科技前沿:科學家朝克隆人又邁近一步

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

科學家利用克隆技術將人體皮膚細胞轉化爲胚胎幹細胞。這一實驗可能再次引發有關克隆人的爭論。

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.

研究人員的成果距創造出克隆人還很遙遠，但他們首次表明，創造出同人類基因完全相同的克隆胚胎幹細胞是可能的。這些胚胎幹細胞就來自人類。

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.

這些幹細胞可以分化成心臟、神經、肌肉、骨骼和其它所有組成人體的組織型。

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年克隆綿羊多莉(Dolly)誕生以來，研究人員已經克隆出大約20個不同物種，包括兔子、山羊、奶牛和貓。然而研究人員至今無法創造出在生物性上完全相同的猴子或靈長類動物（包括人類）的克隆體，原因可能在於這些生物的生殖生物學更復雜。

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.

但密歇根州立大學(Michigan State University)克隆專家奇貝利(Jose Cibelli)說，上述最新實驗所描述的種種改進表明，研究人員創造出一隻克隆猴只是時間問題。奇貝利沒有參與這項實驗。他還說，這同時意味着這些研究人員距離有人願意嘗試克隆人只有一步之遙，雖然克隆人還是一個遙遠且令人不安的前景。

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.

實驗過程週三發佈在專業期刊《細胞》(Cell)雜誌的網站上。這項研究由俄勒岡健康與科學大學(Oregon Health and Science University)資助，法國勒迪克基金會(Leducq Foundation)提供贈款。

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.

研究人員並不只是試圖達到克隆科學的一座里程碑。相反，他們正在尋找一種更好的方法以培養新鮮的人體組織，並將其用於治療嚴重傷害或疾病。

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.

實驗室培養的組織有可能改變醫學，但它距離臨牀常規使用還有很長的路要走。例如，新鮮的神經細胞可以減輕脊髓損傷，新培養的心臟細胞可以修復心臟病發作造成的創傷區域。

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.

獲取新鮮組織的來源之一是人類胚胎。但這種做法存在爭議，因爲胚胎在這個過程中會被摧毀。另一種方法是將成熟細胞進行重新編碼，繼而改造成類似胚胎的狀態。改造後的細胞隨後可以變成身體其它組織。但是這種方法相對較新，目前尚未取得一致的結果。

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.

第三種方法是利用克隆技術，就像上述《細胞》雜誌刊發的論文所描述的那樣。這種技術可以產生在遺傳上同病人完全匹配的新鮮組織。培養出的新鮮組織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.

科學家首先從一個未受精的卵子中取出DNA，然後在卵子中植入含有病人DNA的成熟皮膚細胞。之後科學家觸發一個化學反應，引發細胞融合、發育。

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.

這導致胚泡的形成。胚泡是含有50個至100個細胞的中空球。想要形成胎兒，胚泡必須植入子宮。胚泡中的內層細胞隨後形成胚胎，外層細胞則形成胎盤。

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

對於培養組織的實驗來說，研究人員關注的是含有胚胎幹細胞的這羣細胞。

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.

俄勒岡州波特蘭市俄勒岡健康與科學大學的發育生物學家米塔利波夫(Shoukhrat Mitalipov)說，在某些“增長”化學物質的幫助下，他們能夠將幹細胞變成各種細胞系和組織，包括人類心臟細胞。米塔利波夫是該研究的主要作者之一。

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

研究人員所取得的成就距離創造克隆人類胚胎還有很長的路。

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.

即使整個胚泡被植入子宮，它也不會產生出克隆人。米塔利波夫博士說，胚泡還缺少一些其需要植入的細胞類型，同時也存在其它缺陷。

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──儘管經過多年實驗，科學家還未能成功克隆猴子。

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.

米塔利波夫博士說，他的實驗室曾嘗試將整個胚泡植入猴子的子宮，但這些實驗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.'

米塔利波夫博士說，我們不知道這是爲什麼，你可以創造出胚胎幹細胞，但這並不意味着胚胎能夠被植入。

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.

他推測克隆猴子和人類的難度更大的原因之一可能是和其它物種相比，猴子和人類的卵細胞更脆弱。

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標是使用克隆技術治病。他下一步計劃使用實驗室培養的組織，並觀察他是否能成功地治療一種發生在猴子身上的、可導致失明的退行性疾病。