Evaluation of 28 Human Embryonic Stem Cell Lines for Use as Unrelated Donors in Stem Cell Therapy: Implications of HLA and ABO Genotypes

Changes in Methylation Patterns of Tumor Suppressor Genes during Extended Human Embryonic Stem Cell Cultures

While studies on embryonic stem cells have been actively conducted, little is known about the epigenetic mechanisms in human embryonic stem cells (hESCs) in extended culture systems. Here, we investigated whether CpG island (CGI) methylation patterns of 24 tumor suppressor genes could be maintained during extended hESC cultures. In total, 10 hESC lines were analyzed. For each cell line, genomic DNA was extracted from early and late passages of cell cultures. CGI methylation levels of 24 tumor suppressor genes were analyzed using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA), pyrosequencing, and real-time polymerase chain reaction (PCR). Different CGI methylation patterns of CASP8, FHIT, and CHFR genes were identified in between early and late passages in some hESC lines. CGI methylation levels of CASP8 significantly increased at late passage in CHA-36, CHA-40, and CHA-42 cell lines compared to those at early passage. The CGI methylation of the FHIT gene was higher at late passage than at early passage in CHA-15, CHA-31, CHA-32, and iPS (FS)-1 cell lines but decreased at the late passage in CHA-20 and H1 cell lines. Different CGI methylation patterns were detected for the CHFR gene only in iPS (FS)-1, and the level significantly increased at late passage. Thus, our findings show that CGI methylation patterns could be altered during prolonged ESC cultures and examining these epigenetic changes is important to assess the maintenance, differentiation, and clinical usage of stem cells.

Rapid Production and Genetic Stability of Human Mesenchymal Progenitor Cells Derived from Human Somatic Cell Nuclear Transfer-Derived Pluripotent Stem Cells

Pluripotent stem cell-derived mesenchymal progenitor cells (PSC-MPCs) are primarily derived through two main methods: three-dimensional (3D) embryoid body-platform (EB formation) and the 2D direct differentiation method. We recently established somatic cell nuclear transfer (SCNT)-PSC lines and showed their stemness. In the present study, we produced SCNT-PSC-MPCs using a novel direct differentiation method, and the characteristics, gene expression, and genetic stability of these MPCs were compared with those derived through EB formation. The recovery and purification of SCNT-PSC-Direct-MPCs were significantly accelerated compared to those of the SCNT-PSC-EB-MPCs, but both types of MPCs expressed typical surface markers and exhibited similar proliferation and differentiation potentials. Additionally, the analysis of gene expression patterns using microarrays showed very similar patterns. Moreover, array CGH analysis showed that both SCNT-PSC-Direct-MPCs and SCNT-PSC-EB-MPCs exhibited no significant differences in copy number variation (CNV) or single-nucleotide polymorphism (SNP) frequency. These results indicate that SCNT-PSC-Direct-MPCs exhibited high genetic stability even after rapid differentiation into MPCs, and the rate at which directly derived MPCs reached a sufficient number was higher than that of MPCs derived through the EB method. Therefore, we suggest that the direct method of differentiating MPCs from SCNT-PSCs can improve the efficacy of SCNT-PSCs applied to allogeneic transplantation.

Off-the-Shelf, Immune-Compatible Human Embryonic Stem Cells Generated Via CRISPR-Mediated Genome Editing

Human embryonic stem cells (hESCs) hold promise in regenerative medicine but allogeneic immune rejections caused by highly polymorphic human leukocyte antigens (HLAs) remain a barrier to their clinical applications. Here, we used a CRISPR/Cas9-mediated HLA-editing strategy to generate a variety of HLA homozygous-like hESC lines from pre-established hESC lines. We edited four pre-established HLA-heterozygous hESC lines and created a mini library of 14 HLA-edited hESC lines in which single HLA-A and HLA-B alleles and both HLA-DR alleles are disrupted. The HLA-edited hESC derivatives elicited both low T cell- and low NK cell-mediated immune responses. Our library would cover about 40% of the Asian-Pacific population. We estimate that HLA-editing of only 19 pre-established hESC lines would give rise to 46 different hESC lines to cover 90% of the Asian-Pacific population. This study offers an opportunity to generate an off-the-shelf HLA-compatible hESC bank, available for immune-compatible cell transplantation, without embryo destruction. Graphical Abstract.

