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It is generally accepted that priming of antitumor CD8+cytotoxic T lymphocytes (CTLs) needs help that can be provided by CD4+T cells. We show that interactions between dendritic cells (DCs) and natural killer (NK) cells can bypass the T helper arm in CTL induction. Bone marrow–derived DCs caused rejection of the A20 lymphoma and induced tumor-specific long-term memory, although they were not loaded with tumor-derived antigen. Experiments using CD40-knock-out mice and cell depletion showed that this effect did not require CD4+cells. Both primary rejection and long-term CTL memory were the result of NK cell activation by DCs. NK cytotoxicity, which was necessary for primary rejection, was dependent on expression of natural killer group 2 D (NKG2D) ligands on tumor cells. Blocking of these ligands using NKG2D tetramers abrogated tumor killing in vitro and in vivo. The long-term response was due to CTLs directed against antigen(s) expressed on A20 and in vitro–differentiated DCs. The mechanism leading to CD4+helper cell–independent CTL responses was elucidated as a cascade that was initiated by NK cell activation. This pathway was dependent on inter-feron-γ expression and involved priming endogenous DCs for interleukin-12 production. Our data suggest a novel pathway linking innate and adaptive immunity.