Assessment of the Immune Potential of Calcium Phosphate-Outer Membrane Protein-Nanoparticles (CaP-Omp-Nps) Adjuvanted Nano-Vaccine Against Salmonella Typhimurium in Poultry Birds

Background: Salmonella Typhimurium is a major pathogen causing non-typhoidal salmonellosis in humans. Poultry is a major reservoir of S. Typhimurium. Currently available vaccines against S. Typhimurium are not very effective. Therefore, the search for novel adjuvants to improve vaccine efficacy is a priority for developing effective and efficient vaccines. Method: In this study, next-generation adjuvants, such as calcium phosphate nanoparticles, are being evaluated. Our objective was to assess the potential of calcium phosphate nanoparticles, using outer membrane proteins of Salmonella Typhimurium as antigens, for immune-potential testing in poultry, with Montanide as a control. The toxicity of the prepared vaccine formulation was evaluated in rats. Results: CaP-Omp-Nps in the 30–45 nm size range showed a protein entrapment efficiency of 42.5% and a loading capacity of 50.3%. Both vaccinated groups, calcium phosphate outer membrane protein nanoparticles (CaP-Omp-Nps) and Montanide, induced an efficient humoral immune response, with mean titers of 3.48 + 0.0245 and 4.9 + 0.0142 on the 15th day, 3.5 + 0.0118 and 4.79 + 0.009 on the 30th day, and 4.48 + 0.427 and 5.31 + 0.154 on the 45th day post vaccination, respectively, indicating an improvement (CaP-Omp-Nps group) or stability (Montanide group) over the study period. Further, the CaP-Omp-Nps group revealed a better cell-mediated immune response than the Montanide-Omp group. The toxicity study in rats showed no significant differences in serum biomarkers and blood chemistry parameters, indicating that the nano-vaccine formulation is non-toxic and safe. Outer membrane proteins of Salmonella Typhimurium, when used with a few conventional adjuvants, could not produce a balanced Th1 and Th2 immune response against Salmonella Typhimurium. Conclusions: In this study, we developed a novel nano-vaccine formulation composed of outer membrane proteins of Salmonella Typhimurium and calcium phosphate nanoparticles. The vaccine formulation was found to be safe and could elicit the desired Th1 and Th2 immune responses, as evidenced by humoral, cell-mediated, and protective immunity produced by the nano vaccine in poultry. Therefore, the present findings suggest that the CaP-Omp-Nps vaccine may be an efficient, safe, and cost-effective vaccine against Salmonella Typhimurium.