TPO and TNF-α have opposing effects on FLT3-L–mediated IPC generation from human HPCs. Purified CD34⁺CD45RA^- HPCs from fetal liver were cultured in medium supplemented with FLT3-L or FLT3-L and with TPO, EPO, or TNF-α, as described in “Materials and methods.” Samples of cells from each culture condition were harvested, counted, and analyzed on days 10, 15, 20, and 25. (A) Percentages of HLA-DR⁺CD123^high IPCs by immunofluorescence flow cytometry. (B) Total cell expansion. (C) Total IPC yields per 10 × 10⁶ HPCs at day 20. Data shown in panels A and B are representative results from 1 of 3 experiments. Data shown in panel C are aggregate results from 3 experiments and are presented as mean ± SD. ^*P < .001 (compared day 20 IPC yield from FLT3-L/TPO cultures with IPC yield from other culture conditions).