This work was funded by Yale School of Medicine and Child Health Research Award from Charles Hood Foundation.

1. Reprogramming by Retrovirus Expressing Reprogramming Factors
<ol>
 <li>Human fibroblasts are cultured in fibroblast medium (10% FBS in DMEM with Pen/Strep).</li>
 <li>One day before infection, plate 1x105 human fibroblasts into one well of a 6-well plate.</li>
 <li>Aspirate medium to remove dead cells and add 2 ml of fresh fibroblast medium. Add protamine sulfate at a final concentration of 5 &mu;g/ml.</li>
 <li>Carefully add the appropriate amount of each GFP-expressing virus corresponding to a multiplicity of infection (MOI) 55.</li>
 <li>One day after infection, remove the viral supernatant, wash three times with 2 ml PBS, then add 2 ml fibroblast medium.</li>
 <li>Three days after infection, check the GFP fluorescence and replenish the well with 2 ml fibroblast medium.</li>
 <li>Four days after infection, plate 1x104 /cm2 of irradiated mouse embryonic fibroblast (MEFs) feeder cells in fibroblast medium onto a 10-cm Petri dish coated with 0.1% gelatin. Incubate at 37 &deg;C overnight.</li>
 <li>Five days after infection, detach infected human fibroblasts with 1 ml 0.05% typsin/EDTA for 5 minutes at 37 &deg;C, and centrifuge for 5 minutes at 200 g. Aspirate the medium and resuspend the cells with 10ml of fibroblast medium. Transfer the cells into a pre-coated 10-cm plate.</li>
 <li>After 24 hours, replace the medium with hESC culture medium (20% Knock-Out serum replacement, DMEM/F12, 0.1 ml Non-essential Amino Acids, 4 ng/ml bFGF, Pen/Strep/Glutamate, beta-merceptoethanol). Change the medium daily. ESC-like colonies will start to appear by day 20-27 after infection.</li>
</ol>
2. Isolation and Expansion of iPSCs
<ol>
 <li>Under a fluorescence microscope, check for the absence of GFP fluorescence in a colony that shows a similar morphology to hESCs.</li>
 <li>Using a 10 &mu;l pipette, pick individual iPSC colonies and place them into one well of a gelatin- and MEF-coated 12-well plate and supplemented with hESC medium. Change medium daily.</li>
 <li>For passaging, wash the plate with 1 ml of DMEM/F12, then add 0.5 ml of collagenase, and incubate for 10 minutes at 37 &deg;C.</li>
 <li>Wash the cells twice with DMEM/F12.</li>
 <li>Add 2 ml of fresh hESC medium. Using a cell lifter, break up the colonies into small pieces and detach remaining cells from the plate.</li>
 <li>Transfer the resuspended pieces of colonies into one well of a gelatin- and MEF- coated 6-well plate.</li>
</ol>
3. Immunofluorescence Analysis of Pluripotent Markers
<ol>
 <li>Wash the cells three times with PBS and fix with 4% paraformaldehyde for 20 min at room temperature.</li>
 <li>Gently wash the cells three times with PBS and permeabilize with 0.2% Triton X-100 in PBS for 30 min.</li>
 <li>Block non-specific binding by incubating cells with 3% BSA in PBS for two hours.</li>
 <li>Incubate the cells with primary antibody overnight at 4 &deg;C.</li>
 <li>Wash the cells three times with PBS and incubate the cells with specific secondary antibody for one hour at room temperature, shielding from light.</li>
 <li>Wash the cells three times with PBS and add DAPI during the last wash followed by incubation at room temperature for 5 minutes.</li>
 <li>Detect the staining with a fluorescence microscope.</li>
</ol>
4. Quantitative Real-time PCR Assay for the Pluripotent Markers
<ol>
 <li>Isolate total RNA from the human iPSCs derived from human fibroblasts using Qiagen's RNeasy kit.</li>
 <li>Synthesize the first-strand cDNA using SuperScript II Reverse Transcriptase.</li>
 <li>Perform qPCR to detect pluripotency genes using primers previously reported.6</li>
</ol>
5. Representative Results
<ol>
 <li>Morphological change during reprogramming 
 We infected human fibroblasts BJ1 and Detroit 551 with a cocktail of retroviruses carrying OCT4, SOX2, KLF4 and MYC, and were able to detect morphological changes during reprogramming (Figure 1). Twenty-one days after infection, we recognize small iPSC colonies by their hESC-like morphology. Furthermore, we recognize iPSCs by the GFP fluorescence. Pluripotent stem cells, such as ESCs and iPSCs, express the molecular machinery to repress the proviral gene expression7-9. Our unique retroviral vector expresses GFP together with reprogramming genes by retroviral LTR. Thus, cells continuously expressing GFP are considered to express transgenes without proviral gene silencing. Faithfully reprogrammed iPSC colonies that acquire the pluripotency molecular network show the absence of GFP expression (Figure 2)10. </li>
 <li>Characterization of pluripotency of human iPSCs 
 We analyzed colonies derived from Detroit-551 fibroblasts via immunohistochemistry with Tra-1-81, Tra-1-60, SSEA-4, SSEA-3, OCT4 and NANOG antibodies (Table 2). Successfully reprogrammed iPSCs express all of these markers (Figure 3A). We also analyzed gene expression via quantitative RT-PCR analysis. We observed that the expression of OCT4, SOX2, KLF4, MYC and NANOG was significantly increased compared to the parental fibroblast cells but commensurate with that of H9 hESCs (Figure 3B).</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/3804/3804fig1.jpg" /> 
Figure 1. Morphological changes of retrovirus-infected human fibroblasts. (A-D) Progressive morphological change in colonies from Detroit-551 fibroblasts infected with reprogramming factors. Day 5 (A), Day 10 (B), Day 14 (C), day 21 (D). Cells show the hESC-like morphology after 21 days.
<img alt="Figure 2" src="/files/ftp_upload/3804/3804fig2.jpg" /> 
Figure 2. Representative GFP fluorescent expression in cells undergoing reprogramming. BJ and Detroit 551 fibroblasts were infected with retrovirus expressing four reprogramming factors4, and incubated in hESC medium for four weeks. BJ fibroblasts (A, B) and Detroit 551 (C, D) show similar morphological. From day 21, GFP negative colonies start to form, which represent the bona fide iPSCs10. (E, F) show transformed Detroit 551 cells that have not undergone proper reprogramming. (A, C, E) colonies under phase contrast view. (B, D) properly reprogrammed cells that show the GFP silencing. (F) bright GFP expression from transformed colony.
<img alt="Figure 3" src="/files/ftp_upload/3804/3804fig3.jpg" /> 
Figure 3. Characterization of the human induced pluripotent stem cells. (A) Human 551-iPS-K1 cell colonies express markers common to pluripotent cells. DAPI staining indicates the total cell content per field. (B) Quantitative real time-PCR (RT-qPCR) for expression of OCT4, SOX2, KLF4, MYC in parental fibroblast, 551-iPS-K1 iPSCs, and H9 human embryonic stem cells (hESCs). Data were normalized against &beta;-actin housekeeping gene and plotted relative to the expression level in the parental fibroblast cells4.

