CiRA | M&M

March 5, 2009

Generation of Human induced Pluripotent Stem Cells
Center for iPS Cell Research and Application (CiRA)
Institute for Integrated Cell-Material Sciences (iCeMS)
Kyoto University

In the first protocol (Ver.1, released on July 4th, 2008), we have introduced how toestablish human iPS cells using 4 reprogramming factors. In this revised protocol,
which we designate Protocol Version 2, we explain our protocol of human iPS cell
generation in a practical way focusing on problems we have encountered. A uniquestep is the introduction of mouse solute carrier family 7 (cationic amino acidtransporter, y+ system), member 1 (Slc7a1) gene encoding the ecotropic
retrovirus receptor into human cells. This step enables ecotropic retroviruses totransduce human cells. In this manuscript, we particularly put in
TROUBLESHOOTING, ANTICIPATED RESULTS and figures to make it easier tounderstand.

1. MATERIALS

1.1. Cells & Vectors
pMXs retroviral vectors and Plat-E packaging cells1
Available from Dr. Toshio Kitamura at the University of Tokyo(kitamura@ims.u-tokyo.ac.jp). Also purchasable from Cell biolabs, Inc.
(http://www.cellbiolabs.com/). pMXs consists of the 5’long terminal repeat (LTR)
and 3’LTR of Moloney Murine Leukemia Virus (MMLV). Plat-E cells were derived
from 293T cells and contain env-IRES-puroR and gag-pol-IRES-bsR cassettes driven
by the EF1-α promoter.
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pMXs containing cDNA of OCT3/4, SOX2, KLF4, or c-MYC
Available from addgene (http://www.addgene.org/Shinya_Yamanaka). We use apMXs retroviral vector encoding the green fluorescence protein (GFP) to monitor
tranfection efficiency. It also serves as a negative control for iPS cell induction.
pMXs vector encoding GFP can be purchased from Cell biolabs, Inc.

pLenti6/UbC containing mouse Slc7a1 gene
Available from addgene (http://www.addgene.org/Shinya_Yamanaka). This vector
was constructed by insertion of the mouse Slc7a1 gene into pLenti6/UbC/V5-DEST(Invitrogen) with the gateway technology. Mouse Slc7a1 gene is driven by thehuman Ubiquitin C promoter.

Human cells
Various primary human cells are available from the following resources:
Cell applications Inc. (http://www.cellapplications.com/)
Lonza (http://www.lonza.com/group/en.html)
American Type Culture Collection; ATCC (http://www.atcc.org/)
European Collection of Cell Cultures; ECACC (http://www.ecacc.org.uk/)
Riken Bioresource Center (http://www.brc.riken.jp/)
Japanese Collection of Research Bioresources (http://cellbank.nibio.go.jp/)

SNL feeder cells2
Available from Dr. Allan Bradley of the Sanger Institute(http://www.sanger.ac.uk/Teams/Team82/) or European Collection of Cell

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Cultures; ECACC (http://www.ecacc.org.uk). SNL cell is a subclone of STO cell andstably expresses the neomycin resistance and LIF genes.

293FT cells
This cell line can be purchased from Invitrogen. 293FT cell is a subclone of HEK
293T cell line. These cells allow higher gene expression from vectors containing thesimian virus 40 (SV40) replication origins because they constitutively express SV40
large T antigen.

1.2. Reagentsz

Dulbecco’s modified eagle medium contains 4.5 g/l glucose (DMEM;
14247-15, Nacalai tesque, Japan)z

Phosphate-buffered saline without calcium and magnesium (PBS; 14249-95,
Nacalai tesque, Japan)z

DMEM/F12 (10565-018, Invitrogen)z

Knockout serum replacement (KSR, 10828028, Invitrogen)z

L-glutamine (25030-081, Invitrogen)z

Non-essential amino acids solution (11140-050, Invitrogen)z

2-mercaptoethanol (21985-023, Invitrogen)z

Sodium pyruvate (S8636, Sigma)zPenicillin/streptomycin (15140-122, Invitrogen)zCollagenase IV (17104-019, Invitrogen), see REAGENT SETUPz

Recombinant basic fibroblast growth factor, human (bFGF, 064-04541,
WAKO, Japan), see REAGENT SETUP

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Y-27632 (253-00513, WAKO, Japan), see REAGENT SETUPz

Bovine serum albumin (810-661, ICN)z

2.5% Trypsin (15090-046, Invitrogen)z

0.25% Trypsin/1 mM EDTA solution (25200-056, Invitrogen)z

0.5% Trypsin/5.3 mM EDTA solution (25300-054, Invitrogen), see
REAGENT SETUPz

Gelatin (G1890, Sigma), see REAGENT SETUPz

G418 sulfite, 50 mg/ml solution (10131-035, Invitrogen)z

Puromycin (P7255, Sigma), see REAGENT SETUPz

Blasticidin S hydrochloride (KK-400, Funakoshi, Japan) , see REAGENT
SETUP

z

Virapower Lentiviral expression system (K4990-00, Invitrogen)z

Fugene 6 transfection reagent (1 814 443, Roche)z

Lipofectamine 2000 (11668-019, Invitrogen)z

OPTI-MEM I (31985-062, Invitrogen)z

Hexadimethrine Bromide (Polybrene; 17736-44, Nacalai tesque, Japan) ,see REAGENT SETUPz

Acetamide (015-00115, WAKO, Japan), see REAGENT SETUPz

Propylene glycol (164-04996, WAKO, Japan)zDimethyl sulfoxide (D2650, Sigma)z

Human ES medium, see REAGENT SETUPz

SNL medium, see REAGENT SETUPz

293FT medium, see REAGENT SETUPz

FP medium (for fibroblasts and Plat-E cells) , see REAGENT SETUP

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Povidone iodine (Isodine solution, Meiji Seika, Japan)z

