Strong immune response and protection against Brucella abortus by Omp25 and BP26 mRNA vaccine candidates

Brucellosis, a globally prevalent zoonotic disease caused by Brucella species, remains without safe and effective human vaccines. This study focuses on the outer membrane proteins Omp25 and BP26 of Brucella as targets, employing a multidimensional strategy to develop novel mRNA vaccines and systematically evaluate their immunoprotective efficacy. First, bioinformatics tools were used to predict the antigenicity, immunogenicity, and physicochemical properties of Omp25 and BP26, while the C-ImmSim server simulated their potential to induce innate and adaptive immune responses. Building on these predictions, we designed and synthesized lipid nanoparticle-encapsulated nucleoside-modified mRNA vaccines (Omp25-Fc and BP26-Fc mRNA-LNPs) and compared their immunogenicity with traditional alum-adjuvanted protein vaccines (alum-BP26 and alum-Omp25). Animal experiments demonstrated that three immunizations with Omp25-Fc and BP26-Fc mRNA-LNPs induced significantly stronger humoral and cellular immune responses in mice compared to conventional vaccines. Evaluation of protective efficacy through challenge experiments revealed a marked reduction in splenic bacterial load in both mRNA vaccine groups relative to the controls. Mechanistic analysis further showed that Omp25-Fc and BP26-Fc mRNA vaccines activated mixed Th1/Th2 immune responses, effectively reducing bacterial burden and inflammatory damage in systemic infection models. Notably, the mRNA vaccines exhibited more durable immune memory and broader protective coverage than the alum-adjuvanted protein vaccines. Our findings demonstrate that Omp25- and BP26-based mRNA-LNP vaccines exhibit high immunogenicity and clinical translational potential, providing innovative strategies and experimental evidence for the development of brucellosis vaccines.