Vesicular stomatitis virus vectored chimeric hemagglutinin constructs as broadly cross-reactive influenza vaccines

Seasonal influenza virus infections cause significant disease each year, and there is a constant threat of the emergence of reassortant influenza strains that are capable of causing a new pandemic. Available influenza vaccines are variably effective each season, are of limited scope at protecting against viruses that have undergone significant antigenic drift, and offer little in the way of protection against newly emergent pandemic trains. "Universal" influenza vaccine strategies that focus on the development of humoral immunity directed against the stalk domains of the viral hemagglutinin (HA) show promise for protecting against diverse influenza viruses. The following chapters describe such a strategy that utilizes vesicular stomatitis virus (VSV) as a vector for chimeric hemagglutinin (cHA) antigens. This vaccination strategy is effective at generating HA stalk-specific, broadly cross-reactive serum antibodies by both the intramuscular and intranasal routes of vaccination. The data presented show that prime-boost vaccination strategies provide protection against both lethal homologous and heterosubtypic influenza challenge, and that protection is significantly improved with intranasal vaccine administration. Additionally, the data indicate that vaccination with VSV-cHAs generates greater stalk-specific and cross-reactive serum antibodies than does vaccination with VSV vectored full-length HAs, confirming that the cHA-based vaccination strategies are superior at generating stalk-specific humoral immunity. Curiously, however, mice that were vaccinated with either VSV-cHAs or corresponding VSV-HAs, experienced similar protection against disease from a heterologous influenza challenge virus, despite the difference in serum antibody titers. This may indicate that other mechanisms are contributing to the protection conferred by vaccination.;In order to elucidate some of the immune mechanisms underlying the effectiveness of these VSV-cHA vaccines, we conducted experiments to deplete mice of CD4+ and/or CD8+ T-cells at different points in the vaccination regimen. We show that, in addition to potent HA-specific serum antibody production, there is also a significant contribution of both CD4+ and CD8+ T-cells to the protection afforded by VSV-cHA vaccines. We also show that the increase in serum antibody titer in response to boosting vaccination is highly dependent on CD4+ T-cells. These findings suggest that universal influenza vaccination strategies that utilize cHAs as immunogens establish protection against influenza disease through both humoral and cellular immune mechanisms.;The emergence of novel influenza viruses that cause devastating human disease is an ongoing threat and serves as an impetus for the continued development of novel approaches to influenza vaccines. In order to directly address vaccination against influenza strains with the potential for causing pandemic disease, we describe an additional vaccine candidate that utilizes a replication-defective vesicular stomatitis virus (VSV) vector backbone that lacks the native G surface glycoprotein gene (VSVDeltaG). The expression of the H5 HA of an H5N1 highly pathogenic avian influenza virus (HPAIV), A/Vietnam/1203/04 (VN1203), and the NA of the H1N1 influenza virus A/Puerto Rico/8/34 (PR8) in the VSVDeltaG vector restored the ability of the recombinant virus to replicate in cell culture, without the requirement for the addition of trypsin. We show that this recombinant virus vaccine candidate was nonpathogenic in mice when given by either the intramuscular or intranasal route of immunization and that the in vivo replication of VSVDeltaG-H5N1 is profoundly attenuated. This recombinant virus also provided protection against lethal H5N1 infection after a single dose. This novel approach to vaccination against HPAIVs may be widely applicable to other emerging strains of influenza virus, and could be incorporated into vaccination strategies that produce broadly cross-protective responses.;VSV-vectored influenza vaccines offer a novel means for protecting against widely diverged influenza viruses while limiting exposure to a single viral vector. The results described in the following chapters offer promising insights into the mechanisms by which protection against influenza is achieved, and contribute to the further development of universal influenza vaccines.