Embryonic versus Adult Stem Cells
Embryonic versus Adult Stem Cells
By the 1990s Dr Steenblock, like many physicians had become keenly aware of the work being done with embryonic stem cells and their purported promise to usher in a new age of regenerative medicine. However, as ethical objections to use of embryonic stem cells gained traction and then momentum in the US and studies appeared signaling that these stem cells produce teratomas in lab animals, many researchers and doctors began focusing on adult stem cells.
In order to appreciate the appeal of adult stem cells to doctors like me who were looking for ways to remediate or cure a wide swath of diseases and medical conditions, it helps to understand the type and nature of stem cells that reside in embryos versus those typically found in non-embryonic, somatic tissues:
Embryonic stem cells are pluripotent; that is, they possess the potential to differentiate into any of the three germ layers: endoderm, mesoderm, or ectoderm. This means they can become any fetal or adult cell type. In their native embryonic environment they get a carefully orchestrated series of signals from surrounding tissue that guides them to follow specific developmental pathways in precise ways. When these signals are missing, out of their normal order, conflicted or present in the wrong quantities as happens when these embryonic stem cells are implanted in somatic tissues or organs in animals, they can remain undifferentiated, differentiate into a cell type at odds with the tissue they are in, or even form a teratoma.
Adult stem cells, which arise after early stage or embryonic development and are found in our organs, plus adipose, dental pulp and many other tissues, are more restricted in terms of the types of somatic cell types they can become. This makes sense as most of these stem cells never leave the tissue or organ they are part of and basically serve to replenish somatic cells that die off as well as promote the repair and regeneration of local tissues that incur damage due to disease or injury. In addition, stem cells exist in umbilical cord blood & Wharton’s Jelly, as well as the amnion and amniotic fluid which function as adult stem cells; which is to say, they have more lineage restrictions on them than embryonic stem cells but are more plastic than those found in more developmentally advanced tissues in pre- and post- term babies.
The adult stem cells in most of the body’s organs and tissues tend to be a mix of multipotent, oligopotent and unipotent stem cells. These terms refer to the potency of these stem cells. Briefly: Multipotent stem cells can differentiate into a number of somatic cell types, but only those of a closely related family of cells. Oligopotent stem cells on-the-other-hand can differentiate into only a few cell types such as lymphoid or myeloid cells, while unipotent cells can generate only one somatic cell type, their own, though they possess the property of self-renewal (which sets them apart from non-stem cells).
Interestingly, bone marrow tissue and umbilical cord blood contains a wealth of multipotent stem cells including mesenchymal stem cells but also some pluripotent stem cells such as a small number of very small embryonic-like stem cells (VSELs). So why don’t these pluripotent stem cells form teratomas when implanted or infused in animals or people? Apparently they have been exposed to growth factors or other bioactive molecules in the more developmentally advanced tissues they come from that are absent in embryos, and which leave them far less prone to form teratomas.
Like many doctors in the closing years of the last century I had a handle on the safety advantages of adult stem cells over embryonic stem cells, as well as enough evidence from laboratory and clinical studies plus foreign stem cell patient case histories to argue that adult stem cells were not only safe but effective in terms of producing clinical benefits in a number of diseases and medical conditions in both adults and children. With an eye out for opportunities to wade into the world of stem cell medicine, I crossed paths with a prominent physician in Mexico who had worked extensively with xenotransplants (e.g., blue shark embryonic stem cells) in humans, and who was interested in and had the legal clearance to begin working with pure umbilical cord stem cells in his country.