Production of pancreatic hormone-expressing endocrine cells from human embryonic stem cells.

Of paramount importance for the development of cell therapies to treat diabetes is the production of sufficient numbers of pancreatic endocrine cells that function similarly to primary islets. We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, gut-tube endoderm, pancreatic endoderm and endocrine precursor--en route to cells that express endocrine hormones. The hES cell-derived insulin-expressing cells have an insulin content approaching that of adult islets. Similar to fetal beta-cells, they release C-peptide in response to multiple secretory stimuli, but only minimally to glucose. Production of these hES cell-derived endocrine cells may represent a critical step in the development of a renewable source of cells for diabetes cell therapy.

Characterization and culture of human embryonic stem cells.

Human embryonic stem cells have been defined as self-renewing cells that can give rise to many types of cells of the body. How and whether these cells can be manipulated to replace cells in diseased tissues, used to screen drugs and toxins, or studied to better understand normal development, however, depends on knowing more about their fundamental properties. Many different human embryonic stem cell lines--which are pluripotent, proliferate indefinitely in vitro and maintain a normal, euploid karyotype over extended culture--have now been derived, but whether these cell lines are in fact equivalent remains unclear. It will therefore be important to define robust criteria for the assessment of both existing and newly derived cell lines and for the validation of new culture conditions.

The Challenges of First-in-Human Stem Cell Clinical Trials: What Does This Mean for Ethics and Institutional Review Boards?

Stem cell-based clinical interventions are increasingly advancing through preclinical testing and approaching clinical trials. The complexity and diversity of these approaches, and the confusion created by unproven and untested stem cell-based "therapies," create a growing need for a more comprehensive review of these early-stage human trials to ensure they place the patients at minimal risk of adverse events but are also based on solid evidence of preclinical efficacy with a clear scientific rationale for that effect. To address this issue and supplement the independent review process, especially that of the ethics and institutional review boards who may not be experts in stem cell biology, the International Society for Stem Cell Research (ISSCR) has developed a set of practical questions to cover the major issues for which clear evidence-based answers need to be obtained before approving a stem cell-based trial.

Telomerase immortalization of neuronally restricted progenitor cells derived from the human fetal spinal cord.

Lineage-restricted progenitors of the central nervous system (CNS) are not readily expandable because their mitotic competence is limited. Here we used retroviral overexpression of human telomerase reverse transcriptase (hTERT) to immortalize progenitors from human fetal spinal cord. The hTERT-immortalized cells divided in basic fibroblast growth factor (bFGF) expressed high telomerase activity, and gave rise to phenotypically restricted subpopulations of either glia or neurons. The latter included a prototypic line, hSC11V-TERT, that gave rise only to neurons. These included both chx10(+) interneurons and Islet1(+)/Hb9(+)/ChAT(+) motor neurons; the latter were recognized by green fluorescent protein (GFP) driven by the Hb9 enhancer. The neurons were postmitotic and achieved electrophysiologic competence. Upon xenograft to both fetal rat brain and injured adult spinal cord, they matured as neurons and survived for 6 months, with no evident tumorigenesis. The cells have survived >168 doublings in vitro, with karyotypic normalcy and without replicative senescence. hTERT overexpression thus permits the generation of progenitor lines able to give rise to phenotypically restricted neurons.

Regulatory considerations for pluripotent stem cell therapies.

The development of pluripotent stem cell (PSC) therapies is rapidly advancing, and a number of PSC-derived cell products are currently being tested in clinical trials. The biological complexity of these therapies results in specific challenges in complying with regulatory guidelines. This includes the choice of starting material, reproducible and consistent manufacturing, and preclinical safety and efficacy assessment of the PSC-derived product. This review discusses current US cell therapy regulations and strategies for compliance with these regulations when developing PSC-derived products.

Human embryonic stem cell-derived cardiomyocytes can be maintained in defined medium without serum.

Current procedures for the maintenance of cardiomyocytes from human embryonic stem (hES) cells rely on either co-culture with mouse cells or medium containing fetal bovine serum (FBS). Due to exposure to animal products, these methods carry the risk of potential pathogen contamination and increased immunogenicity. Additionally, FBS introduces inherent variability in the cultures due to the inevitable differences in serum lots. Here we investigated whether a defined serum-free medium containing creatine, carnitine, taurine, and insulin (CCTI) could maintain hES cell-derived cardiomyocytes. We show that hES cell-derived cardiomyocytes maintained in the CCTI medium in the absence of any feeders exhibit similar phenotypes to those maintained in serum, as indicated by the following observations: (1) comparable levels of cardiac gene transcription were found in cells grown in serum-containing medium versus those in the CCTI medium; (2) cardiomyocyte-associated proteins were expressed in cells cultured in the CCTI medium; (3) beating cells in the CCTI medium responded to pharmacological agents in a dose-dependent manner; and (4) the vast majority of the beating embryoid bodies displayed ventricular-like action potentials (APs), and the ventricular cells in serum-containing medium and the CCTI medium had indistinguishable AP properties. Therefore, culturing hES cell-derived cardiomyocytes in serum-free medium as described here should facilitate the use of the cells for in vitro and in vivo applications.

