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Stem cells are a class of undifferentiated cells that are able to become specialized cell types. They are sourced during a specific phase of the embryo’s development or from adult tissue. Once extracted, scientists place the cells in a controlled culture that prohibits them from further specializing or differentiating but usually allows them to divide and replicate. The process of growing large numbers of embryonic stem cells has been easier than growing large numbers of adult stem cells, but progress is being made for both cell types.

Once stem cells have been allowed to divide and propagate in a controlled culture, the collection of healthy, dividing, and undifferentiated cells is called a stem cell line. These stem cell lines are subsequently managed and shared among researchers. Once under control, the stem cells can be stimulated to specialize as directed by a researcher. This process is known as directed differentiation.

Scientists and researchers are interested in stem cells for several reasons. Although stem cells do not serve any one function, many have the capacity to serve any function after they are instructed to specialize. Embryonic stem cells are able to differentiate into more cell types than adult stem cells. Every cell in the body, for example, is derived from first few stem cells formed in the early stages of embryological development. Therefore, stem cells extracted from embryos can be induced to become any desired cell type. This property makes stem cells powerful enough to regenerate damaged tissue under the right conditions.

Applications of stem cell research

• Tissue regeneration: This is probably the most important possible application of stem cell research. Stem cells could potentially be used to grow a particular type of tissue or organ if directed to differentiate in a certain way. Stem cells that lie just beneath the skin, for example, have been used to engineer new skin tissue that can be grafted on to burn victims.
• Cardiovascular disease treatment: A team of researchers from Massachusetts General Hospital reported in PNAS Early Edition (July 2013 issue) that they were able to create blood vessels, using human stem cells, in laboratory mice. The scientists extracted vascular precursor cells derived from human-induced stem cells from one group of adults with type 1-diabetes as well as from another group of “healthy” adults. They were then implanted onto the surface of the brains of the mice. Within two weeks of implanting the stem cells, networks of blood vessels had been formed and lasted for 280 days. These new blood vessels were as good as the adjacent natural ones. The authors explained that using stem cells to repair or regenerate blood vessels could eventually help treat human patients with cardiovascular and vascular diseases.

• Brain disease treatment: Additionally, replacement cells and tissues may be used to treat brain disease such as Parkinson's and Alzheimer's by replenishing damaged tissue, bringing back the specialized brain cells that keep unneeded muscles from moving. Embryonic stem cells have recently been directed to differentiate into these types of cells, and treatments are promising.
• Cell deficiency therapy: Healthy heart cells developed in a laboratory may one day be transplanted into patients with heart disease, repopulating the heart with healthy tissue. Similarly, people with type 1-diabetes may receive pancreatic cells to replace the insulin-producing cells that have been lost or destroyed by the patient's own immune system. The only current therapy is a pancreatic transplant, and it is unlikely to occur due to a small supply of pancreases available for transplant.
• Blood disease treatments: Adult stem cells found in blood and bone marrow have been used for years to treat diseases such as leukemia, sickle cell anemia, and other immuno-deficiencies. These cells are capable of producing all blood cell types, such as red blood cells that carry oxygen and white blood cells that fight disease. Difficulties arise in the extraction of these cells through the use of invasive bone marrow transplants. However, such stem cells have also been found in the umbilical cord and placenta. This has led some scientists to call for an umbilical cord blood bank to make these powerful cells more easily obtainable and to decrease the chances of a body rejecting the therapy.

Stem cells and genetics
Stem cell research is also useful for learning about human development. Undifferentiated stem cells eventually differentiate partly because a particular gene is turned on or off. Stem cell researchers may help to clarify the role that genes play in determining what genetic traits or mutations we receive. Cancer and other birth defects are also affected by abnormal cell division and differentiation. New therapies for diseases may be developed if we better understand how these agents attack the human body.

Drug Testing
Another reason stem cell research is being pursued is to develop new drugs. Scientists could measure a drug's effect on healthy, normal tissue by testing the drug on tissue grown from stem cells rather than testing the drug on human volunteers.

This type of research is proceeding as quickly as ever, but there are a few federal laws and a variety of state laws that were put in place to protect the privacy of research subjects but can be easily misinterpreted. This burgeoning area of research has a huge potential for helping many people who currently lack treatment for their ailments.