Adaptation to culture of human embryonic stem cells and oncogenesis in vivo

Chromosome 7 and 19 trisomy in cultured human neural progenitor cells

Background

Stem cell expansion and differentiation is the foundation of emerging cell therapy technologies. The potential applications of human neural progenitor cells (hNPCs) are wide ranging, but a normal cytogenetic profile is important to avoid the risk of tumor formation in clinical trials. FDA approved clinical trials are being planned and conducted for hNPC transplantation into the brain or spinal cord for various neurodegenerative disorders. Although human embryonic stem cells (hESCs) are known to show recurrent chromosomal abnormalities involving 12 and 17, no studies have revealed chromosomal abnormalities in cultured hNPCs. Therefore, we investigated frequently occurring chromosomal abnormalities in 21 independent fetal-derived hNPC lines and the possible mechanisms triggering such aberrations.

Methods and Findings

While most hNPC lines were karyotypically normal, G-band karyotyping and fluorescent in situ hybridization (FISH) analyses revealed the emergence of trisomy 7 (hNPC⁺⁷) and trisomy 19 (hNPC⁺¹⁹), in 24% and 5% of the lines, respectively. Once detected, subsequent passaging revealed emerging dominance of trisomy hNPCs. DNA microarray and immunoblotting analyses demonstrate epidermal growth factor receptor (EGFR) overexpression in hNPC⁺⁷ and hNPC⁺¹⁹ cells. We observed greater levels of telomerase (hTERT), increased proliferation (Ki67), survival (TUNEL), and neurogenesis (β_III-tubulin) in hNPC⁺⁷ and hNPC⁺¹⁹, using respective immunocytochemical markers. However, the trisomy lines underwent replicative senescence after 50–60 population doublings and never showed neoplastic changes. Although hNPC⁺⁷ and hNPC⁺¹⁹ survived better after xenotransplantation into the rat striatum, they did not form malignant tumors. Finally, EGF deprivation triggered a selection of trisomy 7 cells in a diploid hNPC line.

Conclusions

We report that hNPCs are susceptible to accumulation of chromosome 7 and 19 trisomy in long-term cell culture. These results suggest that micro-environmental cues are powerful factors in the selection of specific hNPC aneuploidies, with trisomy of chromosome 7 being the most common. Given that a number of stem cell based clinical trials are being conducted or planned in USA and a recent report in PLoS Medicine showing the dangers of grafting an inordinate number of cells, these data substantiate the need for careful cytogenetic evaluation of hNPCs (fetal or hESC-derived) before their use in clinical or basic science applications.

Gene targeting in human pluripotent stem cells with adeno-associated virus vectors

Human pluripotent stem cells, such as embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), have the ability to differentiate into various cell types, and will become a potential source of cellular materials for regenerative medicine. To make full use of hESCs or hiPSCs for both basic and clinical research, genetic modification, especially gene targeting via homologous recombination (HR), would be an essential technique. This report describes the successful gene targeting of the hypoxanthine phosphoribosyl transferase 1 (HPRT1) and the NANOG loci in human pluripotent stem cells with adeno-associated virus (AAV) vectors. At the HPRT1 locus, up to 1% of stable transformants were targeted via HR with an AAV-HPRT1 targeting vector, without loss of pluripotency. On the other hand, 20-87% of stable transformants were targeted using an AAV-NANOG-targeting vector designed for the promoter-trap strategy. In the KhES-3 cell line, which shows particularly high fragility to experimental manipulation, gene targeting was successful only by using an AAV vector but not by electroporation. In addition to hESC, gene targeting was achieved in hiPSC lines at similar frequencies. These data indicate that AAV vectors may therefore be a useful tool to introduce genetic modifications in hESCs and hiPSCs.

Integrated chemical genomics reveals modifiers of survival in human embryonic stem cells

Understanding how survival is regulated in human embryonic stem cells (hESCs) could improve expansion of stem cells for production of cells for regenerative therapy. There is great variability in comparing the differentiation potential of multiple hESC lines. One reason for this is poor survival upon dissociation, which limits selection of homogeneous populations of cells. Understanding the complexity of survival signals has been hindered by the lack of a reproducible system to identify modulators of survival in pluripotent cells. We therefore developed a high-content screening approach with small molecules to examine hESC survival. We have identified novel small molecules that improve survival by inhibiting either Rho-kinase or protein kinase C. Importantly, small molecule targets were verified using short hairpin RNA. Rescreening with stable hESCs that were genetically altered to have increased survival enabled us to identify groups of pathway targets that are important for modifying survival. Understanding how survival is regulated in hESCs could overcome severe technical difficulties in the field, namely expansion of stem cells to improve production of cells and tissues for regenerative therapy.

Deconstructing stem cell tumorigenicity: a roadmap to safe regenerative medicine

Many of the earliest stem cell studies were conducted on cells isolated from tumors rather than from embryos. Of particular interest was research on embryonic carcinoma cells (EC), a type of stem cell derived from teratocarcinoma. The EC research laid the foundation for the later discovery of and subsequent work on embryonic stem cells (ESC). Both ESC isolated from the mouse (mESC) and then later from humans (hESC) shared not only pluripotency with their EC cousins, but also robust tumorigenicity as each readily form teratoma. Surprisingly, decades after the discovery of mESC, the question of what drives ESC to form tumors remains largely an open one. This gap in the field is particularly serious as stem cell tumorigenicity represents the key obstacle to the safe use of stem cell-based regenerative medicine therapies. Although some adult stem cell therapies appear to be safe, they have only a very narrow range of uses in human disease. Our understanding of the tumorigenicity of human induced pluripotent stem cells (IPSC), perhaps the most promising modality for future patient-specific regenerative medicine therapies, is rudimentary. However, IPSC are predicted to possess tumorigenic potential equal to or greater than that of ESC. Here, the links between pluripotency and tumorigenicity are explored. New methods for more accurately testing the tumorigenic potential of IPSC and of other stem cells applicable to regenerative medicine are proposed. Finally, the most promising emerging approaches for overcoming the challenges of stem cell tumorigenicity are highlighted.