<ol>
	<li>Murry, C. E., Keller, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differentiation+of+embryonic+stem+cells+to+clinically+relevant+populations:+lessons+from+embryonic+development.">Differentiation of embryonic stem cells to clinically relevant populations: lessons from embryonic development.</a> Cell. 132, 661-680 (2008).</li><li>Takahashi, K., Tanabe, K., Ohnuki, M., Narita, M., Ichisaka, T., Tomoda, K., Yamanaka, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induction+of+pluripotent+stem+cells+from+adult+human+fibroblasts+by+defined+factors.">Induction of pluripotent stem cells from adult human fibroblasts by defined factors.</a> Cell. 131, 861-872 (2007).</li><li>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. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induced+pluripotent+stem+cell+lines+derived+from+human+somatic+cells.">Induced pluripotent stem cell lines derived from human somatic cells.</a> Science. 318, 1917-1920 (2007).</li><li>Park, I. H., Zhao, R., West, J. A., Yabuuchi, A., Huo, H., Ince, T. A., Lerou, P. H., Lensch, M. W., Daley, G. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reprogramming+of+human+somatic+cells+to+pluripotency+with+defined+factors.">Reprogramming of human somatic cells to pluripotency with defined factors.</a> Nature. 451, 141-146 (2008).</li><li>Park, I. H., Lerou, P. H., Zhao, R., Huo, H., Daley, G. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+human-induced+pluripotent+stem+cells.">Generation of human-induced pluripotent stem cells.</a> Nature Protocols. 3, 1180-1186 (2008).</li><li>Park, I. H., Zhao, R., West, J. A., Yabuuchi, A., Huo, H., Ince, T. A., Lerou, P. H., Lensch, M. W., Daley, G. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reprogramming+of+human+somatic+cells+to+pluripotency+with+defined+factors.">Reprogramming of human somatic cells to pluripotency with defined factors.</a> Nature. 451, 141-146 (2008).</li><li>Hotta, A., Ellis, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retroviral+vector+silencing+during+iPS+cell+induction:+an+epigenetic+beacon+that+signals+distinct+pluripotent+states.">Retroviral vector silencing during iPS cell induction: an epigenetic beacon that signals distinct pluripotent states.</a> Journal of Cellular Biochemistry. 105, 940-948 (2008).</li><li>Matsui, T., Leung, D., Miyashita, H., Maksakova, I. A., Miyachi, H., Kimura, H., Tachibana, M., Lorincz, M. C., Shinkai, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proviral+silencing+in+embryonic+stem+cells+requires+the+histone+methyltransferase+ESET.">Proviral silencing in embryonic stem cells requires the histone methyltransferase ESET.</a> Nature. 464, 927-931 (2010).</li><li>Wolf, D., Goff, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Embryonic+stem+cells+use+ZFP809+to+silence+retroviral+DNAs.">Embryonic stem cells use ZFP809 to silence retroviral DNAs.</a> Nature. 458, 1201-1204 (2009).</li><li>Chan, E. M., Ratanasirintrawoot, S., Park, I. H., Manos, P. D., Loh, Y. H., Huo, H., Miller, J. D., Hartung, O., Rho, J., Ince, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+cell+imaging+distinguishes+bona+fide+human+iPS+cells+from+partially+reprogrammed+cells.">Live cell imaging distinguishes bona fide human iPS cells from partially reprogrammed cells.</a> Nat. Biotechnol. 27, 1033-1037 (2009).</li><li>Yu, J., Hu, K., Smuga-Otto, K., Tian, S., Stewart, R., Slukvin, ., Thomson, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+induced+pluripotent+stem+cells+free+of+vector+and+transgene+sequences.">Human induced pluripotent stem cells free of vector and transgene sequences.</a> Science. 324, 797-801 (2009).</li><li>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. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+human+induced+pluripotent+stem+cells+by+direct+delivery+of+reprogramming+proteins.">Generation of human induced pluripotent stem cells by direct delivery of reprogramming proteins.</a> Cell Stem Cell. 4, 472-476 (2009).</li><li>Warren, L., Manos, P. D., Ahfeldt, T., Loh, Y. H., Li, H., Lau, F., Ebina, W., Mandal, P. K., Smith, Z. D., Meissner, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+efficient+reprogramming+to+pluripotency+and+directed+differentiation+of+human+cells+with+synthetic+modified+mRNA.">Highly efficient reprogramming to pluripotency and directed differentiation of human cells with synthetic modified mRNA.</a> Cell Stem Cell. 7, 618-630 (2010).</li><li>Ban, H., Nishishita, N., Fusaki, N., Tabata, T., Saeki, K., Shikamura, M., Takada, N., Inoue, M., Hasegawa, M., Kawamata, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+generation+of+transgene-free+human+induced+pluripotent+stem+cells+(iPSCs)+by+temperature-sensitive+Sendai+virus+vectors.">Efficient generation of transgene-free human induced pluripotent stem cells (iPSCs) by temperature-sensitive Sendai virus vectors.</a> Proceedings of the National Academy of Sciences of the United States of America. 108, 14234-14239 (2011).</li><li>Wolf, D., Goff, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TRIM28+mediates+primer+binding+site-targeted+silencing+of+murine+leukemia+virus+in+embryonic+cells.">TRIM28 mediates primer binding site-targeted silencing of murine leukemia virus in embryonic cells.</a> Cell. 131, 46-57 (2007).</li><li>Park, I. H., Arora, N., Huo, H., Maherali, N., Ahfeldt, T., Shimamura, A., Lensch, M. W., Cowan, C., Hochedlinger, K., Daley, G. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disease-specific+induced+pluripotent+stem+cells.">Disease-specific induced pluripotent stem cells.</a> Cell. 134, 877-886 (2008).</li><li>Kim, K. Y., Hysolli, E., Park, I. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+maturation+defect+in+induced+pluripotent+stem+cells+from+patients+with+Rett+syndrome.">Neuronal maturation defect in induced pluripotent stem cells from patients with Rett syndrome.</a> Proceedings of the National Academy of Sciences of the United States of America. 108, 14169-14174 (2011).</li></ol>

