Efficacious human metapneumovirus vaccine based on AI-guided engineering of a closed prefusion trimer.

The prefusion conformation of human metapneumovirus fusion protein (hMPV Pre-F) is critical for eliciting the most potent neutralizing antibodies and is the preferred immunogen for an efficacious vaccine against hMPV respiratory infections. Here we show that an additional cleavage event in the F protein allows closure and correct folding of the trimer. We therefore engineered the F protein to undergo double cleavage, which enabled screening for Pre-F stabilizing substitutions at the natively folded protomer interfaces. To identify these substitutions, we developed an AI convolutional classifier that successfully predicts complex polar interactions often overlooked by physics-based methods and visual inspection. The combination of additional processing, stabilization of interface regions and stabilization of the membrane-proximal stem, resulted in a Pre-F protein vaccine candidate without the need for a heterologous trimerization domain that exhibited high expression yields and thermostability. Cryo-EM analysis shows the complete ectodomain structure, including the stem, and a specific interaction of the newly identified cleaved C-terminus with the adjacent protomer. Importantly, the protein induces high and cross-neutralizing antibody responses resulting in near complete protection against hMPV challenge in cotton rats, making the highly stable, double-cleaved hMPV Pre-F trimer an attractive vaccine candidate.

Epidemiological and clinical characteristics of hospitalized human metapneumovirus patients in Israel, 2015-2021: A retrospective cohort study.

This study evaluated the epidemiological and clinical characteristics of human metapneumovirus (hMPV) infection among hospitalized patients with acute respiratory infections during 2015-2021 and assessed the impact of the coronavirus disease 2019 pandemic on hMPV infection. A single-center, retrospective cohort study was performed, including pediatric and adult patients with laboratory-confirmed hMPV. Of a total of 990 patients, 253 (25.6%), 105 (10.6%), 121 (12.2%), and 511 (51.6%) belonged to age groups 0-2, 3-17, 18-59, and ≥60 years, respectively. The highest percentage (23.0%) of patients were hospitalized during 2019 and the lowest (4.7%) during 2020. Patients < 18 years experienced high rates of comorbidities (immunodeficiencies: 14.4% and malignancies: 29.9%). Here, 37/39 (94.9%) of all bronchiolitis cases were diagnosed in patients < 2 years, whereas more patients in older age groups were diagnosed with pneumonia. A greater proportion of hMPV patients diagnosed with viral coinfection (mostly respiratory syncytial virus and adenovirus) were <18 years. The highest percentages of intensive care unit admissions were recorded among patients < 18 years. Our findings demonstrate that hMPV is an important cause of morbidity in young children and a possibly underestimated cause of morbidity among older adults.

Novel insights into the host cell glycan binding profile of human metapneumovirus.

Numerous viruses have been found to exploit glycoconjugates expressed on human cells as their initial attachment factor for viral entry and infection. The virus-cell glycointeractome, when characterized, may serve as a template for antiviral drug design. Heparan sulfate proteoglycans extensively decorate the human cell surface and were previously described as a primary receptor for human metapneumovirus (HMPV). After respiratory syncytial virus, HMPV is the second most prevalent respiratory pathogen causing respiratory tract infection in young children. To date, there is neither vaccine nor drug available to prevent or treat HMPV infection. Using a multidisciplinary approach, we report for the first time the glycointeractome of the HMPV fusion (F) protein, a viral surface glycoprotein that is essential for target-cell recognition, attachment, and entry. Our glycan microarray and surface plasmon resonance results suggest that Galß1-3/4GlcNAc moieties that may be sialylated or fucosylated are readily recognized by HMPV F. The bound motifs are highly similar to the N-linked and O-linked glycans primarily expressed on the human lung epithelium. We demonstrate that the identified glycans have the potential to compete with the cellular receptors used for HMPV entry and consequently block HMPV infection. We found that lacto-N-neotetraose demonstrated the strongest HMPV binding inhibition in a cell infection assay. Our current findings offer an encouraging and novel avenue for the design of anti-HMPV drug candidates using oligosaccharide templates.IMPORTANCEAll cells are decorated with a dense coat of sugars that makes a sugar code. Many respiratory viruses exploit this sugar code by binding to these sugars to cause infection. Human metapneumovirus is a leading cause for acute respiratory tract infections. Despite its medical importance, there is no vaccine or antiviral drug available to prevent or treat human metapneumovirus infection. This study investigates how human metapneumovirus binds to sugars in order to more efficiently infect the human host. We found that human metapneumovirus binds to a diverse range of sugars and demonstrated that these sugars can ultimately block viral infection. Understanding how viruses can take advantage of the sugar code on our cells could identify new intervention and treatment strategies to combat viral disease.

