The use of DNA vectors to elicit an immune response has produced a lot of interest. Unfortunately, one of the limiting factors has been the problem of gene expression. In order to obtain a strong expression of the vaccinating gene, several steps are necessary. The vector has to be delivered in such a way that it is not being degraded by the immune nor by the hepatic system; it has also to enter efficiently the targeted cells; and it must be expressed in the appropriate compartment of the cells at a high level. For these reasons, we have developed a gene expression vector that contains a T7 autogene and is being expressed in the cytoplasm of the cells (1 ,2 ). We will describe this system and two possible applications: infectious disease vaccination and tumor ablation. The latter application may be combined with DNA vaccination against cancer cells.