Current research on respiratory viral infections: Third International Symposium

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.

Respiratory syncytial virus subunit vaccines based on the viral envelope glycoproteins intended for pregnant women and the elderly

Introduction: Respiratory syncytial virus (RSV) causes high morbidity and mortality rates among infants, young children, and the elderly worldwide. Unfortunately, a safe and effective vaccine is still unavailable. In 1966, a formalin-inactivated RSV vaccine failed and resulted in the death of two young children. This failure shifted research toward the development of subunit-based vaccines for pregnant women (to passively vaccinate infants) and the elderly. Among these subunit-based vaccines, the viral envelope glycoproteins show great potential as antigens. Areas covered: In this review, progress in the development of safe and effective subunit RSV vaccines based on the viral envelope glycoproteins and intended for pregnant women and the elderly, are reviewed and discussed. Studies published in the period 2012-2018 were included. Expert opinion: Researchers are close to bringing safe and effective subunit-based RSV vaccines to the market using the viral envelope glycoproteins as antigens. However, it remains a major challenge to elicit protective immunity, with a formulation that has sufficient (storage) stability. These issues may be overcome by using the RSV fusion protein in its pre-fusion conformation, and by formulating this protein as a dry powder. It may further be convenient to administer this powder via the pulmonary route.

The threat and prospects for control of an influenza pandemic

Influenza constitutes the most widespread and significant respiratory infectious disease in the world, resulting in increased morbidity, mortality and economic loss each epidemic year. Pandemic influenza is a worldwide epidemic usually caused by a new virus variant to which the majority of the population has no immunity. As demonstrated in the devastating pandemic of 1918 to 1919, a pandemic virus may infect 30 to 50% of the worlds population and kill 1 to 2% of those infected. Pandemic control must be a concerted and co-ordinated world strategy and under the auspices of the World Health Organization, pandemic preparedness plans have been formulated, including: intensified surveillance for more rapid identification of new reassortant viruses with potential human virulence and infectivity, laboratory characterization of the new viruses so that vaccine may be prepared, development of techniques for more rapid vaccine production and the manufacture and stock piling of antiviral drugs. The H5N1 outbreak of virulent chicken influenza in 1997 in Hong Kong which resulted in the deaths of six of 18 infected persons serves as a wake-up call. Should such a virus attain high transmissibility in humans, a pandemic of tragic proportions might ensue. Even though the timing of onset of the next pandemic cannot be precisely predicted, world governments must understand the urgency of the problem and increase funding for influenza pandemic control.

Differential expression of coxsackievirus and adenovirus receptor on alveolar epithelial cells between fetal and adult mice determines their different susceptibility to coxsackievirus B infection

Coxsackievirus B (CVB) can cause aseptic meningitis, myocarditis and respiratory disease, especially in newborn infants. To compare the susceptibility to CVB infection of fetal and adult mice, we prepared primary alveolar epithelial cells (AECs) from lungs of BALB/c mice. In contrast to fetal mouse AECs, those of adults were less susceptible to CVB3 infection, as indicated by decreased cytopathic effects, and reduced levels of viral particles bound at the cell surface. In adult mouse AECs, amplification of the viral genome and virus capsid protein VP1 synthesis were concomitantly reduced. In addition, the cell-surface expression of coxsackievirus and adenovirus receptor (CAR), which plays a key role in the initiation of CVB and pulmonary infection, was downregulated in adult mouse AECs. These findings demonstrate that adult mouse AECs are less susceptible to CVB3 due to decreased CAR levels. Thus, these findings strongly indicate that the level of virus receptors on AECs is one of the crucial determinants for the age-dependence of CVB virulence in the mouse lung.

