Fusion of foreign T-cell epitopes and addition of TLR agonists enhance immunity against Neospora caninum profilin in cattle

Abstract

We demonstrated recently that immunization with recombinant Neospora caninum profilin (rNcPRO) induces limited protection and a regulatory T-cell response in mice. The aim of this study was to evaluate the immune response elicited by rNcPRO in cattle and assess a strategy to enhance its immunogenicity, combining the addition of T-cell epitopes and immune modulators. We developed a chimeric recombinant profilin fused to functional T-cell epitopes present in the N-terminal sequence of vesicular stomatitis virus (VSV) glycoprotein G (rNcPRO/G). Groups of three cattle were immunized with two doses (2 weeks apart) of rNcPRO or rNcPRO/G formulated with alum hydroxide or a nanoparticulated soya-based adjuvant enriched with Toll-like receptor (TLR) 2 and TLR9 agonists, aimed to tackle the MyD88 pathway (AVECplus). rNcPRO induced only a primary immune response (IgM mediated), while antibodies in rNcPRO/G-vaccinated animals switched to IgG1 after the booster. The vaccine formulated with rNcPRO/G and AVECplus improved the production of systemic IFN-γ and induced long-term recall B-cell responses. Overall, our study provides data supporting the use of T-cell epitopes from VSV glycoprotein G and TLR agonists to enhance and modulate immunity to peptide antigens in bovines, particularly when using small proteins from parasites for which immune responses are usually feeble.