Stem Cells: The Ultimate Cellular Blueprint
Pioneering work with stem cells was performed by Canadian scientists Drs. James Till & Ernest McCulloch. They stumbled across the self-renewing capabilities of bone marrow cells, which we now know is the source of the different types of blood cells2. In their experiments, they exposed mice to radiation to disable their bone marrow from being able to make functional blood cells. After the radiation treatment, they were injected with bone marrow cells from healthy mice. These single-source injected cells produced colonies that contained the three different lineages of blood cell types: 1) erythrocytic, which produce red blood cells; 2) granulocytic, which produce white blood cells; and 3) megakaryocytic, which produce platelets 3. These experiments proved that one type of cell, a stem cell, can become many other types of cells. This work was instrumental in developing the earliest, and currently still the most successful, type of stem cell therapy available: the bone marrow transplant. This treatment is used to treat leukemia, where radiation is used to disable the cancerous bone marrow of the patient and then replaced with healthy bone marrow from a donor.
Even though the functional discovery of stem cells occurred in the 60s, it wasn’t until the 80s before scientists identified embryonic stem cells. Embryonic stem cells are the most versatile stem cell because they have the innate ability to turn into all the different cell types required to build an organism. This trait is called pluripotency and is what makes them so attractive to scientists. Imagine being able to build any tissue from scratch! Studying embryonic stem cells is not only useful for building tissue, but also for understanding how our individual parts develop and work together to become a functional, conscious being. However, global ethical concerns surrounding work with embryonic stem cells inspired scientists to look for alternative techniques to mimic embryonic stem cell behaviour.
Now, just over a decade after their discovery, there are over 6000 scientific publications that have used iPSCs. Access to pluripotent stem cells are important when studying organ development and disease progression; however, there is another category of stem cells that are just as important. They are adult stem cells and everybody has them! Although they can turn in many different cell types, they are limited with the variety of cells they can become and thus are called multipotent. Adult stem cells are present in nearly all the organs and tissues of the body and are responsible for their natural turnover and repair6. As previously mentioned, bone marrow is a source of stem cells. In fact, there are two different types of adult stem cells present in bone marrow: mesenchymal stem cells and hematopoietic stem cells. Mesenchymal stem cells maintain one’s fat, bone, and cartilage tissue whereas hematopoietic stem cells are the source for the many different blood cell types. Adult stem cells in the brain are responsible for memory and both hair and skin cells come from the same stem cell source.
The fascinating discovery of stem cells has propelled the biomedical field forward. It allows scientists to study and better understand how our body grows, functions, and heals itself. This knowledge is important when figuring out how diseases develop and progress. Currently, scientists and engineers are working together using both stem cells and 3D printing, to build healthy new tissues using the patient’s own tissue as the source of cells. Hopefully one day, scientists and physicians will be able to replace diseased tissue with healthy lab grown tissue. For now, much of this research is still in early developmental stages and requires funding and support to keep progressing forward safely.
Ingenious scientists and engineers from many different fields are working together to improve 3D printing for tissue engineering. The next frontier for 3D printing in the tissue engineering field would be to print using living cells to custom-made functional organs. Science isn’t there yet, so if you haven’t already, please consider being a organ donor in your area, because it is the only option available now for those in need. Hopefully one day, it won’t be.
References/More Information
Ramalho-Santos M and Willenbring H. On the Origin of the Term “Stem Cell”. Cell Stem Cell 2007 1(1); 35-38. .
Vieira G. Q & A: James Till on the Discovery of Stem Cells. Maclean’s 26 March 2012. 26 Mar 2012.
Becker AJ, McCulloch EA, and Till JE. Cytological demonstration of the clonal nature of spleen colonies derived from transplanted mouse marrow cells. Nature 1963; 197(4866): 452-454.
Shinya Yamanaka. Nobel Prize Organization.
Takahashi K and Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell 2006; 126: 663-676.
Types of Stem Cells. International Society for Stem Cell Research.