Levamisole: evidence for activity on human haemopoietic progenitor cells.

Levamisole, which has immunostimulant activity, is now being used to treat some forms of cancer. We report that the drug enhances granulocyte colony formation. The mechanism of action appears to be partly through modulation of molecules on cell membranes. The molecular content of colony-stimulating activity (CSA) released into leucocyte-conditioned medium by cells of leukaemic and some preleukaemic patients can be quantitatively altered by levamisole, both in vitro and in vivo, but the CSA produced is qualitatively similar to that released by normal cells. The demonstrated levamisole enhancement of colony formation, and altered CSA types detected in leucocyte-conditioned medium, makes this drug a promising candidate for treatment of selected leukaemic states and in preleukaemia.