Production of tumor necrosis factor-alpha in human long-term marrow cultures from normal subjects and patients with acute myelogenous leukemia: effect of recombinant macrophage colony-stimulating factor.

We have recently reported that normal long-term marrow cultures (LTMC) treated with recombinant human macrophage colony-stimulating factor (rhCSF-1), as well as LTMC from patients with acute myelogenous leukemia (AML), produce a soluble activity capable of inhibiting hemopoietic colony formation in semisolid cultures. In the present study, we have found that such an activity is produced, both in normal and AML LTMC, by an adherent, nonfibroblastic cell population (most likely macrophages), and also by blast cells developed in AML LTMC. The presence of the inhibitory activity correlated with increased levels of tumor necrosis factor (TNF) in the culture supernatants. Part of the activity (30%) produced in rhCSF-1-treated normal LTMC was neutralized in colony assays by anti-TNF alpha monoclonal antibody. In contrast, the soluble inhibitory activity from AML LTMC was completely neutralized by anti-TNF alpha. However, addition of anti-TNF alpha (every 72 h, from day 0 to 21, at 125 ng/ml) to AML LTMC resulted in only partial neutralization of the inhibitory activity, indicating that production of TNF alpha is just one of the mechanisms by which normal hemopoiesis is inhibited in AML LTMC, and that other factors are involved in this process. In keeping with this idea, we found very high levels of prostaglandin E, a hemopoietic inhibitor, in the supernatant of cultures that contained the soluble inhibitory activity. Interestingly, rhCSF-1 showed opposite effects on TNF production in normal (up-regulation) and AML (down-regulation) LTMC, which suggests the presence of functionally abnormal, leukemia-derived macrophages in AML LTMC.