Eradication of microscopic hepatic metastases by active specific immunization.

Strain-2 guinea pigs, each with microscopic deposits of line 10 hepatocarcinoma in the liver, were treated by ID immunization with a mixture of irradiated tumor cells and an oil-in-water emulsion containing cell walls of Mycobacterium bovis strain Bacillus Calmette-Guérin (BCG CWE). Injection of line 10 hepatoma cells into the hepatic portal vein led to the development of tumor foci in the liver, metastasis in the hepatic lymph node, malignant ascites, and death. Active immunization using irradiated line 10 cells and BCG CWE was effective therapy when administered 1, 7, and 14 days after intraportal injection of line 10 cells. Effective immunization required both irradiated line 10 tumor cells and the BCG cell wall emulsion. Immunization with BCG CWE admixed with irradiated line 1 tumor cells, a hepatoma antigenically distinct from line 10, did not prevent outgrowth of line 10 deposits in the liver. Animals rendered free of disease could reject a challenge of line 10 tumor cells but not of line 1 tumor cells.