Characterization and enrichment of cardiomyocytes derived from human embryonic stem cells.

Cell replacement therapy is a promising approach for the treatment of cardiac diseases, but is challenged by a limited supply of appropriate cells. We have investigated whether functional cardiomyocytes can be efficiently generated from human embryonic stem (hES) cells. Cardiomyocyte differentiation was evaluated using 3 parent (H1, H7, and H9) hES cell lines and 2 clonal (H9.1 and H9.2) hES cell lines. All cell lines examined differentiated into cardiomyocytes, even after long-term culture (50 passages or approximately 260 population doublings). Upon differentiation, beating cells were observed after one week in differentiation conditions, increased in numbers with time, and could retain contractility for over 70 days. The beating cells expressed markers characteristic of cardiomyocytes, such as cardiac alpha-myosin heavy chain, cardiac troponin I and T, atrial natriuretic factor, and cardiac transcription factors GATA-4, Nkx2.5, and MEF-2. In addition, cardiomyocyte differentiation could be enhanced by treatment of cells with 5-aza-2'-deoxycytidine but not DMSO or retinoic acid. Furthermore, the differentiated cultures could be dissociated and enriched by Percoll density centrifugation to give a population containing 70% cardiomyocytes. The enriched population was proliferative and showed appropriate expression of cardiomyocyte markers. The extended replicative capacity of hES cells and the ability to differentiate and enrich for functional human cardiomyocytes warrant further development of these cells for clinical application in heart diseases.

Human embryonic stem cell stability.

Human embryonic stem cells (hESCs) are derived from human preimplantation embryos, and exhibit the defining characteristics of immortality and pluripotency. Indeed, these cell populations can be maintained for several years in continuous culture, and undergo hundreds of population doublings. hESCs are thus likely candidates for source of cells for cell replacement therapies. Although hESC lines appear stable in their expression of cytokine markers, expression of telomerase, ability to differentiate, and maintenance of a stable karyotype, several other aspects of stability have not yet been addressed, including mitochondrial sequencing, methylation patterns, and fine resolution cytogenetic analysis. Because of the potential utility of hESCs, it will be of utmost importance to evaluate the stability of these aspects of ESC biology.

2005 Donor Eligibility Requirements: Unintended Consequences for Stem Cell Development.

UNLABELLED: Several human embryonic stem cell (hESC)-derived cell therapeutics have entered clinical testing and more are in various stages of preclinical development. The U.S. Food and Drug Administration (FDA) regulates these products under existing regulations and has stated that these products do not constitute a new class of biologic. However, as human tissue, hESCs are subject to regulations that were developed before hESCs were first described. The regulations have not been revised since 2005, well before the first hESC-derived product entered clinical studies. The current regulations require donors of hESCs to be tested in the same manner as donors of tissues intended for transplantation. However, because hESC-derived cell products are more than minimally manipulated, they are also subject to the same end-of-production release testing as most other biologic agents. In effect, this makes hESC products subject to redundant testing. No other biologic is subject to a similar testing requirement. Furthermore, the regulations that require donor testing are specifically applicable to hESC cells harvested from donors after a date in 2005. It is unclear which regulations cover hESCs harvested before 2005. Ambiguity in the guidelines and redundant testing requirements have unintentionally created a burdensome regulatory paradigm for these products and reluctance on the part of developers to invest in these promising therapeutics. We propose a simple solution that would address FDA safety concerns, eliminate regulatory uncertainty and risk, and provide flexibility for the FDA in the regulation of hESC-derived cell therapies. SIGNIFICANCE: Regulatory ambiguity concerning donor eligibility screening and testing requirements for human embryonic stem cell lines, in particular those lines created before 2005, are causing significant concern for drug developers. Technically, most of these lines fail to meet eligibility under U.S. Food and Drug Administration (FDA) rules for product licensure, and many developers are unaware that FDA approval to begin trials under an exemption is not an assurance that the FDA will grant licensure of the product. This Perspective outlines the ambiguity and the problem it has caused and proposes a workable solution. The intent is to generate stakeholder and FDA discussion on this issue.

Concise review: making and using clinically compliant pluripotent stem cell lines.

