Structure-based design of NS2 mutants for attenuated influenza A virus vaccines

Effect of urea concentration on instant refolding of Nuclear Export Protein (NEP) from Influenza-A virus H1N1: A solution NMR based investigation

Nuclear-export-protein (NEP) plays multiple-functions during influenza virus replication-cycle and shows unique pattern of conserved residues, which altogether make NEP a potential target for developing novel anti-influenza drugs. However, the mechanistic structural biology of NEP has not been fully characterized so far owing to its tendency to aggregate in solution. As structural information is important to guide rational drug-discovery process; therefore, procedural optimization efforts are going on to achieve properly folded NEP in sub-millimolar concentrations for solution-NMR investigations. As a first step in this direction, the refolding-cum-aggregation behavior of recombinant-NEP with N-terminal purification-tag (referred here as NEPN) at different urea-concentrations has been investigated here by NMR-based methods. Several attempts were made to refold denatured NEP-N through step-dialysis. However, owing to its strong tendency to aggregate, excessive precipitation was observed at sub-higher levels of urea concentration (5.0 ± 1.0 M). Finally, we used drip-dilution method with 10.5 M urea-denatured NEP-N and were able to refold NEP-N instantly. The amide ¹H dispersion of 3.6 ppm (6.6-10.2 ppm) in the ¹⁵N-HSQC-spectra of instantly refolded NEP-N confirmed the folded state. This successful instant-refolding of NEP-N has been reported for the first-time and the underlying mechanism has been rationalized through establishing the complete backbone-resonance-assignments of NEP-N at 9.7 M urea-denatured state.

Inhibition of H1N1 influenza virus infection by zinc oxide nanoparticles: another emerging application of nanomedicine

BACKGROUND

Currently available anti-influenza drugs are often associated with limitations such as toxicity and the appearance of drug-resistant strains. Therefore, there is a pressing need for the development of novel, safe and more efficient antiviral agents. In this study, we evaluated the antiviral activity of zinc oxide nanoparticles (ZnO-NPs) and PEGylated zinc oxide nanoparticles against H1N1 influenza virus.

METHODS

The nanoparticles were characterized using the inductively coupled plasma mass spectrometry, x-ray diffraction analysis, and electron microscopy. MTT assay was applied to assess the cytotoxicity of the nanoparticles, and anti-influenza activity was determined by TCID50 and quantitative Real-Time PCR assays. To study the inhibitory impact of nanoparticles on the expression of viral antigens, an indirect immunofluorescence assay was also performed.

RESULTS

Post-exposure of influenza virus with PEGylated ZnO-NPs and bare ZnO-NPs at the highest non-toxic concentrations could be led to 2.8 and 1.2 log10 TCID50 reduction in virus titer when compared to the virus control, respectively (P < 0.0001). At the highest non-toxic concentrations, the PEGylated and unPEGylated ZnO-NPs led to inhibition rates of 94.6 and 52.2%, respectively, which were calculated based on the viral loads. There was a substantial decrease in fluorescence emission intensity in viral-infected cell treated with PEGylated ZnO-NPs compared to the positive control.

CONCLUSIONS

Taken together, our study indicated that PEGylated ZnO-NPs could be a novel, effective, and promising antiviral agent against H1N1 influenza virus infection, and future studies can be designed to explore the exact antiviral mechanism of these nanoparticles.

Heterologous Expression and Isolation of Influenza A Virus Nuclear Export Protein NEP

Influenza A virus nuclear export protein NEP (NS2, 14.4 kDa) plays a key role in various steps of the virus life cycle. Highly purified protein preparations are required for structural and functional studies. In this study, we designed a series of Escherichia coli plasmid constructs for highly efficient expression of the NEP gene under control of the constitutive trp promoter. An efficient method for extraction of NEP from inclusion bodies based on dodecyl sulfate treatment was developed. Preparations of purified NEP with either N- or C-terminal (His)₆-tag were obtained using Ni-NTA agarose affinity chromatography with yield of more than 20 mg per liter of culture. According to CD data, the secondary structure of the proteins matched that of natural NEP. A high propensity of NEP to aggregate over a wide range of conditions was observed.

