We thank Matt Raymond for editorial assistance. This work was supported by funds from the National Institute of Health (U01HL099773, R01HL116221, and P51 RR000167) and The Charlotte Geyer Foundation.

1. Virus Preparations and Transcription Factor Combinations
<ol>
	<li>Prepare solutions with pSIN-EF1&#945; lentiviral expression plasmid containing protein-coding DNA for ETV2, GATA1, GATA2, TAL1 and LMO2 (Table 1).</li>
	<li>Measure the concentration and purity of plasmid preparations used for lentiviral production by recording UV absorption with a spectrophotometer at 230 nm, 260 nm, and 280 nm. Note: DNA preparations demonstrating A260/280 and A260/230 values greater than 1.8 are generally considered good quality. Lower A260/280 values may indicate protein contamination, while lower A260/230&#160;values indicate impurities with salts or some solvent such as phenol. Recommended plasmid concentration is 1-3 &#181;g/&#181;l.</li>
	<li>Produce lentiviruses for transductions as described in previously published protocols11. Induction of HE with pan-myeloid potential requires co-expression of ETV2 and GATA1, or ETV2 and GATA2. Induction of HE with erythro- and megakaryocytic potential requires GATA2 and TAL1. The addition of LMO2 significantly improves the yield of erythro-megakaryocytic cells from hPSCs in the presence of GATA2 and TAL110.</li>
</ol>
2. hPSCs Culture Protocol
<ol>
	<li>Grow pluripotent stem cells in tight colonies with sharp edges to 70-80% confluency before subculturing. Mark and remove spontaneously differentiated colonies before passaging cells.</li>
	<li>Dilute commercial extracellular matrix gel (see Table 2) according to the manufacturer&#8217;s instructions and coat 6-well plates overnight at 4&#160;&#176;C, or for at least one hour at 37&#160;&#176;C prior to use. Before passaging cells, aspirate the matrix, add 2 ml of fresh commercial complete culturemedium (see Table 2) and keep plates at 37 &#176;C, 5% CO2 until the cells are ready for seeding.</li>
	<li>Passage hPSCs
	<ol>
		<li>Aspirate medium from one confluent well of a 6-well plate with hPSCs and add 1.5 ml of pre-warmed Dispase II solution (2 mg/ml in DMEM/F12, sterilized by filtration through 0.22 &#181;m filters). Incubate for 5-7 min at 37 &#176;C, 5% CO2 until the edges of colonies begin to lift from the surface.</li>
		<li>Aspirate Dispase II solution and carefully wash the colonies twice by adding and then aspirating 2 ml of fresh DMEM/F12 medium. Then, using a 5 ml serological glass pipette, dissociate hPSCs with 3 ml of fresh commercial complete culture medium (see Table 2) by pipetting cell suspension up and down several times.</li>
		<li>Add 0.5 ml of cell suspension to each well of a 6-well plate containing 1.5 ml of commercial complete culture medium (see Table 2). Agitate plate back and forth and right to left several times to ensure a uniform cell distribution when situating the plate into the incubator. Keep cells at 37 &#176;C, 5% CO2 for 18-24 hr.</li>
		<li>The next day change medium to fresh commercial complete culture medium (see Table 2) and examine hPSCs morphology. Successful passaging results in small, well-attached colonies retaining hPSC morphology. hPSCs must be fed with 2.5-3 ml freshmedium per well on a daily basis and passaged every 4-5 days at no more than 70-80% confluence. 
		NOTE: If hiPSCs were maintained on mouse embryonic fibroblasts (MEFs), they need to be transferred to feeder-free conditions and passaged 2-3 times before transduction to ensure efficient differentiation.</li>
	</ol>
	</li>
</ol>
3. Induction of Hematoendothelial Pprecursors from hPSCs (day 0, Transduction of hPSCs)
<ol>
	<li>To prepare reaction medium combine 1.3 ml of commercial complete serum-free medium (see Table 2), virus, polybrene, and Y27632 ROCK inhibitor (Table 1): add 1.3 &#181;l of 10 mM ROCK inhibitor to 1.3 ml medium to a final concentration of 10 &#956;M, and polybrene to a final concentration 6 &#181;g/ml.
	<ol>
		<li>Add an appropriate amount of viral concentrate(s) at a final concentration of 0.5-1.0 MOI (multiplicity of infection) of each virus per cell. Keep reaction medium on ice or at 4 &#176;C until the single cell suspension is ready. 
		NOTE: The same amount of MOI for each virus in the GATA1/ETV2, GATA2/TAL1, and GATA2/TAL1/LMO2 reaction mixtures is optimal for induction of differentiation. However, in ETV2/GATA2 transduced cultures doubling MOI for GATA2, relative to ETV2, enhances differentiation. Therefore, for these cultures, ratio 1:2 for MOI of ETV2 and 1 MOI of GATA2 is recommended (e.g. if viral concentrate is estimated approximately 6.8 x 107 particles/ml, add 10 &#181;l of ETV2 and 20 &#181;l of GATA2 viral concentrates to 0.68 x 106 cells per one ETV2/GATA2 reaction in a 35 mm well of a 6-well plate).</li>
	</ol>
	</li>
	<li>Prepare hPSCs in a single cell suspension.
	<ol>
		<li>Grow hPSCs in feeder-free conditions as described in section 2. On day 4 following the last passage, observe cell density and morphology under an inverted microscope. hPSCs should grow in tight colonies with sharp edges with no spontaneous differentiation and reach ~60-70% confluency on the day of transduction.</li>
		<li>Aspirate medium, add 1.5-2 ml of commercial cell dissociation reagent (Table 1) per well and incubate at 37 &#176;C with 5% CO2 for 5-7 min.</li>
		<li>Collect cells into equal volumes of commercial complete medium (see Table 2) with 10 &#181;M of ROCK inhibitor, count the cells and determine viability. Pellet cells by centrifugation at 200 x g for 5 min and then resuspend cells in commercial complete medium with 10 &#181;M of ROCK inhibitor to a concentration of 3.4-5 x 106 cells per ml. 