Embryonic Stem Cells in Clinical Trials: Current Overview of Developments and Challenges

The first isolation of human embryonic stem cells (hESC) reported in the late 90s opened a new window to promising possibilities in the fields of human developmental biology and regenerative medicine. Subsequently, the differentiation of hESC lines into different precursor cells showed their potential in treating different incurable diseases. However, this promising field has consistently had remarkable ethical and experimental limitations. This paper is a review of clinical trial studies dealing with hESC and their advantages, limitations, and other specific concerns. Some of the hESC limitations have been solved, and several clinical trial studies are ongoing so that recent clinical trials have strived to improve the clinical applications of hESC, especially in macular degeneration and neurodegenerative diseases. However, regarding hESC-based therapy, several important issues need more research and discussion. Despite considerable studies to Date, hESC-based therapy is not available for conventional clinical applications, and more studies and data are needed to overcome current clinical and ethical limitations. When all the limitations of Embryonic stem cells (ESC) are wholly resolved, perhaps hESC can become superior to the existing stem cell sources. This overview will be beneficial for understanding the standard and promising applications of cell and tissue-based therapeutic approaches and for developing novel therapeutic applications of hESC.

Single cell-derived clonally expanded mesenchymal progenitor cells from somatic cell nuclear transfer-derived pluripotent stem cells ameliorate the endometrial function in the uterus of a murine model with Asherman's syndrome

Objectives

Because primary mesenchymal progenitor cells (adult‐MPCs) have various functions that depend on the tissue origin and donor, de novo MPCs from human pluripotent stem cells (hPSCs) would be required in regenerative medicine. However, the characteristics and function of MPCs derived from reprogrammed hPSCs have not been well studied. Thus, we show that functional MPCs can be successfully established from a single cell‐derived clonal expansion following MPC derivation from somatic cell nuclear transfer‐derived (SCNT)‐hPSCs, and these cells can serve as therapeutic contributors in an animal model of Asherman's syndrome (AS).

Materials and methods

We developed single cell‐derived clonal expansion following MPC derivation from SCNT‐hPSCs to offer a pure population and a higher biological activity. Additionally, we investigated the therapeutic effects of SCNT‐hPSC‐MPCs in model mice of Asherman's syndrome (AS), which is characterized by synechiae or fibrosis with endometrial injury.

Results

Their humoral effects in proliferating host cells encouraged angiogenesis and decreased pro‐inflammatory factors via a host‐dependent mechanism, resulting in reduction in AS. We also addressed that cellular activities such as the cell proliferation and population doubling of SCNT‐hPSC‐MPCs resemble those of human embryonic stem cell‐derived MPCs (hESC‐MPCs) and are much higher than those of adult‐MPCs.

Conclusions

Somatic cell nuclear transfer‐derived‐hPSCs‐MPCs could be an advanced therapeutic strategy for specific diseases in the field of regenerative medicine.

Inhibition of MicroRNA-221 and 222 Enhances Hematopoietic Differentiation from Human Pluripotent Stem Cells via c-KIT Upregulation

The stem cell factor (SCF)/c-KIT axis plays an important role in the hematopoietic differentiation of human pluripotent stem cells (hPSCs), but its regulatory mechanisms involving microRNAs (miRs) are not fully elucidated. Here, we demonstrated that supplementation with SCF increases the hematopoietic differentiation of hPSCs via the interaction with its receptor tyrosine kinase c-KIT, which is modulated by miR-221 and miR-222. c-KIT is comparably expressed in undifferentiated human embryonic and induced pluripotent stem cells. The inhibition of SCF signaling via treatment with a c-KIT antagonist (imatinib) during hPSC-derived hematopoiesis resulted in reductions in the yield and multi-lineage potential of hematopoietic progenitors. We found that the transcript levels of miR-221 and miR-222 targeting c-KIT were significantly lower in the pluripotent state than they were in terminally differentiated somatic cells. Furthermore, suppression of miR-221 and miR-222 in undifferentiated hPSC cultures induced more hematopoiesis by increasing c-KIT expression. Collectively, our data implied that the modulation of c-KIT by miRs may provide further potential strategies to expedite the generation of functional blood cells for therapeutic approaches and the study of the cellular machinery related to hematologic malignant diseases such as leukemia.

Hepatic esterase activity is increased in hepatocyte-like cells derived from human embryonic stem cells using a 3D culture system

OBJECTIVES

The aim of the study is to generate a spherical three-dimensional (3D) aggregate of hepatocyte-like cells (HLCs) differentiated from human embryonic stem cells and to investigate the effect of the 3D environment on hepatic maturation and drug metabolism.

