Mechanisms for cytotoxic effects of anti-tumor necrosis factor agents on transmembrane tumor necrosis factor α-expressing cells

Objective. Three anti-tumor necrosis factor alpha (anti-TNF alpha) agents have been proved to be effective for rheumatoid arthritis (RA) and other inflammatory disorders. Infliximab and adalimumab have been generated as anti-TNF alpha monoclonal antibodies, while etanercept is engineered from human type II TNF receptors. In spite of all 3 agents' equal efficacy for RA, both infliximab and adalimumab are effective for other diseases such as Crohn's disease and Wegener's granulomatosis, while etanercept is not. We undertook this study to understand the different clinical effects of these anti-TNF alpha agents by analyzing their biologic activities on transmembrane TNF alpha. Methods. Jurkat T cells stably expressing an uncleavable form of transmembrane TNF alpha were used for the following studies: 1) flow cytometric analysis of binding activities of anti-TNF agents to cell surface transmembrane TNF alpha, 2) complement-dependent cytotoxicity (CDC), 3) antibody-dependent cell-mediated cytotoxicity (ADCC) by using peripheral blood mono-nuclear cells, and 4) outside-to-inside (reverse) signal transduction through transmembrane TNF alpha estimated by apoptosis and cell cycle analysis using flow cytometry. Results. All of the anti-TNF alpha agents bound to transmembrane TNF alpha. Infliximab and adalimumab exerted almost equal CDC activities, while etanercept showed considerably lower activity. ADCC activities were almost equal among these 3 agents. Adalimumab and infliximab induced apoptosis and cell cycle arrest in transmembrane TNF alpha-expressing Jurkat T cells, reflecting an outside-to-inside signal transduction through transmembrane TNF alpha. Conclusion. Three different anti-TNF agents showed different biologic effects on transmembrane TNF alpha. This finding suggests that CDC and outside-to-inside signals by anti-TNF alpha antibodies may explain the successful clinical efficacy of adalimumab and infliximab in Crohn's disease and Wegener's granulomatosis.