SYNERGY OF INTERLEUKIN-3 AND TUMOR-NECROSIS-FACTOR-ALPHA IN STIMULATING CLONAL GROWTH OF ACUTE MYELOGENOUS LEUKEMIA BLASTS IS THE RESULT OF INDUCTION OF SECONDARY HEMATOPOIETIC CYTOKINES BY TUMOR-NECROSIS-FACTOR-ALPHA

Colony growth of leukemic colony-forming units (L-CFU) obtained from patients with primary acute myelogenous leukemia stimulated with recombinant human interleukin 3 (rh IL-3) is significantly potentiated when recombinant human tumor necrosis factor-alpha (rh TNF-alpha) is present in cultures. The costimulatory activity of tumor necrosis factor (TNF) alpha is dose dependent and maximum at TNF-alpha concentrations of 10 ng/ml. At high density, L-CFU proliferatively respond to TNF-alpha stimulation in the absence of exogenous rh IL-3. Studies of the mechanism of action of rh TNF-alpha on acute myelogenous leukemia L-CFU growth suggest that TNF-alpha acts by inducing release of growth stimulatory hematopoietic cytokines by the leukemic cells themselves, including IL-1-alpha, IL-1-beta, Granulocyte-macrophage colony-stimulating factor (CSF), granulocyte CSF, and IL-6. Treatment of L-CFU cultures, with neutralizing antibodies to IL-1-alpha, IL-1-beta, granulocyte-macrophage CSF, granulocyte CSF, and IL-6 to eliminate the endogenous source of these factors is associated with significant inhibition of the synergistic interplay of TNF-alpha and IL-3.