Abstract
Pluripotent stem cells are able to self-renew indefinitely and differentiate into all types of cells in the body. They can thus be an inexhaustible source for future cell transplantation therapy to treat degenerative diseases which currently have no cure. However, non-autologous cells will cause immune rejection. Induced pluripotent stem cell (iPSC) technology can convert somatic cells to the pluripotent state, and therefore offers a solution to this problem. Since the first generation of iPSCs, there has been an explosion of relevant research, from which we have learned much about the genetic networks and epigenetic landscape of pluripotency, as well as how to manipulate genes, epigenetics, and microRNAs to obtain iPSCs. In this review, we focus on the mechanism of cellular reprogramming and current methods to induce pluripotency. We also highlight new problems emerging from iPSCs. Better understanding of the fundamental mechanisms underlying pluripotenty and refining the methodology of iPSC generation will have a significant impact on future development of regenerative medicine.
Keywords: reprogramming, induced pluripotent stem cells, pluripotency
References
- Anokye-Danso F., Trivedi C.M., Juhr D., Gupta M., Cui Z., Tian Y., Zhang Y., Yang W., Gruber P.J., Epstein J.A., et al. Highly efficient miRNA-mediated reprogramming of mouse and human somatic cells to pluripotency. Cell Stem Cell. 2011;8:376–388. doi: 10.1016/j.stem.2011.03.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Banito A., Rashid S.T., Acosta J.C., Li S., Pereira C.F., Geti I., Pinho S., Silva J.C., Azuara V., Walsh M., et al. Senescence impairs successful reprogramming to pluripotent stem cells. Genes Dev. 2009;23:2134–2139. doi: 10.1101/gad.1811609. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bar-Nur O., Russ H.A., Efrat S., Benvenisty N. Epigenetic memory and preferential lineage-specific differentiation in induced pluripotent stem cells derived from human pancreatic islet Beta cells. Cell Stem Cell. 2011;9:17–23. doi: 10.1016/j.stem.2011.06.007. [DOI] [PubMed] [Google Scholar]
- Bernstein B.E., Mikkelsen T.S., Xie X., Kamal M., Huebert D.J., Cuff J., Fry B., Meissner A., Wernig M., Plath K., et al. A bivalent chromatin structure marks key developmental genes in embryonic stem cells. Cell. 2006;125:315–326. doi: 10.1016/j.cell.2006.02.041. [DOI] [PubMed] [Google Scholar]
- Card D.A., Hebbar P.B., Li L., Trotter K.W., Komatsu Y., Mishina Y., Archer T.K. Oct4/Sox2-regulated miR-302 targets cyclin D1 in human embryonic stem cells. Mol Cell Biol. 2008;28:6426–6438. doi: 10.1128/MCB.00359-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chambers I., Colby D., Robertson M., Nichols J., Lee S., Tweedie S., Smith A. Functional expression cloning of Nanog, a pluripotency sustaining factor in embryonic stem cells. Cell. 2003;113:643–655. doi: 10.1016/S0092-8674(03)00392-1. [DOI] [PubMed] [Google Scholar]
- Chambers I., Silva J., Colby D., Nichols J., Nijmeijer B., Robertson M., Vrana J., Jones K., Grotewold L., Smith A. Nanog safeguards pluripotency and mediates germline development. Nature. 2007;450:1230–1234. doi: 10.1038/nature06403. [DOI] [PubMed] [Google Scholar]
- Chen Z.Y., He C.Y., Ehrhardt A., Kay M.A. Minicircle DNA vectors devoid of bacterial DNA result in persistent and highlevel transgene expression in vivo. Mol Ther. 2003;8:495–500. doi: 10.1016/S1525-0016(03)00168-0. [DOI] [PubMed] [Google Scholar]
