Information on Stem Cell Basics Available from NIH

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Kaiser Daily Reproductive Health Report

Friday, August 10, 2001

The Stem Cell Decision "Date" content="2001-08-10"

Content="Information on Stem Cell Basics Available from NIH"

description" ="To explain the nature of stem cells and their potential use in health care research, the NIH last year released a white paper titled 'Stem Cells: A Primer.'

The primer includes definitions of different types of stem cells, comparisons between adult and embryonic stem cells and the potential benefits and limitations of both types of cells.

Definition of a Stem Cell = When an egg is fertilized, it becomes totipotent, which means it has 'unlimited capability' to develop into an embryo or any kind of organ or tissue.
However, the cells of the fertilized egg begin to specialize approximately four days after fertilization, with some cells forming the placenta and other tissues needed for fetal development and others forming the inner cell" Information on Stem Cell Basics Available from NIH

      To explain the nature of stem cells and their potential use in health care research, the NIH last year released a white paper titled "Stem Cells: A Primer." The primer includes definitions of different types of stem cells, comparisons between adult and embryonic stem cells and the potential benefits and limitations of both types of cells.

Definition of a Stem Cell
When an egg is fertilized, it becomes totipotent, which means it has "unlimited capability" to develop into an embryo or any kind of organ or tissue. However, the cells of the fertilized egg begin to specialize approximately four days after fertilization, with some cells forming the placenta and other tissues needed for fetal development and others forming the inner cell mass of the embryo. The cells in the inner cell mass are pluripotent, meaning they can develop into most -- but not all -- types of cells necessary for fetal development. They cannot form the placenta or the supporting tissues necessary for fetal development and cannot develop into a fetus on their own. Pluripotent stem cells can develop into stem cells that "are committed to give rise to cells that have a particular function," such as blood stem cells, which can form into red blood cells, white blood cells or platelets, or skin stem cells that give rise to different types of skin cells. These cells that can further specialize, such as blood or skin stem cells, are called multipotent cells. Multipotent stem cells, which serve an important function in the human development process, also are found in children and adults.

Sources of Pluripotent Stem Cells
Pluripotent cells can be derived from two sources: the inner cell mass of human embryos during the blastocyst stage and fetal tissue obtained from terminated pregnancies. Pluripotent cells could potentially be obtained from somatic cell nuclear transfer as well. During somatic cell nuclear transfer, scientists remove the nucleus of a "normal" egg cell and fuse it with a somatic cell, or any cell other than an egg or a sperm cell. The resulting cell and its "immediate descendants" are believed to have the full potential to develop into an entire animal, making them totipotent. Because these totipotent cells would form a blastocyst, the cells from the blastocyst's inner cell mass could potentially be used to develop pluripotent stem cell lines. Stem cells derived from adult tissue are multipotent, although not all types of adult tissue contain multipotent stem cells.

Stem Cell Potential
The NIH white paper states that stem cells have several potential benefits, including allowing scientists to "understand the complex events that occur during human development" and "dramatically chang[ing] the way we develop drugs and test them for safety." But the "most far-reaching potential" of pluripotent embryonic stem cells is the "generation of cells and tissue that could be used" to treat certain diseases and disorders. Pluripotent stem cells, however, may be rejected by a recipient's immune system, and scientists would need to conduct more research to understand how to modify human pluripotent stem cells to "minimize tissue incompatibility or to create tissue banks with the most common tissue-type profiles." Somatic cell nuclear transfer was cited as another way to overcome the problem of tissue compatibility.
Multipotent stem cells found in adult tissue have potential benefits and drawbacks as well.
Although scientists are finding that some types of multipotent adult stem cells can "change course" and develop into other types of cells -- such as a blood stem cell switching to a skin stem cell -- there are "some significant limitations" to what they may do.
The paper adds that adult stem cells are "present only in minute quantities, are difficult to isolate and purify and their numbers may decrease with age" (NIH, "Stem Cell Primer," May 2000). A copy of this report is available online.



-- Cherri (jessam6@home.com), August 16, 2001


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