RESULTS

Quantitative real-time PCR analysis indicated that gene expression of mature hepatocyte markers, drug-metabolizing enzymes, and hepatic transporters was significantly higher in HLCs cultured in the 3D system than in those cultured in a two-dimensional system (p < 0.001). Moreover, hepatocyte-specific functions, including albumin secretion and bile canaliculi formation, were increased in HLCs cultured in the 3D system. In particular, 3D spheroidal culture increased expression of CES1 and BCHE, which encode hepatic esterases (p < 0.001). The enhanced activities of these hepatic esterases were confirmed by the cholinesterase activity assay and the increased susceptibility of HLCs to oseltamivir, which is metabolized by CES1.

CONCLUSIONS

3D spheroidal culture enhances the maturation and drug metabolism of stem cell-derived HLCs, and this may help to optimize hepatic differentiation protocols for hepatotoxicity testing.

Phthalazinone Pyrazole Enhances the Hepatic Functions of Human Embryonic Stem Cell-Derived Hepatocyte-Like Cells via Suppression of the Epithelial-Mesenchymal Transition

During liver development, nonpolarized hepatic progenitor cells differentiate into mature hepatocytes with distinct polarity. This polarity is essential for maintaining the intrinsic properties of hepatocytes. The balance between the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) plays a decisive role in differentiation of polarized hepatocytes. In this study, we found that phthalazinone pyrazole (PP), a selective inhibitor of Aurora-A kinase (Aurora-A), suppressed the EMT during the differentiation of hepatocyte-like cells (HLCs) from human embryonic stem cells. The differentiated HLCs treated with PP at the hepatoblast stage showed enhanced hepatic morphology and functions, particularly with regard to the expression of drug metabolizing enzymes. Moreover, we found that these effects were mediated though suppression of the AKT pathway, which is involved in induction of the EMT, and upregulation of hepatocyte nuclear factor 4α expression rather than Aurora-A inhibition. In conclusion, these findings provided insights into the regulatory role of the EMT on in vitro hepatic maturation, suggesting that inhibition of the EMT may drive transformation of hepatoblast cells into mature and polarized HLCs.

HLA and Histo-Blood Group Antigen Expression in Human Pluripotent Stem Cells and their Derivatives

One prerequisite for a successful clinical outcome of human pluripotent stem cell (hPSC) based therapies is immune compatibility between grafted cells/tissue and recipient. This study explores immune determinants of human embryonic stem cell lines (hESC) and induced human pluripotent stem cell (hiPSC) lines and hepatocyte- and cardiomyocyte-like cells derived from these cells. HLA class I was expressed on all pluripotent hPSC lines which upon differentiation into hepatocyte-like cells was considerably reduced in contrast to cardiomyocyte-like cells which retained class I antigens. No HLA class II antigens were found in the pluripotent or differentiated cells. Histo-blood group carbohydrate antigens SSEA-3/SSEA-4/SSEA-5, Globo H, A, Le^x/Le^y and sialyl-lactotetra were expressed on all hPSC lines. Blood group AB(O)H antigen expression was in accordance with ABO genotype. Interestingly, only a subpopulation of A1O1 cells expressed A. During differentiation of hPSC, some histo-blood group antigens showed congruent alteration patterns while expression of other antigens differed between the cell lines. No systematic difference in the hPSC cell surface tissue antigen expression was detected. In conclusion, hPSC and their derivatives express cell surface antigens that may cause an immune rejection. Furthermore, tissue antigen expression must be established for each individual stem cell line prior to clinical application.

Islet-like organoids derived from human pluripotent stem cells efficiently function in the glucose responsiveness in vitro and in vivo

Insulin secretion is elaborately modulated in pancreatic ß cells within islets of three-dimensional (3D) structures. Using human pluripotent stem cells (hPSCs) to develop islet-like structures with insulin-producing ß cells for the treatment of diabetes is challenging. Here, we report that pancreatic islet-like clusters derived from hESCs are functionally capable of glucose-responsive insulin secretion as well as therapeutic effects. Pancreatic hormone-expressing endocrine cells (ECs) were differentiated from hESCs using a step-wise protocol. The hESC-derived ECs expressed pancreatic endocrine hormones, such as insulin, somatostatin, and pancreatic polypeptide. Notably, dissociated ECs autonomously aggregated to form islet-like, 3D structures of consistent sizes (100–150 μm in diameter). These EC clusters (ECCs) enhanced insulin secretion in response to glucose stimulus and potassium channel inhibition in vitro. Furthermore, ß cell-deficient mice transplanted with ECCs survived for more than 40 d while retaining a normal blood glucose level to some extent. The expression of pancreatic endocrine hormones was observed in tissues transplanted with ECCs. In addition, ECCs could be generated from human induced pluripotent stem cells. These results suggest that hPSC-derived, islet-like clusters may be alternative therapeutic cell sources for treating diabetes.

