بسم ا الرحمن الرحيـــــم
WHAT IS STEM CELL?
Akram al-Hilali 2012
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STEM CELL AS A MEDICAL TERM AND MEDIA TERM
There are many types of “stem cells” In the media: This the totipotent or pluripotent stem cell obtained from the test tube embryos. At a stage when the embryo is just one cell layer with inner cell mass a cell is removed. Any cell of this type can potentially produce all kinds of tissues. More than one cell may be removed and usually the embryo is killed by the process.
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STEM CELL AS A MEDICAL TERM AND MEDIA TERM
Because there are multiple types of stem cells it is better to confine the word “stem cell” to the embryonic pluripotent stem cell. There is the mesothelial (or mesodermal) stem cell which is multipotent for mesodermal tissues, like bone, cartilage and soft tissue. There is the hemopoietic stem cell (HSC), which can produce all kinds of blood cells.
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HEMOPOIETIC STEM CELL
For more than a century hematologists knew of the presence of such a cell but did not have the means of identifying them. Cell sorting by surface markers allowed some insight into stem cells. Culture of cells in the 1970’s allowed the identification of “colony-forming cells” and “Blood-forming units” Flowcytometry simplified the process of identifying and counting the stem cells when it was finally agreed that they are CD34 positive. This is actually shared by a minority of other cells, and other techniques are used to separate HSC from early committed cells that express positive CD34
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WHY DO WE NEED TO IDENTIFY AND COUNT STEM CELLS?
Since these cells can produce all kinds of blood elements their use to compensate for absence or deficiency of one or more of such elements became obvious. A HPSC can give rise to committed cells of various lines depending on the presence of specific “cytokines” .In the body the cytokines are secreted by marrow stromal cells and lymphocytes, according to body need and they will guide the HPSC to go in one direction or the other.
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EXAMPLES OF HPSC DIFFERENTIATION Pro-erythroblast
F SC
HPSC
ot
EPO kines cyto r e h
GM-CSF Thro mbo
G-C S
F
poie tin
Lymphocytes Granulocytes and monocytes Megakaryoblast Granulocytes APCDendritic cell
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Other factors for further differentiation
Stem cell
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FACTORS NEEDED FOR HPSC DIFFERENTIATION AND IMPLANTATION
Cytokines of many types Supportive or “stromal cells” Mesenchymal stem cells
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SOURCES OF HPSC
Bone marrow Peripheral blood Cord blood Adipose tissue Mesenchymal stem cells are also available from the same sources, but in much smaller numbers.
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CAN STEM CELLS BE MODIFIED IN VITRO?
They can be multiplied in culture media, provided the necessary cytokines or growth factors are present. Gene modification before multiplication, can be carried out in vitro
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