Development of vaccine approaches for pandemic influenza infections
Creators: name: Lin, Ivan
Publisher: name: RMIT University
Year: 2024

description: Highly pathogenic avian influenza virus is a continuous threat to the global poultry industry, and results in occasional spill-over infections into the human population. The rapid antigenic shift and drift of influenza virus often results in outbreaks of novel influenza virus, such as the highly pathogenic H5N1 avian flu. The virus has broad reservoirs from sea mammals to avian lives, and thus eradication of the virus has proven difficult. Therefore, the prevention of virus spread and circulation is considered the most effective method for disease control (Wang et al, 2006).<br><br>The first objective of this study was to evaluate the immunogenicity of a recombinant influenza haemagglutinin domain 1 (HA1) expressed in Pichia pastoria (P. Pastoris). The HA1 genes derived from influenza H1N1 (A/PR/8/34) was cloned in P.pastoris vector, and the HA1 was successfully expressed as insoluble secreted protein, and purified using immobilised metal ion chromatography (IMAC) under native conditions. The HA1 protein was administered into mice to evaluate its immunogenicity. The animal trial has revealed that, immunised mice exhibited robust Th2-type T-lymphocyte and anti-HA1 IgG responses, and developed a virus-neutralising antibody response for haemagglutinin inhibition (HI) at titer 7.4 log2. The result suggests that the Phicia0 expressed HA2 may be used an an immunogen for the prevention of influenza infection, and the technique developed in this study could serve as a cost and time effective solution for influenza virus vaccine.<br><br>The second objective of this study was the use Salmonella Typhimurium strain STM1 (an ΔaroA mutant developed at RMIT), as a delivery vector for an influenza antigen. Different strategies were used to present the influenza haemagglutinin (HA) antigen from various destinations to optimise immunogenicity. These include one to display the HA antigen on the outer membrane of Salmonella (utilizing lasmid pHES, encloding the N-terminal signal peptide and the essential C-terminal translocation unit of the ShdA auto-transported from S. Typhimurium strain LT-2) and another to secrete it inot the media (pMOhly1, encoding the necessary components of the E. Coli α-haemolysin secretion system).<br><br>The animal trial that resulted indicated the STMS1 expresing HA2 using pHES were unable to persist/colonise after administration, and neither humoral nor cell0mediated immune responses against influenza HA1 were elicited using the vaccine strain. On the other hand, TEM1 expressing HA2 using pMOhly1 was able to induce Th1-type immune response, indicated by the secretion of INF-γ from splenocytes after being stimulated by either Pichia-expressed rHA1 or inactivated influenza PR-8 virus. However, humoral immune responses were not elicited using this vaccine.<br><br>Even though the results acquired in these studies were less than satisfactory, there were significant responses to the influenza antigen which suggested that further investigation is required. For this to happen, it is possible to induce a more well-balanced immune response against influenza virus by combining both subunit rHA1 and STM1 vaccine strain into a prime-boost vaccine scheme. Such vaccine regimen could ensure the elicitation of both humoral and cell-mediated immunities against influenza infections.