Genetically modified dendritic cells ( DC) constitute a promising approach in cancer immunotherapy. Viral gene delivery systems have been shown to be very efficient strategies, but safety concerns for their clinical use in immunotherapy remain an important issue. Recently, the technique of mRNA electroporation was described as a very efficient tool for the genetic modification of human monocyte-derived DC. Here, we show that transgene expression can be modulated by varying the amount of mRNA used for electroporation. We document that CD40 ligation leads to a significant production of IL-12 by the electroporated DC, although the level of IL-12 production is somewhat lower than for non- or mock-electroporated DC. Furthermore, we show that the electroporated DC can be frozen and thawed without loss of viability or function and that Influenza virus Matrix Protein 1 mRNA electroporated DC are capable of inducing a memory cytotoxic T lymphocyte response and are more potent in doing so than mRNA-pulsed DC. Similar results were obtained with MelanA/MART-1 mRNA electroporated DC. These results clearly indicate that mRNA-electroporated DC represent powerful candidates for use as tumor vaccines and could constitute an improvement compared with vaccines using peptide-pulsed DC.