		NOTE: Cell viability is critical for successful viral transduction and subsequent differentiation. Typically, cell viability before transduction should exceed 90%.</li>
	</ol>
	</li>
	<li>Add 200 &#181;l of the cell suspension, containing 0.68-1 x106 cells, into 1.3 ml of the reaction medium prepared in 3.1.</li>
	<li>Aspirate the matrix solution from the overnight coated 6-well plate prepared in 2.2., transfer the reaction mixture to one well of a 6-well plate and distribute cells evenly. Incubate at 37&#160;&#176;C with 5% CO2 for 24 hr. After 24 hr at least 80% of the cells should be attached to the matrix.</li>
</ol>
4. Induction of Hematoendothelial Precursors from hPSCs (Day 1-7)
<ol>
	<li>24 hr post-transduction, remove virus-containing medium and wash attached cells with commercial incomplete cell culture medium (see Table 1) and then add 3 ml per well of commercial incomplete cell culture medium containing hematopoietic cytokines: SCF 100 ng/ml, TPO 50 ng/ml, bFGF 20 ng/ml (hereafter referred to as 3F-medium).</li>
	<li>Replace total medium with fresh 3F-medium on days 2, 3 and day 4 to remove dead cells and debris. After day 4, when floating hematopoietic cells are emerging, replace half of the 3F-medium every other day while maintaining the total volume at 4 ml. 
	NOTE: pSIN-EF1&#945; lentiviral expression plasmids incorporate puromycin resistance gene thereby allowing for positive selection of transduced cells. The 1 &#956;g/ml of puromycin can be added to medium during the first 1-2 days of differentiation to eliminate the any residual undifferentiated hPSCs.</li>
	<li>Observe cell morphology on day 4 under an inverted microscope: tight clusters of cells with typical endothelial morphology begin to appear (Figures 2A, 3A). Round blood cells appears from day 5 to day 7 of differentiation, while some areas may retain hPSCs morphology. Analyze HE and hematopoietic differentiation as described below. 
	NOTE: Successful hematoendothelial differentiation results in the production of blood cells that appear as refractile round cells loosely attached to underlying flat endothelial cells. These cells actively proliferate forming small aggregates, and eventually detach and float (Figures 2A and 3A). Live blood cells can be visually distinguished from the dead and dying cells based on their ability to reflect the light and expand in culture conditions.</li>
</ol>
5. Analysis of Hemogenic Endothelium (HE) Stage of Differentiation.
<ol>
	<li>Detect the formation of HE between days 3 and 4 of differentiation by microscopic observation of cells with endothelial morphology. There are no floating blood cells in the culture at this stage of differentiation. The presence of HE can be confirmed by immunofluorescent staining and flow cytometric analysis using VE-cadherin, CD73, CD226 and CD43 antibodies.
	<ol>
		<li>To assess HE formation by flow cytometric analysis use cells on day 3 and day 4 from one experiment. Collect cells by incubating of cultures with commercial cell dissociation reagent (see Table 1) for 5-10 min at 37 &#176;C, 5% CO2 and then use up to 1 x 105 cells per staining reaction (flow cytometry staining procedure described in 12). 
		NOTE: VE-cadherin+ HE cells acquire expression of early hematopoietic marker CD226, but lack the expression of CD73 and CD436. In contrast, non-HE cells express CD73 (Figures 2B, 3B).</li>
	</ol>
	</li>
	<li>Immunofluorescence staining for hPSC-derived HE.
	<ol>
		<li>Wash the attached monolayer of cells with phosphate buffered saline (PBS) and then fix cells in 4% paraformaldehyde from 30 to 60 min at room temperature.</li>
		<li>Wash cells again with PBS and then permeabilize using 0.1% Triton X-100 in PBS for 20 min at room temperature.</li>
		<li>Wash cells in PBS two to three times and then incubate in blocking buffer consisting of PBS with 10% fetal bovine serum (FBS), for 30 to 120 min.</li>
		<li>Prepare staining solution, containing both primary antibodies (1:1,000 dilution) mouse anti-human CD43 and rabbit anti-human VE-cadherin in PBS with 5% FBS, (Table 1).</li>
		<li>Aspirate the blocking buffer from the cells and add 1 ml per well of staining buffer with the added primary antibodies; incubate 3 hr at room temperature, or overnight at 4 &#176;C.</li>
		<li>Wash the cells three times by adding 2 ml of PBS with 5% FBS.</li>
		<li>Prepare a second staining buffer, containing secondary antibodies at 1:500 dilution in PBS with 5% FBS: donkey anti-rabbit conjugated with green fluorescent dye, and anti-mouse conjugated with red fluorescent dye (Table 1). Add 1 ml per well of secondary staining buffer and incubate at room temperature for 1 hr.</li>
		<li>Wash three times with PBS without serum. Stain cells with 300 nM DAPI working solution in dH2O for 10-15 min.</li>
		<li>Wash cells with PBS twice and add 2-3 ml of PBS into well with stained cells. Observe fluorescence with green, red and blue microscope filters.</li>
	</ol>
	</li>
</ol>
6. Analysis of Induced Hematopoietic Precursors
<ol>
	<li>Maintain differentiation cultures until floating cells expand significantly, up to 10-14 days, changing half of the 3F-medium, as described in 3.1, every two days.</li>
	<li>Dissociate and collect differentiating monolayers of cells by treating cells with a commercial cell dissociation reagent (see Table 1) for 5-10 min at 37 &#176;C, 5% CO2.</li>
