Development of a Plant-based Vaccine against Porcine reproductive and respiratory syndrome virus: Research Progress and Future Prospects

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of a few important pathogens that threaten the pig industry worldwide. The disease caused by PRRSV is a major source of economic loss for pork producers. PRRSV infects pigs through the mucosal surface of the respiratory tract. Therefore, the production of an oral vaccine to induce specific mucosal immune response may represent the most effective approach to preventing PRRSV infection. As the production of safe subunit vaccines in systems such as mammalian, bacterial or insect cells is either impossible or too expensive, plants become a promising bioreactor. In the past several years, we have investigated the possibility of application of plants for the development of a low cost, orally administered, plant-based vaccine against PRRSV. We used the cholera toxin B subunit (CTB) of Vibrio cholerae as an adjuvant and the PRRSV GP5 or its neutralizing epitope (GP5-NE) as a vaccine antigen. We found GP5 or the CTB-GP5 fusion protein was no detectable in transgenic tobacco plants, though large amounts of corresponding RNA were evident. The expression level of CTB-GP5-NE in transgenic plants was in the range of 0.003 to 0.087% of total soluble proteins. The plant-derived CTB-GP5-NE was biologically active. To increase the yield of the CTB-GP5NE recombinant protein in plant hosts, we developed a Soybean mosaic virus-based viral expression system. In this research review, we summarize our research progress and discuss challenges and future prospects of the development of a plant-based PRRSV vaccine. _____________________________________________________________________________________________________________