Understanding the natural evolution and structural changes involved in broadly neutralizing antibody (bnAb) development holds great promise for improving the design of prophylactic influenza vaccines. Here we report an haemagglutinin (HA) stem-directed bnAb, 3I14, isolated from human memory B cells, that utilizes a heavy chain encoded by the IGHV3-30 germline gene. MAb 3I14 binds and neutralizes groups 1 and 2 influenza A viruses and protects mice from lethal challenge. Analysis of VH and VL germline back-mutants reveals binding to H3 and H1 but not H5, which supports the critical role of somatic hypermutation in broadening the bnAb response. Moreover, a single VLD94N mutation improves the affinity of 3I14 to H5 by nearly 10-fold. These data provide evidence that memory B cell evolution can expand the HA subtype specificity. Our results further suggest that establishing an optimized memory B cell pool should be an aim of ‘universal' influenza vaccine strategies.

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Knockout of the interleukin-18 (IL-18) gene predisposed mice to impaired clearance of neurovirulent influenza A virus-infected neurons from the brain. In wild-type mice, IL-18 molecule-producing microglia/macrophages emerged in virally attacked regions as early as day 3 after infection. Microglial transformation into macrophages culminated at day 7 to 9, with upregulated expression of Iba1, a novel calcium-binding protein that controls phagocytic functions of microglia/macrophages. In IL-18-/- mice, microglial transformation was interrupted with reduced Iba1 expression. Interferon-gamma (IFN-gamma)-immunopositive neurons appeared in and around virally invaded regions in wild-type mice, peaking in number at day 7, whereas such cells were barely detected in IL-18-/- mice. Stereotaxic microinjection of recombinant IFN-gamma triggered microglial transformation in IL-18-/- mice and upregulated Iba1 expression, leading to effective eradication of virally infected neurons. Collectively, these results suggest that IL-18 plays a key role in activating microglial functions directed against the influenza virus infection by inducing neuronal IFN-gamma in the brain parenchyma.

We have previously shown that infection with laboratory-passaged strains of influenza virus causes both specific degradation of the largest subunit of the RNA polymerase II complex (RNAP II) and inhibition of host cell transcription. When infection with natural human and avian isolates belonging to different antigenic subtypes was examined, we observed that all of these viruses efficiently induce the proteolytic process. To evaluate whether this process is a general feature of nonattenuated viruses, we studied the behavior of the influenza virus strains A/PR8/8/34 (PR8) and the cold-adapted A/Ann Arbor/6/60 (AA), which are currently used as the donor strains for vaccine seeds due to their attenuated phenotype. We have observed that upon infection with these strains, degradation of the RNAP II does not occur. Moreover, by runoff experiments we observe that PR8 has a reduced ability to inhibit cellular mRNA transcription. In addition, a hypervirulent PR8 (hvPR8) variant that multiplies much faster than standard PR8 (lvPR8) in infected cells and is more virulent in mice than the parental PR8 virus, efficiently induces RNAP II degradation. Studies with reassortant viruses containing defined genome segments of both hvPR8 and lvPR8 indicate that PA and PB2 subunits individually contribute to the ability of influenza virus to degrade the RNAP II. In addition, recently it has been reported that the inclusion of PA or PB2 from hvPR8 in lvPR8 recombinant viruses, highly increases their pathogenicity. Together, the data indicate that the capacity of the influenza virus to degrade RNAP II and inhibit the host cell transcription machinery is a feature of influenza A viruses that might contribute to their virulence.The genome of the influenza A viruses consists of eight single-stranded RNA segments of negative polarity, encoding a total of 11 proteins. Upon entry into susceptible cells, infecting ribonucleoprotein complexes (RNPs) are transported to the nucleus, where transcription and replication take place. Replication of viral RNAs (vRNAs) involves the synthesis of positivestrand replicative intermediates (cRNAs) that are exact copies of the virion RNAs (for a review, see reference 15). A functional link between viral and cellular transcription has been proposed since influenza virus mRNA transcription is initiated using short capped RNA oligonucleotides as primers that are obtained by endonucleolytic cleavage of de novo-synthesized cellular premRNAs (6, 56). This cap-snatching process is performed by the viral polymerase, a heterotrimeric complex comprised of the PB1, PB2, and PA subunits (15,30,40).The carboxy-terminal domain (CTD) of the largest subunit of the RNA polymerase II (RNAP II) complex plays an essential role in cellular transcription. This domain is differentially phosphorylated during the transcription cycle, dynamically permitting or impeding its association with a large number of factors (27). Two major forms of RNAP II can be found in cells when the CTD of its largest subunit is hyperphosphorylated or hyp...