Presence and Significance of Multiple Respiratory Viral Infections in Children Admitted to a Tertiary Pediatric Hospital in Italy.

Viral co-infections are frequently observed among children, but whether specific viral interactions enhance or diminish the severity of respiratory disease is still controversial. This study aimed to investigate the type of viral mono- and co-infections by also evaluating viral correlations in 3525 respiratory samples from 3525 pediatric in/outpatients screened by the Allplex Respiratory Panel Assays and with a Severe Acute Respiratory Syndrome-COronaVirus 2 (SARS-CoV-2) test available. Overall, viral co-infections were detected in 37.8% of patients and were more frequently observed in specimens from children with lower respiratory tract infections compared to those with upper respiratory tract infections (47.1% vs. 36.0%, p = 0.003). SARS-CoV-2 and influenza A were more commonly detected in mono-infections, whereas human bocavirus showed the highest co-infection rate (87.8% in co-infection). After analyzing viral pairings using Spearman's correlation test, it was noted that SARS-CoV-2 was negatively associated with all other respiratory viruses, whereas a markedly significant positive correlation (p < 0.001) was observed for five viral pairings (involving adenovirus/human bocavirus/human enterovirus/metapneumoviruses/rhinovirus). The correlation between co-infection and clinical outcome may be linked to the type of virus(es) involved in the co-infection rather than simple co-presence. Further studies dedicated to this important point are needed, since it has obvious implications from a diagnostic and clinical point of view.

Genetic Diversity and Detection of Respiratory Viruses Excluding SARS-CoV-2 during the COVID-19 Pandemic in Gabon, 2020-2021.

Acute respiratory infections are a major global burden in resource-limited countries, including countries in Africa. Although COVID-19 has been well studied since the pandemic emerged in Gabon, Central Africa, less attention has been paid to other respiratory viral diseases, and very little data are available. Herein, we provide the first data on the genetic diversity and detection of 18 major respiratory viruses in Gabon during the COVID-19 pandemic. Of 582 nasopharyngeal swab specimens collected from March 2020 to July 2021, which were SARS-CoV-2 negative, 156 were positive (26%) for the following viruses: enterovirus (20.3%), human rhinovirus (HRV) (4.6%), human coronavirus OC43 (1.2%), human adenovirus (0.9%), human metapneumovirus (hMPV) (0.5%), influenza A virus (IAV) (0.3%), and human parainfluenza viruses (0.5%). To determine the genetic diversity and transmission route of the viruses, phylogenetic analyses were performed using genome sequences of the detected viruses. The IAV strain detected in this study was genetically similar to strains isolated in the USA, whereas the hMPV strain belonging to the A2b subtype formed a cluster with Kenyan strains. This study provides the first complete genomic sequences of HRV, IAV, and hMPV detected in Gabon, and provides insight into the circulation of respiratory viruses in the country.

VLPs generated by the fusion of RSV-F or hMPV-F glycoprotein to HIV-Gag show improved immunogenicity and neutralizing response in mice.

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) vaccines have been long overdue. Structure-based vaccine design created a new momentum in the last decade, and the first RSV vaccines have finally been approved in older adults and pregnant individuals. These vaccines are based on recombinant stabilized pre-fusion F glycoproteins administered as soluble proteins. Multimeric antigenic display could markedly improve immunogenicity and should be evaluated in the next generations of vaccines. Here we tested a new virus like particles-based vaccine platform which utilizes the direct fusion of an immunogen of interest to the structural human immunodeficient virus (HIV) protein Gag to increase its surface density and immunogenicity. We compared, in mice, the immunogenicity of RSV-F or hMPV-F based immunogens delivered either as soluble proteins or displayed on the surface of our VLPs. VLP associated F-proteins showed better immunogenicity and induced superior neutralizing responses. Moreover, when combining both VLP associated and soluble immunogens in a heterologous regimen, VLP-associated immunogens provided added benefits when administered as the prime immunization.

Determinants of radiological patterns and severity in immunocompromised adults with Metapneumovirus infection.

