Name: ex vivo expansion of hematopoietic stem cells from human umbilical cord blood-derived cd34+ cells using valproic acid
Uploaded: 2019-04-11T14:30:00
Description: Watch this Scientific Journal Video about Ex Vivo Expansion of Hematopoietic Stem Cells from Human Umbilical Cord Blood-derived CD34+ Cells Using Valproic Acid at JoVE.com

This work was supported by NYSTEM grant C030136 to R.H. We would like to thank Bartek Jablonski for his feedback and revision of the manuscript

The HSC ex vivo expansion protocol follows the guidelines of the Research Ethics Committee at Mount Sinai School of Medicine.
1. Buffer and Media Preparation
<ol>
	<li>Prepare separation buffer 24 h prior to isolation of CD34+ cells from UBCs by adding 2 mL of 0.5 M Ethylene Diamine Tetra-acetic Acid (EDTA) and 33 mL of 7.5% Bovine Serum Albumin (BSA) to 465 mL buffered saline (1x PBS). Mix gently and maintain the buffer overnight at 4 &#176;C.</li>
	<li>Warm media at room tempera...

     

<ol>
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E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aryl+hydrocarbon+receptor+antagonists+promote+the+expansion+of+human+hematopoietic+stem+cells.">Aryl hydrocarbon receptor antagonists promote the expansion of human hematopoietic stem cells.</a> Science. 329 (5997), 1345-1348 (2010).</li><li>Fares, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cord+blood+expansion.+Pyrimidoindole+derivatives+are+agonists+of+human+hematopoietic+stem+cell+self-renewal.">Cord blood expansion. Pyrimidoindole derivatives are agonists of human hematopoietic stem cell self-renewal.</a> Science. 345 (6203), 1509-1512 (2014).</li><li>Chaurasia, P., Gajzer, D. C., Schaniel, C., D&#39;Souza, S., Hoffman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epigenetic+reprogramming+induces+the+expansion+of+cord+blood+stem+cells.">Epigenetic reprogramming induces the expansion of cord blood stem cells.</a> Journal of Clinical Investigation. 124 (6), 2378-2395 (2014).</li><li>Wagner, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+I/II+Trial+of+StemRegenin-1+Expanded+Umbilical+Cord+Blood+Hematopoietic+Stem+Cells+Supports+Testing+as+a+Stand-Alone+Graft.">Phase I/II Trial of StemRegenin-1 Expanded Umbilical Cord Blood Hematopoietic Stem Cells Supports Testing as a Stand-Alone Graft.</a> Cell Stem Cell. 18 (1), 144-155 (2016).</li><li>Peled, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nicotinamide,+a+SIRT1+inhibitor,+inhibits+differentiation+and+facilitates+expansion+of+hematopoietic+progenitor+cells+with+enhanced+bone+marrow+homing+and+engraftment.">Nicotinamide, a SIRT1 inhibitor, inhibits differentiation and facilitates expansion of hematopoietic progenitor cells with enhanced bone marrow homing and engraftment.</a> Experimental Hematology. 40 (4), (2012).</li><li>Nikiforow, S., Ritz, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dramatic+Expansion+of+HSCs:+New+Possibilities+for+HSC+Transplants?.">Dramatic Expansion of HSCs: New Possibilities for HSC Transplants?.</a> Cell Stem Cell. 18 (1), 10-12 (2016).</li><li>Mehta, R. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+Techniques+for+Ex+vivo+Expansion+of+Cord+Blood:+Clinical+Trials.">Novel Techniques for Ex vivo Expansion of Cord Blood: Clinical Trials.</a> Frontiers in Medicine. 2, 89 (2015).</li><li>Papa, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ex+vivo+human+HSC+expansion+requires+coordination+of+cellular+reprogramming+with+mitochondrial+remodeling+and+p53+activation.">Ex vivo human HSC expansion requires coordination of cellular reprogramming with mitochondrial remodeling and p53 activation.</a> Blood Advances. 2 (20), 2766-2779 (2018).</li><li>Papa, L., Djedaini, M., Hoffman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+Role+in+Stemness+and+Differentiation+of+Hematopoietic+Stem+Cells.">Mitochondrial Role in Stemness and Differentiation of Hematopoietic Stem Cells.</a> Stem Cells International. , (2019).</li><li>Genovese, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeted+genome+editing+in+human+repopulating+haematopoietic+stem+cells.">Targeted genome editing in human repopulating haematopoietic stem cells.</a> Nature. 510 (7504), 235-240 (2014).</li><li>Perdomo, J., Yan, F., Leung, H. H. L., Chong, B. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Megakaryocyte+Differentiation+and+Platelet+Formation+from+Human+Cord+Blood-derived+CD34++Cells.">Megakaryocyte Differentiation and Platelet Formation from Human Cord Blood-derived CD34+ Cells.</a> Journal of Visualized Experiments. (130), e56420 (2017).</li><li>Fares, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EPCR+expression+marks+UM171-expanded+CD34(+)+cord+blood+stem+cells.">EPCR expression marks UM171-expanded CD34(+) cord blood stem cells.</a> Blood. 129 (25), 3344-3351 (2017).</li></ol>

