A live attenuated human metapneumovirus vaccine strain provides complete protection against homologous viral infection and cross-protection against heterologous viral infection in BALB/c mice

Probenecid Inhibits Human Metapneumovirus (HMPV) Replication In Vitro and in BALB/c Mice

Human metapneumovirus (HMPV) is an important cause of acute respiratory tract infection and causes significant morbidity and mortality. There is no specific antiviral drug to treat HMPV or vaccine to prevent HMPV. This study determined if probenecid, a host-targeting antiviral drug, had prophylactic (pre-virus) or therapeutic (post-virus) efficacy to inhibit HMPV replication in LLC-MK2 cells in vitro and in the lungs of BALB/c mice. This study showed that ≥0.5 μM probenecid significantly inhibited HMPV replication in vitro, and 2-200 mg/kg probenecid prophylaxis or treatment reduced HMPV replication in BALB/c mice.

Role of human metapneumovirus glycoprotein G in modulation of immune responses

Human metapneumovirus (hMPV) is an important pathogen responsible for acute respiratory tract infections in children, the elderly, and immunocompromised patients, with no effective treatment or vaccine currently available. Knowledge of virus- and host-specific mechanisms contributing to the pathogenesis of hMPV infection is still limited. Studies have shown that hMPV surface glycoprotein G is an important virulence factor, by inhibiting innate immune signaling in airway epithelial cells and immune cells. In this study, we investigated the role of G protein in modulating innate and adaptive immune responses in mice infected with a recombinant virus with deletion of G protein (rhMPV-ΔG). Results show that rhMPV-ΔG was strongly attenuated, as it did not induce significant clinical disease, airway obstruction and airway hyperresponsiveness (AHR), compared to infection with a control strain (rhMPV-WT). By analysis of cells in bronchoalveolar fluid and lung tissue, as well as cytokine production, we found that G protein mediates aspects of both innate and adaptive immune responses, including neutrophils, dendritic cells, natural killer cells and B cells. Lung T cells recruited in response to rhMPV-ΔG had a significantly higher activated phenotype compared to those present after rhMPV-WT infection. Despite highly attenuation characterized by low levels of replication in the lung, rhMPV-ΔG was able to induce neutralizing antibodies and to protect mice from a secondary hMPV challenge. However, challenged mice that had received rhMPV-ΔG as primary infection showed some signs of lung disease at the earliest time points, which were less evident in mice that had received the rhMPV-WT strain as primary infection. These results demonstrate some of the mechanisms by which G protein could contribute to airway disease and modulate immune response to hMPV infection.

Induction of Protective Immunity by a Single Low Dose of a Master Cell Bank cGMP-rBCG-P Vaccine Against the Human Metapneumovirus in Mice

Human metapneumovirus (hMPV) is an emergent virus, which mainly infects the upper and lower respiratory tract epithelium. This pathogen is responsible for a significant portion of hospitalizations due to bronchitis and pneumonia in infants and the elderly worldwide. hMPV infection induces a pro-inflammatory immune response upon infection of the host, which is not adequate for the clearance of this pathogen. The lack of knowledge regarding the different molecular mechanisms of infection of this virus has delayed the licensing of effective treatments or vaccines. As part of this work, we evaluated whether a single and low dose of a recombinant Mycobacterium bovis Bacillus Calmette-Guérin (BCG) expressing the phosphoprotein of hMPV (rBCG-P) can induce a protective immune response in mice. Immunization with the rBCG-P significantly decreased neutrophil counts and viral loads in the lungs of infected mice at different time points. This immune response was also associated with a modulated infiltration of innate cells into the lungs, such as interstitial macrophages (IM) and alveolar macrophages (AM), activated CD4+ and CD8+ T cells, and changes in the population of differentiated subsets of B cells, such as marginal zone B cells and plasma cells. The humoral immune response induced by the rBCG-P led to an early and robust IgA response and a late and constant IgG response. Finally, we determined that the transfer of cells or sera from immunized and infected mice to naïve mice promoted an efficient viral clearance. Therefore, a single and low dose of rBCG-P can protect mice from the disease caused by hMPV, and this vaccine could be a promising candidate for future clinical trials.

