Cytokine modulated cell-membrane bound tumour necrosis factor expression is associated with enhanced monocyte-mediated killing of human leukaemic targets

Abstract 

Cytokines such as interleukin-3 (IL-3) and granulocyte–macrophage colony-stimulating factor (GM-CSF) activate monocytes both in vitro and in vivo. We therefore studied whether the anti-leukaemic activity of monocytes could be augmented by IL-3 alone or in combination with GM-CSF. Using normal human monocytes stimulated with IL-3, GM-CSF, LPS or combinations of growth factor and LPS, we studied their cytotoxic activity against leukaemic cell-lines and primary AML blasts. IL-3 like GM-CSF, augmented the expression and secretion of TNF but did not prime for further expression and secretion of TNF in response to LPS. Neither GM-CSF or IL-3 increased the expression or secretion of TNF receptor p55 (TNF-Rp55), although both agents increased expression of TNF receptor p75 (TNF-Rp75). Monocyte-mediated cytotoxicity (MMC) against K562 and U937 cell-lines was increased by both GM-CSF and IL-3 stimulation, and both cytokines primed monocytes for increased killing of K562 and KG-1 cell-lines as well as primary AML blasts in response to LPS. The mechanism of action of MMC was largely confirmed to be via surface-bound TNF, although other TNF-independent mechanisms must have been involved.

Keywords: GM-CSF, IL-3, Monocyte-mediated cytotoxicity, Tumor necrosis factor, Leukemia, Immunosurveillance, Minimal residual disease, Immunotherapy

Abbreviations: IL-3, interleukin-3, IL-8, interleukin-8, IFN-γ, interferon gamma, GM-CSF, granulocyte-macrophage colony-stimulating factor, MMC, monocyte-mediated cytotoxicity, LPS, lipopolysaccharide, TNF, tumour necrosis factor, fMLP, formyl methionine leucyl phenylalanine, PMA, phorbol-12-myristate-13-acetate, AML, acute myeloid leukemia, EDTA, ethylenediamenetetraacetic acid, sodium, EGTA, ethyleneglycol-bis(β-aminoethyl)-N,N,N′,N′-tetraacetic acid, LDH, lactate dehydrogenase