Schematic representation of the reprogramming protocols adopted to generate human induced pluripotent stem cells (hiPSCs) from somatic cells. Human neonatal foreskin BJ fibroblasts were reprogrammed exploiting three different protocols employing retroviral vectors, Sendai virus vectors, and episomal vectors, respectively. Briefly, for retroviral vector transduction, retroviral vectors were produced by transfecting HEK293T cells with pMIG plasmids (pMIG-SOX2, pMIG-OCT4, pMIG-KLF4, pMXS-cMYC) and the packaging plasmids pGag-Pol and p-VSV-G and used to transduce BJ fibroblasts. For Sendai virus vector transduction, BJ fibroblasts were transduced with Sendai virus vectors expressing the reprogramming factors OCT4 (O), KLF4 (K), SOX2 (S), cMYC (M) at a multiplicity of infection (MOI) of 3 each. For episomal vector transfection, BJ fibroblasts were nucleofected with three episomal plasmids expressing O, K, S, l-Myc, (l-M), LIN28 and a short interfering RNA to knock down p53 pathway (shp53). At 5 or 7 days post transduction or transfection, cells were seeded into MEFs and grown in hES Medium until colonies started to emerge (from 13 to 21 days after transduction/transfection). O: OCT4; K: KLF4; S: SOX2; M: c-Myc; MEFs: mouse embryonic fibroblasts; hES medium: human embryonic stem cells medium.