Age-related decline in proliferative potential of purified stem cell candidates.

Recent studies in our laboratory have shown striking differences in the functional properties of candidate hematopoietic stem cells purified from fetal, neonatal, and adult human tissues. These differences include the ability to produce CD34+ cells, the turnover rate, and the fraction of cells that respond to a mixture of cytokines. All these parameters decrease with the age of the cell donor, and some of these observations are summarized here. Extensive qualitative changes in hematopoietic cells from various stages of development should be taken into account in the design of novel therapeutic strategies.