Embryonic stem cell

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Human embryonic stem cells in cell culture
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 (ES cells) are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage preimplantation embryo.[1][2] Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells. Isolating the embryoblast or inner cell mass (ICM) results in destruction of the blastocyst, which raises ethical issues, including whether or not embryos at the pre-implantation stage should be considered to have the same moral status as more developed human beings.[3][4]

Human ES cells measure approximately 14 while mouse ES cells are closer to 8 μm.[5]

Properties[edit]

The transcriptome of embryonic stem cells

Embryonic stem cells, derived from the blastocyst stage early mammalian embryos, are distinguished by their ability to differentiate into any cell type and by their ability to propagate. Embryonic stem cell's properties include having a normal karyotype, maintaining high telomerase activity, and exhibiting remarkable long-term proliferative potential.

Pluripotent[edit]

Embryonic stem cells of the inner cell mass are pluripotent, that is, they are able to differentiate to generate primitive ectoderm, which ultimately differentiates during gastrulation into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. These include each of the more than 220 cell types in the adult body. Pluripotency distinguishes embryonic stem cells from adult stem cells found in adults; while embryonic stem cells can generate all cell types in the body, adult stem cells are multipotent and can produce only a limited number of cell types. If the pluripotent differentiation potential of embryonic stem cells could be harnessed in vitro, it might be a means of deriving cell or tissue types virtually to order. This would provide a radical new treatment approach to a wide variety of conditions where age, disease, or trauma has led to tissue damage or dysfunction.

microRNA maintenance of pluripotency[edit]

Propagation[edit]

Additionally, under defined conditions, embryonic stem cells are capable of propagating themselves indefinitely in an undifferentiated state and have the capacity when provided with the appropriate signals to differentiate, presumably via the formation of precursor cells, to almost all mature cell phenotypes.[6] This allows embryonic stem cells to be employed as useful tools for both research and regenerative medicine, because they can produce limitless numbers of themselves for continued research or clinical use.

Usefulness[edit]

Because of their plasticity and potentially unlimited capacity for self-renewal, Embryonic stem cell therapies have been proposed for regenerative medicine and tissue replacement after injury or disease. Diseases that could potentially be treated by pluripotent stem cells include a number of blood and immune-system related genetic diseases, cancers, and disorders; juvenile diabetes; Parkinson's; blindness and spinal cord injuries. Besides the ethical concerns of stem cell therapy (see stem cell controversy), there is a technical problem of graft-versus-host disease associated with allogeneic stem cell transplantation. However, these problems associated with histocompatibility may be solved using autologous donor adult stem cells, therapeutic cloning, stem cell banks or more recently by reprogramming of somatic cells with defined factors (e.g. induced pluripotent stem cells). Embryonic stem cells provide hope that it will be possible to overcome the problems of donor tissue shortage and also, by making the cells immunocompatible with the recipient. Other potential uses of embryonic stem cells include investigation of early human development, study of genetic disease and as in vitro systems for toxicology testing.

Utilities[edit]

Potential clinical use[edit]

According to a 2002 article in 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."[7]

Embryoid bodies 24 hours after formation.

Current research focuses on differentiating ES into a variety of cell types for eventual use as cell replacement therapies (CRTs). Some of the cell types that have or are currently being developed include cardiomyocytes (CM), neurons, hepatocytes, bone marrow cells, islet cells and endothelial cells.[8] However, the derivation of such cell types from ESs is not without obstacles and hence current research is focused on overcoming these barriers. For example, studies are underway to differentiate ES in to tissue specific CMs and to eradicate their immature properties that distinguish them from adult CMs.[9]

Besides in the future becoming an important alternative to organ transplants, ES are also being used in field of toxicology and as cellular screens to uncover new chemical entities (NCEs) that can be developed as small molecule drugs. Studies have shown that cardiomyocytes derived from ES are validated in vitro models to test drug responses and predict toxicity profiles.[8] ES derived cardiomyocytes have been shown to respond to pharmacological stimuli and hence can be used to assess cardiotoxicity like Torsades de Pointes.[10]

ES-derived hepatocytes are also useful models that could be used in the preclinical stages of drug discovery. However, the development of hepatocytes from ES has proven to be challenging and this hinders the ability to test drug metabolism. Therefore, current research is focusing on establishing fully functional ES-derived hepatocytes with stable phase I and II enzyme activity.[11]

