Decreased expressions of CD1d molecule on liver dendritic cells in subcutaneous tumor bearing mice

Backgroud/Aims: alpha-Galactosylceramide (alpha-GalCer) has been attracting attention as a novel approach to treat metastatic liver cancer. However, the activation of liver innate immunity by alpha-GalCer should be examined because clinical trials of alpha-GalCer resulted in limited clinical responses. Methods: We examined the activation of liver innate immunity by alpha-GalCer in subcutaneous Colon26 tumor bearing-mice (C26s.c.TB-mice). Results:The expressions of CD1d molecule on liver dendritic cells (DCs) were significantly lower in C26s.c.TB-mice than those in tumor-unbearing normal mice. Although liver NK cells and NKT cells activated in normal mice after alpha-GalCer treatment, the activation of these cells were significantly inhibited in C26s.c.TB-mice. alpha-GalCer treatment resulted in significant antitumor effect against Colon26 metastatic liver tumor in normal mice, but not in C26s.c.TB-mice. The serum levels of TGF-beta, known to suppress the CD1d expressions on DCs, in C26s.c.TB-mice were significantly higher than those in normal mice. Surgical subcutaneous tumor mass reduction resulted in the reduction of serum TGF-beta, the recovery of CD1d expressions on liver DCs and the improvement of antitumor effect of alpha-GalCer against metastatic liver tumor. Conclusions: These results suggested that tumor burden reduces CD1d expressions on liver DCs, thus impeding alpha-GalCer-mediated NK cell activation and antitumor activity in the liver. (C) 2008 Published by Elsevier B.V. on behalf of the European Association for the Study of the Liver.