Many have heard of the two primary types of stem cells: adult stem cells and embryonic stem cells. These two types of stem cells are classified based off of their source. Though common, this is a limiting classification because not every stem cell is an adult or embryonic stem cell. Stem cells can actually be classified further based on their differentiation potential.
For a quick refresher, stem cells are a naturally occurring group of cells found in both the developing and adult human body. They are undifferentiated cells that can differentiate into any of the more than 200 different cell types in our body. There are many different types of stem cells and they are the foundation for every organ and tissue.
In a previous blog, we discussed the very basics of stem cells and their application in stem cell therapy. We only talked about adult stem cells and embryonic stem cells, as those two types of stem cells are widely used in research and stem cell therapy. Stem cells are traditionally classified by their ability to differentiate into various cell types. The five types of stem cells—on the basis of potential differentiation—are as follows:
Totipotent stem cells are the most powerful, as they can differentiate into any cell in the human body. A newly fertilized egg—also called a zygote—is an example of a totipotent stem cell, and these cells can generate an entire living organism. Around four days post-fertilization, these cells start differentiating into pluripotent stem cells.
Pluripotent stem cells are the next most powerful, as they have the ability to differentiate into almost all cell types. A popular example of pluripotent cells is embryonic stem cells. Other examples are cells that come from the three germ layers called the mesoderm, endoderm, and ectoderm germ layers. These layers of cells form as an embryo develops. These germ layers later differentiate to form tissues and organs in the human body.
Multipotent stem cells can differentiate into various types of cells, but are tissue-specific and do not develop into cells outside of their originating tissue. For example, a hematopoietic cell is a multipotent blood stem cell, and can only differentiate into several types of blood cells, but not other cell types like brain or bone cells.
Oligopotent stem cells are similar to multipotent stem cells in that they can differentiate into cells similar to them, but these stem cells have more limits. A good example would be a lymphoid stem cell which can be found in the diagram above. This cell can give rise to T and B cells, but not a myeloblast, a cell that can only originate from a myeloid stem cell.
The least potent stem cell is the unipotent stem cell because it can only differentiate into one cell type. An example is an adult muscle stem cell that can self-renew if damaged, but cannot differentiate into any other cell type.
Click on the links below to learn more about stem cells: