Dear Editor,
Embryonic stem cells (ESCs) are self-renewing pluripotent cells. They generate cells from the three germ layers, neurectoderm, mesoderm and endoderm, and carry the hope to cure a broad range of diseases and injuries, from diabetes, strokes, to neurological diseases and injuries. ESCs are
derived from embryos, primarily from the inner cell mass of blastocystes. Because it involves the destruction of embryos, their derivation from human is the source of ethical and political debates, controversies, and strict regulations. To circumvent these, investigators are devising strategies to
derive ESCs without the destruction of embryos [1]. Meissner and Jaenisch used a variation of somatic cell nuclear transfer to derive ESCs from mice in which a gene crucial for trophectoderm development, the gene CDX2, is
mutated, unabling the embryos to implant into the uterus [2]. Lanza and coworkers derived ESCs by single-blastomere biopsies from mouse and human [3,4]. These studies did not resolve the ethical and political issues over the destruction of embryos to derive ESCs [1,5]. In the recent issue of Stem Cells, Zhang et al. reported the derivation of ESCs from developmentally arrested embryos [6]. Developmentally arrested embryos, produced during
in vitro fertilization process, are believed to be non-viable embryos [7]. This shows that these embryos provide an alternative source of tissue to derive ESCs. But does it solve the ethical and political issues over the derivation of ESCs without the destruction of embryos, and can the derivation
of ESCs from developmentally arrested embryos affects their developmental potential? On the one hand, developmentally arrested embryos are
considered dead and their donation assimilated to organ donation of post-mortem tissue. On the other hand, it is not known whether these embryos would have developed normally after implantation. Therefore, the isolation of ESCs without the destruction of embryos, and ethical and politicaldebates and controversies, remains an unresolved issue. Progenitor and stem cells can be isolated and cultured in vitro from post-mortem tissues [8]. Studies from cloned
embryos revealed the importance of developmental cues for establishing ESC lines [9]. This suggests that contrary to post-mortem tissues, stem cells derived from non-viable tissues may have altered developmental and therapeutic potentials. Studies remain to be performed to further evaluate
the developmental and therapeutic potentials of ESCs derived from developmentally arrested embryos. Strategies to derive ESCs without the destruction of embryos, and ethical and political debates and controversies, remain to be established.

Sincerely,
Philippe Taupin,
National Neuroscience Institute,
National University of Singapore,
11 Jalan Tan Tock Seng, Singapore 308433,
e-mail: [email protected]

REFERENCES:
1. Taupin P: Derivation of embryonic stem cells for cellular therapy: challenges
and new strategies. Med Sci Monit, 2006; 12(4): RA75–78
2. Meissner A, Jaenisch R: Generation of nuclear transfer-derived pluripotent
ES cells from cloned Cdx2-defi cient blastocysts. Nature, 2006;
439: 212–15
3. Chung Y, Klimanskaya I, Becker S et al: Embryonic and extraembryonic
stem cell lines derived from single mouse blastomeres. Nature, 2006;
439: 216–19
4. Klimanskaya I, Chung Y, Becker S et al: Human embryonic stem cell lines
derived from single blastomeres. Nature, in press
5. Weissman IL: Medicine: politic stem cells. Nature, 2006; 439: 145–17
6. Zhang X, Stojkovic P, Przyborski S, et al: Derivation of human embryonic
stem cells from developing and arrested embryos. Stem Cells, in
press
7. Landry DW, Zucker HA: Embryonic death and the creation of human
embryonic stem cells. J Clin Invest, 2004; 114: 1184–86
8. Palmer TD, Schwartz PH, Taupin P et al: Cell culture. Progenitor cells
from human brain after death. Nature, 2001; 411: 42–43
9. Shiels PG, Kind AJ, Campbell KH et al: Analysis of telomere lengths in
cloned sheep. Nature, 1999; 399: 316–17

Received: 2006.11.22

Keywords: Embryo Research - ethics, Embryonic Stem Cells - cytology