The NIH Center for Regenerative Medicine

Hematopoietic Stem Cell (HSC)

Mesoderm Differentiation: Hematopoiesis

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Submitted by: Gordon Keller
Validated by Sunita D’Souza

Title Mesoderm Differentiation Hematopoiesis
Date Submitted January 5th 2012
Submitted by - Kennedy, Marion (mkennedy@uhnresearch.ca) and Keller, Gordon (gkeller@uhnresearch.ca)
Adapted from -
  1. Development of the hemangioblast defines the onset of hematopoiesis in human ES cell differentiation cultures.
    Kennedy M, D'Souza SL, Lynch-Kattman M, Schwantz S, Keller G. Blood. 2007 Apr 1;109(7):2679-87.
  2. Directed differentiation of hematopoietic precursors and functional osteoclasts from human ES and iPS cells.
    Grigoriadis AE, Kennedy M, Bozec A, Brunton F, Stenbeck G, Park IH, Wagner EF, Keller GM. Blood. 2010 Apr 8;115(14):2769-76. Epub 2010 Jan 11.
Contributors -  
Affiliation(s) - McEwen Centre for Regenerative Medicine, University Health Network, Toronto, Ontario, Canada.University/ Institute

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Table of Contents

  1. Introduction
  2. FlowChart
  3. Materials
    1. Materials and Preparation
    2. Induction and Differentiation Media
    3. Images for Hematopoietic Colonies in Methylcellulose Assays
  4. Protocol
  5. Acknowledgements
  6. Contributors

Introduction

The protocol outlined below describes the method for generating hematopoiesis from hESCs, specifically H1 cells. Generally the first hematopoietic progenitors start appearing at T5-7 and are mainly primitive erythroid with a few macrophages. We have defined stages by cell surface markers and colony morphology, in our differentiation cultures, that may reflect the emergence of yolk sac, fetal and definitive hematopoiesis

Flowchart

Flowchart of Mesoderm Differentiation Hematopoiesis

The formation of EBs is the first important step in the differentiation of hESC. This is best achieved by culturing small aggregates of hESCs in miminal amounts of BMP-4 for
24 hours. At this stage, BMP-4 functions to promote the survival of the hESCs.

Materials and Preparation

COLLAGENASE (FOR DISSOCIATION) (SIGMA# C-0130)
Collagenase Type 1 is mainly used for dissociation of the embryoid bodies.

  
Final Conc.
For 1 Liter

Collagenase

 (SIGMA# C-0130)

0.2%

 2g

FCS

  

 

 200mL
PBS (with Ca2+, Mg2 (Cellgro# 21-030-CM)   800mL
  1. Weigh 1 g of Collagenase Type 1 in the fumehood (inhalation is hazardous) and dissolve in 400 mL of PBS by gently stirring. Check carefully that the collagenase is completely dissolved.
  2. Add 100 mL FCS
  3. Filter sterilize (may need more than one filtration apparatus)
  4. Store at -20ºC as 12 mL aliquots in 15 mL screw cap tubes
  5. One cycle of freeze-thaw is acceptable.

Note: final concentration is 0.2% or 2 mg/mL in 20% FCS/

L-ASCORBIC ACID (AA) (SIGMA # A-4544)
Prepare a stock solution of 5 mg/mL in cold TC-H2O. Leave on ice and vortex periodically until completely dissolved. Filter sterilize, aliquot and store at -20ºC. Use once and discard

MONOTHIOGLYCEROL (MTG) (SIGMA# M-6145)
The amounts of MTG indicated in our protocols are recommended concentrations. However, it is important to test each new batch of MTG as there is variability between them. MTG should be aliquoted (1 mL) and stored frozen (-20ºC). When aliquots are thawed, they can be used for several experiments and then discarded. Aliquoting of MTG is strongly recommended as it minimizes the amount of oxidation due to repeated opening

TRANSFERRIN (ROCHE# 10 652 202)
The amounts of Transferrin indicated in our protocols are recommended concentrations. However, it is important to test each new batch of transferrin as there is variability between them. It should be aliquoted (2 mL) and stored at 4ºC.

