Human Embryo/Stem Cell Series

Slate runs the first of a five part series by William Saletan on human embryos and stem cells and their potential uses.  The series is entitle, The Organ Factory.  Today's article is called "Cures Now" and states,

. . . . To get transplantable tissue your body won't reject, cells from somebody else—the cells you'd get from the Castle bill—won't do. You need cells with your DNA. You need a clone. This is why most senators support legislation sponsored by Sens. Orrin Hatch, R-Utah, and Dianne Feinstein, D-Calif., that would ban cloning for procreation but keep it legal for research. The cloning bill forbids preservation of cloned embryos beyond two weeks. "After 14 days, an unfertilized blastocyst begins differentiating into a specific type of cell such as a heart or brain cell and is no longer useful for the purposes of embryonic stem cell research," Feinstein told her colleagues.

But if the goal is tissue, clones aren't less useful after 14 days. They're more useful, precisely because they're differentiating into the cell types that patients need. Why stop research at 14 days? Once you say we can do this much of it, what's the difference?

Four years ago, a team led by John Gearhart, one of the field's top researchers, published a study of cells "derived and cultured from 5-, 6-, 7-, and 11-week postfertilization primordial germ cells." The derived cells, unlike hES cell lines from embryos before 14 days, caused no tumors when they were injected into mice. Gearhart's team found that the derived cells "may be useful … as a resource for cellular transplantation therapies." When Gearhart testified before the President's Council on Bioethics in April 2002, he was asked, "Would it in fact be the greatest advantage if a patient's own cell line could be derived from primordial germ cells?" He replied:

Oh, boy, this committee would—well, wow. Now, think what this means. It means that you would be generating an embryo, and having it implanted. Now, what you don't know is that our fetal tissue comes from 5-to-9 weeks post-fertilization. These are therapeutic abortions. And which means now that you are way beyond—I mean, the point of where a blastocyst is, and obviously way beyond I think anyone subscribing to that approach.

In other words, ethics said no, but science said yes. And science was just beginning to speak. Three weeks before Gearhart testified, a team featuring two other top researchers, George Daley and Rudolf Jaenisch, reported development of a therapeutic cloning system that included "differentiation of [cloned] ES cells in vivo" prior to transplantation. "In vivo" meant that the cells differentiated—matured into specific tissues—in a living organism. When the researchers fixed a gene in mouse ES cells, derived embryos from the cells, and grew the embryos into 1-month-old mice, "bone marrow cells derived from the 'repaired' ES cell mice were able to fully function after transplantation" into the mice that had been cloned. But when the researchers tried "in vitro differentiation of the repaired ES cells instead of in vivo formation of normal bone marrow," they ran into "unanticipated biological principles" that thwarted transplantation.

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