Up-regulation of Fas expression on ex vivo cycling CD34⁺ CB cells is not mediated through endogenous TNF production. CD34⁺ CB cells were cultured for 5 days in SF medium supplemented with SFT3 in the absence or presence of a neutralizing anti-TNF Ab as indicated (“Materials and methods”). Lin^-CD34⁺ cells were gated and investigated for coexpression of Fas. Data are presented as the percentages of Lin^-CD34⁺ cells coexpressing Fas in the absence (□) or presence (▪) of anti-TNF (mean values of 3 independent experiments; error bars, standard errors of the mean [SEMs] are shown).