Low efficacy of NcGRA7, NcSAG4, NcBSR4 and NcSRS9 formulated in poly-ɛ-caprolactone against Neospora caninum infection in mice

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The protective efficacy of vaccination with Neospora caninum recombinant antigens was evaluated in Balb/c pregnant and non-pregnant mouse models of neosporosis. A major immunodominant dense granule protein (NcGRA7) and three bradyzoite-specific surface antigens (NcSAG4, NcBSR4 and NcSRS9) were expressed in Escherichia coli and encapsulated within poly-ɛ-caprolactone (PCL) nanoparticles for the first time. Good efficiencies of entrapment (greater than 50%) were obtained for all encapsulated proteins. Moreover, antigenicity was unaffected after formulation. Afterwards, separate groups of mice were immunised with the nanoparticles and were then challenged with N. caninum tachyzoites. High IgG1 and IgG2a antibody levels of anti-N. caninum and specific antibodies directed against recombinant proteins were developed by all of the immunised groups. Mice previously inoculated with encapsulated rNcGRA7 produced significant levels of IFN-γ. However, in general, a low production of IFN-γ was detected. This may indicate a failure in the complete liberation of antigens after immunisation or an incorrect balance of the Th1/Th2 response to combat acute neosporosis during pregnancy. In fact, high morbidity and mortality rates were observed in dams. Moreover, vertical transmission was not prevented, and high neonatal mortality rates occurred similarly among the groups. Despite the global absence of efficacy, the study reveals some results of positive efficacy regarding dams and pups’ survival and parasite presence for NcSRS9 recombinant protein. Furthermore, vaccination with rNcGRA7 encapsulated alone or combined with rNcSAG4 resulted in a slight decrease of parasite presence in non-pregnant mice. These promising results are further discussed to suggest new approaches that may be more suitable to test vaccine formulations based on bradyzoite stage-specific proteins.