Editing Embryonic stem cell

{{Short description|Type of pluripotent blastocystic stem cell}}
[[File:Humanstemcell.JPG|300px|thumb|right|Human embryonic stem cells in [[cell culture]]]]
[[File:Stem cells diagram.png|300px|thumb|right|Pluripotent: Embryonic stem cells are able to develop into any type of cell, excepting those of the placenta. Only embryonic stem cells of the [[morula]] are [[totipotent]]: able to develop into any type of cell, including those of the placenta.]]

'''Embryonic stem cells''' ('''ESCs''') are [[Cell potency#Pluripotency|pluripotent]] [[stem cell]]s derived from the [[inner cell mass]] of a [[blastocyst]], an early-stage pre-[[Implantation (human embryo)|implantation]] [[embryo]].<ref>{{cite journal |author=Thomson |title=Blastocysts Embryonic Stem Cell Lines Derived from Human |journal=[[Science (journal)|Science]] |volume=282 |issue=5391 |pages=1145–1147 |year=1998 |pmid= 9804556|doi=10.1126/science.282.5391.1145 |last2=Itskovitz-Eldor |first2=J |last3=Shapiro |first3=SS |last4=Waknitz |first4=MA |last5=Swiergiel |first5=JJ |last6=Marshall |first6=VS |last7=Jones |first7=JM|bibcode=1998Sci...282.1145T |doi-access=free }}</ref><ref name="NIH1">{{cite web |title=Stem Cell Basics {{!}} STEM Cell Information |url=https://stemcells.nih.gov/info/basics/stc-basics/#stc-I |website=stemcells.nih.gov |access-date=5 June 2022 |archive-date=9 June 2022 |archive-url=https://web.archive.org/web/20220609014145/https://stemcells.nih.gov/info/basics/stc-basics/#stc-I |url-status=live }}</ref> Human [[embryo]]s reach the [[blastocyst]] stage 4–5 days post [[Human fertilization|fertilization]], at which time they consist of 50–150 cells. Isolating the [[inner cell mass]] (embryoblast) using [[immunosurgery]] results in destruction of the blastocyst, a process [[Stem cell controversy|which raises ethical issues]], including whether or not embryos at the pre-implantation stage have the same moral considerations as embryos in the post-implantation stage of development.<ref>{{cite journal |author=Baldwing A|title= Morality and human embryo research. Introduction to the Talking Point on morality and human embryo research. |journal=[[EMBO Reports]] |volume=10 |issue= 4 |pages= 299–300 |year=2009|pmid= 19337297 |doi=10.1038/embor.2009.37 |pmc=2672902}}</ref><ref>{{cite book|last=Nakaya|first=Andrea C.|title=Biomedical ethics|url=https://archive.org/details/biomedicalethics0000naka|url-access=limited|publisher=ReferencePoint Press|location=San Diego, CA|isbn=978-1601521576|pages=[https://archive.org/details/biomedicalethics0000naka/page/96 96]|date=August 1, 2011}}</ref>

Researchers are currently focusing heavily on the therapeutic potential of embryonic stem cells, with clinical use being the goal for many laboratories.<ref name="NIH1"/> Potential uses include the treatment of [[diabetes]] and [[heart disease]].<ref name="NIH1"/> The cells are being studied to be used as clinical therapies, models of [[genetic disorders]], and cellular/DNA repair. However, adverse effects in the research and clinical processes such as tumors and unwanted [[immune response]]s have also been reported.<ref>{{cite journal |title=Risk factors in the development of stem cell therapy |author1=Carla A Herberts |author2=Marcel SG Kwa |author3=Harm PH Hermsen |journal=Journal of Translational Medicine |doi=10.1186/1479-5876-9-29 |pmid = 21418664|pmc = 3070641|year=2011 |volume=9 |pages = 29|number=29 |doi-access=free }}</ref>

==Properties==
[[File:Ips cells.png|thumb|IPS Cell ]]
[[File:The transcriptome of pluripotent cells..jpg|thumb|The transcriptome of embryonic stem cells]]
Embryonic stem cells (ESCs), derived from the blastocyst stage of early mammalian embryos, are distinguished by their ability to differentiate into any embryonic cell type and by their ability to self-renew. It is these traits that makes them valuable in the scientific and medical fields. ESCs have a normal [[karyotype]], maintain high [[telomerase]] activity, and exhibit remarkable long-term [[cell growth|proliferative]] potential.<ref name=sc>{{cite journal|doi=10.1126/science.282.5391.1145|pmid=9804556|title=Embryonic Stem Cell Lines Derived from Human Blastocysts|journal=Science|volume=282|issue=5391|pages=1145–7|year=1998|last1=Thomson|first1=J. A.|last2=Itskovitz-Eldor|first2=J|last3=Shapiro|first3=S. S.|last4=Waknitz|first4=M. A.|last5=Swiergiel|first5=J. J.|last6=Marshall|first6=V. S.|last7=Jones|first7=J. M.|bibcode=1998Sci...282.1145T|doi-access=free}}</ref>

=== Pluripotent ===

Embryonic stem cells of the inner cell mass are [[Cell potency#Pluripotency|pluripotent]], meaning they are able to [[Cellular differentiation|differentiate]] to generate primitive ectoderm, which ultimately differentiates during [[gastrulation]] into all derivatives of the three primary [[germ layer]]s: [[ectoderm]], [[endoderm]], and [[mesoderm]]. These germ layers generate each of the more than 220 [[List of distinct cell types in the adult human body|cell types]] in the adult human body. When provided with the appropriate signals, ESCs initially form [[precursor cells]] that in subsequently differentiate into the desired cell types. Pluripotency distinguishes embryonic stem cells from [[adult stem cell]]s, which are [[multipotent]] and can only produce a limited number of cell types.

=== Self renewal and repair of structure  ===

Under defined conditions, embryonic stem cells are capable of self-renewing indefinitely in an undifferentiated state. Self-renewal conditions must prevent the cells from clumping and maintain an environment that supports an unspecialized state.<ref>{{cite journal |author=Ying |title=BMP Induction of Id Proteins Suppresses Differentiation and Sustains Embryonic Stem Cell Self-Renewal in Collaboration with STAT3 |journal=Cell |volume=115 |issue= 3|pages= 281–292 |year=2003 |pmid= 14636556|doi=10.1016/S0092-8674(03)00847-X |last2=Nichols |first2=J |last3=Chambers |first3=I |last4=Smith |first4=A|s2cid=7201396 |doi-access=free }}</ref> Typically this is done in the lab with media containing [[fetal bovine serum|serum]] and [[leukemia inhibitory factor]] or serum-free media supplements with two inhibitory drugs ("2i"), the [[MEK inhibitor]] PD03259010 and [[GSK-3 inhibitor]] CHIR99021.<ref>{{cite journal|pmid=25288119|year=2014|last1=Martello|first1=G.|title=The nature of embryonic stem cells|journal=Annual Review of Cell and Developmental Biology|volume=30|pages=647–75|last2=Smith|first2=A.|doi=10.1146/annurev-cellbio-100913-013116|doi-access=free}}</ref>