CYTOKINES
All cytokines are stored lyophilized, at -20oC, except Erythropoietin which is stored at 4oC

Cytokine
  
Buffer
Stock Conc.

hBMP-4

 (R&D Systems# 314-BP)

H20, 4mM HCL, 0.1%BSA

 10ug/mL
hbFGF (R&D Systems# 234-FSE) PBS, 0.1%BSA,1mM DTT 10ug/mL
hVEGF (R&D Systems# 293-VE) PBS, 0.1%BSA 5ug/mL
hSCF (R&D Systems# 255-SC) PBS, 0.1%BSA 50ug/mL
hErythropoietin Janssen-Ortho Inc (EPREX) PBS, 0.1%BSA 2000units/mL

hIL-6

 (R&D Systems# 206-IL)

PBS, 0.1%BSA

 5ug/mL
hIL-11 (R&D Systems# 218-IL) PBS, 0.1%BSA 5ug/mL

STEMPRO 34 (Invitrogen# 10639-011)
Stempro 34 is sold as a kit with 2 components. The supplement is kept at -20oC and the liquid media at 4oC. When combined, the media is unstable, therefore, we use it for a maximum of 2 weeks. If not used right away, we store the medium as 50mL aliquots and supplement them as needed. The supplement is frozen as 1.3mL aliquots which is the amount required for 50mL. of medium

  
Final Conc.
For 500mL

STEMPRO 34 Kit

 (Invitrogen 10639-011)

 

 500 mL
Penicillin/Streptomycin P/S (Gibco# 15070-063) 1% 5 mL
  1. Warm the media, P/S and frozen supplement in a 37oC waterbath for 15 to 20 minutes
  2. Mix the supplement well with a pipette and add to the warm media along with the P/S.
  3. Warm the mixture for another 30 minutes and then aliquot into 50mL. (Label the tube that supplement has been added, to avoid confusion.)
  4. Store for a maximum of 2 weeks

*MATRIGEL (REDUCED FACTOR) (BD# 356 230)
Each batch of matrigel has its own unique levels of endotoxin and protein concentrations. We find that the endotoxin levels should not be higher than 2 endotoxin units/mL and the protein levels should range between 7 to 10 mg/mL. If the protein levels are higher than this you may need to dilute the matrigel more than 1:1. This is determined by observing the hESC colony morphology and the ability of the hESCs to differentiate into the lineage required of them.
Caution: When working with matrigel, all tubes, plates and pipettes should be prechilled, as matrigel solidifies at room temperature.

MATRIGEL1:1 PREPARATION

  1. Thaw frozen bottles of matrigel on ice overnight in the cold room. We normally thaw 6X5-mL bottles per batch.
  2. The next day, make a 50% working stock by adding an equal volume of IMDM+P/S to each bottle. Resuspend gently with a pre-chilled 5 mL pipette.
  3. Leave the bottles on ice all day to allow the matrigel to completely equilibrate with IMDM.
  4. Pool 3 bottles of 1:1 matrigel (30 mL) into a pre-chilled 50 mL tube. Gently mix with a chilled 10 mL pipette and aliquot.
  5. Transfer 2.5 mL into pre-chilled and pre-labelled 4-mL snap cap tubes
  6. Store aliquots at -20ºC

The formation of EBs is the first important step in the differentiation of hESC. This is best achieved by culturing small aggregates of hESCs in the presence of BMP-4 for 24 hours. At this stage, BMP-4 functions to promote the survival of the hESCs.

A. COLLAGENASE B (Roche# 11 088 831 001)
Collagenase B is routinely used for dissociation and passaging of undifferentiated hESCs

  
Final Conc.
For 1 Liter

Collagenase B

 (Sigma# T-4799)

0.25%

 1 g
DMEM/F12 (Cellgro# 10-092-CV) 1 mM 1000 mL
  1. Weigh 1 g of Collagenase B in the fume hood as inhalation is hazardous and dissolve in 1 Liter DMEM/F12 +P/S by stirring gently at room temperature for 1 h (or until completely dissolved)
  2. Filter sterilize and store at -20ºC in 12 mL aliquots

