Stem cells are cells found in all multi cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiate into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian scientists Ernest A. McCulloch and James E. Till in the 1960s. The two broad types of mammalian stem cells are: embryonic stem cells that are isolated from the inner cell mass of blastocysts, and adult stem cells that are found in adult tissues. In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing specialized cells, but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues.

Stem cells can now be grown and transformed into specialized cells with characteristics consistent 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.

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. Stem cells come in three general types:
bullet 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). In the past, they have always been derived from human embryos in a process that causes the death of the embryos. However, new research is developing techniques to convert skin cells into Induced Pluripotent Stem Cells (iPS cells) that emulate embryonic stem cells.

Adult stem cells bear some similarities to embryonic stem cells. Research using adult cells has a two decade head start on embryonic stem cells. Thus, potential treatments have already advanced to human trial stage. Unfortunately, adult cells are limited in flexibility, and are only capable of developing into a few of the cell types.

Induced pluripotent stem cells are specially treated ordinary cells -- e.g. skin cells -- that are specially processed to exhibit some of the properties of embryonic stem cells. Research in this area is just beginning. However the process seems to offer the advantages of embryonic stem cells without the ethical and rejection problems.

Many pro-lifers believe that human life, in the form of an ovum and spermatozoon, becomes a human person at the time of fertilization. They view the killing of any embryo in order to extract its stem cells to be a form of homicide. They are generally opposed to such research. Others disagree. They believe that an embryo has the potential to develop into a person, but is not a person itself. They note that an embryo is not sentient; it has no brain, sensory organs, ability to think, memory, awareness of its surroundings, consciousness, internal organs, arms, legs, head, etc. They feel that research using stem cells derived from embryos is ethical. Fortunately, if iPS cell technology develops as expected, it will eventually replace the need to derive stem cells from embryos.



President Obama signed an order reversing the Bush administration's strict limits on human embryonic stem cell research.

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