Antitumor Activity of Eosinophils Activated by IL-5 and Eotaxin against Hepatocellular Carcinoma

We examined the antitumor effects of eosinophils to explore the potential of eosinophils as effector cells in tumor cytotoxicity. We expressed eotaxin in hepatocellular carcinoma cells, MH134, and injected them into either normal or IL-5 TG mice intradermally and monitored cell growth. In normal mice, growth of MH134 cells containing the expression plasmid pCXN2–eotaxin was similar to that of vector-transfected MH134 cellsm for a period of 2 weeks, suggesting that expression of eotaxin does not change the growth rate of tumor cells. In IL-5 TG mice, however, the growth of eotaxin expressing MH134 cells was significantly suppressed. LPS induced eosinophils to produce TNF-α to kill MH134 cells in vitro. Intratumor injection of LPS is effective to kill MH134-pCXN2 and MH134-pCXN2–eotaxin only in normal mice. Administration of anti-CD4 or anti- CD8 antibodies suppressed growth of MH134-pCXN2–eotaxin cells compared with control antibodies, suggesting that T cells may interfere with immunity against MH134. Administration of anti-IL-5Ra and antiasialo GM1 antibodies enhanced growth of MH134-pCXN2–eotaxin cells, suggesting involvement of eosinophils and NK cells in suppression of tumor cell growth. Although we cannot exclude the possibility that NK cells participate in tumor cell killing in vivo, the presence of NK markers such as DX5, asialo GM1, Ly49, and CD94, and NKG2D on large numbers of eosinophils activated by eotaxin suggests that eosinophils function in such suppression of tumor cell growth. Furthermore, we showed that anti-NKG2D antibodies could significantly inhibit the LPS-induced cytotoxicity against MH134 by highly enriched fraction of eosinophils.