PURIFICATION AND CHARACTERIZATION OF AN INHIBITOR (SOLUBLE TUMOR-NECROSIS-FACTOR RECEPTOR) FOR TUMOR-NECROSIS-FACTOR AND LYMPHOTOXIN OBTAINED FROM THE SERUM ULTRAFILTRATES OF HUMAN CANCER-PATIENTS

Serum ultrafiltrates (SUF) from human patients with different types of cancer contain a blocking factor (BF) that inhibits the cytolytic activity of human tumor necrosis factor α (TNF-α) in vitro. BF is a protein with a molecular mass of 28 kDa on reducing sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE). The active material was purified to homogeneity by a combination of affinity chromatography, PAGE, and high-pressure liquid chromatography. Amino acid sequence analysis revealed that BF is derived from the membrane TNF receptor. Purified BF blocks the lytic activity of recombinant human and mouse TNF-α and recombinant human lymphotoxin on murine L929 cells in vitro. However, BF inhibits the lytic activity of TNF-α more effectively than it does that of lymphotoxin. The BF also inhibits the necrotizing activity of recombinant human TNF-α when coinjected into established cutaneous Meth A tumors in BALB/c mice. The BF may have an important role in (i) the regulation and control of TNF-α and lymphotoxin activity in cancer patients, (ii) interaction between the tumor and the host antitumor mechanisms, and (iii) use of systemically administered TNF-α in clinical trials with human cancer patients.