Everything You Need to Know about Stem Cells

Get the facts about stem cells: what they are, where they come from, and why some stem cells are controversial. Find out what different types of stem cells exist.

Stem cells are undifferentiated or 'blank' cells found in the human body that have the potential to develop into many different cell types that carry out different functions. They are capable of developing into any of several types of cell, such as blood cells, bone cells, nerve cells, skin cells, etc. The definition of a stem cell is a cell with ability to reproduce itself indefinitely. Fully differentiated cells (non-stem cells) either cannot reproduce or can only reproduce a certain number of times.

Many different terms are used to describe various types of stem cells, often based on where in the body or what stage in development they come from. You may have heard the following terms:

• 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. 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. 
• Fetal Stem Cells
  Fetal stem cells - are taken from the germline tissues that will make up the gonads of aborted fetuses. 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.
• 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.
• 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.
• Induced Pluripotent Stem Cells (iPS cells)
  An induced pluripotent stem (iPS) cell is a cell taken from any tissue from a child or adult that has been genetically modified to behave like an embryonic stem cell. As the name implies, these cells are pluripotent, which means that they have the ability to form all adult cell types.

Our bodies use different types of tissue-specific stem cells to fit a particular purpose. Tissue-specific stem cells are limited in their potential and largely make the cell types found in the tissue from which they are derived. Thus, it is unlikely that a single cell type could be used to treat a multitude of unrelated diseases that involve different tissues or organs. 

Be wary of clinics that offer treatments with stem cells that originate from a part of the body that is different from the part being treated.