- Chen Z.Y., He C.Y., Kay M.A. Improved production and purification of minicircle DNA vector free of plasmid bacterial sequences and capable of persistent transgene expression in vivo. Hum Gene Ther. 2005;16:126–131. doi: 10.1089/hum.2005.16.126. [DOI] [PubMed] [Google Scholar]
- Cowan C.A., Atienza J., Melton D.A., Eggan K. Nuclear reprogramming of somatic cells after fusion with human embryonic stem cells. Science. 2005;309:1369–1373. doi: 10.1126/science.1116447. [DOI] [PubMed] [Google Scholar]
- Egli D., Rosains J., Birkhoff G., Eggan K. Developmental reprogramming after chromosome transfer into mitotic mouse zygotes. Nature. 2007;447:679–685. doi: 10.1038/nature05879. [DOI] [PubMed] [Google Scholar]
- Eminli S., Foudi A., Stadtfeld M., Maherali N., Ahfeldt T., Mostoslavsky G., Hock H., Hochedlinger K. Differentiation stage determines potential of hematopoietic cells for reprogramming into induced pluripotent stem cells. Nat Genet. 2009;41:968–976. doi: 10.1038/ng.428. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Esteban M.A., Wang T., Qin B., Yang J., Qin D., Cai J., Li W., Weng Z., Chen J., Ni S., et al. Vitamin C enhances the generation of mouse and human induced pluripotent stem cells. Cell Stem Cell. 2010;6:71–79. doi: 10.1016/j.stem.2009.12.001. [DOI] [PubMed] [Google Scholar]
- Gore A., Li Z., Fung H.L., Young J.E., Agarwal S., Antosiewicz-Bourget J., Canto I., Giorgetti A., Israel M.A., Kiskinis E., et al. Somatic coding mutations in human induced pluripotent stem cells. Nature. 2011;471:63–67. doi: 10.1038/nature09805. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Guo G., Yang J., Nichols J., Hall J.S., Eyres I., Mansfield W., Smith A. Klf4 reverts developmentally programmed restriction of ground state pluripotency. Development. 2009;136:1063–1069. doi: 10.1242/dev.030957. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hanna J., Cheng A.W., Saha K., Kim J., Lengner C.J., Soldner F., Cassady J.P., Muffat J., Carey B.W., Jaenisch R. Human embryonic stem cells with biological and epigenetic characteristics similar to those of mouse ESCs. Proc Natl Acad Sci U S A. 2010;107:9222–9227. doi: 10.1073/pnas.1004584107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hanna J., Saha K., Pando B., van Zon J., Lengner C.J., Creyghton M.P., van Oudenaarden A., Jaenisch R. Direct cell reprogramming is a stochastic process amenable to acceleration. Nature. 2009;462:595–601. doi: 10.1038/nature08592. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hanna J.H., Saha K., Jaenisch R. Pluripotency and cellular reprogramming: facts, hypotheses, unresolved issues. Cell. 2010;143:508–525. doi: 10.1016/j.cell.2010.10.008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Heng J.C., Feng B., Han J., Jiang J., Kraus P., Ng J.H., Orlov Y.L., Huss M., Yang L., Lufkin T., et al. The nuclear receptor Nr5a2 can replace Oct4 in the reprogramming of murine somatic cells to pluripotent cells. Cell Stem Cell. 2010;6:167–174. doi: 10.1016/j.stem.2009.12.009. [DOI] [PubMed] [Google Scholar]
- Heo I., Joo C., Cho J., Ha M., Han J., Kim V.N. Lin28 mediates the terminal uridylation of let-7 precursor MicroRNA. Mol Cell. 2008;32:276–284. doi: 10.1016/j.molcel.2008.09.014. [DOI] [PubMed] [Google Scholar]
- Hong H., Takahashi K., Ichisaka T., Aoi T., Kanagawa O., Nakagawa M., Okita K., Yamanaka S. Suppression of induced pluripotent stem cell generation by the p53-p21 pathway. Nature. 2009;460:1132–1135. doi: 10.1038/nature08235. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Huangfu D., Maehr R., Guo W., Eijkelenboom A., Snitow M., Chen A.E., Melton D.A. Induction of pluripotent stem cells by defined factors is greatly improved by small-molecule compounds. Nat Biotechnol. 2008;26:795–797. doi: 10.1038/nbt1418. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Huangfu D., Osafune K., Maehr R., Guo W., Eijkelenboom A., Chen S., Muhlestein W., Melton D.A. Induction of pluripotent stem cells from primary human fibroblasts with only Oct4 and Sox2. Nat Biotechnol. 2008;26:1269–1275. doi: 10.1038/nbt.1502. [DOI] [PubMed] [Google Scholar]