Human Metapneumovirus Infection and Genotyping of Infants in Rural Nepal

BACKGROUND

Acute respiratory tract infections are a serious clinical burden in infants; human metapneumovirus (HMPV) is an important etiological agent. We investigated genotypic variation and molecular epidemiological patterns among infants infected with HMPV in Sarlahi, Nepal, to better characterize infection in a rural, low-resource setting.

METHODS

Between May 2011 and April 2014, mid-nasal swabs were collected from 3528 infants who developed respiratory symptoms during a longitudinal maternal influenza vaccine study. Sequencing glycoprotein genes permitted genotyping and analyses among subtypes.

RESULTS

HMPV was detected by reverse-transcriptase polymerase chain reaction (RT-PCR) in 187 (5%) infants, with seasonality observed during fall and winter months. Phylogenetic investigation of complete and partial coding sequences for the F and G genes, respectively, revealed that 3 genotypes were circulating: A2, B1, and B2. HMPV-B was most frequently detected with a single type predominating each season. Both HMPV genotypes exhibited comparable median viral loads. Clinically significant differences between genotypes were limited to increased cough duration and general respiratory symptoms for type B.

CONCLUSIONS

In rural Nepal, multiple HMPV genotypes circulate simultaneously with an alternating predominance of a single genotype and definitive seasonality. No difference in viral load was detected by genotype and symptom severity was not correlated with RT-PCR cycle threshold or genotype.

Membrane Microvesicles as Potential Vaccine Candidates

The prevention and control of infectious diseases is crucial to the maintenance and protection of social and public healthcare. The global impact of SARS-CoV-2 has demonstrated how outbreaks of emerging and re-emerging infections can lead to pandemics of significant public health and socio-economic burden. Vaccination is one of the most effective approaches to protect against infectious diseases, and to date, multiple vaccines have been successfully used to protect against and eradicate both viral and bacterial pathogens. The main criterion of vaccine efficacy is the induction of specific humoral and cellular immune responses, and it is well established that immunogenicity depends on the type of vaccine as well as the route of delivery. In addition, antigen delivery to immune organs and the site of injection can potentiate efficacy of the vaccine. In light of this, microvesicles have been suggested as potential vehicles for antigen delivery as they can carry various immunogenic molecules including proteins, nucleic acids and polysaccharides directly to target cells. In this review, we focus on the mechanisms of microvesicle biogenesis and the role of microvesicles in infectious diseases. Further, we discuss the application of microvesicles as a novel and effective vaccine delivery system.

Prospects of and Barriers to the Development of Epitope-Based Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is a major cause of respiratory illnesses in children, the elderly and immunocompromised patients. Although this pathogen was only discovered in 2001, an enormous amount of research has been conducted in order to develop safe and effective vaccines to prevent people from contracting the disease. In this review, we summarize current knowledge about the most promising experimental B- and T-cell epitopes of human metapneumovirus for the rational design of HMPV vaccines using vector delivery systems, paying special attention to the conservation of these epitopes among different lineages/genotypes of HMPV. The prospects of the successful development of an epitope-based HMPV vaccine are discussed in the context of recent findings regarding HMPV’s ability to modulate host immunity. In particular, we discuss the lack of data on experimental human CD4 T-cell epitopes for HMPV despite the role of CD4 lymphocytes in both the induction of higher neutralizing antibody titers and the establishment of CD8 memory T-cell responses. We conclude that current research should be focused on searching for human CD4 T-cell epitopes of HMPV that can help us to design a safe and cross-protective epitope-based HMPV vaccine.

Addicted to sugar: roles of glycans in the order Mononegavirales

Glycosylation is a biologically important protein modification process by which a carbohydrate chain is enzymatically added to a protein at a specific amino acid residue. This process plays roles in many cellular functions, including intracellular trafficking, cell-cell signaling, protein folding and receptor binding. While glycosylation is a common host cell process, it is utilized by many pathogens as well. Protein glycosylation is widely employed by viruses for both host invasion and evasion of host immune responses. Thus better understanding of viral glycosylation functions has potential applications for improved antiviral therapeutic and vaccine development. Here, we summarize our current knowledge on the broad biological functions of glycans for the Mononegavirales, an order of enveloped negative-sense single-stranded RNA viruses of high medical importance that includes Ebola, rabies, measles and Nipah viruses. We discuss glycobiological findings by genera in alphabetical order within each of eight Mononegavirales families, namely, the bornaviruses, filoviruses, mymonaviruses, nyamiviruses, paramyxoviruses, pneumoviruses, rhabdoviruses and sunviruses.