Design of alternative live attenuated influenza virus vaccines

Each year due to the ever-evolving nature of influenza, new influenza vaccines must be produced to provide protection against the influenza viruses in circulation. Currently, there are two mainstream strategies to generate seasonal influenza vaccines: inactivated and live-attenuated. Inactivated vaccines are non-replicating forms of whole influenza virus, while live-attenuated vaccines are viruses modified to be replication impaired. Although it is widely believed that by inducing both mucosal and humoral immune responses the live-attenuated vaccine provides better protection than that of the inactivated vaccine, there are large populations of individuals who cannot safely receive the LAIV vaccine. Thus, safer LAIV vaccines are needed to provide adequate protection to these populations. Improvement is also needed in the area of vaccine production. Current strategies relying on traditional tissue culture-based and egg-based methods are slow and delay production time. This chapter describes experimental vaccine generation and production strategies that address the deficiencies in current methods for potential human and agricultural use.

Current and emerging cell culture manufacturing technologies for influenza vaccines

Annually, influenza virus infects millions of people worldwide. Vaccination programs against seasonal influenza infections require the production of hundreds of million doses within a very short period of time. The influenza vaccine is currently produced using a technology developed in the 1940s that relies on replicating the virus in embryonated hens' eggs. The monovalent viral preparation is inactivated and purified before being formulated in trivalent or tetravalent influenza vaccines. The production process has depended on a continuous supply of eggs. In the case of pandemic outbreaks, this mode of production might be problematic because of a possible drastic reduction in the egg supply and the low flexibility of the manufacturing process resulting in a lack of supply of the required vaccine doses in a timely fashion. Novel production systems using mammalian or insect cell cultures have emerged to overcome the limitations of the egg-based production system. These industrially well-established production systems have been primarily selected for a faster and more flexible response to pandemic threats. Here, we review the most important cell culture manufacturing processes that have been developed in recent years for mass production of influenza vaccines.

Vaccinia-based influenza vaccine overcomes previously induced immunodominance hierarchy for heterosubtypic protection

Growing concerns about unpredictable influenza pandemics require a broadly protective vaccine against diverse influenza strains. One of the promising approaches was a T cell-based vaccine, but the narrow breadth of T-cell immunity due to the immunodominance hierarchy established by previous influenza infection and efficacy against only mild challenge condition are important hurdles to overcome. To model T-cell immunodominance hierarchy in humans in an experimental setting, influenza-primed C57BL/6 mice were chosen and boosted with a mixture of vaccinia recombinants, individually expressing consensus sequences from avian, swine, and human isolates of influenza internal proteins. As determined by IFN-γ ELISPOT and polyfunctional cytokine secretion, the vaccinia recombinants of influenza expanded the breadth of T-cell responses to include subdominant and even minor epitopes. Vaccine groups were successfully protected against 100 LD50 challenges with PR/8/34 and highly pathogenic avian influenza H5N1, which contained the identical dominant NP366 epitope. Interestingly, in challenge with pandemic A/Cal/04/2009 containing mutations in the dominant epitope, only the group vaccinated with rVV-NP + PA showed improved protection. Taken together, a vaccinia-based influenza vaccine expressing conserved internal proteins improved the breadth of influenza-specific T-cell immunity and provided heterosubtypic protection against immunologically close as well as distant influenza strains.