Xeno-sensing activity of the aryl hydrocarbon receptor in human pluripotent stem cell-derived hepatocyte-like cells

Although hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) are considered a promising model for predicting hepatotoxicity, their application has been restricted because of the low activity of drug metabolizing enzymes (DMEs). Here we found that the low expression of xenobiotic receptors (constitutive androstane receptor, CAR; and pregnane X receptor, PXR) contributes to the low activity of DMEs in hPSC-HLCs. Most CAR- and PXR-regulated DMEs and transporters were transcriptionally down-regulated in hPSC-HLC. Transcriptional expression of CAR and PXR was highly repressed in hPSC-HLCs, whereas mRNA levels of aryl hydrocarbon receptor (AHR) were comparable to those of adult liver. Furthermore, ligand-induced transcriptional activation was observed only at AHR in hPSC-HLCs. Bisulfite sequencing analysis demonstrated that promoter hypermethylation of CAR and PXR was associated with diminished transcriptional activity in hPSC-HLCs. Treatment with AHR-selective ligands increased the transcription of AHR-dependent target genes by direct AHR-DNA binding at the xenobiotic response element. In addition, an antagonist of AHR significantly inhibited AHR-dependent target gene expression. Thus, AHR may function intrinsically as a xenosensor as well as a ligand-dependent transcription factor in hPSC-HLCs. Our results indicate that hPSC-HLCs can be used to screen toxic substances related to AHR signaling and to identify potential AHR-targeted therapeutics.

Differences in the Epigenetic Regulation of Cytochrome P450 Genes between Human Embryonic Stem Cell-Derived Hepatocytes and Primary Hepatocytes

Human pluripotent stem cell-derived hepatocytes have the potential to provide in vitro model systems for drug discovery and hepatotoxicity testing. However, these cells are currently unsuitable for drug toxicity and efficacy testing because of their limited expression of genes encoding drug-metabolizing enzymes, especially cytochrome P450 (CYP) enzymes. Transcript levels of major CYP genes were much lower in human embryonic stem cell-derived hepatocytes (hESC-Hep) than in human primary hepatocytes (hPH). To verify the mechanism underlying this reduced expression of CYP genes, including CYP1A1, CYP1A2, CYP1B1, CYP2D6, and CYP2E1, we investigated their epigenetic regulation in terms of DNA methylation and histone modifications in hESC-Hep and hPH. CpG islands of CYP genes were hypermethylated in hESC-Hep, whereas they had an open chromatin structure, as represented by hypomethylation of CpG sites and permissive histone modifications, in hPH. Inhibition of DNA methyltransferases (DNMTs) during hepatic maturation induced demethylation of the CpG sites of CYP1A1 and CYP1A2, leading to the up-regulation of their transcription. Combinatorial inhibition of DNMTs and histone deacetylases (HDACs) increased the transcript levels of CYP1A1, CYP1A2, CYP1B1, and CYP2D6. Our findings suggest that limited expression of CYP genes in hESC-Hep is modulated by epigenetic regulatory factors such as DNMTs and HDACs.

Autophagy regulates homeostasis of pluripotency-associated proteins in hESCs

The pluripotency of embryonic stem cells (ESCs) is maintained by intracellular networks of many pluripotency-associated (PA) proteins such as OCT4, SOX2, and NANOG. However, the mechanisms underlying the regulation of protein homeostasis for pluripotency remain elusive. Here, we first demonstrate that autophagy acts together with the ubiquitin-proteasome system (UPS) to modulate the levels of PA proteins in human ESCs (hESCs). Autophagy inhibition impaired the pluripotency despite increment of PA proteins in hESCs. Immunogold-electron microscopy confirmed localization of OCT4 molecules within autophagosomes. Also, knockdown of LC3 expression led to accumulation of PA proteins and reduction of pluripotency in hESCs. Interestingly, autophagy and the UPS showed differential kinetics in the degradation of PA proteins. Autophagy inhibition caused enhanced accumulation of both cytoplasmic and nuclear PA proteins, whereas the UPS inhibition led to preferentially degrade nuclear PA proteins. Our findings suggest that autophagy modulates homeostasis of PA proteins, providing a new insight in the regulation of pluripotency in hESCs.

