EXPANSION OF HUMAN NEONATAL PROGENITOR CELLS IN-VITRO UNDER SERUM-DEPRIVED CONDITIONS

Over time CD34(+) cells purified from human cord blood generate large numbers of progenitor and precursor cells in liquid culture under seru m-deprived conditions if stimulated with a cocktail of growth factors which include stem cell factor (SCF). The ex vivo expansion observed i n liquid cultures is not homogeneous over time but involves the recrui tment of different cell compartments and can be triggered by different growth factor combinations, We have recognized at least three phases in these liquid cultures. Phase I spans the first 20 days of culture. In this phase, progenitor and precursor cells are generated from the p rogenitor cell compartment itself in response to SCF in combination wi th either IL-3, erythropoietin, or G-CSF, Phase II spans the second mo nth of culture and involves the recruitment of less and less different iated cells by IL-3 and SCF. Phase III spans from the third month on a nd results in the indefinite proliferation of human mast cells. These results raise caution on the biological equivalence of liquid culture en vivo expanded hematopoietic cells at different time points.