CAMBRIDGE -- The basement laboratory where Harvard researchers grow embryonic stem cells is secret. Not a big secret: The scientists are happy to talk about the lab and what they do here. But the work is sensitive enough -- and controversial enough -- that they would prefer not to tell the world exactly where it is.

Here, amid the sharp smell of disinfectant and the loud drone of a freezer, Douglas Melton and his colleagues took embryos donated from the fertility clinic Boston IVF and extracted new lines of stem cells. Because the federal government will not fund this work, all money came from private sources.

Some of the embryos, which are kept in rose-colored growth media, were a few cells in size when they arrived, said Chad Cowan, a scientist in the Melton lab. These had to be grown until they reached the blastocyst phase -- a ball of between 100 and 200 cells, about five days after conception. Other embryos had developed into a blastocyst -- or "blast," in research shorthand. This blast is about one-tenth of a millimeter and contains no hint -- no skin, blood, brain, or other specialized cells -- of the human it has the potential to become.

The embryonic stem cells grow inside the blast, so a scientist uses a treatment to kill the outer, protective layer of cells, which ends the embryo's ability to develop into a child. Once they have these cells, they place them in a fluid that coaxes them to grow without specializing. Often the cells die at this point, for reasons the scientists don't understand.

Each of the lab's 17 new cell lines is the descendant of one embryo, and each cell in the line contains the DNA that a child would have had, a unique combination taken from each parent. And each cell line, again for reasons the scientists don't understand, will have its own quirks: some might be hard to grow, others might be particularly easy to coax into forming neurons, or cells from the kidney. None of the donating couples will know what became of their own embryos.

-- GARETH COOK

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