- Hussein S.M., Batada N.N., Vuoristo S., Ching R.W., Autio R., Närvä E., Ng S., Sourour M., Hämäläinen R., Olsson C., et al. Copy number variation and selection during reprogramming to pluripotency. Nature. 2011;471:58–62. doi: 10.1038/nature09871. [DOI] [PubMed] [Google Scholar]
- Ichida J.K., Blanchard J., Lam K., Son E.Y., Chung J.E., Egli D., Loh K.M., Carter A.C., Di Giorgio F.P., Koszka K., et al. A small-molecule inhibitor of tgf-Beta signaling replaces sox2 in reprogramming by inducing nanog. Cell Stem Cell. 2009;5:491–503. doi: 10.1016/j.stem.2009.09.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jia F., Wilson K.D., Sun N., Gupta D.M., Huang M., Li Z., Panetta N.J., Chen Z.Y., Robbins R.C., Kay M.A., et al. A nonviral minicircle vector for deriving human iPS cells. Nat Methods. 2010;7:197–199. doi: 10.1038/nmeth.1426. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Judson R.L., Babiarz J.E., Venere M., Blelloch R. Embryonic stem cell-specific microRNAs promote induced pluripotency. Nat Biotechnol. 2009;27:459–461. doi: 10.1038/nbt.1535. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kaji K., Norrby K., Paca A., Mileikovsky M., Mohseni P., Woltjen K. Virus-free induction of pluripotency and subsequent excision of reprogramming factors. Nature. 2009;458:771–775. doi: 10.1038/nature07864. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kane N.M., Nowrouzi A., Mukherjee S., Blundell M.P., Greig J.A., Lee W.K., Houslay M.D., Milligan G., Mountford J.C., von Kalle C., et al. Lentivirus-mediated reprogramming of somatic cells in the absence of transgenic transcription factors. Mol Ther. 2010;18:2139–2145. doi: 10.1038/mt.2010.231. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kawamura T., Suzuki J., Wang Y.V., Menendez S., Morera L.B., Raya A., Wahl G.M., Belmonte J.C. Linking the p53 tumour suppressor pathway to somatic cell reprogramming. Nature. 2009;460:1140–1144. doi: 10.1038/nature08311. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kim D., Kim C.H., Moon J.I., Chung Y.G., Chang M.Y., Han B.S., Ko S., Yang E., Cha K.Y., Lanza R., et al. Generation of human induced pluripotent stem cells by direct delivery of reprogramming proteins. Cell Stem Cell. 2009;4:472–476. doi: 10.1016/j.stem.2009.05.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kim J., Chu J., Shen X., Wang J., Orkin S.H. An extended transcriptional network for pluripotency of embryonic stem cells. Cell. 2008;132:1049–1061. doi: 10.1016/j.cell.2008.02.039. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kim J.B., Greber B., Araúzo-Bravo M.J., Meyer J., Park K.I., Zaehres H., Schöler H.R. Direct reprogramming of human neural stem cells by OCT4. Nature. 2009;461:649–653. doi: 10.1038/nature08436. [DOI] [PubMed] [Google Scholar]
- Laurenti E., Wilson A., Trumpp A. Myc’s other life: stem cells and beyond. Curr Opin Cell Biol. 2009;21:844–854. doi: 10.1016/j.ceb.2009.09.006. [DOI] [PubMed] [Google Scholar]
