Approaches towards rapid protective response to influenza virus infection using vector based technologies

Abstract

In fact, influenza viruses still pose a major burden to human health and cannot be eradicated due to their large natural reservoir. Annual epidemics cause significant morbidity and mortality, imposing a substantial economic burden. Of greater concern are periodic influenza pandemics that can range from mild to devastating. Many public health officials feel that the next pandemic may be imminent, and efforts to minimize its impact are crucial. Egypt is ranked the worst affected country with AIV in the world. Vaccination of domestic poultry against AIV has been used on a large-scale in in Egypt since the end of 2006 to fight HPAI H5N1 epidemics. The decision to use mass vaccination against HPAI in Egypt was taken as an emergency measure based on positive impact of such control measures in Vietnam and the People’s Republic of China. However, about eight years on, the impact on disease control of AI vaccination in Egypt has been very limited and poultry outbreaks and human cases are reported regularly despite the continuous vaccination of poultry against HPAI. H9N2 virus has recently emerged in Egypt, a country where H5N1 viruses are enzootic. Co-circulation of H9N2 with H5N1 can increase the possibility of novel reassortant viruses and add a huge risk factor to the Egyptian poultry industry. Egyptian authority resorted to import commercial vaccines to control both circulating viruses. A major problem with using these vaccines was that most of commercial vaccines are genetically distinct from the Egyptian clade 2.2.1 H5N1 viruses. This was probably the reason for the disappointing results of protective efficacy for such vaccines. Additionally, shortage in the number of vaccine doses required to Egyptian market is a major problem concern. Results in this study were summarized as follows: In section A of this thesis, an overview of the current situation of using commercial inactivated AI H5 vaccines to protect poultry in Egypt from enzootic H5N1 viruses and problems related to their use were highlighted. Based on the genetic and antigenic analyses data, most vaccine seed strains are not related to that of contemporary H5N1 viruses circulating in Egypt. Vaccination with genetically and antigenically distinct commercial vaccines may have played a role in antigenic drift of Egyptian H5N1 viruses as well as inefficiency of used vaccines to control enzootic disease. Our results demonstrated that most commercially available vaccines do not provide cross-reactive antibodies with Egyptian isolates. ________________________________________________ Summary 182 In section B, we establish a standard platform to develop RG vaccine seed strains based on the genetic and antigenic analyses of detected H5N1 viruses during active surveillance in Egypt. The protective potential of the developed inactivated vaccines in birds showed full protection without any observed symptoms of the disease post infection with the wild HPAI H5N1 viruses. In section C, the following results have been obtained: 1. The immunological effects of several adjuvants in inactivated AI vaccine were evaluated. The results showed that the vaccine formulated with the seppic adjuvant showed significant difference compared with other groups. The seppic adjuvant could be the best as a new type of adjuvant applied in the production of avian influenza vaccines. It is recommended to administer two doses of avian influenza vaccines in order to achieve proper protection. 2. Caution is necessary to avoid over interpretation of mutations in influenza vaccine strains during sequential passaging of vaccine strains in ovo. 3. Mutation A134T in the HA of RG H5N1 improves viral replication capacity in embryonated chicken eggs without any effect in the antigenicity of mutated virus. 4. Updating of influenza vaccine strains to be antigenically matched with circulating viruses in Egypt was reinforced. In section D: Our finding demonstrated that the in ovo growth and the HA yield of the H5 candidate vaccine strain can be improved by incorporation of the NA of H9N2 virus that showed impressive replication rate of H9N2 virus in embryonated chicken eggs. The developed H5N2 virus offers a promising strategy to provide broader coverage of protection against dual H5N1 and H9N2 virus infection. This method is a novel strategy to improve the in ovo growth of this vaccine strain and may be useful for other vaccine candidates having yield problems and could increase vaccine productivity by reducing the time and the cost. In section E: we successfully developed influenza VLP based on Egyptian isolate as an alternative approach to control influenza virus infection and to overcome shortage in the vaccine production. The formation of influenza VLPs of the Egyptian H5N1 isolate released from the surface of Sf9 cells following expression of only two viral structural proteins (HA and M1) using baculovirus as a viral vector. In section F: a newly constructed multi-epitope engineered HA DNA vaccine was evaluated against multi- influenza subtypes (H5, H7& H9). Our results showed the cross reactivity of MHA DNA vaccine in vitro and in vivo. ________________________________________________ Summary 183 Results of this study highlighted the problem associated with one of the major obstacle to control influenza virus infection in Egypt. Hence, several aspects should be considered such as matching vaccine strains to currently circulating strains, assuring vaccine efficacy by evaluation using currently circulating strains as a challenge strain and regular updating of vaccine strains according to active surveillance programs. Searching for new alternative effective vaccines is a major concern in Egypt to overcome shortage in vaccine production. Obtaining results from this study, can direct us to many approaches to control several subtypes of influenza viruses and develop a universal multivalent influenza vaccine.