Natural Killer T Cell Ligand α‐Galactosylceramide Inhibited Lymph Node Metastasis of Highly Metastatic Melanoma Cells

The role of natural killer T (NKT) cells in the prevention of multiple tumor metastasis was examined. The i.v. inoculation of a highly metastatic subline of B16‐BL6 (B16‐BL6‐HM) melanoma cells resulted in the formation of metastatic nodules in lymph nodes in addition to lung, intrapleural cavity, and ovary. However, treatment of the mice with the NKT cell ligand α‐galactosylceramide (α‐GalCer) three times from 1 day after B16‐BL6‐HM melanoma inoculation caused a significant inhibition of multiple metastasis. Lymph node metastasis of B16‐BL6‐HM was almost completely blocked by α‐GalCer treatment. This antimetastatic effect of α‐GalCer was abolished in NKT celldeficient mice. These results suggest that α‐GalCer‐activated NKT cells played a critical role in the prevention of lymph node metastasis of melanoma cells.