=== Growth ===

ESCs divide very frequently due to a shortened [[G1 phase]] in their [[cell cycle]]. Rapid [[cell division]] allows the cells to quickly grow in number, but not size, which is important for early embryo development. In ESCs, [[cyclin A]] and [[cyclin E]] proteins involved in the [[G1/S transition]] are always expressed at high levels.<ref name="Boward">{{cite journal|pmid=26889666|pmc=5201256|year=2016|last1=Boward|first1=B.|title=Concise Review: Control of Cell Fate Through Cell Cycle and Pluripotency Networks|journal=Stem Cells|volume=34|issue=6|pages=1427–36|last2=Wu|first2=T.|last3=Dalton|first3=S.|doi=10.1002/stem.2345}}</ref> [[Cyclin-dependent kinase]]s such as [[CDK2]] that promote cell cycle progression are overactive, in part due to downregulation of their inhibitors.<ref>{{cite journal|pmid=15703208|pmc=1073679|year=2005|last1=White|first1=J.|title=Developmental activation of the Rb-E2F pathway and establishment of cell cycle-regulated cyclin-dependent kinase activity during embryonic stem cell differentiation|journal=Molecular Biology of the Cell|volume=16|issue=4|pages=2018–27|last2=Stead|first2=E.|last3=Faast|first3=R.|last4=Conn|first4=S.|last5=Cartwright|first5=P.|last6=Dalton|first6=S.|doi=10.1091/mbc.e04-12-1056}}</ref> [[Retinoblastoma protein]]s that inhibit the [[transcription factor]] [[E2F]] until the cell is ready to enter [[S phase]] are hyperphosphorylated and inactivated in ESCs, leading to continual expression of proliferation genes.<ref name="Boward" /> These changes result in accelerated cycles of cell division. Although high expression levels of pro-proliferative proteins and a shortened G1 phase have been linked to maintenance of pluripotency,<ref>{{Cite journal|last1=Ter Huurne|first1=Menno|last2=Stunnenberg|first2=Hendrik G.|date=21 April 2021|title=G1-phase progression in pluripotent stem cells|journal=Cellular and Molecular Life Sciences|volume=21|issue=10|pages=4507–4519|doi=10.1007/s00018-021-03797-8|issn=1875-9777|pmid=33884444|pmc=8195903|doi-access=free}}</ref><ref>{{Cite journal|last1=Singh|first1=Amar M.|last2=Dalton|first2=Stephen|date=2009-08-07|title=The cell cycle and Myc intersect with mechanisms that regulate pluripotency and reprogramming|journal=Cell Stem Cell|volume=5|issue=2|pages=141–149|doi=10.1016/j.stem.2009.07.003|issn=1875-9777|pmc=2909475|pmid=19664987}}</ref> ESCs grown in serum-free 2i conditions do express hypo-phosphorylated active Retinoblastoma proteins and have an elongated G1 phase.<ref>{{Cite journal|last1=Ter Huurne|first1=Menno|last2=Chappell|first2=James|last3=Dalton|first3=Stephen|last4=Stunnenberg|first4=Hendrik G.|date=5 October 2017|title=Distinct Cell-Cycle Control in Two Different States of Mouse Pluripotency|journal=Cell Stem Cell|volume=21|issue=4|pages=449–455.e4|doi=10.1016/j.stem.2017.09.004|issn=1875-9777|pmc=5658514|pmid=28985526}}</ref> Despite this difference in the cell cycle when compared to ESCs grown in media containing serum these cells have similar pluripotent characteristics.<ref>{{Cite journal|last1=Ying|first1=Qi-Long|last2=Wray|first2=Jason|last3=Nichols|first3=Jennifer|last4=Batlle-Morera|first4=Laura|last5=Doble|first5=Bradley|last6=Woodgett|first6=James|last7=Cohen|first7=Philip|last8=Smith|first8=Austin|date=2008-05-22|title=The ground state of embryonic stem cell self-renewal|journal=Nature|volume=453|issue=7194|pages=519–523|doi=10.1038/nature06968|issn=1476-4687|pmc=5328678|pmid=18497825|bibcode=2008Natur.453..519Y}}</ref> Pluripotency factors [[Oct4]] and [[Homeobox protein NANOG|Nanog]] play a role in transcriptionally regulating the embryonic stem cell cycle.<ref>{{cite journal|pmid=19968627|pmc=2825734|year=2010|last1=Lee|first1=J.|title=Oct-4 controls cell-cycle progression of embryonic stem cells|journal=The Biochemical Journal|volume=426|issue=2|pages=171–81|last2=Go|first2=Y.|last3=Kang|first3=I.|last4=Han|first4=Y. M.|last5=Kim|first5=J.|doi=10.1042/BJ20091439}}</ref><ref>{{cite journal|pmid=19139263|pmc=2615089|year=2009|last1=Zhang|first1=X.|title=A role for NANOG in G1 to S transition in human embryonic stem cells through direct binding of CDK6 and CDC25A|journal=The Journal of Cell Biology|volume=184|issue=1|pages=67–82|last2=Neganova|first2=I.|last3=Przyborski|first3=S.|last4=Yang|first4=C.|last5=Cooke|first5=M.|last6=Atkinson|first6=S. P.|last7=Anyfantis|first7=G.|last8=Fenyk|first8=S.|last9=Keith|first9=W. N.|last10=Hoare|first10=S. F.|last11=Hughes|first11=O.|last12=Strachan|first12=T.|last13=Stojkovic|first13=M.|last14=Hinds|first14=P. W.|last15=Armstrong|first15=L.|last16=Lako|first16=M.|doi=10.1083/jcb.200801009}}</ref>

=== Uses ===

Due to their plasticity and potentially unlimited capacity for self-renewal, embryonic [[Stem-cell therapy|stem cell therapies]] have been proposed for [[regenerative medicine]] and tissue replacement after injury or disease. Pluripotent stem cells have shown promise in treating a number of varying conditions, including but not limited to: [[spinal cord injuries]], [[age related macular degeneration]], [[diabetes]], [[neurodegenerative disorders]] (such as [[Parkinson's disease]]), [[AIDS]], etc.<ref>{{cite journal |last1=Mahla |first1=Ranjeet |title=Stem Cell Applications in Regenerative Medicine and Disease Therapeutics |journal=International Journal of Cell Biology |volume=2016 |date=July 19, 2016 |pages=6940283 |doi=10.1155/2016/6940283 |pmid=27516776|pmc=4969512 |doi-access=free }}</ref> In addition to their potential in regenerative medicine, embryonic stem cells provide a possible alternative source of tissue/organs which serves as a possible solution to the donor shortage dilemma. There are some ethical controversies surrounding this though (see '''Ethical debate''' section below). Aside from these uses, ESCs can also be used for research on early human development, certain genetic disease, and ''in vitro'' [[toxicology]] testing.<ref name=sc/>

==Utilizations==

According to a 2002 article in ''[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]]'', "Human embryonic stem cells have the potential to differentiate into various cell types, and, thus, may be useful as a source of cells for transplantation or tissue engineering."<ref>{{Cite journal | last1 = Levenberg | first1 = S. | title = Endothelial cells derived from human embryonic stem cells | doi = 10.1073/pnas.032074999 | journal = Proceedings of the National Academy of Sciences | volume = 99 | issue = 7 | pages = 4391–4396 | year = 2002 | pmid =  11917100| pmc = 123658| bibcode = 2002PNAS...99.4391L | doi-access = free }}</ref>

=== Tissue engineering ===
[[File:MESC EBs.jpg|thumb|Embryoid bodies 24 hours after formation.]]
In [[tissue engineering]], the use of stem cells are known to be of importance. In order to successfully engineer a tissue, the cells used must be able to perform specific biological functions such as secretion of cytokines, signaling molecules, interacting with neighboring cells, and producing an extracellular matrix in the correct organization. Stem cells demonstrates these specific biological functions along with being able to self-renew and differentiate into one or more types of specialized cells. Embryonic stem cells is one of the sources that are being considered for the use of tissue engineering.<ref>{{Cite journal|last1=Vats|first1=A|last2=Tolley|first2=N S|last3=Bishop|first3=A E|last4=Polak|first4=J M|date=2005-08-01|title=Embryonic Stem Cells and Tissue Engineering: Delivering Stem Cells to the Clinic|journal=Journal of the Royal Society of Medicine|language=en|volume=98|issue=8|pages=346–350|doi=10.1177/014107680509800804|pmid=16055897|pmc=1181832|issn=0141-0768|doi-access=free}}</ref>  The use of human embryonic stem cells have opened many new possibilities for tissue engineering, however, there are many hurdles that must be made before human embryonic stem cell can even be utilized. It is theorized that if embryonic stem cells can be altered to not evoke the immune response when implanted into the patient then this would be a revolutionary step in tissue engineering.<ref>{{Cite journal|date=2000-01-01|title=Cells for tissue engineering|url=https://www.sciencedirect.com/science/article/abs/pii/S0167779999013967|journal=Trends in Biotechnology|language=en|volume=18|issue=1|pages=17–19|doi=10.1016/S0167-7799(99)01396-7|issn=0167-7799|last1=Heath|first1=Carole A.|pmid=10631775|access-date=2021-04-13|archive-date=2021-04-13|archive-url=https://web.archive.org/web/20210413183507/https://www.sciencedirect.com/science/article/abs/pii/S0167779999013967|url-status=live|url-access=subscription}}</ref> Embryonic stem cells are not limited to tissue engineering.

===Cell replacement therapies===

Research has focused on differentiating ESCs into a variety of cell types for eventual use as cell replacement therapies. Some of the cell types that have or are currently being developed include [[cardiomyocytes]], [[neurons]], [[hepatocytes]], [[bone marrow]] cells, [[Pancreatic islets|islet]] cells and [[endothelial]] cells.<ref name="davila">{{cite journal|pmid=15014205|year=2004|last1=Davila|first1=JC|last2=Cezar|first2=GG|last3=Thiede|first3=M|last4=Strom|first4=S|last5=Miki|first5=T|last6=Trosko|first6=J|title=Use and application of stem cells in toxicology|volume=79|issue=2|pages=214–223|doi=10.1093/toxsci/kfh100|journal=Toxicological Sciences|doi-access=free}}</ref>  However, the derivation of such cell types from ESCs is not without obstacles, therefore research has focused on overcoming these barriers. For example, studies are underway to differentiate ESCs into tissue specific cardiomyocytes and to eradicate their immature properties that distinguish them from adult cardiomyocytes.<ref name="pmid17584049">{{cite journal|year=2007|last1=Siu|first1=CW|last2=Moore|first2=JC|last3=Li|first3=RA|title=Human embryonic stem cell-derived cardiomyocytes for heart therapies|journal=Cardiovascular & Hematological Disorders Drug Targets|volume=7|issue=2|pages=145–152|pmid=17584049|doi=10.2174/187152907780830851}}</ref>