Histone deacetylase inhibition elicits an evolutionarily conserved self-renewal program in embryonic stem cells

Recent evidence indicates that mouse and human embryonic stem cells (ESCs) are fixed at different developmental stages, with the former positioned earlier. We show that a narrow concentration of the naturally occurring short-chain fatty acid, sodium butyrate, supports the extensive self-renewal of mouse and human ESCs, while promoting their convergence toward an intermediate stem cell state. In response to butyrate, human ESCs regress to an earlier developmental stage characterized by a gene expression profile resembling that of mouse ESCs, preventing precocious Xist expression while retaining the ability to form complex teratomas in vivo. Other histone deacetylase inhibitors (HDACi) also support human ESC self-renewal. Our results indicate that HDACi can promote ESC self-renewal across species, and demonstrate that ESCs can toggle between alternative states in response to environmental factors.

Characterization of CD30 expression in human embryonic stem cell lines cultured in serum-free media and passaged mechanically

BACKGROUND

The presence of chromosomal abnormalities could have a negative impact for human embryonic stem cell (hESC) applications both in regenerative medicine and in research. A biomarker that allows the identification of chromosomal abnormalities induced in hESC in culture before they take over the culture would represent an important tool for defining optimal culture conditions for hESC. Here we investigate the expression of CD30, reported to be a biomarker of hESCs with abnormal karyotype, in undifferentiated and spontaneously differentiated hESC.

METHODS AND RESULTS

hESC were derived and cultured on mouse fibroblasts in KO-SR containing medium (serum free media) and passaged mechanically. Our results based on analysis at mRNA (RT-PCR) and protein (fluorescence-activated cell sorting and immunocytochemistry) level show that CD30 is expressed in undifferentiated hESC, even at very early passages, without any correlation with the presence of chromosomal anomalies. We also show that the expression of CD30 is rapidly lost during early spontaneous differentiation of hESC.

CONCLUSION

We conclude that CD30 expression in hESC cultures is probably a consequence of culture conditions, and that KO-SR may play a role. In addition, the expression of so-called 'stemness' markers does not change in undifferentiated hESC during long-term culture or when cells acquire chromosomal abnormalities.

The immune boundaries for stem cell based therapies: problems and prospective solutions

Stem cells have fascinated the scientific and clinical communities for over a century. Despite the controversy that surrounds this field, it is clear that stem cells have the potential to revolutionize medicine. However, a number of significant hurdles still stand in the way of the realization of this potential. Chiefly among these are safety concerns, differentiation efficiency and overcoming immune rejection. Here we review current progress made in this field to optimize the safe use of stem cells with particular emphasis on prospective interventions to deal with challenges generated by immune rejection.

A self-renewal program controls the expansion of genetically unstable cancer stem cells in pluripotent stem cell-derived tumors

Human germ cell tumors are often metastatic, presumably due to distal site tumor growth by cancer stem cells. To determine whether cancer stem cells can be identified in a transplantation model of testicular germ cell tumor, we transplanted murine embryonic germ cells (EGCs) into the testis of adult severe combined immunodeficient mice. Transplantation resulted in a locally invasive solid tumor, with a cellular component that generated secondary tumors upon serial transplantation. The secondary tumors were invariably metastatic, a feature not observed in the primary tumors derived from EGCs. To characterize the differences between EGCs and the tumor-derived stem cells, we performed karyotype and microarray analysis. Our results show that generation of cancer stem cells is associated with the acquisition of nonclonal genomic rearrangements not found in the originating population. Furthermore, pretreatment of EGCs with a potent inhibitor of self-renewal, retinoic acid, prevented tumor formation and the emergence of these genetically unstable cancer stem cells. Microarray analysis revealed that EGCs and first- and second-generation cancer stem cells were highly similar; however, approximately 1,000 differentially expressed transcripts could be identified corresponding to alterations in oncogenes and genes associated with motility and development. Combined, the data suggest that the activation of oncogenic pathways in a cellular background of genetic instability, coupled with an inherent ability to self-renew, is involved in the acquisition of metastatic behavior in the cancer stem cell population of tumors derived from pluripotent cells.

Specific knockdown of OCT4 in human embryonic stem cells by inducible short hairpin RNA interference

Manipulation of gene function in embryonic stem cells by either over expression or downregulation is critical for understanding their subsequent cell fate. We have developed a tetracycline-inducible short hairpin RNA interference (shRNAi) for human embryonic stem cells (hESCs) and demonstrated doxycycline dose-dependent knockdown of the transcription factor OCT4 and the cell surface antigen β2-microglobulin. The induced knockdown of OCT4 resulted in rapid differentiation of hESCs with a significant increase in transcription of genes associated with trophoblast and endoderm lineages, the extent of which was controlled by the degree of induction. Transgene toxicity, which may occur in conditional over-expression strategies with hESCs, was not observed with wild-type Tet repressor protein. The system allows efficient, reversible, and long-term downregulation of target genes in hESCs and enables the generation of stable transfectants for the knockdown of genes essential for cell survival and self-renewal, not necessarily possible by nonconditional shRNAi methods.

Human umbilical cord blood-derived mesenchymal stem cells do not differentiate into neural cell types or integrate into the retina after intravitreal grafting in neonatal rats

This study investigated the ability of mesenchymal stem cells (MSCs) derived from full-term human umbilical cord blood to survive, integrate and differentiate after intravitreal grafting to the degenerating neonatal rat retina following intracranial optic tract lesion. MSCs survived for 1 week in the absence of immunosuppression. When host animals were treated with cyclosporin A and dexamethasone to suppress inflammatory and immune responses, donor cells survived for at least 3 weeks, and were able to spread and cover the entire vitreal surface of the host retina. However, MSCs did not significantly integrate into or migrate through the retina. They also maintained their human antigenicity, and no indication of neural differentiation was observed in retinas where retinal ganglion cells either underwent severe degeneration or were lost. These results have provided the first in vivo evidence that MSCs derived from human umbilical cord blood can survive for a significant period of time when the host rat response is suppressed even for a short period. These results, together with the observation of a lack of neuronal differentiation and integration of MSCs after intravitreal grafting, has raised an important question as to the potential use of MSCs for neural repair through the replacement of lost neurons in the mammalian retina and central nervous system.

