A recombinant influenza virus vaccine expressing the F protein of respiratory syncytial virus

Establishment of a safe and convenient assay for detection of HA subtype-specific antibodies with PB2 gene-knockout influenza viruses

Monitoring of the epidemic situation is imperative to control the risk of infection with avian influenza H5 and H7 subtype viruses. A microneutralization (MN) assay was employed to detect hemagglutinin (HA) subtype-specific antibodies. However, the conventional MN assay raises biosafety concerns and is labor-intensive and time-consuming. Therefore, a safer and more convenient assay that can be applied in a high-throughput format is warranted. In this study, PB2 knockout (PB2-KO) influenza viruses of H5 and H7 subtypes expressing different colored fluorescent proteins were generated using a reverse genetics system and applied to a novel MN assay for the detection of specific antibodies. The detection sensitivity of our PB2-KO virus-based MN assay was evaluated by observing fluorescent proteins under a fluorescence microscope and measuring fluorescence intensities using a plate reader. In addition, the PB2-KO virus-based MN assay was used for the simultaneous detection of H5 and H7 subtype-specific antibodies in a single assay. Expression of the reporter fluorescent protein from H5 and H7 PB2-KO viruses was restricted toin PB2 protein-expressing cells. The MN titer as determined using fluorescence microscopy and plate reader revealed that the detection sensitivity of our PB2-KO virus-based MN assay was comparable to that of the conventional MN assay. Moreover, H5 and H7 PB2-KO viruses could be usedapplied forto the simultaneous detection of H5 and H7 subtype-specific antibodies in a single assay. Our study demonstrates a safe and convenient assay for the detection of H5 and H7 subtype-specific antibodies.

Uric acid pathway activation during respiratory virus infection promotes Th2 immune response via innate cytokine production and ILC2 accumulation

Respiratory syncytial virus (RSV) infects a majority of infants and can cause severe disease leading to increased risk to develop asthma later in life. In the present studies we detected high levels of uric acid pathway components during RSV infection and examined whether they altered the pathogenesis of RSV infection. Inhibition of uric acid (UA) pathway activation during RSV infection in airway epithelial cells using XOI decreased the expression of IL-33, thymic stromal lymphopoietin (TSLP), and CCL2. In addition, treatment of RSV infected bone marrow-derived macrophages with XOI decreased production of IL-1β. Thus, UA activation of different cell populations contributes different innate immune mediators that promote immunopathogenesis. When mice were treated with XOI or interleukin-1 receptor antagonist (IL1-ra) during RSV infection decreased pulmonary mucus was observed along with significantly reduced numbers of ILC2 and macrophages, accompanied by decreased IL-33 in bronchoalveolar lavage of the treated mice. These findings provide mechanistic insight into the development of RSV immunopathology and indicate that xanthine metabolites and UA are key immunoregulator molecules during RSV infection. Moreover, these findings suggest uric acid and IL-1β as possible therapeutic targets to attenuate severe RSV disease.

AGL2017-82570-RReverse genetics approaches for the development of new vaccines against influenza A virus infections

Influenza A viruses (IAVs) represent a serious concern globally because they are capable of rapid spread and cause severe disease in humans and other animals. The development and implementation of plasmid-based reverse genetics approaches have allowed the manipulation and recovery of recombinant IAVs from complementary DNA copies of the viral genome. Furthermore, IAV reverse genetics have provided researchers an efficient and powerful platform to introduce specific changes in the viral genome with the final goal of studying IAV biology, designing more effective vaccine strategies, and to reduce the rates of incidence and mortality associated with viral infections. In this review, we briefly discuss IAV reverse genetics and their applications to prevent IAV infections.

