between the iPSC clones and the original lymphoblast line (performed by Genetica DNA Lab, Cincinnati, OH, USA). The episomal vector copy number per cell was determined by the quantitative PCR method. The Foxb15 gene served as a chromosome number control to determine the cell number input. The primer sets for Oct4, Klf4 and L-Myc were used to determine the copy number of three vectors. The standard curve for each quantitative PCR assay was performed using the plasmid DNA that contained the target sequence. The primer sequence and PCR condition were described in Okita et al.53
