Further Observations on the Inhibition of Tumor Growth by Corynebacterium parvum With Cyclophosphamide. V. Comparison of the Effects of Tilorone Hydrochloride, Levamisole, Methanol-Soluble Fraction of Mycobacterium butyricum, BCG, and a Nonviable Aqueous Ether Extract of Brucella abortus Preparation in Treatment of Mice With Tumors2

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Abstract
In a murine system, when Corynebacterium parvum was used in combination with cyclophosphamide (CY), the inhibition of tumor growth (TG) was greater than when either agent was used alone. An effort was made to enhance the effectiveness of the combination by variation of the administration of both components and by substitution for or addition to CY of different chemotherapeutic agents. This report presents results of investigations in which attempts were made to improve the immunotherapy component of the combination by either substitution of other systemically administered nonspecific immunomodulators for C. parvum or by use of these immunomodulators in conjunction with C. parvum. Immunomodulators chosen for evaluation were those that had been used as antitumor agents in animal systems, had been clinically studied, and were presumed to have variable mechanisms of action. Despite diversity of dosages and schedules of administration, none of the immunomodulators used alone or substituted for C. parvum in combination with CY was as effective as, or more effective than, C. parvum. The addition of the agents to either C. parvum or to C. parvum combined with CY was also without benefit in improving the control of TG. The findings obtained with the use of each of the immunomodulators alone support our contention that immunotherapy by itself is in most circumstances likely to be an ineffectual form of therapy, and they suggest that little justification exists for the simultaneous use of more than one systemically administered nonspecific immunomodulator.