CD30 expression reveals that culture adaptation of human embryonic stem cells can occur through differing routes

Human embryonic stem cells undergo adaptive changes that can increase their growth capacity upon prolonged culture in vitro. This is frequently associated with nonrandom karyotypic changes, commonly involving amplification of genetic material from chromosomes 12, 17, and X. A recent study suggested that the karyotypically abnormal cells can be identified by their expression of CD30, which confers resistance to apoptosis. We have now investigated CD30 expression and apoptosis in karyotypically normal and abnormal sublines of the human ES cell line, H7, but our results were contrary to those previously observed. In this cell line, CD30 expression did not segregate the normal and abnormal cells, and abnormal cells were not protected from apoptosis. These data suggest that culture adaptation can occur through a variety of mechanisms.

Mesenchymal stem cells from multiple myeloma patients display distinct genomic profile as compared with those from normal donors

It is an open question whether in multiple myeloma (MM) bone marrow stromal cells contain genomic alterations, which may contribute to the pathogenesis of the disease. We conducted an array-based comparative genomic hybridization (array-CGH) analysis to compare the extent of unbalanced genomic alterations in mesenchymal stem cells from 21 myeloma patients (MM-MSCs) and 12 normal donors (ND-MSCs) after in vitro culture expansion. Whereas ND-MSCs were devoid of genomic imbalances, several non-recurrent chromosomal gains and losses (>1 Mb size) were detected in MM-MSCs. Using real-time reverse transcription PCR, we found correlative deregulated expression for five genes encoded in regions for which genomic imbalances were detected using array-CGH. In addition, only MM-MSCs showed a specific pattern of 'hot-spot' regions with discrete (<1 Mb) genomic alterations, some of which were confirmed using fluorescence in situ hybridization (FISH). Within MM-MSC samples, unsupervised cluster analysis did not correlate with particular clinicobiological features of MM patients. We also explored whether cytogenetic abnormalities present in myelomatous plasma cells (PCs) were shared by matching MSCs from the same patients using FISH. All MM-MSCs were cytogenetically normal for the tested genomic alterations. Therefore we cannot support a common progenitor for myeloma PCs and MSCs.

Analysis of the distinct functions of growth factors and tissue culture substrates necessary for the long-term self-renewal of human embryonic stem cell lines

The role of individual supplements necessary for the self-renewal of human embryonic stem (hES) cells is poorly characterized, and furthermore we have found that previously reported feeder cell- and serum-free culture systems used for individual hES cell lines are unable to maintain HUES7 cells for more than one passage. We have therefore derived a feeder/serum-free culture system that can support the long-term (at least 10 passages) self-renewal of several euploid hES cell lines including MAN1, HUES7, and HUES1 with minimal spontaneous differentiation and without the need for manual propagation. This system contains fibroblast growth factor 2, activin A, neurotrophin 4, and the N2, B27 supplements together with a human fibronectin substrate. We demonstrate that these components exert distinct functions: both FGF2 and activin A were necessary to prevent differentiation of hES cells while NT4 promoted cell survival, FGF2 could not be substituted by IGFII, and the fibronectin substrate supported a rapid rate of hES culture expansion. Inhibition studies showed that β1 integrin-dependent attachment of hES cells to fibronectin was at least partially via the α5 subunit but independent of integrin αV.

Generation of mice by transplantation of an adult spermatogonial cell line after cryopreservation

OBJECTIVES

The key to fertility in adult males is production of mature spermatogenic cells. Spermatogonial stem cells (SSC) have the dual capacity of self-renewal and of differentiation into mature sperm. SSC transplantation may provide potential treatment for specific male infertilities. However, until now, there has been no evidence of offspring produced by transplantation of adult SSC line cells in humans or other mammals.

MATERIALS AND METHODS

A new line of SSCs from adult C57BL/6 mouse was established by using magnetic-activated cell sorting. The cell line was characterized by immunocytochemistry, karyotype analysis and telomeric repeat amplification protocol (TRAP) telomerase activity assay. Spermatogenic function was examined by allograft into germ cell-ablated recipient mice.

RESULTS

For more than 14 months with more than 65 maintenance passages, the cell line showed a normal karyotype (40, XY) and high telomerase activity. It represented a Thy-1+, Oct4+, SSEA-1-, c-kit- (99 +/- 1%) cell subpopulation. We cryopreserved these SSCs and successfully produced normal offspring after transplanting them into testes of busulphan-sterilized mice.

CONCLUSIONS

We established and long-term maintained an adult SSC line with normal spermatogenic function, without the need of genetic modification; thus, this study provides a model system for basic research and clinical application.

Fibroblast growth factor-2 increases the expression of neurogenic genes and promotes the migration and differentiation of neurons derived from transplanted neural stem/progenitor cells

The capacity of neural stem cells (NSC) to generate different types of neurons and glia depends on the action of intrinsic determinants and extracellular signals. Here, we isolated adult olfactory bulb stem cells (aOBSC) that express nestin, RC2 and Sox2, and that have the capacity to generate neurons possessing mature features in culture and in vivo. The differentiation of aOBSC into neurons and glia, as well as their genetic profile, was compared to that of embryonic OBSC (eOBSC) and ganglionic eminence stem cells (GESC). While these eOBSC express neurogenin (Ngn) 1 and 2, two telencephalic dorsal markers, GESC only express Ngn2. Adult OBSC express either little or no detectable Ngn1 and 2, and they produced significantly fewer neurons in culture than eOBSC. By contrast, Dlx2 transcripts (a telencephalic ventral marker) were only clearly detected in GESC. When transplanted into the early postnatal P5-P7 OB, each of the three populations gave rise to cells with a distinct pattern of neuronal migration and/or dendritic arborization. Overall, these findings suggest that cultured NSC partially maintain their regional and temporal specification. Notably, significant neuronal migration and differentiation were only observed in vivo when the NSC were briefly exposed to fibroblast growth factor-2 (FGF-2) before grafting, a treatment that enhanced the neurogenin expression. Hence, the migration and maturation of neurons derived from transplanted NSC can be promoted by upregulating neurogenic gene expression with FGF-2.

