NK4, a 4-kringle antagonist of hepatocyte growth factor (HGF), is a potent inhibitor of tumor angiogenesis and functions independently of its HGF-antagonistic activity. We have shown previously that in vivo genetic modification of tumors with an adenovirus vector that expresses NK4 (AdNK4) restrains tumor angiogenesis and slows the rate of tumor growth in vivo. In the present study, we investigated the hypothesis that this can be made more efficient by also administering bone marrow–generated dendritic cells (DCs) to the tumor. The data show that the growth of mouse subcutaneous tumors is significantly suppressed by direct administration of DCs into established tumors that had been pretreated with AdNK4 3 days previously. The synergistic antitumor effect produced by the combination therapy of AdNK4 with DCs correlated with the in vivo priming of tumor-specific cytotoxic T lymphocytes. Analysis of mice treated with fluorescence-labeled DCs suggested that DCs injected into the flank tumor could migrate to lymphoid organs in vivo for activation of immune-relevant processes. Knockout mice experiments demonstrated that the tumor regression produced by this combination therapy depends on both major histocompatibility complex (MHC) class I antigen presentation of DCs injected into the tumors and CD8⁺ T cells of the treated host. Finally, a mechanism for this synergism was suggested by the histological observation that tumor necrosis and apoptosis were induced by genetic engineering of the tumors to express NK4. These findings should be useful in designing novel strategies that use a combination of 2 monotherapies directed against the vascular and immune systems for cancer therapy.