Bacillus Toyonensis BCT-7112T Spores as Parenteral Adjuvant of BoHV-5 Vaccine in a Murine Model.

Bacterial spores of the genus Bacillus are being evaluated as adjuvant molecules capable of improving the immune response to vaccines. In this study, we investigate whether subcutaneously administered spores of B. toyonensis BCT-7112T could enhance a vaccine immune response in mice. Three groups of mice were subcutaneously vaccinated on day 0 and received a booster on day 21 of the experiment, with the following vaccine formulations: 40 µg of recombinant glycoprotein D (rgD) from bovine herpesvirus type 5 (BoHV-5) adsorbed in 10% aluminum hydroxide (alum) without B. toyonensis spores (group 1) and B. toyonensis (1 × 106 viable spores) + 40 µg of rgD adsorbed in 10% alum (group 2); and B. toyonensis (1 × 106 viable spores) without rgD (group 3). Group 2 showed significantly higher titers (P < 0.05) of total specific serum IgG, IgG2a, and neutralizing antibodies, when compared with the groups 1 and 3. A significantly higher (P < 0.05) transcription level of cytokines IL-4, IL-12, and IFN-γ was observed in splenocytes from mice that received the B. toyonensis spores in the vaccine formulation. In addition, stimulation of the macrophage-like cell line RAW264.7 with spores of B. toyonensis markedly enhanced the cell proliferation and mRNA transcription levels of IL-4, and IL-12 cytokines in these cells. Our findings indicated that the subcutaneous administration of B. toyonensis BCT-7112T spores enhanced the humoral and cellular immune response against BoHV-5 in mice.