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Summary The recent identification of hemogenic endothelium (HE) in human pluripotent stem cell (hPSC) cultures presents opportunities to investigate signaling pathways that are essential for blood development from endothelium and provides an exploratory platform for de novo generation of hematopoietic stem cells (HSCs). However, the use of poorly defined human or animal components limits the utility of the current differentiation systems for studying specific growth factors required for HE induction and manufacturing clinical-grade therapeutic blood cells. Here, we identified chemically defined conditions required to produce HE from hPSCs growing in Essential 8 (E8) medium and showed that Tenascin C (TenC), an extracellular matrix protein associated with HSC niches, strongly promotes HE and definitive hematopoiesis in this system. hPSCs differentiated in chemically defined conditions undergo stages of development similar to those previously described in hPSCs cocultured on OP9 feeders, including the formation of VE-Cadherin+CD73−CD235a/CD43− HE and hematopoietic progenitors with myeloid and T lymphoid potential., Graphical Abstract, Highlights • Hemogenic endothelium is generated in a completely defined xenogen-free system • The system reproduces all stages of hematopoietic development • Tenascin C enhances hematoendothelial development from pluripotent stem cells • Tenesacin C uniquely supports T cell specification, In this article, Slukvin and colleagues describe a feeder- and xenogene-free chemically defined platform for differentiating human pluripotent stem cells into definitive hematopoietic cells. They find that Tenascin C, a matrix protein associated with hematopoietic stem cell niches, strongly promotes hemogenic endothelium development and T lymphoid commitment in this system.

Induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity for modeling of human diseases in vitro, as well as for developing novel approaches for regenerative therapy based on immunologically compatible cells. In this study, we employed an OP9 differentiation system to characterize the hematopoietic and endothelial differentiation potential of seven human iPSC lines obtained from human fetal, neonatal, and adult fibroblasts through reprogramming with POU5F1, SOX2, NANOG, and LIN28 and compared it with the differentiation potential of five human embryonic stem cell lines (hESC, H1, H7, H9, H13, and H14). Similar to hESCs, all iPSCs generated CD34+CD43+ hematopoietic progenitors and CD31+CD43− endothelial cells in coculture with OP9. When cultured in semisolid media in the presence of hematopoietic growth factors, iPSC-derived primitive blood cells formed all types of hematopoietic colonies, including GEMM colony-forming cells. Human induced pluripotent cells (hiPSCs)-derived CD43+ cells could be separated into the following phenotypically defined subsets of primitive hematopoietic cells: CD43+CD235a+CD41a± (erythro-megakaryopoietic), lin−CD34+CD43+CD45− (multipotent), and lin−CD34+CD43+CD45+ (myeloid-skewed) cells. Although we observed some variations in the efficiency of hematopoietic differentiation between different hiPSCs, the pattern of differentiation was very similar in all seven tested lines obtained through reprogramming of human fetal, neonatal, or adult fibroblasts with three or four genes. Although several issues remain to be resolved before iPSC-derived blood cells can be administered to humans for therapeutic purposes, patient-specific iPSCs can already be used for characterization of mechanisms of blood diseases and for identification of molecules that can correct affected genetic networks.

Objective Cellular and molecular changes that occur during the genesis of the hematopoietic system and hematopoietic stem cells in the human embryo are mostly inaccessible to study and remain poorly understood. To address this gap we have exploited the human embryonic stem cell (hESC) system to molecularly characterize the global transcriptomes of the two functionally discreet and phenotypically separable populations of multipotent hematopoietic cells that first appear when hESCs are induced to differentiate on OP9 cells. Materials and Methods We prepared long serial analysis of gene expression libraries from lin − CD34 + CD43 + CD45 − and lin − CD34 + CD43 + CD45 + subsets of primitive hematopoietic cells derived in vitro from hESCs, sequenced them to a depth of 200,000 tags and compared their content with similar libraries prepared from highly purified populations of very primitive human fetal liver and cord blood hematopoietic cells. Results Comparison of libraries obtained from hESC-derived lin − CD34 + CD43 + CD45 − and lin − CD34 + CD43 + CD45 + revealed differences in their expression of genes associated with myeloid development, cellular biosynthetic processes, and cell-cycle regulation. Further comparisons with analogous data for primitive hematopoietic cells isolated from first-trimester human fetal liver and newborn cord blood showed an apparent similarity between the transcriptomes of the most primitive hESC- and in vivo–derived populations, with the main differences involving genes that regulate HSC self-renewal and homing, chromatin remodeling, AP1 transcription complex genes, and noncoding RNAs. Conclusion These data suggest that primitive hematopoietic cells are generated from hESCs in vitro by processes similar to those operative during human embryogenesis in vivo, although some differences were also detected.