- Li H., Collado M., Villasante A., Strati K., Ortega S., Cañamero M., Blasco M.A., Serrano M. The Ink4/Arf locus is a barrier for iPS cell reprogramming. Nature. 2009;460:1136–1139. doi: 10.1038/nature08290. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Li R., Liang J., Ni S., Zhou T., Qing X., Li H., He W., Chen J., Li F., Zhuang Q., et al. A mesenchymal-to-epithelial transition initiates and is required for the nuclear reprogramming of mouse fibroblasts. Cell Stem Cell. 2010;7:51–63. doi: 10.1016/j.stem.2010.04.014. [DOI] [PubMed] [Google Scholar]
- Lin C.H., Jackson A.L., Guo J., Linsley P.S., Eisenman R.N. Myc-regulated microRNAs attenuate embryonic stem cell differentiation. EMBO J. 2009;28:3157–3170. doi: 10.1038/emboj.2009.254. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lin S.L., Chang D.C., Chang-Lin S., Lin C.H., Wu D.T., Chen D.T., Ying S.Y. Mir-302 reprograms human skin cancer cells into a pluripotent ES-cell-like state. RNA. 2008;14:2115–2124. doi: 10.1261/rna.1162708. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lister R., Pelizzola M., Kida Y.S., Hawkins R.D., Nery J.R., Hon G., Antosiewicz-Bourget J., O’Malley R., Castanon R., Klugman S., et al. Hotspots of aberrant epigenomic reprogramming in human induced pluripotent stem cells. Nature. 2011;471:68–73. doi: 10.1038/nature09798. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Maekawa M., Yamaguchi K., Nakamura T., Shibukawa R., Kodanaka I., Ichisaka T., Kawamura Y., Mochizuki H., Goshima N., Yamanaka S. Direct reprogramming of somatic cells is promoted by maternal transcription factor Glis1. Nature. 2011;474:225–229. doi: 10.1038/nature10106. [DOI] [PubMed] [Google Scholar]
- Maherali N., Hochedlinger K. Tgfbeta signal inhibition cooperates in the induction of iPSCs and replaces Sox2 and cMyc. Curr Biol. 2009;19:1718–1723. doi: 10.1016/j.cub.2009.08.025. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mali P., Ye Z., Hommond H.H., Yu X., Lin J., Chen G., Zou J., Cheng L. Improved Efficiency and Pace of Generating Induced Pluripotent Stem Cells from Human Adult and Fetal Fibroblasts. Stem Cells. 2008;26:1998–2005. doi: 10.1634/stemcells.2008-0346. [DOI] [PubMed] [Google Scholar]
- Marión R.M., Strati K., Li H., Murga M., Blanco R., Ortega S., Fernandez-Capetillo O., Serrano M., Blasco M.A. A p53-mediated DNA damage response limits reprogramming to ensure iPS cell genomic integrity. Nature. 2009;460:1149–1153. doi: 10.1038/nature08287. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Masui S., Nakatake Y., Toyooka Y., Shimosato D., Yagi R., Takahashi K., Okochi H., Okuda A., Matoba R., Sharov A.A., et al. Pluripotency governed by Sox2 via regulation of Oct3/4 expression in mouse embryonic stem cells. Nat Cell Biol. 2007;9:625–635. doi: 10.1038/ncb1589. [DOI] [PubMed] [Google Scholar]
- Mikkelsen T.S., Hanna J., Zhang X., Ku M., Wernig M., Schorderet P., Bernstein B.E., Jaenisch R., Lander E.S., Meissner A. Dissecting direct reprogramming through integrative genomic analysis. Nature. 2008;454:49–55. doi: 10.1038/nature07056. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Miyoshi N., Ishii H., Nagano H., Haraguchi N., Dewi D.L., Kano Y., Nishikawa S., Tanemura M., Mimori K., Tanaka F., et al. Reprogramming of mouse and human cells to pluripotency using mature microRNAs. Cell Stem Cell. 2011;8:633–638. doi: 10.1016/j.stem.2011.05.001. [DOI] [PubMed] [Google Scholar]
- Nakagawa M., Koyanagi M., Tanabe K., Takahashi K., Ichisaka T., Aoi T., Okita K., Mochiduki Y., Takizawa N., Yamanaka S. Generation of induced pluripotent stem cells without Myc from mouse and human fibroblasts. Nat Biotechnol. 2008;26:101–106. doi: 10.1038/nbt1374. [DOI] [PubMed] [Google Scholar]
