Types of Stem Cells

A brief look at the different types of Stem Cells and their comparisons. You can click on the image for a larger view

The ISSCR has published a large list of the various TYPES of stem cells, and it warrants a closer look at them to develop a deeper understanding of what they are.

1. Adult Stem Cells or Tissue-specific Stem Cells

Many adult tissues contain stem cells that can replace cells that die or restore tissue after injury. Skin, muscle, intestine and bone marrow, for example, each contain their own stem cells. In the bone marrow, billions of new blood cells are made every day from blood-forming stem cells.
Adult stem cells are tissue-specific, meaning they are found in a given tissue in our bodies and generate the mature cell types within that particular tissue or organ. It is not clear whether all organs, such as the heart, contain stem cells. The term ‘adult stem cells’ is often used very broadly and may include fetal and cord blood stem cells.
There are a few stem cell therapies that are widely accepted by the medical community and these use tissue-specific stem cells. These are bone marrow or cord blood stem cell transplantation to treat diseases and conditions of the blood or to restore the blood system after treatment for specific cancers, skin stem cell therapies for burns and limbal stem cells for corneal replacement. In each case, the stem cells repair the same tissue from which they came.
Another type of adult stem cell is the mesenchymal stem cell. These are found in a number of tissues, including bone marrow, and may be able to produce bone, cartilage and fat. It is also possible that these or similar cells may aid in the regeneration of tissues. Extensive animal studies are currently ongoing to determine if these cells may be used for treatment of diseases such as arthritis and non-healing bone fractures. It is also possible that these or similar cells modulate the immune system in response to injury.

2. Fetal Stem Cells

As their name suggests, fetal stem cells are taken from the fetus. The developing baby is referred to as a fetus from approximately 10 weeks of gestation. Most tissues in a fetus contain stem cells that drive the rapid growth and development of the organs. Like adult stem cells, fetal stem cells are generally tissue-specific, and generate the mature cell types within the particular tissue or organ in which they are found.

3. Cord Blood Stem Cells

At birth the blood in the umbilical cord is rich in blood-forming stem cells. The applications of cord blood are similar to those of adult bone marrow and are currently used to treat diseases and conditions of the blood or to restore the blood system after treatment for specific cancers. Like the stem cells in adult bone marrow, cord blood stem cells are tissue-specific.

4. Embryonic Stem Cells

Embryonic stem cells are derived from very early embryos and can in theory give rise to all cell types in the body. However, coaxing these cells to become a particular cell type in the laboratory is not trivial. Furthermore, embryonic stem cells carry the risk of transforming into cancerous tissue after transplantation. To be used in cell transplant treatments the cells will most likely need to be directed into a more mature cell type, both to be therapeutically effective and to minimize risk that cancers develop. While these cells are already helping us better understand diseases and hold enormous promise for future therapies, there are currently no treatments using embryonic stem cells accepted by the medical community.

5. Induced Pluripotent Stem Cells (iPS cells)

In 2006, scientists discovered how to “reprogram” cells with a specialized function (for example, skin cells) in the laboratory, so that they behave like an embryonic stem cell. These cells, called induced pluripotent cells or iPS cells, are created by inducing the specialized cells to express genes that are normally made in embryonic stem cells and that control how the cell functions. Embryonic stem cells and iPS cells share many characteristics, including the ability become the cells of all organs and tissues, but they are not identical and can sometimes behave slightly differently. IPS cells are a powerful method for creating patient- and disease-specific cell lines for research. However, the techniques used to make them need to be carefully refined before they can be used to generate iPS cells suitable for safe and effective therapies.

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
Stem Cell Information

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:
1. determining precisely how stem cells remain unspecialized and self renewing for many years;
and
2. identifying the signals that cause stem cells to become specialized cells.

The International Society for Stem Cell Research lists out several types of Stem Cells. Look for that in our next post. 

Source: National Institutes of Health

Stem Cells - The Basics

Stem cells have the remarkable potential to develop into many different cell types in the body. Serving as a sort of repair system for the body, they can theoretically divide without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.

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.

We will take you dear readers through various topics related to Stem Cells to 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?

Source: http://stemcells.nih.gov