Ferritin as a Nanoparticle Scaffold for Plant-Produced Next-Generation Subunit Vaccines

Protein nanoparticles offer an innovative approach to next-generation subunit vaccine development by displaying antigenic sequences on the nanoparticle surface. Compared to traditional subunit vaccines, protein nanoparticle vaccines often show improved interaction with the immune system due to their particulate size and repetitive epitope display. Ferritin from Helicobacter pylori assembles into a spherical shape composed of 24 subunits that can display foreign peptides on its surface for use in vaccine development. Surface display can be achieved via genetic fusion of sequences encoding antigenic peptides to the N-terminus of the protein. Ferritin-based vaccine candidates have been increasingly explored through recombinant production in bacteria, insect cells, and mammalian cells; however, this protein had not been produced in plants before. We expressed ferritin from H. pylori in Nicotiana benthamiana and targeted it to the secretory pathway. We also modified ferritin to prevent glycosylation. We found this ferritin variant accumulates to over 0.2 mg/g fresh weight in plant leaves, and genetic fusion of a viral glyco-epitope to this protein significantly increases accumulation. We determined that the epitope is efficiently glycosylated and the protein fusion assembles into characteristic nanoparticles. We found that this fusion protein shows similar iron mineralization to the unmodified ferritin, and introducing a two amino acid substitution decreased this function. This study provides the groundwork for further exploration of plant-produced ferritin as a scaffold for vaccine development.