During hematopoietic differentiation of human embryonic stem cells (hESCs), early hematopoietic progenitors arise along with endothelial cells within the CD34(+) population. Although hESC-derived hematopoietic progenitors have been previously identified by functional assays, their phenotype has not been defined. Here, using hESC differentiation in coculture with OP9 stromal cells, we demonstrate that early progenitors committed to hematopoietic development could be identified by surface expression of leukosialin (CD43). CD43 was detected on all types of emerging clonogenic progenitors before expression of CD45, persisted on differentiating hematopoietic cells, and reliably separated the hematopoietic CD34(+) population from CD34(+)CD43(-)CD31(+)KDR(+) endothelial and CD34(+)CD43(-)CD31(-)KDR(-) mesenchymal cells. Furthermore, we demonstrated that the first-appearing CD34(+)CD43(+)CD235a(+)CD41a(+/-)CD45(-) cells represent precommitted erythro-megakaryocytic progenitors. Multipotent lymphohematopoietic progenitors were generated later as CD34(+)CD43(+)CD41a(-)CD235a(-)CD45(-) cells. These cells were negative for lineage-specific markers (Lin(-)), expressed KDR, VE-cadherin, and CD105 endothelial proteins, and expressed GATA-2, GATA-3, RUNX1, C-MYB transcription factors that typify initial stages of definitive hematopoiesis originating from endothelial-like precursors. Acquisition of CD45 expression by CD34(+)CD43(+)CD45(-)Lin(-) cells was associated with progressive myeloid commitment and a decrease of B-lymphoid potential. CD34(+)CD43(+)CD45(+)Lin(-) cells were largely devoid of VE-cadherin and KDR expression and had a distinct FLT3(high)GATA3(low)RUNX1(low)PU1(high)MPO(high)IL7RA(high) gene expression profile.

Problem Tumor necrosis factor (TNF) and soluble TNF receptors (sTNF-Rs) system related with Th1 and Th2 and activity of NF-κB/IκB regulatory system. This study was designed to compare sTNF-R1 and sTNF-R2 production (shedding) and levels of late activated CD8+ T-lymphocytes in non-pregnant (n = 30) and pregnant (n = 20) normal women and non-pregnant (n = 20) and pregnant (n = 30) RSA women. Effects of progesterone (natural structure) injections in RSA women were studied. Methods of study Levels of sTNF-R1, sTNF-R2, TNF in peripheral blood serum were detected by enzyme-linked immunosorbent assay. Lymphocyte subsets were estimated by multicolor flow cytometry. NK cell cytotoxic activity of peripheral blood lymphocytes (PBL) in whole blood against K562 targets was determined using Europium-release cytotoxicity assay. Mitogen-induced proliferative response of PBL to PHA-P, Con A and PWM were determined by standard 3H-thymidine incorporation assay. Results Levels of soluble TNF-R1 and TNF-R2 in normal pregnancy were elevated when compared with non-pregnant normal women and pregnant RSA women. Levels of late activated CD8+ T-lymphocytes in normal pregnancy were decreased but no changes were detected in RSA women. After progesterone therapy (i.m. injections of 2.5% oil solution) in RSA women elevation of sTNF-R1 and sTNF-R2 to normal pregnancy ranges was observed. No changes in levels of late activated CD8+ T-lymphocytes after progesterone treatment were detected. Conclusions Elevation of levels of sTNF-R1, sTNF-R2 and decrease of late activated cytotoxic T-lymphocytes are pronounce markers of normal human pregnancy. In RSA women there are no elevation of sTNF-R1 and sTNF-R2 levels during pregnancy. This deficiency may be restored by progesterone treatment.

Embryonic stem (ES) cells have the potential to serve as an alternative source of hematopoietic precursors for transplantation and for the study of hematopoietic cell development. Using coculture of human ES (hES) cells with OP9 bone marrow stromal cells, we were able to obtain up to 20% of CD34+ cells and isolate up to 107 CD34+ cells with more than 95% purity from a similar number of initially plated hES cells after 8 to 9 days of culture. The hES cell–derived CD34+ cells were highly enriched in colony-forming cells, cells expressing hematopoiesis-associated genes GATA-1, GATA-2, SCL/TAL1, and Flk-1, and retained clonogenic potential after in vitro expansion. CD34+ cells displayed the phenotype of primitive hematopoietic progenitors as defined by co-expression of CD90, CD117, and CD164, along with a lack of CD38 expression and contained aldehyde dehydrogenase–positive cells as well as cells with verapamil-sensitive ability to efflux rhodamine 123. When cultured on MS-5 stromal cells in the presence of stem cell factor, Flt3-L, interleukin 7 (IL-7), and IL-3, isolated CD34+ cells differentiated into lymphoid (B and natural killer cells) as well as myeloid (macrophages and granulocytes) lineages. These data indicate that CD34+ cells generated through hES/OP9 coculture display several features of definitive hematopoietic stem cells.

Decidual and peripheral blood lymphocyte subsets were studied for their expression of CD44, L-selectin (Leu-8), CD54, and CD11b cell adhesion molecules (CAM). Most CD3+, CD4+, CD8+, and CD56+ cells in decidua were L-selectin- and CD44+, i.e., had a phenotype consistent with mucosa-homing preference of decidual lymphocytes (DL). We observed trimodal staining of decidual and peripheral blood CD56+ and CD8+ cells with anti-CD44 monoclonal antibody; negative, weakly positive, and brightly positive subpopulations were evident. Relatively high levels of CD44-negative CD56+ and CD8+ cells were found in decidua. Most decidual T and natural killer (NK) cells expressed high amounts of the CD54 molecule. Substantially higher numbers of CD3+, CD4+, and CD8+ cells in decidua bore CD11b, whereas the percentage of CD11b-positive NK cells was significantly lower in decidua, compared with that seen in peripheral blood. As opposed to peripheral blood lymphocytes (PBL), phorbol 12-myristate 13-acetate (PMA) stimulation of decidual NK cells elicited a rapid increase in the numbers of CD11b-positive cells but not increased fluorescence intensity of CD11b on the stained cells. The CD54 molecule was also up-regulated on decidual and peripheral blood NK cells but only after 15 hr of stimulation with PMA. In contrast to peripheral blood cells, activation of decidual mononuclear cells by K562 did not lead to an augmentation of the CD11b and CD54 expression on NK lymphocytes. These findings suggest that expression of CAM on DL is regulated in a manner different from that of PBL, and CAM expression may be adapted to accommodate placentation in human beings. The interaction of lymphocytes by means of antigen-independent cell-cell adhesion could be essential for the development of the placenta and the regulation of the local maternal immune response to the genetically foreign fetus.