B. DNASE I (VWR, Cat # 80510-412, 10MU)

  1. Want final concentration to be 1mg/ml
  2. 10MU X 1X106U ⁄ 1 MU X 1mg ⁄ 65150 U = 153mg
  3. In the hood transfer powder to a 125 ml bottle
  4. Bring the volume up to 153 ml with ice cold sterile water
  5. Let dissolve on ice for 1-2 hours
  6. Filter and aliquot 1ml/eppendorf
  7. Store at –20.
  8. Filter sterilize, aliquot in 1 mL amounts and store frozen at -20ºC
  9. Use aliquots once and discard excess

C. TRYPSIN-EDTA

  
Final Conc.
For 1 Liter

Trypsin

 (Sigma# T-4799)

0.25%

 2.5 g
EDTA 0.5 M (pH 8)   1 mM 2 mL
PBS (without Ca2+, Mg2+) (Cellgro# 21-031-CM)   1000 mL
  1. Warm to dissolve (15 min, 37ºC), filter sterilize, aliquot and store at -20ºC
  2. For aggregate formation we use a 1/4 dilution of the above (ie: 10mL of TRYPSIN-EDTA in 30mL of PBS (without Ca2+, Mg2+

D. STOP MEDIUM

  
Final Conc.
For 40 mL

hESC WASH Medium

  

50%

 20 mL
WASH Medium 50% 20 mL
   50% 20 mL
+/- Matrigel (1:1)* (BD# 356 230) 1:800 100 uL

E. hESC WASH MEDIUM

  
Final Conc.
For 500 mL

Supplemented DMEM/F12

  

 

 475 mL
KnockoutTM Serum Replacement (Gibco# 10828-028) 5% 25 mL

SUPPLEMENTED DMEM/F12

 
Final Conc.
For 500 mL

DMEM/F12

(Cellgro# 10-092-CV)

 

 500 mL
Penicillin/Streptomycin (Gibco# 15070-063) 1% 5 mL
  1. Make 40 mL aliquots of the hESC WASH MEDIUM
  2. You can add 100 uL of Matrigel 1:1 to each aliquot when needed

INDUCTION / DIFFERENTIATION MEDIA

F. AGGREGATION MEDIUM

Stock Conc.
Final Conc.
per mL
For 50 ml

STEMPRO 34

 

 

   50ml
Glutamine 100x 1% 10uL 500ul
Transferrin 300mg/ml 150ug/mL 5uL 250ul
Ascorbic Acid 5mg/ml 50ng/mL 10uL 500ul
MTG 26 λ/2mls   3uL 150ul
BMP4* 10ug/ml 10ng/mL 1uL 50ul

G. INDUCTION 1 MEDIUM

 Stock Conc.
Final Conc.
per mL
For 50 ml

STEMPRO 34

 

 

   50ml
Glutamine 100x 1% 10uL 500ul
Transferrin 300mg/ml 150ug/mL 5uL 250ul
Ascorbic Acid 5mg/ml 50ng/mL 10uL 500ul
MTG 26 λ/2mls   3uL 150ul
BMP4* 10ug/ml 10ng/mL 1uL 50
ActA** 10ug/ml 0.3ng/ml 0.03uL 1.5ul
bFGF 10ug/ml 5ng/ml 0.5uL 25ul

* Bmp4 and ActA**concentration may vary according to lot# or the hES cell line used…these concentrations are for H1 cells.

H. IMDM+10%FCS

 
Final Conc.
For 500 mL

Iscove's Modified Dulbecco's Medium

(Cellgro# 15-016-CV)

 

 450 mL

FCS (batch tested)

(Gibco# 10828-028 )

10%

 50 mL

I. INDUCTION 2 MEDIUM

 Stock Conc.
Final Conc.
per mL
For 50 ml

STEMPRO 34

 

 

   50ml
Glutamine 100x 1% 10uL 500ul
Transferrin 300mg/ml 150ug/mL 5uL 250ul
Ascorbic Acid 5mg/ml 50ng/mL 10uL 500ul
MTG 26 λ/2mls   3uL 150ul
VEGF 5ug/ml 10ng/mL 1uL 100ul
Dkk 50ug/ml 150ng/mL 3uL 150ul
bFGF 10ug/ml 5ng/ml 0.5uL 25ul

J. INDUCTION 2 MEDIUM (Feed T6)

 Stock Conc.
Final Conc.
per mL
For 50 ml

STEMPRO 34

 

 

