Although tumor microenvironments play a key role in successful tumor immunotherapy, effective manipulation of local immunity is difficult because of the lack of an appropriate target system. It is well known that bone marrow-derived endothelial progenitor cells (EPCs) are actively recruited during tumor angiogenesis. Using this feature, we attempted to establish a novel therapeutic modality that targets tumor vessels of multiple metastases using embryonic endothelial progenitor cells (eEPCs) transduced with an immune-activating gene. The eEPCs were retrovirally transduced with the mouse CC chemokine ligand 19 (CCL19) gene, a lymphocyte-migrating chemokine. The mouse ovarian cancer cell line OV2944-HM-1 (HM-1) was inoculated subcutaneously into B6C3F1 mice, along with CCL19-tranduced eEPCs (eEPC-CCL19), resulting in immunologic activity and tumor-inhibitory effects. In this model, eEPC-CCL19 showed tumor repression accompanied by increased tumor-infiltrating CD8+ lymphocytes compared with the control group. In contrast, no tumor repression was observed when the same experiment was done in immunodeficient (SCID) mice, suggesting a crucial role of T-cell function in this system. Next, we established a lung metastasis model by injecting HM-1 cells or B16 melanoma cells via the tail vein. Subsequent intravenous injection of eEPC-CCL19 leads to a decrease in the number of lung metastasis and prolonged survival. Antitumor effects were also observed in a peritoneal dissemination model using HM-1. These results suggest that systemic delivery of an immune-activating signal using EPCs can alter the tumor immune microenvironment and lead to a therapeutic effect, which may provide a novel strategy for targeting multiple metastases of various malignancies.