Stem Cells and the Future of Regenerative Medicine (2002) / Chapter Skim
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2. Adult Stem Cells
2. Adult Stem Cells
Pages 19-30
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From page 19... ...
to self-renew continuously in the marrow and to differentiate into the fuD complement of cell types found in blood qualifies them as the premier adult stem cells (Figure 3~. HSCs are among the few stem cells to be isolated in adult humans.
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From page 20... ...
or progenitor cells, which are precursors to various blood cell types. HSCs are found mainly in bone marrow, although T cells develop in thymus, and some other cell types develop from blood monocytes.
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From page 21... ...
and the difficulty of separating them from other components of the blood, so-called bone marrow stem cell transplants are generally impure (NIH, 2001~. The significance of such impurity is great.
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From page 22... ...
There is also evidence that transplants derived from umbilical cord blood are less likely to provoke graft versus host disease, possibly because the cells in cord blood are immature and less reactive immunologically (Laughlin, 2001~. The quantity of HSCs present in cord blood and its attached placenta is small, and transplants from cord blood take longer to graft, but for children, whose smaller bodies require fewer HSCs, cord blood transplants are valuable, especially when there is no related sibling to donate HSCs (Gluckman et al, 2001~.
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From page 23... ...
OTHER ADULT STEM CELLS During the past 2 years, scientific reports of stem cells in other organs of adult mice including brain, muscle, skin, digestive system, cornea, retina, liver, and pancreas have cast a new light on the body's own capability to replenish its tissues (NIH, 2001~. Their discovery has also fostered speculation that these cells exist in the adult human, that they have the characteristic of plasticity that enables them to change into precursors of cell types of other tissues, and that they will someday be used to produce the tissues for therapeutic use.
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From page 24... ...
However, because recent findings of adult stem cells are so new and studies of them raise so many questions, even the most preliminary generalizations and conclusions as to therapeutic potential are tentative. As was noted by James Thomson at the workshop, the hematopoietic stem cell is the most characterized cell in the body, and "The amount of knowledge we have on other adult stem cells goes down dramatically from there." First, human adult stem cells are rare and it is difficult to isolate a unique group of stem cells in pure form.
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From page 25... ...
If the labeled stem cell is injected into a mouse, any cell or tissue that is eventually found to have the label can be assumed to have come from the original single stem cell, and this is the kind of evidence for a definitive relationship that stem cell researchers are seeking. A second factor that complicates adult stem cell research is that the environment in which stem cells grow or are placed to grow has an important but poorly understood effect on their fate a theme that was echoed by many speakers at the workshop.
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From page 26... ...
However, in his experiment, HSCs and pancreatic stem cells were very inefficient in repopulating the liver relative to the ability of transplanted hepatocytes themselves. This could mean that the plasticity of adult stem cells is a marginal capacity that can be exploited only with a much greater understanding of the environmental signals that influence adult stem cells.
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From page 27... ...
However, with a few exceptions, the appropriate culture conditions to sustain most adult stem cells indefinitely have yet to be found. Very few stem cells, strictly defined, have even been isolated from adult human organs, in part because they constitute only a tiny fraction of the cells present and are not likely to be very distinct from the partially differentiated cells they give rise to as they mature and differentiate.
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From page 28... ...
Confirmed reports of truly multipotent human adult stem cells are scarce. For its recently released report on stem cells, the National Institutes of Health could find few published accounts of the isolation of multipotent adult stem cells from human tissues (NIH, 2001~.
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From page 29... ...
Emphasizing how little is understood about the process that controls a cell's commitment to one course of action or another, Thor Lemischka explained his findings that many genes found to be active in stem cells do not correspond to any known gene function ever described. A comparison of mouse and human HSCs shows that only about half of the genes expressed in the mouse HSCs correspond to genes expressed in human HSCs, so there are going to be differences as we move from experiments with mice to regenerative therapies in humans.
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From page 30... ...
Box: International Perspective on Public Policy on Human ESC Research Germany: Prohibits the derivation and use of human ESCs Tom blastocysts. United States: As articulated by President Bush on August 9, 2001, permits federal Ending only for research using cells from approximately 60 stem cell lines identified by the National Institutes of Health as having been denved from excess human embryos prior to the August 9 announcement.
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