Endotoxin-stimulated immune response to modified lymphoma cells.

Bacterial endotoxin was administered with iodoacetamide-modified P1798 lymphoma cells to immunize syngenic BALB/cJ mice against this lymphoma to which they are naturally unresponsive. Three or four vaccinations with endotoxin (6.6 mug/injection) alone or the modified cells alone did not produce host resistance. A significant number (30 percent) of mice receiving both endotoxin and modified cells rejected a subsequent implant of viable tumor cells. Even those mice having progressive tumor growth exhibited prolonged survival. High doses of endotoxin given with the modified P1798 cells caused 70-75 percent of the mice to reject the tumor implants. When resistance developed, antibodies reacting with tumor cell membrane were demonstrable. These results indicate that B-lymphocyte stimulators can produce an effective immune response against lymphoma cells.