Improved immunogenicity and protective efficacy of a divalent DNA vaccine encoding Brucella L7/L12-truncated Omp31 fusion protein by a DNA priming and protein boosting regimen

•rL7/L12-TOmp31 DNA priming protein boosting immunizations induces a vigorous humoral response and Th1 cellular response more than a DNA vaccine or protein alone.•rL7/L12-TOmp31 DNA priming protein boosting immunizations induces the same protection level as RB51 and REV-1 vaccines against B. melitensis and B. abortus challenge.•rL7/L12-TOmp31 DNA priming protein boosting regimen could be a potential vaccine strategy against both B. melitensis and B. abortus.

Brucellosis is one of the most common zoonotic diseases caused by species of Brucella. At present, there is no commercially available vaccine for the human brucellosis. Brucella melitensis and Brucella abortus are the main causes of human brucellosis, worldwide. The outer membrane protein 31 (Omp31) and L7/L12 are immunodominant and protective antigens conserved among human Brucella pathogens. The purpose of the current study was to evaluate and compare the immunogenicity and protective efficacy of the L7/L12-TOmp31 construct administered as DNA/DNA and DNA/Pro vaccine regimens. Vaccination of BALB/c mice with the DNA/Pro regimen provided more protection levels against B. melitenisis and B. abortus challenge than did the DNA/DNA regimen. IgG1 and IgG2a titers were higher in the sera from DNA/Pro-immunized mice than in those from mice immunized with DNA alone. Moreover, splenocytes from DNA/Pro-immunized mice produced significantly higher levels of IFN-γ than did those from mice given DNA alone. The pcDNA-L7/L12-TOmp31 priming followed by rL7/L12-TOmp31 boosting led to improved protection against B. abortus or B. melitensis infection.