What are Stem Cells
Dennis M. Lox M.D.
Stem cells are often misunderstood. Quite simply they are normal cells in every one of us. They serve important functions for normal everyday repair and body maintenance. To begin mammals possess three broad categories of stem cells. Embryonic, umbilical cord, and adult stem cells.
Embryonic stem cells can form virtually any tissue type. This is where a lot of early controversy existed and still persists. Research has been limited in many countries for religious and political reasons. Embryonic stem cells are both good and bad. The ability to form any tissue type can be ideal for use in a variety of settings to aid in research and medical breakthroughs. However, the ability to create any tissue type carries the down side of lack of control. The new tissue formed may be undesirable tissue such as neoplasms (cancer).
Umbilical cord cells are really day one adult cells. This means they are young and may have more utility in several clinical settings, as compared to a 20 year old stem cell or a 90 year old stem cell. Each time the stem cell divides some changes may occur and the effectiveness of a stem cell may be less effective. This is true of all cells.
Adult stem cells may divide to create more stem cells and this process may continue almost indefinitely outliving our own body cells. This process of cell dying is part of normal life and ultimately the aging process. Stem cells may also differentiate into other tissue cell types in adult stem cells. Tissue cells are present in every body system. In the heart and muscle these cells known as myocytes. Brain and the nervous system have neurons. Cartilage cells are called chondrocytes, while bone cells are known as osteocytes. Each cell in our body is surrounded by an environment known as the matrix. This is what gives tissue its inherent appearance and characteristics such as skin or bone.
Stem cells are important in the maintenance of the health of each tissue cell. This may be through chemical signaling molecules which direct cell health, or by differentiating into a new tissue cell. Adult stem cells are undifferentiated cells that can only form certain cells.
Hematopoietic stem cells form new blood cells, while mesenchymal stem cells form bone, cartilage, muscle, and fat (adipose cells).
Adult stem cells may undergo partial differentiation to become precursor cells. Not quite the tissue type, yet nearby to become a tissue cell if needed.
This is an important aspect of aging and medical research. As we age there are less stem cells available to body tissues to assist in repair. Skin, the walls of the gastrointestinal tract, and the reproductive tract need a rich supply of stem cells and continue to have such compared to other body areas as we age.
In adults there are three primary sources of larger quantities of stem cells. These include the bone marrow, the adipose tissue, and the peripheral blood. The peripheral blood has few stem cells per quantity of blood, and therefore special harvesting techniques such as apheresis are needed to concentrate the number of stem cells from a large quantity of blood.
Bone marrow has been used since the 1960's to obtain stem cells in bone marrow transplants. These early methods were crude and resulted in not just stem cell transplantation, but tissue from the donor as well. This required the use of harsh immune suppressive drugs to prevent graft rejection. Isolated more select bone marrow stem cells and concentrating them has led to the use of the patients own stem cells (autologous).
Adipose tissue has larger quantities of stem cells compared to bone marrow or peripheral blood This is a function of available storage. The peripheral blood stream and bone marrow are closed systems, allowing only so much volume to be contained. Humans have a tremendous capacity to store new fat cells, thus the requirement for more more fat precursor cells and stem cells.
Adult stem cells in clinics and research today may involve the patients own stem cells (autologous) or another persons stem cells (allogenic). These cells are often grown in laboratory culture to much greater numbers for clinical and research use.
New frontiers to evade the use of embryonic stem cells has included the Induced pluripotent stem cell (IPS). These IPS cells can be easily obtainable skin stem cells which are programmed to go back to becoming a stem cell. This allows research without the controversy of using embryos. This retains the ability of becoming any cell type, yet at the same time lacks the controllability if adult stem cells in that IPS may become cancerous.
The future of stem cells is immense. Today we are creating entire body organs such as kidneys with 3-D printers. The current technology may seem scientific fiction, yet it is as real as automated self directing cars. The problem is how to implement and carry forward not just safely, but practically with cost and insurance coverage for these technological breakthroughs.
We put a man on the moon in 1969. We can do as much with stem cells given the advancements in computer technology. Stem cells are not some mystery or magical cell. They are with us when we are conceived to our elder adulthood. Using stem cells to our advantage to heal and repair cells is putting Mother Nature to good use.