Development of a Promising Ferritin-Based Bioconjugate Nanovaccine Candidate against Brucellosis.

Brucellosis, a global zoonosis caused by Brucella species, currently lacks safe vaccines for human use, while existing veterinary live-attenuated vaccines pose infection risks. Although ferritin nanoparticle materials have shown significant advantages in delivery, there is not much research on loading complex polysaccharide antigens. Here, we engineered a bioconjugate nanovaccine (Fn-OPS) through a bacterial glycosylation-driven synthetic strategy, which couples Yersinia enterocolitica O:9 (YeO9) O-specific polysaccharide (OPS)─a structural analogue of Brucella antigens─to a self-assembled ferritin nanoparticle (Fn). This nanocarrier platform combines the symmetrical architecture and antigen-presenting advantages of Fn with the precision of enzymatic glycosylation, addressing the limitations of complex chemical synthesis methods. After confirming the presence of monodisperse nanoparticles with stability at room temperature and great in vivo safety, we performed murine immunization studies and demonstrated a robust activation of T follicular helper (Tfh) cells and germinal center B cells, leading to the production of high-titer IgG antibodies that are cross-reactive with Brucella lipopolysaccharide. This immune response provides strong protection against Brucella infection. This work establishes a ferritin-based nanoconjugate platform for targeted delivery of complex polysaccharide antigens. It advances a scalable, biosafe strategy for Brucella vaccines, expanding the toolkit for targeted antigen delivery in conjugate vaccine design and broadening applications in infectious disease prophylaxis.