Immunotherapy of cancer: tumor suppression and regression by cell walls of Mycobacterium phlei attached to oil droplets.

Components of mycobacterial cell wall(s) (CW) attached to oil droplets were evaluated for their ability 1) to inhibit the growth of line-10 tumor transplants in the skin of syngeneic guinea pigs when inoculated together with 10(6) tumor cells (suppression experiments) and 2) to regress established 7-day-old intradermal tumors and eradicate microscopic lymph node metastases upon injection into the tumors (regression experiments). CW and cell-wall skeleton (CWS) preparations from Mycobacterium phlei, a fast-growing saprophyte of group IV of the atypical mycobacteria, suppressed tumor growth in essentially all animals when 37.5-mug doses were administered; at a dose of 300 mug, they cured 50-60% of the animals in regression tests. The addition of 300 mug of a purified trehalose mycolate, isolated from M. tuberculosis strain Aoyama B, to 300 mug M. phlei CW or CWS preparations significantly increased their tumor regressive potency to provide cure rates to about 90%. Because M. phlei can be propagated more readily, it can be used advantageously in place of BCG to prepare stable, non-living immunologic adjuvants of defined composition and consistently high potency to meet the need for standards with minimal residual malignant disease.