Pluripotent stem cells as new drugs? The example of Parkinson's disease

Cell replacement therapy is a widely discussed novel concept of medical treatment. The increased knowledge in the stem cell field, particularly pluripotent stem cells, potentially provides powerful tools for this therapeutic concept. A large number of disease characterized by the loss of functional cells are potential candidates for cell replacement therapy and, in this regards, Parkinson's disease is of particular interest. It is one of the most prevalent neurodegenerative diseases caused by the loss of dopaminergic neurons in the Substantia nigra pars compacta. Pharmacological therapies are valuable but suffer from the progressive decline of efficacy as the disease progresses. Cell therapy application has emerged about two decades ago as a valid therapeutic alternative and recent advances in stem cell research suggest that pluripotent stem cell transplantation may be a promising approach to replace degenerated neurons in Parkinson's disease. Various sources of pluripotent stem cells (PSC) currently tested in animal models of Parkinson's disease have proven their efficacy in relieving symptoms and restoring damaged brain function. This review summarizes and discusses the important challenges that actually must be solved before the first studies of PSC transplantation can be undertaken into humans.

The anti-apoptotic gene survivin contributes to teratoma formation by human embryonic stem cells

Teratomas derived from human embryonic stem (hES) cells are unique among oncogenic phenomena as they are polyclonal and develop from apparently normal cells. A deeper understanding of this process should aid in the development of safer cell therapies and may help elucidate the basic principles of tumor initiation. We find that transplantation of diploid hES cells from four independent cell lines generates benign teratomas with no sign of malignancy or persisting embryonal carcinoma-like cells. In contrast, mouse embryonic stem (mES) cells from four cell lines consistently generate malignant teratocarcinomas. Global gene expression analysis shows that survivin (BIRC5), an anti-apoptotic oncofetal gene, is highly expressed in hES cells and teratomas but not in embryoid bodies. Genetic and pharmacological ablation of survivin induces apoptosis in hES cells and in teratomas both in vitro and in vivo. We suggest that continued expression of survivin upon differentiation in vivo may contribute to teratoma formation by hES cells.

Telomere length maintenance in stem cell populations

The maintenance of telomere length is essential for upholding the integrity of the genome. There is good evidence to suggest that telomere length maintenance in stem cell populations is important to facilitate the cell division required for tissue homeostasis. This is balanced against the requirement in long lived species for proliferative life span barriers for tumour suppression; the gradual erosion of telomeres provides one such barrier. The dynamics of telomeres in stem cell populations may thus be crucial in the balance between tumour suppression and tissue homeostasis. Here we briefly discuss our current understanding of telomere dynamics in stem cell populations, and provide some data to indicate that telomeres in human embryonic stem cells may be more stable and less prone to large-scale stochastic telomeric deletion.

Epigenome and chromatin structure in human embryonic stem cells undergoing differentiation

Epigenetic histone (H3) modification patterns and the nuclear radial arrangement of select genetic elements were compared in human embryonic stem cells (hESCs) before and after differentiation. H3K9 acetylation, H3K9 trimethylation, and H3K79 monomethylation were reduced at the nuclear periphery of differentiated hESCs. Differentiation coincided with centromere redistribution, as evidenced by perinucleolar accumulation of the centromeric markers CENP-A and H3K9me3, central repositioning of centromeres 1, 5, 19, and rearrangement of other centromeres at the nuclear periphery. The radial positions of PML, RARalpha genes, and human chromosomes 10, 12, 15, 17, and 19 remained relatively stable as hESCs differentiated. However, the female inactive H3K27-trimethylated X chromosome occupied a more peripheral nuclear position in differentiated cells. Thus, pluripotent and differentiated hESCs have distinct nuclear patterns of heterochromatic structures (centromeres and inactive X chromosome) and epigenetic marks (H3K9me3, and H3K27me3), while relatively conserved gene density-related radial chromatin distributions are already largely established in undifferentiated hES cells.

Cells derived from human umbilical cord blood support the long-term growth of undifferentiated human embryonic stem cells

Various types of human cells have been tested as feeder cells for the undifferentiated growth of human embryonic stem cells (hESCs) in vitro. We report here the successful culture of two hESC lines (H1 and H9) on human umbilical cord blood (UCB)-derived fibroblast-like cells. These cells permit the long-term continuous growth of undifferentiated and pluripotent hESCs. The cultured hESCs had normal karyotypes, expressed OCT-4, SSEA-4, TRA-1-60, and TRA-1-81, formed cystic embryonic body in vitro and teratomas in vivo after injected into immunodeficient mice. The wide availability of clinical-grade human UCB makes it a promising source of support cells for the growth of hESC for use in cell therapies.

