Inhibition of murine sarcoma virus oncogenesis with living BCG

Intramuscular inoculation of murine sarcoma virus of Moloney (MSV‐M) leads to the development of tumors at the site of injection. The effect of BCG treatment on tumor induction by MSV‐M in BALB/c mice was studied. Mice injected with BCG 28 days before induction of tumors with MSV‐M alone had shorter latent periods for tumor development and longer survivals than mice not previously exposed to BCG. When BCG was mixed with the MSV‐M used for tumor induction there was a significant decrease in mortality, tumor incidence, and tumor size compared to those seen in mice inoculated with MSV‐M alone. Previous exposure of the mice to BCG before attempted induction of tumors with the mixture of BCG and MSV‐M completely inhibited tumor development. In addition, these mice were effectively immunized against tumor development when subsequently challenged with a lethal dose of MSV‐M. The mechanisms of BCG's impressive activity are discussed.