Modulation of the immune response by BCG: a review.

Bacillus Calmette-Guerin (BCG),4 an attenuated strain of Mycobacterium bovis, was developed as a vaccine against human tuberculosis by Calmette and Guerin at the Pasteur Institute in 1908. BCG has recently regained the spotlight in completely different roles, that of an immunological adjuvant and "'antitumor" agent. Investigations with this agent in the immunotherapy of cancer have met with variable success in different animal systems and with limited success in a small number of human trials. The majority of this work has been done on an empirical basis using tumor regression or animal survival as the end point. The effects of BCG on the immune response are multifaceted, and a clearer understanding of its mechanism of action may lead to a more rational basis for its use, not only in cancer immunotherapy, but in other immunologic applications.