Stem Cell Research FAQs
- A glossary of terms.
Stem cells are unspecialized cells that act as a precursor to specific cells and are able to self-renew. They are unspecialized because they do not perform a tissue-specific function, such as carrying oxygen in the bloodstream or sending and receiving signals in the brain. Instead, they are important for generating specialized cells and helping to repair tissue. There are six types of stem cells frequently referred to in the scientific literature:
Adult stem cells are found in many organs including the brain, heart, liver, bone marrow and skin but have limited self-renewal capacity. They have been successfully used for therapy in the organs from which they were originally derived. Bone marrow transplants are an example of the life-saving capabilities of adult stem cells (See successful clinical applications below).
Embryonic stem (ES) cells are derived from pre-implantation embryos that were created through in vitro fertilization. They are pluripotent, meaning they can differentiate into almost any type of cell in the body.
Nuclear transfer (NT)-ES cells were developed using human cells in 2013. These are stem cells created by taking the DNA from a somatic cell and using it to replace the genetic material in an egg cell.
Induced human pluripotent stem (iPS) cells were first developed in 2007. These are adult cells that have been genetically reprogrammed to an ES cell-like state. This is done by adding transcription factors or other molecules to the cells that changes what genes are expressed.
Amniotic stem cells were first isolated from amniotic fluid in 2007. In 2010, researchers converted amniotic fluid cells into pluripotent stem cells, which are similar to ES cells.
Stem cells derived from fetal tissue are also being researched. These stem cells are multipotent.
Adult stem cells are multipotent, which means that they can become only a limited number of types of tissues and cells in the body. ES cells have greater potential to treat a wider variety of diseases because they are pluripotent, which means that they can become almost any type of tissue or cell in the body.
Adult stem cells are found in small quantities in many organs, and scientists believe they do not have the same capacity to produce diverse tissues or multiply as ES cells. In addition, adult stem cells may have more genetic abnormalities, which occur during the aging process and with exposure to environmental factors.
In 2010, researchers converted amniotic fluid cells into pluripotent stem cells, which are very similar to ES cells, but they “remember” where they came from. Since they have this memory capacity, it is not yet clear how they will respond in medical treatment. Scientists suggest that both ES cells and amniotic stem cells should be used since they will likely be useful for different therapies, thus broadening the potential for these cells.
The first isolation of human ES cells was documented in 1998 by James Thomson, Ph.D. Federal funding for research on ES cells began in 2001 and was, until recently, limited to a small number of stem cell lines that many scientists deemed not suitable for research. A new treatment or cure can take many years to develop because scientists and doctors must ensure that it is effective and safe for patients. However, as described below, there have been promising clinical applications of stem cell research.
Adult stem cells from bone marrow are a great example of the long and arduous process of developing a new treatment or cure. Bone marrow was first identified as a possible treatment for leukemia in the early 20th century. The first bone marrow transplants, which involve replacement of the patient’s bone marrow stem cells with those from a healthy donor, were attempted in the late 1950s. At first, the only successful transplants were among identical twins. It took scientists a decade to discover how to perform transplants among siblings who were not identical twins, and it was not until 1973 that bone marrow from an unrelated donor was used successfully for a transplant.
More recently, several clinical trials have shown promising therapeutic applications of stem cells. Using ES cells, scientists generated retinal cells and transplanted them into individuals with macular degeneration. Studies in 2012 and 2014 concluded that the procedure was safe and improved vision in the majority of those treated.
There have been several clinical trials transplanting stem cells into the site of spinal cord injuries. Promising gains in sensory and motor function were seen in some of these patients and more clinical trials are underway. Both adult stem cells, from various sources such as the brain and lining of the nasal cavity, and ES cells have been tested in the treatment. The therapy is thought to work by replacing dead nerve cells as well as producing more support cells that spur axon re-growth and decrease inflammation.
Several studies have shown the potential of stem cells to treat heart disease. Transplantation of stem cells, with adult stem cells extracted from the patient’s heart or bone marrow, have helped regenerate heart tissue following a heart attack and open heart surgery. Clinical trials using this treatment are ongoing.
Promising work suggests stem cell therapy may one day be able to treat neurological disorders in humans, including ALS, Parkinson’s disease, and strokes. Preclinical studies show that transplanted ES cells can fully integrate in a brain and send and receive nerve signals.
Research!America believes that because adult, induced pluripotent, amniotic and embryonic stem cell research show great potential to treat and cure illness, all types of stem cell research should be pursued.
Adult stem cells
Undifferentiated cells that have the potential to become a limited number of specific cell types. These multipotent cells are found in small quantities in a large number of organs and tissue.
Amniotic stem cells
Cells found in the amniotic fluid that surrounds a fetus. They are not pluripotent like ES cells, but can be induced to become pluripotent. They can differentiate into more cell types than adult stem cells.
An embryo of 30 to 150 cells before uterine implantation. It is composed of an outer layer of cells that will become the placenta, a fluid-filled cavity and an inner cell mass.
The process by which stem cells acquire the features of specialized adult cells, such as those found in heart, brain and pancreatic tissue. Signals from both inside and outside the cell guide this process, determining which type of cell it becomes.
A medical term that refers to a group of cells that arise from a fertilized egg (after merging of egg and sperm). An embryo has the potential to become a complete organism. The embryonic stage ends at eight weeks of development.
Embryonic stem (ES) cells
Primitive (undifferentiated) cells that have the potential to become a wide variety of specialized cell types (i.e., cardiac myocytes, neuronal, pancreatic). They are pluripotent cells derived from the inner cell mass of a blastocyst. ES cells are not embryos and cannot become a complete organism.
Induced pluripotent stem cells (iPSCs)
Adult cells that have been genetically reprogrammed to an ES cell-like state.
In vitro fertilization (IVF)
An assisted reproduction technology in which fertilization (merging of sperm and egg) occurs outside the body.
Have the capacity to become a limited number of types of tissues and cells in the adult body.
Have the capacity to become many types of tissues and cells in the adult body.