Modular Display of <i>Plasmodium yoelii</i> Circumsporozoite Surface Protein and Merozoite Surface Protein-1 on Norovirus-like Particles

Recently, virus-like particles have been regarded as a promising platform for displaying foreign peptides or proteins on their surface. In this study, a dual-protein-displaying platform based on the norovirus-like particle (NoV-LP) was developed using SpyTag (SpT)/SpyCatcher (SpC) protein bioconjugation. A short 14-amino-acid SpT peptide was added to the C-terminus of VP1, with a rigid "EAAAK" spacer in between. Antigenic proteins from a rodent malaria parasite, <i>Plasmodium yoelii</i>, specifically the circumsporozoite protein (PyCSP) and the 19 kDa C-terminal region of merozoite surface protein 1 (PyMSP1₁₉), were displayed on the surface of NoV-LPs in both monovalent and bivalent formats. The immunogenicity of these VLP-based vaccines was assessed, and they were found to induce antigen-specific IgG responses against both PyCSP and PyMSP1₁₉ in BALB/c mice in the absence of an adjuvant, at levels comparable to those induced by subunit antigenic proteins with an alum adjuvant added. Interestingly, the bivalent vaccine raised IgG responses at a similar titer to the monovalent vaccine. This finding hints that the NoV-LP possesses an inherent adjuvanted property in the presence of a foreign antigen. The measured anti-PyCSP and anti-PyMSP1₁₉ antibodies through ELISA indicate that surface display of PyCSP and PyMSP1₁₉ on SpTagged-NoV-LP has the potential for further development as a bivalent vaccine against two different life-cycle stages of malaria.