Coupling of the Hla-IsdB fusion antigen to mi3 nanoparticles enhances dendritic cell activation and protects against Staphylococcus aureus skin infection.

Staphylococcus aureus remains a leading cause of skin and soft-tissue infections, and antibiotic resistance undermines treatment. Vaccination is a key strategy that has the potential to address antibiotic resistance. However, subunit vaccines require multiple doses and have a slower response. In this study, we engineered a nanoparticle vaccine that multivalently displays a fusion antigen (HI) composed of the non-hemolytic HlaH35L variant and the N2 domain of IsdB on the self-assembling mi3 scaffold. We systematically characterized the physicochemical properties of HI-mi3 and evaluated its immunogenicity and protective efficacy. Moreover, its mechanisms underlying its protective effect were investigated in vitro and in vivo. Here, HI-mi3 assembled into monodisperse nanoparticles with high purity and thermal robustness. Two doses elicited rapid, high anti-HI IgG titers with a predominance of IgG1 over IgG2a/IgG2b. HI-mi3 significantly reduced the lesion area and bacterial burden. In addition, HI-mi3 enhanced antigen uptake, increased CD80/CD86 and MHC II expression on BMDCs, and elevated CD11c+CD80+/CD86+ cells in draining nodes. Thus, HI-mi3 is a stable, safe, and highly immunogenic nanoparticle vaccine that confers protection against SA skin infection after a short, two-dose regimen, supporting further development toward clinical translation.