Picornaviral 3C protease inhibitors and the dual 3C protease/coronaviral 3C-like protease inhibitors

IMPORTANCE OF THE FIELD

Picornaviruses are small non-enveloped RNA viruses with genomic RNA of 7500 - 8000 nucleotides, whereas coronaviruses (CoV) are RNA viruses with larger genome of 27 - 32 kb. Both types of viruses translate their genetic information into polyprotein precursors that are processed by virally encoded 3C proteases (3C(pro)) and 3C-like proteases (3CL(pro)), respectively, to generate functional viral proteins. The most studied human rhinoviruses (HRV) belonging to picornaviridae family are the main etiologic agents of the common cold. Due to lack of effective drugs, 3C(pro) has served as an excellent target for anti-viral intervention and considerable efforts have been made in the development of inhibitors. Interestingly, the inhibitors of 3C(pro) cannot inhibit 3CL(pro) potently without modification due to subtle differences in their active-site structures, but a group of common inhibitors against 3C(pro) and 3CL(pro) were found recently.

AREAS COVERED IN THIS REVIEW

The inhibitors against 3C(pro) reported in the literatures and patents, with a focus on those inhibiting HRV and the dual picornaviral 3C(pro)/coronaviral 3CL(pro) inhibitors, are summarized in this review.

WHAT THE READERS WILL GAIN

Readers will rapidly gain an overview of the individual and dual 3C(pro) inhibitors and the structural basis for discriminating them.

TAKE HOME MESSAGE

In the future, more selective potent inhibitors against each protease and dual inhibitors against both proteases can be further developed to treat the diseases caused by picornaviruses and CoV.

Duplex-PCR assay for the detection of adenovirus and respiratory syncytial virus in nasopharyngeal samples

Human adenovirus (HAdV) and human respiratory syncytial virus (HRSV) are important etiologic agents of acute respiratory infections. In this study, a duplex polymerase chain reaction (PCR) assay was developed for the simultaneous detection of HAdV and HRSV in clinical samples. Sixty previously screened nasopharyngeal aspirates were used: 20 HAdV-positive, 20 HRSV-positive and 20 double-negative controls. Eight samples were positive for both viruses. The duplex PCR assay proved to be as sensitive and specific as single-target assays and also detected the mixed infections with certainty. The identification of both viruses in a single reaction offers a reduction in both cost and laboratory diagnostic time.

Natural killer cells regulate T-cell proliferation during human parainfluenza virus type 3 infection

Human parainfluenza virus type 3 (HPIV3) is a major respiratory pathogen in humans. Failure to induce immunological memory associated with HPIV3 infection has been attributed to inhibition of lymphocyte proliferation. We demonstrate that the inability of mixed lymphocytes to respond to virally infected antigen-presenting cells is due to an interleukin-2-dependent, nonapoptotic mechanism involving natural killer (NK) cells and their influence is exerted in a contact-dependent manner. These results suggest a novel regulatory mechanism for NK cells during HPIV3 infection, offering an explanation for viral persistence and poor memory responses.

Community-acquired pneumonia: paving the way towards new vaccination concepts

Despite the availability of antimicrobial agents and vaccines, community-acquired pneumonia remains a serious problem. Severe forms tend to occur in very young children and among the elderly, since their immune competence is eroded by immaturity and immune senescence, respectively. The main etiologic agents differ according to patient age and geographic area. Streptococcus pneumoniae, Haemophilus influenzae, respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV-3) are the most important pathogens in children, whereas influenza viruses are the leading cause of fatal pneumonia in the elderly. Effective vaccines are available against some of these organisms. However, there are still many agents against which vaccines are not available or the existent ones are suboptimal. To tackle this problem, empiric approaches are now being systematically replaced by rational vaccine design. This is facilitated by the growing knowledge in the fields of immunology, microbial pathogenesis and host response to infection, as well as by the availability of sophisticated strategies for antigen selection, potent immune modulators and efficient antigen delivery systems. Thus, a new generation of vaccines with improved safety and efficacy profiles compared to old and new agents is emerging. In this chapter, an overview is provided about currently available and new vaccination concepts.

Treatment of respiratory virus infections

Respiratory viral infections (RVIs) can be associated with a wide range of clinical manifestations ranging from self-limited upper respiratory tract infections to more devastating conditions, such as pneumonia. RVIs constitute the most frequent reason for medical consultations in the world and they have a considerable impact on quality of life and productivity. Therefore, the prevention and control of RVIs remain major clinical goals. Currently, there are approximately 200 known respiratory viruses that can be grouped into one family of DNA viruses (Adenoviridae) and four families of RNA viruses (Orthomyxoviridae, Paramyxoviridae, Picornaviridae and Coronaviridae). In this paper, we review the major respiratory viruses that cause disesases in humans, with an emphasis on current treatment options.

