[Modeling T2 high severe asthma using human induced pluripotent stem cells (hiPSC)]. / Modélisation de l'asthme sévère par la technologie des cellules humaines souches pluripotentes induites (hiPSC).

Severe asthma patients with persistent airflow obstruction are characterized by functional obstruction due to mucus plugs containing mucins, fibrin, and eosinophil derived Charcot- Leyden crystals. The molecular mechanisms underlying this endotype are not clearly understood. Developing new models is crucial to respiratory research insofar as critical differences exist between human and rodent airway epithelium. We (and other teams) have shown that it is possible to reconstitute in vitro a complex and functional airway epithelium displaying all the features described in vivo from human-induced pluripotent stem cells (hiPSC). Our aim is to establish a human in vitro model of severe asthma that will recapitulate airway epithelium remodeling and mucus plugs.

[Production of innervated bronchial epithelium from a blood sample]. / Fabrication d'un épithélium bronchique innervé à partir d'une prise de sang.

Asthma is a frequent respiratory disease, with severe asthma occurring in 3 to 5% of cases. Chronic inflammation of the bronchial epithelium is essential to its pathophysiology. When activated by the bronchial environment, the peripheral sensory nervous system contributes to inflammation of the airways. However, due to a lack of reliable models, the mechanisms of action remain largely unknown. Using induced pluripotent stem cells reprogrammed from blood cells, we have set up a model of bronchial epithelium innervated by sensory neurons. This model will ensure better understanding of the mechanisms of action underlying neurogenic inflammation.

[Modelling the bronchial epithelium in chronic obstructive pulmonary disease using human induced pluripotential stem cells]. / Modélisation de l'épithélium bronchique dans la bronchopneumopathie chronique obstructive par les cellules souches pluripotentes induites humaines.

Chronic obstructive pulmonary disease (COPD) is a chronic lung disease leading to irreversible destruction of the terminal bronchioles. Although the precise patho-physiological mechanisms remain to be elucidated, the bronchial epithelium seems to play a pivotal role in the disease. Recent studies have highlighted a great heterogeneity among COPD patients, with various disease courses including, in about half the cases, an origin in childhood. Modelling of COPD is a major goal but currently available models are imperfect. Our work aims to create a new in vitro cellular model to study the pathology of the disease. The differentiation of human induced pluripotential stem cells (hiPSCs) in bronchial epithelium is a step towards a better understanding of the developmental origin and the identification of new therapeutic targets.

Induced pluripotent stem cells: An unlimited source of organs for transplantation.

Organ production outside the human body could address the shortage of organs for transplantation. However, in vitro organ production is still a faraway perspective, particularly because of the difficulty in establishing an effective vascularization. A new emerging technology proposes to use carrier animals for the development of human organs. In this approach, induced pluripotent stem cells (iPSC) are injected in animal embryos to produce chimeric animals that contain autologous human organs.

Human induced pluripotent stem cells: A disruptive innovation.

This year (2016) will mark the 10th anniversary of the discovery of induced pluripotent stem cells (iPSCs). The finding that the transient expression of four transcription factors can radically remodel the epigenome, transcriptome and metabolome of differentiated cells and reprogram them into pluripotent stem cells has been a major and groundbreaking technological innovation. In this review, we discuss the major applications of this technology that we have grouped in nine categories: a model to study cell fate control; a model to study pluripotency; a model to study human development; a model to study human tissue and organ physiology; a model to study genetic diseases in a dish; a tool for cell rejuvenation; a source of cells for drug screening; a source of cells for regenerative medicine; a tool for the production of human organs in animals.

[Effects of artificial shrinkage prior to vitrification in a closed system: a randomized controlled trial]. / Effets de la réduction artificielle du blastocèle avant vitrification en système fermé : étude contrôlée randomisée.

OBJECTIVE: To evaluate the effect of induced blastocoele shrinkage before vitrification in a closed carrier device. PATIENTS AND METHODS: Prior to vitrification, blastocyst cavity was artificially shrinked by laser pulse or not treated according to a 2:1 randomized procedure. A total of 185 warming cycles from April 2011 to March 2013 have been analyzed. Clinical pregnancy rate and survival rate were compared between the two groups. The mean (±SD) women age was 33.5±5.7 years for both groups. RESULTS: The pregnancy rate in the group with artificial reduction of the cavity was higher ([32/67] 47.7%) than in the control group but not significantly ([43/113] 38%). The survival rate in the artificial shrinkage group was significantly higher compared with the control group : 99% (102/103) and 91.8% (168/183) respectively (P=0.01). DISCUSSION AND CONCLUSION: This study reveals that artificial shrinkage of blastocoelic cavity by laser pulse before vitrification in a closed carrier device improves survival rate after warming.