Human embryonic stem cells: derivation, maintenance and cryopreservation

Human embryonic stem cells (hESCs) are the most powerful candidate for the treatment of incurable diseases through the replacement of damaged cells and/or tissues in patients, although there are some obstacles to overcome for the clinical application of hESCs such as the assurance of guided differentiation and control of the immune response following cell therapy or tissue grafting. To obtain genetically stable hESCs and use them clinically, it is important to develop appropriate culture conditions. Additionally, the establishment of a hESC bank with a large number of hESC lines will be required for their clinical application because each hESC line is directed to have a different differentiation ability and immune characteristics such as HLA type. In this review, we describe the derivation and culture conditions of hESCs based on recent advances. Then, we will introduce several cryopreservation methods for hESCs, which is important for the development of cell bank.

Human somatic cell nuclear transfer using adult cells

Derivation of patient-specific human pluripotent stem cells via somatic cell nuclear transfer (SCNT) has the potential for applications in a range of therapeutic contexts. However, successful SCNT with human cells has proved challenging to achieve, and thus far has only been reported with fetal or infant somatic cells. In this study, we describe the application of a recently developed methodology for the generation of human ESCs via SCNT using dermal fibroblasts from 35- and 75-year-old males. Our study therefore demonstrates the applicability of SCNT for adult human cells and supports further investigation of SCNT as a strategy for regenerative medicine.

Three-step method for proliferation and differentiation of human embryonic stem cell (hESC)-derived male germ cells

The low efficiency of differentiation into male germ cell (GC)-like cells and haploid germ cells from human embryonic stem cells (hESCs) reflects the culture method employed in the two-dimensional (2D)-microenvironment. In this study, we applied a three-step media and calcium alginate-based 3D-culture system for enhancing the differentiation of hESCs into male germ stem cell (GSC)-like cells and haploid germ cells. In the first step, embryoid bodies (EBs) were derived from hESCs cultured in EB medium for 3 days and re-cultured for 4 additional days in EB medium with BMP4 and RA to specify GSC-like cells. In the second step, the resultant cells were cultured in GC-proliferation medium for 7 days. The GSC-like cells were then propagated after selection using GFR-α1 and were further cultured in GC-proliferation medium for 3 weeks. In the final step, a 3D-co-culture system using calcium alginate encapsulation and testicular somatic cells was applied to induce differentiation into haploid germ cells, and a culture containing approximately 3% male haploid germ cells was obtained after 2 weeks of culture. These results demonstrated that this culture system could be used to efficiently induce GSC-like cells in an EB population and to promote the differentiation of ESCs into haploid male germ cells.

Isolation and characterization of novel, highly proliferative human CD34/CD73-double-positive testis-derived stem cells for cell therapy

Human adult stem cells are a readily available multipotent cell source that can be used in regenerative medicine. Despite many advantages, including low tumorigenicity, their rapid senescence and limited plasticity have curtailed their use in cell-based therapies. In this study, we isolated CD34/CD73-double-positive (CD34(+)/CD73(+)) testicular stromal cells (HTSCs) and found that the expression of CD34 was closely related to the cells' stemness and proliferation. The CD34(+)/CD73(+) cells grew in vitro for an extended period of time, yielding a multitude of cells (5.6×10(16) cells) without forming tumors in vivo. They also differentiated into all three germ layer lineages both in vitro and in vivo, produced cartilage more efficiently compared to bone marrow stem cells and, importantly, restored erectile function in a cavernous nerve crush injury rat model. Thus, these HTSCs may represent a promising new autologous cell source for clinical use.

Strategy for the creation of clinical grade hESC line banks that HLA-match a target population

Here, we describe a pre-derivation embryo haplotyping strategy that we developed in order to maximize the efficiency and minimize the costs of establishing banks of clinical grade hESC lines in which human leukocyte antigen (HLA) haplotypes match a significant proportion of the population. Using whole genome amplification followed by medium resolution HLA typing using PCR amplification with sequence-specific primers (PCR-SSP), we have typed the parents, embryos and hESC lines from three families as well as our eight clinical grade hESC lines and shown that this technical approach is rapid, reliable and accurate. By employing this pre-derivation strategy where, based on HLA match, embryos are selected for a GMP route on day 3-4 of development, we would have drastically reduced our cGMP laboratory running costs.