Quantitative adenovirus neutralization assays based on the secreted alkaline phosphatase reporter gene: application in epidemiologic studies and in the design of adenovector vaccines

Replication-defective recombinant adenoviruses (rAd) are used as vectors for vaccines as well as for gene therapy. To determine type-specific antibodies to adenovirus (Ad) serotypes 2, 5, 24, 34, and 35, we developed quantitative neutralization assays using recombinant adenoviruses with the secreted alkaline phosphatase (SEAP) reporter gene. Among the standardized parameters, the concentration of infectious and noninfectious adenoviral particles used in the assay is critical for a reliable comparison of data from different studies. The usefulness of this assay was demonstrated in a pilot epidemiologic study of 40 healthy individuals. In this study, the highest prevalence of antiadenovirus antibodies was found for the Ad2 serotype (82.5%), followed by Ad5 (35%). The prevalence of antiadenovirus antibodies for the serotypes 24, 34, and 35 was low (7.5%, 2.5%, and 0%, respectively). In addition, epidemiologic parameters such as gender and age were statistically evaluated. A positive association was found between age and the presence of anti-Ad5 antibodies. The assay was also useful for evaluating the presence of antiadenovirus antibodies in the design of vaccines using a rhesus monkey model. In this animal model, it was possible to determine differential dose and time responses, and the specificity for the detection of neutralizing antibodies was assessed. The evaluation of serotype-specific neutralizing antibodies can be of both clinical and epidemiologic importance as a means of selecting the appropriate serotype adenovector(s).

Reduced clearance of respiratory syncytial virus infection in a preterm lamb model

Respiratory syncytial virus (RSV) causes significant respiratory disease in children worldwide. For the study of severe RSV disease seen in preterm infants, a suitable animal model is lacking. The novel hypothesis of this study was that preterm lambs are susceptible to bovine RSV (bRSV) infection, an analogous pneumovirus with ruminant host specificity, and that there would be age-dependent differences in select RSV disease parameters. During RSV infection, preterm lambs had elevated temperatures and respiration rates with mild anorexia and cough compared to controls. Gross lesions included multifocal consolidation and atelectasis with foci of hyperinflation. Microscopic lesions included multifocal alveolar septal thickening and bronchiolitis. Immunohistochemistry localized the RSV antigen to all layers of bronchiolar epithelium from a few basal cells to numerous sloughing epithelia. A few mononuclear cells were also immunoreactive. To assess for age-dependent differences in RSV infection, neonatal lambs were infected similarly to the preterm lambs or with a high-titer viral inoculum. Using morphometry at day 7 of infection, preterm lambs had significantly more cellular immunoreactivity for RSV antigen (P <0.05) and syncytial cell formation (P <0.05) than either group of neonatal lambs. This work suggests that perinatal RSV clearance is age-dependent, which may explain the severity of RSV infection in preterm infants. The preterm lamb model is useful for assessing age-dependent mechanisms of severe RSV infection.

Vaccines for the prevention of respiratory viral infections: problems and current status

Acute respiratory virus infections cause the majority of lower respiratory tract illnesses and hospitalisations of infants and the elderly. The emergence of new respiratory viruses and a high probability that influenza will cause further pandemics highlights the necessity for developing better preventative strategies. Although there is a clear and pressing need for vaccines to prevent respiratory syncytial virus, rhinoviruses, coronaviruses, parainfluenza and human metapneumovirus, progress has been extremely slow. This review presents the current status of vaccine development for respiratory viral diseases and outlines novel approaches for the future.