===Clinical potential===
* Researchers have differentiated ESCs into dopamine-producing cells with the hope that these neurons could be used in the treatment of Parkinson's disease.<ref>{{cite journal|doi=10.1073/pnas.0404700101|pmid=15310843|title=Derivation of midbrain dopamine neurons from human embryonic stem cells|year=2004|last1=Perrier|first1=A. L.|journal=Proceedings of the National Academy of Sciences|volume=101|issue=34|pages=12543–12548|bibcode=2004PNAS..10112543P|pmc=515094|doi-access=free}}</ref><ref>{{cite journal|pmid=17627139|year=2007|last1=Parish|first1=CL|last2=Arenas|first2=E|title=Stem-cell-based strategies for the treatment of Parkinson's disease|volume=4|issue=4|pages=339–347|doi=10.1159/000101892|journal=Neuro-Degenerative Diseases|s2cid=37229348}}</ref>
* ESCs have been differentiated to [[natural killer cell]]s and bone tissue.<ref>{{cite journal|pmid=18193216|year=2008|last1=Waese|first1=EY|last2=Kandel|first2=RA|last3=Stanford|first3=WL|title=Application of stem cells in bone repair|volume=37|issue=7|pages=601–608|doi=10.1007/s00256-007-0438-8|journal=Skeletal Radiology|s2cid=12401889}}</ref>
* Studies involving ESCs are underway to provide an alternative treatment for diabetes. For example ESCs have been differentiated into insulin-producing cells,<ref>{{cite journal|pmid=17053790|year=2006|last1=d'Amour|first1=KA|last2=Bang|first2=AG|last3=Eliazer|first3=S|last4=Kelly|first4=OG|last5=Agulnick|first5=AD|last6=Smart|first6=NG|last7=Moorman|first7=MA|last8=Kroon|first8=E|last9=Carpenter|first9=MK|last10=Baetge|first10=EE|title=Production of pancreatic hormone-expressing endocrine cells from human embryonic stem cells|volume=24|issue=11|pages=1392–1401|doi=10.1038/nbt1259|journal=Nature Biotechnology|s2cid=11040949}}</ref> and researchers at [[Harvard University]] were able to produce large quantities of pancreatic [[beta cell]]s from ESCs.<ref>Colen, B.D. (9 October 2014) [http://news.harvard.edu/gazette/story/2014/10/giant-leap-against-diabetes/ Giant leap against diabetes] {{Webarchive|url=https://web.archive.org/web/20141202163707/http://news.harvard.edu/gazette/story/2014/10/giant-leap-against-diabetes/ |date=2014-12-02 }} The Harvard Gazette, Retrieved 24 November 2014</ref>
* An article published in the ''[[European Heart Journal]]'' describes a translational process of generating human embryonic stem cell-derived cardiac progenitor cells to be used in clinical trials of patients with severe heart failure.<ref>{{cite journal |last1=Menasché |first1=Phillip |last2=Vanneaux |first2=Valérie |last3=Fabreguettes |first3=Jean-Roch |last4=Bel |first4=Alain |last5=Tosca |first5=Lucie |last6=Garcia |first6=Sylvie |title=Towards a clinical use of human embryonic stem cell derived-cardiac progenitors: a translational experience |journal=European Heart Journal |date=21 March 2015 |volume=36 |issue=12 |pages=743–750 |doi=10.1093/eurheartj/ehu192|pmid=24835485 |doi-access=free }}</ref>

===Drug discovery===

Besides becoming an important alternative to organ transplants, ESCs are also being used in the field of toxicology, and as cellular screens to uncover new chemical entities that can be developed as [[small-molecule drug]]s. Studies have shown that cardiomyocytes derived from ESCs are validated ''in vitro'' models to test drug responses and predict toxicity profiles.<ref name="davila" />  ESC derived cardiomyocytes have been shown to respond to pharmacological stimuli and hence can be used to assess cardiotoxicity such as [[torsades de pointes]].<ref>{{cite journal|pmid=19277978|year=2009|last1=Jensen|first1=J|last2=Hyllner|first2=J|last3=Björquist|first3=P|title=Human embryonic stem cell technologies and drug discovery|volume=219|issue=3|pages=513–519|doi=10.1002/jcp.21732|journal=Journal of Cellular Physiology|s2cid=36354049}}</ref>

ESC-derived hepatocytes are also useful models that could be used in the preclinical stages of drug discovery. However, the development of hepatocytes from ESCs has proven to be challenging and this hinders the ability to test drug metabolism. Therefore, research has focused on establishing fully functional ESC-derived hepatocytes with stable phase I and II enzyme activity.<ref>{{cite journal|pmid=17346923|year=2007|last1=Söderdahl|first1=T|last2=Küppers-Munther|first2=B|last3=Heins|first3=N|last4=Edsbagge|first4=J|last5=Björquist|first5=P|last6=Cotgreave|first6=I|last7=Jernström|first7=B|title=Glutathione transferases in hepatocyte-like cells derived from human embryonic stem cells|volume=21|issue=5|pages=929–937|doi=10.1016/j.tiv.2007.01.021|journal=Toxicology in Vitro}}</ref>

===Models of genetic disorder===
Several new studies have started to address the concept of modeling genetic disorders with embryonic stem cells. Either by genetically manipulating the cells, or more recently, by deriving diseased cell lines identified by prenatal genetic diagnosis (PGD), modeling genetic disorders is something that has been accomplished with stem cells. This approach may very well prove valuable at studying disorders such as [[Fragile-X syndrome]], [[Cystic fibrosis]], and other genetic maladies that have no reliable model system.

[[Yury Verlinsky]], a Russian-American [[medical researcher]] who specialized in [[embryo]] and cellular [[genetics]] (genetic [[cell biology|cytology]]), developed [[prenatal diagnosis]] testing methods to determine genetic and [[chromosomal disorders]] a month and a half earlier than standard [[amniocentesis]]. The techniques are now used by many pregnant women and prospective parents, especially couples who have a history of genetic abnormalities or where the woman is over the age of 35 (when the risk of genetically related disorders is higher). In addition, by allowing parents to select an embryo without genetic disorders, they have the potential of saving the lives of siblings that already had similar disorders and diseases using cells from the disease free offspring.<ref name=ChicagoTribune>[http://www.chicagotribune.com/news/chi-hed-verlinsky-20-jul20,0,1789019.story "Dr. Yury Verlinsky, 1943–2009: Expert in reproductive technology"] {{Webarchive|url=https://web.archive.org/web/20090808061655/http://www.chicagotribune.com/news/chi-hed-verlinsky-20-jul20,0,1789019.story |date=2009-08-08 }} ''Chicago Tribune'', July 20, 2009</ref>

===Repair of DNA damage===
Differentiated somatic cells and ES cells use different strategies for dealing with DNA damage.  For instance, human foreskin fibroblasts, one type of somatic cell, use [[Non-homologous end joining|non-homologous end joining (NHEJ)]], an error prone DNA repair process, as the primary pathway for repairing double-strand breaks (DSBs) during all cell cycle stages.<ref name="pmid18769152">{{cite journal |vauthors=Mao Z, Bozzella M, Seluanov A, Gorbunova V |title=DNA repair by nonhomologous end joining and homologous recombination during cell cycle in human cells |journal=Cell Cycle |volume=7 |issue=18 |pages=2902–2906 |date=September 2008 |pmid=18769152 |pmc=2754209 |doi=10.4161/cc.7.18.6679}}</ref>   Because of its error-prone nature, NHEJ tends to produce mutations in a cell's clonal descendants.

ES cells use a different strategy to deal with DSBs.<ref name=Tichy>{{cite journal |vauthors=Tichy ED, Pillai R, Deng L |title=Mouse embryonic stem cells, but not somatic cells, predominantly use homologous recombination to repair double-strand DNA breaks |journal=Stem Cells Dev. |volume=19 |issue=11 |pages=1699–1711 |date=November 2010 |pmid=20446816 |pmc=3128311 |doi=10.1089/scd.2010.0058 |display-authors=etal}}</ref>  Because ES cells give rise to all of the cell types of an organism including the cells of the germ line, mutations arising in ES cells due to faulty DNA repair are a more serious problem than in differentiated somatic cells. Consequently, robust mechanisms are needed in ES cells to repair DNA damages accurately, and if repair fails, to remove those cells with un-repaired DNA damages.  Thus, mouse ES cells predominantly use high fidelity [[Homology directed repair|homologous recombinational repair (HRR)]] to repair DSBs.<ref name=Tichy />  This type of repair depends on the interaction of the two sister chromosomes{{Verify source|date=June 2020}} formed during S phase and present together during the G2 phase of the cell cycle.  HRR can accurately repair DSBs in one sister chromosome by using intact information from the other sister chromosome.  Cells in the G1 phase of the cell cycle (i.e. after metaphase/cell division but prior the next round of replication) have only one copy of each chromosome (i.e. sister chromosomes aren't present).  Mouse ES cells lack a G1 checkpoint and do not undergo cell cycle arrest upon acquiring DNA damage.<ref>{{cite journal |vauthors=Hong Y, Stambrook PJ |title=Restoration of an absent G1 arrest and protection from apoptosis in embryonic stem cells after ionizing radiation |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=101 |issue=40 |pages=14443–14448 |date=October 2004 |pmid=15452351 |pmc=521944 |doi=10.1073/pnas.0401346101 |bibcode=2004PNAS..10114443H |doi-access=free }}</ref>  Rather they undergo programmed cell death (apoptosis) in response to DNA damage.<ref name="pmid9443911">{{cite journal |vauthors=Aladjem MI, Spike BT, Rodewald LW |title=ES cells do not activate p53-dependent stress responses and undergo p53-independent apoptosis in response to DNA damage |journal=Curr. Biol. |volume=8 |issue=3 |pages=145–155 |date=January 1998 |pmid=9443911 |doi=10.1016/S0960-9822(98)70061-2|s2cid=13938854 |display-authors=etal|doi-access=free }}</ref>  Apoptosis can be used as a fail-safe strategy to remove cells with un-repaired DNA damages in order to avoid mutation and progression to cancer.<ref name="pmid12052432">{{cite journal |vauthors=Bernstein C, Bernstein H, Payne CM, Garewal H |title=DNA repair/pro-apoptotic dual-role proteins in five major DNA repair pathways: fail-safe protection against carcinogenesis |journal=Mutat. Res. |volume=511 |issue=2 |pages=145–178 |date=June 2002 |pmid=12052432 |doi=10.1016/S1383-5742(02)00009-1}}</ref>   Consistent with this strategy, mouse ES stem cells have a mutation frequency about 100-fold lower than that of isogenic mouse somatic cells.<ref>{{cite journal |vauthors=Cervantes RB, Stringer JR, Shao C, Tischfield JA, Stambrook PJ |title=Embryonic stem cells and somatic cells differ in mutation frequency and type |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=99 |issue=6 |pages=3586–3590 |date=March 2002 |pmid=11891338 |pmc=122567 |doi=10.1073/pnas.062527199 |bibcode=2002PNAS...99.3586C |doi-access=free }}</ref>

