REGULATION OF TUMOR-NECROSIS-FACTOR-ALPHA PRODUCTION AND GENE-EXPRESSION IN MONOCYTES

Tumor necrosis factor-alpha (TNF-alpha), produced predominantly by activated monocytes/macrophages, inhibits leukemic cell growth and may contribute to a graft-versus-leukemia effect after marrow transplantation. We examined the recombinant cytokines interferon (IFN)-alpha, IFN-gamma, granulocyte- macrophage colony-stimulating factor (GM-CSF), and macrophage colony-stimulating factor (M-CSF), alone or in combination, for their ability to induce monocytes from normal donors and patients after marrow grafting to express TNF-alpha mRNA and secrete TNF-alpha bioactivity. Monocytes were isolated from peripheral blood by Percoll separation of E-rosette-negative cells, and cultured with cytokines under non-adherent, endotoxin-free conditions. TNF-alpha transcripts were undetectable in freshly isolated monocytes from normal donors. Only the combination of IFN-gamma/GM-CSF was consistently capable of inducing substantial TNF-alpha mRNA transcript levels and protein secretion. Levels of TNF-alpha transcripts induced by IFN-gamma/GM-CSF were maintained for at least 36 h, in contrast to lipopolysaccharide (LPS) stimulation which caused TNF-alpha mRNA levels to peak after 2 h and decline rapidly thereafter. IFN-gamma/GM-CSF was also capable of inducing a prolonged (at least 48 h) secretion of TNF-alpha bioactivity. In contrast, >80% of the total TNF-alpha bioactivity secreted by LPS-stimulated monocytes was secreted in the first 8 h. When monocytes were incubated with IFN-gamma alone ('priming'), washed and then exposed to GM-CSF, both TNF-alpha mRNA expression and TNF-alpha protein production occurred. Monocytes obtained from patients (n=19) early (less-than-or-equal-to 4 months) after autologous or allogeneic marrow transplantation who did not have acute graft-versus-host disease or documented infections were fully capable of secreting normal levels of TNF-alpha bioactivity in response to IFN-gamma/GM-CSF or LPS. Our results indicate that IFN-gamma/GM-CSF can induce a sustained production of TNF-alpha by monocytes and may be useful in therapeutic strategies to eliminate residual disease remaining after marrow grafting, particularly when a locoregional (site specific) release of TNF-alpha is desired.