Experimental studies on modulation of antitumor immunity by administration of
levamisole (LMS) were performed using a metastasizing rat's mammary
tumor (MRMT-1) which was routinely inoculated subcutaneously at one back side of the Slc-SD rat. Experiment 1: The optimal ip dose of LMS for getting antitumor effects was found to be 2.5 mg/kg/day, administered every other day for 7 times. Administration at doses between 0.5 mg/kg and 2.5 mg/kg tended to cause
tumor suppression and the doses over 10 mg/kg tended to cause
tumor progression. Experiment 2: Optimal timing of starting LMS administration was found to be on day 2 of
tumor inoculation. Starting LMS on day 14 of inoculation caused a tendency of transient
tumor progression. Experiment 3: A slight
tumor suppression was observed when
splenectomy was done on day 14 of inoculation. However, when LMS was, given simultaneously, the
tumor suppressive effect of
splenectomy was cancelled. Experiment 4: According to immunological parameters with whole lymphocyte of peripheral blood, spleen cells and thymus cells, the mechanism of modulation of antitumor immunity by LMS administration was suggested to be an increase in immunocompetency of peripheral lymphocytes and augmentation of specific cytotoxicity. Immunocompetency of NK cells was found to be reduced. LMS was found to have some effects also on spleen and thymus cell functions.