A comparison of human cord blood- and embryonic stem cell-derived endothelial progenitor cells in the treatment of chronic wounds

Endothelial progenitor cells (EPCs) promote new blood vessel formation and increase angiogenesis by secreting growth factors and cytokines in ischemic tissues. Therefore, EPCs have been highlighted as an alternative cell source for wound healing. EPCs can be isolated from various sources, including the bone marrow, cord blood, and adipose tissue. However, several recent studies have reported that isolating EPCs from these sources has limitations, such as the isolation of insufficient cell numbers and the difficulty of expanding these cells in culture. Thus, human embryonic stem cells (hESCs) have generated great interest as an alternative source of EPCs. Previously, we established an efficient preparation method to obtain EPCs from hESCs (hESC-EPCs). These hESC-EPCs secreted growth factors and cytokines, which are known to be important in angiogenesis and wound healing. In this study, we directly compared the capacity of hESC-EPCs and human cord blood-derived EPCs (hCB-EPCs) to benefit wound healing. The number of hESC-EPCs increased during culture and was always higher than the number of hCB-EPCs during the culture period. In addition, the levels of VEGF and Ang-1 secreted by hESC-EPCs were significantly higher than those produced by hCB-EPCs. After transplantation in a mouse dermal excisional wound model, all EPC-transplanted wounds exhibited better regeneration than in the control group. More importantly, we found that the wounds transplanted with hESC-EPCs showed significantly accelerated re-epithelialization. Thus, hESC-EPCs may be a promising cell source for the treatment of chronic wounds.

Haplotype-based banking of human pluripotent stem cells for transplantation: potential and limitations

High expectations surround the area of stem cells therapeutics. However, the cells' source-adult or embryonic-and the cells' origin-patient-derived autologous or healthy donor genetically unrelated-remain subjects of debate. Autologous origins have the advantage of a theoretical absence of immune rejection by the recipient. However, this approach has several limitations with regard to the disease of the recipient and to potential problems with the generation, expansion, and manipulation of autologous induced pluripotent stem cells (iPS cells) preparation. An alternative to using autologous cells is the establishment of a bank of well-characterized adult cells that would be used to generate iPS cells and their derivatives. In the context of transplantation, such cells would come from genetically unrelated donors and the immune system of the recipient would reject the graft without immunosuppressive therapy. To minimize the risk of rejection, human leukocyte antigen (HLA) compatibility is certainly the best option, and the establishment of an HLA-organized bank would mean having a limited number of stem cells that would be sufficient for a large number of recipients. The concept of haplobanking with HLA homozygous cell lines would also limit the number of HLA mismatches, but such an approach will not necessarily be less immunogenic in terms of selection criteria, because of the limited number of HLA-compatible loci and the level of HLA typing resolution.

Inhibition of kupffer cell activity improves transplantation of human adipose-derived stem cells and liver functions

Numerous approaches to cell transplantation of the hepatic or the extrahepatic origin into liver tissue have been developed; however, the efficiency of cell transplantation remains low and liver functions are not well corrected. The liver is a highly immunoreactive organ that contains many resident macrophages known as Kupffer cells. Here, we show that the inhibition of Kupffer cell activity improves stem cell transplantation into liver tissue and corrects some of the liver functions under conditions of liver injury. We found that, when Kupffer cells were inhibited by glycine, numerous adipose-derived stem cells (ASCs) were successfully transplanted into livers, and these transplanted cells showed hepatoprotective effects, including decrease of liver injury factors, increase of liver regeneration, and albumin production. On the contrary, injected ASCs without glycine recruited numerous Kupffer cells, not lymphocytes, and showed low transplantation efficiency. Intriguingly, successfully transplanted ASCs in liver tissue modulated Kupffer cell activity to inhibit tumor necrosis factor-α secretion. Thus, our data show that Kupffer cell inactivation is an important step in order to improve ASC transplantation efficiency and therapeutic potential in liver injuries. In addition, the hepatoprotective function of glycine has synergic effects on liver protection and the engraftment of ASCs.

Immunological applications of stem cells in type 1 diabetes

Current approaches aiming to cure type 1 diabetes (T1D) have made a negligible number of patients insulin-independent. In this review, we revisit the role of stem cell (SC)-based applications in curing T1D. The optimal therapeutic approach for T1D should ideally preserve the remaining β-cells, restore β-cell function, and protect the replaced insulin-producing cells from autoimmunity. SCs possess immunological and regenerative properties that could be harnessed to improve the treatment of T1D; indeed, SCs may reestablish peripheral tolerance toward β-cells through reshaping of the immune response and inhibition of autoreactive T-cell function. Furthermore, SC-derived insulin-producing cells are capable of engrafting and reversing hyperglycemia in mice. Bone marrow mesenchymal SCs display a hypoimmunogenic phenotype as well as a broad range of immunomodulatory capabilities, they have been shown to cure newly diabetic nonobese diabetic (NOD) mice, and they are currently undergoing evaluation in two clinical trials. Cord blood SCs have been shown to facilitate the generation of regulatory T cells, thereby reverting hyperglycemia in NOD mice. T1D patients treated with cord blood SCs also did not show any adverse reaction in the absence of major effects on glycometabolic control. Although hematopoietic SCs rarely revert hyperglycemia in NOD mice, they exhibit profound immunomodulatory properties in humans; newly hyperglycemic T1D patients have been successfully reverted to normoglycemia with autologous nonmyeloablative hematopoietic SC transplantation. Finally, embryonic SCs also offer exciting prospects because they are able to generate glucose-responsive insulin-producing cells. Easy enthusiasm should be mitigated mainly because of the potential oncogenicity of SCs.

