One clone is not enough
(January 22nd 2008) Last week the scientific press was animated by another stem cell research report. US-scientists announced their cloning of human blastocytes from adult fibroblasts. Appraisals of this feat ranged from 'important first step' to 'spectacular breakthrough'. However, is one clone enough? asks Karin Hollricher.
Cloning human blastocytes by inserting DNA from a fibroblast cell into a human egg cell seems to be a Holy Grail of stem cell research, religiously pursued by many researchers. However, their ongoing lack of success has been accompanied by silence with the notable exception of the Korean, Woo Suk Hwang, who became a highly publicised figure with his fabricated report on stem cell lines from cloned human embryos.
Now, Andrew French from Stemagen, a private company in La Jolla, California, reports in the journal,
Stem Cells, that he and his colleagues are the first to have successfully cloned a human blastocyte using a technique called somatic cell nuclear transfer.
Three young women donated a total of 29 oocytes, whose nuclei were replaced with those obtained from two adult male skin cell lines, to yield five embryonic blastocyte clones containing the males' genome.
However, because the Hwang case has left a legacy of mistrust in the field, the Stemagen researchers asked the Genesis Genetics Institute in Detroit (USA) for independent genetic verification of the clones. The results have been published in the same article.
DNA fingerprinting showed that three of the blastocytes contained nuclear DNA from the male donors with no nuclear DNA contamination from the egg donors. But the esential proof of successful human cloning - mitochondrial DNA fingerprinting - has been reported in only one of these cases. This confirmed that in addition to the male nuclear DNA, the embryo contained mitochondrial DNA from the female oocyte. Unfortunately, though, this leaves the field open to speculation about the other two blastocytes: were they true clones or were the authors simply in a hurry to publish their success ahead of the competition?
Is this a breakthrough? Stem cell expert Miodrag Stojkovic (Centro de Investigacion Principe Felipe, Valencia, Spain), Co-Editor of
Stem Cells comments "Considering such a small number of blastocysts, a completely different result may just as well have been reached. The experiment could easily have rendered zero true clones."
Above all, only a few months ago, two research groups reported reprogramming human somatic cells to pluripotent stem cells that showed almost all the features of embryonic stem cells. The so-called induced pluripotent stem (iPS) cells were created by transferring stem cell-specific genes like Oct3/4, Sox2 and Nanog into human skin cells.
Although the Stemagen scientists may be on the right track, they have not yet established pluripotent stem cell lines from their clones. Nevertheless, this is precisely the result that stem cell research is really pursuing. Only cell lines derived from individual patients contain the material necessary for cultivation of tailored replacement tissue for treating diseases like Diabetes and Parkinson's Disease. In the final analysis, this is why the latest progress report on cloning human embryos cannot really be considered as a spectacular breakthrough.