Cell-free nucleic acids as non-invasive biomarkers of gynecological cancers, ovarian, endometrial and obstetric disorders and fetal aneuploidy.

BACKGROUND: Proper folliculogenesis is fundamental to obtain a competent oocyte that, once fertilized, can support the acquisition of embryo developmental competence and pregnancy. MicroRNAs (miRNAs) are crucial regulators of folliculogenesis, which are expressed in the cumulus-oocyte complex and in granulosa cells and some can also be found in the bloodstream. These circulating miRNAs are intensively studied and used as diagnostic/prognostic markers of many diseases, including gynecological and pregnancy disorders. In addition, serum contains small amounts of cell-free DNA (cfDNA), presumably resulting from the release of genetic material from apoptotic/necrotic cells. The quantification of nucleic acids in serum samples could be used as a diagnostic tool for female infertility. METHODS: An overview of the published literature on miRNAs, and particularly on the use of circulating miRNAs and cfDNA as non-invasive biomarkers of gynecological diseases, was performed (up to January 2014). RESULTS: In the past decade, cell-free nucleic acids have been studied for potential use as biomarkers in many diseases, particularly in gynecological cancers, ovarian and endometrial disorders, as well as in pregnancy-related pathologies and fetal aneuploidy. The data strongly suggest that the concentration of cell-free nucleic acids in serum from IVF patients or in embryo culture medium could be related to the ovarian hormone status and embryo quality, respectively, and be used as a non-invasive biomarker of IVF outcome. CONCLUSIONS: The profiling of circulating nucleic acids, such as miRNAs and cfDNA, opens new perspectives for the diagnosis/prognosis of ovarian disorders and for the prediction of IVF outcomes, namely (embryo quality and pregnancy).

Developmental regulated expression of anti- and pro-apoptotic BCL-2 family genes during human early embryonic development.

Apoptotic cell death has been reported in human oocytes and preimplantation embryos under in vivo and in vitro conditions. BCL-2 family proteins comprise both anti- and pro-apoptotic members, which are likely to play a key role in controlling oocyte and early embryo survival. However, very limited data are available on their expression kinetics during human early embryonic development. Using our DNA microarray data, we analyzed the expression pattern of 21 BCL-2 family genes in human mature MII oocytes, day 3 embryos and day 5/6 blastocysts from patients who underwent in vitro fertilization (IVF). Selected genes were further validated by qRT-PCR and their subcellular localization analyzed by immunofluorescence confocal microscopy. Our results suggest a switch from oocyte-inherited BCL-2 family transcripts, such as BCL2L10, to embryo-produced transcripts after embryonic genome activation, including BIK, BCL2L11 and NOXA. Moreover, the pro-apoptotic gene BCL2L13 was constitutively expressed throughout human early embryonic development. Remarkably, day 3 embryos expressed more BCL-2 pro-apoptotic genes than mature MII oocytes and day 5/6 blastocysts, suggesting that embryos at this stage are more prone to apoptosis. This is further supported by an absence of cleaved Caspase-3 in the oocyte and its presence in the embryo. Using a drug that induces apoptosis (gambogic acid), we were able to show activated Caspase-3 in the oocyte in addition to an alteration of BCL2L13 protein localization. Similarly BCL2L13 localization was altered in degenerated oocytes. This study opens new perspectives for understanding the molecular regulation of human oocyte and pre-implantation embryo survival and death.

MicroRNAs: new candidates for the regulation of the human cumulus-oocyte complex.

