New procedures to obtain embryonic stem cells
Research on embryonic stem cells is hindered by serious ethical concerns, related to the use of human embryos. Two reports, published this week, describe novel approaches to produce embryonic stem cells that may partially solve this problem. These new methods have been successfully tested in laboratory animals, and they might be used in future to produce human stem cells.
their remarkable potential for generating many different types of specialized
cells, embryonic stem cells represent a most promising tool to develop novel
therapeutic strategies to treat a great variety of human diseases. They are
usually derived from early developing embryos, called blastocysts, before the
implantation into the molther’s uterus. At this stage, the embryo is made of
two types of cells: the trophoectoderm,
the outer cell layer, which is necessary for the implantation and later forms
the embryo-mother interface, and the inner
cell mass, that will give rise to the entire organism. Embryonic stem cells
to be used for research or therapeutic purposes are dissociated from the inner
cell mass, a procedure that unavoidably destroys the embryo. For this reason, the
use of such cells has been subject of intense ethical and political debate,
leading to severe restriction of research in different countries, such as the
The second report (3) concerns a modification of the method, called nuclear transfer, which is used to produce cells that are genetically identical to a particular individual (this type of cells can be safely used for transplantation, because they will be not rejected by the donor patient). In this procedure, the nucleus of an ovocyte (a non-fertilised egg cell) is removed and replaced by that of cell taken from an adult donor (for example a blood or skin cell). In the egg environment the genetic material present in the adult donor nucleus is reprogrammed and an embryo-like blastocyst (embryoid) is formed, which can be used to isolate stem cells. Embryoid blastocysts are not usually able to develop into a full organism. However, the procedure is severely restricted by law because it may lead to human cloning. By exploiting methods derived from genetic engineering, the authors of this second article designed an altered nuclear transfer procedure. They inserted into egg cells the nuclei of donor cells defective for a gene (Cdx2), necessary for the generation of the trophoectoderm. As a consequence, the obtained embryoids have an inner cell mass, from which embryonic stem cells can be isolated, but are completely unable to implant into the uterus and, therefore, cannot develop further.Both procedures have been successfully tested by using cells from laboratory animals, but it is not known whether they can be safely transferred to human cells. In addition, they are not likely to provide satisfactory answers to all the ethical concerns and legal limitations that now hamper the research on embryonic stem cells. For instance, the recently enacted Italian law forbids the genetic testing of preimplantation embryos. However, this kind of attempt should be pursued: in the long run, such technological advancements may prove to be suitable in setting up procedures that can be both therapeutically efficient and ethically acceptable.
1. Weissman IL, Nature, 439, 146-148(2006)<>
2. Chung, Y. et al,. Nature 439, 216–219 (2006). <>
3. Meissner, A. & Jaenisch, R. Nature, 439, 212–215 (2006).