Cell surface biomarkers of embryonic stem cells

Embryonic stem cells (ESCs) can give rise to any adult cell type and thus offer enormous potential for regenerative medicine and drug discovery. Molecular biomarkers serve as valuable tools to classify and isolate ESCs and to monitor their differentiation state by antibody-based techniques. A number of biomarkers, such as certain cell surface antigens, are used to assign pluripotent ESCs; however, accumulating evidence suggests that ESCs are heterogeneous in morphology, phenotype and function, and are thereby classified into subpopulations characterized by multiple sets of molecular biomarkers. Biomarker discovery is also important for ESC biology to elucidate the molecular mechanisms that regulate pluripotency and differentiation. This review summarizes studies of ESC biomarker discovery. "Genome-wide" expression profiling of ESC mRNAs and proteins and direct analyses of the cell surface subproteome have demonstrated that ESCs express a diverse range of biomarkers, cell surface antigens, and signaling molecules found in different cell lineages, as well as a number of key molecules that assure "stemness". Clearly, future quantitative proteomics approaches will enhance our knowledge of the stage- and lineage-specific expression of the proteome and its temporal changes upon differentiation, and provide a more detailed view of nascent and clonally amplified ESCs.

Studying early lethality of 45,XO (Turner's syndrome) embryos using human embryonic stem cells

Turner's syndrome (caused by monosomy of chromosome X) is one of the most common chromosomal abnormalities in females. Although 3% of all pregnancies start with XO embryos, 99% of these pregnancies terminate spontaneously during the first trimester. The common genetic explanation for the early lethality of monosomy X embryos, as well as the phenotype of surviving individuals is haploinsufficiency of pseudoautosomal genes on the X chromosome. Another possible mechanism is null expression of imprinted genes on the X chromosome due to the loss of the expressed allele. In contrast to humans, XO mice are viable, and fertile. Thus, neither cells from patients nor mouse models can be used in order to study the cause of early lethality in XO embryos. Human embryonic stem cells (HESCs) can differentiate in culture into cells from the three embryonic germ layers as well as into extraembryonic cells. These cells have been shown to have great value in modeling human developmental genetic disorders. In order to study the reasons for the early lethality of 45,XO embryos we have isolated HESCs that have spontaneously lost one of their sex chromosomes. To examine the possibility that imprinted genes on the X chromosome play a role in the phenotype of XO embryos, we have identified genes that were no longer expressed in the mutant cells. None of these genes showed a monoallelic expression in XX cells, implying that imprinting is not playing a major role in the phenotype of XO embryos. To suggest an explanation for the embryonic lethality caused by monosomy X, we have differentiated the XO HESCs in vitro an in vivo. DNA microarray analysis of the differentiated cells enabled us to compare the expression of tissue specific genes in XO and XX cells. The tissue that showed the most significant differences between the clones was the placenta. Many placental genes are expressed at much higher levels in XX cells in compare to XO cells. Thus, we suggest that abnormal placental differentiation as a result of haploinsufficiency of X-linked pseudoautosomal genes causes the early lethality in XO human embryos.

Macroporous scaffolds associated with cells to construct a hybrid biomaterial for bone tissue engineering

Bone tissue has the ability to heal without a scar and to remodel, which promotes three basic functions: locomotion, protection of internal organs and mineral homeostasis. Although bone regeneration is highly efficient, some clinical situations - such as large bone defects - require specific treatments in order to promote bone healing. Allogenic or autologous bone grafts have been used in these procedures with limited success and, based on this, bone tissue-engineering approaches have been investigated extensively. Tissue engineering has been defined as the application of principles and techniques of the life sciences and engineering to the design, modification and growth of living tissues using biomaterials, cells and growth factors, alone or in combination. The association of cells with porous scaffolds to produce 3D hybrid osteogenic constructs is a common subject in bone tissue-engineering research and will be the focus of this review. We will present some aspects of bone biology, the cells and scaffolds used to engineer bone, and techniques to fabricate the hybrid biomaterial.

A gene expression signature shared by human mature oocytes and embryonic stem cells

BACKGROUND

The first week of human pre-embryo development is characterized by the induction of totipotency and then pluripotency. The understanding of this delicate process will have far reaching implication for in vitro fertilization and regenerative medicine. Human mature MII oocytes and embryonic stem (ES) cells are both able to achieve the feat of cell reprogramming towards pluripotency, either by somatic cell nuclear transfer or by cell fusion, respectively. Comparison of the transcriptome of these two cell types may highlight genes that are involved in pluripotency initiation.

RESULTS

Based on a microarray compendium of 205 samples, we compared the gene expression profile of mature MII oocytes and human ES cells (hESC) to that of somatic tissues. We identified a common oocyte/hESC gene expression profile, which included a strong cell cycle signature, genes associated with pluripotency such as LIN28 and TDGF1, a large chromatin remodelling network (TOP2A, DNMT3B, JARID2, SMARCA5, CBX1, CBX5), 18 different zinc finger transcription factors, including ZNF84, and several still poorly annotated genes such as KLHL7, MRS2, or the Selenophosphate synthetase 1 (SEPHS1). Interestingly, a large set of genes was also found to code for proteins involved in the ubiquitination and proteasome pathway. Upon hESC differentiation into embryoid bodies, the transcription of this pathway declined. In vitro, we observed a selective sensitivity of hESC to the inhibition of the activity of the proteasome.

CONCLUSION

These results shed light on the gene networks that are concurrently overexpressed by the two human cell types with somatic cell reprogramming properties.

Characterization of human embryonic stem cells with features of neoplastic progression

Cultured human embryonic stem (hES) cells can acquire genetic and epigenetic changes that make them vulnerable to transformation. As hES cells with cancer-cell characteristics share properties with normal hES cells, such as self-renewal, teratoma formation and the expression of pluripotency markers, they may be misconstrued as superior hES cells with enhanced 'stemness'. We characterize two variant hES cell lines (v-hESC-1 and v-hESC-2) that express pluripotency markers at high levels and do not harbor chromosomal abnormalities by standard cytogenetic measures. We show that the two lines possess some features of neoplastic progression, including a high proliferative capacity, growth-factor independence, a 9- to 20-fold increase in frequency of tumor-initiating cells, niche independence and aberrant lineage specification, although they are not malignant. Array comparative genomic hybridization reveals an amplification at 20q11.1-11.2 in v-hESC-1 and a deletion at 5q34a-5q34b;5q3 and a mosaic gain of chromosome 12 in v-hESC-2. These results emphasize the need for functional characterization to distinguish partially transformed and normal hES cells.

