The present invention provides new lentiviral vectors that include an anti-repressor element (ARE) and, optionally, a scaffold attachment region (SAR). The lentiviral vectors provide expression of a heterologous nucleic acid in at least 50% of the cells of multiple cell types when used for lentiviral transgenesis. In certain embodiments of the invention the heterologous nucleic acid encodes an RNAi agent such as an shRNA. The invention further provides transgenic nonhuman animals generated using a lentiviral vector that includes an ARE and optional SAR. In addition, the invention provides a variety of methods for using the vectors including for achieving gene silencing in eukaryotic cells and transgenic animals, and methods of treating disease. The invention also provides animal models of human disease in which one or more genes is functionally silenced using a lentiviral vector of the invention.