- Nichols J., Zevnik B., Anastassiadis K., Niwa H., Klewe-Nebenius D., Chambers I., Schöler H., Smith A. Formation of pluripotent stem cells in the mammalian embryo depends on the POU transcription factor Oct4. Cell. 1998;95:379–391. doi: 10.1016/S0092-8674(00)81769-9. [DOI] [PubMed] [Google Scholar]
- Niwa H., Ogawa K., Shimosato D., Adachi K. A parallel circuit of LIF signalling pathways maintains pluripotency of mouse ES cells. Nature. 2009;460:118–122. doi: 10.1038/nature08113. [DOI] [PubMed] [Google Scholar]
- Pardo M., Lang B., Yu L., Prosser H., Bradley A., Babu M.M., Choudhary J. An expanded Oct4 interaction network: implications for stem cell biology, development, and disease. Cell Stem Cell. 2010;6:382–395. doi: 10.1016/j.stem.2010.03.004. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Plews J.R., Li J., Jones M., Moore H.D., Mason C., Andrews P.W., Na J. Activation of pluripotency genes in human fibroblast cells by a novel mRNA based approach. PLoS One. 2010;5:e14397. doi: 10.1371/journal.pone.0014397. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Roush S., Slack F.J. The let-7 family of microRNAs. Trends Cell Biol. 2008;18:505–516. doi: 10.1016/j.tcb.2008.07.007. [DOI] [PubMed] [Google Scholar]
- Shi Y., Do J.T., Desponts C., Hahm H.S., Schöler H.R., Ding S. A combined chemical and genetic approach for the generation of induced pluripotent stem cells. Cell Stem Cell. 2008;2:525–528. doi: 10.1016/j.stem.2008.05.011. [DOI] [PubMed] [Google Scholar]
- Silva J., Barrandon O., Nichols J., Kawaguchi J., Theunissen T.W., Smith A. Promotion of reprogramming to ground state pluripotency by signal inhibition. PLoS Biol. 2008;6:e253. doi: 10.1371/journal.pbio.0060253. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Suh M.R., Lee Y., Kim J.Y., Kim S.K., Moon S.H., Lee J.Y., Cha K. Y., Chung H.M., Yoon H.S., Moon S.Y., et al. Human embryonic stem cells express a unique set of microRNAs. Dev Biol. 2004;270:488–498. doi: 10.1016/j.ydbio.2004.02.019. [DOI] [PubMed] [Google Scholar]
- Szymczak A.L., Workman C.J., Wang Y., Vignali K.M., Dilioglou S., Vanin E.F., Vignali D.A. Correction of multi-gene deficiency in vivo using a single ’self-cleaving’ 2A peptide-based retroviral vector. Nat Biotechnol. 2004;22:589–594. doi: 10.1038/nbt957. [DOI] [PubMed] [Google Scholar]
- Takahashi K., Tanabe K., Ohnuki M., Narita M., Ichisaka T., Tomoda K., Yamanaka S. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell. 2007;131:861–872. doi: 10.1016/j.cell.2007.11.019. [DOI] [PubMed] [Google Scholar]
- Takahashi K., Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell. 2006;126:663–676. doi: 10.1016/j.cell.2006.07.024. [DOI] [PubMed] [Google Scholar]
- Taranger C.K., Noer A., Sørensen A.L., Håkelien A.M., Boquest A. C., Collas P. Induction of dedifferentiation, genomewide transcriptional programming, and epigenetic reprogramming by extracts of carcinoma and embryonic stem cells. Mol Biol Cell. 2005;16:5719–5735. doi: 10.1091/mbc.E05-06-0572. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Urbach A., Bar-Nur O., Daley G.Q., Benvenisty N. Differential modeling of fragile X syndrome by human embryonic stem cells and induced pluripotent stem cells. Cell Stem Cell. 2010;6:407–411. doi: 10.1016/j.stem.2010.04.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Utikal J., Maherali N., Kulalert W., Hochedlinger K. Sox2 is dispensable for the reprogramming of melanocytes and melanoma cells into induced pluripotent stem cells. J Cell Sci. 2009;122:3502–3510. doi: 10.1242/jcs.054783. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Utikal J., Polo J.M., Stadtfeld M., Maherali N., Kulalert W., Walsh R.M., Khalil A., Rheinwald J.G., Hochedlinger K. Immortalization eliminates a roadblock during cellular reprogramming into iPS cells. Nature. 