===Clinical trial===
{{Main|Human embryonic stem cells clinical trials}}
On January 23, 2009, Phase I clinical trials for transplantation of [[oligodendrocyte]]s (a cell type of the brain and spinal cord) derived from human ESCs into [[spinal cord injury|spinal cord-injured]] individuals received approval from the [[Food and Drug Administration (United States)|U.S. Food and Drug Administration]] (FDA), marking it the world's first human ESC human trial.<ref name="urlFDA approves human embryonic stem cell study - CNN.com">{{cite news |url=http://www.cnn.com/2009/HEALTH/01/23/stem.cell/ |title=FDA approves human embryonic stem cell study – CNN.com |access-date=May 1, 2010 |date=January 23, 2009 |archive-date=April 9, 2016 |archive-url=https://web.archive.org/web/20160409183450/http://edition.cnn.com/2009/HEALTH/01/23/stem.cell/ |url-status=live }}</ref> The study leading to this scientific advancement was conducted by Hans Keirstead and colleagues at the [[University of California, Irvine]] and supported by [[Geron Corporation]] of [[Menlo Park, CA]], founded by [[Michael D. West]], PhD. A previous experiment had shown an improvement in locomotor recovery in spinal cord-injured rats after a 7-day delayed transplantation of human ESCs that had been pushed into an oligodendrocytic lineage.<ref name="pmid15888645">{{cite journal |vauthors=Keirstead HS, Nistor G, Bernal G |title=Human embryonic stem cell-derived oligodendrocyte progenitor cell transplants remyelinate and restore locomotion after spinal cord injury |journal=J. Neurosci. |volume=25 |issue=19 |pages=4694–4705 |year=2005 |pmid=15888645 |doi=10.1523/JNEUROSCI.0311-05.2005 |pmc=6724772 |display-authors=etal |url=https://escholarship.org/content/qt66v3f6js/qt66v3f6js.pdf?t=lnpzq0 |access-date=2019-09-03 |archive-date=2020-06-06 |archive-url=https://web.archive.org/web/20200606221607/https://escholarship.org/content/qt66v3f6js/qt66v3f6js.pdf?t=lnpzq0 |url-status=live }}</ref> The phase I clinical study was designed to enroll about eight to ten paraplegics who have had their injuries no longer than two weeks before the trial begins, since the cells must be injected before scar tissue is able to form.  The researchers emphasized that the injections were not expected to fully cure the patients and restore all mobility.  Based on the results of the rodent trials, researchers speculated that restoration of myelin sheathes and an increase in mobility might occur.  This first trial was primarily designed to test the safety of these procedures and if everything went well, it was hoped that it would lead to future studies that involve people with more severe disabilities.<ref>Reinberg, Steven (2009-01-23) [https://www.washingtonpost.com/wp-dyn/content/article/2009/01/23/AR2009012302168.html FDA OKs 1st Embryonic Stem Cell Trial] {{Webarchive|url=https://web.archive.org/web/20171025022629/http://www.washingtonpost.com/wp-dyn/content/article/2009/01/23/AR2009012302168.html |date=2017-10-25 }}. ''The Washington Post''</ref> The trial was put on hold in August 2009 due to FDA concerns regarding a small number of microscopic cysts found in several treated rat models but the hold was lifted on July 30, 2010.<ref>[https://web.archive.org/web/20110212042712/http://www.geron.com/media/pressview.aspx?id=1188 Geron comments on FDA hold on spinal cord injury trial]. geron.com (August 27, 2009)</ref>

In October 2010 researchers enrolled and administered ESCs to the first patient at [[Shepherd Center]] in [[Atlanta]].<ref name="UST20101011">{{cite news|url=https://www.usatoday.com/tech/science/2010-10-12-stemcells12_ST_N.htm|title=Embryonic stem cells used on patient for first time|date=11 October 2010|work=[[USA Today]]|access-date=12 October 2010|first=Dan|last=Vergano|archive-date=13 October 2010|archive-url=https://web.archive.org/web/20101013014925/http://www.usatoday.com/tech/science/2010-10-12-stemcells12_ST_N.htm|url-status=live}}</ref>  The makers of the stem cell therapy, [[Geron Corporation]], estimated that it would take several months for the stem cells to replicate and for the [[Geron Corporation#GRNOPC1|GRNOPC1]] therapy to be evaluated for success or failure.

In November 2011 Geron announced it was halting the trial and dropping out of stem cell research for financial reasons, but would continue to monitor existing patients, and was attempting to find a partner that could continue their research.<ref>{{cite news|last=Brown|first=Eryn|title=Geron exits stem cell research|url=http://www.latimes.com/health/boostershots/la-heb-geron-stem-cells-20111115,0,7471215.story?track=rss|newspaper=LA Times|access-date=2011-11-15|date=November 15, 2011|archive-date=2011-11-16|archive-url=https://web.archive.org/web/20111116124546/http://www.latimes.com/health/boostershots/la-heb-geron-stem-cells-20111115,0,7471215.story?track=rss|url-status=live}}</ref> In 2013 [[BioTime]], led by CEO Dr. [[Michael D. West]], acquired all of Geron's stem cell assets, with the stated intention of restarting Geron's embryonic stem cell-based clinical trial for [[spinal cord injury research]].<ref>{{cite news|title= Great news: BioTime Subsidiary Asterias Acquires Geron Embryonic Stem Cell Program|url= http://www.ipscell.com/2013/10/great-news-biotime-subsidiary-asterias-acquires-geron-embryonic-stem-cell-program/|work= iPScell.com|date= October 1, 2013|access-date= November 27, 2013|archive-date= October 25, 2013|archive-url= https://web.archive.org/web/20131025000704/http://www.ipscell.com/2013/10/great-news-biotime-subsidiary-asterias-acquires-geron-embryonic-stem-cell-program/|url-status= live}}</ref>

BioTime company Asterias Biotherapeutics (NYSE MKT: AST) was granted a $14.3 million Strategic Partnership Award by the California Institute for Regenerative Medicine (CIRM) to re-initiate the world's first embryonic stem cell-based human clinical trial, for spinal cord injury.  Supported by California public funds, CIRM is the largest funder of stem cell-related research and development in the world.<ref name=cal>[http://www.biotimeinc.com/california-institute-of-regenerative-medicine/ California Institute of Regenerative Medicine] {{Webarchive|url=https://web.archive.org/web/20171024205728/http://www.biotimeinc.com/california-institute-of-regenerative-medicine/ |date=2017-10-24 }}. BioTime, Inc.</ref>

The award provides funding for Asterias to reinitiate clinical development of AST-OPC1 in subjects with spinal cord injury and to expand clinical testing of escalating doses in the target population intended for future pivotal trials.<ref name=cal/>

AST-OPC1 is a population of cells derived from human embryonic stem cells (hESCs) that contains oligodendrocyte progenitor cells (OPCs). OPCs and their mature derivatives called oligodendrocytes provide critical functional support for nerve cells in the spinal cord and brain. Asterias recently presented the results from phase 1 clinical trial testing of a low dose of AST-OPC1 in patients with neurologically complete thoracic spinal cord injury. The results showed that AST-OPC1 was successfully delivered to the injured spinal cord site. Patients followed 2–3 years after AST-OPC1 administration showed no evidence of serious adverse events associated with the cells in detailed follow-up assessments including frequent neurological exams and MRIs. Immune monitoring of subjects through one year post-transplantation showed no evidence of antibody-based or cellular immune responses to AST-OPC1. In four of the five subjects, serial MRI scans performed throughout the 2–3 year follow-up period indicate that reduced spinal cord cavitation may have occurred and that AST-OPC1 may have had some positive effects in reducing spinal cord tissue deterioration. There was no unexpected neurological degeneration or improvement in the five subjects in the trial as evaluated by the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) exam.<ref name=cal/>

The Strategic Partnership III grant from CIRM will provide funding to Asterias to support the next clinical trial of AST-OPC1 in subjects with spinal cord injury, and for Asterias' product development efforts to refine and scale manufacturing methods to support later-stage trials and eventually commercialization. CIRM funding will be conditional on FDA approval for the trial, completion of a definitive agreement between Asterias and CIRM, and Asterias' continued progress toward the achievement of certain pre-defined project milestones.<ref name=cal/>

==Concern and controversy==
===Adverse effects===
The major concern with the possible transplantation of ESCs into patients as therapies is their ability to form tumors including teratomas.<ref>{{cite journal|doi=10.1002/stem.37|pmid=19415771|title=Deconstructing Stem Cell Tumorigenicity: A Roadmap to Safe Regenerative Medicine|year=2009|last1=Knoepfler|first1=Paul S.|journal=Stem Cells|volume=27|issue=5|pages=1050–1056|pmc=2733374}}</ref>  Safety issues prompted the FDA to place a hold on the first ESC clinical trial, however no tumors were observed.

The main strategy to enhance the safety of ESCs for potential clinical use is to differentiate the ESCs into specific cell types (e.g. neurons, muscle, liver cells) that have reduced or eliminated ability to cause tumors. Following differentiation, the cells are subjected to sorting by [[flow cytometry]] for further purification. ESCs are predicted to be inherently safer than [[iPS cells]] created with genetically integrating [[viral vectors]] because they are not genetically modified with genes such as c-Myc that are linked to cancer. Nonetheless, ESCs express very high levels of the iPS inducing genes and these genes including Myc are essential for ESC self-renewal and pluripotency,<ref>{{cite journal|doi=10.1016/j.diff.2010.05.001|title=Myc maintains embryonic stem cell pluripotency and self-renewal|year=2010|last1=Varlakhanova|first1=Natalia V.|last2=Cotterman|first2=Rebecca F.|last3=Devries|first3=Wilhelmine N.|last4=Morgan|first4=Judy|last5=Donahue|first5=Leah Rae|last6=Murray|first6=Stephen|last7=Knowles|first7=Barbara B.|last8=Knoepfler|first8=Paul S.|journal=Differentiation|volume=80|pages=9–19|pmid=20537458|issue=1|pmc=2916696}}</ref> and potential strategies to improve safety by eliminating c-Myc expression are unlikely to preserve the cells' "stemness". However, N-myc and L-myc have been identified to induce iPS cells instead of c-myc with similar efficiency.<ref>{{cite journal|doi= 10.1016/j.stem.2007.12.001|pmid= 18371415|title= C-Myc is Dispensable for Direct Reprogramming of Mouse Fibroblasts|journal= Cell Stem Cell|volume= 2|issue= 1|pages= 10–12|year= 2008|last1= Wernig|first1= Marius|last2= Meissner|first2= Alexander|last3= Cassady|first3= John P|last4= Jaenisch|first4= Rudolf|doi-access= free}}</ref> Later protocols to induce pluripotency bypass these problems completely by using non-integrating RNA viral vectors such as [[sendai virus]] or [[mRNA]] transfection.

