Takahiko Horiuchi

Transmembrane TNF-alpha, a precursor of the soluble form of TNF-alpha, is expressed on activated macrophages and lymphocytes as well as other cell types. After processing by TNF-alpha-converting enzyme (TACE), the soluble form of TNF-alpha is cleaved from transmembrane TNF-alpha and mediates its biological activities through binding to Types 1 and 2 TNF receptors (TNF-R1 and -R2) of remote tissues. Accumulating evidence suggests that not only soluble TNF-alpha, but also transmembrane TNF-alpha is involved in the inflammatory response. Transmembrane TNF-alpha acts as a bipolar molecule that transmits signals both as a ligand and as a receptor in a cell-to-cell contact fashion. Transmembrane TNF-alpha on TNF-alpha-producing cells binds to TNF-R1 and -R2, and transmits signals to the target cells as a ligand, whereas transmembrane TNF-alpha also acts as a receptor that transmits outside-to-inside (reverse) signals back to the cells after binding to its native receptors. Anti-TNF agents infliximab, adalimumab and etanercept bind to and neutralize soluble TNF-alpha, but exert different effects on transmembrane TNF-alpha-expressing cells (TNF-alpha-producing cells). In the clinical settings, these three anti-TNF agents are equally effective for RA, but etanercept is not effective for granulomatous diseases. Moreover, infliximab induces granulomatous infections more frequently than etanercept. Considering the important role of transmembrane TNF-alpha in granulomatous inflammation, reviewing the biology of transmembrane TNF-alpha and its interaction with anti-TNF agents will contribute to understanding the bases of differential clinical efficacy of these promising treatment modalities.

OBJECTIVES: A systematic review was conducted to explore the immunogenicity of biologic agents across inflammatory diseases and its potential impact on efficacy/safety. METHODS: Literature searches were conducted through November 2016 to identify controlled and observational studies of biologics/biosimilars administered for treatment of rheumatoid arthritis (RA), psoriatic arthritis (PsA), juvenile idiopathic arthritis (JIA), ankylosing spondylitis (AS), non-radiographic axial spondyloarthritis (nr-axSpA), psoriasis (Ps), Crohn's disease, and ulcerative colitis. RESULTS: Of >21,000 screened publications, 443 were included. Anti-drug antibody (ADAb) rates varied widely among biologics across diseases (and are not directly comparable because of immunoassay heterogeneity); the highest overall rates were reported with infliximab (0-83%), adalimumab (0-54%), and infliximab biosimilar CT-P13 (21-52%), and the lowest with secukinumab (0-1%), ustekinumab (1-11%), etanercept (0-13%), and golimumab (0-19%). Most ADAbs were neutralizing, except those to abatacept and etanercept. ADAb+ versus ADAb- patients had lower rates of clinical response to adalimumab (RA, PsA, JIA, AS, Ps), golimumab (RA), infliximab (RA, PsA, AS, Ps), rituximab (RA), ustekinumab (Ps), and CT-P13 (RA, AS). Higher rates of infusion-related reactions were reported in infliximab- and CT-P13-treated ADAb+ patients. Background immunosuppressives/anti-proliferatives reduced biologic immunogenicity across diseases. CONCLUSIONS: Based on reviewed reports, biologic/biosimilar immunogenicity differs among agents, with the highest rates observed with infliximab and adalimumab. As ADAb formation in biologic-/biosimilar-treated patients may increase the risk of lost response, the immunogenicity of these agents is an important (albeit not the only) consideration in the treatment decision-making process.

Abstract Objective Three anti–tumor necrosis factor α (anti‐TNFα) agents have been proved to be effective for rheumatoid arthritis (RA) and other inflammatory disorders. Infliximab and adalimumab have been generated as anti‐TNFα 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‐TNFα agents by analyzing their biologic activities on transmembrane TNFα. Methods Jurkat T cells stably expressing an uncleavable form of transmembrane TNFα were used for the following studies: 1) flow cytometric analysis of binding activities of anti‐TNF agents to cell surface transmembrane TNFα, 2) complement‐dependent cytotoxicity (CDC), 3) antibody‐dependent cell‐mediated cytotoxicity (ADCC) by using peripheral blood mononuclear cells, and 4) outside‐to‐inside (reverse) signal transduction through transmembrane TNFα estimated by apoptosis and cell cycle analysis using flow cytometry. Results All of the anti‐TNFα agents bound to transmembrane TNFα. 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 TNFα–expressing Jurkat T cells, reflecting an outside‐to‐inside signal transduction through transmembrane TNFα. Conclusion Three different anti‐TNF agents showed different biologic effects on transmembrane TNFα. This finding suggests that CDC and outside‐to‐inside signals by anti‐TNFα antibodies may explain the successful clinical efficacy of adalimumab and infliximab in Crohn's disease and Wegener's granulomatosis.