Hemogenic endothelium (HE) has been recognized as a source of hematopoietic stem cells (HSCs) in the embryo. Access to human HE progenitors (HEPs) is essential for enabling the investigation of the molecular determinants of HSC specification. Here, we show that HEPs capable of generating definitive hematopoietic cells can be obtained from human pluripotent stem cells (hPSCs) and identified precisely by a VE-cadherin(+)CD73(-)CD235a/CD43(-) phenotype. This phenotype discriminates true HEPs from VE-cadherin(+)CD73(+) non-HEPs and VE-cadherin(+)CD235a(+)CD41a(-) early hematopoietic cells with endothelial and FGF2-dependent hematopoietic colony-forming potential. We found that HEPs arise at the post-primitive-streak stage of differentiation directly from VE-cadherin-negative KDR(bright)APLNR(+)PDGFRα(low/-) hematovascular mesodermal precursors (HVMPs). In contrast, hemangioblasts, which are capable of forming endothelium and primitive blood cells, originate from more immature APLNR(+)PDGFRα(+) mesoderm. The demarcation of HEPs and HVMPs provides a platform for modeling blood development from endothelium with a goal of facilitating the generation of HSCs from hPSCs.

Mesenchymal stem/stromal cells (MSCs) are fibroblastoid cells capable of long-term expansion and skeletogenic differentiation. While MSCs are known to originate from neural crest and mesoderm, immediate mesodermal precursors that give rise to MSCs have not been characterized. Recently, using human embryonic stem cells (hESCs), we demonstrated that mesodermal MSCs arise from APLNR+ precursors with angiogenic potential, mesenchymoangioblasts, which can be identified by FGF2-dependent colony-forming assay in serum-free semisolid medium. In this overview we provide additional insights on cellular pathways leading to MSC establishment from mesoderm, with special emphasis on endothelial-mesenchymal transition as a critical step in MSC formation. In addition, we highlight an essential role of FGF2 in induction of angiogenic cells with potential to transform into MSCs (mesenchymoangioblasts) or hematopoietic cells (hemangioblasts) from mesoderm, and discuss correlations of our in vitro findings with the course of angioblast development during embryogenesis.

Differentiation of human induced pluripotent stem cells (hiPSCs) and embryonic stem cells (hESCs) into the erythroid lineage of cells offers a novel opportunity to study erythroid development, regulation of globin switching, drug testing, and modeling of red blood cell (RBC) diseases in vitro. Here we describe an approach for the efficient generation of RBCs from hiPSC/hESCs using an OP9 coculture system to induce hematopoietic differentiation followed by selective expansion of erythroid cells in serum-free media with erythropoiesis-supporting cytokines. We showed that fibroblast-derived transgenic hiPSCs generated using lentivirus-based vectors and transgene-free hiPSCs generated using episomal vectors can be differentiated into RBCs with an efficiency similar to that of H1 hESCs. Erythroid cultures established with this approach consisted of an essentially pure population of CD235a(+)CD45(-) leukocyte-free RBCs with robust expansion potential and long life span (up to 90 days). Similar to hESCs, hiPSC-derived RBCs expressed predominately fetal γ and embryonic ɛ globins, indicating complete reprogramming of β-globin locus following transition of fibroblasts to the pluripotent state. Although β-globin expression was detected in hiPSC/hESC-derived erythroid cells, its expression was substantially lower than the embryonic and fetal globins. Overall, these results demonstrate the feasibility of large-scale production of erythroid cells from fibroblast-derived hiPSCs, as has been described for hESCs. Since RBCs generated from transgene-free hiPSCs lack genomic integration and background expression of reprogramming genes, they would be a preferable cell source for modeling of diseases and for gene function studies.

In this paper, we describe a protocol for hematopoietic differentiation of human pluripotent stem cells (hPSCs) and generation of mature myeloid cells from hPSCs through expansion and differentiation of hPSC-derived lin(-)CD34(+)CD43(+)CD45(+) multipotent progenitors. The protocol comprises three major steps: (i) induction of hematopoietic differentiation by coculture of hPSCs with OP9 bone marrow stromal cells; (ii) short-term expansion of multipotent myeloid progenitors with a high dose of granulocyte-macrophage colony-stimulating factor; and (iii) directed differentiation of myeloid progenitors into neutrophils, eosinophils, dendritic cells, Langerhans cells, macrophages and osteoclasts. The generation of multipotent hematopoietic progenitors from hPSCs requires 9 d of culture and an additional 2 d to expand myeloid progenitors. Differentiation of myeloid progenitors into mature myeloid cells requires an additional 5-19 d of culture with cytokines, depending on the cell type.

Genetic reprogramming of human somatic cells to induced pluripotent stem cells (iPSCs) could offer replenishable cell sources for transplantation therapies. To fulfill their promises, human iPSCs will ideally be free of exogenous DNA (footprint-free), and be derived and cultured in chemically defined media free of feeder cells. Currently, methods are available to enable efficient derivation of footprint-free human iPSCs. However, each of these methods has its limitations. We have previously derived footprint-free human iPSCs by employing episomal vectors for transgene delivery, but the process was inefficient and required feeder cells. Here, we have greatly improved the episomal reprogramming efficiency using a cocktail containing MEK inhibitor PD0325901, GSK3β inhibitor CHIR99021, TGF-β/Activin/Nodal receptor inhibitor A-83-01, ROCK inhibitor HA-100 and human leukemia inhibitory factor. Moreover, we have successfully established a feeder-free reprogramming condition using chemically defined medium with bFGF and N2B27 supplements and chemically defined human ESC medium mTeSR1 for the derivation of footprint-free human iPSCs. These improvements enabled the routine derivation of footprint-free human iPSCs from skin fibroblasts, adipose tissue-derived cells and cord blood cells. This technology will likely be valuable for the production of clinical-grade human iPSCs.

