Protein nanoparticles assemble in plants, display antigenic viral peptides, and produce an epitope-specific immune response.

Porcine reproductive and respiratory syndrome (PRRS) is one of the major diseases affecting the global swine industry. Current methods to control this viral disease are insufficient or pose safety concerns; therefore, there is a need for a safer and more effective vaccine against PRRS. In this study, we designed a chimeric nanoparticle vaccine through genetic fusion of an epitope composed of portions from two PRRS viral proteins, M and GP5, with lumazine synthase from Aquifex aeolicus. Transient expression in the leaves of Nicotiana benthamiana plants resulted in soluble levels around 0.18 mg·g-1 of plant fresh weight. This fusion protein assembles into nanoparticle structures surface-displaying the PRRS epitope and is efficiently glycosylated with oligomannose N-linked glycans. A mouse immunization trial was conducted using this protein as well as a previously described protein consisting of the same epitope displayed on a modified tobacco mosaic virus coat protein, and both vaccine candidates induced epitope-specific antibodies. This study demonstrates the feasibility of protein nanoparticle-based vaccines against PRRS produced in plants and lays the foundation for future studies to evaluate vaccine efficacy in pigs.