Fig. 2.
Delivery systems of protein- and VLP-based vaccines against viral infectious diseases. a The 3M2e-rHF fusion protein and 3M2e-rHF fusion protein-based nanoparticle. Reprinted with permission from [38]. b Double-layered protein nanoparticles for protein antigen delivery. Reprinted with permission from [39]. c Schematic illustration of the expression and in vivo assembly of P22-SpyTag and preparation of P22-HAhead. Reprinted with permission from [45]. d Schematic illustration of preparation of an avian coronavirus VLP. Reprinted with permission from [50]