Novel Approaches for The Development of Live Attenuated Influenza Vaccines

Influenza virus still represents a considerable threat to global public health, despite the advances in the development and wide use of influenza vaccines. Vaccination with traditional inactivate influenza vaccines (IIV) or live-attenuated influenza vaccines (LAIV) remains the main strategy in the control of annual seasonal epidemics, but it does not offer protection against new influenza viruses with pandemic potential, those that have shifted. Moreover, the continual antigenic drift of seasonal circulating influenza viruses, causing an antigenic mismatch that requires yearly reformulation of seasonal influenza vaccines, seriously compromises vaccine efficacy. Therefore, the quick optimization of vaccine production for seasonal influenza and the development of new vaccine approaches for pandemic viruses is still a challenge for the prevention of influenza infections. Moreover, recent reports have questioned the effectiveness of the current LAIV because of limited protection, mainly against the influenza A virus (IAV) component of the vaccine. Although the reasons for the poor protection efficacy of the LAIV have not yet been elucidated, researchers are encouraged to develop new vaccination approaches that overcome the limitations that are associated with the current LAIV. The discovery and implementation of plasmid-based reverse genetics has been a key advance in the rapid generation of recombinant attenuated influenza viruses that can be used for the development of new and most effective LAIV. In this review, we provide an update regarding the progress that has been made during the last five years in the development of new LAIV and the innovative ways that are being explored as alternatives to the currently licensed LAIV. The safety, immunogenicity, and protection efficacy profile of these new LAIVs reveal their possible implementation in combating influenza infections. However, efforts by vaccine companies and government agencies will be needed for controlled testing and approving, respectively, these new vaccine methodologies for the control of influenza infections.

Innate Immune Cell Suppression and the Link With Secondary Lung Bacterial Pneumonia

Secondary infections arise as a consequence of previous or concurrent conditions and occur in the community or in the hospital setting. The events allowing secondary infections to gain a foothold have been studied for many years and include poor nutrition, anxiety, mental health issues, underlying chronic diseases, resolution of acute inflammation, primary immune deficiencies, and immune suppression by infection or medication. Children, the elderly and the ill are particularly susceptible. This review is concerned with secondary bacterial infections of the lung that occur following viral infection. Using influenza virus infection as an example, with comparisons to rhinovirus and respiratory syncytial virus infection, we will update and review defective bacterial innate immunity and also highlight areas for potential new investigation. It is currently estimated that one in 16 National Health Service (NHS) hospital patients develop an infection, the most common being pneumonia, lower respiratory tract infections, urinary tract infections and infection of surgical sites. The continued drive to understand the mechanisms of why secondary infections arise is therefore of key importance.

Stimulation of alpha2-adrenergic receptors impairs influenza virus infection

Influenza A viruses cause seasonal epidemics and occasional pandemics. The emergence of viruses resistant to neuraminidase (NA) inhibitors and M2 ion channel inhibitors underlines the need for alternate anti-influenza drugs with novel mechanisms of action. Here, we report the discovery of a host factor as a potential target of anti-influenza drugs. By using cell-based virus replication screening of a chemical library and several additional assays, we identified clonidine as a new anti-influenza agent in vitro. We found that clonidine, which is an agonist of the alpha2-adrenergic receptor (α2-AR), has an inhibitory effect on the replication of various influenza virus strains. α2-AR is a Gi-type G protein-coupled receptor that reduces intracellular cyclic AMP (cAMP) levels. In-depth analysis showed that stimulation of α2-ARs leads to impairment of influenza virus replication and that α2-AR agonists inhibit the virus assembly step, likely via a cAMP-mediated pathway. Although clonidine administration did not reduce lung virus titers or prevent body weight loss, it did suppress lung edema and improve survival in a murine lethal infection model. Clonidine may thus protect against lung damage caused by influenza virus infection. Our results identify α2-AR-mediated signaling as a key pathway to exploit in the development of anti-influenza agents.

Factors Affecting the Immunity to Respiratory Syncytial Virus: From Epigenetics to Microbiome

Respiratory syncytial virus (RSV) is a common pathogen that infects virtually all children by 2 years of age and is the leading cause of hospitalization of infants worldwide. While most children experience mild symptoms, some children progress to severe lower respiratory tract infection. Those children with severe disease have a much higher risk of developing childhood wheezing later in life. Many risk factors are known to result in exacerbated disease, including premature birth and early age of RSV infection, when the immune system is relatively immature. The development of the immune system before and after birth may be altered by several extrinsic and intrinsic factors that could lead to severe disease predisposition in children who do not exhibit any currently known risk factors. Recently, the role of the microbiome and the resulting metabolite profile has been an area of intense study in the development of lung disease, including viral infection and asthma. This review explores both known risk factors that can lead to severe RSV-induced disease as well as emerging topics in the development of immunity to RSV and the long-term consequences of severe infection.

