A California research team has become the first to report, and painstakingly document, the cloning of a human embryo using donated oocytes (egg cells) and DNA from the cells of an adult donor. The study was published online by the journal "Stem Cells."
The experiments, using a technique called somatic cell nuclear transfer (SCNT), provide key steps toward the development of patient-specific embryonic stem cells for use in developing new treatments for conditions such as Alzheimer's disease, Parkinson's disease, and spinal cord injury, among others. The lead author was Andrew J. French, Ph.D., of Stemagen Corp., a private company headquartered in La Jolla, Calif.
In the experiments, the researchers removed the nuclei of mature oocytes from healthy young women who had previously donated eggs for successful infertility treatments. The SCNT technique was then used to insert DNA from an adult male donor into the oocytes. The DNA was derived from a type of cell called fibroblasts, obtained from skin biopsies.
Subsequently, several of the reconstructed oocytes continued to develop as normal embryos, to the blastocyst stage. Extensive and carefully documented genetic tests were performed to confirm the genetic identity of the cloned embryos. In three embryos, tests showed the same DNA as the male fibroblast donor.
In one of the three cases, additional tests showed that the embryo had another type of DNA, called mitochondrial DNA, from both the female oocyte donor and the male DNA donor.
Mitochondrial DNA testing is viewed as an essential proof of successful human cloning -- particularly after previous fabricated reports from a South Korean research group. Amidst this background of controversy, the researchers took extraordinary steps to ensure that their experiments were properly conducted and documented. These included approval by an independent review board and confirmation of the genetic results by an independent laboratory, among other steps.
The ability to generate stem cells using the patient's own DNA holds great promise for the treatment of currently incurable degenerative diseases, as well as for cell-based drug discovery. Previous studies reporting the development of cloned human embryos have used embryonic stem cells as the DNA donors.
"This study demonstrates, for the first time, that SCNT can be utilized to generate cloned human blastocysts using differentiated adult donor nuclei remodeled and reprogrammed by human oocytes," the researchers write. They believe that some key technical factors contributed to their successful results, including the use of freshly donated oocytes from successful egg donors.
While the study is an important step toward the development of stem cells for therapeutic cloning, much more research will be needed to confirm and extend the results.
Dr. French comments, "The data we present are not in any way the final word on this topic, but, we anticipate, just one of many publications from a variety of researchers who will use a variety of methods to conduct and analyze similar experiments."