===Ethical debate===
{{Main|Stem cell controversy}}
Due to the nature of embryonic stem cell research, there are a lot of controversial opinions on the topic. Since harvesting embryonic stem cells usually necessitates destroying the embryo from which those cells are obtained, the moral status of the embryo comes into question. Some people claim that the embryo is too young to achieve personhood or that the embryo, if donated from an IVF clinic (where labs typically acquire embryos), would otherwise go to medical waste anyway. Opponents of ESC research claim that an embryo is a human life, therefore destroying it is murder and the embryo must be protected under the same ethical view as a more developed human being.<ref>{{cite journal |last1=King |first1=Nancy |last2=Perrin |first2=Jacob |title=Ethical issues in stem cell research and therapy |journal=Stem Cell Research & Therapy |volume=5 |issue=4 |pages=85 |date=July 7, 2014 |doi=10.1186/scrt474 |pmid=25157428 |pmc=4097842 |doi-access=free }}</ref>

==History==
* 1964: Lewis Kleinsmith and G. Barry Pierce Jr. isolated a single type of cell from a [[teratocarcinoma]], a tumor now known from a [[germ cell]].<ref>{{cite journal | vauthors = Kleinsmith LJ, ((Pierce GB Jr)) | title = Multipotentiality of Single Embryoncal Carcinoma Cells | journal = Cancer Res | volume = 24 | pages = 1544–1551 | year = 1964 | pmid = 14234000 | url = http://cancerres.aacrjournals.org/content/24/9/1544.short | access-date = 2016-04-05 | archive-date = 2016-10-06 | archive-url = https://web.archive.org/web/20161006125242/http://cancerres.aacrjournals.org/content/24/9/1544.short | url-status = live }}</ref> These cells were isolated from the teratocarcinoma replicated and grew in cell culture as a stem cell and are now known as embryonal carcinoma (EC) cells.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  Although similarities in morphology and differentiating potential ([[pluripotency]]) led to the use of EC cells as the ''in vitro'' model for early mouse development,<ref>{{cite journal | author = Martin GR | title = Teratocarcinomas and mammalian embryogenesis | journal = Science | volume = 209 | issue = 4458 | pages = 768–776 | year = 1980 | pmid = 6250214 | doi = 10.1126/science.6250214| bibcode = 1980Sci...209..768M }}</ref> EC cells harbor genetic mutations and often abnormal [[karyotypes]] that accumulated during the development of the teratocarcinoma.  These genetic aberrations further emphasized the need to be able to culture [[pluripotent]] cells directly from the [[inner cell mass]].
[[File:Martin Evans Nobel Prize.jpg|thumb|140px|Martin Evans revealed a new technique for culturing the mouse embryos in the uterus to allow for the derivation of ES cells from these embryos.]]
* 1981: Embryonic stem cells (ES cells) were independently first derived from a mouse embryos by two groups.  [[Martin Evans]] and [[Matthew Kaufman]] from the Department of Genetics, [[University of Cambridge]] published first in July, revealing a new technique for culturing the mouse embryos in the uterus to allow for an increase in cell number, allowing for the derivation of ES cell from these embryos.<ref name="Evans M, Kaufman M 1981 154–6">{{cite journal | vauthors = Evans M, Kaufman M | title = Establishment in culture of pluripotent cells from mouse embryos | journal = Nature | volume = 292 | issue = 5819 | pages = 154–156 | year = 1981 | pmid = 7242681 | doi = 10.1038/292154a0| bibcode = 1981Natur.292..154E | s2cid = 4256553 }}</ref> [[Gail R. Martin]], from the Department of Anatomy, [[University of California, San Francisco]], published her paper in December and coined the term "Embryonic Stem Cell".<ref name="Martin G 1981 7634–8">{{cite journal | author = Martin G | title = Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells | journal = Proc Natl Acad Sci USA | volume = 78 | issue = 12 | pages = 7634–7638 | year = 1981 | pmid = 6950406 | doi = 10.1073/pnas.78.12.7634 | pmc = 349323| bibcode = 1981PNAS...78.7634M | doi-access = free }}</ref> She showed that embryos could be cultured ''in vitro'' and that ES cells could be derived from these embryos.
* 1989: Mario R. Cappechi, [[Martin J. Evans]], and [[Oliver Smithies]] publish their research that details their isolation and genetic modifications of embryonic stem cells, creating the first "[[knockout mice]]".<ref>{{cite web |title=The 2007 Nobel Prize in Physiology or Medicine – Advanced Information |url=https://www.nobelprize.org/nobel_prizes/medicine/laureates/2007/advanced.html |website=Nobel Prize |publisher=Nobel Media |access-date=2018-06-25 |archive-date=2018-06-25 |archive-url=https://web.archive.org/web/20180625075849/https://www.nobelprize.org/nobel_prizes/medicine/laureates/2007/advanced.html |url-status=live }}</ref> In creating knockout mice, this publication provided scientists with an entirely new way to study disease.
* [[File:Dolly clone.svg|thumb|Dolly the sheep cell differentiation]]1996: [[Dolly (sheep)|Dolly]], was the first mammal cloned from an adult cell by the [[Roslin Institute|Roslin Institute of the University of Edinburgh]].<ref>{{Cite web|title=The Life of Dolly {{!}} Dolly the Sheep|url=https://dolly.roslin.ed.ac.uk/facts/the-life-of-dolly/index.html|access-date=2022-02-21|language=en-US|archive-date=2021-11-11|archive-url=https://web.archive.org/web/20211111151011/http://dolly.roslin.ed.ac.uk/facts/the-life-of-dolly/index.html|url-status=dead}}</ref> This experiment instituted the proposition that specialized adult cells obtain the genetic makeup to perform a specific task; which established a basis for further research within a variety of cloning techniques. The Dolly experiment was performed by obtaining the mammalian udder cells from a sheep (Dolly) and differentiating these cells until division was concluded. An egg cell was then procured from a different sheep host and the nucleus was removed. An udder cell was placed next to the egg cell and connected by electricity causing this cell to share DNA. This egg cell differentiated into an [[embryo]] and the embryo was inserted into a third sheep which gave birth to the clone version of Dolly.<ref>{{Cite book|last1=Klotzko|first1=Arlene Judith|url=https://books.google.com/books?id=JVagpD0snTsC&dq=dolly+the+sheep+first+cloned+mammal&pg=PR14|title=A Clone of Your Own?|last2=Klotzko|first2=Visiting Scholar Royal Free and University College Medical School Arlene Judith|year=2006|publisher=Cambridge University Press|isbn=978-0-521-85294-4|language=en|access-date=2022-02-21|archive-date=2022-12-22|archive-url=https://web.archive.org/web/20221222121202/https://books.google.com/books?id=JVagpD0snTsC&dq=dolly+the+sheep+first+cloned+mammal&pg=PR14|url-status=live}}</ref>
* 1998: A team from the [[University of Wisconsin, Madison]] (James A. Thomson, Joseph Itskovitz-Eldor, Sander S. Shapiro, Michelle A. Waknitz, Jennifer J. Swiergiel, Vivienne S. Marshall, and Jeffrey M. Jones) publish a paper titled "Embryonic Stem Cell Lines Derived From Human Blastocysts". The researchers behind this study not only created the first embryonic stem cells, but recognized their pluripotency, as well as their capacity for self-renewal. The abstract of the paper notes the significance of the discovery with regards to the fields of developmental biology and drug discovery.<ref>{{cite journal |last1=Thompson |first1=James A. |last2=Itskovitz-Eldor |first2=Joseph |last3=Shapiro |first3=Sander S. |last4=Waknitz |first4=Michelle A. |last5=Swiergiel |first5=Jennifer J. |last6=Marshall |first6=Vivienne S. |last7=Jones |first7=Jeffrey M. |title=Embryonic Stem Cell Lines Derived From Human Blastocyst |journal=Science |date=6 November 1998 |volume=282 |issue=5391 |pages=1145–1147 |doi=10.1126/science.282.5391.1145 |pmid=9804556 |bibcode=1998Sci...282.1145T |doi-access=free }}</ref>
* 2001: [[President George W. Bush]] allows federal funding to support research on roughly 60—at this time, already existing—lines of embryonic stem cells. Seeing as the limited lines that Bush allowed research on had already been established, this law supported embryonic stem cell research without raising any [[Stem cell controversy|ethical questions]] that could arise with the creation of new lines under federal budget.<ref>{{cite news |title=President George W. Bush's address on stem cell research |url=http://edition.cnn.com/2001/ALLPOLITICS/08/09/bush.transcript/ |publisher=CNN Inside Politics |date=Aug 9, 2001 |access-date=June 25, 2018 |archive-date=June 13, 2018 |archive-url=https://web.archive.org/web/20180613180507/http://edition.cnn.com/2001/ALLPOLITICS/08/09/bush.transcript/ |url-status=dead }}</ref>
* 2006: Japanese scientists [[Shinya Yamanaka]] and Kazutoshi Takashi publish a paper describing the induction of pluripotent stem cells from cultures of adult mouse [[fibroblasts]]. [[Induced pluripotent stem cell|Induced pluripotent stem cells (iPSCs)]] are a huge discovery, as they are seemingly identical to embryonic stem cells and could be used without sparking the same moral controversy.<ref>{{cite journal |last1=Yamanaka |first1=Shinya |last2=Takahashi |first2=Kazutoshi |title=Induction of Pluripotent Stem Cells From Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors |journal=Cell |date=25 Aug 2006 |volume=126 |issue=4 |pages=663–676 |doi=10.1016/j.cell.2006.07.024|pmid=16904174 |hdl=2433/159777 |s2cid=1565219 |hdl-access=free }}</ref>
* January, 2009: The [[US Food and Drug Administration]] (FDA) provides approval for [[Geron Corporation]]'s phase I trial of their human embryonic stem cell-derived treatment for [[spinal cord injuries]]. The announcement was met with excitement from the scientific community, but also with wariness from stem cell opposers. The treatment cells were, however, derived from the cell lines approved under George W. Bush's [[Stem-cell policy|ESC policy]].<ref>{{cite journal |last1=Wadman |first1=Meredith |title=Stem cells ready for primetime |journal=Nature |volume=457 |issue=7229 |pages=516 |doi=10.1038/457516a |pmid=19177087 |date=27 January 2009|doi-access=free }}</ref>
* March, 2009: Executive Order 13505 is signed by [[President Barack Obama]], removing the restrictions put in place on federal funding for human stem cells by the previous presidential administration. This would allow the [[National Institutes of Health]] (NIH) to provide funding for hESC research. The document also states that the NIH must provide revised federal funding guidelines within 120 days of the order's signing.<ref>{{cite journal |title=Executive Order 13505—Removing Barriers To Responsible Scientific Research Involving Human Stem Cells |journal=Federal Register: Presidential Documents |date=11 March 2009 |volume=74 |issue=46 |url=https://www.gpo.gov/fdsys/pkg/FR-2009-03-11/pdf/E9-5441.pdf |access-date=2018-06-25 |archive-date=2018-11-01 |archive-url=https://web.archive.org/web/20181101193558/https://www.gpo.gov/fdsys/pkg/FR-2009-03-11/pdf/E9-5441.pdf |url-status=live }}</ref>

