Analysis of the effects of tumor necrosis factor inhibitors on human hematopoiesis

Truncated soluble fragments of tumor necrosis factor (TNF) receptors have recently been isolated from human serum and urine. These shed forms of TNF receptors bind TNF‐α and lymphotoxin and inhibit various effects of TNF in culture. In this study, we evaluated the role of these molecules in the hematopoietic system. TNF‐α and lymphotoxin inhibited colony forming units granulocyte‐macro‐phage (CFU‐GM) and burst forming units‐erythroid (BFU‐E) in a dose‐dependent fashion at concentrations ranging from 1 to 5,000 U/ml and 25 to 250 U/ ml, respectively. TNF‐α exerted a similar dose‐dependent inhibitory effect on a CD34 enriched marrow cell population, suggesting that its effect is not mediated through CD34∼ accessory ceils. Its suppressive effect was partially reversed by anti‐TNF‐α neutralizing antibodies, thus proving its specificity. Two shed forms of TNF receptors, TNF binding protein (TNF‐bp) and TNF receptor fusion protein (TNFR‐fc), had no significant effect on CFU‐GM proliferation. Both molecules, however, significantly reversed the inhibitory effect of TNF‐α (p < 0.015 and p < 0.03, respectively), whereas they had no effect on the lymphotoxin‐induced CFU‐GM growth inhibition. These results indicate that TNF‐bp and TNFR‐fc may modulate the inhibitory effects of TNF‐α in the hematopoietic system.