While cloning stem cells is a technical breakthrough, there's already a method of deriving embryonic-like stem cells that doesn't require the use of embryos at all: induced pluripotent stem (IPS) cells, said Dr. George Daley, who is director of the Stem Cell Transplantation Program at Children's Hospital Boston and an international expert in stem cells.

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That technique for generating embryonic-like stem cells (called induced pluripotent stem cells, or iPS cells) bypassed the need for transferring the cells into eggs, as Wilmut had done, and also averted the ethical issues attached to extracting stem cells from embryos as Thomson had done.

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The technique used by Green and Hollister is part of a burgeoning field called regenerative medicine, which involves engineering therapies -- using things like stem cells, or "body parts" constructed out of biological material -- to harness the body's ability to heal itself.

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But another approach to using embryonic stem cells--and cloning--has been in inventing drugs much like the ones we already have.

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This is true whether they use so-called adult stem cells, as Osiris Therapeutics and Cytori do, or the embryonic kind, like Geron.

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There are some cells on the margin of adult retinas that have been identified as having stem cell-like properties, which the team says could be suitable.

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Weissman says these results shed doubt on the arguments against using embryonic stem cells, which are being pioneered by companies like Geron (nasdaq: GERN - news - people), Cythera and Bresagen .

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Only last year, she said, Egli and Paull and their colleagues demonstrated that the nuclear transfer of eggs cells could generate patient-specific stem cell lines for potential cell replacement therapy to treat diseases like diabetes.

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