Phenotypic drug susceptibility assay for influenza virus neuraminidase inhibitors

A flow cytometric (fluorescence-activated cell sorter [FACS]) assay was developed for analysis of the drug susceptibilities of wild-type and drug-resistant influenza A and B virus laboratory strains and clinical isolates for the neuraminidase (NA) inhibitors oseltamivir carboxylate, zanamivir, and peramivir. The drug susceptibilities of wild-type influenza viruses and those with mutations in the hemagglutinin (HA) and/or NA genes rendering them resistant to one or more of the NA inhibitors were easily determined with the FACS assay. The drug concentrations that reduced the number of virus-infected cells or the number of PFU by 50% as determined by the FACS assay were similar to those obtained with the more time-consuming and labor-intensive virus yield reduction assay. The NA inhibition (NAI) assay confirmed the resistance patterns demonstrated by the FACS and virus yield assays for drug-resistant influenza viruses with mutations in the NA gene. However, only the FACS and virus yield assays detected NA inhibitor-resistant influenza viruses with mutations in the HA gene but not in the NA gene. The FACS assay is more rapid and less labor-intensive than the virus yield assay and just as quantitative. The FACS assay determines the drug susceptibilities of influenza viruses with mutations in either the HA or NA genes, making the assay more broadly useful than the NAI assay for measuring the in vitro susceptibilities of influenza viruses for NA inhibitors. However, since only viruses with mutations in the NA gene that lead to resistance to the NA inhibitors correlate with clinical resistance, this in vitro assay should not be used in the clinical setting to determine resistance to NA inhibitors. The assay may be useful for determining the in vivo susceptibilities of other compounds effective against influenza A and B viruses.

Orally active fusion inhibitor of respiratory syncytial virus

BMS-433771 was found to be a potent inhibitor of respiratory syncytial virus (RSV) replication in vitro. It exhibited excellent potency against multiple laboratory and clinical isolates of both group A and B viruses, with an average 50% effective concentration of 20 nM. Mechanism-of-action studies demonstrated that BMS-433771 inhibits the fusion of lipid membranes during both the early virus entry stage and late-stage syncytium formation. After isolation of resistant viruses, resistance was mapped to a series of single amino acid mutations in the F1 subunit of the fusion protein. Upon oral administration, BMS-433771 was able to reduce viral titers in the lungs of mice infected with RSV. This new class of orally active RSV fusion inhibitors offers potential for clinical development.

National disease burden of respiratory viruses detected in children by polymerase chain reaction

BACKGROUND

The epidemiology of community-acquired respiratory viruses at the Children's Hospital of Wisconsin between 1996 and 1998 was examined with molecular [multiplex (M) PCR] and standard virologic methods.

METHODS AND RESULTS

A total of 3325 patients with lower respiratory infection (LRI) [bronchiolitis (42%), pneumonia (38%) and croup (12%)] were identified. It is estimated that 545,000 LRI hospitalizations occur each year in the United States in children younger than 18 years old (viral, 428,000; pneumonia, 221,000; bronchiolitis, 222,000; croup, 65,000), including a continued increase in bronchiolitis hospitalizations (47.8/1000; <1 year). The most common viruses detected each year in hospitalized children included respiratory syncytial virus (A and B; 117,000), parainfluenza virus (PIV-1 and -2, 48 000; PIV-3, 18,000) and influenza (A and B, 39,000). With multiplex reverse transcription polymerase chain reaction (MPCR), different patient populations demonstrated different LRI epidemiology in relation to specific syndromes and viral causes. At least 21% of LRI hospitalizations were in children with significant medical problems.PIVs were detected much more frequently in immunocompromised children than in previously healthy children (33% vs. 16%). Similarly 15% of respiratory syncytial virus was detected between May and October, mostly in immunocompromised children. Influenza caused 19% of bronchiolitis in previously healthy children, and no virus could be reliably predicted based on clinical presentation, including wheezing. Of children hospitalized for LRI, 40% tested positive for the seven most common respiratory viruses by MPCR.

CONCLUSIONS

Work is under way to expand the number of viruses detected by MPCR and to determine whether newly discovered viruses, such as human metapneumovirus, contribute to the burden of pediatric LRI hospitalizations.

Respiratory syncytial virus vaccine: Is it coming?