Development of a live attenuated vaccine against Muscovy duck reovirus infection

The Muscovy duck reovirus (MDRV) is a highly pathogenic virus that causes substantial economic losses in the Muscovy duck industry. While MDRV poses a significant threat to Muscovy ducklings, no vaccine candidates are available to date to alleviate MDRV infection throughout the world. The present study presents efforts toward establishing an attenuated vaccine for MDRV. For this purpose, a live attenuated vaccine strain named CA was obtained via alternate propagation of the MDRV isolate MW9710 in both Muscovy duck embryo fibroblasts (MDEFs) and chicken embryo fibroblasts (CEFs) for 90 passages. The CA strain achieved an adaptive growth capacity in CEFs with a viral titer that ranged between 10^5.0-10^5.5 TCID₅₀/100 μL and lost its pathogenicity in 1-day-old Muscovy ducklings. Compared to the parent strain MW9710, the CA strain has 42 scattered amino acid substitutions, most of which are located in the λB, λC, μB, σB, and σC protein. The CA strain maintained its attenuation and showed no gene mutation or virulence reversion after back propagation into 1-day-old ducklings for five rounds. The minimum protective dose was calculated to be 300 TCID₅₀ of the CA strain. Furthermore, a single dose of CA vaccine protected immunized ducklings against lethal challenge by the virulent MDRV strain MW9710 and significantly decreased viral loads. In summary, the CA strain exhibited striking genetic stability, excellent safety, and effective immunogenicity. This CA strain of MDRV is a promising vaccine candidate for the prevention and control of MDRV infection.

Prophylactic and therapeutic approaches for human metapneumovirus

Human metapneumovirus (HMPV) is an important pneumovirus which causes acute respiratory disease in human beings. The viral infection leads to mild to severe respiratory symptoms depending on the age and immune status of the infected individual. Several groups across the world are working on the development of immunogens and therapy to manage HMPV infection with promising results under laboratory conditions but till date any virus specific vaccine or therapy has not been approved for clinical use. This minireview gives an overview of the prophylactic and therapeutic approaches to manage HMPV infections.

Modulation of Host Immunity by the Human Metapneumovirus

Globally, as a leading agent of acute respiratory tract infections in children <5 years of age and the elderly, the human metapneumovirus (HMPV) has gained considerable attention. As inferred from studies comparing vaccinated and experimentally infected mice, the acquired immune response elicited by this pathogen fails to efficiently clear the virus from the airways, which leads to an exaggerated inflammatory response and lung damage. Furthermore, after disease resolution, there is a poor development of T and B cell immunological memory, which is believed to promote reinfections and viral spread in the community. In this article, we discuss the molecular mechanisms that shape the interactions of HMPV with host tissues that lead to pulmonary pathology and to the development of adaptive immunity that fails to protect against natural infections by this virus.

Current developments and prospects on human metapneumovirus vaccines

INTRODUCTION

Human metapneumovirus (hMPV) has become one of the major pathogens causing acute respiratory infections (ARI) mainly affecting young children, immunocompromised patients, and the elderly. Currently there are no licensed vaccines against this virus. Areas covered: Since the discovery of hMPV in 2001, many groups have focused on developing vaccines against this pathogen. This review presents the outcomes and perspectives derived from preclinical studies performed in cell cultures and animals as well as the only candidate that has reached evaluation in a clinical trial. Limitations of the current vaccine candidates are discussed and perspectives for the development of plant-based vaccines are analyzed. Expert commentary: Several hMPV vaccine candidates are under development with the potential to progress into clinical trials. In parallel, the molecular farming field offers new opportunities to generate innovative vaccines that will offer several advantages in the fight against hMPV.

