A new vaccine against tuberculosis shows greater protection in a mouse model with progressive pulmonary tuberculosis.

SETTING

The effectiveness of Bacillus Calmette-Guerin (BCG) vaccination in reducing tuberculosis (TB) prevalence rates is poor, resulting in urgent need for improved immunization programs, with new and more effective vaccines against TB.

OBJECTIVE

To develop a recombinant Tice BCG vaccine against TB that overexpresses the 38-kDa antigen of Mycobacterium tuberculosis in order to protect against infection by M. tuberculosis H37Rv and hyper-virulent M. tuberculosis Beijing genotype.

DESIGN

M. tuberculosis 38-kDa protein was cloned into a mycobacterial shuttle plasmid, which was used to overexpress the 38 kDa protein in BCG Tice to produce the recombinant vaccine, rBCG38 Tice (rBCG38).

RESULTS

Compared with BCG Tice, which conferred little protection against the Beijing strain of M. tuberculosis, vaccination with the rBCG38 increased survival of mice infected with either M. tuberculosis H37Rv or a Beijing strain of M. tuberculosis, isolate 9501000. Vaccination with either BCG Tice or rBCG38 resulted in enhanced protection against mycobacterial growth in lung tissue by reducing the number of colony-forming units (CFU). The vaccine induced a strong and highly significant Th1 response, shown by the high level of IL-2 and IFN-gamma cytokine producer cells found in the lungs of challenged mice, and an increase in the IgG2a:IgG1 ratio found in the pooled sera of the vaccinated mice.

CONCLUSIONS

This study showed that rBCG38 vaccine induced a strong Th1 response, demonstrated by the high levels of IL-2 and IFN-gamma producer cells and IgG2a. Protection was mediated for as long as 6 and 4 months after challenge with M. tuberculosis H37Rv and Beijing genotypes, respectively.