The field of pluripotent stem cells (PSCs) is in a state of dynamic flux driven by significant advances in the derivation of specific phenotypes from embryonic stem cells, breakthroughs in somatic cell nuclear transfer, and dramatic improvements in generating induced PSCs using zero footprint methods. Spurred by these technological advances, companies have begun to plan clinical studies using human PSC derivatives manufactured in current Good Manufacturing Practice-compliant conditions. In the present review, we discuss the challenges in making these biological products, starting from tissue sourcing to the processes involved in manufacture, storage, and distribution. Additional challenges exist to meeting the regulatory requirements and keeping costs affordable. A model is described that has been proposed by the U.S. National Institutes of Health for reducing the costs and permitting flexibility and innovation by individual investigators. This model, combined with small adjustments in the regulatory processes tailored to address the unique properties of PSCs, has the potential of significantly accelerating the implementation of PSC-based cell therapy.

Monitoring early differentiation events in human embryonic stem cells by massively parallel signature sequencing and expressed sequence tag scan.

To identify genes that may be involved in the process of human embryonic stem cell (hESC) differentiation, we profiled gene expression by expressed sequenced tag (EST) enumeration and massively parallel signature sequencing (MPSS) using RNA samples from feeder-free cultures of undifferentiated (passages 40-50) and differentiated (day 14) H1, H7, and H9 lines. MPSS and EST scan analysis showed good concordance and identified a large number of genes that changed rapidly as cultures transition from a pluripotent to a differentiated state. These included known and unknown ES cell-specific genes as well as a large number of known genes that were altered as cells differentiate. A subset of genes that were either up- or down-regulated were selected and their differential expression confirmed by a variety of independent methods, including comparison of expression after further differentiation, publicly available databases, and direct assessments by reverse transcriptase (RT)-PCR and immunocytochemistry. The analysis identified markers unique to the hESC and embryoid bodies (hEBs) stage as well as signaling pathways that likely regulate differentiation. The data generated can be used to monitor the state of hESC isolated by different laboratories using independent methods and maintained under differing culture conditions.

Generation of hepatocyte-like cells from human embryonic stem cells.

Use of human hepatocytes for therapeutic and drug discovery applications is hampered by limited tissue source and the inability of hepatocytes to proliferate and maintain function long term in vitro. Human embryonic stem (hES) cells are immortal and pluripotent and may provide a cell source for functional human hepatocytes. We report here that hES cells can be induced to differentiate into hepatocyte-like cells. Treatment with sodium butyrate induced hepatic differentiation as well as significant cell death, resulting in approximately 10-15% yield of a homogeneous population of cells. The differentiated cells have morphological features similar to that of primary hepatocytes and 70-80% of the cells express liver-associated proteins (albumin, alpha-1-antitrypsin, cytokeratin 8 and 18), accumulate glycogen, have inducible cytochrome P450 activity, and do not express alpha-fetoprotein. Because of the inherent proliferative capacity of hES cells, these cells may provide a reliable source of normal human hepatocytes for research and transplantation.

Scalable GMP compliant suspension culture system for human ES cells.

Suspension bioreactors are an attractive alternative to static culture of human embryonic stem cells (hESCs) for the generation of clinically relevant cell numbers in a controlled system. In this study, we have developed a scalable suspension culture system using serum-free defined media with spinner flasks for hESC expansion as cell aggregates. With optimized cell seeding density and splitting interval, we demonstrate prolonged passaging and expansion of several hESC lines with overall expansion, yield, viability and maintenance of pluripotency equivalent to adherent culture. Human ESCs maintained in suspension as aggregates can be passaged at least 20 times to achieve over 1×10(13) fold calculated expansion with high undifferentiation rate and normal karyotype. Furthermore, the aggregates are able to differentiate to cardiomyocytes in a directed fashion. Finally, we show that the cells can be cryopreserved in serum-free medium and thawed into adherent or suspension cultures to continue passaging and expansion. We have successfully used this method under cGMP or cGMP-equivalent conditions to generate cell banks of several hESC lines. Taken together, our suspension culture system provides a powerful approach for scale-up expansion of hESCs under defined and serum-free conditions for clinical and research applications.

Cell-surface markers for the isolation of pancreatic cell types derived from human embryonic stem cells.

Using a flow cytometry-based screen of commercial antibodies, we have identified cell-surface markers for the separation of pancreatic cell types derived from human embryonic stem (hES) cells. We show enrichment of pancreatic endoderm cells using CD142 and of endocrine cells using CD200 and CD318. After transplantation into mice, enriched pancreatic endoderm cells give rise to all the pancreatic lineages, including functional insulin-producing cells, demonstrating that they are pancreatic progenitors. In contrast, implanted, enriched polyhormonal endocrine cells principally give rise to glucagon cells. These antibodies will aid investigations that use pancreatic cells generated from pluripotent stem cells to study diabetes and pancreas biology.

Normal human pluripotent stem cell lines exhibit pervasive mosaic aneuploidy.