Large scale production of stem cells and their derivatives

Stem cells have been envisioned to become an unlimited cell source for regenerative medicine. Notably, the interest in stem cells lies beyond direct therapeutic applications. They might also provide a previously unavailable source of valuable human cell types for screening platforms, which might facilitate the development of more efficient and safer drugs. The heterogeneity of stem cell types as well as the numerous areas of application suggests that differential processes are mandatory for their in vitro culture. Many of the envisioned applications would require the production of a high number of stem cells and their derivatives in scalable, well-defined and potentially clinical compliant manner under current good manufacturing practice (cGMP). In this review we provide an overview on recent strategies to develop bioprocesses for the expansion, differentiation and enrichment of stem cells and their progenies, presenting examples for adult and embryonic stem cells alike.

Feeder-free culture of human embryonic stem cells in conditioned medium for efficient genetic modification

Realizing the potential of human embryonic stem cells (hESCs) in research and commercial applications requires generic protocols for culture, expansion and genetic modification that function between multiple lines. Here we describe a feeder-free hESC culture protocol that was tested in 13 independent hESC lines derived in five different laboratories. The procedure is based on Matrigel adaptation in mouse embryonic fibroblast conditioned medium (CM) followed by monolayer culture of hESC. When combined, these techniques provide a robust hESC culture platform, suitable for high-efficiency genetic modification via plasmid transfection (using lipofection or electroporation), siRNA knockdown and viral transduction. In contrast to other available protocols, it does not require optimization for individual lines. hESC transiently expressing ectopic genes are obtained within 9 d and stable transgenic lines within 3 weeks.

Human embryonic stem cells reveal recurrent genomic instability at 20q11.21

By analyzing five human embryonic stem (hES) cell lines over long-term culture, we identified a recurrent genomic instability in the human genome. An amplification of 2.5-4.6 Mb at 20q11.21, encompassing approximately 23 genes in common, was detected in four cell lines of different origins. This amplification, which has been associated with oncogenic transformation, may provide a selective advantage to hES cells in culture.

Recurrent chromosomal abnormalities in human embryonic stem cells

Cultured human embryonic stem (hES) cells have a known predisposition to aneuploidy of chromosomes 12, 17 and X. We studied 17 hES cell lines by array-based comparative genomic hybridization (aCGH) and found that the cells accumulate other recurrent chromosomal abnormalities, including amplification at 20q11.21 and a derivative chromosome 18. These genomic changes have a variable impact at the transcriptional level.

Separation and maintenance of normal cells from human embryonic stem cells with trisomy 12 mosaicism

Human embryonic stem cells (hESCs) are pluripotent and hold great promise as useful tools in basic scientific research and in the field of regenerative medicine. However, several studies have recently reported chromosomal abnormalities such as gains of chromosomes 12, 17 and X in hESCs. This genetic instability presents an obstacle in the application of hESCs as sources of cell therapies. We found that trisomy 12 was correlated with changes in hESC colony morphology during hESC maintenance. In this study, we investigated whether normal and trisomy 12 cells could be separated in hESC cultures displaying trisomy 12 mosaicism with two types of colony morphology using a mechanical transfer technique. Eight sublines were cultured from eight hESC colonies displaying normal or abnormal morphology. Four sublines with normal morphology had normal chromosome 12 numbers, whereas the four sublines with abnormal morphology displayed trisomy 12. These results indicate that a hESC colony with a minor degree of chromosomal mosaicism and normal morphology could proceed to a colony with normal chromosomes after prolonged cultures with mechanical transfer. Therefore, analysis of cultures for chromosomal abnormalities when changes in colony morphology are observed during culture is essential for maintaining normal hESC lines.

Isolation and characterization of Oct-4+/HLA-G+ mesenchymal stem cells from human umbilical cord matrix: differentiation potential and detection of new markers

The presence of multipotent cells in several adult and embryo-related tissues opened new paths for their use in regenerative medicine. Extraembryonic tissues such as umbilical cord are considered a promising source of stem cells, potentially useful in therapy. The characterization of cells from the umbilical cord matrix (Wharton's Jelly) and amniotic membrane revealed the presence of a population of mesenchymal-like cells, sharing a set of core-markers expressed by "mesenchymal stem cells". Several reports enlightened the differentiation capabilities of these cells, even if at times the lack of an extensive characterization of surface markers and immune co-stimulators expression revealed hidden pitfalls when in vivo transplantation was performed. The present work describes a novel isolation protocol for obtaining mesenchymal stem cells from the umbilical cord matrix. These cells are clonogenic, retain long telomeres, can undergo several population doublings in vitro, and can be differentiated in mature mesenchymal tissues as bone and adipose. We describe for the first time that these cells, besides expressing all of the core-markers for mesenchymal stem cells, feature also the expression, at both protein and mRNA level, of tolerogenic molecules and markers of all the three main lineages, potentially important for both their differentiative potential as well as immunological features.

Innovation in the culture and derivation of pluripotent human stem cells

In recent years, substantial progress has been made in identifying culture conditions and specific molecular factors that maintain human embryonic stem cells (hESCs) in a self-renewing, pluripotent state. As science and medicine move closer to producing viable hESC-based therapeutics, effective methods of isolating and maintaining undifferentiated hESCs using clinically acceptable good manufacturing practices must be developed. In recent years, progress toward this goal has included the identification of molecular factors that induce or repress hESC self-renewal and the development of defined media that support long-term hESC expansion. In addition, the recent discovery of novel means to derive pluripotent cells that avoid embryo destruction, including induced pluripotent stem (iPS cells), may mitigate ethical concerns associated with the use of hESCs.