Herein, we present a protocol to rapidly expand to a significant degree the number of functional human HSCs from UCBs. The pilot and kinetic studies using this protocol indicate that the ex vivo expanded cells promptly acquire and retain the expression of several HSC phenotypic markers including CD90 as well as primitive HSC metabolic characteristics9.
This ex vivo expansion protocol is relatively simple and reliable. Purification of CD34+ cells with the cell...

Ex vivo expansion of hematopoietic stem cells (HSCs) from umbilical cord blood (UCB) units holds great promise for HSC applications in regenerative medicine and transplantation therapy. Transplantation with UCB units has several unique advantages such as easy collection, high availability, minimal risk of infection, low risk of disease relapse, and low frequency of graft-versus host disease (GVHD). However, the major disadvantages of their use in clinical settings are the limited number of HSCs present within each UCB unit1. The insufficient number of HSCs results in delayed engraftment and hematopoietic recovery, risk of graft rejection, and aberrant immune reconstitution.
Currently, various methods and strategies have been developed to ex vivo expand the limited number of HSCs from UCBs. Combinations of different cytokine cocktails with small molecules or compounds in ex vivo cultures result in various degrees of expansion in HSC numbers2,3,4,5,6,7,8. Importantly, ex vivo culture conditions induce stress, leading to rapid cell proliferation, increased metabolic activity and loss of the primitive characteristics that define primary HSCs. Therefore, developing protocols that lead to expansion of a great number of functional HSCs with characteristics that closely resemble primary primitive HSCs are needed.
Serum-free cultures of CD34+ cells isolated from UCBs and treated with valproic acid (VPA) result in the expansion of large numbers of primitive HSCs4,9,10. The HSC expansion is not solely due to the proliferation of the existing HSCs derived from UCBs. Instead, this expansion is due to the acquisition of a primitive phenotype combined with a limited number of cell divisions and proliferation9. Within the initial 24&#8211;48 h of incubation with a combination of cytokines and VPA, CD34+ cells acquire a transcriptomic and phenotypic profile that characterize long-term HSCs. The significant increase in the percentage of HSCs is accompanied by a prompt increase in the number of HSCs (63 fold increase within 24 h of VPA treatment)9. Notably, the VPA-ex vivo expansion strategy expands HSCs with low metabolic activity, which further highlights their primitive characteristics.
The method described here provides conditions and treatments that lead to a significant degree of ex vivo expansion of primitive HSCs for either clinical or laboratory applications. This ex vivo expansion strategy uses a cytokine cocktail combined with VPA treatment. VPA is an FDA approved drug for treatment of bipolar disorders and other neurological diseases. The HSC expansion with VPA is prompt and occurs within 7 days, minimizing both the time of manipulation and the risk of contamination. Importantly, this protocol allows for the acquisition of long-term HSC phenotypic markers such as CD90 and CD49f within 24-48 h following treatment with VPA9. Expanded HSC grafts created with this protocol have the capacity to regenerate the hematopoietic system since they can differentiate into all hematopoietic cell lineages and establish long-term engraftment following transplantation into myeloablated NSG mice&#160;models4. Moreover, this protocol is highly reproducible and allows for efficient and rapid isolation of viable CD34+ cells from UCBs, which is critical for industrialization of this procedure.
The VPA ex vivo expansion protocol also has the potential to overcome the significant loss of HSCs which occurs during gene editing11. Gene editing requires exposure to cytokines, which are necessary for cycling cells and activation of DNA-repair mechanisms. Due to the prompt effects of VPA treatment, this method might be beneficial for the generation of a higher number of genetically modified cells within a period of time that is relevant for currently utilized gene modification protocols.

