Methanol extraction residue fraction of tubercle bacilli (MER) and other mycobacterial extracts as systemic immunity adjuvants in cancer immunotherapy.

Four mycobacterial extracts--two water soluble and two water insoluble--were tested for their immunostimulatory and antitumor activities: MER, the methanol extraction residue fraction of tubercle bacilli (insoluble); HIU I, an insoluble component of the membrane of whole cells of bacillus Calmette-Guérin (BCG); HIU II, a soluble component of BCG; AND Lederer's WSA, a soluble extract of Mycobacterium smegmatis. In a hemolytic plaque-forming cell assay, MER, HIU II and WSA showed immunostimulatory activity. However, only MER was active in the immunoprophylaxis of L1210 leukemia and of the solid Lewis tumor. The loss of antitumor activity does not seem to be related to water solubility, but appears rather to occur during purification.