We have nothing to disclose.

Expression of four transcription factors reprograms human fibroblasts to iPSCs. Many attempts were made to generate human iPSCs using non-integrating or non-genetic approaches to generate clinically safe iPSCs. So far, these methods show extremely low efficiency and require further optimization to improve the reproducibility11-14. Retro- or lentiviral methods are readily used to derive and apply iPSCs for human in vitro disease models, which are less dependent on the safety issues caused by viral integration. Reprogramming method described here is available for the efficient derivation of human iPSCs. Selection of human iPSCs is primarily based on colony morphology that resembles human ESCs. More importantly, our method takes advantage of the feature of silencing of the retroviral long terminal repeats (LTR) in pluripotent stem cells7,15. The retroviral vector used in this protocol contains the GFP gene linked to the reprogramming factors via an Internal Ribosome Entry Sequence (IRES) and5. GFP expression is driven by proviral LTR. The fibroblasts infected with these viruses initially show the bright GFP expression. Once fully reprogrammed, iPSCs will lose GFP expression, which is easily visualized under a fluorescence microscope. In this protocol, we described the generation of iPSCs from fetal and neonatal fibroblasts (Detroit 551 and BJ1). However, this retroviral vector has been used to generate iPSCs from normal adult fibroblasts as well as a variety of patients with Mendelian and complex disorders4,16,17.
Previously we have analyzed the change in cellular surface markers during human somatic cell reprogramming10. There is a progressive change in cell surface markers. Fibroblasts express CD13, which is repressed by the expression of reprogramming. Cells undergoing reprogramming start to express SSEA4 together with GFP. Then, they lose the expression of GFP via proviral silecing and express additional pluripotency maker TRA1-6010. The expression of TRA1-60 is well correlated with GFP silencing and the well-developed teratoma formation, suggesting that TRA1-60 is a marker for faithfully reprogrammed iPSCs. GFP silencing is the alternative marker for TRA1-60 expression and allows the identification of iPSC colonies without laborious live cell staining. Using the loss of GFP expression as a marker for iPSCs, stem cell scientists who have no prior experience in reprogramming will readily and consistently isolate iPSCs.