BACKGROUND: Human Metapneumovirus (HMPV) belongs to the Pneumoviridae family and is responsible for respiratory infections. Mild infections are well-recognized in children, while its precise impact in various categories of immunocompromised adults has not been well addressed. RESEARCH QUESTION: We retrospectively studied HMPV infections in immunocompromised adults followed in two large French university medical centers. STUDY DESIGN AND METHODS: We identified immunocompromised adults with positive HMPV Polymerase Chain Reaction (PCR) for 36 months and reviewed their medical charts. For lung transplant recipients (LTR), FEV1 was collected at baseline, during and after infection. Imaging was centralized and chest involvement was categorized by dominant CT patterns. We compared severe patients (requiring oxygen or ventilation) and non hypoxemic patients. RESULTS: Seventy-two patients were included, 27 were LTR, 25 had a hematological malignancy or were hematopoietic stem cell recipients, 20 had another immunocompromised status. Twenty patients (28%) presented a hypoxemic infection, requiring hospitalization and intensive care units transfers in 50/72 (69.4%) and 9/72 (12.5%) respectively, with only one death. Hypoxemia was less pronounced in LTRs (p = 0.014). Finally, age and dyspnea remained independent factors associated with hypoxemia (p < 0.005). The most frequent radiological patterns were bronchopneumonia (34.2%) and bronchiolitis (39.5% and 64.3% in the overall population and in LTRs respectively, p = 0.045). FEV1 improved in LTRs at one month and 85% had recovered their baseline FEV1 within 6 months. INTERPRETATIONS: In immunocompromised adults, HMPV infections required frequent hospitalizations and ICU transfers, while mortality is low. In LTRs, bronchiolitis pattern was predominant with short and long-term favorable outcome.

IFN-λ drives distinct lung immune landscape changes and antiviral responses in human metapneumovirus infection.

Human metapneumovirus (HMPV) is a primary cause of acute respiratory infection, yet there are no approved vaccines or antiviral therapies for HMPV. Early host responses to HMPV are poorly characterized, and further understanding could identify important antiviral pathways. Type III interferon (IFN-λ) displays potent antiviral activity against respiratory viruses and is being investigated for therapeutic use. However, its role in HMPV infection remains largely unknown. Here, we show that IFN-λ is highly upregulated during HMPV infection in vitro in human and mouse airway epithelial cells and in vivo in mice. We found through several immunological and molecular assays that type II alveolar cells are the primary producers of IFN-λ. Using mouse models, we show that IFN-λ limits lung HMPV replication and restricts virus spread from upper to lower airways but does not contribute to clinical disease. Moreover, we show that IFN-λ signaling is predominantly mediated by CD45- non-immune cells. Mice lacking IFN-λ signaling showed diminished loss of ciliated epithelial cells and decreased recruitment of lung macrophages in early HMPV infection along with higher inflammatory cytokine and interferon-stimulated gene expression, suggesting that IFN-λ may maintain immunomodulatory responses. Administration of IFN-λ for prophylaxis or post-infection treatment in mice reduced viral load without inflammation-driven weight loss or clinical disease. These data offer clinical promise for IFN-λ in HMPV treatment. IMPORTANCE: Human metapneumovirus (HMPV) is a common respiratory pathogen and often contributes to severe disease, particularly in children, immunocompromised people, and the elderly. There are currently no licensed HMPV antiviral treatments or vaccines. Here, we report novel roles of host factor IFN-λ in HMPV disease that highlight therapeutic potential. We show that IFN-λ promotes lung antiviral responses by restricting lung HMPV replication and spread from upper to lower airways but does so without inducing lung immunopathology. Our data uncover recruitment of lung macrophages, regulation of ciliated epithelial cells, and modulation of inflammatory cytokines and interferon-stimulated genes as likely contributors. Moreover, we found these roles to be distinct and non-redundant, as they are not observed with knockout of, or treatment with, type I IFN. These data elucidate unique antiviral functions of IFN-λ and suggest IFN-λ augmentation as a promising therapeutic for treating HMPV disease and promoting effective vaccine responses.

Non-SARS-CoV-2 respiratory viral detection and whole genome sequencing from COVID-19 rapid antigen test devices: a laboratory evaluation study.

