AB1297 Bridging ELISA as a secreening assay to monitor immunogenicity in routine clinical practice
Authors: S. Garcês, J. Demengeot, J. Canas-da-Silva, L. Aarden
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> The clinical and scientific relevance of monitoring immunogenicity in clinical practice have been recognized and recommended by the European Agency of Medicine (EMA)<sup>1</sup>. However, its assessment is technically challenging and no consensus exists about the way immunogenicity can be monitored. Newly developed fluid-phase radio-immuno assays (RIA) have proven quite effective in detecting anti-drug antibodies and as been presented as a "gold standard" method to assess immunogenicity<sup>2,3</sup>. However, RIA requires high doses of radioactivity and special conditions, preventing its use as a routine assay. By contrast, enzyme-linked immunoassay (ELISA) it's a simple and cheap method, ideal candidate to be used as a high-throughput screening assay. Bridging ELISA is a particular type of ELISA with increased specificity over the conventional ELISAs methods. Several optimizations of this method were made so that it can become a good screeningassay to monitor drug immunogenicity in routine clinical practice. <h3>Objectives</h3> We tested, in a same cohort of patients receiving infliximab, this newly optimized bridging ELISA in comparison with a fluid-phase antigen-binding RIA to quantify anti-infliximab antibodies. <h3>Methods</h3> A total of 82 consecutive patients were evaluated (38 rheumatoid arthritis patients, 27 ankylosing spondylitis, 9 psoriatic arthritis and 18 patients with inflammatory bowel disease), 61 females, with a mean age of 41 (4.2) years, that were receiving Infliximab in a dosage of 3-5mg/kg every 6 or 8 weeks for a mean period of 3.5 (2.0) years. Blood samples were collected immediately before the next infliximab infusion. Anti-infliximab antibodies were quantified by 1) Bridging ELISA where the antibodies bind to the infliximab coated in a solid phase and revealed by the addition of biotinylated infliximab and by 2) fluid-phase RIA-ABA that uses a sepharose-immobilized protein A, IgG total and IgG4-specific, to bind IgGs in the patient's serum. Anti-infliximab specific IgGs are revealed by theaddition of <sup>125</sup>I-labeled infliximab F(ab')2. A simple ELISA method was used to quantify serum infliximab levels,based on the principle that infliximab are captured through their ability to bind immobilized TNFα on a solid phase. The binding assessment is revealed by incubation with biotinylated rabbit IgG directed to infliximab idiotype. Therapeutic response was assessed according to validated criteria established for each disease. <h3>Results</h3> A total of 22 (27%) were tested positive for the presence of anti-infliximab abs using RIA, coinciding with the samples that were also positives in Bridging ELISA. Bridging ELISA cannot detect monovalent IgG4. No samples testing exclusively IgG4 specific anti-infliximab were detected. All patients (100%) with detectable anti-infliximab antibodies had undetectable serum trough drug levels and were not able to sustain the therapeutic response. <h3>Conclusions</h3> By its simplicity, cost and robustness, Bridging ELISA is a suitable test to be implemented in routine clinical practice as a screening assay to monitor drug immunogenicity. <h3>References</h3> E.M.A. http://www.ema.europa.eu/docs/en_GB/document_library/Scientific_guideline/2009/09/WC500003946.pdf L et al. Curr Opin Immunol, 2008; 20: 431-5. Svenson M et al. Rheumatology (Oxford), 2007; 46: 1828-34. <h3>Disclosure of Interest</h3> None Declared