<table border="1">
	<tbody>
		<tr>
			<td>Name</td>
			<td>Concentration</td>
			<td>Company</td>
			<td>Catalogue Number</td>
		</tr>
		<tr>
			<td colspan="4">hESC medium</td>
		</tr>
		<tr>
			<td>DMEM/F12</td>
			<td>80%</td>
			<td>Invitrogen</td>
			<td>11330057</td>
		</tr>
		<tr>
			<td>Knockout Serum Replacer</td>
			<td>20%</td>
			<td>Invitrogen</td>
			<td>10828-028</td>
		</tr>
		<tr>
			<td>L-Glutamine (200 mM)</td>
			<td>2 mM</td>
			<td>Invitrogen</td>
			<td>25030081</td>
		</tr>
		<tr>
			<td>Nonessential Amino Acids (10 mM)</td>
			<td>0.1 mM</td>
			<td>Invitrogen</td>
			<td>11140050</td>
		</tr>
		<tr>
			<td>&beta;-Mercaptoethanol (14.3 M) or MTG</td>
			<td>0.1 mM</td>
			<td>Invitrogen</td>
			<td>M-6250</td>
		</tr>
		<tr>
			<td>bFGF-2 10 &mu;g/ml</td>
			<td>4 ng/ml</td>
			<td>GIBCO/BRL</td>
			<td>GF003AF</td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>1%</td>
			<td>Millipore</td>
			<td>15140-122</td>
		</tr>
		<tr>
			<td colspan="4">Fiboblasts Medium</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>90%</td>
			<td>Invitrogen</td>
			<td>11965118</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>10%</td>
			<td>Invitrogen</td>
			<td>10407028</td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>1%</td>
			<td>Millipore</td>
			<td>15140-122</td>
		</tr>
	</tbody>
</table>
Table 1. Culture Medium
<table border="1">
	<tbody>
		<tr>
			<td>Name</td>
			<td>Concentration</td>
			<td>Company</td>
			<td>Catalogue Number</td>
		</tr>
		<tr>
			<td colspan="4">Antibodies</td>
		</tr>
		<tr>
			<td>OCT4</td>
			<td>1:500</td>
			<td>Abcam</td>
			<td>Ab19857</td>
		</tr>
		<tr>
			<td>SSEA3</td>
			<td>1:100</td>
			<td>Milipore</td>
			<td>MAB4303</td>
		</tr>
		<tr>
			<td>SSEA4</td>
			<td>1:100</td>
			<td>BD Biosciences</td>
			<td>BD560218</td>
		</tr>
		<tr>
			<td>Tra-1-81</td>
			<td>1:100</td>
			<td>BD Biosciences</td>
			<td>BD560173</td>
		</tr>
		<tr>
			<td>Tra-1-60</td>
			<td>1:100</td>
			<td>BD Biosciences</td>
			<td>BD560174</td>
		</tr>
		<tr>
			<td>NANOG</td>
			<td>1:500</td>
			<td>Abcam</td>
			<td>Ab21624</td>
		</tr>
		<tr>
			<td>Alexa-Flur 488</td>
			<td>1:1000</td>
			<td>Invitrogen</td>
			<td>A11008</td>
		</tr>
		<tr>
			<td>Alexa-Flur 555</td>
			<td>1:1000</td>
			<td>Invitrogen</td>
			<td>A21422</td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>1:5000</td>
			<td>Invitrogen</td>
			<td>D1306</td>
		</tr>
		<tr>
			<td colspan="4">Plasmids</td>
		</tr>
		<tr>
			<td>pMIG-OCT4</td>
			<td>&nbsp;</td>
			<td>Addgene</td>
			<td>17225</td>
		</tr>
		<tr>
			<td>pMIG-SOX2</td>
			<td>&nbsp;</td>
			<td>Addgene</td>
			<td>17226</td>
		</tr>
		<tr>
			<td>pMIG-KLF4</td>
			<td>&nbsp;</td>
			<td>Addgene</td>
			<td>17227</td>
		</tr>
		<tr>
			<td>pMIG-MYC</td>
			<td>&nbsp;</td>
			<td>Addgene</td>
			<td>18119</td>
		</tr>
		<tr>
			<td colspan="4">Other Materials</td>
		</tr>
		<tr>
			<td>Collagenase type IV</td>
			<td>1mg/ml</td>
			<td>Invitrogen</td>
			<td>17104019</td>
		</tr>
		<tr>
			<td>Gelatin, Porcine</td>
			<td>0.1%</td>
			<td>Sigma</td>
			<td>G 1890</td>
		</tr>
		<tr>
			<td>Triton</td>
			<td>0.2%</td>
			<td>Sigma</td>
			<td>X100-500ML</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>4%</td>
			<td>Sigma</td>
			<td>47608</td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>3%</td>
			<td>American Bioanalytical</td>
			<td>AB01800</td>
		</tr>
		<tr>
			<td>MEF feeder cells</td>
			<td>&nbsp;</td>
			<td>Millipore</td>
			<td>PMEF-N</td>
		</tr>
		<tr>
			<td>Cell Lifter</td>
			<td>&nbsp;</td>
			<td>Corning</td>
			<td>3008</td>
		</tr>
		<tr>
			<td colspan="4">Equipment</td>
		</tr>
		<tr>
			<td colspan="4">Fluorescent microscopy: inverted microscope with GFP filter</td>
		</tr>
	</tbody>
</table>
Table 2. Reagents and equipment.

reprogramming human somatic cells into induced pluripotent stem cells (ipscs) using retroviral vector with gfp

Human embryonic stem cells (hESCs) are pluripotent and an invaluable cellular sources for in vitro disease modeling and regenerative medicine1. It has been previously shown that human somatic cells can be reprogrammed to pluripotency by ectopic expression of four transcription factors (Oct4, Sox2, Klf4 and Myc) and become induced pluripotent stem cells (iPSCs)2-4 . Like hESCs, human iPSCs are pluripotent and a potential source for autologous cells. Here we describe the protocol to reprogram human fibroblast cells with the four reprogramming factors cloned into GFP-containing retroviral backbone4. Using the following protocol, we generate human iPSCs in 3-4 weeks under human ESC culture condition. Human iPSC colonies closely resemble hESCs in morphology and display the loss of GFP fluorescence as a result of retroviral transgene silencing. iPSC colonies isolated mechanically under a fluorescence microscope behave in a similar fashion as hESCs. In these cells, we detect the expression of multiple pluripotency genes and surface markers.

Watch this Scientific Journal Video about Reprogramming Human Somatic Cells into Induced Pluripotent Stem Cells iPSCs Using Retroviral Vector with GFP at JoVE.com

Reprogramming Human Somatic Cells into Induced Pluripotent Stem Cells iPSCs Using Retroviral Vector with GFP

A method to generate human induced pluripotent stem cells (iPSCs) via retrovirus-mediated ectopic expression of OCT4, SOX2, KLF4 and MYC is described. A practical way to identify human iPSC colonies based on GFP expression is also discussed.

