On 5 October 2011, the prestigious journal Nature (478; 70-75, 2011) published an article describing the first successful production of a stem-cell line derived from cloned human embryos for use with patients suffering from certain diseases.

The first time we heard of the cloning of human embryos it was in the announcement made by Woo Suk Hwang, who in 2005 published his famous article in Science magazine—results which later proved to be fraudulent.

There have been other attempts made in the cloning of human embryos since then: (Stokovic M, Reprod Biomed Online 11; 226-231, 2005 / Hall V, Human Reprod 22; 52-62, 2007 / Hcindryckxt B, Human Reprod 22; 1982-1990, 2007 / French D, Stern Cells 26; 485-493, 2008 / Me Elroy S, Reprod Biomed Online 16; 684-693, 2008 / Chung Y, Cloning Stern Cells 11; 213-223, 2009 / Egli D, Cell Stern Cell doi: 10.1016/j.stern.2011.08.002), yet none of these experiments led to stem-cell lines derived from embryos. However, there has been some success along these lines in the recent paper of  Nature (478; 70-75, 2011).

To obtain these results, the authors employed two methods. The first, known as somatic-cell nuclear transfer, involves the exchange of an oocyte’s genome with the genome of a somatic cell. That is, the genome of the oocyte is replaced with that of an adult cell. However, even though the authors employed a large number of oocytes (270), the resulting embryos did not develop normally; these also showed serious transcriptional abnormalities. Nevertheless, in a second method in which the oocyte genome is not removed and the adult somatic cell genome is simply added, the resulting hybrid zygote develops to the blastocyst stage, from which stem cell lines can be derived. These cell lines contain a haploid genome (23 chromosomes from the oocyte) and a diploid (46 chromosomes) from the reprogrammed adult cell.

From blastocysts, the authors isolated the inner cell mass and derived cell lines containing the genome of a type I diabetes patient and that of a healthy subject. Naturally both cell lines were triploid (69 chromosomes). These cells were cultured during a six-month period, representing more than 30 cultivation passages without showing any abnormalities. Both cell lines also carried the characteristic markers of pluripotent stem cells.

In the opinion of the authors, these results demonstrate the feasibility of adult somatic cell reprogramming using human oocytes. Moreover, they believe that if they had access to a sufficiently reliable source of oocytes and their genomes to allow for reprogramming of adult somatic cells they would be able to generate diploid pluripotent stem cells, a procedure that could be employed in the study of a variety of human diseases.

JUSTO AZNAR

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