	<li>Perform flow cytometry using anti-VE-cadherin, CD43 and CD45 antibodies to evaluate hematopoiesis in cultures12. Note that a large fraction of cells, up to 40% of ETV2 and GATA2 transduced cells, co-expresses VE-cad and CD43. The following antibodies can be used to detect specific cell lineages following expansion or differentiation of induced blood progenitors: CD235a (erythroid cells), CD41a (megakaryocytic), CD32 (all types of myeloid cells), CD66b (neutrophils) and CD163 (macrophages).</li>
	<li>Perform CFC-assay using a commercial clonogenic medium (Table 1) according to the manufacturer&#8217;s instructions.
	<ol>
		<li>Transfer 1-2 x 104 cells into 3 ml of commercial clonogenic medium (see Table 3) to assess the number of colony-forming cells and types of hematopoietic colonies. Optimal seeding density allows for the identification and isolation of single colonies that grow separately from each other and do not overlap. Seeding density may vary between experiments depending on differentiation efficiency, but should not exceed 1 x 104 cells per 1 ml of commercial clonogenic medium.</li>
		<li>Mix cells in commercial clonogenic medium by gentle vortexing, and transfer 3 ml of suspension to two 35 mm ultra-low attachment dishes for CFC assay, 1.5 ml of suspension to each dish. Distribute medium evenly and incubate at 37 &#176;C, 5% CO2 for 14 days. Avoid disturbing the dishes; observe colony formation on day 7 and day 10 of assay.</li>
		<li>Identify and count hematopoietic colonies according to their morphologies on day 14.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Zape, J. P., Zovein, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemogenic+endothelium:+origins,+regulation,+and+implications+for+vascular+biology.">Hemogenic endothelium: origins, regulation, and implications for vascular biology.</a> Semin Cell Dev Biol. 22, 1036-1047 (2011).</li><li>Swiers, G., Rode, C., Azzoni, E., de Bruijn, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+short+history+of+hemogenic+endothelium.">A short history of hemogenic endothelium.</a> Blood Cells, Mol &amp; Dis. 51, 206-212 (2013).</li><li>Kennedy, M., 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=T+lymphocyte+potential+marks+the+emergence+of+definitive+hematopoietic+progenitors+in+human+pluripotent+stem+cell+differentiation+cultures.">T lymphocyte potential marks the emergence of definitive hematopoietic progenitors in human pluripotent stem cell differentiation cultures.</a> Cell Rep. 2, 1722-1735 (2012).</li><li>Wang, 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=Endothelial+and+hematopoietic+cell+fate+of+human+embryonic+stem+cells+originates+from+primitive+endothelium+with+hemangioblastic+properties.">Endothelial and hematopoietic cell fate of human embryonic stem cells originates from primitive endothelium with hemangioblastic properties.</a> Immunity. 21, 31-41 (2004).</li><li>Rafii, 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=Human+ESC-derived+hemogenic+endothelial+cells+undergo+distinct+waves+of+endothelial+to+hematopoietic+transition.">Human ESC-derived hemogenic endothelial cells undergo distinct waves of endothelial to hematopoietic transition.</a> Blood. 121 (5), 770-780 (2012).</li><li>Choi, K. D., 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=Identification+of+the+hemogenic+endothelial+progenitor+and+its+direct+precursor+in+human+pluripotent+stem+cell+differentiation+cultures.">Identification of the hemogenic endothelial progenitor and its direct precursor in human pluripotent stem cell differentiation cultures.</a> Cell Rep. 2, 553-567 (2012).</li><li>Vodyanik, M. A., Thomson, J. A., Slukvin, I. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leukosialin+(CD43)+defines+hematopoietic+progenitors+in+human+embryonic+stem+cell+differentiation+cultures.">Leukosialin (CD43) defines hematopoietic progenitors in human embryonic stem cell differentiation cultures.</a> Blood. 108, 2095-2105 (2006).</li><li>Wang, C., 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=TGFbeta+inhibition+enhances+the+generation+of+hematopoietic+progenitors+from+human+ES+cell-derived+hemogenic+endothelial+cells+using+a+stepwise+strategy.">TGFbeta inhibition enhances the generation of hematopoietic progenitors from human ES cell-derived hemogenic endothelial cells using a stepwise strategy.</a> Cell Res. 22, 194-207 (2012).</li><li>Uenishi, G., 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=Tenascin+C+promotes+hematoendothelial+development+and+T+lymphoid+commitment+from+human+pluripotent+stem+cells+in+chemically+defined+conditions.">Tenascin C promotes hematoendothelial development and T lymphoid commitment from human pluripotent stem cells in chemically defined conditions.</a> Stem Cell Rep. 3, 1073-1084 (2014).</li><li>Elcheva, 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=Direct+induction+of+haematoendothelial+programs+in+human+pluripotent+stem+cells+by+transcriptional+regulators.">Direct induction of haematoendothelial programs in human pluripotent stem cells by transcriptional regulators.</a> Nat Commun. 5, 4372 (2014).</li><li>Tiscornia, G., Singer, O., Verma, I. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+and+purification+of+lentiviral+vectors.">Production and purification of lentiviral vectors.</a> Nat Protoc. 1, 241-245 (2006).</li><li>Vodyanik, M. A., Slukvin, I. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hematoendothelial+differentiation+of+human+embryonic+stem+cells.">Hematoendothelial differentiation of human embryonic stem cells.</a> Curr Protoc Cell Biol. Chapter 23, Unit 23.6 (2007).</li><li>Cao, F., 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=Comparison+of+gene-transfer+efficiency+in+human+embryonic+stem+cells.">Comparison of gene-transfer efficiency in human embryonic stem cells.</a> Mol Imgn and Biol. 12, 15-24 (2010).</li></ol>