Immunological considerations for embryonic and induced pluripotent stem cell banking

Recent advances in stem cell technology have generated enthusiasm for their potential to study and treat a diverse range of human disease. Pluripotent human stem cells for therapeutic use may, in principle, be obtained from two sources: embryonic stem cells (hESCs), which are capable of extensive self-renewal and expansion and have the potential to differentiate into any somatic tissue, and induced pluripotent stem cells (iPSCs), which are derived from differentiated tissue such as adult skin fibroblasts and appear to have the same properties and potential, but their generation is not dependent upon a source of embryos. The likelihood that clinical transplantation of hESC- or iPSC-derived tissues from an unrelated (allogeneic) donor that express foreign human leucocyte antigens (HLA) may undergo immunological rejection requires the formulation of strategies to attenuate the host immune response to transplanted tissue. In clinical practice, individualized iPSC tissue derived from the intended recipient offers the possibility of personalized stem cell therapy in which graft rejection would not occur, but the logistics of achieving this on a large scale are problematic owing to relatively inefficient reprogramming techniques and high costs. The creation of stem cell banks comprising HLA-typed hESCs and iPSCs is a strategy that is proposed to overcome the immunological barrier by providing HLA-matched (histocompatible) tissue for the target population. Estimates have shown that a stem cell bank containing around 10 highly selected cell lines with conserved homozygous HLA haplotypes would provide matched tissue for the majority of the UK population. These simulations have practical, financial, political and ethical implications for the establishment and design of stem cell banks incorporating cell lines with HLA types that are compatible with different ethnic populations throughout the world.

Efficient differentiation of human pluripotent stem cells into mesenchymal stem cells by modulating intracellular signaling pathways in a feeder/serum-free system

Mesenchymal stem cells (MSCs) derived from human pluripotent stem cells (hPSC-derived MSCs) will be one promising alternative cell source for MSC-based therapies. Here, an efficient protocol is demonstrated for generating hPSC-derived MSCs under a feeder-free culture system by regulating signaling pathways. Simultaneous treatments with Activin A, BIO (6-bromoindirubin-3'-oxime), and bone morphogenetic protein 4 (ABB) activated the transcription of mesoderm-lineage genes such as T, MIXL1, and WNT3 in hPSCs. The ABB-treated hPSCs could develop into CD105(+) cells with a high efficiency of 20% in the MSC-induction medium. The properties of the hPSC-derived CD105(+) cells were similar to those of adult MSCs in terms of surface antigens. Also, hPSC-derived MSCs had the potential to differentiate into adipocytes, osteoblasts, and chondrocytes in vitro. The results demonstrated that functional MSCs could be generated efficiently from hPSCs by the combined modulation of signaling pathways.

The promise of human embryonic stem cells in aging-associated diseases

Aging-associated diseases are often caused by progressive loss or dysfunction of cells that ultimately affect the overall function of tissues and organs. Successful treatment of these diseases could benefit from cell-based therapy that would regenerate lost cells or otherwise restore tissue function. Human embryonic stem cells (hESCs) promise to be an important therapeutic candidate in treating aging-associated diseases due to their unique capacity for self-renewal and pluripotency. To date, there are numerous hESC lines that have been developed and characterized. We will discuss how hESC lines are derived, their molecular and cellular properties, and how their ability to differentiate into all three embryonic germ layers is determined. We will also outline the methods currently employed to direct their differentiation into populations of tissue-specific, functional cells. Finally, we will highlight the general challenges that must be overcome and the strategies being developed to generate highly-purified hESC-derived cell populations that can safely be used for clinical applications.

Registration of human embryonic stem cell lines: Korea, 2010

In an effort to increase the credibility of human embryonic stem cell (hESC) lines established in Korea, obligatory registration was introduced by the Bioethics and Safety Act 2008, effective as of January 1, 2010.

The DNA fingerprint, chromosome stability, expression of pluripotency markers, and contamination of mycoplasma of the submitted lines were analyzed by Korea Centers for Disease Control and Prevention (KCDC). The characterization data and ethical aspects, such as informed consent for donation of surplus embryos, were reviewed by a 10-member advisory review committee for stem cell registry.

