TNFR55 mediates the negative effect of TNF on CD34⁺CD38⁻ candidate stem cells.

CD34⁺CD38⁻ BM (3 experiments) or CB (1 experiment) cells were expanded in SF medium supplemented with KFT3 in the absence or presence of TNF (20 ng/mL), or mutants binding specifically to TNFR55 (200 ng/mL) or TNFR75 (500 ng/mL). After 5 to 7 days the EEs of 50 CD34⁺CD38⁻ cells of each group were seeded into LTC-IC cultures, as described in “Materials and methods.” Results show the mean number of LTC-CFC (SEM) of cells expanded in the presence of TNF, or the mutants relative to the KFT3-expanded group (control). For the control group the mean number of CFCs generated in the 4 experiments varied from 106 to 350.