Preferential expression of tmTNF-α in leukemia cells. (A) Lysates of Jurkat cells transfected with control, N-terminal truncated fragment (NTF), or tmTNF-α plasmid were precipitated with C1 and then were analyzed by western blotting. Infliximab and IgG served as controls. The image of immunoprecipitation (IP)-western blot is representative of 3 independent experiments. Infliximab bound only tmTNF-α protein but not NTF (middle panel). C1 could bind both tmTNF-α and NTF (black arrow) protein (right panel). Mouse IgG1 could not bind tmTNF-α or NTF protein (left panel). (B) tmTNF-α-negative Jurkat cells were transfected with control, NTF, or tmTNF-α plasmid and stained with fluorescence in situ hybridization, fluorescein isothiocyanate–conjugated C1 and phycoerythrin-conjugated infliximab. The image of confocal microscopy (magnification, ×1000) is representative of 3 independent experiments. (C) A scatter plot shows the percentages of tmTNF-α⁺ leukemia cells vs levels of serum sTNF-α in 18 patients with de novo AL. tmTNF-α expression was analyzed by flow cytometry using C1 in BM mononuclear cells from 69 AML, 30 ALL, and 30 nonmalignant donors (D), in CD34⁺CD38^– or CD34⁺CD7^–/CD19^– fractions of AML, ALL, or nonmalignant cells (E), in CD34⁺CD7^– (for T-ALL, n = 16) or CD34⁺CD19^– (for B-ALL, n = 14) fractions of ALL (F), and in CD34⁺CD38^– fractions among various French-American-British classification systems (FAB) AML subtypes (G). Data represent means ± SEM. ***P < .001 vs NBM (D) or HSC (E).