Comparison of freeze-dried vaccines prepared from four different strains of BCG.

Cancer patients in many centers throughout the world are being treated with a variety of immunological procedures and one of the most widely used requires the administration of BCG vaccine. BCG vaccines made under the same conditions from four different strains of BCG were investigated as to their viable counts and residual virulence. The highest number of culturable particles (CP) was obtained from the vaccines prepared with the Japanese and Connaught strains, whereas the lowest number was obtained from the vaccines prepared from the French and Danish strains. The virulence of the vaccines in Syrian golden hamsters was independent of the number of CP present in each vaccine. The most virulent vaccines were the French and Danish vaccines, the least virulent was the Japanese vaccine and the Connaught vaccine was of intermediate virulence. Although the hamster can be used as a good model to determine the level of residual virulence of BCG, it should be said that, thus far, there is no evidence to show that a BCG vaccine with a high level of virulence for the hamster will necessarily be a better adjuvant or immunostimulant in the treatment of malignancies in man than a vaccine with low virulence.