A total of 55 domestic hESC lines were submitted for registration in 2010; among them 51 were registered. Among these submitted lines, 26 were additionally characterized by KCDC, while 25 lines previously characterized by the Ministry of Education, Science and Technology were not additionally analyzed by KCDC.

Registration completed an oversight system for embryo research by registering the products of licensed embryo research projects, making embryo research more transparent in Korea. Information about hESC lines is available at the website of the Korea Stem Cell Registry (kscr.nih.go.kr).

Assessment of differentiation aspects by the morphological classification of embryoid bodies derived from human embryonic stem cells

In general, the formation of embryoid bodies (EBs) is a commonly known method for initial induction of human embryonic stem cells (hESCs) into their derivatives in vitro. Despite the ability of EBs to mimic developmental processing, the specification and classifications of EBs are not yet well known. Because EBs show various differentiation potentials depending on the size and morphology of the aggregated cells, specification is difficult to attain. Here, we sought to classify the differentiation potentials of EBs by morphologies to enable one to control the differentiation of specific lineages from hESCs with high efficiency. To induce the differentiation of EB formation, we established floating cultures of undifferentiated hESCs in Petri dishes with hESC medium lacking basic fibroblast growth factor. Cells first aggregated into balls; ∼10 days after suspension culture, some different types of EB morphology were present, which we classified as cystic-, bright cavity-, and dark cavity-type EBs. Next, we analyzed the characteristics of each type of EB for its capacity to differentiate into the 3 germ layers via multiplex polymerase chain reaction (PCR), real-time PCR, and immunocytochemistry. Our results indicated that most cells within the cystic EBs were composed of endoderm lineage populations, and both of the cavity EB types were well organized with 3 germ-layer cells. However, the differentiation capacity of the bright cavity EBs was faster than that of the dark cavity EBs. Thus, the bright cavity EBs in this study, which showed equal differentiation tendencies compared with other types of EBs, may serve as the standard for in vitro engineering of EBs. These results indicate that the classification of EB morphologies allows the estimation of the differentiation status of the EBs and may allow the delineation of subsets of conditions necessary for EBs to differentiate into specific cell types.

How to cross immunogenetic hurdles to human embryonic stem cell transplantation

Implantation of human embryonic stem cells (hES), derived progenitors or mature cells derived from hES has great therapeutic potential for many diseases. If hES would come from genetically unrelated individuals, it would be probably rejected by the immune system of the recipient. Blood groups, MHC and minor antigens are the immunogenetic hurdles that have to be crossed for successful transplantation. Autologous transplantation with adult stem cells would be the best approach but several elements argue against this option. Classical immunosuppression, depleting antibody, induction of tolerance and stem cell banking are alternative methods that could be proposed to limit the risk of rejection.

Gene expression profiles in CHA3 and CHA4 human embryonic stem cells and embryoid bodies

The establishment of the first human embryonic stem cells (hESCs) in 1998 provided a unique tool for studying human development. Although several Western embryoderived hESC lines are well characterized, the biological properties of Asian embryo-derived hESC lines remain unexamined. The aim of this study was to characterize Korean embryo-derived hESC lines and their differentiation potential. In this context, we conducted microarraybased differential gene expression analyses using two Korean embryo-derived hESC lines (CHA3 and CHA4) to identify undifferentiated and spontaneously differentiated (human embryoid body, or hEB) status. These two cell lines showed great similarity in gene expression. By comparing their expression patterns, we determined novel hESC-specific genes and transcriptomes that could serve as reliable hESC markers associated with the "stemness" phenotype. Additionally, we sought to identify hEB markers that could be used to determine the presence of differentiated cells in specific tissues, allowing for the purification of homogeneous cell populations or serving as indicators of hESC differentiation. Novel sets of 68 hESC-specific markers, 12 hESC-specific transcripts and 36 hEB markers were identified and shown by quantitative RTPCR to be similarly expressed in CHA3- and CHA4-hESC lines, as compared to the Western embryo-derived H9-hESC line. Furthermore, our data analysis revealed that the cell cycle, urea cycle, p53 signaling, and metabolism of amino groups are significantly implicated in the regulation of hESC differentiation. These results provide another unique set of hESC/hEB markers and foster a better understanding of the molecular mechanisms underlying hESC biology. These results may thus facilitate studies of human developmental events and provide information regarding Korean embryo-derived hESCs, which could be used to determine differences in developmental events between human races.