Epicutaneous immunization using synthetic virus-like particles efficiently boosts protective immunity to respiratory syncytial virus.

Despite the substantial health and economic burden caused by RSV-associated illness, no vaccine is available. The sole licensed treatment (palivizumab), composed of a monoclonal neutralizing antibody, blocks the fusion of the virus to the host cell but does not prevent infection. The development of a safe and efficacious RSV vaccine is therefore a priority, but also a considerable challenge, and new innovative strategies are warranted. Most of the adult population encounter regular RSV infections and can elicit a robust neutralizing antibody response, but unfortunately it wanes over time and reinfections during subsequent seasons are common. One approach to protect the mother and young infant from RSV infection is to administer a vaccine capable of boosting preexisting RSV immunity during pregnancy, which would provide protection to the fetus through passive transfer of maternal antibodies, thus preventing primary RSV infection in newborns during their first months of life. Here, we describe the preclinical evaluation of an epicutaneous RSV vaccine booster that combines epicutaneous patches as a delivery platform and a Synthetic Virus-Like Particles (SVLP)-based vaccine displaying multiple RSV F-protein site II (FsII, palivizumab epitope) mimetic as antigen (V-306). We demonstrated in mice that epicutaneous immunization with V-306 efficiently boosts preexisting immunity induced by the homologous V-306 administered subcutaneously. This boosting was characterized by a significant increase in F- and FsII-specific antibodies capable of competing with palivizumab for its target antigen and neutralize RSV. More importantly, epicutaneous booster immunization with V-306 significantly decreased lung viral replication in experimental mice after intranasal RSV challenge, without inducing enhanced RSV disease. In conclusion, an epicutaneous booster vaccine based on V-306 is safe and efficacious in enhancing RSV preexisting immunity in mice. This needle-free vaccine candidate would be potentially suited as a booster vaccine for vulnerable populations such as young infants via pregnant women, and the elderly.

Host Response Comparison of H1N1- and H5N1-Infected Mice Identifies Two Potential Death Mechanisms.

Highly pathogenic influenza A viruses (IAV) infections represent a serious threat to humans due to their considerable morbidity and mortality capacities. A good understanding of the molecular mechanisms responsible for the acute lung injury observed during this kind of infection is essential to design adapted therapies. In the current study, using an unbiased transcriptomic approach, we compared the host-responses of mice infected with two different subtypes of IAV: H1N1 vs. H5N1. The host-response comparison demonstrated a clear difference between the transcriptomic profiles of H1N1- and H5N1-infected mice despite identical survival kinetics and similar viral replications. The ontological analysis of the two transcriptomes showed two probable causes of death: induction of an immunopathological state of the lung for the H1N1 strain vs. development of respiratory dysfunction in the case of the H5N1 IAV. Finally, a clear signature responsible for lung edema was specifically associated with the H5N1 infection. We propose a potential mechanism of edema development based on predictive bioinformatics tools.

RSV N-nanorings fused to palivizumab-targeted neutralizing epitope as a nanoparticle RSV vaccine.

Respiratory syncytial virus (RSV) is the leading cause of acute respiratory infections in children, yet no vaccine is available. The sole licensed preventive treatment against RSV is composed of a monoclonal neutralizing antibody (palivizumab), which targets a conformational epitope located on the fusion protein (F). Palivizumab reduces the burden of bronchiolitis but does not prevent infection. Thus, the development of RSV vaccines remains a priority. We previously evaluated nanorings formed by RSV nucleoprotein (N) as an RSV vaccine, as well as an immunostimulatory carrier for heterologous antigens. Here, we linked the palivizumab-targeted epitope (called FsII) to N, to generate N-FsII-nanorings. Intranasal N-FsII immunization elicited anti-F antibodies in mice that were non-neutralizing in vitro. Nevertheless, RSV-challenged animals were better protected against virus replication than mice immunized with N-nanorings, especially in the upper airways. In conclusion, an N-FsII-focused vaccine is an attractive candidate combining N-specific cellular immunity and F-specific antibodies for protection.

Visualizing the replication of respiratory syncytial virus in cells and in living mice.

Respiratory syncytial virus (RSV) is the most important cause of severe lower-respiratory tract disease in calves and young children, yet no human vaccine nor efficient curative treatments are available. Here we describe a recombinant human RSV reverse genetics system in which the red fluorescent protein (mCherry) or the firefly luciferase (Luc) genes are inserted into the RSV genome. Expression of mCherry and Luc are correlated with infection rate, allowing the monitoring of RSV multiplication in cell culture. Replication of the Luc-encoding virus in living mice can be visualized by bioluminescent imaging, bioluminescence being detected in the snout and lungs of infected mice after nasal inoculation. We propose that these recombinant viruses are convenient and valuable tools for screening of compounds active against RSV, and can be used as an extremely sensitive readout for studying effects of antiviral therapeutics in living mice.

Kinetic characterization of PB1-F2-mediated immunopathology during highly pathogenic avian H5N1 influenza virus infection.

The PB1-F2 protein encoded by influenza A viruses can contribute to virulence, a feature that is dependent of its sequence polymorphism. Whereas PB1-F2 from some H1N1 viruses were shown to exacerbate the inflammatory response within the airways, the contribution of PB1-F2 to highly pathogenic avian influenza virus (HPAIV) virulence in mammals remains poorly described. Using a H5N1 HPAIV strain isolated from duck and its PB1-F2 knocked-out mutant, we characterized the dynamics of PB1-F2-associated host response in a murine model of lethal pneumonia. The mean time of death was 10 days for the two viruses, allowing us to perform global transcriptomic analyses and detailed histological investigations of the infected lungs at multiple time points. At day 2 post-infection (pi), while no histopathological lesion was observed, PB1-F2 expression resulted in a significant inhibition of cellular pathways involved in macrophage activation and in a transcriptomic signature suggesting that it promotes damage to the epithelial barrier. At day 4 pi, the gene profile associated with PB1-F2 expression revealed dysfunctions in NK cells activity. At day 8 pi, PB1-F2 expression was strongly associated with increased transcription of genes encoding chemokines and cytokines implicated in the recruitment of granulocytes, as well as expression of a number of genes encoding enzymes expressed by neutrophils. These transcriptomic data were fully supported by the histopathological analysis of the mice lungs which evidenced more severe inflammatory lesions and enhanced recruitment of neutrophils in the context of PB1-F2 expression, and thus provided a functional corroboration to the insight obtained in this work. In summary, our study shows that PB1-F2 of H5N1 HPAIV markedly influences the expression of the host transcriptome in a different way than its H1N1 counterparts: H5N1 PB1-F2 first delays the initial immune response but increases the pulmonary inflammatory response during the late stages of infection.