Reprogramming Human Somatic Cells into Induced Pluripotent Stem Cells (iPSCs) Using Retroviral Vector with GFP

Human embryonic stem cells (hESCs) are pluripotent and an invaluable cellular sources for in vitro disease modeling and regenerative medicine1. It has ...

reprogramming-human-somatic-cells-into-induced-pluripotent-stem-cells

Nanyang Technological University

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JoVE Journal

Biology

20.4K Views.  Yale School of Medicine. A method to generate human induced pluripotent stem cells (iPSCs) via retrovirus-mediated ectopic expression of OCT4, SOX2, KLF4 and MYC is described. A practical way to identify human iPSC colonies based on GFP expression is also discussed.

Video: Reprogramming Human Somatic Cells into Induced Pluripotent Stem Cells iPSCs Using Retroviral Vector with GFP

Generation of Induced Pluripotent Stem Cells by Reprogramming Mouse Embryonic Fibroblasts with a Four Transcription Factor, Doxycycline Inducible Lentiviral Transduction System

Using a defined set of transcription factors and cell culture conditions, Yamanaka and colleagues demonstrated that retrovirus-mediated delivery and expression of Oct4, Sox2, c-Myc, and Klf4 is capable of inducing pluripotency in mouse fibroblasts.1 Subsequent reports have demonstrated the utility of the doxycycline (DOX) inducible lentiviral delivery system for the generation of both primary and secondary iPS cells from a variety of other adult mouse somatic cell types.2,3
Induced pluripotent stem (iPS) cells are similar to embryonic stem (ES) cells in morphology, proliferation and ability to induce teratoma formation. Both types of cell can be used as the pluripotent starting material for the generation of differentiated cells or tissues in regenerative medicine.4-6 iPS cells also have a distinct advantage over ES cells as they exhibit key properties of ES cells without the ethical dilemma of embryo destruction.
Here we demonstrate the protocol for reprogramming mouse embryonic fibroblast (MEF) cells with the Stemgent DOX Inducible Mouse TF Lentivirus Set. We also demonstrate that the Stemgent DOX Inducible Mouse TF Lentivirus Set is capable of expressing each of the four transcription factors upon transduction into MEFs thereby inducing a pluripotent stem cell state that displays the pluripotency markers characteristic of ES cells.

The Stemgent Dox Inducible Mouse TF Lentivirus Set can reprogram mouse embryonic fibroblasts (MEFs) to induced pluripotent stem (iPS) cells. Here we demonstrate the protocol for DOX-inducible expression of mouse reprogramming transcription factors Oct4, Sox2, Klf4 and c-Myc to generate iPS colonies that express common mES pluripotency markers.

Using a defined set of transcription factors and cell culture conditions, Yamanaka and colleagues demonstrated that retrovirus-mediated delivery and ...

Generation of Induced Pluripotent Stem Cells by Reprogramming Human Fibroblasts with the Stemgent Human TF Lentivirus Set

In 2006, Yamanaka and colleagues first demonstrated that retrovirus-mediated delivery and expression of Oct4, Sox2, c-Myc and Klf4 is capable of inducing the pluripotent state in mouse fibroblasts.1 The same group also reported the successful reprogramming of human somatic cells into induced pluripotent stem (iPS) cells using human versions of the same transcription factors delivered by retroviral vectors.2 Additionally, James Thomson et al. reported that the lentivirus-mediated co-expression of another set of factors (Oct4, Sox2, Nanog and Lin28) was capable of reprogramming human somatic cells into iPS cells.3
iPS cells are similar to ES cells in morphology, proliferation and the ability to differentiate into all tissue types of the body. Human iPS cells have a distinct advantage over ES cells as they exhibit key properties of ES cells without the ethical dilemma of embryo destruction. The generation of patient-specific iPS cells circumvents an important roadblock to personalized regenerative medicine therapies by eliminating the potential for immune rejection of non-autologous transplanted cells.
Here we demonstrate the protocol for reprogramming human fibroblast cells using the Stemgent Human TF Lentivirus Set. We also show that cells reprogrammed with this set begin to show iPS morphology four days post-transduction. Using the Stemolecule Y27632, we selected for iPS cells and observed correct morphology after three sequential rounds of colony picking and passaging. We also demonstrate that after reprogramming cells displayed the pluripotency marker AP, surface markers TRA-1-81, TRA-1-60, SSEA-4, and SSEA-3, and nuclear markers Oct4, Sox2 and Nanog.

We demonstrate the protocol for the generation of induced pluripotent stem cells from human somatic cells using lentivirus-mediated delivery of the human factors Oct4, Sox2, Nanog, and Lin28. Pluripotency was confirmed by morphology and the presence of embryonic stem (ES) cell-specific markers.

In 2006, Yamanaka and colleagues first demonstrated that retrovirus-mediated delivery and expression of Oct4, Sox2, c-Myc and Klf4 is capable of inducing ...

Differentiation of Embryonic Stem Cells into Oligodendrocyte Precursors

Oligodendrocytes are the myelinating cells of the central nervous system. For regenerative cell therapy in demyelinating diseases, there is significant interest in deriving a pure population of lineage-committed oligodendrocyte precursor cells (OPCs) for transplantation. OPCs are characterized by the activity of the transcription factor Olig2 and surface expression of a proteoglycan NG2. Using the GFP-Olig2 (G-Olig2) mouse embryonic stem cell (mESC) reporter line, we optimized conditions for the differentiation of mESCs into GFP+Olig2+NG2+ OPCs. In our protocol, we first describe the generation of embryoid bodies (EBs) from mESCs. Second, we describe treatment of mESC-derived EBs with small molecules: (1) retinoic acid (RA) and (2) a sonic hedgehog (Shh) agonist purmorphamine (Pur) under defined culture conditions to direct EB differentiation into the oligodendroglial lineage. By this approach, OPCs can be obtained with high efficiency (&gt;80%) in a time period of 30 days. Cells derived from mESCs in this protocol are phenotypically similar to OPCs derived from primary tissue culture. The mESC-derived OPCs do not show the spiking property described for a subpopulation of brain OPCs in situ. To study this electrophysiological property, we describe the generation of spiking mESC-derived OPCs by ectopically expressing NaV1.2 subunit. The spiking and nonspiking cells obtained from this protocol will help advance functional studies on the two subpopulations of OPCs.

