The poliovirus receptor CD155 and its family member CD112 (nectin-2) are the ligands for the activating cell-surface receptor DNAM-1 on CD8+ T cells and natural killer (NK) cells. Here, we demonstrate that, whereas the RMA tumor grew in syngeneic mice, DNAM-1 ligand-transduced RMA was rejected, in which CD8+ T cells and NK cells played an essential role. Importantly, CD8+ memory cytotoxic T cells to parental RMA were generated in these mice. We found that DNAM-1 was also expressed on CD8alpha+, rather than CD8alpha-, dendritic cells (DCs). Cross-linking DNAM-1 induced maturation of CD8alpha+ DCs. Antigen presentation by these stimulated DCs drove Th1 cells. Moreover, the rejection of DNAM-1 ligand-transduced RMA was canceled in CD4+ T-cell-depleted and major histocompatibility complex class II-deficient mice. Taken together, these results suggest that DNAM-1 ligands stimulate innate immunity by CD8alpha+ DCs as well as NK cells, which efficiently prime cell-mediated tumor-specific immunity.