Possibility of cross-species/subtype reassortments in influenza A viruses: an analysis of nonstructural protein variations

The reassortment of genetic segments from different host species and from different subtypes of influenza A viruses occurs frequently, which may generate new strains causing flu epidemic or pandemic. However, the underlined mechanisms of reassortment were less addressed from the viewpoint of protein variations. Recently, we used the amino-acid pair predictability as an indicator to convert eight types of influenza A virus proteins into predictable portion of amino-acid pairs, and then applied the models I and II ANOVA to estimate their differences in terms of subtypes and host species. In order to get a full picture, 2729 and 1063 non-structural 1 and 2 proteins of influenza A viruses were analyzed in this study. The results are consistent with those obtained from hemagglutinin, neuraminidase, nucleoprotein, polymerase acidic protein, polymerase basic proteins 1 and 2, and matrix proteins 1 and 2, indicating that inter-species/subtypes variations are smaller than intra-species/subtype ones. Our findings provide statistical evidence that can partially explains why cross-subtype mutation and cross-species infection easily occur during co-infecting of different strains.

Vaccine development for protecting swine against influenza virus

Influenza virus infects a wide variety of species including humans, pigs, horses, sea mammals and birds. Weight loss caused by influenza infection and/or co-infection with other infectious agents results in significant financial loss in swine herds. The emergence of pandemic H1N1 (A/CA/04/2009/H1N1) and H3N2 variant (H3N2v) viruses, which cause disease in both humans and livestock constitutes a concerning public health threat. Influenza virus contains eight single-stranded, negative-sense RNA genome segments. This genetic structure allows the virus to evolve rapidly by antigenic drift and shift. Antigen-specific antibodies induced by current vaccines provide limited cross protection to heterologous challenge. In pigs, this presents a major obstacle for vaccine development. Different strategies are under development to produce vaccines that provide better cross-protection for swine. Moreover, overriding interfering maternal antibodies is another goal for influenza vaccines in order to permit effective immunization of piglets at an early age. Herein, we present a review of influenza virus infection in swine, including a discussion of current vaccine approaches and techniques used for novel vaccine development.

Mutations in the M-gene segment can substantially increase replication efficiency of NS1 deletion influenza A virus in MDCK cells

Influenza viruses unable to express NS1 protein (delNS1) replicate poorly and induce large amounts of interferon (IFN). They are therefore considered candidate viruses for live-attenuated influenza vaccines. Their attenuated replication is generally assumed to result from the inability to counter the antiviral host response, as delNS1 viruses replicate efficiently in Vero cells, which lack IFN expression. In this study, delNS1 virus was parallel passaged on IFN-competent MDCK cells, which resulted in two strains that were able to replicate to high virus titers in MDCK cells due to adaptive mutations especially in the M-gene segment but also in the NP and NS gene segments. Most notable were clustered U-to-C mutations in the M segment of both strains and clustered A-to-G mutations in the NS segment of one strain, which presumably resulted from host cell-mediated RNA editing. The M segment mutations in both strains changed the ratio of M1 to M2 expression, probably by affecting splicing efficiency. In one virus, 2 amino acid substitutions in M1 additionally enhanced virus replication, possibly through changes in the M1 distribution between the nucleus and the cytoplasm. Both adapted viruses induced levels of IFN equal to that of the original delNS1 virus. These results show that the increased replication of the adapted viruses is not primarily due to altered IFN induction but rather is related to changes in M1 expression or localization. The mutations identified in this paper may be used to enhance delNS1 virus replication for vaccine production.

Recent progress in structure-based anti-influenza drug design

Seasonal and pandemic influenza have caused high morbidity and mortality worldwide. Recent emergence of influenza A H5N1 and H1N1 strains has heightened concern, especially as a result of their drug resistance. The life cycle of influenza viruses has been well studied and nearly all the viral proteins are becoming potential therapeutic targets. In this review, we present an overview of recent progress in structure-based anti-influenza drug design, paying close attention to the increasing role of computation and strategies for overcoming drug resistance.

