Non-destructive embryonic stem cells

It's all over the web (here and here, at the "news@nature.com" site,for instance), three separate labs have been able to reproduce embryonic stem cells by "reprogramming" adult cells from skin.

Much of the commentary is like Art Caplan's comments quoted in the first (Blog.bioethics.net) link above. Paraphrased, the bulk of the "mainstream remarks include, "It's only in mice, and they had to used viral vectors." Well, if you will look at all the much-hyped embryonic "break-throughs," you will see that they are "only in mice" and many of them "used viral vectors."


Caplan, who notes the coincidental timing with legislation in Washington and who chronically sees bioethics through a political lens, couldn't pass up the chance for a rant on "embryos are not people." When I was an embryo, it was close enough for me - and my Mama. I actually agree with Art Caplan's comment that ". . . ditching embryos and jumping to fund alternatives is not the right response to this fascinating news about mouse cells." The reason we won't fund embryonic stem cell research requiring the distruction of human embryos is not because we have an alternative source. It's because we won't fund research that depends on the destruction of embryonic humans.

The abstracts for two of the articles are published on the Nature advance publication online page. (I don't yet have access to the third, in Cell's Stem Cell journal.

Nature advance online publication 6 June 2007 | doi:10.1038/nature05934; Received 6 February 2007; Accepted 22 May 2007; Published online 6 June 2007

Generation of germline-competent induced pluripotent stem cells
Keisuke Okita1, Tomoko Ichisaka1,2 & Shinya Yamanaka1,2
1. Department of Stem Cell Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8507, Japan
2. CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
Correspondence to: Shinya Yamanaka1,2 Correspondence and requests for materials should be addressed to S.Y. (Email: yamanaka@frontier.kyoto-u.ac.jp).

We have previously shown that pluripotent stem cells can be induced from mouse fibroblasts by retroviral introduction of Oct3/4 (also called Pou5f1), Sox2, c-Myc and Klf4, and subsequent selection for Fbx15 (also called Fbxo15) expression. These induced pluripotent stem (iPS) cells (hereafter called Fbx15 iPS cells) are similar to embryonic stem (ES) cells in morphology, proliferation and teratoma formation; however, they are different with regards to gene expression and DNA methylation patterns, and fail to produce adult chimaeras. Here we show that selection for Nanog expression results in germline-competent iPS cells with increased ES-cell-like gene expression and DNA methylation patterns compared with Fbx15 iPS cells. The four transgenes (Oct3/4, Sox2, c-myc and Klf4) were strongly silenced in Nanog iPS cells. We obtained adult chimaeras from seven Nanog iPS cell clones, with one clone being transmitted through the germ line to the next generation. Approximately 20% of the offspring developed tumours attributable to reactivation of the c-myc transgene. Thus, iPS cells competent for germline chimaeras can be obtained from fibroblasts, but retroviral introduction of c-Myc should be avoided for clinical application.
Although ES cells are promising donor sources in cell transplantation therapies1, they face immune rejection after transplantation and there are ethical issues regarding the usage of human embryos. These concerns may be overcome if pluripotent stem cells can be directly derived from patients' somatic cells2. We have previously shown that iPS cells can be generated from mouse fibroblasts by retrovirus-mediated introduction of four transcription factors (Oct3/4 (refs 3, 4), Sox2 (ref. 5), c-Myc (ref. 6) and Klf4 (ref. 7)) and by selection for Fbx15 expression8. Fbx15 iPS cells, however, have different gene expression and DNA methylation patterns compared with ES cells and do not contribute to adult chimaeras. We proposed that the incomplete reprogramming might be due to the selection for Fbx15 expression, and that by using better selection markers, we might be able to generate more ES-cell-like iPS cells. We decided to use Nanog as a candidate of such markers.
Although both Fbx15 and Nanog are targets of Oct3/4 and Sox2 (refs 9–11), Nanog is more tightly associated with pluripotency. In contrast to Fbx15-null mice and ES cells that barely show abnormal phenotypes9, disruption of Nanog in mice results in loss of the pluripotent epiblast12. Nanog-null ES cells can be established, but they tend to differentiate spontaneously12. Forced expression of Nanog renders ES cells independent of leukaemia inhibitory factor (LIF) for self-renewal12, 13 and confers increased reprogramming efficiency after fusion with somatic cells14. These results prompted us to propose that if we use Nanog as a selection marker, we might be able to obtain iPS cells displaying a greater similarity to ES cells.

and

Article Nature advance online publication 6 June 2007 | doi:10.1038/nature05944; Received 27 February 2007; Accepted 22 May 2007; Published online 6 June 2007

In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state

Marius Wernig1,6, Alexander Meissner1,6, Ruth Foreman1,2,6, Tobias Brambrink1,6, Manching Ku3,6, Konrad Hochedlinger1,7, Bradley E. Bernstein3,4,5 & Rudolf Jaenisch1,2
1. Whitehead Institute for Biomedical Research and,
2. Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
3. Molecular Pathology Unit and Center for Cancer Research, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
4. Broad Institute of Harvard and MIT, Cambridge, Massachusetts 02142, USA
5. Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
6. These authors contributed equally to this work.
7. Present address: Center for Regenerative Medicine and Cancer Center, Massachusetts General Hospital, Harvard Medical School and Harvard Stem Cell Institute, Boston, Massachusetts 02414, USA.
Correspondence to: Rudolf Jaenisch1,2 Correspondence and requests for materials should be addressed to R.J. (Email: jaenisch@wi.mit.edu).

Nuclear transplantation can reprogramme a somatic genome back into an embryonic epigenetic state, and the reprogrammed nucleus can create a cloned animal or produce pluripotent embryonic stem cells. One potential use of the nuclear cloning approach is the derivation of 'customized' embryonic stem (ES) cells for patient-specific cell treatment, but technical and ethical considerations impede the therapeutic application of this technology. Reprogramming of fibroblasts to a pluripotent state can be induced in vitro through ectopic expression of the four transcription factors Oct4 (also called Oct3/4 or Pou5f1), Sox2, c-Myc and Klf4. Here we show that DNA methylation, gene expression and chromatin state of such induced reprogrammed stem cells are similar to those of ES cells. Notably, the cells—derived from mouse fibroblasts—can form viable chimaeras, can contribute to the germ line and can generate live late-term embryos when injected into tetraploid blastocysts. Our results show that the biological potency and epigenetic state of in-vitro-reprogrammed induced pluripotent stem cells are indistinguishable from those of ES cells.