Development of primitive and definitive hematopoiesis from nonhuman primate embryonic stem cells in vitro

Directed differentiation of human embryonic stem cells into functional dendritic cells through the myeloid pathway

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+CD123(low)HLA-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-alpha 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.

A regulatory role for 1-acylglycerol-3-phosphate-O-acyltransferase 2 in adipocyte differentiation

Mutations in the 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2) gene have been identified in individuals affected with congenital generalized lipodystrophy (CGL). AGPAT2 catalyzes acylation of lysophosphatidic acid to phosphatidic acid, a precursor for both triacylglycerol (TAG) and phospholipid synthesis. Recent studies suggest that reduced AGPAT2 enzymatic activity may underlie the CGL clinical phenotype. To gain insight into how altered AGPAT2 activity causes lipodystrophy, we examined the effect of knockdown of AGPAT2 expression in preadipocytes on TAG synthesis and storage, and on adipocyte differentiation. We show that AGPAT2 mRNA expression is induced 30-fold during adipocyte differentiation and that AGPAT2 enzymatic activity is required for TAG mass accumulation in mature adipocytes. We demonstrate that small interference RNA-mediated knockdown of AGPAT2 expression prevents appropriate early induction of C/EBPbeta and PPARgamma, key transcriptional activators of the adipogenic program, and delays expression of multiple adipocyte-related genes. The unexpected finding, that levels of several phospholipid species, including phosphatidic acid (PA), are elevated in TAG-depleted adipocytes with AGPAT2 knockdown, suggests that impaired AGPAT2 activity affects availability of PA for TAG synthesis but not overall PA synthesis nor utilization of PA for phospholipid synthesis. These findings underscore the importance of an AGPAT2-mediated metabolic pathway in adipocyte differentiation.

Hematopoiesis from human embryonic stem cells: overcoming the immune barrier in stem cell therapies

The multipotency and proliferative capacity of human embryonic stem cells (hESCs) make them a promising source of stem cells for transplant therapies and of vital importance given the shortage in organ donation. Recent studies suggest some immune privilege associated with hESC-derived tissues. However, the adaptability of the immune system makes it unlikely that fully differentiated tissues will permanently evade immune rejection. One promising solution is to induce a state of immune tolerance to a hESC line using tolerogenic hematopoietic cells derived from it. This could provide acceptance of other differentiated tissues from the same line. However, this approach will require efficient multilineage hematopoiesis from hESCs. This review proposes that more efficient differentiation of hESCs to the tolerogenic cell types required is most likely to occur through applying knowledge gained of the ontogeny of complex regulatory signals used by the embryo for definitive hematopoietic development in vivo. Stepwise formation of mesoderm, induction of definitive hematopoietic stem cells, and the application of factors key to their self-renewal may improve in vitro production both quantitatively and qualitatively.

Differentiation of human embryonic stem cells into hematopoietic cells by coculture with human fetal liver cells recapitulates the globin switch that occurs early in development

OBJECTIVE

To find a human cell line that could support differentiation of human embryonic stem cells (hESCs) into hematopoietic cells. To determine in detail the expression profiles of the beta-like globin genes in hESC-derived erythroid cells.

MATERIALS AND METHODS

FH-B-hTERT, a human fetal liver-derived cell line, and S17, a mouse bone marrow stromal cell line, were used as stromas to induce the differentiation of hESC into hematopoietic cells. The number of hematopoietic progenitors and surface antigen expression were monitored during time-course experiments using colony assays and flow cytometry. Globin expression patterns in individual erythroid colonies were determined by real-time quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Comparison of coculture of hESCs with FH-B-hTERT or S17 cells revealed that the fraction of CD34(+) cells and the number of clonogenic progenitors per 250,000 cells plated were higher with FH-B-hTERT than with S17. Analysis of beta-like globin expression in individual burst-forming unit erythroid and colony-forming unit erythroid colonies revealed that erythroid cells derived from hESC cocultured for 8 to 21 days on either FH-B-hTERT or S17 produced epsilon- and gamma-globin mRNAs in similar amounts. With increasing time in coculture, the mean ratio of gamma/epsilon increased by more than 10-fold on both S17 and FH-B-hTERT stroma. Importantly, beta-globin expression was barely detectable at all time point examined.

CONCLUSIONS

FH-B-hTERT can induce hESCs differentiation into hematopoietic cells more efficiently than S17. In vitro differentiation of hESCs recapitulates the epsilon-globin to gamma-globin switch but not the gamma-globin to beta-globin switch that occurs around birth. This experimental system will be useful for studying the regulation of globin gene expression during early human hematopoiesis.

