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Stem Cells are also categorized according to their source, as either adult, embryonic, cancer 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
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 Pluripotent. 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.
Cancer Stem Cells arising through malignant transformation of adult
Stem Cells are proposed to be the source of some or all tumors and
cause metastasis and relapse of the disease.[5] The stem cell origin of
leukemias is well established[6]. The role of Stem Cells in other
tumors is under intensive investigation.
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.
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