Stem Cell Basics
- What are the unique properties of all stem cells?
- What are embryonic stem cells?
- What are adult stem cells?
- What are the similarities and differences between embryonic and adult stem cells?
- What are the potential uses of human stem cells and the obstacles that must be overcome before these potential uses will be realized?
- Where can I get more information?
Research on stem cells is advancing knowledge about how an organism develops from a single cell and how healthy cells replace damaged cells in adult organisms. This promising area of science is also leading scientists to investigate the possibility of cell-based therapies to treat disease, which is often referred to as regenerative or reparative medicine.
Stem cells are one of the most fascinating areas of biology today. But like many expanding fields of scientific inquiry, research on stem cells raises scientific questions as rapidly as it generates new discoveries.
The NIH developed this primer to help readers understand the answers to questions such as: What are stem cells? What different types of stem cells are there and where do they come from? What is the potential for new medical treatments using stem cells? What research is needed to make such treatments a reality?
A. What are stem cells and why are they important?
Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods through cell division. The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Scientists primarily work with two kinds of stem cells from animals and humans: embryonic stem cells and adult stem cells, which have different functions and characteristics that will be explained in this document. Scientists discovered ways to obtain or derive stem cells from early mouse embryos more than 20 years ago. Many years of detailed study of the biology of mouse stem cells led to the discovery, in 1998, of how to isolate stem cells from human embryos and grow the cells in the laboratory. These are called human embryonic stem cells. The embryos used in these studies were created for infertility purposes through in vitro fertilization procedures and when they were no longer needed for that purpose, they were donated for research with the informed consent of the donor.
Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old embryo, called a blastocyst, stem cells in developing tissues give rise to the multiple specialized cell types that make up the heart, lung, skin, and other tissues. In some adult tissues, such as bone marrow, muscle, and brain, discrete populations of adult stem cells generate replacements for cells that are lost through normal wear and tear, injury, or disease.
It has been hypothesized by scientists that stem cells may, at some point in the future, become the basis for treating diseases such as Parkinson's disease, diabetes, and heart disease.
Scientists want to study stem cells in the laboratory so they can learn about their essential properties and what makes them different from specialized cell types. As scientists learn more about stem cells, it may become possible to use the cells not just in cell-based therapies, but also for screening new drugs and toxins and understanding birth defects. However, as mentioned above, human embryonic stem cells have only been studied since 1998. Therefore, in order to develop such treatments scientists are intensively studying the fundamental properties of stem cells, which include:
- determining precisely how stem cells remain unspecialized and self renewing for many years; and
- identifying the signals that cause stem cells to become specialized cells.
B. Scope of this document
This primer on stem cells is intended for anyone who wishes to learn more about the biological properties of stem cells, the important questions about stem cells that are the focus of scientific research, and the potential use of stem cells in research and in treating disease. The primer includes information about stem cells derived from the embryo and adult. Much of the information included here is about stem cells derived from human tissues, but some studies of animal-derived stem cells are also described.