Lidocaine (1% Xylocaine, Astrazeneka)

2. REAGENT SETUP
Gelatin-coated culture dishes
Gelatin stock is prepared as 10 x concentration (1% w/v) stocks. Dissolve 1 g ofgelatin powder in 100 ml of distilled water, autoclave and store at 4oC. To prepare
0.1% (1 x) gelatin solution, thaw the 10 x gelatin stock by microwave, add 50 ml ofthis to 450 ml of distilled water. Filter the solution with a bottle-top filter (0.22 μm)
and store at 4oC.
To coat a culture dish, add enough volume of 0.1% gelatin solution to cover theentire area of the dish bottom. For example, 1, 3 or 5 ml of gelatin solution is used
for a 35, 60 or 100 mm dish, respectively. Incubate the dish for at least 30 min at
37oC. Before using, aspirate excess gelatin solution.

0.05% Trypsin / 0.53 mM EDTA solution
To prepare 0.05% Trypsin / 0.53 mM EDTA, dilute 10 ml of 0.5% Trypsin/5.3 mM
EDTA solution with 90 ml of PBS. To prepare 0.1% Trypsin/1 mM EDTA, add 20 mlof 0.5% Trypsin/5.3 mM EDTA to 80 ml of PBS. Aliquot and store at -20oC.

2 x Freezing medium
Mix 2 ml of DMSO, 2ml of FBS and 6 ml of DMEM, and sterilize through a 0.22 μm
filter.

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Puromycin
Dissolve in distilled water at 10 mg/ml and sterilize through a 0.22 μm filter. Aliquot
and store at -20oC.

Blasticidin S hydrochloride
Dissolve in distilled water at 10 mg/ml and sterilize through a 0.22 μm filter. Aliquot
and store at -20oC.

Hexadimethrine Bromide (Polybrene)
Dissolve 0.8 g of polybrene in 10 ml of distilled water for a 10 x stock (80 mg/ml).
Dilute 1 ml of 10 x stock solution with 9 ml of distilled water, and filter with a 0.22
μm filter. Store at 4oC.

Recombinant basic fibroblast growth factor, human
To prepare PBS containing 0.1% bovine serum albumin (BSA), add 50 μl of 10%
BSA into 5 ml of PBS. Dissolve 50 μg of bFGF in 5 ml of PBS containing 0.1% BSA(10 μg/ml). Aliquot and store at -20oC.

Y-27632
Dissolve 5 mg of Y-27632 in 1.48 ml of distilled water (10 mM). Aliquot and store at-20oC.

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1 mg/ml collagenase IV
Dissolve 10 mg of collagenase IV in 10 ml of distilled water, and through with a 0.22
μm pore filter. Aliquot and store at -20oC.

0.1 M CaCl2
Dissolve 0.11 g of CaCl2 in 10 ml of distilled water, and through with a 0.22 μm porefilter.

Store at 4oC.

CTK solution
Add 5 ml of 2.5% trypsin, 5 ml of 1 mg/ml collagenase IV, 0.5 ml of 0.1 M CaCl2 and
10 ml of KSR into 30 ml of distilled water. Store at -20oC. Avoid repeated freezing
and thawing.

10 M acetamide
Dissolve 5.9 g of acetamide in 10 ml of distilled water. Store at room temperature.

DAP213 solution
Add 1.43 ml of DMSO, 1 ml of 10 M of acetamide and 2.2 ml of propylene glycol into
5.37 ml of human ES medium. Store at -80oC.

Human ES medium
DMEM/F12 containing 20% KSR, 2 mM L-glutamine, 1 x 10-4 M non essential aminoacids, 1 x 10-4 M 2-mercaptoethanol, and 50 units and 50 mg/ml penicillin andstreptomycin. To prepare 500 ml of the medium, mix 100 ml of KSR, 5 ml of

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L-glutamine, 5 ml of non-essential amino acids, 1 ml of 2-mercaptoethanol and 2.5
ml of penicillin/streptomycin, and then fill to 500 ml with DMEM/F12. Add 0.2 ml of
10 μg/ml basic fibroblast growth factor (bFGF) into 500 ml of the medium before
use. Store at 4oC up to a week.

293FT medium
DMEM containing 10% FBS, 2 mM L-glutamine, 1 x 10-4 M non essential amino acids,
1 mM sodium pyruvate, and 50 units and 50 mg/ml penicillin and streptomycin. To
prepare 500 ml of the medium, mix 50 ml of FBS, 5 ml of L-glutamine, 5 ml of
non-essential amino acids, 5 ml of sodium pyruvate and 2.5 ml of
penicillin/streptomycin, and then fill to 500 ml with DMEM.

Store at 4oC up to a

week. Add 0.1 ml of 50 mg/ml G418 into 10 ml 293FT medium.

SNL medium
DMEM containing 7% FBS, 2 mM L-glutamine, and 50 units and 50 mg/ml penicillin
and streptomycin. To prepare 500 ml of the medium, mix 35 ml of FBS, 5 ml of
L-glutamine and 2.5 ml of penicillin/streptomycin, and then fill up to 500 ml with
DMEM. Store at 4oC up to a week.

FP medium (for fibroblasts and Plat-E cells)
DMEM containing 10% FBS, and 50 units and 50 mg/ml penicillin and streptomycin.
To prepare 500 ml of FP medium, mix 50 ml of FBS and 2.5 ml of
penicillin/streptomycin, and then fill up to 500 ml with DMEM. Store at 4oC up to a

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week. For Plat-E cells, add 1 μl of 10 mg/ml puromycin stock and 10 μl of 10 mg/ml
blastcidin S into 10 ml of FP medium.