The tumorigenicity of human embryonic stem cells

Human embryonic stem cells (HESCs) are the in vitro descendants of the pluripotent inner cell mass (ICM) of human blastocyst stage embryos. HESCs can be kept undifferentiated in culture or be differentiated to tissues representing all three germ layers, both in vivo and in vitro. These properties make HESC-based therapy remarkably appealing for the treatment of various disorders. Upon transplantation in vivo, undifferentiated HESCs rapidly generate the formation of large tumors called teratomas. These are benign masses of haphazardly differentiated tissues. Teratomas also appear spontaneously in humans and in mice. When they also encompass a core of malignant undifferentiated cells, these tumors are defined as teratocarcinomas. These malignant undifferentiated cells are termed embryonic carcinoma (EC), and are the malignant counterparts of embryonic stem cells. Here we review the history of experimental teratomas and teratocarcinomas, from spontaneous teratocarcinomas in mice to induced teratomas by HESC transplantation. We then discuss cellular and molecular aspects of the tumorigenicity of HESCs. We also describe the utilization of HESC-induced teratomas for the modeling of early human embryogenesis and for modeling developmental diseases. The problem of HESC-induced teratomas may also impede or prevent future HESC-based therapies. We thus conclude with a survey of approaches to evade HESC-induced tumor formation.

Tumor progression of culture-adapted human embryonic stem cells during long-term culture

Human embryonic stem cells (hESCs) during long-term culture acquire chromosomal changes similar to those occurring in tumorigenesis. This was raised concerns about the progression from hESCs to malignant cells. This study aimed to investigate the changes in chromosomes, cell phenotype, and genes in culture-adapted hESCs to ascertain whether tumorigenic transformation occurred. By cytogenetic analysis we found progressive karyotypic changes from simple to complex in chHES-3, one of the hESC lines established in our laboratory, during a long-term suboptimal culture. We further compared chHES-3 cells at different karyotypic stages in cell surface markers, in vivo differentiation, cell cycle, apoptosis, and gene expression profiles. We found that the karyotypically aberrant chHES-3 had higher S-phase fraction in cell cycle distributions and antiapoptosis ability. In vivo differentiation of karyotypically normal chHES-3 resulted in relatively mature teratoma, whereas karyotypically aberrant chHES-3 formed immature teratoma (grade III), in which more primary neural epithelium was revealed by pathological analysis. The microarray analysis and real-time PCR results showed that some oncogenes were upregulated in karyotypically aberrant chHES-3 cells, whereas the genes related to differentiation were downregulated, and that Wnt signal pathway was activated. In conclusion, chHES-3 cells underwent deregulation of self-renewal and dysfunction of related genes in long-term culture adaptation, leading to malignant transformation.

Derivation and maintenance of human embryonic stem cells from poor-quality in vitro fertilization embryos

Human embryonic stem (hES) cells are self-renewing, pluripotent cells that are valuable research tools and hold promise for use in regenerative medicine. Most hES cell lines are derived from cryopreserved human embryos that were created during in vitro fertilization (IVF) and are in excess of clinical need. Embryos that are discarded during the IVF procedure because of poor morphology and a low likelihood for generating viable pregnancies or surviving the cryopreservation process are also a viable source of hES cells. In this protocol, we describe how to derive novel hES cells from discarded poor-quality embryos and how to maintain the hES cell lines.

Pluripotent human stem cell lines: what we can learn about cancer initiation

Although the cancer stem cell (CSC) hypothesis has become an attractive model to account for tumor recurrence, failure to define a cell of origin has created the need to explore alternative models for cancer initiation and maintenance. Recent studies have linked an embryonic stem cell (ESC)-like gene signature with poorly defined high-grade tumors. Here, we review advances in the ESC field with an emphasis on how human pluripotent stem cells (hPSCs) can be used to define early tumorigenic events, including potential miRNA and epigenetic targets, as well as proto-oncogene and tumor suppressor networks that might facilitate hierarchal transformation. These studies allow for investigation of cancer initiation in a manner that cannot be achieved using primary tumors, where only retrospective evaluation of CSC development is possible. By comparing transformed hPSCs with their normal counterparts, we hope to develop novel cell-specific therapies that selectively target CSCs.

Recombinant vitronectin is a functionally defined substrate that supports human embryonic stem cell self-renewal via alphavbeta5 integrin

Defined growth conditions are essential for many applications of human embryonic stem cells (hESC). Most defined media are presently used in combination with Matrigel, a partially defined extracellular matrix (ECM) extract from mouse sarcoma. Here, we defined ECM requirements of hESC by analyzing integrin expression and ECM production and determined integrin function using blocking antibodies. hESC expressed all major ECM proteins and corresponding integrins. We then systematically replaced Matrigel with defined medium supplements and ECM proteins. Cells attached efficiently to natural human vitronectin, fibronectin, and Matrigel but poorly to laminin + entactin and collagen IV. Integrin-blocking antibodies demonstrated that alphaVbeta5 integrins mediated adhesion to vitronectin, alpha5beta1 mediated adhesion to fibronectin, and alpha6beta1 mediated adhesion to laminin + entactin. Fibronectin in feeder cell-conditioned medium partially supported growth on all natural matrices, but in defined, nonconditioned medium only Matrigel or (natural and recombinant) vitronectin was effective. Recombinant vitronectin was the only defined functional alternative to Matrigel, supporting sustained self-renewal and pluripotency in three independent hESC lines.

