First published online January 17, 2008
Stem Cells
Vol. 26 No.
2
February 2008, pp.
494
-495
doi:10.1634/stemcells.2008-0025; www.StemCells.com
© 2008 AlphaMed Press
OPEN ACCESS ARTICLE
Commentary: Somatic Cell Nuclear Transfer—Progress and Promise
Rita Pilar Cervera,
Miodrag Stojkovic
Cellular Reprogramming Laboratory, Centro de Investigación Príncipe Felipe, Valencia, Spain
Key Words. Embryonic stem cells • Somatic stem cells • Reprogramming • Nuclear transfer
Correspondence: Miodrag Stojkovic, Ph.D., DVM. Centro de Investigación Principe Felipe, C/E.P. Avda. Autopista del Saler, 16-3 (junto Oceanográfico), 46013 Valencia, Spain. Telephone: +34 963289680; Fax: +34 963289701; e-mail: mstojkovic{at}cipf.es
Received January 10, 2008;
accepted for publication January 14, 2008.
First published online in STEM CELLS EXPRESS January 17, 2008.
 |
ABSTRACT
|
|---|
Disclosure of potential conflicts of interest is found at the end of this article.
The generation of patient-specific embryonic stem cells would revolutionize our understanding of human diseases, as well as the development of compounds to prevent or reverse further progression of the disease (reviewed in [1]). Currently, two different approaches (Fig. 1) are being studied to derive patient-specific stem cells: somatic cell nuclear transfer (SCNT) and direct reprogramming [2, 3]. The recent generation of induced pluripotent stem (iPS) cells has put the feasibility of SCNT in regenerative medicine under intense scrutiny. Along with many other scientists, we applaud the former achievement. However, at this early-stage of development, we do not consider iPS cells as a substitute for SCNT. As has been stated by other scientists, the use of genes and retroviruses known to cause cancer in mammals and retroviruses known to have the ability to disrupt the normal DNA function and stimulate the birth of cancer cells [4, 5] makes questionable any possible application of iPS in regenerative medicine, especially cell therapy. Although some proponents of reprogramming argue that these problems are purely technical and easily surmountable, currently it is vital to maintain the pace of research on more controversial fronts, such as the use of human oocytes in SCNT.
View larger version (44K):
[in this window]
[in a new window]
|
Figure 1. Derivation of patient-specific stem cells to study inherited human diseases, the role of mtDNA, epigenetic, genetic and differentiation profiles and abilities of pluripotent stem cells. Abbreviations: hESC: human embryonic stem cells; NTSC: nuclear transfer stem cells; iPS cells: induced pluripotent stem cells; MII: metaphase II; mtDNA: mitochondrial DNA.
|
|
Derivation of human embryos by SCNT remains in its infancy stages, with just a few papers reporting the generation of nuclear transfer human embryos [6–11]. However, none of them have resulted in the derivation of nuclear transfer stem cells (NTSC). Clearly, a number of hurdles, both ethical and technical, need to be surmounted if SCNT is to lead to the successful application of patient-specific NTSC in regenerative medicine. In addition to the ethical issues surrounding the use of human oocytes, which require legal regulation, the scarcity of voluntarily donated, human metaphase II oocytes available for research is the most significant barrier [8–10]. Moreover, it is being reported [8–12] that the use of high-quality oocytes (fresh, mature oocytes from young donors) is required to assure successful human SCNT. Unfortunately, this considerably reduces the availability of oocytes and, at the same time, makes absolutely necessary the use of the best technical methodology in approaching human SCNT. According to published papers on non-human primate SCNT, removing the minimum cytoplasm possible during enucleation and avoiding the use of Hoechst (by using the Oosight spindle imaging system, CRI Inc., Woburn, MA, http://www.cri-inc.com) was crucial to the success in deriving two NTSC lines [13]. Surprisingly, French et al. [12] used the traditional aspiration or squeezing enucleation methods, based on Hoechst staining, to evaluate the absence of the chromosomes. The authors concluded that the rates of oocyte lysis or degeneration did not differ between the two methods but increased the exposure (45 minutes) of oocytes to cytochalasin B to decrease oocyte lysis.
