Expanded and Activated Natural Killer Cells for Immunotherapy of Hepatocellular Carcinoma

Viral infection of the liver is a major risk factor for hepatocellular carcinoma (HCC). Natural killer (NK) cells recognize virally infected and oncogenically transformed cells, suggesting a therapeutic role for NK-cell infusions in HCC. Using the K562-mb15-41BBL cell line as a stimulus, we obtained large numbers of activated NK cells from the peripheral blood of healthy donors. Expanded NK cells exerted remarkably high cytotoxicity against HCC cell lines, which was generally much higher than that of unstimulated or IL2-activated NK cells. In immunodeficient NOD/scid IL2RGnull mice engrafted with Hep3B, treatment with expanded NK cells markedly reduced tumor growth and improved overall survival. HCC cells exposed for 48 hours to 5 mmol/L of sorafenib, a kinase inhibitor currently used for HCC treatment, remained highly sensitive to expanded NK cells. HCC cell reductions of 39.2% to 53.8% caused by sorafenib in three cell lines further increased to 80.5% to 87.6% after 4 hours of culture with NK cells at a 1: 1 effector-to-target ratio. NK-cell cytotoxicity persisted even in the presence of sorafenib. We found that NKG2D, an NK-cell-activating receptor, was an important mediator of anti-HCC activity. We therefore enhanced its signaling capacity with a chimeric NKG2D-CD3 zeta-DAP10 receptor. This considerably increased the anti-HCC cytotoxicity of expanded NK cells in vitro and in immunodeficient mice. The NK expansion and activation method applied in this study has been adapted to clinical-grade conditions. Hence, these results warrant clinical testing of expanded NK-cell infusions in patients with HCC, possibly after genetic modification with NKG2D-CD3 zeta-DAP10.