Scientists in U.S. have for the first time created cloned primate embryos and used them to make embryonic stem-cell lines, according to the British scientific journal of Nature published on Wednesday.(File Photo)

    WASHINGTON, Nov. 14 (Xinhua) -- Scientists in U.S. have for the first time created cloned primate embryos and used them to make embryonic stem-cell lines, according to the British scientific journal of Nature published on Wednesday.

    Scientists at Oregon Health & Science University's Oregon National Primate Research Center reported that they firstly obtained skin cells from a 9-year-old male rhesus macaque monkey called Semos.

    Then they used specialized imaging software called Oosight Spindle Imaging System, to spot and remove the nuclear material attached to the spindle fibers of female rhesus monkeys' eggs.

    In the end, they inserted the nuclei of skin cells into nucleus-free eggs, and eventually cloned monkey embryos. Using the embryos, they successfully developed two embryonic stem cell lines -- groups of cells that can grow indefinitely and differentiate into any cells of the body.

    The genetic material (DNA) of cell lines was then matched to DNA from the male donor monkey to ensure that they were a direct clone.

    Successful development of the cell lines required numerous attempts. Overall, 304 monkey eggs from 14 female rhesus monkeys were used to generate the two stem cell lines, a 0.7 percent success rate, according to the brief report released Wednesday by the university.

    Before publishing the researchers' papers, Nature took an unusual step of asking another team of researchers to verify the work.

    Science community has painful memories when the claim of a similar breakthrough with human embryos by a South Korean scientist Woo Suk Hwang in 2004 turned out to be false.

    The only other animal in which cloned embryonic stem cells have been created is mice.

    Although the rapid succession of clones after Dolly the Sheep was announced in 1997 gave confidence to the field of cloning, continued failure to clone human or monkey embryos led to some pessimism.

    Primate-cloning researcher Gerald Schatten stated in 2003, after his study of 716 monkey eggs that failed to produce a clone, that it might be impossible to do so.

    "With current approaches, NT (nuclear transfer, a cloning technique) to produce embryonic stem cells in non-human primates may prove difficult -- and reproductive cloning unachievable," said Schatten.

    Therefore, today's accomplishment in primates by Oregon team is "like breaking the sound barrier", says Robert Lanza, with Advanced Cell Technology in Los Angeles, California.

    The team led by Shoukhrat Mitalipov at Oregon Health and Science University had been trying for nearly a decade to achieve reproductive cloning in primates, and had used some 15,000 eggs in the process.

    After Hwang's results was proved to be fraudulent, the group decided to move from reproductive cloning to try to establish a cloned embryonic stem-cell line instead -- theoretically, a more achievable goal.

    Last autumn, the researchers had a false start when a cloned embryo, created by inserting a monkey skin cell into a monkey egg that had had its DNA removed, produced what seemed to be viable embryonic stem cells.

    After a week, they watched in dismay as the cells started to differentiate uncontrollably, losing their nature as embryonic stem cells.

    But by January 2007, they had another line that retained its embryonic stem-cell properties, and a couple of months later, they had created yet another.

    These results are outlined in Nature. David Cram, a researcher from Monash University in Australia, and his colleagues have independently confirmed the results, according to Nature.

    The achievement has led to speculation about when similar success in humans might open up the door for therapeutic cloning, Nature said in a news release on Wednesday.

    Mitalipov, the lead researcher says that it is still too early to hope for success in reproductive cloning in monkeys, let alone humans; the science community is generally against reproductive cloning in humans.