Human Metapneumovirus

Human metapneumovirus (HMPV), a paramyxovirus identified in 2001, is a leading cause of respiratory tract infections in both children and adults. Seroprevalence studies demonstrate that the primary infection occurs before the age of 5 years, and humans are reinfected throughout life. The four subgroups of HMPV occur with year-to-year variability, and infection with one subgroup confers some serologic cross-protection. Experimental vaccines elicit a humoral response in both animal and human models and have been used to identify antigenic determinants. The main target of protective antibodies is the fusion (F) protein, although many of the remaining eight proteins are immunogenic. Monoclonal antibodies (mAbs) targeting the F protein are both protective and therapeutic in animal models. Most recently, the identification of broadly neutralizing antibodies against HMPV and respiratory syncytial virus demonstrates that common epitopes are present between the two viruses. Broadly neutralizing mAbs have significant clinical implications for prophylaxis and treatment of high-risk hosts as well as vaccine development.

Immune Response to Human Metapneumovirus Infection: What We Have Learned from the Mouse Model

Human Metapneumovirus (hMPV) is a leading respiratory viral pathogen associated with bronchiolitis, pneumonia, and asthma exacerbation in young children, the elderly and immunocompromised individuals. The development of a potential vaccine against hMPV requires detailed understanding of the host immune system, which plays a significant role in hMPV pathogenesis, susceptibility and vaccine efficacy. As a result, animal models have been developed to better understand the mechanisms by which hMPV causes disease. Several animal models have been evaluated and established so far to study the host immune responses and pathophysiology of hMPV infection. However, inbred laboratory mouse strains have been one of the most used animal species for experimental modeling and therefore used for the studies of immunity and immunopathogenesis to hMPV. This review summarizes the contributions of the mouse model to our understanding of the immune response against hMPV infection.

New Approaches for Immunization and Therapy against Human Metapneumovirus

Human metapneumovirus (HMPV) is a paramyxovirus discovered in 2001 in the Netherlands. Studies have identified HMPV as an important causative agent of acute respiratory disease in infants, the elderly, and immunocompromised individuals. Clinical signs of infection range from mild upper respiratory illness to more serious lower respiratory illness, including bronchiolitis and pneumonia. There are currently no licensed therapeutics or vaccines against HMPV. However, several research groups have tested vaccine candidates and monoclonal antibodies in various animal models. Several of these approaches have shown promise in animal models. This minireview summarizes the current therapies used to treat HMPV infection as well as different approaches for immunization.

Lung CD8+ T Cell Impairment Occurs during Human Metapneumovirus Infection despite Virus-Like Particle Induction of Functional CD8+ T Cells

Human metapneumovirus (HMPV) is a major cause of respiratory disease in infants, the elderly, and immunocompromised individuals worldwide. There is currently no licensed HMPV vaccine. Virus-like particles (VLPs) are an attractive vaccine candidate because they are noninfectious and elicit a neutralizing antibody response. However, studies show that serum neutralizing antibodies are insufficient for complete protection against reinfection and that adaptive T cell immunity is important for viral clearance. HMPV and other respiratory viruses induce lung CD8(+) T cell (TCD8) impairment, mediated by programmed death 1 (PD-1). In this study, we generated HMPV VLPs by expressing the fusion and matrix proteins in mammalian cells and tested whether VLP immunization induces functional HMPV-specific TCD8 responses in mice. C57BL/6 mice vaccinated twice with VLPs and subsequently challenged with HMPV were protected from lung viral replication for at least 20 weeks postimmunization. A single VLP dose elicited F- and M-specific lung TCD8s with higher function and lower expression of PD-1 and other inhibitory receptors than TCD8s from HMPV-infected mice. However, after HMPV challenge, lung TCD8s from VLP-vaccinated mice exhibited inhibitory receptor expression and functional impairment similar to those of mice experiencing secondary infection. HMPV challenge of VLP-immunized μMT mice also elicited a large percentage of impaired lung TCD8s, similar to mice experiencing secondary infection. Together, these results indicate that VLPs are a promising vaccine candidate but do not prevent lung TCD8 impairment upon HMPV challenge.

