The antitumor effects of levamisole in mice are mediated by NC-1.1+ cells

 Murine natural cytotoxicity, which is a major component of the innate immune response in cancer, is mediated by leukocytes that express the NC-1.1 receptor. Mice depleted of natural cytotoxicity by treatment with an anti-NC-l.1 mAb show enhanced growth of certain transplantable tumors, so agents that enhance natural cytotoxicity by NC-1.1⁺ cells have the potential to be effective anticancer therapeutic agents. We have examined the immunomodulatory effect of levamisole on natural cytotoxicity mediated by NC-1.1⁺ cells against the BALB/c WEHI-164 murine fibrosarcoma. Administration of levamisole to BALB/c mice significantly enhanced in vitro splenic natural cytotoxicity against ⁵¹Cr-labeled WEHI-164 tumor cells. The effect was most marked 48 h after levamisole treatment, at a dose of 10 mg/kg body weight. This enhancement of natural cytotoxicity by levamisole could be completely abrogated by pretreatment of mice with an anti-NC-1.1 mAb. Treatment of BALB/c mice with 10 mg/kg levamisole significantly reduced the growth of WEHI-164 and this effect was abrogated by pretreatment of mice with anti-NC-1.1, indicating that the antitumor effect of levamisole was mediated, at least in part, via NC-1.1⁺ cells. Received: 5 June 1997 / Accepted: 31 July 1997