Researchers working on induced pluripotent stem cell (iPS) have announced another breakthrough today. Earlier results showed that organs grown from retrovirally produced iPS cells in mice grew cancer very soon after. This most recent methodology "added cell-reprogramming genes to adenoviruses, a type of virus that infects cells without affecting their DNA." The adenoviruses, after producing cell-reprogramming proteins, turning the cells embryonic, departed. The goal was to produce genetically unmodified iPS cells.
Link to paper abstract here.