3. EQUIPMENTz

Needlez

Thread (4-0 or 5-0 nylon)zScissorsz

Tweezersz

Forcepsz

100 mm tissue culture dish (353003, Falcon)z

6-well tissue culture plate (353046, Falcon)z

24-well tissue culture plate (353047, Falcon)z

96-well tissue culture plate (351172, Falcon)z

15 ml conical tube (352196, Falcon)z

50 ml conical tube (352070, Falcon)z

1 ml plastic disposable pipette (357520, Falcon)z

5 ml plastic disposable pipette (357543, Falcon)z

10 ml plastic disposable pipette (357551, Falcon)z

25 ml plastic disposable pipette (357525, Falcon)z0.22 µm pore size filter (Millex GP, SLGP033RS, Millipore)z0.45 µm pore size cellulose acetate filter (FP30/0.45 CA-S, Schleicher &Schuell)z

10 ml disposable syringe (SS-10ESZ, Terumo, Japan)z

Coulter counter (Z2, Beckman Coulter)9 / 35Center for iPS Cell Research and Application, iCeMS, Kyoto University

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CO2 incubatorz

Cell scraper (9000-220, IWAKI)z

Pipette aid (Falcon)z

Pipetman and tips (GILSON)z

2 ml cryovials (72. 694. 006, SARSTEDT)

4. PROCEDURE
4.1. Preparation of fibroblasts (biopsy as an example in thisprotocol)Prepare primary human fibroblasts from skin biopsy specimens or purchase cells
from vendors.
CAUTION: Prior to skin biopsy, proper informed consent should be obtained fromdonors.

4.1.1.Biopsy
1. Disinfect skin surface three times with povidone iodine.
2. Administer lidocaine as a local anesthesia.
3. Push and twist a disposable biopsy punch against the skin. Deep enough toreach the fatty layer of subcutaneous tissue.
4. Raise the biopsy punch and cut the tissue away from the donor.
5. Using tweezers, put the tissue into a 50 ml conical tube containing 10 ml of FP
medium.
6. Suture the incision.

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4.1.2.Establishment of human skin fibroblasts; TIMING 1 month
7. Transfer the skin biopsy sample to a 100 mm dish, and cut it into 1 mm pieces
by using sterile scissors.
8. Transfer them to a 35 mm dish (or a well of 6-well plate) with sterile forceps.
9.

Put the coverslip onto the tissues, and then add 2 ml of FP medium into thedish.

10. Incubate at 37oC, 5% CO2. Leave the dish untouched for a week, and laterchange the medium twice a week.
NOTE: Generally, you may be able to see the fibroblastic cells at the edge of tissues
under the coverslip.
11. When cells cover 30~50% of the dish, it’s time to transfer the cells to a larger
dish (3~4 weeks from started).

4.1.3.Passage of fibroblasts; TIMING 0.5 hour
12. Aspirate the medium and wash once with PBS.
13. Add 0.3 ml of 0.05% Trypsin / 0.53 mM EDTA, and incubate the dish at 37oC for
10 minutes.
14. Neutralize by addition of 3 ml of FP medium, and transfer the cell suspension to
a 15 ml conical tube.
15. Count the cells and plate them at 3 x 105 cells to per 60 mm dish. When the cells
become confluent, passage the cells to a 100 mm dish in the same manner.
NOTE: If the cell number is greater than 5 x 105, plate the cells onto a 100 mm dish.
If it is lower, seed the cells onto a 60 mm dish.

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4.1.4.Making frozen stocks of fibroblasts; TIMING 0.5 hour
When fibroblasts become confluent on a 100 mm dish, you should make frozen
stocks.
16. Aspirate off the medium and wash with PBS.
17. Add 1 ml of 0.05% Trypsin/0.53 mM EDTA, and incubate the dish at 37oC for 10
min.
18. Add 9 ml of FP medium, suspend by pippeting up and down, and transfer thecell suspension to a 15 ml conical tube.
19. Count cell number, and spin the cells at 160 g for 5 minutes.
20. Aspirate off the supernatant, and add appropriate amount of FP medium toadjust concentration to 1 x 106 cells/ml.
21. Add same amount of 2 x freezing medium to cell suspension, mix gently by
pippeting up and down.
22. Aliquot 1 ml of cell suspension to per cryovial.
23. Transfer the tubes into a freezing container, and keep it in a -80oC freezer
overnight.
PAUSE POINT: Fibroblasts can be stored at -80oC in short term.

For long term

storage, keep them in the gas phase of a liquid nitrogen tank.

4.1.5.Thawing fibroblasts; TIMING 0.5 hour
If you use fibroblasts obtained from cell banks or vendors, here is a starting point.
24. Prepare 9 ml of FP medium in a 15 ml conical tube.
25. Take a vial of frozen fibroblasts from the liquid nitrogen tank and put the vial
into 37oC water bath until most (but not all) cells are thawed.

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26. Wipe the vial with ethanol, open the cap, and transfer the cell suspension to thetube prepared in step 24.
27. Centrifuge at 160 g for 5 minutes, and then discard the supernatant.
28. Re-suspend the cells with 10 ml of FP medium, and transfer to a 100 mm dish(at least 5 x 105 cells/dish). Incubate the cells in a 37oC, 5% CO2 incubator,
until the cells become 80~90% confluent. Change the medium every other day.

