What's the difference between Adult Stem Cells and Embryonic Stem Cells?
There are significant biological differences between human, embryonic, and adult stem cells. Embryonic stem cells can be isolated from embryos with relative ease and have an unlimited ability to self-renew and proliferate in culture in huge numbers for many generations. Further, they are the only stem cell lines known to be undifferentiated and pluripotent that are available for study. This means that they are more likely to generate a wider range of cell types. Such characteristics, in combination, give embryonic stem cells a remarkably broad therapeutic potential. Yet the availability of human embryos for the production of stem cells is limited and subject to considerable ethical controversy and legal restrictions. Many of the existing stem cell lines are incompletely characterized and may not be robust or stable in their properties.
Adult stem cells, in contrast, are found in low numbers in the human body, can be difficult to obtain, do not expand readily in culture, and may be capable of differentiation into only a limited number of cell types. It seems likely that a few known adult stem cells exhibit stem cell plasticity and can differentiate into cell types outside their usual path. Such adult stem cells would need somehow to be isolated, expanded, and then efficiently reprogrammed onto a new pathway of differentiation if they were to be used to treat patients. This extra reprogramming step makes the development of specialized cells from adult stem cells more complicated than from embryonic stem cells.
All of these factors seem to give embryonic stem cells an edge over adult stem cells for research and therapy, based on the current state of scientific knowledge. Consequently, some stem cell scientists and research experts consider human embryonic stem cell research more promising than adult stem cell research and, ultimately, more promising for patient treatment. Yet most in the Weld appear to see both kinds of stem cells as providing complementary avenues for research and therapy. The National Research Council of the National Academies maintains that the ‘‘best available scientific and medical evidence indicates that research on both embryonic and adult human stem cells will be needed.’’ The National Institutes of Health has come to a similar conclusion.
The extent to which these two different stem cell types will be useful in generating replacement cells and tissues in patients with disease and injury is unknown at this point in time. Substantially more research on both sorts of stem cells is needed before it can be definitively determined whether one provides a better route to therapies than the other. There are multiple technical hurdles that must first be overcome. Over the next several years, it will be important to continue to analyze the difference between adult stem cells and embryonic stem cells, and to compare them in terms of their ability to proliferate, differentiate, survive and function after transplant, and avoid immune rejection.
If stem cell therapies of either kind are to be of clinical benefit and of demonstrated safety, a much clearer understanding of the processes of differentiation and dedifferentiation will be needed. It will also be important to develop clear and rigorous standards for evaluating embryonic and adult stem cells so that their potential uses can be accurately compared. There is increasing evidence that stem cells, like other cells, accumulate mutations as they are maintained in culture and may become transformed into cancerous cells. Sensitive methods for testing cells used for therapies must be developed.
Since few animal studies have looked at results much longer than a year after transplantation, the long-term consequences of both of these sorts of stem cell therapies need to be studied. In short, continued intensive research on both sorts of stem cells is needed before one kind can be said to be overwhelmingly superior to the other for research and therapy.