BACKGROUND: There has been high uptake of rapid antigen test device use for point-of-care COVID-19 diagnosis. Individuals who are symptomatic but test negative on COVID-19 rapid antigen test devices might have a different respiratory viral infection. We aimed to detect and sequence non-SARS-CoV-2 respiratory viruses from rapid antigen test devices, which could assist in the characterisation and surveillance of circulating respiratory viruses in the community. METHODS: We applied archival clinical nose and throat swabs collected between Jan 1, 2015, and Dec 31, 2022, that previously tested positive for a common respiratory virus (adenovirus, influenza, metapneumovirus, parainfluenza, rhinovirus, respiratory syncytial virus [RSV], or seasonal coronavirus; 132 swabs and 140 viral targets) on PCR to two commercially available COVID-19 rapid antigen test devices, the Panbio COVID-19 Ag Rapid Test Device and Roche SARS-CoV-2 Antigen Self-Test. In addition, we collected 31 COVID-19 rapid antigen test devices used to test patients who were symptomatic at The Royal Melbourne Hospital emergency department in Melbourne, Australia. We extracted total nucleic acid from the device paper test strips and assessed viral recovery using multiplex real-time PCR (rtPCR) and capture-based whole genome sequencing. Sequence and genome data were analysed through custom computational pipelines, including subtyping. FINDINGS: Of the 140 respiratory viral targets from archival samples, 89 (64%) and 88 (63%) were positive on rtPCR for the relevant taxa following extraction from Panbio or Roche rapid antigen test devices, respectively. Recovery was variable across taxa: we detected influenza A in nine of 18 samples from Panbio and seven of 18 from Roche devices; parainfluenza in 11 of 20 samples from Panbio and 12 of 20 from Roche devices; human metapneumovirus in 11 of 16 from Panbio and 14 of 16 from Roche devices; seasonal coronavirus in eight of 19 from Panbio and two of 19 from Roche devices; rhinovirus in 24 of 28 from Panbio and 27 of 28 from Roche devices; influenza B in four of 15 in both devices; and RSV in 16 of 18 in both devices. Of the 31 COVID-19 devices collected from The Royal Melbourne Hospital emergency department, 11 tested positive for a respiratory virus on rtPCR, including one device positive for influenza A virus, one positive for RSV, four positive for rhinovirus, and five positive for SARS-CoV-2. Sequences of target respiratory viruses from archival samples were detected in 55 (98·2%) of 56 samples from Panbio and 48 (85·7%) of 56 from Roche rapid antigen test devices. 98 (87·5%) of 112 viral genomes were completely assembled from these data, enabling subtyping for RSV and influenza viruses. All 11 samples collected from the emergency department had viral sequences detected, with near-complete genomes assembled for influenza A and RSV. INTERPRETATION: Non-SARS-CoV-2 respiratory viruses can be detected and sequenced from COVID-19 rapid antigen devices. Recovery of near full-length viral sequences from these devices provides a valuable opportunity to expand genomic surveillance programmes for public health monitoring of circulating respiratory viruses. FUNDING: Australian Government Medical Research Future Fund and Australian National Health and Medical Research Council.

[Pathogenic agents causing acute respiratory tract infections in pediatric patients in Spring, 2023, in Beijing].