4.1.6.Passaging fibroblasts; TIMING 0.5 hour
29. Discard the medium and wash the cells once with PBS.
30. Aspirate PBS, add 1 ml per dish of 0.05% trypsin/0.53 mM EDTA, and incubate
for 10 minutes at 37oC.
31. Add 9 ml of FP medium, and break up the cells into a single cell suspension by
pipetting up and down several times.
32. Adjust the cell suspension to 40 ml by addition of FP medium, and transfer todishes (10 ml per 100 mm dish). This splits the cells 1:4. Incubate the cells at
37oC, 5% CO2 until the cells become 80~90% confluent (approximately 2 x 106
cells per 100 mm dish, Fig. 2a). It commonly takes 4~5 days after passage.
CRITICAL STEP: We recommend 1:3~1:4 split ratio. Lower density would induce
replicative senescence. Older fibroblasts may not be suitable for generation of iPS
cells, because transduction efficiency of retrovirus is quite low (Fig. 2b).

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4.2. Lentivirus production
CAUTION: The experiment using lentivirus should be performed in a safety cabinet.
Wear a designated lab coat and gloves. Wastes should be treated withhypochlorous acid and following ethanol, and then autoclaved.

4.2.1.Passaging 293FT cells; TIMING 0.5 hour
33. Aspirate the medium and wash the cells with PBS.
34. Add 1 ml of 0.25% trypsin/1 mM EDTA and incubate the dish for 2 min at room
temperature.
35. Add 10 ml of the medium and dissociate the cells by pipetting up and down
(about 10 times)
36. Collect the cell suspension into a 15 ml conical tube, and count the cell number.
37. Adjust the concentration to 4 x 105 cells per milliliter with 293FT medium
without antibiotics. Seed cells at 4 x 106 cells (10 ml) per 100 mm dish, andincubate overnight at 37oC, 5% CO2.

4.2.2.Transfection to 293FT cells; TIMING 1 hour
38. Dilute 9 μg of Virapower packaging mix (pLP1, pLP2 and pLP/VSVG mixture)and 3 µg of pLenti6/UbC encoding the mouse Slc7a1 gene in 1.5 ml of
OPTI-MEM I, and mix gently by finger tapping.
39. In a separate tube, dilute 36 µl of Lipofectamine 2000 in 1.5 ml of OPTI-MEM I.
Mix gently by finger tapping and incubate for 5 min at room temperature.
40. After incubation, combine the diluted DNA with the diluted Lipofectamine 2000.
Mix gently by finger tapping and incubate for 20 min at room temperature.

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March 5, 200941. During incubation, remove the medium from 293FT dishes, and add 9 ml offresh medium to each dish.
42. Then add 3 ml of the DNA-Lipofectamine 2000 complexes in each dish. Mix
gently by rocking the dish back and forth. Incubate the dish overnight at 37oC,
5% CO2.
43. Twenty four hours after transfection, aspirate the medium containing thetransfection cocktail, and add 10 ml of fresh FP medium. Incubate the dishovernight at 37oC, 5% CO2.

4.2.3.Collection of virus-containing supernatant; TIMING 0.5 hour
44. Forty eight hours after transfection, collect the supernatant of the 293FT
culture with a 10 ml disposable syringe, and then filtrate it with a 0.45 µm poresize cellulose acetate filter.
PAUSE POINT: The lentivirus-containing medium can be stored at -80oC. Do notrepeat freeze/thaw cycles to avoid the reduction of viral titer.

4.3. Lentiviral infection
4.3.1.Seeding fibroblasts; TIMING 1 hour
45. Aspirate the medium and wash the cells with PBS.
46. Add 1 ml of 0.05% trypsin/0.53 mM EDTA and incubate the dish for 10 min at
37oC.
47. Add 9 ml of FP medium and dissociate the cells by pipetting up and down.
48. Collect the cell suspension into a conical tube. Count the cell number. Adjust
the concentration to 8 x 104 cells/ml by adding appropriate volume of FP

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medium.
49. Seed the cells at 8 x 105 cells (10 ml of cell suspension) per 100 mm dish.
Incubate overnight at 37oC, 5% CO2.

4.3.2.Transduction of fibroblasts; TIMING 0.5 hour
50. Replace medium with 10 ml/dish of the virus-containing supernatant,
supplemented with 4 μg/ml polybrene. Incubate the dishes for 5 hours toovernight at 37oC, 5% CO2 (See TROUBLE SHOOTING).
51. Twenty four hours after transduction, aspirate off the virus-containing medium,
wash cells once with 10 ml of PBS (optional), and add 10 ml of fresh FP medium.
CRITICAL POINT: Three to 5 days after infection, transgene expression of lentivirus
should reach the maximum level.
PAUSE POINT: You may use the cells immediately or freeze them at -80oC for
storage.

4.4. Preparation of SNL feeder cells
4.4.1.Thawing SNL cells; TIMING 0.5 hour
52. Prepare 9 ml of SNL medium in a 15 ml conical tube.
53. Remove a vial of frozen SNL cells from the liquid nitrogen tank and put the vial
into 37oC water bath until most (but not all) cells thawed.
54. Wipe the vial with ethanol, open the cap, and transfer the cell suspension to thetube prepared in step 52. Pipet up and down several times to mix.
55. Centrifuge at 160 g for 5 minutes, and then discard the supernatant.
56. Re-suspend the cells with 10 ml of SNL medium, and transfer to a

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gelatin-coated 100 mm dish. Incubate the cells in a 37oC, 5% CO2 incubator,
until the cells become 80~90% confluent. This usually take 3~4 days.
CRITICAL STEP: Do not let the cells get over-confluent, or their ability as feeder
cells might deteriorate.