Respiratory syncytial virus (RSV) is recognized as an important cause of childhood morbidity and mortality. Vaccine development has been challenging in young infants and has required the advent of molecular technologies to optimize the safety profile, while maintaining immunogenicity of live-attenuated vaccines. Protein-based vaccines have been evaluated in clinical trials and are promising candidates for RSV-primed populations or for maternal vaccination to provide early life protection. This review provides a summary of the need for an RSV vaccine, as well as the challenges and progress in the vaccine's development.

Induction of short interspersed nuclear repeat-containing transcripts in epithelial cells upon infection with a chicken adenovirus

Chicken embryo lethal orphan adenovirus (CELO) is used as a vector for expression of exogenous genes in mammalian cells. Here, we analyzed transcriptional alterations in mouse epithelial host cells following infection with CELO using cDNA microarray analysis. Sequence data characterization revealed that a major portion of CELO-induced genes contained short interspersed nuclear elements of the B2 subclass (B2 SINEs). In fact, we could identify SINEs and other repetitive sequences as contributing significantly to the cDNAs used for microarray construction. Moreover, we found that the CELO protein Gam1 was able to mediate transcriptional activation of these B2 SINE-containing RNAs. We hypothesize that upregulation of B2-SINE-containing RNAs could be a novel contribution of Gam1 to CELO host cell infection.

Viral respiratory infections due to rhinoviruses: current knowledge, new developments

Viral respiratory infections (VRIs) are among the most common reasons for which primary care providers are consulted. VRIs due to rhinoviruses-the most commonly implicated etiologic agent-constitute a syndrome characterized by signs and symptoms of a cold. Rhinoviruses have been implicated in respiratory tract illnesses such as sinusitis and otitis media, as well as lower respiratory complications in high-risk populations. Most patients treat VRI with over-the-counter remedies that have been demonstrated to produce marginal clinical benefits. The development of novel antiviral agents has intensified interest in VRIs. Pleconaril, a capsid-function inhibitor currently under FDA review, has been shown in clinical trials to reduce the duration and severity of rhinovirus VRIs. By targeting the cause of illness, antiviral agents represent an opportunity to reduce the substantial clinical burden of VRI. Furthermore, effective therapies can potentially reduce inappropriate antibiotic use for viral infections.

Management of respiratory syncytial virus with lower respiratory tract infection in infants and children

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection in infants and children requiring pediatric hospitalizations. Infants with chronic lung, cardiac, or neuromuscular conditions are at increased risk for RSV infection. Early RSV is associated with subsequent diagnosis of reactive airway disease. The management of RSV with lower respiratory track infection in infants and children remains controversial. Bronchodilators may have some short-term benefit, but are not recommended as standard practice for infants and children. Antiviral therapy may be used for high-risk and severely ill patients. Corticosteroids may be effective in cases of moderate to severe RSV with lower respiratory track infection. Monoclonal antibodies have shown some promise in achieving passive immunity for those at greatest risk, including preterm infants younger than 1 year or infants younger than 2 years with chronic lung disease. Emergency management remains primarily supportive, with vigilant monitoring of oxygenation and hydration status. Interventions include supplemental oxygen therapy, ventilation, and fluid and nutrition therapy. Respiratory syncytial virus prophylaxis for high-risk patients includes intramuscular injections of palivizumab (Synagis) each month during RSV season, from November through April. Prevention strategies include washing hands, cleaning environment surfaces, and isolating infants and children with RSV in the emergency care area.

Respiratory syncytial virus--viral biology and the host response

Respiratory syncytial virus (RSV) is the most important cause of respiratory tract infection in infants. We have an incomplete understanding of the reasons why some infants are more severely affected by RSV than others. There is no effective antiviral treatment for the infection. Advances in our understanding of the biology of RSV, particularly in relation to the attachment protein G and the fusion protein F, have revealed potential targets for new antiviral therapies and vaccine development. In response to RSV infection an intense inflammatory response is triggered, mediated initially by the infected airway epithelial cells. Cell mediated responses are important in controlling the extent of infection and in viral clearance. Humoral responses are important in protection. There is early evidence that genetic variation of the host response can influence the outcome of RSV-induced bronchiolitis.

