Special Susceptibility to Apoptosis of CD1a+ Dendritic Cell Precursors Differentiating from Cord Blood CD34+ Progenitors

We analyzed the effect of tumor necrosis factor (TNF)-α on the differentiation and viability of dendritic cells (DC) generated from cord blood CD34+ progenitors cultured for five days with GM-CSF, Flt-3 ligand (FL), and stem cell factor (SCF), and then with GM-CSF only [TNF(−) cultures]. Adding TNF-α from the start [TNF(+) cultures] potentiated progenitor cell proliferation and promoted early differentiation of CD1a+ DC precursors without affecting differentiation of CD14+ cells, which comprise bipotent precursors of DC and macrophages, nor of CD15+ granulocytic cells. Use of TNF-α was associated with increased cell mortality, which peaked on culture day 10 and mainly involved CD1a+ DC. Selective apoptosis of CD1a+ DC precursors was confirmed by showing that survival of day-7-sorted CD1a+CD14− cells from TNF(+) cultures was lower than that of CD1a−CD14+ cells. That similar findings were noted for sorted CD1a+CD14− cells of TNF(−) cultures, further cultured with GM-CSF without or with TNF-α, indicates that apoptosis of CD1a+ DC precursors was not induced by TNF-α. Apoptosis of CD1a+ DC precursors occurred after the cells had lost the capacity to incorporate bromodeoxyuridin. Finally, using higher GM-CSF concentrations or adding interleukin 3 (IL-3) improved viability of CD1a+ cells. Other cytokines, such as IL-4 and transforming growth factor (TGF)-β1, were ineffective in this respect, though they promoted differentiation of CD1a+ DC. These results indicate that TNF-α promotes the differentiation of CD1a+ DC precursors, which display a high susceptibility to apoptosis that can be prevented by high concentrations of GM-CSF or use of IL-3, without affecting the differentiation of the CD14+ DC precursors.