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What is a Stem Cell?

The human body is comprised of approximately 200 different cell types1. From skin cells to muscle cells, to red blood cells. These cells originate, in the case of the human body, from one original cell called the zygote. The zygote has the potential to differentiate into the variety of cells that make up the adult human body, acting as a sort of stem cell for the growth of the entire organism. There are many different types of stem cells that exist, and each has a different role in the body2.

 

WHAT IS A STEM CELL?

Stem cells are a specialized type of cell that must meet two important criteria. First, they must possess the ability to differentiate into multiple types of cells. In the case of hematopoietic stem cells, these cell types can differentiate into the range of cells that contribute to the bone marrow and blood. Second, these stem cells must possess a “self-renewal” capacity. This means that in addition to the variety of daughter cells they produce, it must replicate itself as well to maintain what is referred to as the “stem cell pool” (FIGURE 1). While the exact defining characteristics of a stem cell is still hotly debated, a variety of experimental techniques can be used by researchers to test whether a proposed cell type meets these criteria, and therefore can be considered a stem cell2,3.

Figure 1: Stems cells must possess two essential characteristics.

WHAT DOES A STEM CELL DO?

Many types of stem cells exist. These include the stem cells that produce our blood and its components, HSC, as well as stem cells that produce connective tissue, MSCs. These stem cells can reside in many parts of the body, including bone marrow, and fat (adipose), respectively.

The function of a stem cell in development is different than in an adult. In development, the stem cells’ role is to produce the variety of cells necessary for a fully-functioning organism. During this time, stem cells are active and plentiful. In adults, however, stem cells may serve a different purpose. There are much less of them, and they are relatively dormant. In the event of a stimulus such as an injury, these stem cells can respond, become “activated”, and re-enter their earlier proliferation and division activities. This activity aims to repair the damaged tissue(s) and promote healing. This makes them a very good candidate for the practice of regenerative medicine4.

 

HOW DO WE USE STEM CELLS?

Since stem cells exist normally in our bodies, we can harvest and employ them for therapeutic benefit. However, the research about what stem cells can be used for, and where we can use them is still in its early stages. Therefore, while stem cells hold a huge potential for future therapies, they are currently only employed where they have been proven to be both SAFE and EFFECTIVE. The studies used to determine HOW and WHERE we can use these cells are called Clinical Trials. These trials are rigorously reviewed to ensure that the therapy studied will not be harmful and will be more effective than the current standard of care.

Currently, stem cells can be used to aid in the normal healing process our body undertakes. Since adults generally have fewer stem cells than during development, the addition of stem cells to damaged tissues has shown to have a positive impact on healing. Generally, treatments that introduce stem cells (from a variety of sources) can increase the body’s ability to regenerate and heal. If this is a therapy you may be interested in, it is important to discuss with your doctor the aspects of your condition to see if it will be right for you. Treatments like PRP or stem cell therapies utilize these types of cells and may provide a benefit for a variety of conditions.

 

  1. Bianconi, E. et al.An estimation of the number of cells in the human body. Annals of Human Bioogy40,463–471 (2013).
  2. Alvarez, C. V. et al.Defining stem cell types: understanding the therapeutic potential of ESCs, ASCs, and iPS cells. Journal of Molecular Endocrinology49,R89–R111 (2012).
  3. Graf, T. & Enver, T. Forcing cells to change lineages. Nature462,587–594 (2009).
  4. Hoggatt, J., Kfoury, Y. & Scadden, D. T. Hematopoietic Stem Cell Niche in Health and Disease. Annu Rev Pathol11,555–581 (2016)

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