Immunization with Plant-Expressed Hemagglutinin Protects Chickens from Lethal Highly Pathogenic Avian Influenza Virus H5N1 Challenge Infection

Highly pathogenic avian influenza (HPAI) is a striking disease in susceptible poultry, which leads to severe economic losses. Inactivated vaccines are the most widely used vaccines in avian influenza virus (AIV) vaccination programs. However, these vaccines interfere with the serological detection of wild-type AIV infections in immunized populations. The use of vaccines that allow differentiation between infected and vaccinated animals (DIVA strategy) would stop current stamping-out policies. Therefore, novel vaccination strategies are needed to allow improved protection of animals and humans against HPAI virus (HPAIV) infection. The presented study analyzed for the first time the immunogenic capacity of plant-expressed full-length hemagglutinin (rHA0) of HPAIV H5N1 in several vaccine formulations within the highly relevant host species chicken. We were able to express plant-expressed rHA0 at high levels and could show that, when administered with potent adjuvants, it is highly immunogenic and can fully protect chicken against lethal challenge infection. Real-time reverse transcription (RT)-PCR and serological tests demonstrated only marginally increased virus replication in animals vaccinated with plant-derived rHA0 compared to animals immunized with an inactivated reference vaccine. In addition, the use of plant-expressed rHA0 also allowed an easy serological differentiation of vaccinated from AIV-infected animals based on antibodies against the influenza virus NP protein.