The present invention concerns the delivery of certain reprogramming factor proteins into cells, such as differenti-atedsomatic cells, in order to induce the epi-genetic reprogramming of the cell so it becomes a pluripotent stem cell. The reprogramming factor protein(s) may be Sox2, Klf4, Oct3/4, c-Myc, Lin28, Nanog, or any protein with reprogramming (-enhancing) activity. These proteins may be linked recombinantly or chemically to a cell penetrating peptide that helps facilitate the introduction of these proteins into the target cell and may be preferably expressed in mammalian cells to maintain them in active forms. Accordingly, the present method of inducing pluripotent stem cell (iPS) formation avoids the use of viral or DNA-based expression vectors or the expression of reprogramming factor genes within target cells, which are known to be harmful to the host target cell and cause cancer.