Origin of pluripotent germ cell tumours: the role of microenvironment during embryonic development

Carcinoma in situ (CIS) testis, known also as intratubular germ cell neoplasia, is the cancer stem cell from which the great majority of testicular germ cell derived tumours (TGCTs) of the testis arise. TGCTs can proliferate into morphologically homogeneous seminomas or can differentiate into virtually any type of tissue and form teratomas (non-seminomas). CIS cells display a close phenotypic similarity to fetal germ cells (primordial germ cells or gonocytes) suggesting an origin due to a developmental delay or arrest of differentiation of early germ cells. The pluripotency of these neoplasms has recently been explained by a close resemblance of their expression profile to that of embryonic inner cell mass cells studied in culture as embryonic stem cells, with high expression of transcription factors associated with pluripotency, such as NANOG and OCT3/4, as well as proteins found in several tissue specific stem cells, such as TFAP2C (AP-2gamma) or KIT. CIS and seminomas highly express a number of pre-meiotic germ cell specific genes, which are down-regulated during development to non-seminomas, while the expression of other embryonic markers, such as SOX2, is up-regulated. The mechanistic pathways and causative factors remain to be elucidated of both the initial transformation of fetal germ cells into CIS cells and the progression of CIS cells into an invasive tumour in the young adult. However, evidence supported by epidemiological studies indicate that disturbances in the hormonal microenvironment of the differentiating gonads may results in both the neoplasia and a host of other problems later in life, such as genital malformations, decreased spermatogenesis, and signs of hypogonadism.

Enhanced plating efficiency of trypsin-adapted human embryonic stem cells is reversible and independent of trisomy 12/17

Human embryonic stem cells (hESCs) can be cultured abundantly and indefinitely, but are subject to accumulations of chromosomal aberrations. To preserve their genetic integrity, hESCs are commonly maintained as cell aggregates or clumps during passaging. However, clump passaging hinders large-scale culture and complicates the isolation of single cell clones. To facilitate the isolation of genetically modified clones of hESCs while preserving their genetic integrity, we employed trypsin single-cell passaging for brief periods before returning to clump passaging for long-term maintenance. We observed that accommodation to trypsin passage as single cells is an adaptive process where over three to four passages considerably increases the plating efficiency. However, trypsin passage was associated with abnormalities of chromosomes 12 and 17. Nevertheless, the high plating efficiency of trypsin passaged hESCs is a reversible phenotype, regardless of chromosomal abnormalities, suggesting that epigenetic events are responsible for the switch in phenotype.

Proteomics and human embryonic stem cells

The derivation of human embryonic stem cells (hESCs) brought cell therapy-based regenerative medicine significantly closer to clinical application. However, expansion of undifferentiated cells and their directed differentiation in vitro have proven difficult to control. This is mainly because of a lack of knowledge of the intracellular signaling events that direct these complex processes. Additionally, extracellular factors, either secreted by feeder cells that support self-renewal and maintain pluripotency or present in serum supplementing proprietary culture media, that influence hESC behavior are largely unknown. Xeno-free media that effectively support long-term hESC self-renewal and differentiation to specific types of specialized cells are only slowly becoming available. Microarray-based transcriptome analyses have produced valuable gene expression profiles of hESCs and indicated changes in transcription that occur during differentiation. However, proteins are the actual effectors of these events and changes in their levels do not always match changes in their corresponding mRNA. Furthermore, information on posttranslational modifications that influence the activity of pivotal proteins is still largely missing. Over the years, mass spectrometry has experienced major breakthroughs in high-throughput identification of proteins and posttranslational modifications in cells under different conditions. Mass spectrometry-based proteomic techniques are being applied with increasing frequency to analyze hESCs, as well as media conditioned by feeder cells, and have generated proteome profiles that not only support, but also complement, existing microarray data. In this review, the various proteomic studies on hESCs and feeder cells are discussed. In a meta-analysis, comparison of published data sets distinguished 32 intracellular proteins and 16 plasma membrane proteins that are present in multiple hESC lines but not in differentiated cells, which were therefore likely to include proteins important for hESCs. In addition, 13 and 24 proteins, respectively, were commonly found in different feeder cell lines of mouse and human origin, some of which may be extracellular signaling molecules that play a key role in the undifferentiated propagation of hESCs. These findings underscore the power of mass spectrometry-based techniques to identify novel proteins associated with hESCs by studying these cells in an unbiased, discovery-oriented manner on a proteome-wide scale.

Plasma membrane proteomics of human embryonic stem cells and human embryonal carcinoma cells

Human embryonic stem cells (hESCs) are of immense interest in regenerative medicine as they can self-renew indefinitely and can give rise to any adult cell type. Human embryonal carcinoma cells (hECCs) are the malignant counterparts of hESCs found in testis tumors. hESCs that have acquired chromosomal abnormalities in culture are essentially indistinguishable from hECC. Direct comparison of karyotypically normal hESCs with hECCs could lead to understanding differences between their mechanisms of growth control and contribute to implementing safe therapeutic use of stem cells without the development of germ cell cancer. While several comparisons of hECCs and hESCs have been reported, their cell surface proteomes are largely unknown, partly because plasma membrane proteomics is still a major challenge. Here, we present a strategy for the identification of plasma membrane proteins that has been optimized for application to the relatively small numbers of stem cells normally available, and that does not require tedious cell fractionation. The method led to the identification of 237 and 219 specific plasma membrane proteins in the hESC line HUES-7 and the hECC line NT2/D1, respectively. In addition to known stemness-associated cell surface markers like ALP, CD9, and CTNNB, a large number of receptors, transporters, signal transducers, and cell-cell adhesion proteins were identified. Our study revealed that several Hedgehog and Wnt pathway members are differentially expressed in hESCs and hECCs including NPC1, FZD2, FZD6, FZD7, LRP6, and SEMA4D, which play a pivotal role in stem cell self-renewal and cancer growth. Various proteins encoded on chromosome 12p, duplicated in testicular cancer, were uniquely identified in hECCs. These included GAPDH, LDHB, YARS2, CLSTN3, CSDA, LRP6, NDUFA9, and NOL1, which are known to be upregulated in testicular cancer. Distinct HLA molecules were revealed on the surface of hESCs and hECCs, despite their low abundance. Results were compared with genomic and proteomic data sets reported previously for mouse ESCs, hECCs, and germ cell tumors. Our data provides a surface signature for HUES-7 and NT2/D1 cells and distinguishes normal hESCs from hECCs, helping explain their 'benign' versus 'malignant' nature.