Stem cells in animals are primal undifferentiated cells that retain the ability to divide and differentiate into other cell types. In higher plants this function is the defining property of the meristematic cells. Stem cells have the ability to act as a repair system for the body, because they can divide and differentiate, replenishing other cells as long as the host organism is alive.

Medical researchers believe stem cell research has the potential to change the face of human disease by being used to repair specific tissues or to grow organs. Yet there is general agreement that, "significant technical hurdles remain that will only be overcome through years of intensive research."^[1]

The study of stem cells is attributed as beginning in the 1960s after research by Canadian scientists Ernest A. McCulloch and James E. Till.

Stem cells are categorized according to their source, as either adult, embryonic or cord blood stem cells.

Adult stem cells are undifferentiated cells found among differentiated cells of a specific tissue and are mostly multipotent cells. They are already being used in treatments for over one hundred diseases and conditions.

They are more accurately called somatic (Greek σωμα sōma = body) stem cells, because they need not come from adults but can also come from children or umbilical cords. Particularly interesting are adult stem cells termed "spore-like cells". They are present in all tissues^[2] and seem to survive long time periods and harsh conditions.

Embryonic stem cells are cultured cells obtained from the undifferentiated inner mass cells of an early stage human embryo (sometimes called a blastocyst, which is an embryo that is between 50 to 150 cells). Embryonic stem cell research is "thought to have much greater developmental potential than adult stem cells," according to the National Institutes of Health.^[3] Research using embryonic stem cells remains at the zenith of stem cell science because, unlike somatic cells, embryonic stem cells are totipotent. However, research using stem cells derived from the human embryo is still in the basic research phase, as these stem cells were first isolated in 1998 (at least for humans), whereas adult stem cells have been studied since the 1960s.^[4]

Research with embryonic stem cells derived from humans is controversial because, in order to start a stem cell 'line' or lineage, the destruction of a human embryo and/or therapeutic cloning is usually required. Some believe this to be a slippery slope to reproductive cloning and tantamount to the objectification of a potential human being. In an attempt to overcome these moral, political and ethical hurdles, medical researchers have been experimenting with alternative techniques of obtaining embryonic stem cells by extraction, which does not involve cloning and/or the destruction of a human embryo.

Cord blood stem cells are derived from the blood of the placenta and umbilical cord after birth. Since 1988 these cord blood stem cells have been used to treat Gunther's disease, Hunter syndrome, Hurler syndrome, Acute lymphocytic leukemia and many more problems occurring mostly in children.

Umbilical cord blood use has become so common that there are now umbilical cord blood banks that accept donations from parents. It is collected by removing the umbilical cord, cleansing it and withdrawing blood from the umbilical vein. This blood is then immediately analyzed for infectious agents and the tissue-type is determined. The cord blood is processed and depleted of red blood cells before being stored in liquid nitrogen for later use, at which point it is thawed, washed of the cryoprotectant, and injected through a vein of the patient. This kind of treatment, where the stem cells are collected from another donor, is called allogeneic treatment. When the cells are collected from the same patient on whom they will be used, it is called autologous and when collected from identical individuals (i.e. homozygous twin), it is referred to as syngeneic.

Stem cells are also categorized by potency, which specifies the ameliorative potential of the cell type.

• Totipotent stem cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg cell are also totipotent. These cells can grow into any type of cell without exception.

• Pluripotent stem cells are the descendants of totipotent cells and can grow into any cell type except for totipotent stem cells.

• Multipotent stem cells can produce only cells of a closely related family of cells (e.g. blood cells such as red blood cells, white blood cells and platelets).

• Unipotent cells can produce only one cell type, but have the property of self-renewal which distinguishes them from non-stem cells.

Widespread controversy exists over stem cell research, emanating from the techniques used in the cells' creation and use. In particular, research using human embryonic stem cells has proven to be an immensely sensitive topic. This is because, with current technology, starting a stem cell 'line' requires the destruction of a human embryo and/or therapeutic cloning. Opponents of the research argue that this practice is a slippery slope to reproductive cloning and tantamount to the objectification of a potential human being. Contrarily, medical researchers in the field argue that it is necessary to pursue embryonic stem cell research because the resultant technologies are expected to have significant medical potential. The ensuing debate has prompted national and international authorities to seek suitable regulatory frameworks and highlighted the fact that stem cell research represents a moral, social and ethical minefield.

Anti-abortion and ethics groups oppose such research because it results in human embryos being destroyed. The Coalition of Americans for Research Ethics argues the case like this: "The destruction of human embryonic life is unnecessary for medical progress, as alternative methods of obtaining human stem cells and of repairing and regenerating human tissue exist and continue to be developed." [1]

There is also a strong religious lobby opposing embryonic stem cell research. When the Pope visited George Bush , he told the US president that the work was as evil as infanticide, because obtaining the cells involves destroying early stage human embryos, and US Catholic bishops told him that the work is "illegal, immoral and unnecessary" [2]

In his 1995 encyclical The Gospel of Life, Pope John Paul II wrote: "Human embryos obtained in vitro are human beings and are subjects with rights; their dignity and right to life must be respected from the first moment of their existence. It is immoral to produce human embryos destined to be exploited as disposable 'biological material'" (1,5).

"Government must not treat any living human being as research material, as a mere means for benefit to others," wrote Bishop Fiorenza.

Finally, the debate has now prompted national and international authorities to seek suitable regulatory frameworks, and highlighted the fact that stem cell research represents a moral and political minefield. In an attempt to overcome these hurdles, medical researchers have been experimenting with alternative techniques of obtaining embryonic stem cells by extraction, which does not involve cloning and/or the destruction of a human embryo.

• Stem cell line
• Cellular differentiation
• Hwang Woo-Suk

• International Society for Cellular Therapy
• International Society for Stem Cell Research
• Progenitor Cell Therapy
• Video Archive: The Stem Cell Controversy
• Limb Regeneration

• Cytotherapy
• Cloning and Stem Cells
• Stem Cells and Development

1. Shostak S (2006). "(Re)defining stem cells". Bioessays. 28 (3): 301–8. PMID 16479584.

• Cells Limited Research, Processing & Storage of Stem Cells. Cord Blood & Bone Marrow Stem Cells.
• International Society for Stem Cell Research Stem cell information for the public from a global research society
• National Institutes of Health Guide
• Embryoperson Web site: Showing that the human embryo is a person, and distinguishing between a sick embryo and a pseudo-embryo
• A Guide to the Benefits, Responsibilities and Opportunities of Embryonic Stem Cell Research, from the British-North American Committee
• Harvard College Stem Cell Society A student organization dedicated to advancing stem cell research by "raising awareness and promoting education".
• Virtual Stem Cell Laboratory Cause cells to differentiate and learn about stem cell research through this interactive feature.
• [3] Stem cells science & ethics from the stem cell research program of the University of California, San Diego. Large multimedia gallery of stem cells and public presentations.

• Cell Therapy News.
• Do No Harm: The Coalition of Americans for Research Ethics
• Congressional Research Service (CRS) Reports regarding Stem Cell Research
• Stem Cells & Cloning Club (SCCC) - online community dedicated to the provision and discussion of information related to stem cell, cloning and cell therapy research; news, articles, interviews, business, discussion and more....
• Stem cell Research - Biology News Net.
• Stem Cell Research Blog - updated daily with latest stem cell news.
• Latest Advances In Stem Cell Research.
• New Scientist's list of stem-cell and cloning related articles it has covered.
• Stem Cell News.
• Latest cell therapy progress.
• Stem Cell Research