Cell culture is now available as a method for the production of influenza vaccines in addition to eggs. In accordance with currently accepted practice, viruses recommended as candidates for vaccine manufacture are isolated and propagated exclusively in hens' eggs prior to distribution to manufacturers. Candidate vaccine viruses isolated in cell culture are not available to support vaccine manufacturing in mammalian cell bioreactors so egg-derived viruses have to be used. Recently influenza A (H3N2) viruses have been difficult to isolate directly in eggs. As mitigation against this difficulty, and the possibility of no suitable egg-isolated candidate viruses being available, it is proposed to consider using mammalian cell lines for primary isolation of influenza viruses as candidates for vaccine production in egg and cell platforms.To investigate this possibility, we tested the antigenic stability of viruses isolated and propagated in cell lines qualified for influenza vaccine manufacture and subsequently investigated antigen yields of such viruses in these cell lines at pilot-scale. Twenty influenza A and B-positive, original clinical specimens were inoculated in three MDCK cell lines. The antigenicity of recovered viruses was tested by hemagglutination inhibition using ferret sera against contemporary vaccine viruses and the amino acid sequences of the hemagglutinin and neuraminidase were determined. MDCK cell lines proved to be highly sensitive for virus isolation. Compared to the virus sequenced from the original specimen, viruses passaged three times in the MDCK lines showed up to 2 amino acid changes in the hemagglutinin. Antigenic stability was also established by hemagglutination inhibition titers comparable to those of the corresponding reference virus. Viruses isolated in any of the three MDCK lines grew reasonably well but variably in three MDCK cells and in VERO cells at pilot-scale. These results indicate that influenza viruses isolated in vaccine certified cell lines may well qualify for use in vaccine production.

Summary Recent advances in instrumentation and data analysis in field flow fractionation and multi-angle light scattering (FFF-MALS) have enabled greater use of this technique to characterize and quantitate viruses. In this study, the FFF-MALS technique was applied to the characterization and quantitation of type A influenza virus particles to assess its usefulness for vaccine preparation. The use of FFF-MALS for quantitation and measurement of control particles provided data accurate to within 5% of known values, reproducible with a coefficient of variation of 1.9 %. The methods, sensitivity and limit of detection were established by analyzing different volumes of purified virus, which produced a linear regression with fitting value R2 of 0.99. FFF-MALS was further applied to detect and quantitate influenza virus in the supernatant of infected MDCK cells and allantoic fluids of infected eggs. FFF fractograms of the virus present in these different fluids revealed similar distribution of monomeric and oligomeric virions. However, the monomer fraction of cell grown virus has greater size variety. Notably, β-propialactone (BPL) inactivation of influenza viruses did not influence any of the FFF-MALS measurements. Quantitation analysis by FFF-MALS was compared to infectivity assays and real-time RT-PCR (qRT-PCR) and the limitations of each assay were discussed.

The SAM-P1 strain of senescence-accelerated model mice shows an impaired T helper type 1 (Th1) immune response upon infection with influenza virus, which results in high susceptibility to the virus. Treatment of spleen cells from SAM-P1 mice with an immunostimulatory oligodeoxynucleotide containing a cytidine-guanosine motif (CpG ODN) in vitro increased the ratio of the titre of IFN-c to that of IL-4. Administration of CpG ODN to SAM-P1 mice generated satisfactory virus-specific cytotoxic T-lymphocyte responses and natural killer cell activation and the virus-specific immunoglobulin (Ig) isotype switched from IgG1 to IgG2a. Virus growth in the lungs of CpG ODN-treated SAM-P1 mice was cleared quickly and mice survived the lethal influenza virus infection. It could be inferred that a possible mechanism of CpG ODN for normalization of senescence-associated dysregulation of the Th1/Th2 balance involves the upregulated expression of CD154 and CD40 molecules on immune-competent cells. These results suggest that CpG ODN could contribute to the development of a protective strategy against infectious diseases, especially among immunocompromised elderly persons, by stimulating Th1 immune responses.

Summary To develop a more effective vaccination method against H5N1 virus, we investigated the immunogenicity and protective efficacy after skin vaccination using microneedles coated with influenza virus-like particles containing hemagglutinin derived from A/Vietnam/1203/04 H5N1 virus (H5 VLPs). A single microneedle vaccination of mice with H5 VLPs induced increased levels of antibodies and provided complete protection against lethal challenge without apparent disease symptoms. In contrast, intramuscular injection with the same vaccine dose showed low levels of antibodies and provided only partial protection accompanied by severe body weight loss. Post-challenge analysis suggested that improved protection was associated with lower lung viral titers and enhanced generation of recall antibody secreting cells by microneedle vaccination. Thus, this study provides evidence that skin delivery of H5 VLP vaccines using microneedles designed for self-administration induces improved protection compared to conventional intramuscular immunization.