Embryonic versus Adult Stem Cells
What is an embryo? An embryo is formed within 5 days after an egg is fertilized by a sperm cell. Embryonic stem cells at this very early stage contain all the material necessary for the complete development of a human being. This is truly a marvel of the human body!
As the cells multiply the inner mass of cells will become the developing embryo, and the outer cells the placenta. When used for research, it is most often the embryo cells that are used.
Embryonic cells are very specialized cells that are:
1. Pluripotent – meaning they can give rise to every cell in the body
2. Undifferentiated – have not developed into a specialized cell line
3. Capable of replicating indefinitely in the right lab conditions
The upside is that just a few cells can produce millions of cells for research. The downside is that they cannot be transplanted into a human without the potential risk of developing a tumor. This is because they have not yet gone through what we call the differentiation process – the cells are signaled as they normally would be, under normal developmental conditions in utero, to form some type of specialized cell.
In 1998, a group of scientists at the University of Wisconsin successfully isolated embryonic stem cells.
Since that time, scientists also have been deciphering the code of growth factors and other chemical signals within the body that trigger cells to differentiate. Unlocking this code will unlock greater potential and targeted therapies that can selectively turn on stem cells to regenerate the desired target cells – cartilage cells, muscle cells, etc.
Think of embryonic cells as a dorm full of students with undeclared majors. They still need a bit more help to make up their minds regarding their future fate!
There are ethical debates for obvious reasons, and beyond the scope of this guide, as to the use of embryonic cells, even if donated unused embryos from in vitro fertilization (IVF) clinics.
Adult stem cells are not just from adult-age humans, but essentially given that name from the time of a live birth through adult age.
Adult stem cells are also very specialized cells that can be:
1. Pluripotent – Once differentiated can give rise to any cell in the body
2. Mesenchymal stem cells (MSCs)– can produce more than one type of specialized cell in the body, but not all types
In stem cell therapy for Orthopedic applications, we are looking for MSCs that can be signaled by the body’s internal chemical signals to differentiate into cells and form new cartilage, bone, muscle, ligament and tendon tissue for repair and regeneration of injured tissue.
Let us go one level deeper, and then we will depart from the depths of cell biology!
In an attempt to standardize the definition of an MSC, the International Society for Cellular Therapy (ISCT) proposed the concept of essential minimal criteria for MSCs in culture as follows:
• They must adhere to plastic under standard tissue culture conditions
• They must express surface markers of CD105, CD73, CD90
• They must lack expression of CD45, CD34, CD14/CD11b, CD79/CD19 and HLA-DR surface markers
• They can differentiate into adipocytes (fat cells), osteoblasts (bone cells) and chondroblasts (cartilage cells) in vitro
So then, for the purpose of this guide, and our discussion regarding the Orthopedic application of stem cells, an ideal candidate cell for stem cell therapy would have the following properties:
1. Be an adult mesenchymal stem cell (MSC)
2. Express appropriate surface markers (CD105, CD73, CD90) that identify it as a stem cell
3. Have the ability to differentiate into the musculoskeletal tissues we aim to treat
The richest, most-plentiful, and most easily accessible supply of cells that meet these criteria are found within your bone marrow – the hollow channels within the big bones of your body such as the ilium (pelvic bone). More on how exactly we extract those cells later in the guide. (It’s not as painful as you may be thinking!)
Ok. That is as deep as we are going to go with the science in this guide.
Over the past decade, the use of stem cells, as a targeted therapy or treatment, has expanded beyond cancer treatment.
In the Orthopedic setting for injuries and damage to bone, cartilage, muscles, tendons, and ligaments – stem cell therapy has been done in the United States since 2007.
Stem cells in this application have shown the ability to repair and regenerate damaged tissue through a process of differentiation specifically that allows a stem cell to regenerate:
• Bone (osteocyte)
• Tendon (tenocyte)
• Ligament (fibroblast)
• Muscle (myocyte)
• Cartilage (chondrocyte)
When the MSCs are introduced into the environment of the injured tissue being treated, natural chemical signals generated by the damaged cells communicate and direct the stem cells how to differentiate.
With regeneration by thousands to millions of cells, non-healing injured tissue has the capacity to repair, regain strength and function, and become more resilient to ongoing demand and/or further damage.
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