I.S. is a founding shareholder and consultant for Cynata.

The above-described method for hematopoietic differentiation of hPSCs by overexpression of TFs, represents a rapid and efficient approach for the generation of HE and myeloid and erytho-magakaryocytic progenitors from hESCs and iPSCs, thereby allowing the production of up to 30 millions blood cells from one million pluripotent stem cells10. This method exhibited consistent differentiation in multiple hESC and iPSCs lines10. During differentiation by ETV2 and GATA2, GATA1 factors as well as GATA2 and...

The unique ability of human pluripotent stem cells (hPSCs) to self-renew and to differentiate into cells of the three germ layers, including blood, make them a valuable tool for the mechanistic studies of hematopoietic development, modeling of blood diseases, drug screening, toxicity studies, and the development of cellular therapies. Because blood formation in the embryo proceeds from hemogenic endothelium (HE) through an endothelial hematopoietic transition1,2, the generation of HE in cultures would be essential to study the molecular mechanisms regulating the endothelial to hematopoietic transition and hematopoietic specification. Current methods for studies of HE are based on the induction of hematoendothelial differentiation in aggregates (EBs) with the addition of hematopoietic cytokines3-5, and coculture of hPSCs with hematopoiesis-supportive stromal cells6,7 or in two-dimensional cultures with extracellular matrices and cytokines8,9. These classical differentiation methods are based on the introduction of external signals acting at the cell surface and initiating cascades of molecular pathways that eventually lead to the activation of transcriptional program guiding hematoendothelial development. Thus, the efficiency of hPSCs differentiations in these systems relies on an effective induction of those signals, signal transduction to the nucleus, and the resulting activation of specific transcriptional regulators. In addition, the study of HE in conventional differentiation cultures requires the additional step of isolating HE cells using cell sorting. Here, we describe a simple protocol for the direct induction of HE and blood by overexpression of hematopoietic transcription factors. This method allows for the efficient induction of HE in a dish and direct observation of the endothelial to hematopoietic transition without the need for isolation of HE using a cumbersome cell sorting procedure.
Formation of HE and blood from human pluripotent stem cells can be efficiently induced by overexpressing just a few transcription factors (TFs). The optimal combination of TFs capable of inducing robust pan-myeloid hematopoiesis from hPSCs includes ETV2 and GATA1 or GATA2. In contrast, combination of GATA2 and TAL1 induces erythromegakaryocytopoiesis10. Programming hPSCs through overexpression of these factors differentiates hPSCs directly to the VE-cad+CD43-CD73- HE cells that gradually acquire the hematopoietic phenotype defined by the expression of the early hematopoietic marker CD437. This lentiviral-based method for the direct programming of human pluripotent stem cells method is applicable for the generation of HE and blood cells for mechanistic studies, studies of endothelial to hematopoietic transition, and transcriptional regulation of hematopoietic development and specification. Although the current protocol describes blood production using constitutive expression of the transgenes, similar results could be obtained using modified mRNA10.

