中國(guó)科學(xué)家稱,，他們已通過(guò)將人類皮膚細(xì)胞與兔子卵細(xì)胞融合的方法培植出了人類胚胎干細(xì)胞,，開(kāi)創(chuàng)了克隆研究方面的一個(gè)先河。
中國(guó)的學(xué)術(shù)期刊《細(xì)胞研究》(Cell Research)網(wǎng)絡(luò)版周三刊載了此項(xiàng)研究的成果,。然而,，美國(guó)科學(xué)家卻對(duì)此產(chǎn)生了質(zhì)疑。此類研究在美國(guó)仍存在爭(zhēng)議,。
據(jù)知情的研究人員稱,，包括《科學(xué)》(Science)及《美國(guó)國(guó)家科學(xué)院院刊》(Proceedings of the National Academy of Sciences)在內(nèi)的西方頂級(jí)期刊對(duì)中國(guó)科學(xué)家的此項(xiàng)研究進(jìn)行評(píng)審之后，均拒絕進(jìn)行刊載,。
此項(xiàng)研究是在曾于美國(guó)留學(xué)的上海第二醫(yī)科大學(xué)(Shanghai Second Medical University)沈慧真(HuiZhen Sheng)博士的領(lǐng)導(dǎo)下展開(kāi)的,。盡管他們的研究成果剛剛被刊載出來(lái)，但學(xué)術(shù)界對(duì)該項(xiàng)研究的爭(zhēng)論已長(zhǎng)達(dá)一年半以上,。
如果成果屬實(shí),，這將是人類首次通過(guò)克隆培植出人類胚胎干細(xì)胞。有人提議將這種被稱為治療性克隆的方法用來(lái)培育與病人完全相匹配的神經(jīng)或其他組織,。
美國(guó)學(xué)術(shù)界對(duì)治療性克隆的研究?jī)H獲得了有限的成果,。在2001年11月，一家名為Advanced Cell Technology Inc.的小型生物科技公司表示,，該公司利用從女性志愿者身上采集的卵細(xì)胞培植出了早期胚胎,，但未能得到干細(xì)胞。
在美國(guó)，進(jìn)行克隆人類胚胎的研究會(huì)遭遇多重阻礙,，如在倫理道德方面,、以及人類卵細(xì)胞的采集方面。
中國(guó)的研究人員在實(shí)驗(yàn)中則選用了較為容易獲得的兔子卵細(xì)胞,。研究人員先將兔子卵細(xì)胞中的DNA去除,，然后將人類皮膚細(xì)胞植入其中。這些經(jīng)過(guò)處理的卵細(xì)胞隨后發(fā)育成含有人類基因物質(zhì)的胚胎,。數(shù)天之后,，研究人員將這些卵細(xì)胞解剖，從中提取出干細(xì)胞,。
一位曾對(duì)刊載在《細(xì)胞研究》上的此項(xiàng)研究成果進(jìn)行過(guò)評(píng)審的美國(guó)科學(xué)家表示,，研究人員未能證明所獲得的便是真正的胚胎干細(xì)胞，而且也未能滿足學(xué)術(shù)界要求其提供更多數(shù)據(jù)這一非常合理的要求,。
記者未能聯(lián)系到沈慧真博士,，請(qǐng)其對(duì)這位美國(guó)科學(xué)家的講話發(fā)表評(píng)論。
但熟悉此項(xiàng)研究的德州大學(xué)西南醫(yī)學(xué)中心(University of Texas Southwestern Medical Cente)研究人員David Garbers指出,，如果沈慧真博士的工作得到驗(yàn)證,，這將是醫(yī)學(xué)界一個(gè)非常了不起的進(jìn)步。醫(yī)生以后可以不用借助人類卵細(xì)胞便可從患者身上提取出胚胎干細(xì)胞,，之后利用變異的方法把它們培育成一個(gè)可供人類移植的細(xì)胞,。
Chinese fusion method promises fresh route to human stem cells
CARINA DENNIS
Biologists in China have reprogrammed human cells by fusing them with rabbit eggs emptied of their genetic material. And they have extracted stem cells, which have the potential to form a wide array of different cell types, from the resulting embryos.