==Techniques and conditions for derivation and culture==

===Derivation from humans===
[[In vitro fertilization]] generates multiple embryos. The surplus of embryos is not clinically used or is unsuitable for implantation into the patient, and therefore may be donated by the donor with consent. Human embryonic stem cells can be derived from these donated embryos or additionally they can also be extracted from cloned embryos created using a cell from a patient and a donated egg through the process of [[somatic cell nuclear transfer]].<ref>{{cite journal|last=Mountford|first=JC|title=Human embryonic stem cells: origins, characteristics and potential for regenerative therapy|journal=Transfus Med|year=2008|volume=18|pages=1–12|doi=10.1111/j.1365-3148.2007.00807.x|pmid=18279188|issue=1|s2cid=20874633}}</ref> The inner cell mass (cells of interest), from the blastocyst stage of the embryo, is separated from the trophectoderm, the cells that would differentiate into extra-embryonic tissue. [[Immunosurgery]], the process in which antibodies are bound to the trophectoderm and removed by another solution, and mechanical dissection are performed to achieve separation. The resulting inner cell mass cells are plated onto cells that will supply support. The inner cell mass cells attach and expand further to form a human embryonic cell line, which are undifferentiated. These cells are fed daily and are enzymatically or mechanically separated every four to seven days. For differentiation to occur, the human embryonic stem cell line is removed from the supporting cells to form embryoid bodies, is co-cultured with a serum containing necessary signals, or is grafted in a three-dimensional scaffold to result.<ref>{{cite journal|vauthors=Thomson JA, Itskovitz-Eldor J, Shapiro SS, Waknitz MA, Swiergiel JJ, Marshall VS, Jones JM |title=Embryonic stem cell lines derived from human blastocysts|journal=Science|year=1998|volume=282|pages=1145–1147|doi= 10.1126/science.282.5391.1145|pmid=9804556|issue=5391|bibcode=1998Sci...282.1145T|doi-access=free}}</ref>

===Derivation from other animals===
<!-- Deleted image removed: [[File:ES cell derivation.jpeg|thumb|ES cells are derived from the [[inner cell mass]] of the early embryo.  This schematic shows one method of derivation. {{deletable image-caption}}]] -->
Embryonic stem cells are derived from the [[inner cell mass]] of the early [[embryo]], which are harvested from the donor mother animal.  [[Martin Evans]] and [[Matthew Kaufman]] reported a technique that delays embryo implantation, allowing the inner cell mass to increase.  This process includes removing the donor mother's [[ovaries]] and dosing her with [[progesterone]], changing the hormone environment, which causes the embryos to remain free in the uterus.  After 4–6 days of this intrauterine culture, the embryos are harvested and grown in ''in vitro'' culture until the inner cell mass forms “egg cylinder-like structures,” which are dissociated into single cells, and plated on [[fibroblasts]] treated with [[Mitomycin|mitomycin-c]] (to prevent fibroblast [[mitosis]]).  Clonal [[cell lines]] are created by growing up a single cell.  Evans and Kaufman showed that the cells grown out from these cultures could form [[teratoma]]s and [[Embryoid body|embryoid bodies]], and differentiate ''in vitro,'' all of which indicating that the cells are [[pluripotent]].<ref name="Evans M, Kaufman M 1981 154–6"/>

[[Gail R. Martin|Gail Martin]] derived and cultured her ES cells differently.  She removed the embryos from the donor mother at approximately 76 hours after copulation and cultured them overnight in a medium containing serum.  The following day, she removed the [[inner cell mass]] from the late [[blastocyst]] using [[microsurgery]].  The extracted [[inner cell mass]] was cultured on [[fibroblasts]] treated with [[Mitomycin|mitomycin-c]] in a medium containing serum and conditioned by ES cells.  After approximately one week, colonies of cells grew out.  These cells grew in culture and demonstrated [[pluripotent]] characteristics, as demonstrated by the ability to form [[teratoma]]s, differentiate ''in vitro,'' and form [[Embryoid body|embryoid bodies]].  Martin referred to these cells as ES cells.<ref name="Martin G 1981 7634–8"/>

It is now known that the [[Fibroblast|feeder cells]] provide [[leukemia inhibitory factor]] (LIF) and serum provides [[bone morphogenetic proteins]] (BMPs) that are necessary to prevent ES cells from differentiating.<ref>{{cite journal | vauthors = Smith AG, Heath JK, Donaldson DD, Wong GG, Moreau J, Stahl M, Rogers D| title = Inhibition of pluripotential embryonic stem cell differentiation by purified polypeptides| journal = Nature | volume = 336 | issue = 6200 | pages = 688–690 | year = 1988 | pmid = 3143917 | doi = 10.1038/336688a0| bibcode = 1988Natur.336..688S| s2cid = 4325137}}</ref><ref>{{cite journal | vauthors = Williams RL, Hilton DJ, Pease S, Willson TA, Stewart CL, Gearing DP, Wagner EF, Metcalf D, Nicola NA, Gough NM | title = Myeloid leukaemia inhibitory factor maintains the developmental potential of embryonic stem cells | journal = Nature | volume = 336 | issue = 6200 | pages = 684–687 | year = 1988 | pmid = 3143916| doi = 10.1038/336684a0| bibcode = 1988Natur.336..684W | s2cid = 4346252 }}</ref> These factors are extremely important for the efficiency of deriving ES cells.  Furthermore, it has been demonstrated that different mouse strains have different efficiencies for isolating ES cells.<ref>{{cite journal | vauthors = Ledermann B, Bürki K | title = Establishment of a germ-line competent C57BL/6 embryonic stem cell line | journal = Exp Cell Res | volume = 197 | issue = 2 | pages = 254–258 | year = 1991 | pmid = 1959560 | doi = 10.1016/0014-4827(91)90430-3}}</ref> Current uses for mouse ES cells include the generation of [[transgenic]] mice, including [[knockout mice]].  For human treatment, there is a need for patient specific pluripotent cells.  Generation of human ES cells is more difficult and faces ethical issues.  So, in addition to human ES cell research, many groups are focused on the generation of [[induced pluripotent stem cells]] (iPS cells).<ref>{{cite journal | vauthors = Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K, Yamanaka S | title = Induction of pluripotent stem cells from adult human fibroblasts by defined factors | journal = Cell| volume = 131 | issue = 5 | pages = 861–872 | year = 2007 | pmid = 18035408| doi = 10.1016/j.cell.2007.11.019| hdl = 2433/49782 | s2cid = 8531539 | hdl-access = free }}</ref>

===Potential methods for new cell line derivation===
On August 23, 2006, the online edition of ''[[Nature (journal)|Nature]]'' scientific journal published a letter by Dr. [[Robert Lanza]] (medical director of [[Advanced Cell Technology]] in Worcester, MA) stating that his team had found a way to extract embryonic stem cells without destroying the actual embryo.<ref>{{cite journal | vauthors = Klimanskaya I, Chung Y, Becker S, Lu SJ, Lanza R | title = Human embryonic stem cell lines derived from single blastomeres| journal = Nature | volume = 444 | issue = 7118 | pages = 481–485 | year = 2006 | pmid = 16929302 | doi = 10.1038/nature05142| bibcode = 2006Natur.444..481K| s2cid = 84792371}}</ref> This technical achievement would potentially enable scientists to work with new lines of embryonic stem cells derived using public funding in the US, where federal funding was at the time limited to research using embryonic stem cell lines derived prior to August 2001.  In March, 2009, the limitation was lifted.<ref name="restriction_lifted">[https://www.theguardian.com/world/2009/mar/10/obama-stem-cell-research US scientists relieved as Obama lifts ban on stem cell research] {{Webarchive|url=https://web.archive.org/web/20130726203242/http://www.guardian.co.uk/world/2009/mar/10/obama-stem-cell-research |date=2013-07-26 }}, ''[[The Guardian]]'', 10 March 2009</ref>