   50ml
Glutamine 100x 1% 10uL 250ul
Transferrin 300mg/ml 150ug/mL 5uL 100ul
Ascorbic Acid 5mg/ml 50ng/mL 10uL 500ul
MTG 26 λ/2mls   3uL 150ul
VEGF 5ug/ml 10ng/mL 2uL 100ul
bFGF 10ug/ml 5ng/mL 0.5uL 50ul
hIL6 10ug/ml 10ng/ml 2ul 100ul
hSCF 50ug/ml 50ng/ml 2ul 100ul
hIL-11 5ug/ml 5ng/ml 2ul 100ul
hEPO 2000units/ml 2units/ml 2ul 100ul
hIGF-1 25ug/ml 25ng/ml 2ul 100ul

Bold type indicates a 2x concentration of the cytokine as the media will be diluted by 1/2

K. HEMATOPOIETIC EXPANSION MEDIUM

 Stock Conc.
Final Conc.
per mL
For 50 ml

STEMPRO 34

 

 

   50ml
Glutamine 100x 1% 10uL 500ul
Transferrin 300mg/ml 150ug/mL 5uL 250ul
Ascorbic Acid 5mg/ml 25ng/mL 5uL 250ul
MTG 26 λ/2mls   2uL 100ul
hTPO 10ug/ml 50ng/mL 5uL 250ul
hIL-3 10ug/ml 50ng/mL 5uL 250ul
hFLT3L 10ug/ml 20ng/ml 2ul 100ul
hSCF 50ug/ml 100ng/ml 2ul 100ul
hIL-11 5ug/ml 5ng/ml 1ul 50ul
hEPO 2000units/ml 2units/ml 1ul 50ul
hIGF-1 25ug/ml 25ng/ml 1ul 50ul

HEMATOPOIETIC MEC MIX

Mec Mix
               

Reagent

Stock/ml

Final

10ml 14ml 18ml 24ml 32ml 45ml
MEC 100% 55% 5.5ml 7.7ml 10ml 13ml 17.6ml 25ml
PDS 100% 15% 1.5ml 2.1ml 2.7ml 3.6ml 4.8ml 6.8ml
PFHM-11 100%l 5% 0.5ml 0.7ml 0.9ml 1.2ml 1.6ml 1.3ml
Glutamine 100% 1x 100ul 140ul 180ul 240ul 320ul 450ul
Transferrin 30mg 150ug/ml 50ul 70ul 90ul 120ul 160ul 275ul
TPO 10ug 50ng/mL 50ul 70ul 90ul 120ul 160ul 225ul
IL-3 10ug 50ng/ml 50ul 70ul 90ul 120ul 160ul 225ul
VEGF 5ug 10ng/ml 20ul 28ul 36ul 48ul 64ul 90ul
SCF 50ug 100ng/ml 20ul 28ul 36ul 48ul 64ul 90ul
EPO 2000units/ml 4units 20ul 28ul 36ul 48ul 64ul 90ul
IL-6 5ug/ml 10ng 20ul 28ul 36ul 48ul 64ul 90ul
IGF-1 25ug 50ng 20ul 28ul 36ul 48ul 64ul 90ul
IL-11 5ug 5ng 10ul 14ul 18ul 24ul 32ul 45ul
GM-CSF 1ug 1ng 10ul 14ul 18ul 24ul 32ul 45ul
IMDM 100%   2.2ml 3ml 3.9ml 5.2ml 7ml 9.7ml

Protocol

T0: Generation of embryoid bodies (EBs)

