Cerium Nanoparticles Can Enhance Humoral and Cellular Immune Responses of Multi-epitope Vaccine Candidates

Recent studies have revealed nanoparticles can modulate immune responses and improve the immunogenicity of antigens. In the current study, immune responses against Mtb10.4-Rv2660c fusion protein along with cerium nanoparticles were assessed in a mouse model. The fusion protein was expressed in BL21(DE3) E. coli strain, confirmed by western blot, and purified using Ni–NTA chromatography with a molecular weight of ~ 20 kDa. Circular dichroism analysis indicated the fusion protein is mainly structured into alpha-helix conformation. Cerium nanoparticles were prepared by the precipitation method and characterized by field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction pattern, dynamic light scattering, and in vitro cytotoxicity. Cerium nanoparticles had a spherical shape with a zeta potential of − 42.8 mV and a z -average size of 395.5 d nm without exhibiting cytotoxicity on L929 cells. After subcutaneous immunization of female C57BL6/J mice, total IgG levels were significantly increased in all groups, except for cerium nanoparticles. This increase was significantly more for fusion protein plus cerium nanoparticles. Cerium nanoparticles did not change the total IgG level and IL-4 or IFN-γ secretions. Similarly, the mixtures showed a significant increase in IL-4 and IFN-γ levels compared to the protein groups. IL-4/IFN-γ calculations indicated cellular and humoral immune responses are equally stimulated in mice by the mixture. However, the fusion protein could only stimulate the humoral response in the mice. This can be attributed to the probable adjuvanticity role of nanoparticles. Such a preparation can be considered a new formulation for enhancing the immunogenicity of multi-epitope vaccines.