Stem Cells

Two main properties of stem cells is their ability to give rise to more differentiated cells and their self-renewing capacity (each division of a stem cell creates at least one stem cell). Four levels of stem cells are generally recognized:

• totipotent stem cells such as a fertilized egg can give rise to an entire organism.

• pluripotent or embryonic stem cells arise from totipotent cells and can give rise to most but not all of the cell types. For many years now it has been possible to grow mouse ES cells as cell lines in the laboratory and also recently human pluripotent stem cells. Research is being done into the use of human pluripotent stem cells as a means to generate cells and tissues that could be used to replace diseased or damged ones.

• multipotent stem cells can give rise to only a limited number of cell types.

• unipotent stem cells give rise to a single cell type.

Adult Stem Cells

Adult stem cells typically regenerate the cell types of the tissues  in which they reside, although an active area of research into the phenomenon called "plasticity" where adult stem cells may be able to generate cells of a completely different tissue is occuring.

Transplantation of Stem Cells

In humans it is necessary to inject as little as 10% of a donor's total volume of bone marrow to provide enough hematopoietic stem cells (HSCs) to completely restore the hematopoietic system. Once injected into a vein, HSCs enter the circulation and find their own way to the bone marrow. Experiments in mice indicate that only a few (maby even a single HSC) can completely restore the erythroid population and the immune system.

Transplantation of stem cells populations may be autologous (the recipient is also the donor), syngeneic (the donor is genetically identical) or allogeneic (the donor and recipient are not genetically identical)

Haematopoietic-cell transplantation (HCT) is a potential therapy for people wich severe, therapy-resistant progressive autoimmunity. HCT involves the administration of haematopoietic stem cells which are self renewing and capable of giving rise to all mature cell types. The HSC phenotype is characterized by a lack of cell-surface lineage markers and the expression of CD34 in humans. The recipient is prepared for the transplant by potent immunosuppressive treatment, usually by chemotherapy and/or radiotherapy. This may then be followed by the transfer of autologous haematopoietic cells (auto-HCT); cell s harvested from the recipient before patient conditioning or allogeneic haematopoietic cells (allo-HCT; cells harvested from donors rather than the recipient to restore the host immune system. This procedure can cure autoimmune disease in experimental animal models and is now being explored in human clinical trials.

Cord Blood: or "placental blood" is the blood which remains in the umbilical cord and placenta after birth when the cord is cut. It is rich in stem cells. It is also routinely discarded. However, people can donate their baby's cord blood for possible future use.

NIH stem cell information    Cures Florida  

Companies:  Geron

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