Q&A of iPS !(ZT)
Human Skin Cells at the Embryonic Stage?Sch?ler: Not one, but two research groups have managed to transfer human skin cells back into a kind of embryonic state using a “cocktail” of four defined transcription factors. Many researchers see this as a breakthrough in stem cell research. A few months ago researchers turned mouse skin cells into cells which are very similar to embryonic stem cells with the same four factors. Hans Sch?ler, Director of the Max-Planck Institute for Molecular Biomedical Sciences in Münster, explains the scientific basis in an interview, including why research on human embryonic stem cells will continue to be of importance.
Do these latest findings in human skin cell reprogramming really constitute a breakthrough or is it just media hype?
Sch?ler: In my opinion, as a biologist, it is not only a breakthrough, it is a sensation! For the first time ever, researchers can reverse the axis of time in the development of cell cultures: a somatic cell can be changed into a cell which is similar to those of an early embryo – a pluripotent stem cell. Even if the cells, reprogrammed to be younger, are not perfect, the importance of this discovery could go way beyond the significance of the creation of Dolly.
How did the Japanese and American researchers manage to reprogram skin cells?
Sch?ler: The genes for merely four factors were planted in skin cells with viral vectors. Once integrated into the DNA, they are copied along with the other genes in the cell. The proteins, which code the genes, then perform their functions in the cell. This mixture of proteins turns the embryonic program in the cell on again. Because the pluripotency in the skin cells, which means having the capability to change into all kinds of cells in the body, was induced, we are talking about induced pluripotent stem cells or iPS.
Why did the scientists use viral vectors?
Sch?ler: The insertion of genes through viral vectors is very efficient and is used a lot in basic genetic research. However, because viral vectors are integrated into genetic material they also can present a problem: if a vector is integrated near a tumor gene, this gene could be switched on and create tumors. Furthermore, two of the genes, that Yamanaka and his colleagues inserted into skins cells, had themselves the characteristics of tumor genes. The procedure carried out by Thomson and his colleagues was much better in this respect, because their "cocktail" did not contain any known tumor genes. However, one should note that both research groups induced the factor Oct4, which is not a tumor gene, but can lead to the creation of tumors when present in large amounts.
Can these induced pluripotent cells be used for therapeutic purposes?
Sch?ler: These cells cannot be used for therapies. Because it is not possible at the moment to remove viral and “foreign” DNA, researchers are now looking for other alternatives. Perhaps it would work with other viral systems that don’t integrate or are no longer present in the cells afterwards. Another possibility, which is very promising, is to use the knowledge gained with the four factors to look for so-called small molecules, which can replace individually those factors inserted by viral vectors.
When will alternatives to the viral vectors be available?
Sch?ler: That I cannot say with any certainty. However, since the publication of Yamanaka in the magazine “Cell” in August 2006, the transference to the human system is going a lot faster than I had thought possible. If, in the next steps, that is also the case, it should go relatively quickly. I think that embryonic stem cell derived therapies will probably not become clinical routine before there are optimized induced pluripotent stem cells.
Does reprogramming also work with skin cells from older people or with other cell types?
Sch?ler: Yamanaka and his research team used skin cells from cell lines. One of the lines came from cells from the face of a 36 year old woman and the other from the joint skin cells of a 69 year old man. Thomson and his colleages used cells from the foreskin of a new born baby. The reprogramming of these cells is a huge step forward in comparison to the mouse studies, where the reprogramming only worked with the skin cells of unborn mice. So, yes, it’s also possible to reprogram the skin cells of older people. However, there could be a problem if these induced pluripotent stem cells need to be used for therapies: over the course of a life, defects work their way into genetic material and these defects cannot be ironed out through reprogramming. Mutations could still be found relatively easily, but not the changes in the regulation of the gene.
Skin cells were used because they are readily available. Now we need to see if other cells can be reprogrammed, as carried out in nuclear transfer. Basically, every type of cell should be able to be reprogrammed. It’s highly promosing that cells from bone marrow could be made younger as they contain stem cells. These cells would probably be less damaged than skin cells, for example, since they are contantly influenced by many environmental factors.
How do you rank these findings for the future with respect to their future significance?