STUDY QUESTION: What is the expression pattern of microRNAs (miRNAs) in human cumulus-oocyte complexes (COCs)? SUMMARY ANSWER: Several miRNAs are enriched in cumulus cells (CCs) or oocytes, and are predicted to target genes involved in biological functions of the COC. WHAT IS KNOWN ALREADY: The transcriptional profiles of human MII oocytes and the surrounding CCs are known. However, very limited data are available about post-transcriptional regulators, such as miRNAs. This is the first study focussing on the identification and quantification of small RNAs, including miRNAs, in human oocytes and CCs using a deep-sequencing approach. STUDY DESIGN, SIZE, DURATION: MII oocytes and CCs were collected from women who underwent IVF. PARTICIPANTS/MATERIALS, SETTING, METHODS: Using the Illumina/deep-sequencing technology, we analyzed the small RNAome of pooled MII oocytes (n = 24) and CC samples (n = 20). The mRNA targets of CC and MII oocyte miRNAs were identified using in silico prediction algorithms. Using oligonucleotide microarrays, genome-wide gene expression was studied in oocytes (10 pools of 19 ± 3 oocytes/each) and 10 individual CC samples. TaqMan miRNA assays were used to confirm the sequencing results in independent pools of MII oocytes (3 pools of 8 ± 3 oocytes/each) and CC samples (3 pools of 7 ± 3 CCs/each). The functional role of one miRNA, MIR23a, was assessed in primary cultures of human CCs. MAIN RESULTS AND THE ROLE OF CHANCE: Deep sequencing of small RNAs yielded more than 1 million raw reads. By mapping reads with a single location to the human genome, known miRNAs that were abundant in MII oocytes (MIR184, MIR100 and MIR10A) or CCs (MIR29a, MIR30d, MIR21, MIR93, MIR320a, MIR125a and the LET7 family) were identified. Predicted target genes of the oocyte miRNAs were associated with the regulation of transcription and cell cycle, whereas genes targeted by CC miRNAs were involved in extracellular matrix and apoptosis. Comparison of the predicted miRNA target genes and mRNA microarray data resulted in a list of 224 target genes that were differentially expressed in MII oocytes and CCs, including PTGS2, CTGF and BMPR1B that are important for cumulus-oocyte communication. Functional analysis using primary CC cultures revealed that BCL2 and CYP19A1 mRNA levels were decreased upon MIR23a overexpression. LIMITATIONS, REASONS FOR CAUTION: Only known miRNAs were investigated in the present study on COCs. Moreover, the source of the material is MII oocytes that failed to fertilize. WIDER IMPLICATIONS OF THE FINDINGS: The present findings suggest that miRNA could play a role in the regulation of the oocyte and CC crosstalk. STUDY FUNDING/COMPETING INTEREST(S): This work was partially supported by a grant from Ferring Pharmaceuticals. The authors of the study have no conflict of interest to report. TRIAL REGISTRATION NUMBER: Not applicable.

Altered gene expression profile in cumulus cells of mature MII oocytes from patients with polycystic ovary syndrome.

STUDY QUESTION: Oocyte developmental competence is altered in patients with polycystic ovary syndrome (PCOS); is gene expression in cumulus cells (CCs) from mature metaphase II oocytes of patients with PCOS altered as well? SUMMARY ANSWER: Compared with CCs from non-PCOS patients, the gene expression profile of CCs isolated from mature oocytes of patients with PCOS present alterations that could explain the abnormal folliculogenesis and reduced oocyte competence in such patients. WHAT IS KNOWN ALREADY: Abnormal mRNA expression of several members of the insulin-like growth factor (IGF) family in CCs from PCOS patients was previously reported. Moreover, the whole transcriptome has been investigated in cultured CCs from PCOS patients. STUDY DESIGN, SIZE AND DURATION: This retrospective study included six PCOS patients diagnosed following the Rotterdam Criteria and six non-PCOS patients who all underwent ICSI for male infertility in the assisted reproduction technique (ART) Department of Montpellier University Hospital, between 2009 and 2011. PARTICIPANTS/MATERIALS, SETTING AND METHODS: CCs from PCOS and non-PCOS patients who underwent controlled ovarian stimulation (COS) were isolated mechanically before ICSI. Gene expression profiles were analysed using the microarray technology and the Significance Analysis of Microarray was applied to compare the expression profiles of CCs from PCOS and non-PCOS patients. MAIN RESULTS: The gene expression profile of CCs from patients with PCOS was significantly different from that of CCs from non-PCOS patients. Specifically, CCs from women with PCOS were characterized by abnormal expression of many growth factors, including members of the epidermal growth factor-like (EGFR, EREG and AREG) and IGF-like families (IGF1R, IGF2R, IGF2BP2 and IGFBP2), that are known to play a role in oocyte competence. In addition, mRNA transcripts of factors involved in steroid metabolism, such as CYP11A1, CYP1B1, CYP19A1 and CYP2B7P1, were deregulated in PCOS CCs, and this could explain the abnormal steroidogenesis observed in these women. Functional annotation of the differentially expressed genes suggests that defects in the transforming growth factor ß and estrogen receptors signalling cascades may contribute to the reduced oocyte developmental competence in patients with PCOS. LIMITATIONS AND REASONS FOR CAUTION: Owing to the strict selection criteria (similar age, weight and reasons for ART), this study included a small sample size (six cases and six controls), and thus, further investigations using a large cohort of patients are needed to confirm these results. WIDER IMPLICATIONS OF THE FINDINGS: This study opens a new perspective for understanding the pathogenesis of PCOS. STUDY FUNDING/COMPETING INTERESTS: This work was partially supported by a grant from the Ferring Pharmaceutical. The authors of the study have no competing interests to report. TRIAL REGISTRATION NUMBER: Not applicable.

