Lethal Influenza Virus Challenge Research Articles

IL-6 induces long-term protective immunity against a lethal challenge of influenza virus

The coadministration of cytokines can modulate immunity in DNA based viral vaccines. In order to determine the effects of various cytokines on long-term protection against the influenza virus, mice were intramuscularly coinoculated with plasmids that encoded either the granulocyte-macrophage colony-stimulating factor (GMCSF), interleukin-4 (IL-4), interleukin-12 (IL-12), or the interleukin-6 (IL-6) gene, in the presence of two plasmids that encoded the nucleoprotein (NP) and the hemagglutinin (HA) gene of the influenza A virus. The coadministration of IL-4, IL-6 and IL-12 transiently enhanced antibody responses against influenza virus in early time points (4 to 7 week post immunization) after post inoculation. The expression of GMCSF gene resulted in the sustained elevation of antibody responses for at least 20 weeks post inoculation. However, NP-specific CTL responses decreased in these animals. Mice that received either the IL-12 or the IL-6 gene had enhanced NP-specific CTL responses. Remarkably, the coadministration of the IL-6 gene completely protected mice from a lethal challenge with influenza virus. Conversely, mice that received the IL-4 gene appeared to be more susceptible to lethal challenge than mice that were inoculated with the NP and the HA genes alone. These results demonstrate that the use of cytokines as molecular adjuvants when coadministered in influenza DNA vaccination must be specific. Our data also demonstrates that the coadministration of IL-6 should be considered to enhance the efficacy of influenza DNA vaccines.

A recombinant vector derived from the host range-restricted and highly attenuated MVA strain of vaccinia virus stimulates protective immunity in mice to influenza virus

The immunogenicity of a recombinant virus derived from modified vaccinia virus Ankara (MVA), a host range-restricted, highly attenuated and safety-tested strain, was investigated. Plasmid transfer vectors that provide strong synthetic early/late promoters for the simultaneous expression of two genes as well as a transient or stable selectable marker and flanking sequences for homologous recombination with the MVA genome were constructed. A recombinant MVA containing influenza virus haemagglutinin and nucleoprotein genes was isolated in avian cells and shown to express both proteins efficiently upon infection of human or mouse cells in which abortive replication occurs. Mice, inoculated by various routes with recombinant MVA, produced antibody and cytotoxic T-lymphocyte responses to influenza virus proteins and were protected against a lethal influenza virus challenge as effectively as mice immunized with a recombinant derived from the replication-competent WR strain of vaccinia virus.

Use of DNA encoding influenza hemagglutinin as an avian influenza vaccine.

Recently, we demonstrated that direct inoculation of a hemagglutinin 7 (H7)-expressing DNA could vaccinate chickens against a lethal H7 influenza virus challenge. These experiments used a defective-retroviral-based vector to express H7 (p188) (Robinson et al., 1993). Here, we report protective immunizations using a non-retroviral-based vector for H7 expression (pCMV/H7). Unlike the previously used retroviral-based vector, this vector cannot be transmitted as an infectious agent (as a consequence of phenotypic mixing with exogenous or endogenous virus proteins). Vaccination was accomplished by inoculating young, immunocompetent chickens by each of three routes (intravenous, intraperitoneal, and intramuscular) with 100 micrograms of cesium chloride-purified pCMV/H7 DNA in saline. After two immunizations, birds were challenged via the nares with a lethal dose of a highly virulent chicken influenza virus of the H7 subtype. The results of five independent vaccine trials demonstrated protective immunizations in approximately 60% of the pCMV/H7 DNA-inoculated chickens. By contrast, only 3% of the chickens inoculated with control DNA survived the lethal challenge.

Recombinant secreted haemagglutinin protects mice against a lethal challenge of influenza virus

Balb/c mice were immunized with 2 × 2 μg of purified recombinant secreted haemagglutinin, derived from the A/Victoria/3/75 (H3N2) virus. In the first immunization, Ribi adjuvant was used, while for the booster injection a monophosphoryl lipid A/muramyl dipeptide combination was chosen. Mice immunized in this way were 90–100% protected against a challenge with 20 LD 50 of mouse-adapted, homologous virus (strain X47). Bromelain-solubilized haemagglutinin gave only 70% protection under comparable conditions.

Protection against a lethal influenza virus challenge by immunization with a haemagglutinin-expressing plasmid DNA

Direct DNA inoculations have been used to demonstrate that in vivo transfections can be used to elicit protective immune responses. The direct inoculation of an H7 haemagglutinin-expressing DNA protected chickens against lethal challenge with an H7N7 influenza virus. Three-week-old chickens were vaccinated by inoculating 100 μg of plasmid DNA by each of three routes (intravenous, intraperitoneal and subcutaneous). One month later, chickens were boosted with 100 μg of DNA by each of the three routes. At 1–2 weeks postboost, chickens were challenged via the nares with 100 lethal doses of an H7N7 virus. Low to undetectable levels of H7-specific antibodies were present postvaccination and boost. High titres of H7-specific antibodies appeared within 1 week of challenge. In a series of four experiments, 50% ( 28 56 ) of the DNA-vaccinated and <2% ( 1 67 ) of the control chickens survived the challenge. This exceptionally simple method of immunization holds high promise for the development of subunit vaccines.

Protection of chickens from lethal influenza infection by vaccinia-expressed hemagglutinin

To study the immune response of the chicken to specific influenza proteins, we have constructed a recombinant vaccinia virus containing the hemagglutinin gene of influenza A/Turkey/Ireland/1378/83 (H5N8). In mammalian cell culture the hemagglutinin expressed by this recombinant virus was full-length, cleaved into HA1 and HA2 in the absence of trypsin, and transported to the cell surface, confirming that other virus products are not required for cleavage activation. Chickens inoculated through the wing web with the live recombinant virus produced extremely low levels of hemagglutination-inhibiting or infectivity-neutralizing antibody. However, they were protected from lethal H5 influenza virus challenge. Protection extended to the antigenically distinct virulent H5 viruses, Chicken/Pennsylvania/1370/83 and Chicken/Scotland/59. Chemically bursectomized vaccinated chickens were not protected, whereas normal chickens with very low antibody levels (<10) obtained by passive transfer were protected in a dose-dependent fashion. This indicates that despite the low antibody titers induced by vaccination, protection was mediated by antibody.