Human embryonic stem cells have also been derived by [[Somatic cell nuclear transfer|somatic cell nuclear transfer (SCNT)]].<ref>{{Cite journal|last1=Tachibana|first1=Masahito|last2=Amato|first2=Paula|last3=Sparman|first3=Michelle|last4=Gutierrez|first4=Nuria Marti|last5=Tippner-Hedges|first5=Rebecca|last6=Ma|first6=Hong|last7=Kang|first7=Eunju|last8=Fulati|first8=Alimujiang|last9=Lee|first9=Hyo-Sang|last10=Sritanaudomchai|first10=Hathaitip|last11=Masterson|first11=Keith|date=2013-06-06|title=Human Embryonic Stem Cells Derived by Somatic Cell Nuclear Transfer|url= |journal=Cell|language=English|volume=153|issue=6|pages=1228–1238|doi=10.1016/j.cell.2013.05.006|pmid=23683578|pmc=3772789|issn=0092-8674|doi-access=free}}</ref><ref>{{Cite journal|last1=Chung|first1=Young Gie|last2=Eum|first2=Jin Hee|last3=Lee|first3=Jeoung Eun|last4=Shim|first4=Sung Han|last5=Sepilian|first5=Vicken|last6=Hong|first6=Seung Wook|last7=Lee|first7=Yumie|last8=Treff|first8=Nathan R.|last9=Choi|first9=Young Ho|last10=Kimbrel|first10=Erin A.|last11=Dittman|first11=Ralph E.|date=2014-06-05|title=Human Somatic Cell Nuclear Transfer Using Adult Cells|journal=Cell Stem Cell|language=English|volume=14|issue=6|pages=777–780|doi=10.1016/j.stem.2014.03.015|issn=1934-5909|pmid=24746675|doi-access=free}}</ref> This approach has also sometimes been referred to as "therapeutic cloning" because SCNT bears similarity to other kinds of cloning in that nuclei are transferred from a somatic cell into an enucleated zygote. However, in this case SCNT was used to produce embryonic stem cell lines in a lab, not living organisms via a pregnancy. The "therapeutic" part of the name is included because of the hope that SCNT produced embryonic stem cells could have clinical utility.

===Induced pluripotent stem cells===
{{main|Induced pluripotent stem cell}}

The iPS cell technology was pioneered by [[Shinya Yamanaka]]'s lab in [[Kyoto]], [[Japan]], who showed in 2006 that the introduction of four specific genes encoding [[transcription factors]] could convert adult cells into pluripotent stem cells.<ref name="ReferenceA">{{cite journal | last1 = Takahashi | first1 = K | last2 = Yamanaka | first2 = S | title = Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors | journal = Cell | volume = 126 | issue = 4 | pages = 663–676 | year = 2006 | pmid = 16904174 | doi = 10.1016/j.cell.2006.07.024 | hdl = 2433/159777 | s2cid = 1565219 | hdl-access = free }}{{open access}}</ref> He was awarded the 2012 Nobel Prize along with Sir [[John Gurdon]] "for the discovery that mature cells can be reprogrammed to become pluripotent."<ref>{{cite web|url=https://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/press.html|publisher=Nobel Media AB|date=8 October 2012|title=The Nobel Prize in Physiology or Medicine – 2012 Press Release|access-date=3 July 2017|archive-date=4 April 2023|archive-url=https://web.archive.org/web/20230404202940/http://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/press.html|url-status=live}}</ref>

In 2007, it was shown that [[pluripotency|pluripotent]] [[stem cell]]s, highly similar to embryonic stem cells, can be induced by the delivery of four factors (''Oct3/4'', ''Sox2'', c-Myc, and ''Klf4'') to differentiated cells.<ref>{{cite journal| doi = 10.1038/nature05944| issn = 1476-4687| volume = 448| issue = 7151| pages = 318–324| last1 = Wernig| first1 = Marius| last2 = Meissner| first2 = Alexander| last3 = Foreman| first3 = Ruth| last4 = Brambrink| first4 = Tobias| last5 = Ku| first5 = Manching| last6 = Hochedlinger| first6 = Konrad| last7 = Bernstein| first7 = Bradley E.| last8 = Jaenisch| first8 = Rudolf| title = In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state| journal = Nature| date = 2007-07-19| pmid = 17554336| bibcode = 2007Natur.448..318W| s2cid = 4377572}}</ref> Utilizing the four genes previously listed, the differentiated cells are "reprogrammed" into pluripotent stem cells, allowing for the generation of pluripotent/embryonic stem cells without the embryo. The morphology and growth factors of these lab induced pluripotent cells, are equivalent to embryonic stem cells, leading these cells to be known as [[induced pluripotent stem cell]]s (iPS cells).<ref>{{Cite journal |last1=Takahashi |first1=Kazutoshi |last2=Yamanaka |first2=Shinya |date=2006-08-25 |title=Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors |journal=Cell |language=English |volume=126 |issue=4 |pages=663–676 |doi=10.1016/j.cell.2006.07.024 |issn=0092-8674 |pmid=16904174|s2cid=1565219 |doi-access=free |hdl=2433/159777 |hdl-access=free }}</ref> This observation was observed in mouse pluripotent stem cells, originally, but now can be performed in human adult [[fibroblast]]s using the same four genes. <ref>{{Cite journal |last1=Takahashi |first1=Kazutoshi |last2=Tanabe |first2=Koji |last3=Ohnuki |first3=Mari |last4=Narita |first4=Megumi |last5=Ichisaka |first5=Tomoko |last6=Tomoda |first6=Kiichiro |last7=Yamanaka |first7=Shinya |date=2007-11-30 |title=Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors |journal=Cell |language=English |volume=131 |issue=5 |pages=861–872 |doi=10.1016/j.cell.2007.11.019 |issn=0092-8674 |pmid=18035408 |s2cid=8531539|doi-access=free |hdl=2433/49782 |hdl-access=free }}</ref>

Because ethical concerns regarding embryonic stem cells typically are about their derivation from terminated embryos, it is believed that reprogramming to these iPS cells may be less controversial. 

This may enable the generation of patient specific ES cell lines that could potentially be used for cell replacement therapies.  In addition, this will allow the generation of ES cell lines from patients with a variety of genetic diseases and will provide invaluable models to study those diseases.

However, as a first indication that the  iPS cell technology can in rapid succession lead to new cures, it was used by a research team headed by [[Rudolf Jaenisch]] of the [[Whitehead Institute for Biomedical Research]] in [[Cambridge, Massachusetts|Cambridge]], [[Massachusetts]], to cure mice of [[sickle cell anemia]], as reported by [[Science (journal)|''Science'' journal's]] online edition on December 6, 2007.<ref>{{cite news | url=https://www.washingtonpost.com/wp-dyn/content/article/2007/12/06/AR2007120602444.html | title=Scientists Cure Mice Of Sickle Cell Using Stem Cell Technique: New Approach Is From Skin, Not Embryos | author=Weiss, Rick | newspaper=[[The Washington Post]] | date=2007-12-07 | pages=A02 | access-date=2017-08-31 | archive-date=2018-12-25 | archive-url=https://web.archive.org/web/20181225160628/http://www.washingtonpost.com/wp-dyn/content/article/2007/12/06/AR2007120602444.html | url-status=live }}</ref><ref>{{cite journal|doi=10.1126/science.1152092|pmid=18063756|title=Treatment of Sickle Cell Anemia Mouse Model with iPS Cells Generated from Autologous Skin|journal=Science|volume=318|issue=5858|pages=1920–1923|year=2007|last1=Hanna|first1=J.|last2=Wernig|first2=M.|last3=Markoulaki|first3=S.|last4=Sun|first4=C.-W.|last5=Meissner|first5=A.|last6=Cassady|first6=J. P.|last7=Beard|first7=C.|last8=Brambrink|first8=T.|last9=Wu|first9=L.-C.|last10=Townes|first10=T. M.|last11=Jaenisch|first11=R.|bibcode=2007Sci...318.1920H|s2cid=657569}}</ref>

On January 16, 2008, a California-based company, Stemagen, announced that they had created the first mature cloned human embryos from single skin cells taken from adults. These embryos can be harvested for patient matching embryonic stem cells.<ref>{{cite news | url=http://news.bbc.co.uk/2/hi/science/nature/7194161.stm | title=US team makes embryo clone of men | author=Helen Briggs | publisher=[[BBC]] | date=2008-01-17 | pages=A01 | access-date=2008-01-18 | archive-date=2018-06-22 | archive-url=https://web.archive.org/web/20180622010307/http://news.bbc.co.uk/2/hi/science/nature/7194161.stm | url-status=live }}</ref>

===Contamination by reagents used in cell culture===
The online edition of ''Nature Medicine'' published a study on January 24, 2005, which stated that the human embryonic stem cells available for federally funded research are contaminated with non-human molecules from the culture medium used to grow the cells.<ref name=ebert>{{cite journal |last=Ebert |first=Jessica |date=24 January 2005 |title=Human stem cells trigger immune attack |journal=Nature News |publisher=[[Nature Publishing Group]] |location=London |url=http://cmbi.bjmu.edu.cn/news/0501/124.htm |doi=10.1038/news050124-1 |access-date=2009-02-27 |url-status=dead |archive-url=https://web.archive.org/web/20100924071349/http://cmbi.bjmu.edu.cn/news/0501/124.htm |archive-date=2010-09-24 |url-access=subscription }}</ref> It is a common technique to use mouse cells and other animal cells to maintain the pluripotency of actively dividing stem cells. The problem was discovered when non-human [[sialic acid]] in the growth medium was found to compromise the potential uses of the embryonic stem cells in humans, according to scientists at the [[University of California, San Diego]].<ref>{{cite journal |vauthors=Martin MJ, Muotri A, Gage F, Varki A |title=Human embryonic stem cells express an immunogenic nonhuman sialic acid |journal=Nat. Med. |volume=11 |issue=2 |pages=228–232 |year=2005 |pmid=15685172 |doi=10.1038/nm1181|s2cid=13739919 }}</ref>

