Stem cells are cells that have the ability to divide and develop into many different cell types in the body during early life and growth. Stem cells may also help repair the body by dividing to replenish cells that are damaged by disease, injury, or normal wear. When a stem cell divides, each new cell has the potential either to remain a stem cell or to become another type of cell with a more specialized function, such as a nerve cell, a skin cell, or a red blood cell.
Three types of stem cells have been identified:
1. adult stem cells
2. human embryonic stem cells
3. induced pluripotent stem cells
These three types of stem cells share properties:
- They are capable of surviving over long periods and divide to make additional stem cells.
- They are unspecialized (“blank slates” that can become specific types of cells).
- They can develop into specialized cell types (cells that do specific work in the body).
Adult stem cells can be found throughout the body. They are found as unspecialized cells among the specialized cells in tissues and organs as well as in umbilical cord blood and peripheral blood (that is, hematopoietic stem cells). An adult stem cell can either divide to make more adult stem cells, or differentiate to produce some or all of the major specialized cell types of the tissue or organ.
Human embryonic stem cells (hESC) come from embryos that develop from eggs that have been fertilized in vitro (in a test tube or another artificial environment). Embryonic stem cells can develop into any specialized cell type in the body.
Induced pluripotent stem cells (iPS) are generated by reprogramming adult cells that have already differentiated into a specific cell, such as a skin cell. After reprogramming, iPS cells are able to develop into any specialized cell type in the body.
Stem cells, like other medical products that are intended to treat, cure or prevent disease, generally require FDA approval before they can be marketed. FDA has not approved any stem cell-based products for use, other than cord blood-derived hematopoietic progenitor cells (blood forming stem cells) for certain indications.