Researchers have also differentiated ES into dopamine-producing cells with the hope that these neurons could be used in the treatment of Parkinson’s disease.[12][13] ESs have also been differentiated to natural killer (NK) cells and bone tissue.[14] Studies involving ES are also underway to provide an alternative treatment for diabetes. For example, D’Amour et al. were able to differentiate ES into insulin producing cells.[15]

Human embryonic stem cells as models of genetic disorders[edit]

Several new studies have started to address this issue. This has been done either by genetically manipulating the cells, or more recently by deriving diseased cell lines identified by prenatal genetic diagnosis (PGD). This approach may very well prove invaluable 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 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 those couples with 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.[16]

Scientists have discovered a new technique for deriving human embryonic stem cell (ESC). Normal ESC lines from different sources of embryonic material including morula and whole blastocysts have been established. These findings allows researchers to construct ESC lines from embryos that acquire different genetic abnormalities; therefore, allowing for recognition of mechanisms in the molecular level that are possibly blocked that could impede the disease progression. The ESC lines originating from embryos with genetic and chromosomal abnormalities provide the data necessary to understand the pathways of genetic defects.[17]

A donor patient acquires one defective gene copy and one normal, and only one of these two copies is used for reproduction. By selecting egg cell derived from embryonic stem cells that have two normal copies, researchers can find variety of treatments for various diseases. To test this theory Dr. McLaughlin and several of his colleagues looked at whether parthenogenetic embryonic stem cells can be used in a mouse model that has thalassemia intermedia. This disease is described as an inherited blood disorder in which there is a lack of hemoglobin leading to anemia. The mouse model used, had one defective gene copy. Embryonic stem cells from an unfertilized egg of the diseased mice were gathered and those stem cells that contained only healthy hemoglobin genes were identified. The healthy embryonic stem cell lines were then converted into cells transplanted into the carrier mice. After five weeks, the test results from the transplant illustrated that these carrier mice now had a normal blood cell count and hemoglobin levels.[18]

Repair of DNA damage[edit]

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 (NHEJ), an error prone DNA repair process, as the primary pathway for repairing double-strand breaks (DSBs) during all cell cycle stages.[19] 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.[20] 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 homologous recombinational repair (HRR) to repair DSBs.[20] This type of repair depends on the interaction of the two sister chromosomes 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.[21] Rather they undergo programmed cell death (apoptosis) in response to DNA damage.[22] 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.[23] Consistent with this strategy, mouse ES stem cells have a mutation frequency about 100-fold lower than that of isogenic mouse somatic cells.[24]

Adverse effect[edit]

The major concern with the possible transplantation of ESC into patients as therapies is their ability to form tumors including teratoma.[25] Safety issues prompted the FDA to place a hold on the first ESC clinical trial (see below), however no tumors were observed.

The main strategy to enhance the safety of ESC for potential clinical use is to differentiate the ESC 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. ESC are predicted to be inherently safer than IPS cells because they are not genetically modified with genes such as c-Myc that are linked to cancer. Nonetheless, ESC express very high levels of the iPS inducing genes and these genes including Myc are essential for ESC self-renewal and pluripotency,[26] and potential strategies to improve safety by eliminating Myc expression are unlikely to preserve the cells' "stemness".

History[edit]

In 1964, researchers isolated a single type of cell from a teratocarcinoma, a tumor now known to be derived from a germ cell. These cells isolated from the teratocarcinoma replicated and grew in cell culture as a stem cell and are now known as embryonic carcinoma (EC) cells.[27] Although similarities in morphology and differentiating potential (pluripotency) led to the use of EC cells as the in vitro model for early mouse development,[28] 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.

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.

