They have been notoriously difficult to distinguish from the blood's other progenitor cells, which are further along in the differentiation process. Having the stem cell purified, we have the possibility finally of characterizing it at a functional, phenotypic and molecular level. Scientists then can generate in the laboratory the circulating blood cells required for blood transfusions, which currently are obtained by transfusions from normal donors. Progenitor cells are immature cells that can differentiate into red blood cells, white blood cells and platelets. They are used to restore patients' blood and immune systems after high-dose chemotherapy or radiation for cancer.
Stem cells are earlier cells which have the unique capacity to self-perpetuate.
They generate progenitor cells and blood cells throughout life. Progenitors have no self-renewal capacity they only give rise to more differentiated precursor cells. Scientists can isolate undifferentiated progenitor cells using a marker on the cell known as CD34. This methodology was pioneered by Dr. Peschle and co-workers in a report in Science in 1990. But identifying hematopoietic stem cells has been more difficult, explains Dr. Peschle.