Stem cells have the remarkable potential to develop into many different cell types in the body during early life and growth. In addition, in many tissues they serve as a sort of internal repair system, dividing essentially 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 either to 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.
Stem cells are distinguished from other cell types by two important characteristics. First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can be induced to become tissue- or organ-specific cells with special functions. In some organs, such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues. In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions.
Stem cells differ from other kinds of cells in the body. All stem cells—regardless of their source—have three general properties: they are capable of dividing and renewing themselves for long periods; they are unspecialized; and they can give rise to specialized cell types.
The two main stem cell types are embryonic stem cells (ES) cells and adult stem cells (i.e., somatic stem cells). Other types, such as induced pluripotent stem cells (iPSCs), are produced in the lab by reprogramming adult cells to express ES characteristics.
Embryonic stem cells are obtained from early-stage embryos — a group of cells that forms when a woman's egg is fertilized with a man's sperm in an in vitro fertilization clinic. Because human embryonic stem cells are extracted from human embryos, several questions and issues have been raised about the ethics of embryonic stem cell research.
The National Institutes of Health created guidelines for human stem cell research in 2009. Guidelines included defining embryonic stem cells and how they may be used in research and donation guidelines for embryonic stem cells. Also, guidelines stated embryonic stem cells may only be used from embryos created by in vitro fertilization when the embryo is no longer needed.
Adult stem cells are plentiful in bone marrow, cord blood and many other organs. In recent years there have been dozens of research reports of successful use of these in treatment of a variety of pathological conditions, e.g., diabetes. Such use is ethical and promises to be a great boon to mankind. Embryonic stem cells are obtained from four-day-old living human embryos. This tiny human is cut open and embryonic stem cells are extracted from him or her. The process directly kills a four-day-old human. Because of this direct killing, the method of “harvesting” these cells has been roundly condemned by traditional ethicists.
Advantages of Embryonic Stem Cells:
Some researchers claim that these cells are more primitive and therefore will more easily be grown into various organs.
They are available from surplus frozen IVF embryos.
They are so primitive that the host recipient will probably not reject them.
They are more “plastic” and easily (and as yet uncontrollably) grow wild into multi-organ tissues e.g. skin, bone, etc., in tumors.
They can carry virus infection from the donor humans, through their
original sperm or ovum.
They are another human’s tissue and can be rejected like other transplanted organs.
So far, unlike adult stem cells, there are almost no reports of their use for successful treatments.
The use of adult stem cells is ethical and beneficial. Obtaining and using embryonic stem cells is unethical, as it requires the direct killing of an innocent human in the so-far not realized hope of benefiting another.