Reverse Genetics Approaches for the Development of Influenza Vaccines

Influenza viruses cause annual seasonal epidemics and occasional pandemics of human respiratory disease. Influenza virus infections represent a serious public health and economic problem, which are most effectively prevented through vaccination. However, influenza viruses undergo continual antigenic variation, which requires either the annual reformulation of seasonal influenza vaccines or the rapid generation of vaccines against potential pandemic virus strains. The segmented nature of influenza virus allows for the reassortment between two or more viruses within a co-infected cell, and this characteristic has also been harnessed in the laboratory to generate reassortant viruses for their use as either inactivated or live-attenuated influenza vaccines. With the implementation of plasmid-based reverse genetics techniques, it is now possible to engineer recombinant influenza viruses entirely from full-length complementary DNA copies of the viral genome by transfection of susceptible cells. These reverse genetics systems have provided investigators with novel and powerful approaches to answer important questions about the biology of influenza viruses, including the function of viral proteins, their interaction with cellular host factors and the mechanisms of influenza virus transmission and pathogenesis. In addition, reverse genetics techniques have allowed the generation of recombinant influenza viruses, providing a powerful technology to develop both inactivated and live-attenuated influenza vaccines. In this review, we will summarize the current knowledge of state-of-the-art, plasmid-based, influenza reverse genetics approaches and their implementation to provide rapid, convenient, safe and more effective influenza inactivated or live-attenuated vaccines.

Development and applications of single-cycle infectious influenza A virus (sciIAV)

The diverse host range, high transmissibility, and rapid evolution of influenza A viruses justify the importance of containing pathogenic viruses studied in the laboratory. Other than physically or mechanically changing influenza A virus containment procedures, modifying the virus to only replicate for a single round of infection similarly ensures safety and consequently decreases the level of biosafety containment required to study highly pathogenic members in the virus family. This biological containment is more ideal because it is less apt to computer, machine, or human error. With many necessary proteins that can be deleted, generation of single-cycle infectious influenza A viruses (sciIAV) can be achieved using a variety of approaches. Here, we review the recent burst in sciIAV generation and summarize the applications and findings on this important human pathogen using biocontained viral mimics.

Protection against respiratory syncytial virus by inactivated influenza virus carrying a fusion protein neutralizing epitope in a chimeric hemagglutinin

A desirable vaccine against respiratory syncytial virus (RSV) should induce neutralizing antibodies without eliciting abnormal T cell responses to avoid vaccine-enhanced pathology. In an approach to deliver RSV neutralizing epitopes without RSV-specific T cell antigens, we genetically engineered chimeric influenza virus expressing RSV F262-276 neutralizing epitopes in the globular head domain as a chimeric hemagglutinin (HA) protein. Immunization of mice with formalin-inactivated recombinant chimeric influenza/RSV F262-276 was able to induce RSV protective neutralizing antibodies and lower lung viral loads after challenge. Formalin-inactivated RSV immune mice showed high levels of pulmonary inflammatory cytokines, macrophages, IL-4-producing T cells, and extensive histopathology. However, RSV-specific T cell responses and enhancement of pulmonary histopathology were not observed after RSV infection of inactivated chimeric influenza/RSV F262-276. This study provides evidence that an inactivated vaccine platform of chimeric influenza/RSV virus can be developed into a safe RSV vaccine candidate without priming RSV-specific T cells and immunopathology.

FROM THE CLINICAL EDITOR

Respiratory syncytial virus (RSV) is a major cause of respiratory tract illness and morbidity in children. Hence, there is a need to develop an effective vaccine against this virus. In this article, the authors engineered chimeric influenza virus to express RSV neutralizing epitopes. The positive findings in in-vivo experiments provide a beginning for future clinical trials and perhaps eventual product realization.

Efficient isolation of Swine influenza viruses by age-targeted specimen collection

The control of swine influenza virus (SIV) infection is paramount for increasing the productivity of pig farming and minimizing the threat of pandemic outbreaks. Thus, SIV surveillance should be conducted by region and on a regular basis. Here, we established a microneutralization assay specific for SIV seroprevalence surveillance by using reporter gene-expressing recombinant influenza viruses. Growth-based SIV seroprevalence revealed that most sows and piglets were positive for neutralizing antibodies against influenza viruses. In contrast, the 90-day-old growing pigs exhibited limited neutralizing activity in their sera, suggesting that this particular age of population is most susceptible to SIV infection and thus is an ideal age group for SIV isolation. From nasal swab specimens of healthy pigs in this age population, we were able to isolate SIVs at a higher incidence (5.3%) than those of previous reports. Nucleotide sequencing and phylogenetic analysis of the hemagglutinin (HA) genes revealed that the isolated SIVs have circulated and evolved in pigs but not have been recently introduced from humans, implying that a large number of SIV lineages may remain "undiscovered" in the global porcine populations. We propose that the 90-day-old growing pig-targeted nasal swab collection presented in this study facilitates global SIV surveillance and contributes to the detection and control of SIV 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.