We describe a small molecule-based protocol for differentiation of mouse embryonic stem cells into oligodendrocyte precursor cells (OPCs). This protocol generates Olig2+NG2+ OPCs with high efficiency by 30 days of differentiation. We also describe a method to generate "spiking" OPCs that can fire action potentials.

Oligodendrocytes are the myelinating cells of the central nervous system. For regenerative cell therapy in demyelinating diseases, there is significant ...

Transfecting and Nucleofecting Human Induced Pluripotent Stem Cells

Genetic modification is continuing to be an essential tool in studying stem cell biology and in setting forth potential clinical applications of human embryonic stem cells (HESCs)1. While improvements in several gene delivery methods have been described2-9, transfection remains a capricious process for HESCs, and has not yet been reported in human induced pluripotent stem cells (iPSCs). In this video, we demonstrate how our lab routinely transfects and nucleofects human iPSCs using plasmid with an enhanced green fluorescence protein (eGFP) reporter. Human iPSCs are adapted and maintained as feeder-free cultures to eliminate the possibility of feeder cell transfection and to allow efficient selection of stable transgenic iPSC clones following transfection. For nucleofection, human iPSCs are pre-treated with ROCK inhibitor11, trypsinized into small clumps of cells, nucleofected and replated on feeders in feeder cell-conditioned medium to enhance cell recovery. Transgene-expressing human iPSCs can be obtained after 6 hours. Antibiotic selection is applied after 24 hours and stable transgenic lines appear within 1 week. Our protocol is robust and reproducible for human iPSC lines without altering pluripotency of these cells.

Despite recent advancements in genetic modification, transfection of human embryonic stem cells (HESCs) remains a capricious process. To our knowledge, systematic and efficient methods to transfect human induced pluripotent stem cells (iPSCs) have not been reported. Here, we describe robust protocols to efficiently transfect and nucleofect human iPSCs.

Genetic modification is continuing to be an essential tool in studying stem cell biology and in setting forth potential clinical applications of human ...

Efficient Derivation of Human Cardiac Precursors and Cardiomyocytes from Pluripotent Human Embryonic Stem Cells with Small Molecule Induction

To date, the lack of a suitable human cardiac cell source has been the major setback in regenerating the human myocardium, either by cell-based transplantation or by cardiac tissue engineering1-3. Cardiomyocytes become terminally-differentiated soon after birth and lose their ability to proliferate. There is no evidence that stem/progenitor cells derived from other sources, such as the bone marrow or the cord blood, are able to give rise to the contractile heart muscle cells following transplantation into the heart1-3. The need to regenerate or repair the damaged heart muscle has not been met by adult stem cell therapy, either endogenous or via cell delivery1-3. The genetically stable human embryonic stem cells (hESCs) have unlimited expansion ability and unrestricted plasticity, proffering a pluripotent reservoir for in vitro derivation of large supplies of human somatic cells that are restricted to the lineage in need of repair and regeneration4,5. Due to the prevalence of cardiovascular disease worldwide and acute shortage of donor organs, there is intense interest in developing hESC-based therapies as an alternative approach. However, how to channel the wide differentiation potential of pluripotent hESCs efficiently and predictably to a desired phenotype has been a major challenge for both developmental study and clinical translation. Conventional approaches rely on multi-lineage inclination of pluripotent cells through spontaneous germ layer differentiation, resulting in inefficient and uncontrollable lineage-commitment that is often followed by phenotypic heterogeneity and instability, hence, a high risk of tumorigenicity6-8 (see a schematic in Fig. 1A). In addition, undefined foreign/animal biological supplements and/or feeders that have typically been used for the isolation, expansion, and differentiation of hESCs may make direct use of such cell-specialized grafts in patients problematic9-11. To overcome these obstacles, we have resolved the elements of a defined culture system necessary and sufficient for sustaining the epiblast pluripotence of hESCs, serving as a platform for de novo derivation of clinically-suitable hESCs and effectively directing such hESCs uniformly towards clinically-relevant lineages by small molecules12 (see a schematic in Fig. 1B). After screening a variety of small molecules and growth factors, we found that such defined conditions rendered nicotinamide (NAM) sufficient to induce the specification of cardiomesoderm direct from pluripotent hESCs that further progressed to cardioblasts that generated human beating cardiomyocytes with high efficiency (Fig. 2). We defined conditions for induction of cardioblasts direct from pluripotent hESCs without an intervening multi-lineage embryoid body stage, enabling well-controlled efficient derivation of a large supply of human cardiac cells across the spectrum of developmental stages for cell-based therapeutics.

We have established a protocol for induction of cardioblasts direct from pluripotent human embryonic stem cells maintained under defined conditions with small molecules, which enables derivation of a large supply of human cardiac progenitors and functional cardiomyocytes for cardiovascular repair.

To date, the lack of a suitable human cardiac cell source has been the major setback in regenerating the human myocardium, either by cell-based ...