Embryonic stem cells represent a pluripotent population of cells capable of self-renewal, large-scale expansion, and differentiation in various cell lineages including cells of hematopoietic lineage. In this chapter, we describe a three-step cell culture method for directed differentiation of human embryonic stem cells (hESCs) to dendritic cells (DCs) that includes (1) hESC differentiation into hematopoietic progenitors by coculture with OP9 stromal cells, (2) expansion of myeloid DC precursors in suspension bulk cultures with granulocyte monocyte-colony stimulating factor (GM-CSF), and (3) differentiation of myeloid precursors to DCs in the serum-free medium with GM-CSF and interleukin-4 (IL-4). The method employs cell culture conditions selecting an almost pure population of myeloid DC precursors and does not require isolation of hematopoietic progenitors. With this method, hESCs can be differentiated to functional DCs within 30 days at an efficiency of at least four DCs per single undifferentiated hESC. Directed differentiation of DCs from hESCs could be useful for studying cellular and molecular mechanisms of DC development and potentially for the generation of antigen-presenting cells for cellular immunotherapy.

An important physiological function of vascular endothelial cells is to detect and respond to physical stimuli. While many efforts have been made to derive endothelial cells from human embryonic stem cells (hESCs), the ability of these derivatives to respond to mechanical forces has yet to be ascertained. hESC-derived endothelial cells (hEECs) were obtained by coculturing hESCs with OP9 stromal cells. Here we applied physiologic levels of shear stress to hEECs in a parallel plate flow chamber and observed changes in cell morphology and gene expression, comparing the response to that of human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells (HMVECs). Shear induced hEECs to elongate and align in the direction of flow, and their overall transcriptional response to shear was similar to the primary cells tested. In response to shear in hEECs, COX2 and MMP1 were upregulated four- and threefold, MCP1 and VCAM1 expression decreased over fivefold, and ICAM1 and TPA were downregulated almost threefold. TGFbeta1 and SOD2 transcription exhibited no change under the conditions tested. Additionally, preshearing of hEECs mitigated TNFalpha-induced VCAM1 surface expression. These findings suggest that hEECs are capable of functionally responding to changes in fluid shear stress by modulating gene expression and cell morphology.

Human embryonic stem cells (hESCs) represent a unique population of cells capable of self-renewal and differentiation into all types of somatic cells, including hematopoietic and endothelial cells. Since the pattern of hematopoietic and endothelial development observed in the embryo can be reproduced using ESCs differentiated in culture, hESCs can be used as a model for studies of specification and diversification of hematoendothelial progenitors. In addition, hESCs can be seen as a scalable source of hematopoietic and endothelial cells for in vitro studies. This unit describes a method for efficient differentiation of hESCs into hematopoietic progenitors and endothelial cells through coculture with mouse OP9 bone marrow stromal cells, as well as an approach for their analysis and isolation. Support protocols are provided for culture of mouse embryonic fibroblasts, evaluation of hematopoietic and endothelial differentiation by flow cytometry and colony-forming assay, removal of OP9 cells, and propagation of hESC-derived endothelial cells. Curr. Protoc.

Embryonic stem cells represent a pluripotent population of cells capable of self-renewal, large-scale expansion, and differentiation in various cell lineages including cells of hematopoietic lineage. In this chapter, we describe a three-step cell culture method for directed differentiation of human embryonic stem cells (hESCs) to dendritic cells (DCs) that includes (1) hESC differentiation into hematopoietic progenitors by coculture with OP9 stromal cells, (2) expansion of myeloid DC precursors in suspension bulk cultures with granulocyte monocyte-colony stimulating factor (GM-CSF), and (3) differentiation of myeloid precursors to DCs in the serum-free medium with GM-CSF and interleukin-4 (IL-4). The method employs cell culture conditions selecting an almost pure population of myeloid DC precursors and does not require isolation of hematopoietic progenitors. With this method, hESCs can be differentiated to functional DCs within 30 days at an efficiency of at least four DCs per single undifferentiated hESC. Directed differentiation of DCs from hESCs could be useful for studying cellular and molecular mechanisms of DC development and potentially for the generation of antigen-presenting cells for cellular immunotherapy.

We have established a system for directed differentiation of human embryonic stem (hES) cells into myeloid dendritic cells (DCs). As a first step, we induced hemopoietic differentiation by coculture of hES cells with OP9 stromal cells, and then, expanded myeloid cells with GM-CSF using a feeder-free culture system. Myeloid cells had a CD4+CD11b+CD11c+CD16+CD123lowHLA-DR− phenotype, expressed myeloperoxidase, and included a population of M-CSFR+ monocyte-lineage committed cells. Further culture of myeloid cells in serum-free medium with GM-CSF and IL-4 generated cells that had typical dendritic morphology; expressed high levels of MHC class I and II molecules, CD1a, CD11c, CD80, CD86, DC-SIGN, and CD40; and were capable of Ag processing, triggering naive T cells in MLR, and presenting Ags to specific T cell clones through the MHC class I pathway. Incubation of DCs with A23187 calcium ionophore for 48 h induced an expression of mature DC markers CD83 and fascin. The combination of GM-CSF with IL-4 provided the best conditions for DC differentiation. DCs obtained with GM-CSF and TNF-α coexpressed a high level of CD14, and had low stimulatory capacity in MLR. These data clearly demonstrate that hES cells can be used as a novel and unique source of hemopoietic and DC precursors as well as DCs at different stages of maturation to address essential questions of DC development and biology. In addition, because ES cells can be expanded without limit, they can be seen as a potential scalable source of cells for DC vaccines or DC-mediated induction of immune tolerance.