4.4.2.Passage of SNL cells; TIMING 0.5 hour
57. Discard medium and wash the cells once with PBS.
58. Aspirate PBS, and add 0.5 ml per 100 mm dish of 0.25% trypsin/1 mM EDTA,
and incubate for 1 minute at room temperature.
59. Add 4.5 ml of SNL medium, and break up the clumps of cells into a single cellsuspension by pipetting up and down several times.
60. Adjust the volume to 160 ml by adding SNL medium, and transfer togelatin-coated dishes (10 ml per 100 mm dish). This splits the cells 1:16.
Incubate the cells at 37oC, 5% CO2 until the cells become 80-90% confluent.
This should take 3~4 days after passage.

4.4.3.Mitomycin C-inactivation of SNL cells; TIMING 3 hours
61. Add 0.3 ml of 0.4 mg/ml mitomycin C solution directly to the culture medium of
SNL dish, swirl it briefly, and incubate 2.25 hours at 37oC, 5% CO2. The final
concentration of mitomycin C will be 12 μg/ml.
62. After incubation, aspirate the mitomycin C-containing medium off the cells, andwash the cells twice with 10 ml of PBS.
63. Aspirate off PBS, add 0.5 ml of 0.25% trypsin/1 mM EDTA, swirl to cover theentire surface, and let sit for 1 minute at room temperature.

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64. Neutralize the trypsin by adding 5 ml of SNL medium, and break up the clumpsof cells to a single cell suspension by pipetting up and down. Pour the cellsuspension into a 50 ml conical tube and count the cell number. Seed the cells
at 1.5 x 106 cells per 100 mm dish, or at 2.5 x 105 cells per well of 6-well plate.
65. Cells should be well spread with space between each other. They should
become ready for usage of the next day.
PAUSE POINT: The mitomycin C-treated SNL dishes can be left for up to three days
before use. In addition, you can make frozen stocks of mitomycin C-treated SNL
cells with a standard technique at -80oC or in vapor phase of liquid nitrogen tank.
These stocks should be woken up in a gelatin-coated dish or plate within the 3 days
before use.
CRITICAL POINT: Old SNL feeder (over three days after mitomycin C-treatment)
may come off from the dish during over three weeks of iPS cell generation.

4.5. Preparation of Plat-E cells
4.5.1.Thawing Plat-E cells; TIMING 0.5 hour
66. Prepare 9 ml of FP medium in a 15 ml conical tube.
67. Take out a vial of frozen stocks from the liquid nitrogen tank and put the vial ina 37oC water bath until most (but not all) cells are thawed.
68. Wipe the vial with ethanol, open the cap, and transfer the cell suspension to a
tube prepared in step 66.
69. Centrifuge at 180 g for 5 minutes, and then discard the supernatant.
70. Resuspend the cells with 10 ml of FP medium, and transfer to a 100 mm dish.
Incubate the cells in a 37oC, 5% CO2 incubator.

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71. Next day, replace the medium with new media supplemented with 1 µg/ml ofpuromycin and 10 µg/ml of blastcidin S. Continue to incubate the cells in a 37oC,
5% CO2 incubator until 80~90% confluent.

4.5.2.Passage of Plat-E cells; TIMING 0.5 hour
72. Wash the cells with PBS, add 4 ml per dish of 0.05% trypsin/0.53 mM EDTA,
and incubate for 1 minute at room temperature. Detach cells from dishes bytapping, resuspend with 10 ml FP medium, and transfer to a 15 ml conical tube.
Centrifuge it at 180 g for 5 minute, and aspirate the supernatant.
73. Add appropriate volume of FP medium, and break up the cells into a single cellsuspension by pipetting up and down several times. Seed them on new 100 mm
dishes at 1:4~1:6 dilution. Cells should become confluent within 2-3 days.

4.6. Generation of iPS cells
4.6.1.Day 1 Plat-E preparation; TIMING 1 hour
74. Wash the cells with PBS, add 4 ml of 0.05% trypsin/0.53 mM EDTA, andincubate for 1 minute at room temperature.
75. After incubation, add 10 ml FP medium into the Plat-E dish, suspend the cells by
gently pippeting, and transfer the cell suspension to a 50 ml conical tube. FP
culture medium used in this period contains neither puromycin nor blasticidin S.
76. Centrifuge the cells at 180 g for 5 minutes.
77. Discard the supernatant, break the pellet by finger tapping, and resuspend thecells in an appropriate amount of FP medium.
78. Count cell number and adjust the concentration to 3.6 x 105 cells/ml with FP

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medium.
79. Seed cells at 3.6 x 106 cells (10 ml) per 100 mm dish, and incubate overnight at
37oC, 5% CO2.

4.6.2.Day 2 Retrovirus production; Transfection into Plat-E cells; TIMING 1
hour
80. Transfer 0.3 ml of OPTI-MEM I into a 1.5 ml tube.
81. Deliver 27 μl of Fugene 6 transfection reagent into the prepared tube in step 80,
mix gently by finger tapping, and incubate for 5 minutes at room temperature.
82. Add 9 μg of pMXs plasmid DNA (respectively encoding Oct3/4, Sox2, Klf4, andc-Myc) drop-by-drop into the Fugene 6/OPTI-MEM I containing tube, mix gently
by finger tapping, and incubate for 15 minutes.
CRITICAL POINT: Introduce one plasmid into one dish. Transfection of more than
two plasmids into a dish causes reduction of efficiency of iPS cell generation.
83. Add the DNA/Fugene 6 complex drop-wise into the Plat-E dish, and incubate
overnight at 37oC, 5% CO2.
CRITICAL STEP: Also transfect with a suitable control; we use pMXs retroviral
vector GFP to monitor transfection efficiency. We routinely obtain efficiency morethan 80%. High efficient transfection is crucial for iPS cell induction.

4.6.3.Day 3 Retrovirus production (continued); TIMING 0.5 hour
84. Aspirate the transfection reagent-containing medium, add 10 ml of fresh FP
medium, and return the cells to the incubator.