However, a study published in the online edition of ''Lancet Medical Journal'' on March 8, 2005, detailed information about a new stem cell line that was derived from human embryos under completely cell- and serum-free conditions. After more than 6 months of undifferentiated proliferation, these cells demonstrated the potential to form derivatives of all three embryonic germ layers both ''in vitro'' and in [[teratoma]]s. These properties were also successfully maintained (for more than 30 passages) with the established stem cell lines.<ref>{{cite journal |vauthors=Klimanskaya I, Chung Y, Meisner L, Johnson J, West MD, Lanza R |title=Human embryonic stem cells derived without feeder cells |journal=Lancet |volume=365 |issue=9471 |pages=1636–1641 |year=2005 |pmid=15885296 |doi=10.1016/S0140-6736(05)66473-2|s2cid=17139951 }}</ref>

===Muse cells===
{{main|Muse cell}}

Muse cells (Multi-lineage differentiating stress enduring cell) are [[Carcinogenesis|non-cancerous]] [[pluripotent stem cell]] found in adults.<ref name="Kuroda">{{cite journal |doi=10.1073/pnas.0911647107 |pmid=20421459 |pmc=2889306 |title=Unique multipotent cells in adult human mesenchymal cell populations |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=19 |pages=8639–8643 |year=2010 |last1=Kuroda |first1=Y. |last2=Kitada |first2=M. |last3=Wakao |first3=S. |last4=Nishikawa |first4=K. |last5=Tanimura |first5=Y. |last6=Makinoshima |first6=H. |last7=Goda |first7=M. |last8=Akashi |first8=H. |last9=Inutsuka |first9=A. |last10=Niwa |first10=A. |last11=Shigemoto |first11=T. |last12=Nabeshima |first12=Y. |last13=Nakahata |first13=T. |last14=Nabeshima |first14=Y.-i. |last15=Fujiyoshi |first15=Y. |last16=Dezawa |first16=M. |bibcode=2010PNAS..107.8639K |doi-access=free }}</ref><ref>{{Cite book|url=https://www.springer.com/us/book/9784431568452|title=Muse Cells &#124; SpringerLink|access-date=2022-01-13|archive-date=2019-02-19|archive-url=https://web.archive.org/web/20190219130237/https://www.springer.com/us/book/9784431568452|url-status=live}}</ref> They were discovered in 2010 by Mari Dezawa and her research group.<ref name="Kuroda" /> Muse cells reside in the connective tissue of nearly every organ including the umbilical cord, bone marrow and peripheral blood.<ref>Zikuan Leng 1 2, Dongming Sun 2, Zihao Huang 3, Iman Tadmori 2, Ning Chiang 2, Nikhit Kethidi 2, Ahmed Sabra 2, Yoshihiro Kushida 4, Yu-Show Fu 3, Mari Dezawa 4, Xijing He 1, Wise Young 2Quantitative Analysis of SSEA3+ Cells from Human Umbilical Cord after Magnetic SortingCell Transplant
. 2019 Jul;28(7):907–923.</ref><ref name="Kuroda" /><ref name="WakaoPNAS">{{cite journal |doi=10.1073/pnas.1100816108 |pmid=21628574 |pmc=3116385 |title=Multilineage-differentiating stress-enduring (Muse) cells are a primary source of induced pluripotent stem cells in human fibroblasts |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=24 |pages=9875–9880 |year=2011 |last1=Wakao |first1=S. |last2=Kitada |first2=M. |last3=Kuroda |first3=Y. |last4=Shigemoto |first4=T. |last5=Matsuse |first5=D. |last6=Akashi |first6=H. |last7=Tanimura |first7=Y. |last8=Tsuchiyama |first8=K. |last9=Kikuchi |first9=T. |last10=Goda |first10=M. |last11=Nakahata |first11=T. |last12=Fujiyoshi |first12=Y. |last13=Dezawa |first13=M. |bibcode=2011PNAS..108.9875W |doi-access=free }}</ref><ref name=":3">{{cite journal |doi=10.3727/096368916X690881 |pmid=26884346 |title=Muse Cells Provide the Pluripotency of Mesenchymal Stem Cells: Direct Contribution of Muse Cells to Tissue Regeneration |journal=Cell Transplantation |volume=25 |issue=5 |pages=849–861 |year=2016 |last1=Dezawa |first1=Mari |doi-access=free }}</ref><ref name=":4">{{cite journal |doi=10.1016/j.jstrokecerebrovasdis.2015.12.033 |pmid=27019988 |title=Mobilization of Pluripotent Multilineage-Differentiating Stress-Enduring Cells in Ischemic Stroke |journal=Journal of Stroke and Cerebrovascular Diseases |volume=25 |issue=6 |pages=1473–1481 |year=2016 |last1=Hori |first1=Emiko |last2=Hayakawa |first2=Yumiko |last3=Hayashi |first3=Tomohide |last4=Hori |first4=Satoshi |last5=Okamoto |first5=Soushi |last6=Shibata |first6=Takashi |last7=Kubo |first7=Michiya |last8=Horie |first8=Yukio |last9=Sasahara |first9=Masakiyo |last10=Kuroda |first10=Satoshi }}</ref> They are collectable from commercially obtainable mesenchymal cells such as human [[fibroblast]]s, bone marrow-mesenchymal stem cells and adipose-derived stem cells.<ref name=KurodaNature>{{cite journal |doi=10.1038/nprot.2013.076 |pmid=23787896 |title=Isolation, culture and evaluation of multilineage-differentiating stress-enduring (Muse) cells |journal=Nature Protocols |volume=8 |issue=7 |pages=1391–1415 |year=2013 |last1=Kuroda |first1=Yasumasa |last2=Wakao |first2=Shohei |last3=Kitada |first3=Masaaki |last4=Murakami |first4=Toru |last5=Nojima |first5=Makoto |last6=Dezawa |first6=Mari |s2cid=28597290 }}{{medrs|date=November 2013}}</ref><ref name=":5">{{cite journal |doi=10.1089/scd.2013.0473 |pmid=24256547 |title=Human Adipose Tissue Possesses a Unique Population of Pluripotent Stem Cells with Nontumorigenic and Low Telomerase Activities: Potential Implications in Regenerative Medicine |journal=Stem Cells and Development |volume=23 |issue=7 |pages=717–728 |year=2014 |last1=Ogura |first1=Fumitaka |last2=Wakao |first2=Shohei |last3=Kuroda |first3=Yasumasa |last4=Tsuchiyama |first4=Kenichiro |last5=Bagheri |first5=Mozhdeh |last6=Heneidi |first6=Saleh |last7=Chazenbalk |first7=Gregorio |last8=Aiba |first8=Setsuya |last9=Dezawa |first9=Mari }}</ref><ref name="Heneidi">{{cite journal |doi=10.1371/journal.pone.0064752 |pmid=23755141 |pmc=3673968 |title=Awakened by Cellular Stress: Isolation and Characterization of a Novel Population of Pluripotent Stem Cells Derived from Human Adipose Tissue |journal=PLOS ONE |volume=8 |issue=6 |pages=e64752 |year=2013 |last1=Heneidi |first1=Saleh |last2=Simerman |first2=Ariel A. |last3=Keller |first3=Erica |last4=Singh |first4=Prapti |last5=Li |first5=Xinmin |last6=Dumesic |first6=Daniel A. |last7=Chazenbalk |first7=Gregorio |bibcode=2013PLoSO...864752H |doi-access=free }}</ref> Muse cells are able to generate cells representative of all three germ layers from a single cell both spontaneously and under [[cytokine]] induction. Expression of pluripotency genes and triploblastic differentiation are self-renewable over generations. Muse cells do not undergo [[teratoma]] formation when transplanted into a host environment in vivo, eradicating the risk of [[tumorigenesis]] through unbridled cell proliferation.<ref name="Kuroda" />

==See also==
* [[Embryoid body]]
* [[Embryonic Stem Cell Research Oversight Committees]]
* [[Fetal tissue implant]]
* [[Induced stem cells]]
* [[KOSR]] (KnockOut Serum Replacement)
* [[Stem cell controversy]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Embryonic stem cells}}
* [http://dels.nas.edu/bls/stemcells/booklet.shtml Understanding Stem Cells: A View of the Science and Issues from the National Academies] {{Webarchive|url=https://web.archive.org/web/20100409081447/http://dels.nas.edu/bls/stemcells/booklet.shtml |date=2010-04-09 }}
* [http://stemcells.nih.gov/ National Institutes of Health]
* [http://www.conted.ox.ac.uk/courses/C130-1 University of Oxford practical workshop on pluripotent stem cell technology] {{Webarchive|url=https://web.archive.org/web/20160408070246/https://www.conted.ox.ac.uk/courses/C130-1 |date=2016-04-08 }}
* [http://www.eurostemcell.org/factsheet/embryonic-stem-cells-where-do-they-come-and-what-can-they-do Fact sheet on embryonic stem cells]
* [http://www.eurostemcell.org/factsheet/embyronic-stem-cell-research-ethical-dilemma Fact sheet on ethical issues in embryonic stem cell research]
* [http://www.stemcellresearch.org Information & Alternatives to Embryonic Stem Cell Research]
* [http://www.ipscell.com/ A blog focusing specifically on ES cells and iPS cells including research, biotech, and patient-oriented issues]

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