Tumor necrosis factor (TNF) and soluble TNF receptors (sTNF-Rs) system related with Th1 and Th2 and activity of NF-kappaB/IkappaB regulatory system. This study was designed to compare sTNF-R1 and sTNF-R2 production (shedding) and levels of late activated CD8+ T-lymphocytes in non-pregnant (n = 30) and pregnant (n = 20) normal women and non-pregnant (n = 20) and pregnant (n = 30) RSA women. Effects of progesterone (natural structure) injections in RSA women were studied.Levels of sTNF-R1, sTNF-R2, TNF in peripheral blood serum were detected by enzyme-linked immunosorbent assay. Lymphocyte subsets were estimated by multicolor flow cytometry. NK cell cytotoxic activity of peripheral blood lymphocytes (PBL) in whole blood against K562 targets was determined using Europium-release cytotoxicity assay. Mitogen-induced proliferative response of PBL to PHA-P, Con A and PWM were determined by standard 3H-thymidine incorporation assay.Levels of soluble TNF-R1 and TNF-R2 in normal pregnancy were elevated when compared with non-pregnant normal women and pregnant RSA women. Levels of late activated CD8+ T-lymphocytes in normal pregnancy were decreased but no changes were detected in RSA women. After progesterone therapy (i.m. injections of 2.5% oil solution) in RSA women elevation of sTNF-R1 and sTNF-R2 to normal pregnancy ranges was observed. No changes in levels of late activated CD8+ T-lymphocytes after progesterone treatment were detected.Elevation of levels of sTNF-R1, sTNF-R2 and decrease of late activated cytotoxic T-lymphocytes are pronounce markers of normal human pregnancy. In RSA women there are no elevation of sTNF-R1 and sTNF-R2 levels during pregnancy. This deficiency may be restored by progesterone treatment.

Here, we examine the ability of undifferentiated human embryonic stem cells (hESCs) to reprogram the nuclei of hESC-derived myeloid precursors following cell–cell fusion. Using an OP9 coculture system, we produced CD45+ CD33+ myeloperoxidase+ myeloid precursors from an Oct4–enhanced green fluorescent protein (EGFP) knock-in hESC line and demonstrated that Oct4-EGFP expression was extinguished in these precursors. Upon fusion with undifferentiated hESCs, EGFP expression from the endogenous Oct4 promoter/regulatory region was re-established, ESC-specific surface antigens and marker genes were expressed, and myeloid precursor-specific antigens were no longer detectable. When the hybrid cells were formed into embryoid bodies, upregulation of genes characteristic of the three germ layers and extraembryonic tissues occurred, indicating that the hybrid cells had the potential to differentiate into multiple lineages. Interestingly, the hybrid cells were capable of redifferentiating into myeloid precursors with efficiency comparable with that of diploid hESCs despite their neartetraploid chromosome complement. These results indicate that hESCs are capable of reprogramming nuclei from differentiated cells and that hESC hybrid cells provide a new model system for studying the mechanisms of nuclear reprogramming.

Negative correlation between serum IgE levels and production of IFN-gamma by lymphocytes and positive correlation between serum IgE levels and production of IL-4 by lymphocytes was detected in 12 children with allergic asthma and recurrent respiratory diseases. Deficiency of reduced glutathione in whole blood and some disorders in phagocytic and oxidative burst activity of monocytes were observed in these children. Use of reduced glutathione, L-cysteine and anthocyane (Recancostat, Clear Vision, Switzerland) resulted in elevation of IFN-gamma production, lymphocyte response to mitogens, NK cell activity, increase in percentage of naive CD4(+) T lymphocytes (refreshment effect) and improvement of clinical status. Positive clinical results were lasted during 6 months.

Advancing pluripotent stem cell technologies for modelling haematopoietic stem cell development and blood therapies requires identifying key regulators of haematopoietic commitment from human pluripotent stem cells (hPSCs). Here, by screening the effect of 27 candidate factors, we reveal two groups of transcriptional regulators capable of inducing distinct haematopoietic programs from hPSCs: pan-myeloid (ETV2 and GATA2) and erythro-megakaryocytic (GATA2 and TAL1). In both cases, these transcription factors directly convert hPSCs to endothelium, which subsequently transform into blood cells with pan-myeloid or erythro-megakaryocytic potential. These data demonstrate that two distinct genetic programs regulate the haematopoietic development from hPSCs and that both of these programs specify hPSCs directly to haemogenic endothelial cells. In addition, this study provides a novel method for the efficient induction of blood and endothelial cells from hPSCs via the overexpression of modified mRNA for the selected transcription factors.

Increase of respiratory tract diseases and chronic inflammatory foci in children residing at the radionuclides contaminated territories as a result of the Chernobyl nuclear accident were found by epidemiologic studies [1].

