Eradication by immunization with mycobacterial vaccines and tumor cells of microscopic metastases remaining after surgery

Guinea pigs, each with a growing tumor from hepatoma cells implanted in the skin, were treated either by surgical excision alone of the dermal tumor or by surgery followed by administration of emulsified Bacillus Calmette-Guérin (BCG) cell walls alone or mixed with hepatoma cells. Animals treated by surgery alone developed malignant disease characterized by progressive lethal growth of lymph node metastasis. Injections of cell walls intradermally between the site of excision and the draining lymph node (regional injection) prevented the development of palpable metastasis in some animals; cell walls given intradermally on the side contralateral to the surgical site (remote injection) cured no animals. Similar treatments with preparations containing both cell walls and hepatoma cells prevented the development of malignant disease in a significant number of animals whether the injections were regional or remote. Treatment with mixtures consisting of living BCG and tumor cells was not as effective as treatment with cell walls mixed with tumor cells. A mixture consisting of modified BCG cell walls known as skeletons, trehalose dimycolate also known as cord factor or P3, and endotoxin was an effective substitute for BCG cell walls. There was no particular advantage in the use of the mixture containing BCG cell wall skeletons, trehalose dimycolate, and endotoxin instead of BCG cell walls. Neither preparation produced any gross systemic toxicity, and there was no statistical difference in their therapeutic efficacy. Undegraded cell wall emulsions were easier and less costly to prepare than was the three-component mixture. Animals treated by surgery followed by administration of BCG cell walls together with cells from another syngeneic hepatoma, immunologically distinct from the dermally implanted tumor, failed to eradicate microscopic lymph node metastases.