Synthesis, cytotoxicity and antiviral activity of N,N'-bis-5-nitropyrimidyl derivatives of dispirotripiperazine

During the search for new antivirals, various N,N'-bis-5-pyrimidyl derivatives of 3,12-diaza-6,9-diazonia(5,2,5,2)dispirohexadecane dichloride (dispirotripiperazine) were synthesized. To reveal relationships between chemical structure and antiviral activity, the compounds were characterized by fast atom bombardment mass, nuclear magnetic resonance, infra red spectroscopy, and elemental analysis and examined for cytotoxicity, inhibition of cell growth and antiviral activity under in vitro conditions. The results of this study demonstrate an excellent compatibility of the test compounds for confluent as well as proliferating cells and a potent structure-dependent inhibition of herpes simplex virus type 1 replication when added during viral adsorption. Functional group analysis revealed that both the dispirotripiperazine as well as the pyrimidine ring with a nitro group in the 5 position are necessary for activity. A reduction of electron density in the terminal pyrimidine rings enhanced the antiviral activity whereas electron donor substitutions reduced it. Introduction of a methyl group in position 2 of the pyrimidine had no influence on cytotoxicity or antiviral activity.

Respiratory viral infections in adults

Respiratory viral infections in adults cause significant morbidity and mortality, especially in high-risk patients. The impact of influenza virus, rhinoviruses, and respiratory syncytial virus in immunocompromised cancer patients and in asthma and chronic bronchitis patients has been documented in recent publications. Cytomegalovirus pneumonia continues to be a major cause of morbidity and mortality in transplant recipients. Newer rapid diagnostic tests and the use of polymerase chain reaction technology have provided better understanding of the causes and epidemiology of acute respiratory illness in adults. The approved neuraminidase inhibitors for influenza viruses and the nonapproved capsid inhibitors of rhinoviruses may be useful in treating high-risk individuals. The inactivated influenza vaccine has been shown to benefit healthy adults and to be safe in asthmatic adults and children.

Structure-based design, synthesis, and biological evaluation of irreversible human rhinovirus 3C protease inhibitors. 6. Structure-activity studies of orally bioavailable, 2-pyridone-containing peptidomimetics

The structure-based design, chemical synthesis, and biological evaluation of various 2-pyridone-containing human rhinovirus (HRV) 3C protease (3CP) inhibitors are described. These compounds are comprised of a peptidomimetic binding determinant and a Michael acceptor moiety, which forms an irreversible covalent adduct with the active site cysteine residue of the 3C enzyme. The 2-pyridone-containing inhibitors typically display improved 3CP inhibition properties relative to related peptide-derived molecules along with more favorable antiviral properties. The cocrystal structure of one pyridone-derived 3CP inhibitor complexed with HRV-2 3CP is also described along with certain ab initio conformation analyses. Optimization of the 2-pyridone-containing compounds is shown to provide several highly active 3CP inhibitors (k(obs)/[I] > 500,00 M(-1) s(-1)) that function as potent antirhinoviral agents (EC(50) = <0.05 microM) against multiple virus serotypes in cell culture. One 2-pyridone-containing 3CP inhibitor is shown to be bioavailable in the dog after oral dosing (F = 48%).

Immunoprophylaxis of respiratory syncytial virus: global experience

Respiratory syncytial virus (RSV) infects nearly all children by age 2 years, and it causes considerable illness and death in certain high-risk pediatric populations. Historically, treatment for RSV has been symptomatic, and developing a safe and effective vaccine has been a challenge. Therefore, research efforts have turned to passive immunization as the best option to control RSV. Palivizumab, a genetically engineered humanized monoclonal antibody, has been shown to reduce RSV-related hospitalizations significantly, with few adverse effects. It was approved for use in high-risk children in the USA in 1998 and in Europe in 1999; it is now approved for use in more than 45 countries. The efficacy and safety of palivizumab continue to be supported by both clinical trial and outcomes data.