Abstract: Genetically modified stem cells and the selection of cells differentiated therefrom are disclosed. Particularly, the herein disclosed invention relates to stem cells or cells differentiated therefrom containing a copy of a stably inheritable expression construct that is suitable for the expression of transgenes in stem cells, wherein said construct comprises at least a double-feature constitutive promoter being operable both in stem cells and in differentiated tissues, the expression level thereof being subject to a tissue or cell type specific regulation in differentiated cells, and, optionally, under the control of said promoter, a transgene, wherein said transgene is expressed in the stem cell. Furthermore methods are disclosed to produce such stem cells, as well as specific uses of said stem cells in assay methods and in human therapy and in veterinary practice.