Nasal Nanoparticle Vaccine Induces a Cross-Strain T-Cell Immunity Against Toxoplasma gondii

Background/Objectives: Toxoplasma gondii is a globally distributed parasite responsible for significant morbidity in both humans and animals. VXN-Toxo, is an intranasal vaccine based on maltodextrin nanoparticles formulated with inactivated T. gondii parasites. A vaccination campaign conducted worldwide in zoological parks demonstrated high efficacy across multiple species and geographical regions. These findings suggest that VXN-Toxo may induce broad cross-reactive immunity against T. gondii strains circulating in various regions. Methods: To further characterize the immune mechanisms, we evaluated the cellular immune response induced by VXN-Toxo in C57BL/6 mice. Following vaccination, splenocytes were stimulated with antigens derived from multiple T. gondii strains, representing the major haplogroups (types I, II, III, and atypical strains). Results: ELISPOT analysis demonstrated that VXN-Toxo induced strong antigen-specific T cell responses, characterized by robust IFN-γ and IL-17 production upon stimulation with both homologous and heterologous antigens. Flow cytometry analysis further revealed the activation of both CD4⁺ and CD8⁺ T cells, with the notable presence of IFN-γ-producing CD8⁺ central and effector memory cells and CD4⁺ effector memory T cells. Conclusions: Altogether, these results indicate that VXN-Toxo induces a broad, T cell-mediated immune response with cross-reactive properties and highlight its potential as a promising vaccine candidate for both human and veterinary applications.