You’ve posted this exact same topic before, and you have obviously not learnt anything from that occasion.
Now, please pay attention to what I am telling you.....
Embryonic stem cells (ES cells) are only present during a narrow window of very early embryonic development. They are present during a stage of embryo development known as the blastocyst stage which, in humans, occurs about one week after fertilization. The developing embryo is known as a blastocyst when it is a hollow ball of a few hundred cells. It has not even implanted into the uterine wall at this stage. Inside the blastocyst are about a dozen ES cells. Shortly after the blastocyst stage, a human embryo implants into the uterine wall of the womb. From this stage onwards all the ES cells are gone – they have differentiated into more lineage restricted stem cells types of the three germ layers.
So the take-home message is:
ES cells can only be extracted from a blastocyst. They cannot be obtained from later foetal tissue, such as tissue from an abortion. Thus, the only source of human ES cells are leftover blastocysts from IVF treatments (or from blastocysts created by nuclear transfer cloning).
Now, “adult” stem cells are another matter. Basically, most of the tissues of our adult body have stem cells that divide to produce new cells to replace old ones. They are the only immortal cells in our body. These “adult” stem cells are different to ES cells in that they are lineage restricted ie. they produce only one type of cell that is appropriate for the tissue in which they reside. (Actually, sometimes adult stem cells can produce 2 or 3 different lineages, but even so the different cell types in still restricted to one particular tissue type.)
Basically, any stem cell that is not an ES cell is an “adult” stem cell and is lineage restricted. So the stem cells that are extracted from umbilical cords are not ES cells even though they come from a new born baby. (Umbilical cord stem cells are hematopoietic stem cells that produce the various blood cell lineages.)
The fact of the matter is that, at present, adult stem cell technology cannot replace the need for ES cell research. They are difficult to isolate from an adult person. In fact, only hematopoietic stem cells from the bone marrow can be routinely isolated from an adult person. Furthermore, as discussed above, adult stem cells give rise to only one type of cell and, thus, are very limited in their therapeutic potential. The use of adult stem cells has one great advantage in therapeutic treatments – if they can be extracted from a patient then they are a perfect genetic match for that patient. ES cells (and any cells derived from them in vitro) will not be a match for a patient and any such therapy will need to be accompanied by anti-rejection medication. Of course, cloning by nuclear transfer (so-called “therapeutic cloning”) is the way around this ie. clone a cell from a patient, let it develop into a blastocyst, then extract the ES cells from the blastocyst which will be a perfect match.
The use of stem cells of any type is very much in its infancy and scientists need to work with both ES cells and adult stem cells in order to derive the best possible treatments.