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4.6.4.Preparation of fibroblasts; TIMING 1 hour
85. When human fibroblasts expressing mouse Slc7a1 gene from Step 51 reach to80~90% confluence (Fig. 3), aspirate medium and wash once with 10 ml of
PBS.
86. Discard PBS, add 1 ml per dish of 0.05% trypsin/0.53mM EDTA, and incubate at
37oC for 10 minutes.
87. Add 9 ml of the FP medium per plate, suspend the cells to a single cell by
pipetting, and transfer to a 50 ml conical tube.
88. Count cell numbers, which should be ~2 x 106 cells per dish. Adjust theconcentration to 8 x 104 cells/ml with FP medium. Transfer 10 ml of cellsuspension (8 x 105 cells) per 100 mm dish. Incubate the dish overnight at 37oC,
5% CO2.

4.6.5.Day 4 Retroviral infection; TIMING 0.5 hour
89. Forty eight hours post-transfection, collect the medium from each Plat-E dishby using a 10 ml sterile disposable syringe, filtering it through a 0.45 μm poresize cellulose acetate filter, and transferring into a 15 ml conical tube.
90. Add 5 μl of 8 mg/ml polybrene solution into the filtrated virus-containing
medium, and mix gently by pipetting up and down. The final concentration of
polybrene is 4 μg/ml.
91. Make a mixture of equal parts of the medium containing OCT3/4-, SOX2-,KLF4- and c-MYC-retroviruses.
CRITICAL STEP: RETROVIRUSES SHOULD BE USED FRESHLY! DO NOT FREEZE,
OR YOU WON'T OBTAIN iPS CELLS. The titer of retrovirus is critical for iPS cell

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generation. The titer of retrovirus used in our study is approximately 5 x 106
TU/ml (determined in NIH3T3 cells). The freeze/thaw step decreases the titer ofretrovirus.
92. Aspirate the medium from fibroblast dishes, and add 10 ml per dish of the
polybrene/virus-containing medium. Incubate the cells from 4 hours toovernight at 37oC, 5% CO2.

4.6.6.Day 5 TIMING 5 min.
93. After 4 hours ~ overnight culture, aspirate the medium from the transdued
fibroblasts, and add 10 ml per dish of fresh FP medium.

4.6.7.Day 6~10 TIMING 5 min each day.
94. Discard the medium, and add 10 ml per dish of FP medium.
CRITICAL POINT: At day 8~10, prepare mitomycin C-treated SNL feeder cells (seestep 61-65)

4.6.8.Day 11 Replating transduced fibroblasts onto mitomycin C-treated
SNL feeder. TIMING 1 hour
95. Aspirate the culture medium and wash with 10 ml per dish of PBS.
96. Discard PBS, add 1 ml per dish of 0.05% trypsin/0.53mM EDTA, and incubate at
37oC for 10 minutes.
97. Add 9 mlper dish of FP medium, suspend the cells to a single cell, and transfer
to a 50 ml conical tube.
98. Count cell numbers, and adjust the concentration to 5 x 103 or 5 x 104 cells / ml.

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Transfer 10 ml of cell suspension (5 x 104 or 5 x 105 cells) per 100 mm dish withmitomycin C-treated SNL cells. Incubate the dishes overnight at 37oC, 5% CO2(See TROUBLE SHOOTING).

4.6.9.Day 12~ TIMING 5 min per day
99. Replace the medium with 10 ml of human ES medium. Change the medium
every other day until the colonies become large enough to be picked up.
Colonies should become visible 2~3 weeks after the retroviral infection. They
can be picked up at around day 30 when they become large enough (visible by
the naked eyes, Fig. 4d) ..

4.6.10.

Picking up the iPS colonies; TIMING 1 hour

100.

Aliquot 20 μl of human ES medium per well in 96-well plate.

101.

Remove the medium from the dishes with iPS colonies, and add 10 ml per

dish of PBS.
102.

Aspirate PBS, and add 5 ml per dish of PBS.

103.

Pick colonies from the dish under the stereomicroscope using a P2 or P10
Pipetman set at 2 μl, and transfer it into the 96-well plate prepared in Step

101. We usually pick up 6~12 colonies for a subject.
104.

When colony picking is finished, add 180 μl of human ES medium to eachwell, and pipet up and down to break up the colony to small clumps (20~30
cells) carefully under the stereomicroscope.

105.

Transfer cell suspension into 24-well plates with mitomycin C-treated SNL
feeder cells, add 300 μl per well of human ES medium, and incubate in a

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37oC, 5% CO2. incubator until the cells reach 80~90% confluence. This usuallytakes ~7 days. At this point they should be passaged into 6-well plates.
CRITICAL POINT: Do not break up the cell clumps to single cells (See also TROUBLESHOOTING).

4.6.11.

Passaging of iPS cells; TIMING 0.5 hour

106.

Aspirate culture medium, and wash the cells with 0.5 ml per well of PBS.

107.

Completely remove PBS, add 0.1 ml per well of CTK solution and incubate at
37oC for 2~5 minutes. When feeder cells are removed from the plate while
iPS colonies still attach, go to Step 108.

CAUTION: Incubation time may depend on cell density. Please check the cells by
your eyes every minute.
108.

Aspirate off CTK solution, and add 0.5 ml per well of PBS.

109.

Aspirate off PBS, and add 0.5 ml of PBS.

110.

Remove PBS completely. Most of feeder cells can be removed by these PBS
washings.

Add 0.5 ml of human ES medium and suspend the cells to small

clumps of 20~30 cells by pipetting up and down.
111.

