Engineered embryonic endothelial progenitor cells as therapeutic Trojan horses.

While the hematogenic contribution of circulating endothelial cells to tumor angiogenesis is not entirely understood, one can exploit this phenomenon as a therapeutic strategy. In this issue of Cancer Cell, show that murine embryonic endothelial progenitor cells preferentially home to sites of lung metastases, evade immunological rejection, and can exert a bystander antitumor effect when modified to contain a suicide gene construct that activates a prodrug. Treatment with the prodrug led to improved survival in syngeneic and nonsyngeneic tumor-bearing mouse models. The conceptual advance put forward by this study might result in translational applications.