Somatic cell nuclear transfer allows trans-acting factors present in the mammalian oocyte to reprogram somatic cell nuclei to an undifferentiated state. We show that four factors ( OCT4, SOX2, NANOG , and LIN28 ) are sufficient to reprogram human somatic cells to pluripotent stem cells that exhibit the essential characteristics of embryonic stem (ES) cells. These induced pluripotent human stem cells have normal karyotypes, express telomerase activity, express cell surface markers and genes that characterize human ES cells, and maintain the developmental potential to differentiate into advanced derivatives of all three primary germ layers. Such induced pluripotent human cell lines should be useful in the production of new disease models and in drug development, as well as for applications in transplantation medicine, once technical limitations (for example, mutation through viral integration) are eliminated.

Abstract 1326 Using hESC differentiation system we recently identified a mesenchymoangioblast (MAB) as a novel precursor for mesenchymal stem cells (MSCs) and endothelial cells and demonstrated that mesenchymal and hematopoietic cells develop sequentially from mesodermal precursors with primary angiogenic potential – MAB and hemangioblasts (HB), respectively. In addition, we found that angiogenic mesoderm reminiscent of lateral plate/extraembryonic mesoderm in the embryo can be identified by surface expression of apelin receptor (APLNR) and lack of expression of typical endothelial (CD31, CD144), hematopoietic (CD43, CD45) and mesenchymal (CD73, CD195) markers i.e. as EHMlin-APLNR+ cells. (Vodyanik et al. Cell Stem Cell 2010;7:718). In response to FGF2 APLNR+ cells form morphologically distinct compact mesenchymal or MAB colonies and disperse hematopoietic or blast (HB) colonies in serum-free clonogenic semisolid medium. When transferred to the adherent cultures in serum-free medium with FGF2, individual colonies gave rise to multipotential mesenchymal cell lines with typical phenotype (CD146+CD105+CD73+CD31-CD43-45-), differentiation (chondro-, osteo-, and adipogenesis) and robust proliferation (>80 doublings) potentials. In contrast, HB colonies consisted almost entirely of CD235a and CD41a expressing cells with morphology resembling erythroblasts. Replating of HB colonies in hematopoietic serum-free and serum-containing clonogenic medium demonstrated that they gave rise to erythroid, megakaryocytic and mixed colonies composed of erythroid, megakaryocytic cells and macrophages indicating that BL-CFCs probably reflected the first wave of embryonic hematopoiesis initiated in the yolk sac. To define pathways involved in MAB and HB development we tested the effect of different growth factors and cytokines on mesenchymal and blast colony formation. We confirmed that the development of MAB and HB depends on FGF2, by demonstrating complete suppression of blast and mesenchymal colony formation by elimination of FGF2 from clonogenic culture or by abrogation of FGF2 signaling using PD 173074 inhibitor of FGF2 receptor autophosphorylation. The formation of MAB and HB colonies was also completely abrogated by adding TGFb or activin A, and increased in the presence of SB431542 TGFb signaling inhibitor. PDGF-BB alone lacked colony-forming activity, but its addition to FGF2 significantly increased the frequency and size of mesenchymal but not blast colonies. In contrast, the addition of VEGF essentially abrogated mesenchymal colony formation. Although VEGF had little effect on BL-CFCs, the addition KI8751 KDR inhibitor significantly decreased the number of blast colonies, confirming that their development depends on VEGF signaling. The addition of individual hematopoietic cytokines to FGF2 had a relatively mild effect on the number of blast colonies. However, they increased the size of colonies, which was especially obvious with the addition of EPO. When IL3, IL6, EPO, TPO, and SCF were added to clonogenic cultures together with FGF2, we observed a significant increase in the number and size of blast colonies, some of which had grown into very large grape-like structures. Because we found that emerging CD144+CD235a+ cells generated hematopoietic colonies morphologically resembling blast colonies in the presence of FGF2 and hematopoietic cytokines, we concluded that hematopoietic cytokine-free clonogenic cultures would be more appropriate for detection of BL-CFCs and enhancing the specificity of this assay. The finding that mesenchymal and blast CFCs arise from cells expressing APLNR prompted us to test whether this receptor is involved in the regulation of MAB and HB development. We found that APLNR agonist aplein-12 inhibits mesenchymal colonies, while it significantly increases the formation of blast colonies in synergy with VEGF. Together, these studies demonstrated that the activation of multiple but different signaling pathways regulates the formation of mesenchymal and blast colonies. Disclosures: Slukvin: CDI: Consultancy, Equity Ownership.

