An ESAT-6:CFP10 DNA vaccine administered in conjunction with Mycobacterium bovis BCG confers protection to cattle challenged with virulent M. bovis

The potency of genetic immunization observed in the mouse has demonstrated the utility of DNA vaccines to induce cell-mediated and humoral immune responses. However, it has been relatively difficult to generate comparable responses in non-rodent species. The use of molecular adjuvants may increase the magnitude of these suboptimal responses. In this study, we demonstrate that the co-administration of plasmid-encoded GM-CSF and CD80/CD86 with a novel ESAT-6:CFP10 DNA vaccine against bovine tuberculosis enhances antigen-specific cell-mediated immune responses. ESAT-6:CFP10 + GM-CSF + CD80/CD86 DNA vaccinated animals exhibited significant (p < 0.01) antigen-specific proliferative responses compared to other DNA vaccinates. Increased expression (p ≤ 0.05) of CD25 on PBMC from ESAT-6:CFP10 + GM-CSF + CD80/CD86 DNA vaccinates was associated with increased proliferation, as compared to control DNA vaccinates. Significant (p < 0.05) numbers of ESAT-6:CFP10-specific IFN-γ producing cells were evident from all ESAT-6:CFP10 DNA vaccinated animals compared to control DNA vaccinates. However, the greatest increase in IFN-γ producing cells was from animals vaccinated with ESAT-6:CFP10 + GM-CSF + CD80/CD86 DNA. In a low-dose aerosol challenge trial, calves vaccinated as neonates with Mycobacterium bovis BCG and ESAT-6:CFP10 + GM-CSF + CD80/CD86 DNA exhibited decreased lesion severity in the lung and lung-associated lymph nodes following viruluent M. bovis challenge compared to other vaccinated animals or non-vaccinated controls. These data suggest that a combined vaccine regimen of M. bovis BCG and a candidate ESAT-6:CFP10 DNA vaccine may offer greater protection against tuberculosis in cattle than vaccination with BCG alone.