  1. Remove the medium from hES cells that have been feeder depleted on matrigel coated plates for 24-48 hours(see hES cell maintainance protocol)
  2. To each well, add 1mL of COLLAGENASE B containing 10uL/mL DNase (A,B), for 20 min. and then aspirate. The cells should still be attached.
  3. Add 1mL of 1/4 TRYPSIN-EDTA (C) to the wells and then watch carefully for 1-3min. The cells will separate from each other, but should not lift from the plate. (Note; each cell line has a different time requirement so one should continuously monitor the wells.
  4. Remove the trypsin from the well and stop the reaction with 1mL of STOP MEDIUM +MATRIGEL (D) containing 10uL/mL DNase . Scrape gently with a cell scraper. The ES cells should lift as clusters into the medium.
  5. Add 1ml of hESC WASH MEDIUM +MATRIGEL (E) to each well and resuspend with a 2mL pipette 3-5x, until the clusters are 10-20 cells in size. Transfer to a 15ml tube containing 4ml of hESC WASH MEDIUM +MATRIGEL (usually 3 wells per tube)
  6. Also ,at this time, we completely trypsinize one well of the matrigel hESCs to single cells, to get an accurate cell count for the experiment. The average cell count per starting matrigel well, using this protocal, is 5x10^5 to 1x10^6.
  7. Spin at 800 rpm, aspirate and resuspend each tube with 2mL of AGGREGATION MEDIUM (F) using a 2mL pipette (resuspend gently 2-3 times). To calculate the amount of AGGREGATION MEDIUM required for the experiment you will need 2mls for every 5x10^5 to 1x10^6 cells harvested. Adjust the final volume of each tube appropriately.
  8. With a 5mL pipette, evenly distribute 2 mL of aggregates into each well of a 6 well Locluster plate (Costar#3071). Incubate for 24 hours at 37°C in an 5%CO2,5%O2 Incubator.

T1: Feeding Aggregates and expansion

Add 2mls of AGGREGATION MEDIUM (F) supplemented with 10ng/ml bFGF to the cultures. The final concentration of bFGF in the well will be 5ng/ml.

  • Please note low concentration of BMP4 (1-2ng/ml) at D0, followed by 10ng of BMP4 at D1-D4 and 4-5ng of ActA from D1-D4 led to a drastic increase in the amount of erythroid progenitors. All other cytokines are as described.

  • Whereas 10ng/ml of BMP4 at D0, followed by 10ng of BMP4 from D1-D4 and 0.5 ng of ActA from D1-D4 led to a drastic increase in the amount of myeloid progenitors. All other cytokines are as described.

T1.75: Induction 1

  1. There will be some debris in the cultures. We separate the aggregates from the debris by harvesting 3 wells into one 15ml round bottomed tube and then allowing them to settle for 30min in an 37°C,5%CO2,5%O2 incubator

  2. While the aggregates are settling, make INDUCTION 1 MEDIUM (G) so that there will be 2mL for each well harvested. After the aggregates have settled, aspirate the supernatant and then add INDUCTION 1 MEDIUM . Dispense the aggregates into a new 6 well Locluster plate at 2mL per well. Distribute the aggregates evenly.

  3. Incubate as above until T3-4

Notes

Mesoderm induction and hemangioblast specification in the EBs should be evaluated by flow cytometric analysis, monitoring the cells for expression of KDR and CD117 (c-kit). As each hESC line has its own unique kinetics, it is best to define the hemangioblast stage based on the profile seen below, rather than by time in culture.
The hemangioblast stage is defined by the appearance of a population that expresses medium levels of KDR and are CD117neg . EBs at this stage also contain a KDRneg CD117pos population. This profile is detected in H1-derived EBs at day 3 and in HES2-derived EBs at day 4. The window for hemangioblast development is narrow and occurs before CD31 is expressed on the cells.

T3-4: Harvest for staining

  1. Settle1 well of EBs in a round bottomed tube for 15minutes. Aspirate the medium and add 1ml of TRYPSIN-EDTA. Incubate at 37°C in a waterbath for 5 minutes and then stop the reaction with 0.5ml of STOP MEDIUM+dnase.
  2. Make to single cells by passing the EBs 4-6x through a syringe bearing a 20 Guage needle and wash with IMDM+10%FCS (H).
  3. Spin for 5min at 1000 RPM, aspirate and resuspend in IMDM+FCS (usually 500ul per well harvested). Pass the cells through a 70micron filter to remove any clumps that are still remaining. You should recover 5x10^5-1x10^6 cells per well of EBs harvested

Facs Profiles

Image of square box for Facs profiles

T4-8: Induction 2: Specifying Blood from the EBs

  1. Pipette the EBs into a round bottomed 15ml tube (1-3 wells per tube). Spin for 5 min at 500RPM. Carefully aspirate the media and then add 4ml of Stempro media. Let the EBs settle for 20 min and aspirate again. This step allows for 2 washes to remove the previous cytokines, as well as, any debris floating in the supernatant.
  2. Resuspend the EBs in INDUCTION 2 MEDIA (I) at 2mls per well harvested. This media contains VEGF and FGF at low concentrations which is necessary for expanding the earliest blood precursors. Incubate at 37°C in an 5%CO2,5%O2 Incubator.
  3. Feed the cultures at T6 with 2ml of the INDUCTION 2 MEDIA (J) with supplemental cytokines which are in BOLD and added at a 2x concentration.

