Human stem cells are cells found in most multi-cellular organisms. Human stem cells are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types.
Human stem cells come in three general types: embryonic stem cells, adult stem cells, and induced pluripotent stem cells. Embryonic stem cells are a primitive type of cell that can be coaxed into developing into any of the 220 types of cells found in the human body (e.g. blood cells, heart cells, brain cells, nerve cells, etc). Meanwhile, adult stem cells have some similarities to embryonic stem cells. Unfortunately, they are limited in flexibility, and are only capable of developing into a few of the cell types.
Induced pluripotent stem cells are human stem cells that are specially treated ordinary cells — e.g. skin cells — that are specially processed to exhibit some of the properties of embryonic stem cells. The process in this area seems to offer the advantages of embryonic stem cells without the ethical and rejection problems.
Human stem cells can now be grown and transformed into specialized cells with consistent characteristics with cells of various tissues such as muscles or nerves through cell culture. Highly plastic adult stem cells from a variety of sources, including umbilical cord blood and bone marrow, are routinely used in medical therapies. Embryonic cell lines and autologous embryonic stem cells generated through therapeutic cloning have also been proposed as promising candidates for future therapies.
Human stem cells are seen by many researchers as having virtually unlimited application in the treatment and cure of many human diseases and disorders including Alzheimer’s, diabetes, cancer, strokes, etc.
There are many ways in which human stem cells can be used in research and the clinic. Studies of human embryonic stem cells will yield information about the complex events that occur during human development. A primary goal of this work is to identify how undifferentiated stem cells become the differentiated cells that form the tissues and organs.
Human stem cells could also be used to test new drugs. For example, new medications could be tested for safety on differentiated cells generated from human pluripotent cell lines. Other kinds of cell lines are already used in this way. Cancer cell lines, for example, are used to screen potential anti-tumor drugs.
The most important potential application of human stem cells is the generation of cells and tissues that could be used for cell-based therapies. Today, donated organs and tissues are often used to replace ailing or destroyed tissue, but the need for transplantable tissues and organs far outweighs the available supply.
However, there are dangers associated with human stem cells. For example, the ability of stem cells to divide might not be readily harnessed after transplantation; in other words they may continue to grow unabated and form tumors. Other possible negative reactions include the chance that transplanted stem cells might differentiate into the wrong type of tissue, or that they may be rejected by the recipient’s immune system.
That is why, in the minds of many people, destroying a human embryo, even at very early post-conception ages, is intrinsically immoral. As a result, the ability to do the same in humans is far from being a certainty.