Adaptive mutations in NEP compensate for defective H5N1 RNA replication in cultured human cells

Infection of mammals by avian influenza viruses requires adaptive mutations to achieve high-level replication in the new host. However, the basic mechanism underlying this adaptation process is still unknown. Here we show that avian polymerases, lacking the human signature PB2-E627K, are incapable of generating usable complementary RNA templates in cultured human cells and therefore require adaptation. Characterization of the highly pathogenic human H5N1 isolate A/Thailand/1(KAN-1)/2004 that retained the avian PB2-E627 reveals that the defect in RNA replication is only partially compensated by mutations in the polymerase. Instead, mutations in the nuclear export protein are required for efficient polymerase activity. We demonstrate that adaptive mutations in nuclear export proteins of several human isolates enhance the polymerase activity of avian polymerases in human cultured cells. In conclusion, when crossing the species barrier, avian influenza viruses acquire adaptive mutations in nuclear export protein to escape restricted viral genome replication in mammalian cells.

Structure-based vaccines provide protection in a mouse model of ehrlichiosis

BACKGROUND

Recent advances in bioinformatics have made it possible to predict the B cell and T cell epitopes of antigenic proteins. This has led to design of peptide based vaccines that are more specific, safe, and easy to produce. The obligately intracellular gram negative bacteria Ehrlichia cause ehrlichioses in humans and animals. As yet there are no vaccines to protect against Ehrlichia infection.

METHODOLOGY/PRINCIPAL FINDINGS

We applied the principle of structural vaccinology to design peptides to the epitopes of Ehrlichia muris outer membrane P28-19 (OMP-1/P28) and Ehrlichia Heat shock protein 60 (Hsp60/GroEL) antigenic proteins. Both P28-19 and Ehrlichia Hsp60 peptides reacted with polyclonal antibodies against E. canis and E. chaffeensis and could be used as a diagnostic tool for ehrlichiosis. In addition, we demonstrated that mice vaccinated with Ehrlichia P28-19 and Hsp60 peptides and later challenged with E. muris were protected against the pathogen.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate the power of structural vaccines and could be a new strategy in the development of vaccines to provide protection against pathogenic microorganisms.

Efficacy of live attenuated vaccines against 2009 pandemic H1N1 influenza in ferrets

The advent of the H1N1 influenza pandemic (pH1N1) in 2009 triggered the rapid production of pandemic influenza vaccines, since seasonal influenza vaccines were expected and demonstrated not to provide significant cross-protection against the newly emerged pandemic virus. To increase vaccine production capacity and further evaluate the effectiveness of different candidate pandemic influenza vaccines, the World Health Organization stimulated the evaluation of different vaccination concepts including the use of live attenuated influenza vaccines (LAIVs). Therefore, we have immunized ferrets intranasally with a single dose of pH1N1-LAIV from different manufacturers. They all induced adequate serum HI antibody titers in the ferrets and protected them against intratracheal wild-type pH1N1 virus challenge: pH1N1 virus replication in the upper respiratory tract and lungs was reduced and no disease signs or severe broncho-interstitial pneumonia were observed in any of the vaccinated ferrets. These data together with the relatively efficient production process emphasize the potential of the LAIV concept for pandemic preparedness.

NS1-mediated delay of type I interferon induction contributes to influenza A virulence in ferrets

Interference of the influenza A virus non-structural protein NS1 with type I interferon (IFN) signalling has been characterized extensively in vitro. To assess the contribution of NS1 to the virulence of a specific strain, we generated recombinant USSR/90/77 viruses bearing the NS1 proteins of the attenuated strain PR/8/34 or the highly pathogenic strain 1918 'Spanish flu', all belonging to the H1N1 subtype. In vitro, the extent of interference with type I IFN production exerted by the different NS1 proteins correlated with the reported virulence of the respective strain. Infection of ferrets with the recombinant viruses revealed that the presence of the 1918 NS1 resulted in a slightly more severe disease with generally higher clinical scores and increased lung pathology. Analysis of mRNA from nasal wash cells revealed that viruses carrying the 1918 and, to a lesser extent, USSR/90/77 NS1 proteins caused a delay in upregulation of type I IFNs compared with the NS1 PR/8/34-expressing virus, demonstrating the importance of NS1 for early host-response control and virulence.