Immunology Letters, 16 (1987) 219-226 Elsevier IML 00958 Gene cloning and structure-function relationship of cytokines such as TNF and interleukins Walter Fiers, Rudi Beyaert, Peter Brouckaert, Bart Everaerdt, Guy Haegeman, Philip Suffys, Jan Tavernier l, Peter Vandenabeele, Bart Vanhaesebroeck, Xavier Van Ostade and Frans Van Roy Laboratory of Molecular Biology, University of Ghent, Belgium and 1Biogent, Ghent, Belgium (Received 10 September 1987; accepted 22 September 1987) 1. Summary The genes for a number of proteins, potentially useful in cancer therapy and collectively called "bio- logical response modifiers", have been cloned and expressed in micro-organisms in recent years. These recombinant proteins, which are now available in pure form in nearly unlimited quantities, include in- terferons, interleukins and cytotoxins such as Tumor Necrosis Factor (TNF) and lymphotoxin. Most often the human gene has been cloned and expressed, with view to possible applications in medicine, but usual- ly the mouse equivalent gene was also characterized in order to carry out syngeneic animal model experi- ments. TNF is selectively toxic for many trans- formed cell lines, either alone or in combination with interferon or inhibitors of RNA or protein syn- thesis. Cells sensitive to the cytotoxic action of TNF and cells unaffected by it nonetheless usually carry about an equal number of TNF receptors; hence it is the secondary, intracellular signal which makes the difference between a transformed cell and a nor- mal, diploid cell. TNF can induce a number of different genes in a variety of ceils; for example, en- dothelial cells express a surface antigen responsible for adherence of leucocytes. Another gene which is induced by TNF is interleukin 6 (also called 26 kDa protein or BSF-2). This interleukin, IL-6, is a growth and differentiation factor for B cells as well as for T cells; it is responsible for functions previously ascribed to hepatocyte-stimulating factor, but has no interferon activity. The toxic action of TNF on tumor cells must involve the release of arachidonic acid as phospholipase inhibitors block the TNF- induced effects. At a subsequent stage, proteases must also be involved, as cells can be partially pro- tected from TNF-induced lysis by treatment with protease inhibitors. In mice, murine TNF is much more toxic than human TNF, although in tissue cul- ture there is almost no species preference. A defective liver function strongly enhances the sensitivity to TNF toxicity, as does an infection or the presence of a tumor. Many of the toxic phenomena associated with TNF can be prevented by pretreatment with in- domethacin without interfering with the selective cytotoxicity for transformed cells, either in vitro or in vivo. In conclusion, when the general toxicity of TNF is better understood, it might become feasible to eliminate it to a large extent without affecting the selective anti-tumor cell activity of TNF. On this ba- sis, treatment with TNF, in combination with inter- feron "r, may become an important antitumor ther- apy. Key words." Tumor Necrosis Factor (TNF); Interleukin 6; Lym- photoxin; Cytotoxicity; Heterologous gene expression Correspondence to: W. Fiers, Laboratory of Molecular Biology, University of Ghent, Belgium. 2. Cloning and expression of biological response modifiers Over the past eight years considerable progress has been made in the cloning of nearly full-size cDNAs 0165-2478 / 87 / $ 3.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division) 219