The protective and allergenic potency of four BCG substrains in use in China determined in two animal models

Abstract

The objective of this study was to compare four BCG substrains from regional centres in China with BCG-Copenhagen 1331 (Danish strain) for protective and allergenic potencies. The comparisons were made in two different guinea pig models: one, a rational animal model involving aerosol challenge with 5–10 cfu Mycobacterium tuberculosis (strain H37Rv), and the other an animal model involving subcutaneous challenge with 250 cfu of H37Rv. For either model, the degree of protection was judged by quantitation of the number of H37Rv which could be recovered from the spleen. The results revealed: The allergenic potency of BCG-Shanghai and BCG-Beijing, substrains developed from the Danish strain, were comparable to that of the Danish vaccine. BCG-Lanzhou was significantly less allergenic and BCG-Chanchun, developed from BCG-Japan 172, was devoid of allergenic activity. Based on the number of H37Rv recovered from the spleen of guinea pigs killed 5 weeks after aerosol challenge, the protective effect of BCG-Shanghai and BCG-Beijing were comparable to that of the Danish vaccine. BCG-Lanzhou was of intermediate potency and BCG-Chanchun was devoid of protective activity. Based on the number of H37Rv recovered from the spleen of guinea pigs in the subcutaneous challenge group, the protective effects of BCG-Shanghai and BCG-Beijing were comparable to that of the Danish vaccine; BCG-Lanzhou was only slightly less potent, and BCG-Chanchun was devoid of protective activity. Good agreement was observed between the two animal models with respect to the protective potency of BCG vaccines.