THE SOURCES OF HEMATOPOIETIC STEM CELLS

Bone Marow: The classic source of hematopoietic stem cells is bone marrow.For more than 40 years, doctors performed bone marrow transplants by anesthetizing the stem cell donor,puncturing a bone-typically a hipbone –and drawing out the bone marrow cells with a syringe. About 1 in every 100.000 cells in the marrow is a long term,blood forming stem cell,other cell present include stromal cells,stromal stem cells,blood progenitor cells,and mature and maturing white and red blood cells.

Peripheral Blood: For clinical transplantation of human HSCs, doctors now prefer to harvest donor cells from peripheral, circulating blood . It has been known for decades that a small number of stem and progenitor cells circulate in the bloodstream,but in the past 10 years, researchers have found that they can coax the cells migrate from marrow to blood in greater numbers by injecting the donor with a cytokine,such as granulocyte-colony stimulating factor.The donor is injected with GCSF a few days before the cell harvest.To collect the cells,doctors insert an intravenous tube into the donor’s vein and pass his blood through a filtering system that pulls out CD 34 + white cells and returnes the red blood cells to the donor.

Umblical Cord Blood: In the late 1980s and 1990s,physicians began to recognize that blood from the human umblical cord and placenta was a rich source of HSCs.This tissue supports the developing fetus during pregnancy,is delivered along with the baby,and is usually discarded.Since the first succesful umblical cord blood transplants in children with fanconi anemia, the collection and therapeutic use of these cells has grown quickly. There is a substantial amount of research being conducted on umblical cord blood to search for ways to expand the number of HSCs and compare and contrast the biological properties of cord blood with adult bone marrow stem cells. There have been suggestions that umblical cord blood contains stem cells that have the capability of developing cells of multiple germ layers (multipotent )or even all germ layers,e.g endoderm, ectoderm and mesoderm(pluripotent).

Fetal Hematopoietic System: An important source of HSCs in research, but not in clinical use, is developing blood-producing tissues of fetal animals.

Embryonic Stem Cells and Embryonic Germ Cells: It was shown that it is possible to obtain precursors to many different blood cells from mouse embryonic stem cells. Some scientists were able to obtain all the major lineages of progenitor cells from mouse embryoid bodies,even without adding hematopoietic growth factors.

 

REFERENCES

Stem Cells: Scientific Progress and Future Research Directions
Report Prepared by The National İnstitutes of Health

www.stemcellresearchfoundation.org