Efficacy and immunogenicity of different BCG doses in BALB/c and CB6F1 mice when challenged with H37Rv or Beijing HN878

In this study, 2 strains of mice (BALB/c and CB6F1) were vaccinated with a range of Bacille Calmette-Guerin (BCG) Danish doses from 3x105 to 30 CFU/mouse, followed by either immunogenicity evaluation or aerosol infection with Mycobacterium tuberculosis (a laboratory strain H37Rv or West-Beijing HN878 strain). The results indicated that both strains of mice when infected with HN878 exhibited significant protection in their lungs with BCG doses at 3x105 - 3000 CFU (BALB/c) and 3x105-300 CFU (CB6F1). Whereas, both strains of mice when infected with H37Rv, significant protection was seen in BCG doses at 3x105 - 300 CFU. Immunological evaluation revealed interesting results; i) both strains of mice demonstrated a significant increase in the frequencies of BCG-specific IFN{gamma}+ IL2+ TNF+ CD4 T cells in the BCG doses at 3x105 - 3000 CFU (BALB/c) and 3x105 - 300 CFU (CB6F1); ii) secretion of IL2 and IFN{gamma} were correlated with the bacterial burden in the lungs of HN878 infected CB6F1 mice. The study demonstrated a BCG dose at 3000 CFU (an equivalent single human dose in the mice by body weight index) is protective in both strains of mice and the use of a virulent clinical isolate in testing new tuberculosis vaccine/advancing research is recommended.