Selecting and Isolating Colonies of Human Induced Pluripotent Stem Cells Reprogrammed from Adult Fibroblasts

Herein we present a protocol of reprogramming human adult fibroblasts into human induced pluripotent stem cells (hiPSC) using retroviral vectors encoding Oct3/4, Sox2, Klf4 and c-myc (OSKM) in the presence of sodium butyrate 1-3. We used this method to reprogram late passage (&gt;p10) human adult fibroblasts derived from Friedreich's ataxia patient (GM03665, Coriell Repository). The reprogramming approach includes highly efficient transduction protocol using repetitive centrifugation of fibroblasts in the presence of virus-containing media. The reprogrammed hiPSC colonies were identified using live immunostaining for Tra-1-81, a surface marker of pluripotent cells, separated from non-reprogrammed fibroblasts and manually passaged 4,5. These hiPSC were then transferred to Matrigel plates and grown in feeder-free conditions, directly from the reprogramming plate. Starting from the first passage, hiPSC colonies demonstrate characteristic hES-like morphology. Using this protocol more than 70% of selected colonies can be successfully expanded and established into cell lines. The established hiPSC lines displayed characteristic pluripotency markers including surface markers TRA-1-60 and SSEA-4, as well as nuclear markers Oct3/4, Sox2 and Nanog. 
The protocol presented here has been established and tested using adult fibroblasts obtained from Friedreich's ataxia patients and control individuals 6, human newborn fibroblasts, as well as human keratinocytes.

We present a protocol for efficient reprogramming of human somatic cells into human induced pluripotent stem cells (hiPSC) using retroviral vectors encoding Oct3/4, Sox2, Klf4 and c-myc (OSKM) and identification of correctly reprogrammed hiPSC by live staining with Tra-1-81 antibody.

Herein we present a protocol of reprogramming human adult fibroblasts into human induced pluripotent stem cells (hiPSC) using retroviral vectors encoding ...

Preparation of Mouse Embryonic Fibroblast Cells Suitable for Culturing Human Embryonic and Induced Pluripotent Stem Cells

In general, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs)1 can be cultured under variable conditions. However, it is not easy to establish an effective system for culturing these cells. Since the culture conditions can influence gene expression that confers pluripotency in hESCs and hiPSCs, the optimization and standardization of the culture method is crucial.
The establishment of hESC lines was first described by using MEFs as feeder cells and fetal bovine serum (FBS)-containing culture medium2. Next, FBS was replaced with knockout serum replacement (KSR) and FGF2, which enhances proliferation of hESCs3. Finally, feeder-free culture systems enable culturing cells on Matrigel-coated plates in KSR-containing conditioned medium (medium conditioned by MEFs)4. Subsequently, hESCs culture conditions have moved towards feeder-free culture in chemically defined conditions5-7. Moreover, to avoid the potential contamination by pathogens and animal proteins culture methods using xeno-free components have been established8.
To obtain improved conditions mouse feeder cells have been replaced with human cell lines (e.g. fetal muscle and skin cells9, adult skin cells10, foreskin fibroblasts11-12, amniotic mesenchymal cells13). However, the efficiency of maintaining undifferentiated hESCs using human foreskin fibroblast-derived feeder layers is not as high as that from mouse feeder cells due to the lower level of secretion of Activin A14. Obviously, there is an evident difference in growth factor production by mouse and human feeder cells.
Analyses of the transcriptomes of mouse and human feeder cells revealed significant differences between supportive and non-supportive cells. Exogenous FGF2 is crucial for maintaining self-renewal of hESCs and hiPSCs, and has been identified as a key factor regulating the expression of Tgf&beta;1, Activin A and Gremlin (a BMP antagonist) in feeder cells. Activin A has been shown to induce the expression of OCT4, SOX2, and NANOG in hESCs15-16.
For long-term culture, hESCs and hiPSCs can be grown on mitotically inactivated MEFs or under feeder-free conditions in MEF-CM (MEF-Conditioned Medium) on Matrigel-coated plates to maintain their undifferentiated state. Success of both culture conditions fully depends on the quality of the feeder cells, since they directly affect the growth of hESCs.
Here, we present an optimized method for the isolation and culture of mouse embryonic fibroblasts (MEFs), preparation of conditioned medium (CM) and enzyme-linked immunosorbent assay (ELISA) to assess the levels of Activin A within the media.

The quality of mouse embryonic fibroblasts (MEFs) is dictated by the right strain of mouse such as CF-1. Pluripotency-supportive MEFs and conditioned media (CM) obtained from these should contain optimal concentrations of Activin A, Gremlin and Tgf&beta;1 needed for the Activin/Nodal and FGF pathways to co-operatively maintain self-renewal and pluripotency.

In general, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs)1 can be cultured under variable conditions. However, it ...

Generation of Mice Derived from Induced Pluripotent Stem Cells

The production of induced pluripotent stem cells (iPSCs) from somatic cells provides a means to create valuable tools for basic research and may also produce a source of patient-matched cells for regenerative therapies. iPSCs may be generated using multiple protocols and derived from multiple cell sources. Once generated, iPSCs are tested using a variety of assays including immunostaining for pluripotency markers, generation of three germ layers in embryoid bodies and teratomas, comparisons of gene expression with embryonic stem cells (ESCs) and production of chimeric mice with or without germline contribution2. Importantly, iPSC lines that pass these tests still vary in their capacity to produce different differentiated cell types2. This has made it difficult to establish which iPSC derivation protocols, donor cell sources or selection methods are most useful for different applications.
The most stringent test of whether a stem cell line has sufficient developmental potential to generate all tissues required for survival of an organism (termed full pluripotency) is tetraploid embryo complementation (TEC)3-5. Technically, TEC involves electrofusion of two-cell embryos to generate tetraploid (4n) one-cell embryos that can be cultured in vitro to the blastocyst stage6. Diploid (2n) pluripotent stem cells (e.g. ESCs or iPSCs) are then injected into the blastocoel cavity of the tetraploid blastocyst and transferred to a recipient female for gestation (see Figure 1). The tetraploid component of the complemented embryo contributes almost exclusively to the extraembryonic tissues (placenta, yolk sac), whereas the diploid cells constitute the embryo proper, resulting in a fetus derived entirely from the injected stem cell line.
Recently, we reported the derivation of iPSC lines that reproducibly generate adult mice via TEC1. These iPSC lines give rise to viable pups with efficiencies of 5-13%, which is comparable to ESCs3,4,7 and higher than that reported for most other iPSC lines8-12. These reports show that direct reprogramming can produce fully pluripotent iPSCs that match ESCs in their developmental potential and efficiency of generating pups in TEC tests. At present, it is not clear what distinguishes between fully pluripotent iPSCs and less potent lines13-15. Nor is it clear which reprogramming methods will produce these lines with the highest efficiency. Here we describe one method that produces fully pluripotent iPSCs and "all- iPSC" mice, which may be helpful for investigators wishing to compare the pluripotency of iPSC lines or establish the equivalence of different reprogramming methods.