<table><tbody><tr><td colspan="4">&lt;p class=&quot;jove_content&quot; fo:keep-together.within-page=&quot;1&quot; fo:keep-with-previous.within-page=&quot;always&quot;&gt;&lt;strong&gt;Table 1.&lt;/strong&gt; &lt;strong&gt;Induction of hPSCs differentiation with trancription factors and analysis of hemogenic endothelium and blood cells.&lt;/strong&gt;&lt;/p&gt;</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>pSIN4-EF1a-ETV2-IRES-Puro&amp;nbsp;</td><td>Addgene</td><td>Plasmid #61061</td><td>Lentiviral Vector</td></tr><tr><td>pSIN4-EF1a-GATA2-IRES-Puro&amp;nbsp;</td><td>Addgene</td><td>Plasmid #61063</td><td>Lentiviral Vector</td></tr><tr><td>pSIN4-EF1a-GATA1-IRES-Puro&amp;nbsp;</td><td>Addgene</td><td>Plasmid #61062</td><td>Lentiviral Vector</td></tr><tr><td>pSIN4-EF1a-TAL1-IRES-Puro&amp;nbsp;</td><td>Addgene</td><td>Plasmid #61062</td><td>Lentiviral Vector</td></tr><tr><td>pSIN4-EF1a-LMO2-IRES-Puro&amp;nbsp;</td><td>Addgene</td><td>Plasmid #61064</td><td>Lentiviral Vector</td></tr><tr><td>Hexadimethrine bromide (Polybrene)&amp;nbsp;</td><td>Sigma-Aldrich</td><td>107689-10G</td><td>Cationic polymer used to increase the efficiency of infection</td></tr><tr><td>Y-27632 (Dihydrochloride) ROCK inhibitor</td><td>STEMCELL Technologies</td><td>72302</td><td>RHO/ROCK pathway inhibitor Inhibits ROCK</td></tr><tr><td>StemPro Accutase Cell Dissociation Reagent</td><td>&lt;a href=&quot;http://www.lifetechnologies.com/us/en/home/life-science/stem-cell-research/stem-cell-culture/stem-cell-research-misc/stempro-accutase.html&quot;&gt;Life Technologies&lt;/a&gt;</td><td>A11105-01</td><td>Cell Dissociation Reagent</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>Incomplete (growth factor- free) culture medium&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; mTeSR1 Custom formulation&amp;nbsp;</td><td>WiCell Research Institute (Madison, WI)</td><td>MCF</td><td>&lt;a name=&quot;RANGE!D12&quot;&gt;Serum-free mTeSR1 medium without bFGF and TGFb&amp;nbsp;&lt;/a&gt;</td></tr><tr><td>human SCF</td><td>Peprotech</td><td>300-07</td><td>Premium grade</td></tr><tr><td>human TPO</td><td>Peprotech</td><td>300-18</td><td>Research grade</td></tr><tr><td>human FGF-basic</td><td>Peprotech</td><td>100-18B</td><td>Premium grade</td></tr><tr><td>CD144 (VE-cad) FITC</td><td>BD Biosciences</td><td>560411</td><td>Endothelial marker (FACS)</td></tr><tr><td>CD226 PE</td><td>BD Biosciences</td><td>338305</td><td>Hematopoietic (FACS)</td></tr><tr><td>CD43 PE</td><td>BD Biosciences</td><td>560199</td><td>Hematopoietic (FACS)</td></tr><tr><td>CD73 APC</td><td>R&amp;amp;D Systems</td><td>FAB5795A</td><td>Endothelial marker (FACS)</td></tr><tr><td>CD45 APC</td><td>BD Biosciences</td><td>555485</td><td>Hematopoietic (FACS)</td></tr><tr><td>7AAD</td><td>Life Technologies</td><td>A1310</td><td>Live/Dead assay (FACS)</td></tr><tr><td>Paraformaldehyde&amp;nbsp;</td><td>Sigma-Aldrich</td><td>P6148-500G</td><td>Cell fixation&amp;nbsp;</td></tr><tr><td>Triton X-100&amp;nbsp;</td><td>Sigma-Aldrich</td><td>T9284-500ML&amp;nbsp;</td><td>Permeabilization&amp;nbsp;</td></tr><tr><td>FBS</td><td>Fisher Scientific</td><td>SH3007003</td><td>Fetal bovine serum</td></tr><tr><td>Mouse anti-human CD43</td><td>BD Biosciences</td><td>551457</td><td>Pure, primary antibody for Immunofluorescence (IF) staining</td></tr><tr><td>Rabbit anti-human VE-cadherin</td><td>BenderMedSystem</td><td>BMS158</td><td>Primary (IF)</td></tr><tr><td>Anti-rabbit Alexa Fluor 488-conjugated</td><td>JacksonResearch</td><td>715-486-152</td><td>Secondary (IF)</td></tr><tr><td>Anti-mouse Alexa Fluor 594-conjugated</td><td>JacksonResearch</td><td>715-516-150&amp;nbsp;</td><td>Secondary (IF)</td></tr><tr><td>DAPI nucleic acid stain</td><td>&lt;a href=&quot;http://www.lifetechnologies.com/us/en/home/life-science/stem-cell-research/stem-cell-culture/stem-cell-research-misc/stempro-accutase.html&quot;&gt;Life Technologies&lt;/a&gt;</td><td>D1306&amp;nbsp;</td><td>Live/Dead assay (IF)</td></tr><tr><td>Clonogenic medium MethoCult H4435 Enriched</td><td>STEMCELL Technologies</td><td>4435</td><td>CFC-assay</td></tr><tr><td>Wright Stain solution</td><td>Sigma -Aldrich</td><td>32857</td><td>Staining cytospins</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td colspan="4">&lt;p class=&quot;jove_content&quot; fo:keep-together.within-page=&quot;1&quot; fo:keep-with-previous.within-page=&quot;always&quot;&gt;&lt;/p&gt;</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td colspan="4">&lt;p class=&quot;jove_content&quot; fo:keep-together.within-page=&quot;1&quot; fo:keep-with-previous.within-page=&quot;always&quot;&gt;&lt;strong&gt;Table 2.&lt;/strong&gt; &lt;strong&gt;hPSCs culture.&lt;/strong&gt;&lt;/p&gt;</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>Human Pluripotent Stem Cells (hPSCs)&amp;nbsp;</td><td>WiCell Research Institute (Madison, WI)</td><td>hESCs (WA01, WA09) human Embryonic Stem cells; iPSCs (DF-19-9-7T, DF-4-3-7T) transgene-free induced Pluripotent Stem Cells</td><td>hPSCs are able to self-renew and to differentiate into cells of three germ layers</td></tr><tr><td>Complete serum-free medium for culture of hPSCs&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; mTeSR1 media&amp;nbsp;&amp;nbsp;</td><td>WiCell Research Institute (Madison, WI)</td><td>M500&amp;nbsp;</td><td>Serum-free&amp;nbsp; medium with growth factors for feeder free culture of ESC/iPSCs</td></tr><tr><td>Matrigel</td><td>BD Biosciences/ Corning&amp;nbsp;</td><td>356234</td><td>Matrix for maintenance of human ESC/iPSCs</td></tr><tr><td>DMEM/F-12, powder&amp;nbsp;</td><td>&lt;a href=&quot;http://www.lifetechnologies.com/us/en/home/life-science/stem-cell-research/stem-cell-culture/stem-cell-research-misc/stempro-accutase.html&quot;&gt;Life Technologies&lt;/a&gt;</td><td>12500-062</td><td>Basal Medium&amp;nbsp;</td></tr><tr><td>HyClone Dulbecco&#039;s PBS powder</td><td>Fisher Scientific</td><td>dSH30013.04</td><td>PBS</td></tr><tr><td>Dispase II, powder</td><td>&lt;a href=&quot;http://www.lifetechnologies.com/us/en/home/life-science/stem-cell-research/stem-cell-culture/stem-cell-research-misc/stempro-accutase.html&quot;&gt;Life Technologies&lt;/a&gt;</td><td>17105-041</td><td>Neutral protease, Cell dissociation</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td colspan="4">&lt;p class=&quot;jove_content&quot; fo:keep-together.within-page=&quot;1&quot; fo:keep-with-previous.within-page=&quot;always&quot;&gt;&lt;strong&gt;Table 3.&lt;/strong&gt; &lt;strong&gt;Primers for detection of virus genomic integration.&lt;/strong&gt;&lt;/p&gt;</td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td>&lt;strong&gt;Primer&#039;s Name&lt;/strong&gt;</td><td>&lt;strong&gt;Forward (Fwd)&amp;nbsp; 5&amp;rsquo; --&gt;3&amp;rsquo;&lt;/strong&gt;</td><td>&lt;strong&gt;Reverse (Rev) 5&amp;rsquo;--&gt;3&amp;rsquo;&lt;/strong&gt;</td><td>&lt;strong&gt;Discription&amp;nbsp;&lt;/strong&gt;</td></tr><tr><td>pSIN EF1a Fwd</td><td>TTC CAT TTC AGG TGT CGT GA</td><td>--</td><td>EF1a promoter sequence</td></tr><tr><td>GATA1 Rev</td><td>--</td><td>TCC CTG TAG TAG GCC AGT GC</td><td>&amp;nbsp;Coding Region&amp;nbsp;</td></tr><tr><td>GATA2 Rev</td><td>--</td><td>GGT TGG CAT AGT AGG GGT TG</td><td>&amp;nbsp;Coding Region&amp;nbsp;</td></tr><tr><td>TAL1 Rev</td><td>--</td><td>AGG CGG AGG ATC TCA TTC TT</td><td>&amp;nbsp;Coding Region&amp;nbsp;</td></tr><tr><td>LMO2 Rev</td><td>--</td><td>GGC CCA GTT TGT AGT AGA GGC</td><td>&amp;nbsp;Coding Region&amp;nbsp;</td></tr><tr><td>ETV2 Rev</td><td>--</td><td>GAA CTT CTG GGT GCA GTA AC&amp;nbsp;</td><td>&amp;nbsp;Coding Region&amp;nbsp;</td></tr></tbody></table>

direct induction of hemogenic endothelium and blood by overexpression of transcription factors in human pluripotent stem cells