In 1981, embryonic stem cells (ES cells) were independently first derived from 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 cells from these embryos.[29] 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”.[30] She showed that embryos could be cultured in vitro and that ES cells could be derived from these embryos. In 1998, a breakthrough occurred when researchers, led by James Thomson at the University of Wisconsin-Madison, first developed a technique to isolate and grow human embryonic stem cells in cell culture.[31]

First clinical trial[edit]

On January 23, 2009, Phase I clinical trials for transplantation of oligodendrocytes (a cell type of the brain and spinal cord) derived from human ES cells into spinal cord-injured individuals received approval from the U.S. Food and Drug Administration (FDA), marking it the world's first human ES cell human trial.[32] 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 ES cells that had been pushed into an oligodendrocytic lineage.[33] In the proposed phase I clinical study, about eight to ten paraplegics who have had their injuries no longer than two weeks before the trial begins, will be selected, since the cells must be injected before scar tissue is able to form. However, the researchers are emphasizing that the injections are not expected to fully cure the patients and restore all mobility. Based on the results of the rodent trials, researchers say restoration of myelin sheathes, and an increase in mobility is probable. This first trial is mainly testing the safety of these procedures and if everything goes well, it could lead to future studies that involve people with more severe disabilities.[34] The trial had been put on hold in August 2009 due to concerns made by the FDA regarding a small number of microscopic cysts found in several treated rat models but the hold has been lifted as of July 30, 2010.[35]

In October 2010 researchers enrolled and administered ESTs to the first patient at Shepherd Center in Atlanta.[36] The makers of the stem cell therapy, Geron Corporation, estimate that it will take several months for the stem cells to replicate and for the GRNOPC1 therapy to be evaluated for success or failure. In November 2011 Geron announced it was 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.[37] In 2013 BioTime (NYSE MKTBTX), 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.[38]

Techniques and conditions for embryonic stem cell derivation and culture[edit]

Derivation of human embryonic stem cells[edit]

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 using a cell from a patient and a donated egg.[39] 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.[40]

Derivation of embryonic stem cells from other animals[edit]

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-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 teratomas and embryoid bodies, and differentiate in vitro, all of which indicating that the cells are pluripotent.[29]

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-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 teratomas, differentiate in vitro, and form embryoid bodies. Martin referred to these cells as ES cells.[30]

It is now known that the feeder cells provide leukemia inhibitory factor (LIF) and serum provides bone morphogenetic proteins (BMPs) that are necessary to prevent ES cells from differentiating.[41][42] 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.[43] 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).[44]

Potential method for new cell line derivation[edit]

On August 23, 2006, the online edition of 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.[45] This technical achievement would potentially enable scientists to work with new lines of embryonic stem cells derived using public funding in the USA, 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.[46]

Recently, it was shown that pluripotent stem cells highly similar to embryonic stem cells can be generated by the delivery of three genes (Oct4, Sox2, and Klf4) to differentiated cells.[47] The delivery of these genes "reprograms" differentiated cells into pluripotent stem cells, allowing for the generation of pluripotent stem cells without the embryo. Because ethical concerns regarding embryonic stem cells typically are about their derivation from terminated embryos, it is believed that reprogramming to these "induced pluripotent stem cells" (iPS cells) may be less controversial. Both human and mouse cells can be reprogrammed by this methodology, generating both human pluripotent stem cells and mouse pluripotent stem cells without an embryo.[48]

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 induced pluripotent stem cell (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, to cure mice of sickle cell anemia, as reported by Science journal's online edition on December 6, 2007.[49][50]

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.[51]

Contamination by reagents used in cell culture[edit]

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.[52] 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.[53]

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 teratomas. These properties were also successfully maintained (for more than 30 passages) with the established stem cell lines.[54]

See also[edit]

References[edit]