Slow freezing and vitrification differentially modify the gene expression profile of human metaphase II oocytes.

BACKGROUND: Cryopreservation is now considered as an efficient way to store human oocytes to preserve fertility. However, little is known about the effects of this technology on oocyte gene expression. The aim of this study was to examine the effect of the two cryopreservation procedures, slow freezing and vitrification, on the gene expression profile of human metaphase II (MII) oocytes. METHODS: Unfertilized MII oocytes following ICSI failure were cryopreserved either by slow freezing or by the Cryotip method for vitrification. After thawing, total RNA was extracted and analyzed using Affymetrix Human Genome U133 Plus 2.0 GeneChip arrays. The gene expression profiles and associated biological pathways in slowly frozen/thawed and vitrified MII oocytes were determined and compared with those of non-cryopreserved MII oocytes used as controls. RESULTS: Both cryopreservation procedures negatively affected the gene expression profile of human MII oocytes in comparison with controls. However, slowly frozen and vitrified MI oocytes displayed specific gene expression signatures. Slow freezing was associated with down-regulation of genes involved in chromosomal structure maintenance (KIF2C and KIF3A) and cell cycle regulation (CHEK2 and CDKN1B) that may lead to a reduction in the oocyte developmental competence. In vitrified oocytes, many genes of the ubiquitination pathway were down-regulated, including members of the ubiquitin-specific peptidase family and subunits of the 26S proteasome. Such inhibition of the degradation machinery might stabilize the maternal protein content that is necessary for oocyte developmental competence. CONCLUSIONS: The low pregnancy rates commonly observed when using human MII oocytes after slow freezing-thawing may be explained by the alterations of the oocyte gene expression profile.

[Other actors in the oocyte and follicular growth: the role of microRNAs in the cumulus-oocyte dialog]. / D'autres acteurs dans la croissance folliculaire et ovocytaire: rôle des microARNs dans le dialogue cumulo-ovocytaire.

The good folliculogenesis evolution is fundamental for the obtaining of a competent oocyte, able to lead to pregnancy, once fertilized. During the follicular development, the oocyte is in close contact with surrounding cumulus cells (CCs) to form a cumulus-oocyte complex. The bidirectional exchange between oocyte and contiguous CCs via gap junction communications and paracrine signaling is important for oocyte competence and CCs development. These reciprocal regulations are controlled by some key genes. Recently, it has been demonstrated that these genes are themselves regulated by short RNAs fragments (approximately 22 nucleotides), called microRNAs. The identification and the quantification in the CCs of the microRNAs regulating these genes could promote the development of non invasive tests in order to assess the oocyte quality and its ability to provide embryo with a high implantation potential. This approach could be decisive in the embryo selection to transfer and could avoid the risk of multiple pregnancies by the replacement of a single embryo.

Transcriptome analysis reveals dialogues between human trophectoderm and endometrial cells during the implantation period.