Identification and characterization of hemoangiogenic progenitors during cynomolgus monkey embryonic stem cell differentiation

We identified intermediate-stage progenitor cells that have the potential to differentiate into hematopoietic and endothelial lineages from nonhuman primate embryonic stem (ES) cells. Sequential fluorescence-activated cell sorting and immunostaining analyses showed that when ES cells were cultured in an OP9 coculture system, both lineages developed after the emergence of two hemoangiogenic progenitor-bearing cell fractions, namely, vascular endothelial growth factor receptor (VEGFR)-2(high) CD34(-) and VEGFR-2(high) CD34(+) cells. Exogenous vascular endothelial growth factor increased the proportion of VEGFR-2(high) cells, particularly that of VEGFR-2(high) CD34(+) cells, in a dose-dependent manner. Although either population of VEGFR-2(high) cells could differentiate into primitive and definitive hematopoietic cells (HCs), as well as endothelial cells (ECs), the VEGFR-2(high) CD34(+) cells had greater hemoangiogenic potential. Both lineages developed from VEGFR-2(high) CD34(-)or VEGFR-2(high) CD34(+) precursor at the single-cell level, which strongly supports the existence of hemangioblasts in these cell fractions. Thus, this culture system allows differentiation into the HC and EC lineages to be defined by surface markers. These observations should facilitate further studies both on early developmental processes and on regeneration therapies in human.

Hematopoietic Cells from Primate Embryonic Stem Cells

Embryonic stem (ES) cells, derived from early stage embryos, are pluripotent precursors of all of the tissues and organs of the body. ES cells from the mouse have been shown to undergo differentiation in vitro to form a variety of different cell types, including the differentiated progeny of hematopoietic precursors. These hematopoietic cells, however, exhibit numerous differences from those of human cells, and it has become increasingly clear that mouse ES cell differentiation has significant limitations as a model of human developmental biology. The more recent isolation and characterization of nonhuman primate ES cell lines have made available an experimental model with characteristics considerably more close to human biology. We have developed experimental conditions that promote efficient differentiation of these cells to produce progeny cells with considerable similarity to hematopoietic precursors harvested from bone marrow of adult animals.

Hematopoietic Cells

Murine embryonic stem cells (mESC) readily form embryoid bodies (EBs) that exhibit hematopoietic differentiation. Methods based on EB formation or ESC coculture with murine bone marrow stromal cell lines have revealed pathways of both primitive and definitive hematopoietic differentiation progressing from primitive mesoderm via hemangioblasts to endothelium and hematopoietic stem and progenitor cells. The addition of specific hematopoietic growth factors and morphogens to these cultures enhances the generation of neutrophils, macrophages, megakaryocyte/platelets, and hemoglobinized mature red cells. In addition, selective culture systems have been developed to support differentiation into mature T lymphocytes, natural killer cells, B cells, and dendritic cells. In most cases, culture systems have been developed that support equivalent differentiation of various human ESC (hESC). The major obstacle to translation of ESC hematopoietic cultures to clinical relevance has been the general inability to produce hematopoietic stem cells (HSC) that can engraft adult, irradiated recipients. In this context, the pattern of ES hematopoietic development mirrors the yolk sac phase of hematopoiesis that precedes the appearance of engraftable HSC in the aorta-gonad-mesonephros region. Genetic manipulation of mESC hematopoietic progeny by upregulation of HOXB4 or STAT5 has led to greatly enhanced long- or short-term multilineage hematopoietic engraftment, suggesting that genetic or epigenetic manipulation of these pathways may lead to functional HSC generation from hESC.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.

Designer blood: creating hematopoietic lineages from embryonic stem cells

Embryonic stem (ES) cells exhibit the remarkable capacity to become virtually any differentiated tissue upon appropriate manipulation in culture, a property that has been beneficial for studies of hematopoiesis. Until recently, the majority of this work used murine ES cells for basic research to elucidate fundamental properties of blood-cell development and establish methods to derive specific mature lineages. Now, the advent of human ES cells sets the stage for more applied pursuits to generate transplantable cells for treating blood disorders. Current efforts are directed toward adapting in vitro hematopoietic differentiation methods developed for murine ES cells to human lines, identifying the key interspecies differences in biologic properties of ES cells, and generating ES cell-derived hematopoietic stem cells that are competent to repopulate adult hosts. The ultimate medical goal is to create patient-specific and generic ES cell lines that can be expanded in vitro, genetically altered, and differentiated into cell types that can be used to treat hematopoietic diseases.

