Design and immunological evaluation of a multi-epitope vaccine candidate against Toxoplasma gondii incorporating MIC13, GRA1, and SAG1 antigens in BALB/c mice

Toxoplasmosis, caused by the apicomplexan parasite Toxoplasma gondii, is a globally significant yet neglected disease that can cause serious clinical consequences in humans and extensive losses in the livestock industry. However, no effective vaccine has been provided for this parasite, so this study was designed to evaluate the immunogenicity of a chimeric multi-epitope antigen as a potential toxoplasmosis vaccine candidate in a murine model. The multi-epitope vaccine candidate, designed with bioinformatics tools, MGS: a chimera of T. gondii MIC13, GRA1, and SAG1 antigens, was expressed in Escherichia coli BL21 and purified by immobilized metal affinity chromatography using a His Ni-NTA column. Mice were immunized with MGS protein alone or adjuvanted with Freund's adjuvant, calcium phosphate (CaPNs), or chitosan (CNs) nano-adjuvants on days 0, 21, and 35. Humoral and cellular immune responses to MGS (alone or adjuvanted with Freund's, CNs, or CaPNs) were compared to control groups (PBS, Freund's alone, CNs alone, CaPNs alone) through ELISA assays. The MGS protein, either alone or formulated with adjuvants, significantly increased specific antibody titers, particularly the IgG2a subtype and the cytokine IFN-γ. The highest levels of total antibodies, IFN-γ, and IL-4 were observed in the MGS-Freund group. It also enhanced the proliferation rate of splenic lymphocytes and improved the survival rate of BALB/c mice following challenge with the RH strain of Toxoplasma. The findings demonstrate that the MGS protein significantly enhances both Th1 and Th2 immune responses in experimental groups. These results support the efficacy of multi-epitope vaccines as a promising strategy for the development of effective vaccines against toxoplasmosis.