Transfer the cell suspension to a well of 6-well plates with mitomycin
C-treated SNL feeder cells, add 1.5 ml of human ES medium, and incubate
in a 37oC, 5% CO2 incubator until cells become 80~90% confluent in 6-wellplates. Change the medium every day.

4.6.12.
112.

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Expansion of iPS cells; TIMING 0.5 hour

Aspirate the medium, and wash the cells with 2 ml/well of PBS.

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113.

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Remove PBS completely, add 0.5 ml per well of CTK solution and incubate
at 37oC for 2~5 minutes.

CAUTION: Incubation time may depend on cell density. Please check the cells by
your eyes every minute.
114.

Aspirate off CTK solution, and add 2 ml per well of PBS.

115.

Aspirate off PBS, and add 2 ml per well of PBS.

116.

Remove PBS completely, add 2 ml of human ES medium.

117.

Detach iPS cells by using cell scraper and break up the colonies to small
clumps by pipetting up and down.

118.

Transfer the cell suspension to a 60 mm dish with SNL feeder. Add 2 ml
human ES medium, and incubate in a 37oC, 5% CO2 incubator until cells
reach 80~90% confluence. The cells should be passaged to a 100 mm
dish with the same manner.

4.6.13.

Preparation of freeze stock; TIMING 0.5 hour

When iPS cells reach 80~90% confluence in 100 mm dishes, frozen stocks should
be prepared.
119.

Before making frozen stocks, add 10 μl of 10 mM Y-27632, which is a
specific inhibitor of p160-Rho-associated coiled-coil kinase (ROCK), to eachdish (final concentration,10 μM), and incubate at 37oC for 1 hour.

120.

Aspirate the medium, and wash the cells with 10 ml of PBS.

121.

Remove PBS thoroughly, add 1 ml of CTK solution and incubate at 37oC for
2~5 minutes.

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March 5, 2009CAUTION: Incubation time may depend on cell density. Please check the cells by
your eyes every minute.
122.

Aspirate off CTK solution, and wash twice with 10 ml per dish of PBS.

123.

Remove PBS thoroughly. Add 12 ml of human ES medium. Detach colonies
from dish by using cell scraper and transfer cell suspension to three 15 ml
conical tubes (4 ml each).

124.

Spin at 160 g for 5 minutes.

125.

Remove the supernatant.

126.

Suspend the pellet in 0.2 ml per tube of DAP213 solution by several times of
pipetting.

CAUTION: Do not break up the colonies.
127.

Transfer 0.2 ml of the cell suspension to freeze vials.

128.

Put the vials quickly into liquid nitrogen.

CRITICAL STEP: Step 126~128 should be performed within 15 seconds for goodcell viability.
PAUSE POINT: For long-term storage, store frozen cells in the gas phase of a liquid
nitrogen tank.

4.6.14.
129.

Waking up freeze stock; TIMING 0.5 hourPrepare 10 ml of pre-warmed (37oC) human ES medium in 15 ml conical
tubes

130.

Take frozen stocks of iPS cells out from liquid nitrogen tank.

131.

Add 0.8 ml of human ES medium prepared in Step 129 into each vial offrozen stocks, and thaw quickly by pippeting up and downfor 2~3 times

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with P1000 pippetman.
132.

Transfer the cell suspension to the tube prepared in Step 129.

133.

Spin at 160 g for 5 minutes.

134.

Aspirate off the supernatant, and add 4 ml of human ES medium.

135.

Transfer the cell suspension to 60 mm dishes seeded with mitomycin
C-treated SNL feeder, and incubate in a 37oC, 5% CO2 incubator until cells
reach 80~90% confluence. Do not move the dish for 48 hours. Change themedium every day from day 2.

CRITICAL POINT: For the viability of the iPS cells, Step 130~132 should be as quickas possible. Do not break up cell clumps to single cells.

TROUBLESHOOTINGPROBLEM
Fibroblasts die or do not grow well after lentiviral transduction.
SOLUTION
In some cases, lentivirus is toxic to fibroblasts. This problem should be overcome
by doubling dilution of the supernatant with the fresh medium or shorting exposure
time from overnight to 5 hours.

PROBLEM
No ES-like colonies appear from fibroblast cultures after induction by the four
factors.
SOLUTION
Good preparation of retroviruses is ESSENTIAL. Viruses must be prepared freshly.
DO NOT FREEZE.

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Passage numbers of fibroblast is also critical for iPS generation. Efficiency ofretroviral transduction markedly decreases in older fibroblasts. We recommend
using fibroblasts within passage 8 for iPS production.
When seeding retrovirally transduced fibroblasts onto feeder cells, cell density is
critical for iPS cells generation. Overgrowth of fibroblasts inhibits generation of iPS
cell colonies. On the other hand, if the cell number is too low, no colonies emerge.
Optimal cell densities are different for each fibroblast culture. Two to three different
densities should be tested.

PROBLEM
Isolated clone has an abnormal karyotype or is not pluripotent.
SOLUTION
We recommend to expand multiple clones.

PROBREM
Characters and potentials of iPS cell change during culture.
SOLUTION
Frozen stocks should be prepared at early passages (within passage number 15).

PROBLEM
Cells detach from the bottoms of culture dishes during iPS cell generation.
SOLUTION
This can be caused by two reasons. First, feeder cells may be too old. We
recommend to use SNL feeder cells within 3 days after mitomycin C-treatment.

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Another possibility is that cell density may be too high when reseeding transduced
cell onto feeder cells. Overgrowth of fibroblasts may result in peeling off from theedge of the dish.

PROBLEM
The viability of iPS cells is too low after passage or thawing. .
SOLUTION
Dissociation to single cells decreases the viability of iPS cells. Break colonies tosmall clumps of 20~30 cells.