Establishment of Novel Embryonic Stem Cell Lines Derived from the Common Marmoset (Callithrix jacchus)

The successful establishment of human embryonic stem cell (hESC) lines has inaugurated a new era in regenerative medicine by facilitating the transplantation of differentiated ESCs to specific organs. However, problems with the safety and efficacy of hESC therapy in vivo remain to be resolved. Preclinical studies using animal model systems, including nonhuman primates, are essential to evaluate the safety and efficacy of hESC therapies. Previously, we demonstrated that common marmosets are suitable laboratory animal models for preclinical studies of hematopoietic stem cell therapies. As this animal model is also applicable to preclinical trials of ESC therapies, we have established novel common marmoset ESC (CMESC) lines. To obtain marmoset embryos, we developed a new embryo collection system, in which blastocysts can be obtained every 3 weeks from each marmoset pair. The inner cell mass was isolated by immunosurgery and plated on a mouse embryonic feeder layer. Some of the CMESC lines were cultured continuously for more than 1 year. These CMESC lines showed alkaline phosphatase activity and expressed stage-specific embryonic antigen (SSEA)-3, SSEA-4, TRA-1-60, and TRA-1-81. On the other hand, SSEA-1 was not detected. Furthermore, our novel CMESCs are pluripotent, as evidenced by in vivo teratoma formation in immunodeficient mice and in vitro differentiation experiments. Our established CMESC lines and the common marmoset provide an excellent experimental model system for understanding differentiation mechanisms, as well as the development of regenerative therapies using hESCs.

Long-term extensive expansion of mouse hepatic stem/progenitor cells in a novel serum-free culture system

BACKGROUND & AIMS

The liver has high regenerative potential. We attempted to establish a novel culture system for extensive expansion of fetal mouse hepatic stem/progenitor cells and to characterize cultured cells.

METHODS

Hepatic spheroids collected from 6-day floating cultures were cultured on collagen-coated dishes in serum-free conditions in medium containing growth factors. Cultured cells were mainly characterized by immunocytochemistry and flow cytometry or transplanted into adult mice.

RESULTS

Approximately 400 expanding hepatic spheroids were generated from every 1 x 10(6) fetal liver cells. Subsequently, highly replicative colonies were subcultured with maintaining colony formation on collagen-coated dishes. These colonies consisted of small immature alpha-fetoprotein-positive cells and hepatocytic and cholangiocytic lineage-committed cells. The immature alpha-fetoprotein-positive cells could be expanded in a reproducible manner at least 5 x 10(5)-fold (which involved at least 30 passages over >6 months) without losing differentiation potential. Flow cytometric analysis showed that all cultured cells expressed CD49f, but not CD34, Thy-1, c-kit, or CD45. Nearly 15% of the cells expressed Sca-1, and approximately 5%-20% of the cells were side population cells. Both sorted side population cells and Sca-1-positive cells (especially side population cells) produced a large number of alpha-fetoprotein-positive cells and lineage-committed cells. Expanded cells had bidirectional differentiation potential and improved serum albumin levels in mice with severe liver damage.

CONCLUSIONS

Long-term extensive expansion of transplantable hepatic stem/progenitor cells was reproducibly achieved in a novel serum-free culture system. Moreover, this culture system yielded side population and Sca-1-positive cell populations that included hepatic stem/progenitor cells with differentiation and proliferation properties.

Human embryonic stem cell-derived CD34+ cells: efficient production in the coculture with OP9 stromal cells and analysis of lymphohematopoietic potential

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 10(7) 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.

Directed differentiation and mass cultivation of pure erythroid progenitors from mouse embryonic stem cells

Differentiating embryonic stem (ES) cells are an increasingly important source of hematopoietic progenitors, useful for both basic research and clinical applications. Besides their characterization in colony assays, protocols exist for the cultivation of lymphoid, myeloid, and erythroid cells. With the possible exception of mast cells, however, long-term expansion of pure hematopoietic progenitors from ES cells has not been possible without immortalization caused by overexpression of exogenous genes. Here, we describe for the first time an efficient yet easy strategy to generate mass cultures of pure, immature erythroid progenitors from mouse ES cells (ES-EPs), using serum-free medium plus recombinant cytokines and hormones. ES-EPs represent long-lived, adult, definitive erythroid progenitors that resemble immature erythroid cells expanding in vivo during stress erythropoiesis. When exposed to terminal differentiation conditions, ES-EPs differentiated into mature, enucleated erythrocytes. Importantly, ES-EPs injected into mice did not exhibit tumorigenic potential but differentiated into normal erythrocytes. Both the virtually unlimited supply of cells and the defined culture conditions render our system a valuable tool for the analysis of factors influencing proliferation and maturation of erythroid progenitors. In addition, the system allows detailed characterization of processes during erythroid proliferation and differentiation using wild-type (wt) and genetically modified ES cells.