THEY WERE SUCH TINY DOTS, YET THEY HELD SUCH immense promise. After months of trying, on October 13, 2001, we came into our laboratory at Advanced Cell Technology to see under the microscope what we¿d been striving for¿little balls of dividing cells not even visible to the naked eye. Insignificant as they appeared, the specks were precious because they were, to our knowledge, the first human embryos produced using the technique of nuclear transplantation, otherwise known as cloning.

With a little luck, we hoped to coax the early embryos to divide into hollow spheres of 100 or so cells called blastocysts. We intended to isolate human stem cells from the blastocysts to serve as the starter stock for growing replacement nerve, muscle and other tissues that might one day be used to treat patients with a variety of diseases. Unfortunately, only one of the embryos progressed to the six-cell stage, at which point it stopped dividing. In a similar experiment, however, we succeeded in prompting human eggs¿on their own, with no sperm to fertilize them¿to develop parthenogenetically into blastocysts. We believe that together these achievements, the details of which we reported November 25 in the online journal e-biomed: The Journal of Regenerative Medicine, represent the dawn of a new age in medicine by demonstrating that the goal of therapeutic cloning is within reach.

Therapeutic cloning¿which seeks, for example, to use the genetic material from patients¿ own cells to generate pancreatic islets to treat diabetes or nerve cells to repair damaged spinal cords¿is distinct from reproductive cloning, which aims to implant a cloned embryo into a woman¿s uterus leading to the birth of a cloned baby. We believe that reproductive cloning has potential risks to both mother and fetus that make it unwarranted at this time, and we support a restriction on cloning for reproductive purposes until the safety and ethical issues surrounding it are resolved.

Disturbingly, the proponents of reproductive cloning [see Reproductive Cloning: They Want to Make a Baby] are trying to co-opt the term "therapeutic cloning" by claiming that employing cloning techniques to create a child for a couple who cannot conceive through any other means treats the disorder of infertility. We object to this usage and feel that calling such a procedure "therapeutic" yields only confusion.

What We Did

WE LAUNCHED OUR ATTEMPT to create a cloned human embryo in early 2001. We began by consulting our ethics advisory board, a panel of independent ethicists, lawyers, fertility specialists and counselors that we had assembled in 1999 to guide the company¿s research efforts on an ongoing basis. Under the chairmanship of Ronald M. Green, director of the Ethics Institute at Dartmouth College, the board considered five key issues [see The Ethical Considerations] before recommending that we go ahead.

THERAPEUTIC CLONING: HOW IT'S DONE

The next step was to recruit women willing to contribute eggs to be used in the cloning procedure and also collect cells from individuals to be cloned (the donors). The cloning process appears simple, but success depends on many small factors, some of which we do not yet understand. In the basic nuclear transfer technique, scientists use an extremely fine needle to suck the genetic material from a mature egg. They then inject the nucleus of the donor cell (or sometimes a whole cell) into the enucleated egg and incubate it under special conditions that prompt it to divide and grow [see Therapeutic Cloning: How It's Done].