Scientists have successfully generated new lines of human embryonic stem cells that are exact genetic matches for individual patients, according to a new study. The results bring researchers a small but significant step closer to using stem cell transplants to treat a variety of diseases.

Last year, a team led by Woo Suk Hwang and Shin Yong Moon of Seoul National University in Korea announced that they had harvested embryonic stem cells from cloned embryos, although their technique yielded just 30 blastocysts and a single cell line. Now the scientists report that they have made significant gains in both speed and efficiency and that they have tailored the process to create stem cells that are DNA matches for patients. Eleven male and female volunteers suffering from maladies such as spinal cord injury and diabetes donated skin cells to the researchers, who then implanted nuclei from these cells into donated eggs whose nuclei had been removed. These eggs were then cultured and allowed to grow for six days to the blastocyst stage, which contains roughly 100 cells. Stem cell lines were derived from the inner cell mass of the blastocysts.

The team produced 11 stem cell lines from 31 blastocysts using the new procedure, a tenfold increase in efficiency over their 2004 results. The age and sex of the volunteers donating genetic material did not affect the success rate, but the scientists report lower failure rates using the eggs of younger women (those from females under the age of 30 led to stem cell lines at a rate of one in 13, whereas those from women in their thirties yielded stem cells at a rate closer to one in 30.) A report detailing the new approach was published online yesterday by the journal Science.

The authors caution that a number of issues still need to be addressed before their work can have clinical applications. "What the study shows is that stem cells can be made that are specific to patients regardless of age or sex and that these cells are identical genetic matches to the donor," says study co-author Gerald Schatten of University of Pittsburgh School of Medicine. But because the stem cells were manufactured using genetic material from individuals suffering from a disease, there is a possibility that the stem cells themselves may show disease characteristics. In addition, it remains to be proven that transplantation of the stem cells into recipients can be safe, effective and tolerated.