<table>
	<tbody>
		<tr>
			<td>Expansion Media</td>
			<td>Sigma-Aldrich</td>
			<td>Stemline II stem cell expansion media S0192-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>AO/PI (acridine orange / propidium iodide) staining solution for live/dead Mammalian nucleated cells.</td>
			<td>Nexcelom</td>
			<td>CS2-0106-25mL</td>
			<td></td>
		</tr>
		<tr>
			<td>APC Mouse Anti-Human CD34 Clone 581</td>
			<td>BD BIOSCIENCE</td>
			<td>555824</td>
			<td></td>
		</tr>
		<tr>
			<td>APC Mouse IgG1, &#954; Isotype Control Clone MOPC-21</td>
			<td>BD BIOSCIENCE</td>
			<td>555751</td>
			<td></td>
		</tr>
		<tr>
			<td>autoMACS Rinsing Solution</td>
			<td>MACS Miltenyi Biotec</td>
			<td>130-091-222</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon 15 ml Tube</td>
			<td>BD Biosciences</td>
			<td>352097</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon 5 ml Polystyrene Round-Bottom Tube</td>
			<td>BD Biosciences</td>
			<td>352063</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon 50 ml Tube</td>
			<td>BD Biosciences</td>
			<td>352098</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumine solution</td>
			<td>Sigma-Aldrich</td>
			<td>A8412</td>
			<td></td>
		</tr>
		<tr>
			<td>CD34 MicroBead Kit, contain cd34 beads and fcr blocking reagent, human</td>
			<td>Miltenyi Biotec</td>
			<td>130-046-703</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell analyzer</td>
			<td>BD Biosciences</td>
			<td>FACS Canto II</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell analyzer and sorter</td>
			<td>BD Biosciences</td>
			<td>FACS Aria II</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell counter</td>
			<td>Nexcelom</td>
			<td>Cellometer Auto 2000 Cell Viability Counter</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell separator device</td>
			<td>autoMACS Pro Separator Miltenyi Biotec</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Counting Chambers</td>
			<td>Nexcelom</td>
			<td>CHT4-PD100-002</td>
			<td></td>
		</tr>
		<tr>
			<td>Density gradient media</td>
			<td>GE Healthcare Bio-Sciences AB</td>
			<td>17-1440-03</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylene diamine tetra-acetic acid (EDTA)</td>
			<td>Sigma-Aldrich</td>
			<td>E8008-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC anti-human CD90 (Thy1) Clone 5E10</td>
			<td>BIOLEGEND</td>
			<td>328108</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC Mouse IgG1, &#954; Isotype Ctrl (FC) Antibody</td>
			<td>BIOLEGEND</td>
			<td>400109</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted microscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Corning cellgro</td>
			<td>21-040-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Thermo Fisher Scientific</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human Flt-3 Ligand Protein</td>
			<td>R&#38;D Systems</td>
			<td>308FKN</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human IL-3 Protein (IL-3)</td>
			<td>R&#38;D Systems</td>
			<td>203-IL</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human SCF Protein</td>
			<td>R&#38;D Systems</td>
			<td>255-SC</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human Thrombopoietin Protein (TPO)</td>
			<td>R&#38;D Systems</td>
			<td>288-TP</td>
			<td></td>
		</tr>
		<tr>
			<td>Total Antibody Compensation Bead Kit</td>
			<td>thermofisher</td>
			<td>A10497</td>
			<td></td>
		</tr>
		<tr>
			<td>Umbilical Cord-blood</td>
			<td>Placental Blood Program at the New York Blood Center</td>
			<td>http://nybloodcenter.org/products-services/blood-products/national-cord-blood-program/cord-blood-101/</td>
			<td></td>
		</tr>
		<tr>
			<td>Valproic acid sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>P4543</td>
			<td></td>
		</tr>
	</tbody>
</table>

ex vivo expansion of hematopoietic stem cells from human umbilical cord blood-derived cd34+ cells using valproic acid

