Development of a vectored equine herpesvirus type 1 (EHV-1) vaccine against pandemic influenza A virus (09/H1N1) (2013)

Swine influenza (SI) is a highly contagious viral infection in pigs and is characterized by mild to severe illness, which can lead to death under certain circumstances. The disease is caused by SIV, which belongs to the influenza A virus genus in the Orthomyxoviridae family. The newly emerged pandemic influenza A(H1N1) 2009 virus appears to be a result of reassortment of classical swine H1N1, human H3N2, avian and Eurasian swine influenza viruses. The newly emerging virus is genetically and antigentically different from circulating seasonal H1N1 influenza A virus. SI is not only an important respiratory pathogen in pigs but also a potential threat to human health. An effective vaccine may protect the pork industry from economic losses and curb the development of new virus variants that may threaten public health. Immunization with inactivated vaccines has long been the main strategy for the prevention of influenza infections. However, approaches other than conventional vaccines have also been found to induce protective immunity against infection, the most prominent being recombinant containing the envelope glycoproteins of the H1N1 virus. Therefore, this study aimed at the design, validation and development of a production process for a recombinant hemagglutinin (HA) influenza vaccine for the prevention of pandemic influenza A(H1N1)09 infection. The viral surface protein HA is the key antigen in the host response to influenza virus since neutralizing antibodies directed against HA can mitigate or prevent infection. The equine herpesvirus type 1 (EHV-1) was selected as modified live vector (MLV) for the synthesis of recombinant H1 of pandemic influenza A(H1N1). EHV-1 has recently been demonstrated to be a promising alternative viral vehicle for delivery of foreign antigens. In the second and third chapter of the thesis, we report on the construction of an equine herpesvirus 1 that expresses H1 of pandemic influenza A(H1N1)09 (rH_H1) and the evaluation of its efficacy as a vaccine in mouse model of influenza virus and in the natural host (pigs). Immunofluorescence and western blotting demonstrated expression of the recombinant protein and the in vitro growth properties of the modified live vector were found to be comparable to those of the parental virus. After immunization of mice, the rH_H1 vaccine induced an influenza virus-specific antibody response. Upon challenge infection, protection of vaccinated mice and natural host (pigs) could be demonstrated by reduction of clinical signs of the disease, reduction of virus replication as evidenced by decreased nasal virus shedding and faster virus clearance. Taken together, our results indicated that recombinant EHV-1 encoding H1 of pandemic influenza H1N1 may be a promising alternative for protection of pigs against infection with pandemic influenza A(H1N1)09 or other influenza viruses. Highlights points of the thesis ► Equine herpesvirus type 1 robustly expresses hemagglutinin of pandemic H1N1 (swine influenza virus). ► Mice and pigs are clinically protected against challenge infection after vaccination. ► Vaccine was utilized with no purification or adjuvant. ► Viral loads are reduced in vaccinated versus non-vaccinated animals. Key word Recombinant vaccine, EHV-1, Vector, Pandemic Influenza H1N1, Hemagglutinin, Mice, Pigs.