Abstract 1277 Animal studies demonstrated that the first HSCs are generated in the aorta-gonad-mesonephros from a unique population of endothelial cells, hemogenic endothelium (HE), through endothelial-hematopoietic transition. However, the identity of HE remains obscure and the specific features that distinguish HE from non-HE and the discrete stages of endothelial transition into hematopoietic cells are not characterized. Here we employed hESC differentiation system in coculture with OP9 to define the distinct population of HE, and to develop an experimental system for analysis of endothelial-hematopoietic transition in vitro. Previously, we demonstrated that endothelial cells could be distinguished from hematopoietic progenitors based on the lack of CD43 expression (Vodyanik et al., Blood 2006;108:2095). Here, we analyzed the earliest stages of endothelial development from hESCs before the typical hematopoietic CFCs could be detected. We found that the first CD144+ endothelial cells appear on day 4 of differentiation within a population of APLNR+ cells expressing a high level of KDR. Based on expression of CD235a/CD43, CD73 and CD41a, we identified three major subsets within the emerging CD144+ cells: 1)CD235a/CD43−CD73+, 2)CD235a/CD43−CD73−, and 3)CD235a/CD43+CD41a−. Although all three subsets formed monolayer endothelial cells when grown on fibronectin in endothelial media, only CD235a/CD43+CD41a− cells displayed hematopoietic CFC potential, which required serum-free medium and were dependent on hematopoietic cytokines and FGF2. After culture with OP9, both CD144+CD235a/CD43−CD73− and CD144+CD235a/CD43+CD41a− cells generated CD31+CD43/45− endothelial cells and a significant amount of CD43+ blood cells. In contrast CD144+CD235a/CD43−CD73+ cells formed almost exclusively endothelial cells. Single cell deposition experiments demonstrated that CD144+CD235a/CD43+CD41a− cells formed predominantly hematopoietic cells, while most CD144+CD235a/CD43−CD73− cells gave rise to either hematopoietic or endothelial clusters with approximately 2.5% of cells forming hematoendothelial clusters, indicating the presence of bipotential progenitors within this population. Though all three CD144+ subsets had a very similar molecular signature and expressed typical endothelial genes and genes associated with angiohematopoietic and HSC development, CD235a/CD43+CD41a− showed the higher expression of hematopoietic genes and lower expression of CDH5, CDH2, CAV1, and APOLD1 typical endothelial genes. Based on the functional, phenotypic and molecular properties we designated the identity of subsets as follows: 1) CD144+CD235a/CD43+CD41a− angiogenic blood cells, i.e. cells that possessed primary hematopoietic characteristics but were also capable of generating endothelial cells; 2) CD144+CD235a/CD43−CD73+ endothelial progenitors, i.e. cells that had all functional and molecular features of endothelial cells and endothelial colony-forming potential on OP9; 3) CD144+CD235a/CD43−CD73− HE cells, i.e. cells with primary endothelial characteristics lacking hematopoietic CFC potential and surface markers, but capable of generating blood and endothelial cells after coculture with stromal cells. To find out the direct precursors of HE and blood cells, we analyzed the differentiation potential of major subsets of mesodermal cells isolated on day 4 of hESC coculture with OP9. We found that only APLNR+KDRbrightCD140alow/− mesodermal cells lacking expression of typical hematopoietic (CD43, CD45), endothelial (CD31, CD144), and mesenchymal (CD73, CD105) markers had the potential to generate both blood and endothelium. Moreover, single cell deposition experiments demonstrated that APLNR+KDRbrightCD140alow/− cells formed HE clusters with a high frequency (about 1/10 cells), strongly indicating that these cells represent the direct precursors of HE. Because APLNR+KDRbrightCD140alow/− cells upregulated expression LMO2, TAL1, CBFB, GATA2, and FLI1 transcriptional regulators of hematopoietic and endothelial development, but were lacking expression of primitive streak genes, we designated these cells as angioblasts. Together these studies provide a hESC-based platform for identification of factors required for acquisition of HSC potential by blood cells following transition from endothelium. Disclosures: Thomson: CDI: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Slukvin:CDI: Consultancy, Equity Ownership.

Induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity for modeling of human diseases in vitro as well as for developing novel approaches for regenerative therapy based on immunologically compatible cells. In the present study, we employed an OP9 differentiation system to characterize the hematopoietic differentiation potential of seven human iPSC lines obtained from human fetal, neonatal, and adult fibroblasts through reprogramming with POU5F1, SOX2, NANOG, and LIN28 and compared it with the differentiation potential of five human embryonic stem cell lines (hESC; H1, H7, H9, H13, and H14). Similar to hESCs, all iPSCs in coculture with OP9 generated all types of colony forming cells (CFCs) as well as CD34+ cells that can be separated into distinct subsets based on differential expression of CD43 and CD31. CD34+CD31+CD43− cells obtained from all iPSCs expressed molecules present on endothelial cells and readily formed a monolayer when placed in endothelial conditions, while hematopoietic CFC potential was restricted to CD43+ cells. iPSC-derived CD43+ cells could be separated into three major subsets based on differential expression of CD235a/CD41a and CD45: CD235a+CD41a+/− (erythro-megakaryocytic progenitors), and lin-CD34+CD43+CD45− (multipotent), and lin-CD34+CD43+CD45+ (myeloid-skewed) primitive hematopoietic cells. Both subsets of primitive hematopoietic cells expressed genes associated with myeloid and lymphoid development, although myeloid genes were upregulated in CD45+ cells, which are skewed toward myeloid differentiation. Cytogenetic analysis demonstrated that iPSCs and derived from them CD43+ cells maintained normal karyotype. In addition short tandem repeat analysis of CFCs generated from IMR90-1 cells has been performed to confirm that blood cells are in fact derived from reprogrammed IMR90 cells, and not from contaminating hESCs. While we observed some variations in the efficiency of hematopoietic differentiation between different iPSCs, the pattern of differentiation was very similar in all seven tested iPSC and five hESC lines. Using different cytokine combinations and culture conditions we were able to expand iPSC-derived myeloid progenitors and induce their differentiation toward red blood cells, neutrophils, eosinophils, macrophages, ostoeclasts, dendritic and Langerhans cells. Although several issues remain to be resolved before iPSC-derived blood cells can be administered to humans for therapeutic purposes, patient-specific iPSCs can already be used for characterization of mechanisms of blood diseases and to identify molecules that can correct affected genetic networks.