2009;460:1145–1148. doi: 10.1038/nature08285. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Viswanathan S.R., Daley G.Q., Gregory R.I. Selective blockade of microRNA processing by Lin28. Science. 2008;320:97–100. doi: 10.1126/science.1154040. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wang J., Rao S., Chu J., Shen X., Levasseur D.N., Theunissen T. W., Orkin S.H. A protein interaction network for pluripotency of embryonic stem cells. Nature. 2006;444:364–368. doi: 10.1038/nature05284. [DOI] [PubMed] [Google Scholar]
- Warren L., Manos P.D., Ahfeldt T., Loh Y.H., Li H., Lau F., Ebina W., Mandal P.K., Smith Z.D., Meissner A., et al. Highly efficient reprogramming to pluripotency and directed differentiation of human cells with synthetic modified mRNA. Cell Stem Cell. 2010;7:618–630. doi: 10.1016/j.stem.2010.08.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wilmut I., Schnieke A.E., McWhir J., Kind A.J., Campbell K.H. Viable offspring derived from fetal and adult mammalian cells. Nature. 1997;385:810–813. doi: 10.1038/385810a0. [DOI] [PubMed] [Google Scholar]
- Woltjen K., Michael I.P., Mohseni P., Desai R., Mileikovsky M., Hämäläinen R., Cowling R., Wang W., Liu P., Gertsenstein M., et al. piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells. Nature. 2009;458:766–770. doi: 10.1038/nature07863. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Yu J., Hu K., Smuga-Otto K., Tian S., Stewart R., Slukvin I.I., Thomson J.A. Human induced pluripotent stem cells free of vector and transgene sequences. Science. 2009;324:797–801. doi: 10.1126/science.1172482. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Yu J., Vodyanik M.A., Smuga-Otto K., Antosiewicz-Bourget J., Frane J.L., Tian S., Nie J., Jonsdottir G.A., Ruotti V., Stewart R., et al. Induced pluripotent stem cell lines derived from human somatic cells. Science. 2007;318:1917–1920. doi: 10.1126/science.1151526. [DOI] [PubMed] [Google Scholar]
- Yusa K., Rad R., Takeda J., Bradley A. Generation of transgene-free induced pluripotent mouse stem cells by the piggyBac transposon. Nat Methods. 2009;6:363–369. doi: 10.1038/nmeth.1323. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zhao T., Zhang Z.N., Rong Z., Xu Y. Immunogenicity of induced pluripotent stem cells. Nature. 2011;474:212–215. doi: 10.1038/nature10135. [DOI] [PubMed] [Google Scholar]
- Zhao Y., Yin X., Qin H., Zhu F., Liu H., Yang W., Zhang Q., Xiang C., Hou P., Song Z., et al. Two supporting factors greatly improve the efficiency of human iPSC generation. Cell Stem Cell. 2008;3:475–479. doi: 10.1016/j.stem.2008.10.002. [DOI] [PubMed] [Google Scholar]
- Zhao Y., Yin X., Qin H., Zhu F., Liu H., Yang W., Zhang Q., Xiang C., Hou P., Song Z., et al. Two supporting factors greatly improve the efficiency of human iPSC generation. Cell Stem Cell. 2008;3:475–479. doi: 10.1016/j.stem.2008.10.002. [DOI] [PubMed] [Google Scholar]
- Zhou H., Wu S., Joo J.Y., Zhu S., Han D.W., Lin T., Trauger S., Bien G., Yao S., Zhu Y., et al. Generation of induced pluripotent stem cells using recombinant proteins. Cell Stem Cell. 2009;4:381–384. doi: 10.1016/j.stem.2009.04.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zhu S., Li W., Zhou H., Wei W., Ambasudhan R., Lin T., Kim J., Zhang K., Ding S. Reprogramming of human primary somatic cells by OCT4 and chemical compounds. Cell Stem Cell. 2010;7:651–655. doi: 10.1016/j.stem.2010.11.015. [DOI] [PMC free article] [PubMed] [Google Scholar]
