During
cancer development, a number of regulatory cell subsets and immunosuppressive
cytokines subvert adaptive immune responses. Although it has been shown that
tumor-derived
interleukin (IL)-18 participates in the PD-1-dependent
tumor progression in NK cell-controlled
cancers, the mechanistic cues underlying this immunosuppression remain unknown. Here, we show that
IL-18 converts a subset of Kit(-) (CD11b(-)) into Kit(+) natural killer (NK) cells, which accumulate in all lymphoid organs of
tumor bearers and mediate immunoablative functions. Kit(+) NK cells overexpressed B7-H1/PD-L1, a
ligand for PD-1. The adoptive transfer of Kit(+) NK cells promoted
tumor growth in two pulmonary
metastases tumor models and significantly reduced the dendritic and NK cell pools residing in lymphoid organs in a B7-H1-dependent manner. Neutralization of
IL-18 by RNA interference in
tumors or systemically by IL-18-binding
protein dramatically reduced the accumulation of Kit(+)CD11b(-) NK cells in
tumor bearers. Together, our findings show that
IL-18 produced by
tumor cells elicits Kit(+)CD11b(-) NK cells endowed with B7-H1-dependent immunoablative functions in mice.