Human pluripotent stem cell (hPSC) lines have been considered to be homogeneously euploid. Here we report that normal hPSC--including induced pluripotent--lines are karyotypic mosaics of euploid cells intermixed with many cells showing non-clonal aneuploidies as identified by chromosome counting, spectral karyotyping (SKY) and fluorescent in situ hybridization (FISH) of interphase/non-mitotic cells. This mosaic aneuploidy resembles that observed in progenitor cells of the developing brain and preimplantation embryos, suggesting that it is a normal, rather than pathological, feature of stem cell lines. The karyotypic heterogeneity generated by mosaic aneuploidy may contribute to the reported functional and phenotypic heterogeneity of hPSCs lines, as well as their therapeutic efficacy and safety following transplantation.

Regulatory considerations for the development of autologous induced pluripotent stem cell therapies.

Induced pluripotent stem (iPS) cells offer tremendous opportunity for the creation of autologous cellular therapies, in which gene correction or the avoidance of immune response issues are desirable. In addition, iPS cells avoid the ethical concerns raised by the sourcing of human embryonic stem cells (hESCs) from embryos. iPS cells share many characteristics with hESCs and it is anticipated that existing experience with hESCs will translate to rapid progress in moving iPS cell-derived products toward clinical trials. While the potential clinical value for these products is considerable, the nature of current manufacturing paradigms for autologous iPS cell products raises considerable regulatory concerns. Here, the regulatory challenges posed by autologous iPS cell-derived products are examined. We conclude that there will be considerable regulatory concerns primarily relating to reproducibility of the manufacturing process and safety testing within clinically limited time constraints. Demonstrating safety of the final cell product in an autologous setting will be the single greatest obstacle to progressing autologous iPS cell-based therapies into the clinic.

Pancreatic endoderm derived from human embryonic stem cells generates glucose-responsive insulin-secreting cells in vivo.

Development of a cell therapy for diabetes would be greatly aided by a renewable supply of human beta-cells. Here we show that pancreatic endoderm derived from human embryonic stem (hES) cells efficiently generates glucose-responsive endocrine cells after implantation into mice. Upon glucose stimulation of the implanted mice, human insulin and C-peptide are detected in sera at levels similar to those of mice transplanted with approximately 3,000 human islets. Moreover, the insulin-expressing cells generated after engraftment exhibit many properties of functional beta-cells, including expression of critical beta-cell transcription factors, appropriate processing of proinsulin and the presence of mature endocrine secretory granules. Finally, in a test of therapeutic potential, we demonstrate that implantation of hES cell-derived pancreatic endoderm protects against streptozotocin-induced hyperglycemia. Together, these data provide definitive evidence that hES cells are competent to generate glucose-responsive, insulin-secreting cells.

Human embryonic stem cells differentiate into oligodendrocytes in high purity and myelinate after spinal cord transplantation.

Human embryonic stem cells (hESCs) demonstrate remarkable proliferative and developmental capacity. Clinical interest arises from their ability to provide an apparently unlimited cell supply for transplantation, and from the hope that they can be directed to desirable phenotypes in high purity. Here we present for the first time a method for obtaining oligodendrocytes and their progenitors in high yield from hESCs. We expanded hESCs, promoted their differentiation into oligodendroglial progenitors, amplified those progenitors, and then promoted oligodendroglial differentiation using positive selection and mechanical enrichment. Transplantation into the shiverer model of dysmyelination resulted in integration, differentiation into oligodendrocytes, and compact myelin formation, demonstrating that these cells display a functional phenotype. This differentiation protocol provides a means of generating human oligodendroglial lineage cells in high purity, for use in studies of lineage development, screening assays of oligodendroglial-specific compounds, and treating neurodegenerative diseases and traumatic injuries to the adult CNS.

Basic fibroblast growth factor supports undifferentiated human embryonic stem cell growth without conditioned medium.

Previous studies have shown that prolonged propagation of undifferentiated human embryonic stem cells (hESCs) requires conditioned medium from mouse embryonic feeders (MEF-CM) as well as matrix components. Because hESCs express growth factor receptors, including those for basic fibroblast growth factor (bFGF), stem cell factor (SCF), and fetal liver tyrosine kinase-3 ligand (Flt3L), we evaluated these and other growth factors for their ability to maintain undifferentiated hESCs in the absence of conditioned medium. We found cultures maintained in bFGF alone or in combination with other factors showed characteristics similar to MEF-CM control cultures, including morphology, surface marker and transcription factor expression, telomerase activity, differentiation, and karyotypic stability. In contrast, cells in media containing Flt-3L, thrombopoietin, and SCF, individually or in combination, showed almost complete differentiation after 6 weeks in culture. These data demonstrate that hESCs can be maintained in nonconditioned medium using growth factors.