ARTICLE ABSTRACTPurpose: Plasmacytoid dendritic cells (pDC) are antigen-presenting cells specialized in antiviral response. The measles virus vaccine is proposed as an antitumor agent to target and specifically kill tumor cells without infecting healthy cells.Experimental Design: Here, we investigated, in vitro, the effects of measles virus vaccine–infected tumor cells on the phenotype and functions of human pDC. We studied maturation and tumor antigen cross-presentation by pDC, exposed either to the virus alone, or to measles virus vaccine–infected or UV-irradiated tumor cells.Results: We found that only measles virus vaccine–infected cells induced pDC maturation with a strong production of IFN-α, whereas UV-irradiated tumor cells were unable to activate pDC. This IFN-α production was triggered by the interaction of measles virus vaccine single-stranded RNA (ssRNA) with TLR7. We observed that measles virus vaccine–infected tumor cells were phagocytosed by pDC. Interestingly, we showed cross-presentation of the tumor antigen NYESO-1 to a specific CD8+ T-cell clone when pDC were cocultured with measles virus vaccine–infected tumor cells, whereas pDC were unable to cross-present NYESO-1 after coculture with UV-irradiated tumor cells.Conclusions: Altogether, our results suggest that the use of measles virus vaccine in antitumor virotherapy induces immunogenic tumor cell death, allowing pDC to mature, produce high amounts of IFN-α, and cross-present tumor antigen, thus representing a mode of recruiting these antigen-presenting cells in the immune response. Clin Cancer Res; 19(5); 1147–58. ©2012 AACR.