During development, hematopoietic cells arise from a specialized subset of endothelial cells, hemogenic endothelium (HE). Modeling HE development in vitro is essential for mechanistic studies of the endothelial-hematopoietic transition and hematopoietic specification. Here, we describe a method for the efficient induction of HE from human pluripotent stem cells (hPSCs) by way of overexpression of different sets of transcription factors. The combination of ETV2 and GATA1 or GATA2 TFs is used to induce HE with pan-myeloid potential, while a combination of GATA2 and TAL1 transcription factors allows for the production of HE with erythroid and megakaryocytic potential. The addition of LMO2 to GATA2 and TAL1 combination substantially accelerates differentiation and increases erythroid and megakaryocytic cells production. This method provides an efficient and rapid means of HE induction from hPSCs and allows for the observation of the endothelial-hematopoietic transition in a culture dish. The protocol includes hPSCs transduction procedures and post-transduction analysis of HE and blood progenitors.

The schematic diagram of HE and blood induction from hPSCs by overexpression of transcription factors is shown in Figure 1. ETV2 with GATA1 or GATA2 combination induces pan-myeloid hematopoiesis, while a GATA2, TAL1 +/- LMO2 combination induces predominantly erythro-megakaryocytic hematopoiesis. Both TF combinations directly induced HE cells that subsequently transformed into blood progenitors with a distinct spectrum of hematopoietic differentiation. Differentiation of hPSCs from the pluripotent state t...

Watch this Scientific Journal Video about Direct Induction of Hemogenic Endothelium and Blood by Overexpression of Transcription Factors in Human Pluripotent Stem Cells at JoVE.com

Direct Induction of Hemogenic Endothelium and Blood by Overexpression of Transcription Factors in Human Pluripotent Stem Cells

This protocol describes the efficient induction of hemogenic endothelium and multipotential hematopoietic progenitors from human pluripotent stem cells via the forced expression of transcription factors.

During development, hematopoietic cells arise from a specialized subset of endothelial cells, hemogenic endothelium (HE). Modeling HE development in vitro ...

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Research

JoVE Journal

Developmental Biology

7.5K Views.  University of Wisconsin-Madison. This protocol describes the efficient induction of hemogenic endothelium and multipotential hematopoietic progenitors from human pluripotent stem cells via the forced expression of transcription factors. 

Video: Direct Induction of Hemogenic Endothelium and Blood by Overexpression of Transcription Factors in Human Pluripotent Stem Cells

Direct Induction of Human Neural Stem Cells from Peripheral Blood Hematopoietic Progenitor Cells

Human disease specific neuronal cultures are essential for generating in vitro models for human neurological diseases. However, the lack of access to primary human adult neural cultures raises unique challenges. Recent developments in induced pluripotent stem cells (iPSC) provides an alternative approach to derive neural cultures from skin fibroblasts through patient specific iPSC, but this process is labor intensive, requires special expertise and large amounts of resources, and can take several months. This prevents the wide application of this technology to the study of neurological diseases. To overcome some of these issues, we have developed a method to derive neural stem cells directly from human adult peripheral blood, bypassing the iPSC derivation process. Hematopoietic progenitor cells enriched from human adult peripheral blood were cultured in vitro and transfected with Sendai virus vectors containing transcriptional factors Sox2, Oct3/4, Klf4, and c-Myc. The transfection results in morphological changes in the cells which are further selected by using human neural progenitor medium containing basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). The resulting cells are characterized by the expression for neural stem cell markers, such as nestin and SOX2. These neural stem cells could be further differentiated to neurons, astroglia and oligodendrocytes in specified differentiation media. Using easily accessible human peripheral blood samples, this method could be used to derive neural stem cells for further differentiation to neural cells for in vitro modeling of neurological disorders and may advance studies related to the pathogenesis and treatment of those diseases.

A method was developed to directly derive human neural stem cells from hematopoietic progenitor cells enriched from peripheral blood cells.

Human disease specific neuronal cultures are essential for generating in vitro models for human neurological diseases. However, the lack of access to ...

Reprogramming Mouse Embryonic Fibroblasts with Transcription Factors to Induce a Hemogenic Program

This protocol details the induction of a hemogenic program in mouse embryonic fibroblasts (MEFs) via overexpression of transcription factors (TFs). We first designed a reporter screen using MEFs from human CD34-tTA/TetO-H2BGFP (34/H2BGFP) double transgenic mice. CD34+ cells from these mice label H2B histones with GFP, and cease labeling upon addition of doxycycline (DOX). MEFS were transduced with candidate TFs and then observed for the emergence of GFP+ cells that would indicate the acquisition of a hematopoietic or endothelial cell fate. Starting with 18 candidate TFs, and through a process of combinatorial elimination, we obtained a minimal set of factors that would induce the highest percentage of GFP+ cells. We found that Gata2, Gfi1b, and cFos were necessary and the addition of Etv6 provided the optimal induction. A series of gene expression analyses done at different time points during the reprogramming process revealed that these cells appeared to go through a precursor cell that underwent an endothelial to hematopoietic transition (EHT). As such, this reprogramming process mimics developmental hematopoiesis "in a dish," allowing study of hematopoiesis in vitro and a platform to identify the mechanisms that underlie this specification. This methodology also provides a framework for translation of this work to the human system in the hopes of generating an alternative source of patient-specific hematopoietic stem cells (HSCs) for a number of applications in the treatment and study of hematologic diseases.

The protocol described here details the induction of a hemogenic program in mouse embryonic fibroblasts via overexpression of a minimal set of transcription factors. This technology may be translated to the human system to provide platforms for future study of hematopoiesis, hematologic disease, and hematopoietic stem cell transplant.