  1. ^ Thomson et. al; Itskovitz-Eldor, J; Shapiro, SS; Waknitz, MA; Swiergiel, JJ; Marshall, VS; Jones, JM (1998). "Blastocysts Embryonic Stem Cell Lines Derived from Human". Science 282 (5391): 1145–1147. doi:10.1126/science.282.5391.1145. PMID 9804556. 
  2. ^ "NIH Stem Cell Basics. What are embryonic stem cells?". 
  3. ^ Baldwing A (2009). "Morality and human embryo research. Introduction to the Talking Point on morality and human embryo research.". EMBO reports 10 (4): 299–300. doi:10.1038/embor.2009.37. PMC 2672902. PMID 19337297. 
  4. ^ Nakaya, Andrea C. (August 1, 2011). Biomedical ethics. San Diego, CA: ReferencePoint Press. p. 96. ISBN 160152157X. 
  5. ^ Thomson, James A.; Zwaka (10 February 2003). "Homologous recombination in human embryonic stem cells". Nature Biotechnology 21 (3): 319–321. doi:10.1038/nbt788. PMID 12577066. 
  6. ^ Ying et. al; Nichols, J; Chambers, I; Smith, A (2003). "BMP Induction of Id Proteins Suppresses Differentiation and Sustains Embryonic Stem Cell Self-Renewal in Collaboration with STAT3". Cell 115 (3): 281–292. doi:10.1016/S0092-8674(03)00847-X. PMID 14636556. 
  7. ^ Levenberg, S. (2002). "Endothelial cells derived from human embryonic stem cells". Proceedings of the National Academy of Sciences 99 (7): 4391–4396. doi:10.1073/pnas.032074999.  edit
  8. ^ a b Davila, JC; Cezar, GG; Thiede, M; Strom, S; Miki, T; Trosko, J (2004). "Use and application of stem cells in toxicology". Toxicological sciences : an official journal of the Society of Toxicology 79 (2): 214–23. doi:10.1093/toxsci/kfh100. PMID 15014205. 
  9. ^ Siu, CW; Moore, JC; Li, RA (2007). "Human embryonic stem cell-derived cardiomyocytes for heart therapies". Cardiovascular & hematological disorders drug targets 7 (2): 145–52. doi:10.2174/187152907780830851. PMID 17584049. 
  10. ^ Jensen, J; Hyllner, J; Björquist, P (2009). "Human embryonic stem cell technologies and drug discovery". Journal of cellular physiology 219 (3): 513–9. doi:10.1002/jcp.21732. PMID 19277978. 
  11. ^ Söderdahl, T; Küppers-Munther, B; Heins, N; Edsbagge, J; Björquist, P; Cotgreave, I; Jernström, B (2007). "Glutathione transferases in hepatocyte-like cells derived from human embryonic stem cells". Toxicology in vitro : an international journal published in association with BIBRA 21 (5): 929–37. doi:10.1016/j.tiv.2007.01.021. PMID 17346923. 
  12. ^ Perrier, A. L. (2004). "Derivation of midbrain dopamine neurons from human embryonic stem cells". Proceedings of the National Academy of Sciences 101 (34): 12543. doi:10.1073/pnas.0404700101. 
  13. ^ Parish, CL; Arenas, E (2007). "Stem-cell-based strategies for the treatment of Parkinson's disease". Neuro-degenerative diseases 4 (4): 339–47. doi:10.1159/000101892. PMID 17627139. 
  14. ^ Waese, EY; Kandel, RA; Stanford, WL (2008). "Application of stem cells in bone repair". Skeletal radiology 37 (7): 601–8. doi:10.1007/s00256-007-0438-8. PMID 18193216. 
  15. ^ d'Amour, KA; Bang, AG; Eliazer, S; Kelly, OG; Agulnick, AD; Smart, NG; Moorman, MA; Kroon, E; Carpenter, MK; Baetge, EE (2006). "Production of pancreatic hormone-expressing endocrine cells from human embryonic stem cells". Nature Biotechnology 24 (11): 1392–401. doi:10.1038/nbt1259. PMID 17053790. 
  16. ^ "Dr. Yury Verlinsky, 1943–2009: Expert in reproductive technology" Chicago Tribune, July 20, 2009
  17. ^ Verlinsky, Y; Strelchenko, N; Kukharenko, V; Rechitsky, S; Verlinsky, O; Galat, V; Kuliev, A (2005). "Human embryonic stem cell lines with genetic disorders". Reproductive biomedicine online 10 (1): 105–10. doi:10.1016/S1472-6483(10)60810-3. PMID 15705304. 
  18. ^ Embryonic Stem Cells Help Deliver 'Good Genes' In A Model Of Inherited Blood Disorder, ScienceDaily (February 13, 2011).
