Tumor regression caused by endotoxins and mycobacterial fractions.

A transplantable hepatocarcinoma of guinea pigs was used as an experimental model for immunotherapy of cancer. Earlier work showed that complete regression of 6- to 7-day-old tumors could be obtained in about 60% of cases by inoculation of the tumors with live BCG or certain fractions of BCG attached to minute oil droplets and suspended in Tween-saline. One of the most essential fractions was P3, a nonsensitizing, nonantigenic trehalose mycolate related to, but not identical with, cord factor. We now report that oil-droplet preparations containing P3 and bacterial endotoxin (ET) produced cure rates of up to 90% in the same system. In addition, regression was faster than with BCG, and older tumors could be treated successfully. The most effective ET's were from rough strains of salmonellae, known as Re mutants, which could not synthesize and attach the polysaccharide portion of endotoxin.