科技前沿:科学家朝克隆人又迈近一步

Scientists have used cloning technology to transform human skin cells into embryonic stem cells, an experiment that may revive the controversy over human cloning.

科学家利用克隆技术将人体皮肤细胞转化为胚胎干细胞。这一实验可能再次引发有关克隆人的争论。

The researchers stopped well short of creating a human clone. But they showed, for the first time, that it is possible to create cloned embryonic stem cells that are genetically identical to the person from whom they are derived.

研究人员的成果距创造出克隆人还很遥远，但他们首次表明，创造出同人类基因完全相同的克隆胚胎干细胞是可能的。这些胚胎干细胞就来自人类。

These stem cells can go on to differentiate into heart, nerve, muscle, bone and all the other tissue types that make up a human body.

这些干细胞可以分化成心脏、神经、肌肉、骨骼和其它所有组成人体的组织型。

Since the birth of Dolly the sheep in 1996, researchers have cloned about 20 different species, including rabbits, goats, cows and cats. Yet they so far have been unable to create biologically identical copies of any monkey or primate, including humans, possibly because their reproductive biology is more complicated.

自1996年克隆绵羊多莉(Dolly)诞生以来，研究人员已经克隆出大约20个不同物种，包括兔子、山羊、奶牛和猫。然而研究人员至今无法创造出在生物性上完全相同的猴子或灵长类动物（包括人类）的克隆体，原因可能在于这些生物的生殖生物学更复杂。

But the refinements described in the latest experiment suggest that 'it's a matter of time before they produce a cloned monkey,' said Jose Cibelli, a cloning expert at Michigan State University, who wasn't involved in the study. It also means, he added, 'that they are one step closer to where the efficiency is high enough that someone is willing to try' to clone a person, though that remains a distant─and disturbing─prospect.

但密歇根州立大学(Michigan State University)克隆专家奇贝利(Jose Cibelli)说，上述最新实验所描述的种种改进表明，研究人员创造出一只克隆猴只是时间问题。奇贝利没有参与这项实验。他还说，这同时意味着这些研究人员距离有人愿意尝试克隆人只有一步之遥，虽然克隆人还是一个遥远且令人不安的前景。

The experiment was published online Wednesday in the journal Cell. It was funded by Oregon Health and Science University and a grant from Leducq Foundation of France.

实验过程周三发布在专业期刊《细胞》(Cell)杂志的网站上。这项研究由俄勒冈健康与科学大学(Oregon Health and Science University)资助，法国勒迪克基金会(Leducq Foundation)提供赠款。

The researchers weren't simply trying to reach a cloning milestone. Instead, they were looking for a better way to make fresh human tissue for the treatment of severe injuries or disease.

研究人员并不只是试图达到克隆科学的一座里程碑。相反，他们正在寻找一种更好的方法以培养新鲜的人体组织，并将其用于治疗严重伤害或疾病。

Lab-grown tissue has the potential to transform medicine, though it is still a long way from routine clinical use. For example, fresh nerve cells could alleviate spinal cord injuries, or newly made heart cells could repair a site scarred by a heart attack.

实验室培养的组织有可能改变医学，但它距离临床常规使用还有很长的路要走。例如，新鲜的神经细胞可以减轻脊髓损伤，新培养的心脏细胞可以修复心脏病发作造成的创伤区域。

One way to harvest fresh tissue is from human embryos. That is controversial because the embryos get destroyed in the process. Another way is to reprogram mature cells into an embryonic-like state, which can then be turned into other tissues of the body. But this method is relatively new and has yet to yield consistent results.

获取新鲜组织的来源之一是人类胚胎。但这种做法存在争议，因为胚胎在这个过程中会被摧毁。另一种方法是将成熟细胞进行重新编码，继而改造成类似胚胎的状态。改造后的细胞随后可以变成身体其它组织。但是这种方法相对较新，目前尚未取得一致的结果。

A third approach is to use cloning, as described in the Cell paper. This technique can yield fresh tissue that is an exact genetic match for the patient for whom it is intended.