  19. ^ Mao Z, Bozzella M, Seluanov A, Gorbunova V (September 2008). "DNA repair by nonhomologous end joining and homologous recombination during cell cycle in human cells". Cell Cycle 7 (18): 2902–6. doi:10.4161/cc.7.18.6679. PMC 2754209. PMID 18769152. 
  20. ^ a b Tichy ED, Pillai R, Deng L, et al. (November 2010). "Mouse embryonic stem cells, but not somatic cells, predominantly use homologous recombination to repair double-strand DNA breaks". Stem Cells Dev. 19 (11): 1699–711. doi:10.1089/scd.2010.0058. PMC 3128311. PMID 20446816. 
  21. ^ Hong Y, Stambrook PJ (October 2004). "Restoration of an absent G1 arrest and protection from apoptosis in embryonic stem cells after ionizing radiation". Proc. Natl. Acad. Sci. U.S.A. 101 (40): 14443–8. doi:10.1073/pnas.0401346101. PMC 521944. PMID 15452351. 
  22. ^ Aladjem MI, Spike BT, Rodewald LW, et al. (January 1998). "ES cells do not activate p53-dependent stress responses and undergo p53-independent apoptosis in response to DNA damage". Curr. Biol. 8 (3): 145–55. doi:10.1016/S0960-9822(98)70061-2. PMID 9443911. 
  23. ^ Bernstein C, Bernstein H, Payne CM, Garewal H (June 2002). "DNA repair/pro-apoptotic dual-role proteins in five major DNA repair pathways: fail-safe protection against carcinogenesis". Mutat. Res. 511 (2): 145–78. doi:10.1016/S1383-5742(02)00009-1. PMID 12052432. 
  24. ^ Cervantes RB, Stringer JR, Shao C, Tischfield JA, Stambrook PJ (March 2002). "Embryonic stem cells and somatic cells differ in mutation frequency and type". Proc. Natl. Acad. Sci. U.S.A. 99 (6): 3586–90. doi:10.1073/pnas.062527199. PMC 122567. PMID 11891338. 
  25. ^ Knoepfler, Paul S. (2009). "Deconstructing Stem Cell Tumorigenicity: A Roadmap to Safe Regenerative Medicine". Stem Cells 27 (5): 1050–6. doi:10.1002/stem.37. PMC 2733374. PMID 19415771. 
  26. ^ Varlakhanova, Natalia V.; Cotterman, Rebecca F.; Devries, Wilhelmine N.; Morgan, Judy; Donahue, Leah Rae; Murray, Stephen; Knowles, Barbara B.; Knoepfler, Paul S. (2010). "Myc maintains embryonic stem cell pluripotency and self-renewal". Differentiation 80 (1): 9–19. doi:10.1016/j.diff.2010.05.001. PMC 2916696. PMID 20537458. 
  27. ^ Andrews P, Matin M, Bahrami A, Damjanov I, Gokhale P, Draper J (2005). "Embryonic stem (ES) cells and embryonal carcinoma (EC) cells: opposite sides of the same coin". Biochem Soc Trans 33 (Pt 6): 1526–30. doi:10.1042/BST20051526. PMID 16246161. 
  28. ^ Martin GR (1980). "Teratocarcinomas and mammalian embryogenesis". Science 209 (4458): 768–76. doi:10.1126/science.6250214. PMID 6250214. 
  29. ^ a b Evans M, Kaufman M (1981). "Establishment in culture of pluripotent cells from mouse embryos". Nature 292 (5819): 154–6. doi:10.1038/292154a0. PMID 7242681. 
  30. ^ a b Martin G (1981). "Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells". Proc Natl Acad Sci USA 78 (12): 7634–8. doi:10.1073/pnas.78.12.7634. PMC 349323. PMID 6950406. 
  31. ^ Thomson J, Itskovitz-Eldor J, Shapiro S, Waknitz M, Swiergiel J, Marshall V, Jones J (1998). "Embryonic stem cell lines derived from human blastocysts". Science 282 (5391): 1145–7. doi:10.1126/science.282.5391.1145. PMID 9804556. 
  32. ^ "FDA approves human embryonic stem cell study - CNN.com". January 23, 2009. Retrieved May 1, 2010. 
  33. ^ Keirstead HS, Nistor G, Bernal G, et al. (2005). "Human embryonic stem cell-derived oligodendrocyte progenitor cell transplants remyelinate and restore locomotion after spinal cord injury". J. Neurosci. 25 (19): 4694–705. doi:10.1523/JNEUROSCI.0311-05.2005. PMID 15888645. 
  34. ^ Steven Reinberg FDA OKs 1st Embryonic Stem Cell Trial
