Stem cells

 

 

Cord blood processing and cryopreservation (Cryo-Save Group)

Cells that have the ability to self-replicate and give rise to specialized cells. Stem cells can be found at different stages of fetal development and are present in a wide range of adult tissues. Many of the terms used to distinguish stem cells are based on their origins and the cell types of their progeny.
There are three basic types of stem cells. Totipotent stem cells, meaning their potential is total, have the capacity to give rise to every cell type of the body and to form an entire organism. Pluripotent stem cells, such as embryonic stem cells, are capable of generating virtually all cell types of the body but are unable to form a functioning organism. Multipotent stem cells can give rise only to a limited number of cell types. For example, adult stem cells, also called organ- or tissue-specific stem cells, are multipotent stem cells found in specialized organs and tissues after birth. Their primary function is to replenish cells lost from normal turnover or disease in the specific organs and tissues in which they are found.

Totipotent stem cells occur at the earliest stage of embryonic development. The first differentiation of totipotent cells forms a hollow sphere of cells called the blastocyst, which has an outer layer of cells and an inner cell mass inside the sphere. The outer layer of cells will form the placenta and other supporting tissues during fetal development, whereas cells of the inner cell mass go on to form all three primary germ layers: ectoderm, mesoderm, and endoderm.

Mesenchymal stem cell culture (Source: LSG)

Adult stem cells occur in mature tissues. Like all stem cells, adult stem cells can self-replicate. Their ability to self-renew can last throughout the lifetime of individual organisms. But unlike embryonic stem cells, it is usually difficult to expand adult stem cells in culture. Adult stem cells reside in specific organs and tissues, but account for a very small number of the cells in tissues. They are responsible for maintaining a stable state of the specialized tissues. To replace lost cells, stem cells typically generate intermediate cells called precursor or progenitor cells, which are no longer capable of self-renewal. However, they continue undergoing cell divisions, coupled with maturation, to yield fully specialized cells. Such stem cells have been identified in many types of adult tissues, including bone marrow, blood, skin, gastrointestinal tract, dental pulp, retina of the eye, skeletal muscle, liver, pancreas, and brain.

SEM image of H1 human ES cells (© IBMT)

 

Blood stem cells, or hematopoietic stem cells, are the most studied type of adult stem cells. The concept of hematopoietic stem cells is not new, since it has been long realized that mature blood cells are constantly lost and destroyed. Billions of new blood cells are produced each day to make up the loss. This process of blood cell generation called hematopoiesis, occurs largely in the bone marrow. Another emerging source of blood stem cells is human umbilical cord blood. Similar to bone marrow, umbilical cord blood can be used as a source material of stem cells for transplant therapy. However, because of the limited number of stem cells in umbilical cord blood, most of the procedures are performed for young children of relatively low body weight.

 

Learn more about stem cells here