Immunopotentiation and tumor inhibition with levamisole

The immunopotentiating drug, levamisole, was found to augment human lymphocyte responses to vegetable mitogens in vitro. However, the effect was dose-dependent and at high concentrations suppression rather than augmentation of the immune response was observed. In view of the potential widespread use of the drug in the treatment of human cancer, a study was undertaken in rats bearing breast cancer to determine whether a similar dose-response effect would be observed in terms of tumor growth. Tumor inhibition was found to be dose-dependent, and at high doses tumor inhibition did not occur while at lower doses the growth of the cancer was inhibited. The rate of tumor growth correlated well with the responses of splenic lymphocytes to vegetable mitogens. In a later study, it was not possible to show that levamisole had any effect in boosting immune responses of patients undergoing surgery. It is concluded that levamisole is capable of increasing immune responses in man in vitro, and that the drug is able to inhibit the growth of breast cancer in the rat. However, these effects are dose-dependent, and clinical trials of the use of levamisole in patients with cancer should include careful immune monitoring to be sure that augmentation rather than suppression of the immune response is being achieved.