Work on human SCNT is a breakthrough area of research, but (especially as a consequence of the fraudulent results of Hwang and colleagues) it has become a very sensitive area that requires clear, thorough, and detailed information about the real identity of the clones. That means DNA and mtDNA fingerprinting of embryos and/or NTSC obtained by SCNT have to be provided [14–16]. In proving that human embryos can be obtained by SCNT, French et al. [12] succeeded in obtaining five blastocysts from 21 oocytes using adult somatic cells as karyoplasts. However, the results verified, for the first time through DNA and mtDNA fingerprinting, that of the five blastocysts only one had the donor cell genomic DNA and the oocyte mtDNA. Considering such a small number of blastocysts, a completely different result may just as well have been reached. The experiment could easily have rendered zero true clones.
In order to avoid future uncertainty, and bearing in mind that the final challenge in therapeutic SCNT is NTSC isolation, we believe that any further paper related to human SCNT has to investigate beyond the point of obtaining human blastocysts and pursue the derivation of NTSC lines. Currently, it has been proposed that human embryonic stem cells could be derived from different embryo stages of development, and even from arrested embryos and a single blastomere (for review see [1]). Once a NTSC line is obtained, not only are a huge amount of cells available to carry out all the required studies to prove each clone identity, but these cells can also be used by a different laboratory to prove repeatability.
|
DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST
|
|---|
The authors indicate no potential conflicts of interest.
|
ACKNOWLEDGMENTS
|
|---|
We thank Michael John Reinhold and Donald Phinney for critical reading of this paper.
|
REFERENCES
|
|---|
- Cervera RP, Stojkovic M. Human embryonic stem cell derivation and nuclear transfer: impact on regenerative therapeutics and drug discovery. Clin Pharmacol Ther 2007;82:310–315.[CrossRef][Medline]
- Takahashi K, Tanabe K, Ohnuki M et al. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 2007;131:861–872.[CrossRef][Medline]
- Yu J, Vodyanik MA, Smuga-Otto K et al. Induced pluripotent stem cell lines derived from human somatic cells. Science 2007;318:1917–1920.[Abstract/Free Full Text]
- Löwer R. The pathogenic potential of endogenous retroviruses: facts and fantasies. Trends Microbiol 1999;7:350–356.[CrossRef][Medline]
- Yi Y, Hahm SH, Lee KH. Retroviral gene therapy: safety issues and possible solutions. Curr Gene Ther 2005;5:25–35.[Medline]
- Cibelli JB, Kiessling AA, Cuniff K et al. Somatic cell nuclear transfer in humans: pronuclear and early embryonic development. J Reg Med 2001;2:25–31.
- Lu C, Lin G, Xie X et al. Reconstruction of human embryos derived from somatic cells. Chin Science Bull 2003;48:1840–1843.[CrossRef]
- Stojkovic M, Stojkovic P, Leary C et al. Derivation of a human blastocyst after heterologous nuclear transfer to donated oocytes. Reprod Biomed Online 2005;11:226–231.[Medline]
- Lavoir MC, Weier J, Conaghan J et al. Poor development of human nuclear transfer embryos using failed fertilized oocytes. Reprod Biomed Online 2005;11:740–744.[Medline]
- Hall VJ, Compton D, Stojkovic P et al. Developmental competence of human in vitro aged oocytes as host cells for nuclear transfer. Hum Reprod 2007;22:52–62.[Abstract/Free Full Text]
- Heindryckx B, De Sutter P, Gerris J et al. Embryo development after successful somatic cell nuclear transfer to in vitro matured human germinal vesicle oocytes. Hum Reprod 2007;22:1982–1990.[Abstract/Free Full Text]
- French AJ, Adams CA, Anderson LS et al. Development of human cloned blastocysts following somatic cell nuclear transfer (SCNT) with adult fibroblasts. Stem Cells 2008;26:485–493.[Abstract/Free Full Text]
- Byrne JA, Pedersen DA, Clepper LL et al. Producing primate embryonic stem cells by somatic cell nuclear transfer. Nature 2007;450:497–502.[CrossRef][Medline]
- Yang X, Eggan K, Seidel G Jr et al. A simple system of checks and balances to cut fraud. Nature 2006;439:782.[Medline]
- Cram DS, Song B, Trounson AO. Genotyping of Rhesus SCNT pluripotent stem cell lines. Nature 2007;450:E12–14.[CrossRef][Medline]
- Kim K, Ng K, Rugg-Gunn PJ et al. Recombination signatures distinguish embryonic stem cells derived by parthenogenesis and somatic cell nuclear transfer. Cell Stem Cell 2007;1:346–352.[CrossRef]
Top
Abstract
Disclosure of Potential...