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.

Avian colibacillosis, caused by Escherichia coli, remains a significant threat to poultry health and production, particularly in the context of rising antimicrobial resistance. Efficient and scalable vaccination strategies are needed to reduce economic losses and reliance on antibiotics. This study investigated the safety and immunogenicity of a novel single-dose in ovo vaccine candidate based on three inactivated E. coli strains formulated with cationic maltodextrin nanoparticles. The vaccine was evaluated in broilers under commercial hatchery conditions. In ovo administration was well tolerated and did not adversely affect hatchability, survival, growth performance, or feed efficiency. Vaccinated birds mounted a measurable serum immunoglobulin Y (IgY) response against E. coli from 14 days post-hatch, which persisted until slaughter age. Furthermore, when co-administered with routinely used live-attenuated viral vaccines, no interference with the immunogenicity of these vaccines was observed. These results demonstrate that the inactivated nanovaccine is safe, immunogenic, and compatible with an industrial-scale in ovo vaccination. The findings support its potential as a practical prophylactic approach to prevent avian colibacillosis in broiler production.