Mechanism of BCG induced regression of line 10 hepatocarcinoma in the guinea pig.

In line 10 hepatocellular carcinoma, cellular infiltrates show that there is an ongoing immune response against the tumor. This immune response is changed by intralesional administration of BCG leading to tumor regression and immunity. In the draining lymph node BCG induces a considerable increase in the number of T helper/inducer cells and the T suppressor/cytotoxic cells, as well as an increase in MHC class II antigen expression, but does not alter the ratio of the various leukocyte subpopulations. Moreover, in the tumor the ratio of the various leukocyte subpopulations also is not altered after BCG treatment and no distinct increase of MHC class II antigen expression is found. Thus it is reasonable to assume that the already existing local immune response is reactivated by the response to the mycobacteria, due to renewed communication between the tumor infiltrating leukocytes through secreted lymphokines.