Induced pluripotent stem cells (iPS or iPSCs) are pluripotent stem cells directly generated by introducing combination of genes coding for reprogramming factors into adult cells. These reprogramming factors include Oct4, Sox2, c-Myc, KLF4, NANOG, and LIN28. Yu, et al, generated iPS from a human mesenchymal cell line using lentiviral vectors carrying Oct4, Sox2, NANOG, and LIN28 genes (Science 318:1917 (2007)). Using a similar approach, Takahashi et al, generated iPS from human primary fibroblast cells by introducing genes coding for Oct3, Sox2, KLF4, and c-Myc into these cells (Cell 131:861 (2007)). iPS generated by reprogramming are similar to human ES cells in morphology, the capacity for unlimited proliferation, surface-antigen expression, gene expression, the ability to differentiate into cell types representing the three germ layers in vitro, and the ability to form teratomas after injection into SCID mice.