A self-assembling nanoparticle: Implications for the development of thermostable vaccine candidates

Effective controls on viral infections rely on the continuous development in vaccine technology. Nanoparticle (NP) antigens are highly immunogenic based on their unique physicochemical properties, making them molecular scaffolds to present soluble vaccine antigens. Here, viral targets (113-354 aas) were genetically fused to N terminal of mi3, a protein that self-assembles into nanoparticles composed of 60 subunits. With transmission electron microscopy, it was confirmed that target-mi3 fusion proteins which have insertions of up to 354 aas in N terminal form intact NPs. Moreover, viral targets are surface-displayed on NPs as indicated in dynamic light scattering. NPs exhibit perfect stability after long-term storage at room temperature. Moreover, SP-E2-mi3 NPs enhance antigen uptake and maturation in dendritic cells (DCs) via up-regulating marker molecules and immunostimulatory cytokines. Importantly, in a mouse model, SP-E2-mi3 nanovaccines against Classical swine fever virus (CSFV) remarkably improved CSFV-specific neutralizing antibodies (NAbs) and cellular immunity related cytokines (IFN-γ and IL-4) as compared to monomeric E2. Specially, improved NAb response with more than tenfold increase in NAb titer against both CSFV Shimen and HZ-08 strains indicated better cross-protection against different genotypes. Collectively, this structure-based, self-assembling NP provides an attractive platform to improve the potency of subunit vaccine for emerging pathogens.