Induced pluripotent stem (iPS) cells can be generated from differentiated somatic cells by over-expressing a set of specific transcription factors called reprogramming factors. Typically four reprogramming factors are chosen, Oct4, Klf4, Sox2 and c-Myc (OKSM), which are introduced into the target cells through genetic transduction using retroviral or lentiviral vectors.OKSM lentivirus (CMV, Puro) expresses all four reprogramming factors human Oct4, Sox2, Klf4 and c-Myc (OKSM) under the control of the CMV promoter with puromycin as a selection marker.