  35. ^ Geron comments on FDA hold on spinal cord injury trial http://www.geron.com/media/pressview.aspx?id=1188
  36. ^ Vergano, Dan (11 October 2010). "Embryonic stem cells used on patient for first time". USA Today. Retrieved 12 October 2010. 
  37. ^ Brown, Eryn (November 15, 2011). "Geron exits stem cell research". LA Times. Retrieved 2011-11-15. 
  38. ^ "Great news: BioTime Subsidiary Asterias Acquires Geron Embryonic Stem Cell Program". iPScell.com. October 1, 2013. 
  39. ^ Mountford, JC (2008). "Human embryonic stem cells: origins, characteristics and potential for regenerative therapy". Transfus Med 18 (1): 1–12. doi:10.1111/j.1365-3148.2007.00807.x. PMID 18279188. 
  40. ^ Thomson JA, Itskovitz-Eldor J, Shapiro SS, Waknitz MA, Swiergiel JJ, Marshall VS, Jones JM, J. A.; Itskovitz-Eldor, J; Shapiro, SS; Waknitz, MA; Swiergiel, JJ; Marshall, VS; Jones, JM (1998). "Embryonic stem cell lines derived from human blastocysts". Science 282 (5391): 1145–1147. doi:10.1126/science.282.5391.1145. PMID 9804556. 
  41. ^ Smith AG, Heath JK, Donaldson DD, Wong GG, Moreau J, Stahl M, Rogers D (1988). "Inhibition of pluripotential embryonic stem cell differentiation by purified polypeptides". Nature 336 (6200): 688–690. doi:10.1038/336688a0. PMID 3143917. 
  42. ^ Williams RL, Hilton DJ, Pease S, Willson TA, Stewart CL, Gearing DP, Wagner EF, Metcalf D, Nicola NA, Gough NM (1988). "Myeloid leukaemia inhibitory factor maintains the developmental potential of embryonic stem cells". Nature 336 (6200): 684–687. doi:10.1038/336684a0. PMID 3143916. 
  43. ^ Ledermann B, Bürki K (1991). "Establishment of a germ-line competent C57BL/6 embryonic stem cell line". Exp Cell Res 197 (2): 254–258. doi:10.1016/0014-4827(91)90430-3. PMID 1959560. 
  44. ^ Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K, Yamanaka S. (2007). "Induction of pluripotent stem cells from adult human fibroblasts by defined factors". Cell 131 (5): 861–872. doi:10.1016/j.cell.2007.11.019. PMID 18035408. 
  45. ^ Klimanskaya I, Chung Y, Becker S, Lu SJ, Lanza R. (2006). "Human embryonic stem cell lines derived from single blastomeres". Nature 444 (7118): 481–5. doi:10.1038/nature05142. PMID 16929302. 
  46. ^ US scientists relieved as Obama lifts ban on stem cell research, The Guardian, 10 March 2009
  47. ^ "Human stem cells may be produced without embryos ‘within months’". Zangani. 2007-07-17. 
  48. ^ "Embryonic stem cells made without embryos". Reuters. 2007-11-21. 
  49. ^ Rick Weiss (2007-12-07). "Scientists Cure Mice Of Sickle Cell Using Stem Cell Technique: New Approach Is From Skin, Not Embryos". Washington Post. pp. A02. 
  50. ^ Treatment of Sickle Cell Anemia Mouse Model with iPS Cells Generated from Autologous Skin. Jacob Hanna, Marius Wernig, Styliani Markoulaki, Chiao-Wang Sun, Alexander Meissner, John P. Cassady, Caroline Beard, Tobias Brambrink, Li-Chen Wu, Tim M. Townes, and Rudolf Jaenisch. Science 21 December 2007: 1920-1923. Published online 6 December 2007 [DOI:10.1126/science.1152092]
  51. ^ Helen Briggs (2008-01-17). "US team makes embryo clone of men". BBC. pp. A01. 
  52. ^ Ebert, Jessica (24 January 2005). "Human stem cells trigger immune attack". News from "Nature" (London: Nature Publishing Group). doi:10.1038/news050124-1. Retrieved 2009-02-27. 
  53. ^ Martin MJ, Muotri A, Gage F, Varki A (2005). "Human embryonic stem cells express an immunogenic nonhuman sialic acid". Nat. Med. 11 (2): 228–32. doi:10.1038/nm1181. PMID 15685172. 
  54. ^ Klimanskaya I, Chung Y, Meisner L, Johnson J, West MD, Lanza R (2005). "Human embryonic stem cells derived without feeder cells". Lancet 365 (9471): 1636–41. doi:10.1016/S0140-6736(05)66473-2. PMID 15885296. 

External links[edit]