Umbilical cord blood (UCB) units provide an alternative source of human hematopoietic stem cells (HSCs) for patients who require allogeneic bone marrow transplantation. While UCB has several unique advantages, the limited numbers of HSCs within each UCB unit limits their use in regenerative medicine and HSC transplantation in adults. Efficient expansion of functional human HSCs can be achieved by ex vivo culturing of CD34+ cells isolated from UCBs and treated with a deacetylase inhibitor, valproic acid (VPA). The protocol detailed here describes the culture conditions and methodology to rapidly isolate CD34+ cells and expand to a high degree a pool of primitive HSCs. The expanded HSCs are capable of establishing both short-term and long-term engraftment and are able to give rise to all types of differentiated hematopoietic cells. This method also holds potential for clinical application in autologous HSC gene therapy and provides an attractive approach to overcome the loss of functional HSCs associated with gene editing.

The ex vivo protocol described here increases the number of primitive HSCs generated from CD34+ cells isolated from UCBs (Figure 1). Priming of CD34+ cells for 16 h with a cytokine cocktail, followed by treatment with VPA for an additional 7 days, leads to a great degree of HSC expansion. Remarkably, the pool of expanded cells is highly enriched for HSCs, which are phenotypically defined by CD34+CD90+ markers. The t...

Watch this Scientific Journal Video about Ex Vivo Expansion of Hematopoietic Stem Cells from Human Umbilical Cord Blood-derived CD34+ Cells Using Valproic Acid at JoVE.com

Ex Vivo Expansion of Hematopoietic Stem Cells from Human Umbilical Cord Blood-derived CD34+ Cells Using Valproic Acid

Here, we describe the ex vivo expansion of hematopoietic stem cells from CD34+ cells derived from umbilical cord blood treated with a combination of a cytokine cocktail and VPA. This method leads to a significant degree of ex vivo expansion of primitive HSCs for either clinical or laboratory applications.

Ex Vivo Expansion of Hematopoietic Stem Cells from Human Umbilical Cord Blood-derived CD34+ Cells Using Valproic Acid

Umbilical cord blood (UCB) units provide an alternative source of human hematopoietic stem cells (HSCs) for patients who require allogeneic bone marrow ...

