While political debate over stem cells continues, the science has made tremendous strides during the past 18 months. In the frenzy of activity, Woo Suk Hwang has stood out for the impact his team from Seoul National University has had on the still nascent field. Hwang has achieved remarkable progress in a short period.
In February 2004 Hwang and his research group reported the first embryonic stem cell line derived from a cloned human embryo. By May 2005 they had used cloning techniques to create 11 stem cell lines, each one the perfect genetic match of a different patient, another first. In August 2005 they introduced the first cloned dog. And in October 2005 they announced a plan for a stem cell bank open to scientists worldwide.
Among those accomplishments, it is the second that truly marks the greatest biomedical advance with the greatest direct repercussions. Hwang and his team harvested stem cells—the self-renewing progenitors of all cells in the body—from cloned early-stage embryos made by slipping the nucleus of a skin cell into a nucleus-free egg. They then went on to demonstrate that the stem cell lines originated from the skin cell donors. This work has revolutionized the field of therapeutic cloning and could bring its promise—to better understand and treat a variety of diseases—a step or two closer to reality.
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Hwang's 2004 work illustrated the feasibility of therapeutic cloning, but he was still working out kinks in his protocol. His group began with 242 eggs, but after removing the eggs’ nuclei and swapping in those of somatic cells, the investigators produced only 30 blastocysts (week-old embryos), from which they coaxed just one stem cell line into being. In addition, the sources of the replacement nuclei were the egg donors’ own cumulus cells, which encircle developing eggs in the ovary. This approach meant that it was possible the egg had spontaneously begun to divide on its own rather than developing by cloning.
What a difference a year makes. Although its blastocyst generation remained largely the same (31 blastocysts, after beginning with 185 eggs), Hwang's team was able to establish 11 stem cell lines, a 10-fold improvement over the previous work. Even more remarkable was that each stem cell line genetically matched one of 11 skin cell donors. These 11 patients—nine have spinal cord injuries, one has a genetic immunodeficiency disorder, and another has type 1 diabetes—consisted of males and females whose ages ranged from two to 56 years. In 10 cases, the nucleus of a skin cell was fused with an egg from a biologically unrelated woman (the remaining woman provided both her own egg and skin cells). Before this work, no one knew whether cell lines could be established using nuclei donated from men or young girls.
Hwang's laboratory reported that the 11 stem cell lines were able to differentiate into the trinity of embryonic cell layers that become all cells in the body. Initial tests also indicated that the cell lines would be compatible with the patients’ immune systems. This feature would be critical for clinical uses, such as transplanting stem cells—with their defects corrected—back into patients, but the researchers emphasize that years of further study remain before such treatments might be possible.
Hwang's successes add urgency to many ethical considerations, and the specter of reproductive cloning attempts by fringe scientists lingers (Hwang emphatically denounces such research). But if a time does come when therapeutic cloning becomes the gold standard of care for a variety of diseases, Hwang's innovative and groundbreaking explorations will have paved the way.