We describe a method of monitoring the state of a cell, the method comprising establishing, for a selected microRNA (miRNA) species secreted by the cell, a ratio of: (a) a precursor form of the miRNA species (pre-miRNA) to (b) a mature form of the miRNA species (mature miRNA) in which the pre- to mature miRNA ratio so established is indicative of the state of the cell. We also describe a method comprising the steps of: (a) providing a mesenchymal stem cell (MSC) and (b) introducing an oncogene into the mesenchymal stem cell to thereby transform it in which the transformed mesenchymal stem cell does not secrete a gene product of the oncogene into a medium in which it is grown.
