novel vaccine induced not only a higher level of neutralizing Abs against RSV infection, but, most importantly, also significantly higher levels of Treg cells that suppressed VED in the lung after RSV infection. The induced responses provided protection against RSV challenge with no sign of pneumonia or bronchitis. Treg cell production of IL-10 was one of the key factors to suppress VED. These finding indicate that G protein plus cyclosporine A could be a promising vaccine against RSV infection in children and older people.

Understanding respiratory syncytial virus (RSV) vaccine development and aspects of disease pathogenesis

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infections causing bronchiolitis and some mortality in young children and the elderly. Despite decades of research there is no licensed RSV vaccine. Although significant advances have been made in understanding the immune factors responsible for inducing vaccine-enhanced disease in animal models, less information is available for humans. In this review, we discuss the different types of RSV vaccines and their target population, the need for establishing immune correlates for vaccine efficacy, and how the use of different animal models can help predict vaccine efficacy and clinical outcomes in humans.

Stable Expression of Lentiviral Antigens by Quality-Controlled Recombinant Mycobacterium bovis BCG Vectors

The well-established safety profile of the tuberculosis vaccine strain, Mycobacterium bovis bacille Calmette-Guérin (BCG), makes it an attractive vehicle for heterologous expression of antigens from clinically relevant pathogens. However, successful generation of recombinant BCG strains possessing consistent insert expression has encountered challenges in stability. Here, we describe a method for the development of large recombinant BCG accession lots which stably express the lentiviral antigens, human immunodeficiency virus (HIV) gp120 and simian immunodeficiency virus (SIV) Gag, using selectable leucine auxotrophic complementation. Successful establishment of vaccine stability stems from stringent quality control criteria which not only screen for highly stable complemented BCG ΔleuCD transformants but also thoroughly characterize postproduction quality. These parameters include consistent production of correctly sized antigen, retention of sequence-pure plasmid DNA, freeze-thaw recovery, enumeration of CFU, and assessment of cellular aggregates. Importantly, these quality assurance procedures were indicative of overall vaccine stability, were predictive for successful antigen expression in subsequent passaging both in vitro and in vivo, and correlated with induction of immune responses in murine models. This study has yielded a quality-controlled BCG ΔleuCD vaccine expressing HIV gp120 that retained stable full-length expression after 10(24)-fold amplification in vitro and following 60 days of growth in mice. A second vaccine lot expressed full-length SIV Gag for >10(68)-fold amplification in vitro and induced potent antigen-specific T cell populations in vaccinated mice. Production of large, well-defined recombinant BCG ΔleuCD lots can allow confidence that vaccine materials for immunogenicity and protection studies are not negatively affected by instability or differences between freshly grown production batches.

Central nervous system alterations caused by infection with the human respiratory syncytial virus

Worldwide, the human respiratory syncytial virus (hRSV) is the leading cause of infant hospitalization because of acute respiratory tract infections, including severe bronchiolitis and pneumonia. Despite intense research, to date there is neither vaccine nor treatment available to control hRSV disease burden globally. After infection, an incubation period of 3-5 days is usually followed by symptoms, such as cough and low-grade fever. However, hRSV infection can also produce a larger variety of symptoms, some of which relate to the individual's age at infection. Indeed, infants can display severe symptoms, such as dyspnea and chest wall retractions. Upon examination, crackles and wheezes are also common features that suggest infection by hRSV. Additionally, infection in infants younger than 1 year is associated with several non-specific symptoms, such as failure to thrive, periodic breathing or apnea, and feeding difficulties that usually require hospitalization. Recently, neurological symptoms have also been associated with hRSV respiratory infection and include seizures, central apnea, lethargy, feeding or swallowing difficulties, abnormalities in muscle tone, strabismus, abnormalities in the CSF, and encephalopathy. Here, we discuss recent findings linking the neurological, extrapulmonary effects of hRSV with infection and functional impairment of the CNS.

Respiratory Syncytial Virus: pathology, therapeutic drugs and prophylaxis

Human Respiratory Syncytial Virus (hRSV) is the leading cause of lower respiratory tract diseases, affecting particularly newborns and young children. This virus is able to modulate the immune response, generating a pro-inflammatory environment in the airways that causes obstruction and pulmonary alterations in the infected host. To date, no vaccines are available for human use and the first vaccine that reached clinical trials produced an enhanced hRSV-associated pathology 50 years ago, resulting in the death of two children. Currently, only two therapeutic approaches have been used to treat hRSV infection in high risk children: 1. Palivizumab, a humanized antibody against the F glycoprotein that reduces to half the number of hospitalized cases and 2. Ribavirin, which fails to have a significant therapeutic effect. A major caveat for these approaches is their high economical cost, which highlights the need of new and affordable therapeutic or prophylactic tools to treat or prevents hRSV infection. Accordingly, several efforts are in progress to understand the hRSV-associated pathology and to characterize the immune response elicited by this virus. Currently, preclinical and clinical trials are being conducted to evaluate safety and efficacy of several drugs and vaccines, which have shown promising results. In this article, we discuss the most important advances in the development of drugs and vaccines, which could eventually lead to better strategies to treat or prevent the detrimental inflammation triggered by hRSV infection.

CD8+ T cell immunity against human respiratory syncytial virus

Human respiratory syncytial virus (HRSV) was first discovered in the 1950s, but despite decades of research, a licensed vaccine against it is not available. Epidemiological studies indicate that antibodies directed against the fusion protein (F) partially correlate with protection. In addition, an F-specific monoclonal antibody is licensed as a prophylactic treatment in children who are at high risk of developing complications following HRSV infection. Therefore, most HRSV-oriented vaccination strategies focus on inducing a humoral immune response against F. In the quest for the development of a safe HRSV vaccine, the induction of a T cell immune response has received a lot less attention. T cell immunity directed against HRSV has not been associated unequivocally with protection against HRSV and CD4(+) T helper cell responses may even worsen disease due to HRSV. However, many studies support a protective role for CD8(+) T cells in clearance of HRSV from the lungs. In this review we highlight the clinical and experimental evidence in favor of a CD8(+) T lymphocyte-based vaccination strategy to protect against HRSV. First, we describe how T cell responses and T cell memory are induced in the lungs upon respiratory viral infection. HRSV has evolved mechanisms that hamper CD8(+) T cell priming and effector functions. We appraise the information on HRSV-specific CD8(+) T cell immunity gained from laboratory mouse studies, taking into account the advantages and limitations of this animal model and, where possible, the accordance with clinical evidence. Finally, we focus on recent efforts to develop T cell based vaccines against HRSV.

Induction of protective effector immunity to prevent pathogenesis caused by the respiratory syncytial virus. Implications on therapy and vaccine design

Human respiratory syncytial virus (hRSV) is the leading cause of respiratory illness in infants and young children around the globe. This pathogen, which was discovered in 1956, continues to cause a huge number of hospitalizations due to respiratory disease and it is considered a health and economic burden worldwide, especially in developing countries. The immune response elicited by hRSV infection leads to lung and systemic inflammation, which results in lung damage but is not efficient at preventing viral replication. Indeed, natural hRSV infection induces a poor immune memory that allows recurrent infections. Here, we review the most recent knowledge about the lifecycle of hRSV, the immune response elicited by this virus and the subsequent pathology induced in response to infection in the airways. Novel findings about the alterations that this virus causes in the central nervous system and potential therapies and vaccines designed to treat or prevent hRSV infection are discussed.