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MMC Stem cells present world of opportunity for medical researchers

Tribune Media Services

DEAR MAYO CLINIC: Would you please provide some information on stem cells? What are they? What can they do to cure diseases? Why are they important in research?

Stem-cell research is a new frontier in medicine. Researchers are seeking ways to create stem-cell-based therapies to treat or cure illnesses such as Parkinson's disease, Alzheimer's, diabetes, heart disease and spinal-cord injuries. But the real-world applications, if they occur, are years away.

What are stem cells?

They are different from other cells in the body. When most cells divide, they produce two identical daughter cells. Not so with stem cells. Some stem-cell-borne daughter cells become specialized (e.g., cells of the skin or heart muscle) and some remain stem cells, replenishing the stem cell pool.

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Because some stem cells change into specialized cells, researchers believe they may be useful in repairing tissues damaged by disease, aging or injury. Stem cells are not all the same. Different stem cells can be derived from embryos, umbilical-cord blood and the placenta, and adult tissues.

Embryonic stem cells come from human eggs fertilized in vitro (out of body) as part of infertility treatment. Some embryos may remain after a woman becomes pregnant, and are provided for research with the consent of the donors. Embryonic stem cells can differentiate into any type of cell in the body.

Adult stem cells can be isolated from bone marrow, the liver, muscle, the brain, fat and other tissues. These cells can provide fewer different types of differentiated cells.

Uses, now and in the future:

Though so far stem cells have not cured any condition, doctors have successfully used them in blood and marrow transplants for more than 30 years. These transplants are used in the treatment of leukemia and lymphoma to sustain life after chemotherapy and radiation. Experimentally, they are used to replace a defective immune system in some inherited immune disorders, and to replace an immune system turned against itself, such as in some autoimmune disorders.

In the future, stem cells might be used to:

Replace diseased cells. If stem cells could be directed to differentiate into specific cell types, they could treat Parkinson's disease, spinal cord injuries, burns, Alzheimer's, arthritis, disorders of bone development and other conditions.

Form new tissues: Stem cells could to be used to keep organs, such as a failing heart, functioning.

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Test new medications: Researchers could test new medications for safety on specific cells generated by stem cells.

Improve understanding of cancer and birth defects: Both can be caused by abnormal cell division and differentiation. By learning more about how stem cells divide, researchers may gain new insights into the causes of cancer and birth defects.

Challenges and questions:

Stem cell research is a very young area of science with many unsolved problems. Researchers are learning only now how to predictably "coach" most stem cells into a particular differentiated cell. Equally importantly, stem cells, particularly embryonic stem cells, can give rise to tumors if isolated at an inopportune level of embryonic development and/or implanted in the wrong place in the body.

While it has been shown that the body does not reject some stem cells transplanted from another individual, it is still unclear whether the cells would be rejected once they differentiate. There are many other unanswered questions.

Ethical and legal concerns:

Extracting a stem cell from an embryo destroys the embryo. Some people feel that this should not be done. In 2001, President George Bush issued an executive order limiting federal funding for research on human embryonic stem cells. Researchers who rely on federal funding can work only with a limited number of existing human stem cell lines. However, embryonic stem cell research is legal in the United States, and it has been supported by other sources of funding. Non-embryonic stem cell research is not controversial.

Importance of stem cell research:

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Understanding stem cells and their differentiation into adult tissues is paramount to our understanding of how we develop from a fertilized egg -- the quintessential stem cell -- into an adult human being. The full understanding of this process may allow us to prevent and correct birth defects and remedy conditions so far untreatable.

-- Stanimir Vuk-Pavlovic, Ph.D., Stem Cell Laboratory, Mayo Clinic Cancer Center, Mayo Clinic, Rochester

To submit a question, write to: medicaledge@mayo.edu, or Medical Edge from Mayo Clinic, c/o TMS, 2225 Kenmore Ave., Suite 114, Buffalo, N.Y., 14207.

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