INDUCTION OF DEATH (CD95 FAS), ACTIVATION AND ADHESION (CD54) MOLECULES ON BLAST CELLS OF ACUTE MYELOGENOUS LEUKEMIAS BY TNF-ALPHA AND IFN-GAMMA/

Leukemic growth is determined by the balance of cell proliferation, di fferentiation and cell death. In vitro, the blasts of acute myelogenou s leukemia (AML) proliferate under the influence of certain positive a nd negative regulators (cytokines). We conducted this study to determi ne whether cytokines could induce markers of cell death (FAS/Apo-1/CD9 5), of cell activation (HLA-DR) and cell adhesion (ICAM-1, CD54) in AM L cell lines and primary AML samples. As inducers, tumor necrosis fact or (TNF)-alpha and interferon (IFN)-gamma were chosen. At baseline, CD 95 and CD54 were weakly and HLA-DR was strongly expressed. CD95 was in duced by TNF in 6/12 myeloid leukemia cell lines, and by IFN in 9/12 c ell lines. taken together, CD95 was upregulated by at least one cytoki ne in 11/12 cell lines. HLA-DR was inducible in 10/12 cell lines, with IFN being more potent than TNF. CD54 showed the strongest induction: TNF resulted in a more than 20-fold induction in positive cell lines, and IFN resulted in a more than 10-fold induction. In primary AML samp les, CD95 was induced in 14/14 samples examined, with TNF being more p otent than IFN. HLA-DR expression was increased by IFN in 12/15 sample s and by TNF in 11/13 samples. The inducibility of HLA-DR by IFN was i nversely correlated with baseline expression. As in the cell lines, CD 54 was induced in most cases of AML. In addition to the induction of s urface markers by cytokines, the culture of leukemia cells with fetal calf serum increased the expression of these markers, especially CD95 and CD54. Our results demonstrate that CD95 is not downregulated when TNF binds to its receptors, but is induced in cell lines and patient s amples. Despite the induction of expression of CD95 (all cases of AML and most cell lines), 7/8 myelogenous leukemia lines and 6/7 patient s amples remained resistant to CD95 triggering by antibody or by CD95 li gand, which suggests a lesion in normal cell signaling. As a positive control, a T-cell line (Jurkat) with 60% to >90% apoptotic cells after a 22 h incubation was used. The number of CD95-binding sites was not correlated with the induction of apoptosis. The resistance of most cas es of AML to CD95 triggering despite inducible expression may also be related to leukemia-specific antagonists of CD95 signal transduction, and requires further investigation. Altogether, our results indicate t hat surface markers related to apoptosis, activation and adhesion can be induced on AML blasts, and could be relevant to treatment strategie s that exploit ligand binding to these surface epitopes.