Immunotherapy with tumor cells and BCG in the guinea pig, studied by immunological in vivo and in vitro experiments.

The effect of intradermal immunisation with viable line 1 hepatoma cells and BCG was studied in syngeneic strain 2 guinea pigs. Immunisation with 1.5 X 10(6) hepatoma cells admixed to 200 microgram BCG induced tumor regression in 7/8 animals. Higher or lower doses were less effective and sometimes led to enhanced tumor growth. It appeared that regression or progression of tumors is established as early as 3 weeks after tumor inoculation. Aspects of humoral and cell-mediated tumor immunity in immunised and/or tumor-bearing animals were studied in vitro by the use of mixed cell cultures and of cytotoxicity tests. Immunised tumor-bearing animals reacted more vigorously than those from non-immunised animals when the tumor was small. With increasing tumor volume the specific tumor immunity disappeared in both immunised and non-immunised animals. Sera obtained from immunised or regressor animals were cytotoxic and partially blocked the mixed cell interaction. Sera obtained from progressor animals were neither cytotoxic and nor did they block the mixed cell interaction. Cytotoxic activities resided within immunoglobulin fractions enriched in IgG1 or IgG2, whereas blocking activity was mainly associated with IgG2. The effector cell function was not inhibited by the immunoglobulin fractions tested. In the discussion it is suggested that the ratio of IgG1 and IgG2 antibodies elicited during immune treatment may critically influence the success or failure of immunotherapy.