Objective: To explore the pathogenic agents of acute respiratory infection (ARI) in children in Beijing. Methods: In the cross-sectional study, 3 groups of children from different departments were enrolled from Feb 6th, 2023 (6th week) to May 28th (21th week), 2023, including influenza-like case group from emergency department for nucleic acid testing of influenza virus (Flu) and human metapneumovirus (HMPV), the outpatient ARI group under nucleic acid testing for Flu, respiratory syncytial virus (RSV), adenovirus (ADV), and parainfluenza virus (PIV), and the inpatient ARI group under nucleic acid testing for Flu, RSV, HMPV, ADV, human bocavirus (HBoV), Rhinovirus (Rh), PIV, coronavirus (HCoV), Mycoplasma pneumoniae (Mp) and Chlamydia pneumonia (Cp). Results: There were 320 influenza-like cases enrolled, including 192 males and 128 females, aged 4.7 (3.6, 6.9) years, and 117 cases (36.6%) positive for Flu A, which contained similar proportion of pandemic H1N1 (H1N1) 47.0% (55/117) and H3N2 53.0% (62/117), and 13 cases for HMPV 4.1% (13/320). The rate of Flu reached its peak at the 10th week, with H1N1 as the predominant one from the 6th to 9th week (10.0%-50.0%) and then H3N2 from the 10th to 16th week (15.0%-90.0%). HMPV was detected from the 15th week 5.0% (1/20), and then reached to 30.0% (6/20) at the 20th week. In the outpatient ARI group, 7 573 were enrolled, including 4 131 males and 3 442 females, aged 4.0 (2.1, 5.3) years, and the highest positive rate for RSV 32.9% (2 491/7 573), followed by Flu A 12.1% (915/7 573). The dominant one was Flu A in weeks 6-14 (23.2%-74.7%), then RSV in the 15th week 24.8% (36/145). In the inpatient ARI group, 1 391 patients were enrolled, including 804 males and 587 females, aged 3.3 (0.4, 5.8) years, and the highest positive rate for Rh 18.7% (260/1 391), followed by RSV 12.4% (173/1 391), Flu A 10.2% (142/1 391, of which 116 cases (81.7%) were H1N1, and 26 cases (18.3%) were H3N2) and HMPV 3.1% (43/1 391). H1N1 was detected from the 7th week 10% (6/60), to peak in the 11th week 31.8% (21/66). H3N2 was detected from the 8th week 1.5% (1/68), and then kept in low level. The proportion of H1N1 among Flu was 81.7% (116/142) in the inpatient ARI group. RSV was detected from 12th week 1.3% (1/80), reaching 30.4% (35/115) at 19th week. The positive rate of HMPV reached 12.1% (14/116) at 21th week. Conclusions: In the spring of 2023, the first one in Beijing is the Flu epidemic, with H1N1 being the predominant one in the early stage and H3N2 in the later stage. Then, there is a postponed RSV epidemic and an increased HMPV detection. In addition, nucleic acid testing for outpatient children should be strengthened to provide early warning of epidemics.

Cycle threshold dynamics of non-severe acute respiratory coronavirus virus 2 (SARS-CoV-2) respiratory viruses.

OBJECTIVE: Many providers use severe acute respiratory coronavirus virus 2 (SARS-CoV-2) cycle thresholds (Ct values) as approximate measures of viral burden in association with other clinical data to inform decisions about treatment and isolation. We characterized temporal changes in Ct values for non-SARS-CoV-2 respiratory viruses as a first step to determine whether cycle thresholds could play a similar role in the management of non-SARS-CoV-2 respiratory viruses. DESIGN: Retrospective cohort study. SETTING: Brigham and Women's Hospital, Boston. METHODS: We retrospectively identified all adult patients with positive nasopharyngeal PCRs for influenza, respiratory syncytial virus (RSV), parainfluenza, human metapneumovirus (HMPV), rhinovirus, or adenovirus between January 2022 and March 2023. We plotted Ct distributions relative to days since symptom onset, and we assessed whether distributions varied by immunosuppression and other comorbidities. RESULTS: We analyzed 1,863 positive samples: 506 influenza, 502 rhinovirus, 430 RSV, 219 HMPV, 180 parainfluenza, 26 adenovirus. Ct values were generally 25-30 on the day of symptom onset, lower over the ensuing 1-3 days, and progressively higher thereafter with Ct values ≥30 after 1 week for most viruses. Ct values were generally higher and more stable over time for rhinovirus. There was no association between immunocompromised status and median intervals from symptom onset until Ct values were ≥30. CONCLUSIONS: Ct values relative to symptom onset for influenza, RSV, and other non-SARS-CoV-2 respiratory viruses generally mirror patterns seen with SARS-CoV-2. Further data on associations between Ct values and viral viability, transmissibility, host characteristics, and response to treatment for non-SARS-CoV-2 respiratory viruses are needed to determine how clinicians and infection preventionists might integrate Ct values into treatment and isolation decisions.

A Receptor Integrin ß1 Promotes Infection of Avian Metapneumovirus Subgroup C by Recognizing a Viral Fusion Protein RSD Motif.

Avian metapneumovirus subgroup C (aMPV/C) causes respiratory diseases and egg dropping in chickens and turkeys, resulting in severe economic losses to the poultry industry worldwide. Integrin ß1 (ITGB1), a transmembrane cell adhesion molecule, is present in various cells and mediates numerous viral infections. Herein, we demonstrate that ITGB1 is essential for aMPV/C infection in cultured DF-1 cells, as evidenced by the inhibition of viral binding by EDTA blockade, Arg-Ser-Asp (RSD) peptide, monoclonal antibody against ITGB1, and ITGB1 short interfering (si) RNA knockdown in cultured DF-1 cells. Simulation of the binding process between the aMPV/C fusion (F) protein and avian-derived ITGB1 using molecular dynamics showed that ITGB1 may be a host factor benefiting aMPV/C attachment or internalization. The transient expression of avian ITGB1-rendered porcine and feline non-permissive cells (DQ cells and CRFK cells, respectively) is susceptible to aMPV/C infection. Kinetic replication of aMPV/C in siRNA-knockdown cells revealed that ITGB1 plays an important role in aMPV/C infection at the early stage (attachment and internalization). aMPV/C was also able to efficiently infect human non-small cell lung cancer (A549) cells. This may be a consequence of the similar structures of both metapneumovirus F protein-specific motifs (RSD for aMPV/C and RGD for human metapneumovirus) recognized by ITGB1. Overexpression of avian-derived ITGB1 and human-derived ITGB1 in A549 cells enhanced aMPV/C infectivity. Taken together, this study demonstrated that ITGB1 acts as an essential receptor for aMPV/C attachment and internalization into host cells, facilitating aMPV/C infection.

Viral Pneumonias.

Viral pneumonia is usually community acquired and caused by influenza, parainfluenza, respiratory syncytial virus, human metapneumovirus, and adenovirus. Many of these infections are airway centric and chest imaging demonstrates bronchiolitis and bronchopneumonia, With the exception of adenovirus infections, the presence of lobar consolidation usually suggests bacterial coinfection. Community-acquired viral pathogens can cause more severe pneumonia in immunocompromised hosts, who are also susceptible to CMV and varicella infection. These latter 2 pathogens are less likely to manifest the striking airway-centric pattern. Airway-centric pattern is distinctly uncommon in Hantavirus pulmonary syndrome, a rare environmentally acquired infection with high mortality.

Invasive pulmonary aspergillosis following human metapneumovirus infection in solid-organ transplant recipients: Another virus to add to the list.

There is increasing recognition that respiratory viral infections such as influenza, respiratory syncytial virus, parainfluenza virus, adenovirus, and SARS-CoV-2 can promote the development of invasive fungal pulmonary coinfections, particularly invasive aspergillosis, both in immunocompetent and immunocompromised patients. To date, there are no case reports exploring the role of human metapneumovirus as a risk factor for fungal coinfection. Below, we describe the case of a 63-year-old woman who received a kidney transplant and developed invasive pulmonary aspergillosis after a human metapneumovirus infection and discuss the possible phenomena that could favor this association.

Old foes following news ways?-Pandemic-related changes in the epidemiology of viral respiratory tract infections.

INTRODUCTION: Following lockdown periods and restricting public health measures in response to the COVID-19 pandemic, respiratory tract infections (RTIs) rose significantly worldwide. This led to an increased burden on children's hospitals compromising medical care of acutely and chronically ill children. We characterized changes in the epidemiological pattern of circulating respiratory viral infections. METHODS: We assessed the number of patients with RTIs and the annual distribution of virus detections between 2019 and 2022 based on 4809 clinical samples (4131 patients) from a German pediatric tertiary care-center. We investigated the impact of lockdown periods on spectra of circulating respiratory viruses, pattern of coinfections, age, and seasonality of infections. RESULTS: A fourfold increase in the number of respiratory virus detections was observed in 2022 vs 2019 with numbers doubling in 2022 (vs 2021). In 2022, seasonal patterns of circulating virus, particularly Adeno and seasonal Coronavirus were far less pronounced compared to previous years, in fact almost disappeared for Rhinoviruses.". SARS-CoV-2, Parainfluenza- and human Metapneumovirus detections increased significantly in 2022 (2019 vs 2022, p < 0.01). Coinfections with multiple viruses occurred more frequently since 2021 compared to pre-pandemic years, especially in younger children (2019 vs 2022, p < 0.01). CONCLUSION: Compared to pre-pandemic years, we observed a dramatic increase in pediatric RTIs with an incrementing spectrum of viruses and a predominance in Rhino/Enterovirus infections - leading to a high rate of hospital admissions, particularly in conjunction with other viruses. This caused an acute shortage in medical care and may also be followed by an increase of virus-triggered secondary chronic respiratory diseases like asthma-rendering a burden on the health system.

Upper and/or Lower Respiratory Tract Infection Caused by Human Metapneumovirus After Allogeneic Hematopoietic Stem Cell Transplantation.