C. DENNIS; SHANGHAI SECOND MEDICAL UNIV.
A team led by Huizhen Sheng (left) has devised a technique for reprogramming adult human cells by fusing them with empty rabbit eggs (above).
The researchers, led by Huizhen Sheng of Shanghai Second Medical University, think that these 'derived' stem cells could provide scientists in the field with an alternative to stem-cell lines extracted from human embryos. But some researchers who have seen the work point out that the derived cells don't seem to have the same ability as human embryonic stem cells to grow indefinitely in culture.
The work will be published online this week in Cell Research, a peer-reviewed journal supported by the Chinese Academy of Sciences. The paper will appear in print later this month (Y. Chen et al. Cell Res. 13, 251–263; 2003).
Sheng's work has already created a buzz after rumours of it circulated in the scientific community and were reported in The Wall Street Journal in March 2002 (see Nature 419, 334–336; 2002). The publication is likely to reignite debate over the ethics of cross-species reprogramming. But cell biologists say that having the data available for public discussion will help researchers and regulators to decide what kinds of cross-species work should be pursued.
Reprogramming adult cells to assume an embryonic state could offer a way to grow new cells and tissues to replace those lost to ageing and disease. And using an individual's own cells, in a process often called therapeutic cloning, may avoid problems of the immune system rejecting the cell therapy.
To reprogramme an adult cell, it can either be fused with or have its nucleus injected into an egg that has had its own nucleus removed. The reconstituted cell is then tricked into dividing as if it were an embryo, with all memory of its previous life as a liver, skin or kidney cell erased. After 5–7 days, embryonic stem cells — which can seemingly grow indefinitely — can be extracted from the growing ball of cells. By changing the growth conditions, these cells can then be coaxed to develop into many different cell types.
Until now, scientists have only been able to generate animal stem-cell lines from the reprogrammed nuclei of cells. "This is the first paper to convincingly show that you can get human reprogramming," says Robin Lovell-Badge, a cell biologist at the National Institute for Medical Research in London.
Sheng claims to have successfully reprogrammed cells from the foreskin tissues of males aged 5, 42 and 52 years and from the facial skin of a 60-year old woman. "It just goes to show that age doesn't matter," says Lovell-Badge.
But Sheng has had a tough time convincing some experts. "I first submitted the paper more than two years ago," she says. It is understood that the paper was considered and rejected by other journals before this week's publication in China.
"I was frustrated that it took so long to get the paper published," Sheng says, "and it still may take a while for people to accept the work. But the scientific community has the right to question the details of the work and we have a responsibility to respond to them."
Doug Melton a cell biologist at Harvard University, for one, has concerns about the nature of the derived embryonic stem-cell lines. "I'm convinced that the cells do have the capacity to differentiate into different cell types, but it's unclear how long the cells can grow in culture," he says.
"It would be very surprising if the cell lines were stable," Melton adds, noting that many interspecies hybrids are unstable, because of incompatibilities between the nucleus and mitochondria (the energy-producing compartments of cells) from different species.
And Rudolf Jaenisch, of the Whitehead Institute in Cambridge, Massachusetts, is not convinced that the derived cells meet the usual criteria for embryonic stem cells. "An important criterion is indefinite growth," he says. "This is not shown."
But reservations aside, Melton is pleased that the work has finally seen the light of day. "I'm glad to see it published as it will encourage others to try it," he says.
At this stage, Sheng has no plans to use stem cells created by her method to treat humans. "It is a research tool. But there is the possibility that if it were proved to be safe enough for clinical use, it could provide a solution to human egg shortages for reprogramming in the future," says Sheng.
While the scientific community debates her work, Sheng is keen to test the embryonic stem cells she has generated in an animal model. "It will be important to see whether they will be tolerated by the immune system and whether they can correct an animal model of human disease," she says.
Nature 424, 711 (14 August 2003); doi:10.1038/424711a