We have demonstrated that co-culture of hESCs with OP9 bone-marrow stromal cells induced efficient hESC differentiation into hematopoietic colony-forming cells (CFCs). During hESC/OP9 co-culture, the first CFCs were detectable 1–2 days after emergence of CD34+ cells (day 4–5 of co-culture) and 3–4 days before generation of CD45+ cells, indicating that early CFCs arose in the CD45- population. To define phenotype of early hematopoietic progenitors, we examined the expression of CD41a, CD43, CD61 and glycophorin A (CD235a) on the CD34+ cells in the course of hESC/OP9 co-culture. The first detectable CD34+ cells expressed a high level of VEGF-R2 (KDR) and were CD41a, CD43, CD61 and CD235a negative. Appearance of CFCs was accompanied with down-regulation of KDR and almost simultaneous expression of CD41a, CD43 and CD235a on the CD34+ cells. CD43+ cells gradually increased thereafter, whereas the expression of CD41a was retained on the subset of CD43+ cells that co-express CD235a and CD61. CD45+ cells emerged within CD43+ population and the most of CD45+ cells did not express CD235a, CD41a or CD61. The expression of CD34 was decreased progressively on CD43+CD41a+CD235a+CD61+ cells, but retained by CD43+CD45+ cells. To assay hematopoietic potential of defined subsets, CD34+ cells were isolated by magnetic sorting and further separated into CD34+ CD43+ and CD34+CD43− cell fractions. In addition, CD34−CD43+ cells were isolated from CD34− fraction. CD34+ selection markedly enriched all types CFCs except of E-CFCs. All GEMM-CFCs were found within CD34+ population and none within CD34−. However, CD34− cell fraction contained E-CFCs and minimal numbers of M-CFCs and GM-CFCs. CD34+ cells were also heterogenous in morphologic appearance and contained endothelial cells that were capable to endocytose Ac-LDL. Positive selection of CD43+ cells resulted in total recovery of all types of CFCs. E-CFCs, which consistently detected in the CD34- fraction, were also recovered by CD43 selection. Morphologically, CD43+ cells comprised a homogenous blast-like population and were lack of endothelial-like cells. Thus, expression of CD43 molecule (leukosialin/sialophorin) is detected on the earliest clonogenic hematopoietic progenitors before expression of CD45, persists on developing hematopoietic cells after their lineage specification and most likely defines the divergence of hematopoiesis from endothelial cells during early development in humans.

hES cells provide an unique opportunity to study the earliest stages of hematopoietic commitment which are not easily accessible in the human embryo. To model early hematopoietic development, we cultured H1 and H9 hES cell lines on OP9 stromal cells without the addition of cytokines. On day 2 of co-culture, hES cells up-regulated brachyury expression and began to form mesodermal-like colonies. A transient population of blast colony-forming cells (CFCs) with the potential to differentiate into blood and endothelial cells was detected on days 3–6 of co-culture. CD34+ cells first appeared on day 3–4 of co-culture, which was coincident with induction of the transcription factors GATA-1, GATA-2 and SCL. CD43+ and CD41a+ cells along with CFCs emerged 2 days later within CD34+ population; 3–4 days before the appearance of CD45+ cells. We were able to obtain up to 20% of CD34+ cells from hES/OP9 co-culture and isolate up to 107 CD34+ cells with more than 95% purity from a similar number of initially plated hES cells after 8–9 days of culture. The hES cell-derived CD34+ cells were highly enriched in CFCs, displayed CD90+CD117+CD164+CD38- phenotype of primitive hematopoietic progenitors, and contained ALDHhigh cells as well cells with verapamil-sensitive ability to efflux rhodamine 123. Isolated CD34+ cells differentiated into lymphoid (NK cells) as well as myeloid (neutrophils and macrophages) lineages when cultured on MS-5 stromal cells in the presence of SCF, Flt3-L, IL7 and IL3. These data indicate that hES cell/OP9 co-culture reproduces the major events that are observed during embryonal hematopoietic development, including the formation of lympho-myeloid progenitors. We employed OP9 system for identification of the phenotype of early hematopoietic progenitors in humans and to directly differentiate hES cells into different blood lineages.

SummaryAmong the three embryonic germ layers, the mesoderm is a major source of the mesenchymal precursors giving rise to skeletal and connective tissues, but these precursors have not previously been identified and characterized. Using human embryonic stem cells directed toward mesendodermal differentiation, we show that mesenchymal stem/stromal cells (MSCs) originate from a population of mesodermal cells identified by expression of apelin receptor. In semisolid medium, these precursors form FGF2-dependent compact spheroid colonies containing mesenchymal cells with a transcriptional profile representative of mesoderm-derived embryonic mesenchyme. When transferred to adherent cultures, individual colonies give rise to MSC lines with chondro-, osteo-, and adipogenic differentiation potentials. Although the MSC lines lacked endothelial potential, endothelial cells could be derived from the mesenchymal colonies, suggesting that, similar to hematopoietic cells, MSCs arise from precursors with angiogenic potential. Together, these studies identified a common precursor of mesenchymal and endothelial cells, mesenchymoangioblast, as the source of mesoderm-derived MSCs.

Ninety-two children 5 to 14 years of age living in areas exposed to the radioactive fallout from Chernobyl with recurrent respiratory infections (RRIs) were treated after randomization with either Viscum album praeparatum mali or pini (Iscador M or P). The dosage was two subcutaneous injections a week for 5 weeks with individual doses of 0.001 mg to 1.0 mg. Both Viscum album preparations were effective in significantly reducing clinical symptoms. One year after a single treatment course, the frequency of RRI relapses decreased by 78% and 73%, respectively. Immunomodulatory effects were assessed by investigation of lymphocyte subsets, natural killer (NK) cell activity, phagocytic and oxidative activity of polymorphonuclear leukocytes, and antiviral activity of serum before and 1 week after treatment. Viscum album therapy resulted in normalization of initial immune indices either below or above the normal ranges. High levels of antiviral activity before treatment were significantly decreased by Viscum album mali. Viscum album treatment should be studied further in children with RRI.