This protocol details the induction of a hemogenic program in mouse embryonic fibroblasts (MEFs) via overexpression of transcription factors (TFs). We ...

Induced Pluripotent Stem Cell Generation from Blood Cells Using Sendai Virus and Centrifugation

The recent development of human induced pluripotent stem cells (hiPSCs) proved that mature somatic cells can return to an undifferentiated, pluripotent state. Now, reprogramming is done with various types of adult somatic cells: keratinocytes, urine cells, fibroblasts, etc. Early experiments were usually done with dermal fibroblasts. However, this required an invasive surgical procedure to obtain fibroblasts from the patients. Therefore, suspension cells, such as blood and urine cells, were considered ideal for reprogramming because of the convenience of obtaining the primary cells. Here, we report an efficient protocol for iPSC generation from peripheral blood mononuclear cells (PBMCs). By plating the transduced PBMCs serially to a new, matrix-coated plate using centrifugation, this protocol can easily provide iPSC colonies. This method is also applicable to umbilical cord blood mononuclear cells (CBMCs). This study presents a simple and efficient protocol for the reprogramming of PBMCs and CBMCs.

We propose a protocol for reprogramming peripheral blood mononuclear cells (PBMCs) into induced pluripotent stem cells (iPSCs). By plating the transduced blood cells onto matrix-coated plates with centrifugation, iPSCs are successfully induced from floating cells. This technique suggests a simple and effective reprogramming protocol for cells such as PBMCs and CBMCs.

The recent development of human induced pluripotent stem cells (hiPSCs) proved that mature somatic cells can return to an undifferentiated, pluripotent ...

Generation of Integration-free Induced Pluripotent Stem Cells from Human Peripheral Blood Mononuclear Cells Using Episomal Vectors

Induced Pluripotent Stem Cells (iPSCs) hold great promise for disease modeling and regenerative therapies. We previously reported the use of Episomal Vectors (EV) to generate integration-free iPSCs from peripheral blood mononuclear cells (PB MNCs). The episomal vectors used are DNA plasmids incorporated with oriP and EBNA1 elements from the Epstein-Barr (EB) virus, which&#160;allow for replication and long-term retainment of plasmids in mammalian cells, respectively. With further optimization, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood. Two critical factors for achieving high reprogramming efficiencies&#160;are: 1) the use of a 2A &#34;self-cleavage&#34; peptide to link OCT4 and SOX2, thus achieving equimolar expression of the two factors; 2) the use of two vectors to express MYC and KLF4 individually. Here we describe a step-by-step protocol for generating integration-free iPSCs from adult peripheral blood samples. The generated iPSCs are integration-free as residual episomal plasmids are undetectable after five passages. Although the reprogramming efficiency is comparable to that of Sendai Virus (SV) vectors, EV plasmids are considerably more economical than the commercially available SV vectors. This affordable EV reprogramming system holds potential for clinical applications in regenerative medicine and provides an approach for the direct reprogramming of PB MNCs to integration-free mesenchymal stem cells, neural stem cells, etc.

This protocol describes a detailed method for efficient generation of integration-free iPSCs from human adult peripheral blood cells. With the use of four oriP/EBNA-based episomal vectors to express the reprogramming factors, KLF4, MYC, BCL-XL, or OCT4 and SOX2, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood.

Induced Pluripotent Stem Cells (iPSCs) hold great promise for disease modeling and regenerative therapies. We previously reported the use of Episomal ...

Directed Differentiation of Primitive and Definitive Hematopoietic Progenitors from Human Pluripotent Stem Cells

One of the major goals for regenerative medicine is the generation and maintenance of hematopoietic stem cells (HSCs) derived from human pluripotent stem cells (hPSCs). Until recently, efforts to differentiate hPSCs into HSCs have predominantly generated hematopoietic progenitors that lack HSC potential, and instead resemble yolk sac hematopoiesis.&#160;These resulting hematopoietic progenitors may have limited utility for in vitro disease modeling of various adult hematopoietic disorders, particularly those of the lymphoid lineages. However, we have recently described methods to generate erythro-myelo-lymphoid multilineage definitive hematopoietic progenitors from hPSCs using a stage-specific directed differentiation protocol, which we outline here. Through enzymatic dissociation of hPSCs on basement membrane matrix-coated plasticware, embryoid bodies (EBs) are formed. EBs are differentiated to mesoderm by recombinant BMP4, which is subsequently specified to the definitive hematopoietic program by the GSK3&#946; inhibitor, CHIR99021. Alternatively, primitive hematopoiesis is specified by the PORCN inhibitor, IWP2. Hematopoiesis is further driven through the addition of recombinant VEGF and supportive hematopoietic cytokines. The resulting hematopoietic progenitors generated using this method have the potential to be used for disease and developmental modeling, in vitro.

Here, we present human pluripotent stem cell (hPSC) culture protocols, used to differentiate hPSCs into CD34+ hematopoietic progenitors. This method uses stage-specific manipulation of canonical WNT signaling to specify cells exclusively to either the definitive or primitive hematopoietic program.

One of the major goals for regenerative medicine is the generation and maintenance of hematopoietic stem cells (HSCs) derived from human pluripotent stem ...

Hemogenic Endothelium Differentiation from Human Pluripotent Stem Cells in A Feeder- and Xeno-free Defined Condition

Deriving functional hematopoietic stem and progenitor cells (HSPCs) from human pluripotent stem cells (PSCs) have been an elusive goal for autologous transplants to treat hematological and malignant disorders. Hemogenic endothelium (HE) is an amenable platform to produce functional HSPCs by transcription factors or to induce lymphocytes in a robust manner. However, current methods to derive HE are either costly or variable in yield. In this protocol, we established a cost-effective and precise method to derive HE within 4 days in a feeder- and xeno-free defined condition. The resultant HE underwent an endothelial-to-hematopoietic transition and produced CD34+CD45+ clonogenic hematopoietic progenitors. The potential capacity of our platform for generating functional HSPCs will have broad applications in disease modeling and screening for therapeutic compounds.

