HEMATOPOIETIC STEM-CELLS FROM DIFFERENT SOURCES - BIOLOGICAL AND TECHNICAL ASPECTS

Hematopoietic stem cell (HSC) enumeration is crucial to predict the en graftment potential of a given HSC collection, and currently involves the surrogate count of nucleated cells, CFU or CD34(+) cells. However, there is raising evidence that CFU are HSC involved in shortterm but not in long-term reconstitution, and that only a small fraction of all CD34(+) cells have long term multilineage engraftment potential, In t his regard, there is evidence that cord blood (CB), bone marrow (BM) a nd peripheral blood (PB) derived HSC are highly heterogeneous for a nu mber of antigens useful for HSC enumeration by flow cytometry, Moreove r, there is a raising evidence that a CD34(-) human HSC might exist, T he CD34(-) HSC has been already described in animals and in human Hoec hst 33342 negative HSC, This notwithstanding, clinical data have clear ly demonstrated that purified allogeneic CD34(+) cells can reconstitut e the myeloid and the lymphoid lineages in myeloablated recipients. In the lack of a suitable marker for CD34(-) HSC enumeration, it is hard to predict the role of CD34(-) HSC in hematopoietic reconstitution af ter transplantation, On the other hand, these cells might be a better target for HSC expansion and gene transfer.