BACKGROUND: Crosstalk between human trophectoderm (TE) and endometrial cells during the implantation window is a complex and not well-understood process. The aims of this study were (i) to evaluate the global gene expression profile in TE cells from Day 5 human blastocysts issued from IVF, (ii) to compare these data with the transcriptomic profile of endometrial cells in stimulated cycles for IVF and (iii) to identify potential early dialogues between maternal and embryonic cells during the implantation window. METHODS: Endometrial biopsies (n = 18) from normal responder patients were performed on the day of embryo transfer (Day 5 after human chorionic gonadotrophin administration). TE biopsies from five blastocysts donated for research purposes were mechanically extracted. DNA microarray analysis was carried out to identify the specific gene expression profiles and the biological pathways activated during the implantation window in endometrial and TE cells. RESULTS: Several cytokines (such as PDGFA, placenta growth factor, IGF2BP1 and IGF2BP3) were up-regulated in human TE cells, whereas some of the corresponding receptors (PDGFRA and KDR) were over-expressed in the receptive endometrium, suggesting that these molecules are involved in the early dialogue between blastocyst and maternal endometrial cells. In addition, several adhesion molecules and extracellular matrix proteins (MCAM, ITGAE and LAMA1) were also over-expressed in the TE, while others (ALCAM, CEACAM1, PECAM1, ITGB8 and LAMA2) were restricted to the receptive endometrium. CONCLUSION: The present study shows that several growth factors, cytokines, integrins and adhesion molecules are expressed in the TE and endometrium at the time of implantation. These results could contribute to the understanding of the mechanisms involved in the early dialogue between blastocyst and endometrium during implantation. Such results should be confirmed by further studies.

LH/hCGR gene expression in human cumulus cells is linked to the expression of the extracellular matrix modifying gene TNFAIP6 and to serum estradiol levels on day of hCG administration.

BACKGROUND: Recent studies suggest a role for luteinizing hormone and human chorionic gonadotrophin receptor (LH/hCGR) signalling in the regulation of the oocyte-cumulus oophorus cell interplay. The present study aimed at assessing the LH/hCGR gene expression in cumulus cells (CCs) surrounding oocytes in patients undergoing controlled ovarian hyperstimulation (COS) before ICSI and to relate the LH/hCGR expression to other COS quality parameters. METHODS: CCs from single oocytes of normal responder patients were analysed by DNA microarrays. Concomitantly, estradiol levels on the day of hCG administration, CC morphology, total collected oocyte and metaphase II oocyte number were assessed in relation to LH/hCGR gene expression in CC. RESULTS: The transcriptome analysis of CC indicated a variable expression of LH/hCGR among the patients and intra-patients. LH/hCGR mRNA expression was negatively correlated with serum estradiol level on the day of hCG administration. Eighty-five genes were significantly modulated between CCs from patients with a high and a low LH/hCGR expression. These genes are involved principally in steroid metabolism and in the ovulation process and include TNFAIP6, a gene expressed during CC-oocyte complex (COC) expansion. There were no significant differences in LH/hCGR gene expression profile between COS protocols. CONCLUSIONS: LH/hCGR is expressed in CC under COS conditions. LH/hCGR expression level is associated with TNFAIP6 gene expression and negatively correlated with serum estradiol level on the day of hCG administration.

[Human embryonic stem cells: from the human embryo transgressed to the regenerative medicine of tomorrow]. / Les cellules souches embryonnaires humaines: de la transgression de l'embryon humain à la médecine régénératrice de demain.

Human embryonic stem cells (hESC) are derived from the inner cell mass (ICM) of the human blastocyst at day 5 or 6 of the early embryo development. These cells display two cardinal features: they are able to differentiate into cell types from many if not all human tissue (pluripotency) and they proliferate strongly and indefinitely without senescence in vitro. Therefore, hESC are a source of choice for stem cells for regenerative medicine and are a reference model to study the biology of pluripotency. Since 2004, the French law (loi de Bioéthique) authorizes hESC research under certain conditions.

Gene expression profile of human endometrial receptivity: comparison between natural and stimulated cycles for the same patients.

BACKGROUND: The adjunction of exogenous hormones for controlled ovarian stimulation (COS) may alter endometrial receptiveness. In order to identify the genes misregulated under COS, we compared the endometrium gene expression profiles, from the same patients, in a natural cycle and in a subsequent COS cycle. METHODS: For the same normal-responder patients (n = 21), endometrial biopsies (n = 84) were collected during the pre-receptive (LH + 2) and receptive stages (LH + 7) of a natural cycle and, subsequently, on oocyte retrieval day (hCG + 2) and on transfer day (hCG + 5) of a stimulated cycle. Samples were analyzed using DNA microarrays. Gene expression profiles and biological pathways involved in endometrial receptivity were analyzed. RESULTS: Although endometrium transition profiles from pre-receptive to receptive phases are similar between patients, COS regimens alter endometrial receptivity in comparison with natural cycle. Under COS conditions, two endometrial profiles were identified and were associated either with a moderately altered receptivity profile for the majority of the patients or a strongly altered profile for a sub-category of patients. The receptive endometrium transcription profile under COS was defective for biological functions such as TGFbeta signaling, leukocyte transendothelial migration and the cell cycle. CONCLUSIONS: Gonadotrophin treatments in COS cycles led to disruptions of the transcriptional activation of genes involved in normal endometrial receptivity. We propose that when the receptiveness of the endometrium is seriously compromised by the COS protocol, fresh embryo replacement should be cancelled, the embryo frozen and thawed embryo replacement should be performed under natural cycles.

