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Monitoring Stem Cell Research 
researchers must continually return to patients to obtain 
hematopoietic stem cells from bone marrow, peripheral blood, or 
placental cord blood. Human ES cells can differentiate into 
hematopoietic precursor cells through co-culture with murine bone 
marrow or yolk sac cells [36]. Enrichment of ES cell-derived 
hematopoietic precursors is accomplished by treatment with 
cytokines or BMP-4 [37]. Cell sorting using hematopoietic-specific 
cell surface markers yields myeloid, erythroid, and megakaryocyte 
precursors [36]. 
There are three major areas where human ES cell 
hematopoiesis should impact human medicine. First, because 
human ES cells can be expanded without limit, human 
hematopoiesis can be studied without the need to continually return 
to patients for tissue donations. The knowledge of these in vitro 
studies is likely to improve therapies based on adult hematopoietic 
stem cells. Second, human ES cell-derived blood cells could be used 
either in bone marrow transplants, or as a source of blood products 
such as red blood cells and platelets. And third, ES cell-derived 
hematopoietic stem cells could aid in ES cell-based transplantation 
therapies for other (non-hematopoietic) tissues. Transplantation of 
ES cell-derived hematopoietic stem cells could be used to reduce or 
eliminate immune rejection by creating hematopoietic chimerism in 
patients receiving co-transplantation of other human ES cell-derived 
tissues [45, 56-58). 
Pancreatic Differentiation 
Type 1 diabetes offers one of the most promising applications 
of human ES cell-based transplantation therapy. The destruction of 
pancreatic islet p-cells results in type 1 diabetes. P-cells produce 
insulin, and as their numbers dwindle, the ability to appropriately 
control blood glucose levels is lost. Even with current insulin 
therapies, type 1 diabetes reduces a patient's life expectancy by 10 
to 15 years, and these patients often develop serious complications 
such as blindness and kidney failure [59]. Recently, the 
transplantation of p-cells from cadavers has proven to be an effective 
treatment for some forms of uncontrollable diabetes, but the source 
of tissue for transplantation is severely limiting and will never come 
close to meeting the demands of over one million people with type 1 
diabetes in the United States. Spontaneous in vitro differentiation of 
human ES cells reveals a percentage of cells that produce insulin and 
express other P-cells specific markers, offering hope of a scalable 
source of p-cells for transplantation [38] 
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