Adult Stem Cells (ASCs):
ASCs are undifferentiated cells found living within specific differentiated tissues in our bodies that can renew themselves or generate new cells that can replenish dead or damaged tissue. You may also see the term “somatic stem cell” used to refer to adult stem cells. The term “somatic” refers to non-reproductive cells in the body (eggs or sperm). ASCs are typically scarce in native tissues which have rendered them difficult to study and extract for research purposes.
Resident in most tissues of the human body, discrete populations of ASCs generate cells to replace those that are lost through normal repair, disease, or injury. ASCs are found throughout ones lifetime in tissues such as the umbilical cord, placenta, bone marrow, muscle, brain, fat tissue, skin, gut, etc. The first ASCs were extracted and used for blood production in 1948. This procedure was expanded in 1968 when the first adult bone marrow cells were used in clinical therapies for blood disease.
Studies proving the specificity of developing ASCs are controversial; some showing that ASCs can only generate the cell types of their resident tissue whereas others have shown that ASCs may be able to generate other tissue types than those they reside in. More studies are necessary to confirm the dispute.
Types of Adult Stem Cells:
- Hematopoietic Stem Cells (Blood Stem Cells)
- Mesenchymal Stem Cells
- Neural Stem Cells
- Epithelial Stem Cells
- Skin Stem Cells
Embryonic Stem Cells (ESCs):
During days 3-5 following fertilization and prior to implantation, the embryo (at this stage, called a blastocyst), contains an inner cell mass that is capable of generating all the specialized tissues that make up the human body. ESCs are derived from the inner cell mass of an embryo that has been fertilized in vitro and donated for research purposes following informed consent. ESCs are not derived from eggs fertilized in a woman’s body.
These pluripotent stem cells have the potential to become almost any cell type and are only found during the first stages of development. Scientists hope to understand how these cells differentiate during development. As we begin to understand these developmental processes we may be able to apply them to stem cells grown in vitro and potentially regrow cells such as nerve, skin, intestine, liver, etc for transplantation.
Induced Pluripotent Stem Cells (iPSCs)
Induced pluripotent stem cells are stem cells that are created in the laboratory, a happy medium between adult stem cells and embryonic stem cells. iPSCs are created through the introduction of embryonic genes into a somatic cell (a skin cell for example) that cause it to revert back to a “stem cell like” state. These cells, like ESCs are considered pluripotent Discovered in 2007, this method of genetic reprogramming to create embryonic like cells, is novel and needs many more years of research before use in clinical therapies.