BACKGROUND: Human metapneumovirus (hMPV) epidemiology, clinical characteristics and risk factors for poor outcome after allogeneic stem cell transplantation (allo-HCT) remain a poorly investigated area. METHODS: This retrospective multicenter cohort study examined the epidemiology, clinical characteristics, and risk factors for poor outcomes associated with human metapneumovirus (hMPV) infections in recipients of allo-HCT. RESULTS: We included 428 allo-HCT recipients who developed 438 hMPV infection episodes between January 2012 and January 2019. Most recipients were adults (93%). hMPV infections were diagnosed at a median of 373 days after allo-HCT. The infections were categorized as upper respiratory tract disease (URTD) or lower respiratory tract disease (LRTD), with 60% and 40% of cases, respectively. Patients with hMPV LRTD experienced the infection earlier in the transplant course and had higher rates of lymphopenia, neutropenia, corticosteroid use, and ribavirin therapy. Multivariate analysis identified lymphopenia and corticosteroid use (>30 mg/d) as independent risk factors for LRTD occurrence. The overall mortality at day 30 after hMPV detection was 2% for URTD, 12% for possible LRTD, and 21% for proven LRTD. Lymphopenia was the only independent risk factor associated with day 30 mortality in LRTD cases. CONCLUSIONS: These findings highlight the significance of lymphopenia and corticosteroid use in the development and severity of hMPV infections after allo-HCT, with lymphopenia being a predictor of higher mortality in LRTD cases.

A neutralizing single-domain antibody that targets the trimer interface of the human metapneumovirus fusion protein.

IMPORTANCE: Human metapneumovirus (hMPV) is an important respiratory pathogen for which no licensed antivirals or vaccines exist. Single-domain antibodies represent promising antiviral biologics that can be easily produced and formatted. We describe the isolation and detailed characterization of two hMPV-neutralizing single-domain antibodies that are directed against the fusion protein F. One of these single-domain antibodies broadly neutralizes hMPV A and B strains, can prevent proteolytic maturation of F, and binds to an epitope in the F trimer interface. This suggests that hMPV pre-F undergoes trimer opening or "breathing" on infectious virions, exposing a vulnerable site for neutralizing antibodies. Finally, we show that this single-domain antibody, fused to a human IgG1 Fc, can protect cotton rats against hMPV replication, an important finding for potential future clinical applications.

Structural characterization of M8C10, a neutralizing antibody targeting a highly conserved prefusion-specific epitope on the metapneumovirus fusion trimerization interface.

IMPORTANCE: Human metapneumovirus (hMPV) is a common pathogen causing lower respiratory tract infections worldwide and can develop severe symptoms in high-risk populations such as infants, the elderly, and immunocompromised patients. There are no approved hMPV vaccines or neutralizing antibodies available for therapeutic or prophylactic use. The trimeric hMPV fusion F protein is the major target of neutralizing antibodies in human sera. Understanding the immune recognition of antibodies to hMPV-F antigen will provide critical insights into developing efficacious hMPV monoclonal antibodies and vaccines.

Human Metapneumovirus-Induced Host microRNA Expression Impairs the Interferon Response in Macrophages and Epithelial Cells.

Human metapneumovirus (HMPV) is a nonsegmented, single-stranded negative RNA virus and a member of the Pneumoviridae family. During HMPV infection, macrophages play a critical role in defending the respiratory epithelium by secreting large amounts of type I interferon (IFN). MicroRNAs (miRNAs) are small, noncoding, single-stranded RNAs that play an essential role in regulating gene expression during normal cellular homeostasis and disease by binding to specific mRNAs, thereby regulating at the transcriptional and post-transcriptional levels with a direct impact on the immune response and other cellular processes. However, the role of miRNAs in macrophages and respiratory viral infections remains largely unknown. Here, we characterized the susceptibility of THP-1-derived macrophages to HMPV infection and the effect of hsa-miR-4634 on these cells. Transfection of an miRNA mimic and inhibitor demonstrated that hsa-miR-4634 regulates the IFN response in HMPV-infected macrophages, suggesting that HMPV induces the expression of the miRNA as a subversion mechanism of the antiviral response. This effect was not limited to macrophages, as a similar effect was also observed in epithelial cells. Overall, our results demonstrate that hsa-miR-4634 is an important factor in regulating the IFN response in macrophages and epithelial cells during HMPV infection.