Prime-booster vaccination of cattle with an influenza viral vector Brucella abortus vaccine induces a long-term protective immune response against Brucella abortus infection

This study analyzed the duration of the antigen-specific humoral and T-cell immune responses and protectiveness of a recently-developed influenza viral vector Brucella abortus (Flu-BA) vaccine expressing Brucella proteins Omp16 and L7/L12 and containing the adjuvant Montadine Gel01 in cattle. At 1 month post-booster vaccination (BV), both humoral (up to 3 months post-BV; GMT IgG ELISA titer 214 ± 55 to 857 ± 136, with a prevalence of IgG2a over IgG1 isotype antibodies) and T-cell immune responses were observed in vaccinated heifers (n = 35) compared to control animals (n = 35, injected with adjuvant/PBS only). A pronounced T-cell immune response was induced and maintained for 12 months post-BV, as indicated by the lymphocyte stimulation index (2.7 ± 0.4 to 10.1 ± 0.9 cpm) and production of IFN-γ (13.7 ± 1.7 to 40.0 ± 3.0 ng/ml) at 3, 6, 9, and 12 months post-BV. Prime-boost vaccination provided significant protection against B. abortus infection at 3, 6, 9 and 12 months (study duration) post-BV (7 heifers per time point; alpha = 0.03-0.01 vs. control group). Between 57.1 and 71.4% of vaccinated animals showed no signs of B. abortus infection (or Brucella isolation) at 3, 6, 9 and 12 months post-BV; the severity of infection, as indicated by the index of infection (P = 0.0003 to <0.0001) and rates of Brucella colonization (P = 0.03 to <0.0001), was significantly lower for vaccinated diseased animals than appropriate control animals. Good protection from B. abortus infection was also observed among pregnant vaccinated heifers (alpha = 0.03), as well as their fetuses and calves (alpha = 0.01), for 12 months post-BV. Additionally, 71.4% of vaccinated heifers calved successfully whereas all pregnant control animals aborted (alpha = 0.01). Prime-boost vaccination of cattle with Flu-BA induces an antigen-specific humoral and pronounced T cell immune response and most importantly provides good protectiveness, even in pregnant heifers, for at least 12 months post-BV.