Generating induced pluripotent stem cell (iPSC) lines produces lines of differing developmental potential even when they pass standard tests for pluripotency. Here we describe a protocol to produce mice derived entirely from iPSCs, which defines the iPSC lines as possessing full pluripotency1.

The production of induced pluripotent stem cells (iPSCs) from somatic cells provides a means to create valuable tools for basic research and may also ...

Generation of Human Induced Pluripotent Stem Cells from Peripheral Blood Using the STEMCCA Lentiviral Vector

Through the ectopic expression of four transcription factors, Oct4, Klf4, Sox2 and cMyc, human somatic cells can be converted to a pluripotent state, generating so-called induced pluripotent stem cells (iPSCs)1-4. Patient-specific iPSCs lack the ethical concerns that surround embryonic stem cells (ESCs) and would bypass possible immune rejection. Thus, iPSCs have attracted considerable attention for disease modeling studies, the screening of pharmacological compounds, and regenerative therapies5.
We have shown the generation of transgene-free human iPSCs from patients with different lung diseases using a single excisable polycistronic lentiviral Stem Cell Cassette (STEMCCA) encoding the Yamanaka factors6. These iPSC lines were generated from skin fibroblasts, the most common cell type used for reprogramming. Normally, obtaining fibroblasts requires a skin punch biopsy followed by expansion of the cells in culture for a few passages. Importantly, a number of groups have reported the reprogramming of human peripheral blood cells into iPSCs7-9. In one study, a Tet inducible version of the STEMCCA vector was employed9, which required the blood cells to be simultaneously infected with a constitutively active lentivirus encoding the reverse tetracycline transactivator. In contrast to fibroblasts, peripheral blood cells can be collected via minimally invasive procedures, greatly reducing the discomfort and distress of the patient. A simple and effective protocol for reprogramming blood cells using a constitutive single excisable vector may accelerate the application of iPSC technology by making it accessible to a broader research community. Furthermore, reprogramming of peripheral blood cells allows for the generation of iPSCs from individuals in which skin biopsies should be avoided (i.e. aberrant scarring) or due to pre-existing disease conditions preventing access to punch biopsies.
Here we demonstrate a protocol for the generation of human iPSCs from peripheral blood mononuclear cells (PBMCs) using a single floxed-excisable lentiviral vector constitutively expressing the 4 factors. Freshly collected or thawed PBMCs are expanded for 9 days as described10,11 in medium containing ascorbic acid, SCF, IGF-1, IL-3 and EPO before being transduced with the STEMCCA lentivirus. Cells are then plated onto MEFs and ESC-like colonies can be visualized two weeks after infection. Finally, selected clones are expanded and tested for the expression of the pluripotency markers SSEA-4, Tra-1-60 and Tra-1-81. This protocol is simple, robust and highly consistent, providing a reliable methodology for the generation of human iPSCs from readily accessible 4 ml of blood.

Here we show a simple and effective protocol for the generation of human iPSCs from 3-4 ml of peripheral blood using a single lentiviral reprogramming vector. Reprogramming of readily available blood cells promises to accelerate the utilization of iPSC technology by making it accessible to a broader research community.

Through the ectopic expression of four transcription factors, Oct4, Klf4, Sox2 and cMyc, human somatic cells can be converted to a pluripotent state, ...

Generation of Human Cardiomyocytes: A Differentiation Protocol from Feeder-free Human Induced Pluripotent Stem Cells

In order to investigate the events driving heart development and to determine the molecular mechanisms leading to myocardial diseases in humans, it is essential first to generate functional human cardiomyocytes (CMs). The use of these cells in drug discovery and toxicology studies would also be highly beneficial, allowing new pharmacological molecules for the treatment of cardiac disorders to be validated pre-clinically on cells of human origin. Of the possible sources of CMs, induced pluripotent stem (iPS) cells are among the most promising, as they can be derived directly from readily accessible patient tissue and possess an intrinsic capacity to give rise to all cell types of the body 1. Several methods have been proposed for differentiating iPS cells into CMs, ranging from the classical embryoid bodies (EBs) aggregation approach to chemically defined protocols 2,3. In this article we propose an EBs-based protocol and show how this method can be employed to efficiently generate functional CM-like cells from feeder-free iPS cells.

Pluripotent stem cells, either embryonic or induced pluripotent stem (iPS) cells, constitute a valuable source of human differentiated cells, including cardiomyocytes. Here, we will focus on cardiac induction of iPS cells, showing how to use them to obtain functional human cardiomyocytes through an embryoid bodies-based protocol.

In order to investigate the events driving heart development and to determine the molecular mechanisms leading to myocardial diseases in humans, it is ...