Defenders of embryonic stem cell work say that it is important even in understand adult stem cells and induced pluripotent stem cells, which resemble the embryonic cells but can be created without destroying embryos.

FORBES: The Scientist Who Helped Stall Stem Cell Research

What remains to be seen is whether these cloned embryonic stem cells are more useful therapeutically than the noncontroversial induced pluripotent stem cells, and questions linger about their effectiveness.

CNN: Cloning stem cells: What does it mean?

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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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.

CNN: Cloning stem cells: What does it mean?