IMPORTANCE

Human metapneumovirus (HMPV) is a leading cause of acute respiratory disease for which there is no licensed vaccine. Virus-like particles (VLPs) are an attractive vaccine candidate and induce antibodies, but T cell responses are less defined. Moreover, HMPV and other respiratory viruses induce lung CD8(+) T cell (TCD8) impairment mediated by programmed death 1 (PD-1). In this study, HMPV VLPs containing viral fusion and matrix proteins elicited epitope-specific TCD8s that were functional with low PD-1 expression. Two VLP doses conferred sterilizing immunity in C57BL/6 mice and facilitated HMPV clearance in antibody-deficient μMT mice without enhancing lung pathology. However, regardless of whether responding lung TCD8s had previously encountered HMPV antigens in the context of VLPs or virus, similar proportions were impaired and expressed comparable levels of PD-1 upon viral challenge. These results suggest that VLPs are a promising vaccine candidate but do not prevent lung TCD8 impairment upon HMPV challenge.

Human metapneumovirus infection activates the TSLP pathway that drives excessive pulmonary inflammation and viral replication in mice

Human metapneumovirus (hMPV) is a leading cause of acute respiratory tract infections in children and the elderly. The mechanism by which this virus triggers an inflammatory response still remains unknown. Here, we evaluated whether the thymic stromal lymphopoietin (TSLP) pathway contributes to lung inflammation upon hMPV infection. We found that hMPV infection promotes TSLP expression both in human airway epithelial cells and in the mouse lung. hMPV infection induced lung infiltration of OX40L(+) CD11b(+) DCs. Mice lacking the TSLP receptor deficient mice (tslpr(-/-) ) showed reduced lung inflammation and hMPV replication. These mice displayed a decreased number of neutrophils as well a reduction in levels of thymus and activation-regulated chemokine/CCL17, IL-5, IL-13, and TNF-α in the airways upon hMPV infection. Furthermore, a higher frequency of CD4(+) and CD8(+) T cells was found in tslpr(-/-) mice compared to WT mice, which could contribute to controlling viral spread. Depletion of neutrophils in WT and tslpr(-/-) mice decreased inflammation and hMPV replication. Remarkably, blockage of TSLP or OX40L with specific Abs reduced lung inflammation and viral replication following hMPV challenge in mice. Altogether, these results suggest that activation of the TSLP pathway is pivotal in the development of pulmonary pathology and pulmonary hMPV replication.

Acute clearance of human metapneumovirus occurs independently of natural killer cells

Human metapneumovirus (HMPV) is a major cause of respiratory disease. The role of NK cells in protection against HMPV is unclear. We show that while HMPV-infected C57BL/6 mice had higher numbers of functional lung NK cells than mock-treated mice, comparing NK cell-depleted and control mice did not reveal differences in lung viral titers, histopathology, cytokine levels, or T cell numbers or function. These data indicate that NK cells are not required for host control of HMPV.

Human metapneumovirus: review of an important respiratory pathogen

Human metapneumovirus (hMPV), discovered in 2001, most commonly causes upper and lower respiratory tract infections in young children, but is also a concern for elderly subjects and immune-compromised patients. hMPV is the major etiological agent responsible for about 5% to 10% of hospitalizations of children suffering from acute respiratory tract infections. hMPV infection can cause severe bronchiolitis and pneumonia in children, and its symptoms are indistinguishable from those caused by human respiratory syncytial virus. Initial infection with hMPV usually occurs during early childhood, but re-infections are common throughout life. Due to the slow growth of the virus in cell culture, molecular methods (such as reverse transcriptase PCR (RT-PCR)) are the preferred diagnostic modality for detecting hMPV. A few vaccine candidates have been shown to be effective in preventing clinical disease, but none are yet commercially available. Our understanding of hMPV has undergone major changes in recent years and in this article we will review the currently available information on the molecular biology and epidemiology of hMPV. We will also review the current therapeutic interventions and strategies being used to control hMPV infection, with an emphasis on possible approaches that could be used to develop an effective vaccine against hMPV.