LONG-TERM INHIBITION OF TUMOR-GROWTH BY TUMOR-NECROSIS-FACTOR IN THE ABSENCE OF CACHEXIA OR T-CELL IMMUNITY

The relationship between detrimental (cachectic) and beneficial (antitumor) effects of tumor necrosis factor (TNF) was studied in mice bearing murine tumors transfected to secrete human TNF. In vitro, the TNF-producing transfectants were resistant to the secreted TNF and grew at rates similar to those of untransfected cells or transfected cells that did not secrete TNF. However, tumors formed by the TNF-secreting cells in vivo remained much smaller than the nonsecreting (transfected and untransfected) tumors. This inhibition of tumor growth required only relatively low serum levels of TNF, persisted for many weeks, and was independent of T cells since it occurred in nude mice. Growth of the TNF-secreting tumors increased dramatically after treatment with anti-human TNF antibody, indicating that extracellular TNF secreted by the tumor cells was necessary for the tumor inhibition. Severe weight loss characteristic of cachexia only occurred in animals with very high serum TNF levels (250 pg/ml) and could be prevented or reversed by anti-TNF antibody treatment. These data are consistent with the existence of a therapeutic window in which persistent exposure to human TNF can lead to prolonged inhibition of tumor growth in the absence of T-cell immunity or severe weight loss and without development of resistant tumor variants.