Notes
If one monitors the cultures at this time with FACS, the KDR/CD117 and KDR/CD31 profiles should be the same as the Post-Hemangioblast profiles above.

T8: Expanding Precursors

Settle and wash the EBs as above at T4

Resuspend and distribute as above in HEMATOPOIETIC EXPANSION MEDIUM (K) At this time cocktails of cytokines may vary as well as culture methods according to the lineage one desires. For general expansion of hematopoietic lineages we maintain our cultures in suspension changing the media every 4 days. The cultures at this time can be grown in ambient oxygen conditions at 37° and 5%CO2

Harvest to single cells for FACs, Sort, Counts or Reaggregations

Dissociation T1-8 (Trypsin-EDTA)

  1. Harvest each group of 2 dishes into a 2059 tube and let the EBs settle
  2. Remove supernat.and add 2mls of Cellgro Trypsin
  3. Incubate for 5-8min in 37degree water bath
  4. Stop trypsin with FCS1:1+dnase 30ul/ml
  5. Syringe 6x with a 20Guage needle and then add 7mls of wash media
  6. Spin for 5min at 1100rpms
  7. Resuspend in 1ml of wash media and filter through blue cap of
    2035 tube

Dissociation T8+(Collagenase)

  1. Harvest each group of 2 dishes into a 2059 tube and let the EBs settle
  2. If there are hematopoietic clusters in your supernatant collect the sup., keep on ice during the dissociation step and add back to your cells at step 9
  3. Remove supernat.and add 2mls of Cellgro Trypsin
  4. Incubate for 5-8min in 37degree water bath
  5. Stop trypsin with FCS1:1+dnase 30ul/ml
  6. Syringe 6x with a 20Guage needle and then add 7mls of wash media
  7. Spin at 1200rpm and resuspend in 1ml/well Collogenase Type 1 (L)
  8. Incubate at 37 degrees for 60min
  9. Syringe 6x with a 20Guage needle, add your supernatant cells and wash media.
  10. Spin at 1200rpm and resuspend in 1ml.
  11. Count and use in your assays

IMAGES OF HEMATOPOIETIC COLONIES IN METHYLCELLUOSE COLONIES

MAST COLONY – 20X
Images of Hematopoietic Colonies In Methylcelluose Colonies, Mast Colony - 20X

MAST COLONY – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, Mast Colony - 10X

MAC/MONO – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, MAC/MONO – 10X - Image 1

MAC/MONO – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, MAC/MONO – 10X - Image 2

MACROPHAGE – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, MACROPHAGE – 10X - Image 1

MACROPHAGE – 20X
Images of Hematopoietic Colonies In Methylcelluose Colonies, MACROPHAGE – 20X

ERY-MYELO – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, ERY-MYELO – 10X

MACROPHAGE – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, MACROPHAGE – 10X - Image 2

ERYTHROID – 10X
Images of Hematopoietic Colonies In Methylcelluose Colonies, ERYTHROID – 10X

Granulocyte/Macrophage
Images of Hematopoietic Colonies In Methylcelluose Colonies, Granulocyte/Macrophage

Acknowledgements

References

Blood. 2010 Apr 8;115(14):2769-76. Epub 2010 Jan 11.
Directed differentiation of hematopoietic precursors and functional osteoclasts from human ES and iPS cells.
Grigoriadis AE, Kennedy M, Bozec A, Brunton F, Stenbeck G, Park IH , Wagner EF, Keller GM.
Department of Craniofacial Development and Orthodontics, Guy's Hospital, King's College London, London, UK. agi.grigoriadis@kcl.ac.uk

  1. Development of the hemangioblast defines the onset of hematopoiesis in human ES cell differentiation cultures.
    Kennedy M, D'Souza SL, Lynch-Kattman M, Schwantz S, Keller G. Blood. 2007 Apr 1;109(7):2679-87.

This page was last modified on October 18, 2012