Provided herein are mesenchymal stem cells which have been modified by the introduction of polynucleotides encoding for a mammalian Cdk1 protein. These cells do not sense in culture and are non-tumorigenic thereby providing an ongoing source of cells as well as conditioned medium. The conditioned medium from these cells can be used for tissue repair. Also provided is a method of modifying mesenchymal stem cells which can be continuously propagated in culture and are non-tumorigenic.