A non-invasive test for assessing embryo potential by gene expression profiles of human cumulus cells: a proof of concept study.

Identification of new criteria for embryo quality is required to improve the clinical outcome of in vitro fertilization. The aim of this study was to determine the gene expression profile of cumulus cells (CC) surrounding the oocyte as biomarkers for embryo potential and to identify genes to be used as prognostic indicators of successful pregnancy. CC from single oocytes were analysed using DNA microarrays. Gene expression profiles of CC surrounding the oocyte associated with good embryonic quality and pregnancy outcome were computed. We observed that CC issued from oocytes that developed into embryos with a good morphology had differing gene expression profile according to the pregnancy outcome of the embryo. We demonstrated that the expression of BCL2L11, PCK1 and NFIB in CC is significantly correlated with embryo potential and successful pregnancy. These results were confirmed by quantitative RT-PCR. The gene expression profiling of human CC correlates with embryo potential and pregnancy outcome. BCL2L11, PCK1 and NFIB genes are proposed as biomarkers for predicting pregnancy. Our findings suggest a non-invasive approach, offering a new potential strategy for competent embryo selection. This approach should be validated in single-embryo transfer programmes.

[Human embryo stem cells and gametes: science fiction or near future?]. / Des cellules souches au gamète mâle: science-fiction ou avenir proche?

In mammalian species, gametes are issued from primordial germ cells (PGC). PGC represent a small cell population, appearing during early embryo development. Gametes production is essential for fertilization process and therefore the establishment of the next generation. The gametes are different from somatic cells because they have a haploid number of chromosomes that are normally generated during the cellular division known as meiosis. The embryonic stem cells that appear at the fifth or sixth day within the blastocyst inner cellular mass are pluripotent cells. Therefore, they can differentiate into the three cellular lineages, somatic as well as germinal. It is well established that the mouse embryonic stem cells can be differentiated in vitro into primordial germinal cells. These cells enter into meiosis forming male or female gametes. In vitro production of gametes by induction from embryonic stem cells has become a very important aspect of the actual research constituting an alternative tool for infertility treatment.

[Oocyte and embryo quality: do the apoptotic markers have a place in the preimplantation genetic diagnostic?]. / Qualité ovocytaire et embryonnaire : les marqueurs apoptotiques ont-ils leur place dans le potentiel préimplantatoire ?

In Assisted Reproductive Technology (ART), the pregnancy and birth rates following in vitro fertilization (IVF) attempts are still low. Recently, research in the field of ART has explored new oocyte and embryo quality selection criteria such as apoptotic markers. Many studies provided evidence that bad oocyte and embryo quality can be associated with apoptosis. The aim of this review is to summarize our current knowledge on the apoptosis process in oocytes and embryos, and focus on the possibility of using apoptotic markers as a reliable and predictive marker to select competent oocytes and embryos during IFV.

[Biology and potential of human embryonic stem cells]. / Biologie et potentialités des cellules souches embryonnaires humaines.

Human embryonic stem cells (hESC) are obtained from the inner cell mass from the early embryo at blastocyste stage. Derived in cell lines for the first time in 1998, they can be maintained in culture in an undifferentiated state indefinitely under certain conditions. Two essential properties characterize hESC: pluripotency and self-renewal. Pluripotency is convey by the expression of specific transcription factors such as OCT4 and NANOG, and is under the control of growth factors such as IGF2 and FGFb. Markers used to characterize these cells include surface antigens, notably SSEA-3 and SSEA-4, and nuclear markers such as OCT4. HESC can differentiate into different cell types in vitro. They represent a unique and essential model for early human development research and for regenerative medicine. By their self-renewal capacity and their potential to differentiate into several cell types, hESC are an unlimited source of cells enabling to replace or restore lost or damaged cells in numerous diseases. Even if it is not conceivable today to use them in clinical practice for ethic and scientific reasons, it seems essential to explore the numerous potentialities of these cells. This knowledge might be relevant to handle adult stem cells in vitro and will be mandatory for a therapeutic use of hESC in the future.