Here, we present a protocol to precisely form hemogenic endothelium from human pluripotent stem cells in a feeder- and xeno-free condition. This method will have broad applications in disease modeling and screening for therapeutic compounds.

Deriving functional hematopoietic stem and progenitor cells (HSPCs) from human pluripotent stem cells (PSCs) have been an elusive goal for autologous ...

Hemogenic Reprogramming of Human Fibroblasts by Enforced Expression of Transcription Factors

The cellular and molecular mechanisms underlying specification of human hematopoietic stem cells (HSCs) remain elusive. Strategies to recapitulate human HSC emergence in vitro are required to overcome limitations in studying this complex developmental process. Here, we describe a protocol to generate hematopoietic stem and progenitor-like cells from human dermal fibroblasts employing a direct cell reprogramming approach. These cells transit through a hemogenic intermediate cell-type, resembling the endothelial-to-hematopoietic transition (EHT) characteristic of HSC specification. Fibroblasts were reprogrammed to hemogenic cells via transduction with GATA2, GFI1B and FOS transcription factors. This combination of three factors induced morphological changes, expression of hemogenic and hematopoietic markers and dynamic EHT transcriptional programs. Reprogrammed cells generate hematopoietic progeny and repopulate immunodeficient mice for three months. This protocol can be adapted towards the mechanistic dissection of the human EHT process as exemplified here by defining GATA2 targets during the early phases of reprogramming. Thus, human hemogenic reprogramming provides a simple and tractable approach to identify novel markers and regulators of human HSC emergence. In the future, faithful induction of hemogenic fate in fibroblasts may lead to the generation of patient-specific HSCs for transplantation.

This protocol demonstrates the induction of a hemogenic program in human dermal fibroblasts by enforced expression of the transcription factors GATA2, GFI1B and FOS to generate hematopoietic stem and progenitor cells.

The cellular and molecular mechanisms underlying specification of human hematopoietic stem cells (HSCs) remain elusive. Strategies to recapitulate human ...

Directed Differentiation of Hemogenic Endothelial Cells from Human Pluripotent Stem Cells

Blood vessels are ubiquitously distributed within all tissues of the body and perform diverse functions. Thus, derivation of mature vascular endothelial cells, which line blood vessel lumens, from human pluripotent stem cells is crucial for a multitude of tissue engineering and regeneration applications. In vivo, primordial endothelial cells are derived from the mesodermal lineage and are specified toward specific subtypes, including arterial, venous, capillary, hemogenic, and lymphatic. Hemogenic endothelial cells are of particular interest because, during development, they give rise to hematopoietic stem and progenitor cells, which then generate all blood lineages throughout life. Thus, creating a system to generate hemogenic endothelial cells in vitro would provide an opportunity to study endothelial-to-hematopoietic transition, and may lead to ex vivo production of human blood products and reduced reliance on human donors. While several protocols exist for the derivation of progenitor and primordial endothelial cells, generation of well-characterized hemogenic endothelial cells from human stem cells has not been described. Here, a method for the derivation of hemogenic endothelial cells from human embryonic stem cells in approximately 1 week is presented: a differentiation protocol with primitive streak cells formed in response to GSK3&#946; inhibitor (CHIR99021), then mesoderm lineage induction mediated by bFGF, followed by primordial endothelial cell development promoted by BMP4 and VEGF-A, and finally hemogenic endothelial cell specification induced by retinoic acid. This protocol yields a well-defined population of hemogenic endothelial cells that can be used to further understand their molecular regulation and endothelial-to-hematopoietic transition, which has the potential to be applied to downstream therapeutic applications.

Presented here is a simple protocol for the directed differentiation of hemogenic endothelial cells from human pluripotent stem cells in approximately 1 week.

Blood vessels are ubiquitously distributed within all tissues of the body and perform diverse functions. Thus, derivation of mature vascular endothelial ...

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, ...

Biology

Generation of Human Blood Vessel Organoids from Pluripotent Stem Cells

An organoid is defined as an engineered multicellular in vitro tissue that mimics its corresponding in vivo organ such that it can be used to study defined aspects of that organ in a tissue culture dish. The breadth and application of human pluripotent stem cell (hPSC)-derived organoid research have advanced significantly to include the brain, retina, tear duct, heart, lung, intestine, pancreas, kidney, and blood vessels, among several other tissues. The development of methods for the generation of human microvessels, specifically, has opened the way for modeling human blood vessel development and disease in vitro and for the testing and analysis of new drugs or tissue tropism in virus infections, including SARS-CoV-2. Complex and lengthy protocols lacking visual guidance hamper the reproducibility of many stem cell-derived organoids. Additionally, the inherent stochasticity of organoid formation processes and self-organization necessitates the generation of optical protocols to advance the understanding of cell fate acquisition and programming. Here, a visually guided protocol is presented for the generation of 3D human blood vessel organoids (BVOs) engineered from hPSCs. Presenting a continuous basement membrane, vascular endothelial cells, and organized articulation with mural cells, BVOs exhibit the functional, morphological, and molecular features of human microvasculature. BVO formation is initiated through aggregate formation, followed by mesoderm and vascular induction. Vascular maturation and network formation are initiated and supported by embedding aggregates in a 3D collagen and solubilized basement membrane matrix. Human vessel networks form within 2-3 weeks and can be further grown in scalable culture systems. Importantly, BVOs transplanted into immunocompromised mice anastomose with the endogenous mouse circulation and specify into functional arteries, veins, and arterioles. The present visually guided protocol will advance human organoid research, particularly in relation to blood vessels in normal development, tissue vascularization, and disease.

This protocol describes the generation of self-organizing blood vessels from human pluripotent and induced pluripotent stem cells. These blood vessel networks exhibit an extensive and connected endothelial network surrounded by pericytes, smooth muscle actin, and a continuous basement membrane.

An organoid is defined as an engineered multicellular in vitro tissue that mimics its corresponding in vivo organ such that it can be used to study ...