Ex vivo expansion of hematopoietic stem cell from umbilical cord blood unit hold great promise for HSC application in regenerative medicine and transplantation therapy. This protocol use a cytokine cocktail combined with valproic acid treatment to rapidly expand a great number of functional HSCs with characteristics that closely resemble primary primitive HSCs. Due to the prompt effects of valproic acid treatment, this method also has the potential to overcome the loss of HSCs associated with gene editing.This method might be beneficial for generation of a higher number of genetically-modified cells within a period of time that is relevant for currently-used gene modification protocols. The valproic acid ex vivo expansion protocol is relatively simple and reliable. Purification of CD34-positive cells with the cell separator device is highly reproducible and rapid, allowing for fast recovery of highly purified CD34-positive cells.24 hours prior to the isolation of CD-34 positive cells from umbilical cord blood, prepare the separation buffer by adding two milliliters of 0.5 molar EDTA and 33 milliliters of 7.5%BSA to 465 milliliters of 1X PBS. Mix the buffer gently and maintain it overnight at four degrees Celsius. On the day of purification, warm the media to room temperature.Dispense the whole umbilical cord blood unit into a 75-square-centimeter flask. Dilute the blood with an equal volume of PBS at room temperature and mix gently. Next, determine the number of tubes required for processing the whole umbilical cord blood unit.Add 15 milliliters of density gradient media to each tube. Dispense the diluted blood very slowly on top of the density gradient while holding the tube at a 45-degree angle to create two layers. Centrifuge the tube at 400 g for 30 minutes with a low acceleration and deceleration rate.After the centrifugation, the mononuclear cells will be located in the white layer between the plasma and density gradient media layers. Carefully transfer the buffy coat layer into a new, 50-milliliter tube. Collect all of the mononuclear cells from the same umbilical cord blood unit into a 50-milliliter tube until reaching 25 milliliters.Add 25 milliliters of cold PBS to the tube containing 25 milliliters of mononuclear cells and mix well. Centrifuge at 400 g and at four degrees Celsius for 10 minutes. Carefully aspirate the supernatant and resuspend the cell pellet in 50 milliliters of cold PBS.After this, remove 20 microliters of the cell suspension for counting. Use an automated cell counter to count the number of cells stained with either acridine orange or propidium iodide and calculate the total number of mononuclear cells. Then, centrifuge the cells at 400 g and at four degrees Celsius for 15 minutes.First, mix 300 microliters of separation buffer with 100 microliters of human FCR human IgG and 100 microliters of CD34 magnetic beads to isolate the CD34-positive cells from 10 million mononuclear cells. Next, carefully remove the supernatant from a tube of previously-centrifuged mononuclear cells. Resuspend the pellet in the magnetic bead solution using 500 microliters per 10 million cells.Mix gently and incubate at four degrees Celsius for 30 minutes. During the incubation, prepare the cell separator device by replacing the storage solution with the working buffer and running a washing program followed by a rinsing program. Then, add cold cell separator running buffer to the tube that contains the cell mixture until the tube is completely filled.Centrifuge the tube at 400 g and at four degrees Celsius for 15 minutes. Aspirate the supernatant and resuspend the cell pellet in cold separator running buffer using two milliliters per 10 million cells. Transfer the two-milliliter cell suspension mixture into 15-milliliter tubes.Load three sets of the tubes into the cell separator rack, which has been pre-chilled to four degrees Celsius. One set of tubes contains MMCs, the second set of tubes will be used to collect the negative fraction, and a third set of tubes will be used to collect purified CD34-positive cells. Load the rack into the cell separator device and run the preset program.After this, centrifuge the tubes containing the positive fraction at 400 g at and four degrees Celsius for 15 minutes. Aspirate the supernatant and resuspend the purified CD34-positive cells in one milliliter of serum-free media. Then, use an automated cell counter to count the cells stained with acridine orange or propidium iodide.First, prepare a sufficient volume of media to plate the purified CD34-positive cells at a density of 33, 000 cells per milliliter. Plate the purified CD34-positive cells in a 12-well plate at a cell density of 50, 000 cells in 1.5 milliliters of media per well. Incubate at 37 degrees Celsius in a 5%carbon dioxide humidified incubator for 16 hours.Add valproic acid to the cultures such that the final concentration is one millimolar. Continue culturing the cells at the same conditions for an additional seven days. In this ex vivo protocol, the number of primitive hematopoietic stem cells generated from CD34-positive cells isolated from umbilical cord blood is increased.The total number of nucleated cells is significantly higher in cultures treated with the cytokine cocktail alone. Despite the higher number of total nucleated cells, the number of hematopoietic stem cells in the cultures receiving the cytokine cocktail alone remains low during the entire expansion period, compared to cultures treated with cytokine cocktail and valproic acid. The greatest number of hematopoietic stem cells is generated in cultures treated with a combination of the cytokine cocktail and valproic acid.In particular, the greatest expansion is reached after five to seven days following treatment with valproic acid. This increased number of hematopoietic stem cells correlates with a prompt increase in the percentage of hematopoietic stem cells, which is notable within 24 hours of treatment with valproic acid. While the increase in the percentage is maintained during the first four days of ex vivo culture, it declines progressively after five to seven days of treatment.However, this decrease is inversely correlated with an increase in the absolute number of hematopoietic stem cells. The rapid increase in the percentage of hematopoietic stem cells in valproic-acid-treated cultures is due to the acquisition of the CD90 phenotype. CD34-positive cells expressing the CD90 phenotypic marker reach almost 40 to 50%of cells expanded in ex vivo cultures treated with the cytokine cocktail and valproic acid for four days.The acquisition of the CD90 phenotype is then confirmed by ex vivo expansion of the highly-purified CD34-positive cells that lack expression of the CD90 marker. Within 24 hours of treatment with valproic acid, almost 75%of the ex vivo expanded cells express CD90. This phenotype is highly retained during the first four days in these cultures.The diluted cord blood should be dispensed very slowly on top of the density gradient while holding the tube at a 45-degree angle to create two distinct layers. Following this ex vivo expansion procedure, the expanded cells can be injected into the myeloablated immune-deficient NSG mice to test their functionality and engraftment potential. The expanded cells can be used to test a variety of questions regarding the biology of both human and mouse HSC and the role of different genes or critical player on the functional integrity of HSCs.The functionality of ex vivo expanded HSC from human umbilical cord blood unit, using this technique, will be soon tested in a clinical trial in patient with hematological malignancies who require allogenic bone marrow transplantation. This technique has also allowed us to investigate the mechanism underlying the ex vivo expansion with VPA treatment and get insights into the biology of primitive HSCs.

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