It is my understanding that the consensus and/or majority opinion in the scientific community regarding stem cells is that embryonic stem cells have more potential than adult-derived stem cells, and hence they still should be studied and cannot be completely replaced in studies by adult-derived; at least not yet.
But is this currently the consensus and/or majority opinion in the scientific community, among those who would work with stem cells?
And yes, I know there are several studies that adult stem cells may have some uses. I’m trying to verify that current scientific opinion is still that embryonic cannot be completely replaced by adult derived, not whether or not there are any uses at all for adult stem cells.
Embryonic stem cells can, of course, make any tissue than forms in the embryo (but not some of the extraembryonic membranes which don’t matter after birth). Unfortunately, people don’t know how to convince them to make most tissue types in vitro.
There have been two major papers showing trans-differentiation (changing from one tissue type to another) of blood stem cells. In these papers, scientists were able to detect donor cells (derived from adult blood stem cells) in the muscle, liver, and brain of the recipient. There has been another major paper, using slightly better detection technology, that showed that there was no contribution of the donor cells to the brain or muscle. This latter group suggested that perhaps what the first groups were seeing was simply leakage of donor blood cells into the brain and muscle, not trans-differentiation of blood cells into muscle and neural tissue. The first two groups said the latter group was a bunch of idiots whose experiment failed and were trying to justify it (not in those words). Take your pick. In any of these experiments, the number of trans-differentiated cells was very small, and may or may not be practically useful.
In yet another front, someone was sucessful in trans-differentiating some adult cells (muscle, I think, although I can’t remember) into neural cells, which was quite exciting. This was recent, so I don’t think anyone has tryed to replicate it yet. Also, it hasn’t been shown that these cells could function normally as neural cells in a living organism. To be fair, I don’t think anyone has gotten embryonic-stem cell derived tissues to function in a living organism yet, either.
How you regard cord cells is somewhat a matter of opinion. They are definitely not embryonic stem cells - embryonic stem cells come from an approximately 15-30 cell blastocyst, long before any tissues have formed. They are much more analagous to adult stem cells, but they do seem to be a little more flexible. One certainly could create a third category of fetal stem cells, which would encompass both cord cells and fetal neural tissue (used in brain transplants), or one could regard these as a subset of adult stem cells.
Just to clarify, the blood stem cells -> muscle, brain, liver cells experiments were done by injection of blood stem cells into living animals, so any trans-differentiation shows functional cells. The adult muscle cells -> neural cells were done in a petri dish, so it is not known if those would function in a organism.
And further, embryonic stem cells have been shown to form any tissue by injecting them into embryos, where they incorporate and form multiple tissues. As far as I know, no one has gotten them to form tissues in vitro and then implanted these into an adult. I may have missed something, though.