Definition
While the terms Mesenchymal Stem Cell and Marrow Stromal Cell have been used interchangeably, neither term is sufficiently descriptive as discussed below:
- Mesenchyme is embryonic connective tissue that is derived from the mesoderm and that differentiates into hematopoietic and connective tissue, whereas MSCs do not differentiate into hematopoietic cells.
- Stromal cells are connective tissue cells that form the supportive structure in which the functional cells of the tissue reside. While this is an accurate description for one function of MSCs, the term fails to convey the relatively recently-discovered roles of MSCs in the repair of tissue.
- Because the cells, called MSCs by many labs today, can encompass multipotent cells derived from other non-marrow tissues, such as umbilical cord blood, adipose tissue, adult muscle, corneal stroma or the dental pulp of deciduous baby teeth, yet do not have the capacity to reconstitute an entire organ, the term Multipotent Stromal Cell has been proposed as a better replacement.
The youngest, most primitive MSCs can be obtained from the umbilical cord tissue, namely Wharton's jelly and the umbilical cord blood. However the MSCs are found in much higher concentration in the Wharton’s jelly compared to the umbilical cord blood, which is a rich source of hematopoietic stem cells. The umbilical cord is easily obtained after the birth of the newborn, is normally thrown away and poses no risk for collection. The umbilical cord MSCs have more primitive properties than other adult MSCs obtained later in life, which might make them a useful source of MSCs for clinical applications.
An extremely rich source for mesenchymal stem cells is the developing tooth bud of the mandibular third molar. While considered multipotent, they may prove to be pluripotent. The stem cells eventually form enamel, dentin, blood vessels, dental pulp, nervous tissues, including a minimum of 29 different unique end organs. Because of extreme ease in collection at 8–10 years of age before calcification and minimal to no morbidity they will probably constitute a major source for personal banking, research and multiple therapies. These stem cells have been shown capable of producing hepatocytes. Additionally, amniotic fluid has been shown to be a very rich source of stem cells. As many as 1 in 100 cells collected from and genetic amniocentesis has been shown to be a pluripotent mesenchymal stem cell.
Adipose tissue is one of the richest sources of MSCs. When compared to bone marrow, there is more than 500 times more stem cells in 1 gram of fat when compared to 1 gram of aspirated bone marrow. Adipose stem cells are currently actively being researched in clinical trials for treatment in a variety of diseases.
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