Sch?ler: Even though the virus problem is still not under control, the cells of an aged patient could be used to examine the progress of a degenerative illness in a cell culture. When you think of cell therapies, it is probably not practicable for every patient to have their own, induced pluripotent cells. Stem cell banks, for example, with umbilical cord blood or blood from young donors are, in my opinion, a very sensible alternative. On the one hand the DNA is still relatively young and undamaged. On the other hand, cells could be used that most likely won’t activate an immune defence reaction so that the cells can be reprogrammed to a greater extent and be differentiated in the desired cell type.
What therapeutic potential could induced pluripotent cells offer?
Sch?ler: In principle, diseases in which cells have been lost, meaning degenerative illnesses like Parkinson’s Disease, would be suitable for cell treatments with induced pluripotent cells. Until the functionally capable cells are found which can be used in a treatment, we still have a long list of things that need to be explored. But we don’t have the molecular knowledge at the moment that we need to be able to make a valid prediction.
Will induced pluripotent stem cells be able to replace embryonic stem cells in research?
Sch?ler: I have always said that it is important to support resaerch on embryonic and adult stem cells in equal measure and to continue research in both areas. Now we have something new to consider. Research on induced pluripotent stem cells should now receive the same support as for embryonic and adult stem cells. The research on embryonic stem cells should, however, in no way be further reduced or restricted in any way; quite the opposite. First of all, we don’t know if induced pluripotent stem cells can meet our expectations. The attempts using mice cells naturally offer justified hope, but nothing more. Secondly, it will be necessary to compare the procedures that will be developed for induced pluripotent stem cells with those of human embryonic stem cells. Induced pluripotent stem cells are still very similar to embryonic stem cells, but not the same. In 30,000 of the genes examined, induced pluripotent and embryonic stem cells showed differences in about 1,000 genes, while between embryonic stem cells and skins cells the difference is about 6,000. We still don’t know, for example, which of the 1,000 genes are particularly important in the differentiation in nerve cells.
（转载，内容有点老，是2008年的） [i=s] 本帖最后由 sunsong7 于 2010-12-30 10:07 编辑 [/i]
内容导读：
[b]炒作问题：[/b]iPS不是不仅仅是突破，同改变了细胞发育的时间轴，其意义甚至大于多莉羊；
[b]致瘤性问题：[/b]iPS用病毒载体导入了转录因子“鸡尾酒”，虽然没有直接导入病毒基因，但是可以诱发肿瘤；用病毒或其它外源DNA调教出来的iPS不能用于临床，在用小分子诱导或其他优化的iPS技术成熟之前，此类胚胎性干细胞临床应用不大可能成为常规；
[b]老龄供者问题：[/b]iPS的源细胞取自新生婴儿乃至69岁老人的皮肤，原则上所有细胞都可以被重编程，但是太老的细胞可能没有医疗价值，用骨髓细胞重编程可能更好；对于老人也可以用别人的细胞做iPS——如更年轻的脐血库细胞
[b]治疗前景：[/b]理论上iPS适合所有的退行性疾病，但由于分子生物学机理不清无法做出有效预测，要用于临床需要做大量的工作直到能做出来明确的功能细胞；
[b]iPS替代ES问题：[/b]我们目前还不知道iPS是否能满足人们的预期，况且iPS细胞和天然ES细胞的30000万个基因中有1000个基因不一样，任何借此限制胚胎干细胞研究的做法都是不明智的； iPS细胞和天然ES细胞到底有多大程度不一样，这种不同是否影响iPS细胞的功能应该是个重点要弄清的问题。不支持用同种异基因做移植，如果身体的干细胞用了黑人的，皮肤是否会逐渐变黑？ 感觉没必要一定要去追求iPS与ES相同，可能我们现在获得的ES细胞不是真正的ES，或者我们获得的iPS实际上比ES的时期更早。 感觉没必要一定要去追求iPS与ES相同，可能我们现在获得的ES细胞不是真正的ES，或者我们获得的iPS实际上比ES的时期更早。 [i=s] 本帖最后由 sunsong7 于 2010-12-30 16:14 编辑 [/i]
不好意思帖子有个笔误！更正一下：“[b]致瘤性问题：[/b]iPS用病毒载体导入了转录因子“鸡尾酒”，虽然没有直接导入原癌基因，但是可以诱发肿瘤；”
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