PROBLEM
iPS cells spontaneously differentiate.
SOLUTION
In someiPS cells can be unstable during early passages. During the passaging
procedures, you can remove the differentiated colonies by aspirating and transfer
only undifferentiated colonies to a new dish. In addition, the qualities of feeder cells,such as density and freshness, are quite important

ANTICIPATED RESULTS
When 293FT cells produced lentivirus, they become multinucleated (Fig. 3a,b). More than 90% of human fibroblasts can be infected with this lentivirus
preparation (Fig. 3 c, d).

And the transduction efficiency of subsequent retroviral

infection can reach to more than 60% (Fig. 3e, f). The infection efficiency can beevaluated by analyzing GFP-infected cells with a flow cytometer. The morphology of

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March 5, 2009human dermal fibroblasts starts to change ~6 days after the introduction of
OCT3/4, SOX2, KLF4 and c-MYC (Fig. 4a).
From 5 x 104 adult human fibroblasts that are commercially available (Cellapplications Inc.), we usually observe more than 100 of non ES-like colonies
around day 10 after retroviral transduction (Fig. 4b). In contrast, ~10 ES-likecolonies emerge from 5 x 104 fibroblasts by day 30 after retroviral infection (Fig. 4c,d). However, these numbers vary greatly among fibroblast cultures, since they are
different in proliferation, retroviral transduction efficiency, and iPS cell generation
efficiency. If the density of fibroblasts or the efficiency of iPS cell generation is too
high, the dishes will be covered with numerous non-ES like cells and no iPS cellcolony emerges (Fig. 4e).
Most, although not all, of clones can be established as iPS cell lines, whichshow similar proliferation, morphology, and gene expression to human ES cells (Fig.
4f). The average success rate is 60~100%. Most clones also express
undifferentiated ES cell surface antigen, SSEAs and TRAs, and are positive foralkaline phosphatase activity. Differentiation potentials of human iPS cells can beevaluated by the methods established for human ES cells, such as embryonic bodyformation and teratoma experiments.
CTK solution developed by Dr. Suemori’s group is suitable for passaging
human iPS cells3. The treatment makes feeder cells detach from the culture plate
faster than iPS cells (Fig. 4g). Simple washing with PBS can remove floating feeder
cells (Fig. 4h). After washing, remaining human iPS cells can be collected by
pipetting (Fig. 4i). We routinely passage human iPS cells once a week at a ratio of
1:3 or 1:4 (Fig. 4 j, k, l). We normally prepare three vials of frozen stocks per 100

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mm dish, with DAP213 solution3. Pretreatment with Y-27632 improves viability4.
When one vial of stock is waken up on a 60 mm dish with mitomycin C-treated SNL
feeder, cells become confluent in ~7 days. In addition to SNL feeder cells, human
iPS cells can be maintained on mouse embryonic fibroblasts (MEF).

ACKNOWLEDGEMENT
This protocol is originally prepared by Dr. Kazutoshi Takahashi at CiRA and PhD
student Koji Tanabe at Stem Cell Biology, and modified by Research Management
Office of CiRA, Kyoto University.

REFERENCES
1. Morita, S., Kojima, T. & Kitamura, T. Plat-E: an efficient and stable system fortransient packaging of retroviruses. Gene Ther. 7, 1063-6 (2000)

2. McMahon, A. P. & Bradley, A. The Wnt-1 (int-1) proto-oncogene is required fordevelopment of a large region of the mouse brain. Cell 62, 1073-85. (1990)

3. Fujioka, T. et al. A simple and efficient cryopreservation method for primate
embryonic stem cells. Int. J. Dev. Biol. 48, 1149-54 (2004)

4. Watanabe, K. et al. A ROCK inhibitor permits survival of dissociated humanembryonic stem cells. Nat. Biotech. 25, 681-6 (2007)

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February 19, 2009

Figure 1

Figure 1. Schematic diagram of human iPS cell generation

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Figure 2

February 19, 2009

Figure 2.
Morphologies of human dermal fibroblasts
used for iPS cell induction.
a. Good fibroblast preparation suitable for iPS cell
generation.
b. Cell undergoing senescence, with lowtransduction efficiency by retroviruses. Bar
indicates 200 μm

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Figure 3

February 19, 2009

Figure 3.
Lentiviral and retroviral transduction system for
iPS cell generation.
a. Phase contrast image of 293FT cells transfected withplasmids for GFP lentiviruses.
b. Fluorescent image of the cells shown in the panel (a).
c. Phase contrast image of human dermal fibroblasts
infected with GFP lentiviruses.
d. Fluorescent image of the cells shown in the panel (c).
e. Phase contrast image of human dermal fibroblasts
transduced with lentiviruses expressing mouse Slc7a1
gene and then transduced with GFP retroviruses.
f. Fluorescent image of the cells shown in the panel (e).
Bars indicate 100 μm.

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Figure 4

February 19, 2009

Figure 4.
Human iPS cells from dermal fibroblasts.
a. Human dermal fibroblasts expressing mouse
Slc7a1 introduced, day 6 after retroviraltransduction of OCT3/4, SOX2, KLF4 and c-MYC.
b. Non-ES-like (non-iPS) colony.
c. Putative human iPS colony observed at day 20
after retroviral transduction.
d. Representative human iPS colony at day30.
e. Phase contrast images of iPS and non-iPS
colonies in the same field.
f. Established human iPS cells at passage number
14.
g. iPS cells treated with CTK solution.
h. iPS cells after PBS washing.
i. iPS cells immediately after passage onto
mitomycin C-treated SNL feeder cells.
j. iPS cells one day after passage.
k. iPS cells at day 3 after passage.
l. iPS cells at day 6 after passage. Bars indicate 200μm.

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