Evaluation of protective effect of DNA vaccines encoding the BAB1_0263 and BAB1_0278 open reading frames of Brucella abortus in BALB/c mice.

The immunogenicity of two DNA vaccines encoding open reading frames (ORFs) of genomic island 3 (GI-3), specific for Brucella abortus and Brucella melitensis, has been examined. Intramuscular injection of plasmid DNA carrying the BAB1_0263 and BAB1_0278 genes (pVF263 and pVF278, respectively) into BALB/c mice elicited both humoral and cellular immune responses. Mice injected with pVF263 or pVF278 had a dominant immunoglobulin G2a (IgG2a) response. In addition, both DNA vaccines elicited a T-cell-proliferative response, but only pVF263 induced significant levels of interferon gamma (INF-γ) upon restimulation with recombinant 263 protein. Neither DNA vaccine induced interleukin (IL)-10, nor IL-4, upon stimulation with an appropriate recombinant protein or crude Brucella protein, suggesting the induction of a typical T-helper 1 (Th1)-dominated immune response. Furthermore, the pVF278 DNA vaccines induced protection in BALB/c mice against challenge with the virulent strain B. abortus 2308. Taken together, these data suggest that DNA vaccination offers an improved delivery strategy for the BAB1_0278 antigen, and provide the first evidence of a protective effect of this antigen.