第三种方法是利用克隆技术，就像上述《细胞》杂志刊发的论文所描述的那样。这种技术可以产生在遗传上同病人完全匹配的新鲜组织。培养出的新鲜组织就是要用在同一病人身上。

The scientists first removed the DNA from an unfertilized human egg, and then inserted a patient's mature skin cell─containing the patient's DNA─into that egg. Next, they prompted a chemical reaction, causing the cells to fuse and begin development.

科学家首先从一个未受精的卵子中取出DNA，然后在卵子中植入含有病人DNA的成熟皮肤细胞。之后科学家触发一个化学反应，引发细胞融合、发育。

That led to a blastocyst, a hollow ball of 50 to 100 cells. For a fetus to form, the blastocyst must be implanted in a womb. An inner clump of cells in the blastocyst goes on to form the embryo, while an outer layer goes on to make the placenta.

这导致胚泡的形成。胚泡是含有50个至100个细胞的中空球。想要形成胎儿，胚泡必须植入子宫。胚泡中的内层细胞随后形成胚胎，外层细胞则形成胎盘。

For the tissue-growing experiment, the researchers focused on the clump of cells containing embryonic stem cells.

对于培养组织的实验来说，研究人员关注的是含有胚胎干细胞的这群细胞。

With the help of certain 'growth' chemicals, they were able to transform the stem cells into 'various cell lines and tissues, including beating human heart cells,' said Shoukhrat Mitalipov, a development biologist at Oregon Health and Science University, in Portland, Ore., and a lead author of the study.

俄勒冈州波特兰市俄勒冈健康与科学大学的发育生物学家米塔利波夫(Shoukhrat Mitalipov)说，在某些“增长”化学物质的帮助下，他们能够将干细胞变成各种细胞系和组织，包括人类心脏细胞。米塔利波夫是该研究的主要作者之一。

The achievement is a long way from creating a cloned human embryo.

研究人员所取得的成就距离创造克隆人类胚胎还有很长的路。

Even if the entire blastocyst had been implanted into a womb, it wouldn't have yielded a human clone. The blastocyst was 'missing a few cell types that it would need to implant,' as well as suffering other deficiencies, said Dr. Mitalipov.

即使整个胚泡被植入子宫，它也不会产生出克隆人。米塔利波夫博士说，胚泡还缺少一些其需要植入的细胞类型，同时也存在其它缺陷。

Never mind the prospect of cloned humans; despite years of experiments, scientists have failed to clone monkeys.

就更不用提克隆人的前景了──尽管经过多年实验，科学家还未能成功克隆猴子。

Dr. Mitalipov said his lab had tried transplanting entire blastocysts into a monkey's womb, but those experiments hadn't yielded a single successful pregnancy.

米塔利波夫博士说，他的实验室曾尝试将整个胚泡植入猴子的子宫，但这些实验尚未形成一次成功的妊娠。

'We don't know why this is,' said Dr. Mitalipov. 'You can make embryonic stem cells but it doesn't mean the embryo will implant.'

米塔利波夫博士说，我们不知道这是为什么，你可以创造出胚胎干细胞，但这并不意味着胚胎能够被植入。

He speculates that one reason why it may be more difficult to clone monkeys and humans is because the egg cells are more fragile than those of other species.

他推测克隆猴子和人类的难度更大的原因之一可能是和其它物种相比，猴子和人类的卵细胞更脆弱。

Dr. Mitalipov's main goal is to use cloning to treat illnesses. He next plans to use lab-made tissue and see if he can successfully treat a degenerative, blindness-causing eye disease in monkeys.

米塔利波夫博士的主要目标是使用克隆技术治病。他下一步计划使用实验室培养的组织，并观察他是否能成功地治疗一种发生在猴子身上的、可导致失明的退行性疾病。