Defined transcription factors can induce epigenetic reprogramming of adult mammalian cells into induced pluripotent stem cells. Although DNA factors are integrated during some reprogramming methods, it is unknown whether the genome remains unchanged at the single nucleotide level. Here we show that 22 human induced pluripotent stem (hiPS) cell lines reprogrammed using five different methods each contained an average of five protein-coding point mutations in the regions sampled (an estimated six protein-coding point mutations per exome). The majority of these mutations were non-synonymous, nonsense or splice variants, and were enriched in genes mutated or having causative effects in cancers. At least half of these reprogramming-associated mutations pre-existed in fibroblast progenitors at low frequencies, whereas the rest occurred during or after reprogramming. Thus, hiPS cells acquire genetic modifications in addition to epigenetic modifications. Extensive genetic screening should become a standard procedure to ensure hiPS cell safety before clinical use.
Bibliographical noteFunding Information:
Acknowledgements We thank J. M. Akey, G. M. Church, S. Ding, J. B. Li and J. Shendure for discussions and suggestions, S. Vassallo for assistance with DNA shearing, and G.L.Boultingand S.Ratansirintrawoot for assistance withhiPScellculture.This study is supported by NIH R01 HL094963 and a UCSD new faculty start-up fund (to K.Z.), a training grant from the California Institute for Regenerative Medicine (TG2-01154) and a CIRM grant (RC1-00116) (to L.S.B.G.). L.S.B.G. is an Investigator of the Howard Hughes Medical Institute. A. Gore is supported by the Focht-Powell Fellowship and a CIRM predoctoral fellowship. M.L.W. issupported byan institutional training grantfrom the National Institute of General Medical Sciences (T32 GM008666). Y.-H.L. is supported by the A*Star Institute of Medical Biology and the Singapore Stem Cell Consortium. Work in the laboratory of J.C.I.B. was supported by grants from MICINN, Sanofi-Aventis, the G. Harold and Leila Y. Mathers Foundation and the Cellex Foundation. G.Q.D. is an investigator of the Howard Hughes Medical Institute and supported by grants from the NIH.
ASJC Scopus subject areas