Lázár‐Molnár, Eszter

Abstract Background Adalimumab is a fully human monoclonal antibody developed against tumor necrosis factor (TNF), used for the treatment of autoimmune and chronic inflammatory diseases. Immunogenicity to this drug may lead to therapeutic failure. Various laboratory assays are used for measuring serum adalimumab and anti-drug antibodies (ADA) to adalimumab, for therapeutic monitoring and evaluation of clinical non-responsiveness. This study compared the performance of 2 clinical assays used by different reference laboratories. Methods In total, 120 residual clinical samples were tested at both laboratories. A sandwich ELISA for adalimumab detecting free drug and a bridging ELISA capable of detecting both free and bound ADA were performed at the Mayo Clinic. A functional cell-based reporter gene assay (RGA) was used at ARUP Laboratories for measuring bioactive serum drug concentrations, and neutralizing ADA. Results Seventy-eight samples had measurable concentrations of adalimumab by both methods and yielded a correlation coefficient r = 0.93, slope = 0.886, and intercept = 0.950. Overall agreement of 92.5% was observed between the assays, with most discrepant drug results being attributed to a higher positivity rate with ELISA (8/9). One outlier positive with RGA and negative with ELISA was confirmed by LC-MS/MS to be attributed to infliximab. Overall agreement of 79.2% was observed between the ADA assays. Differences in ADA results may be due to the bridging ELISA detecting total ADA (free, drug-bound, neutralizing, and non-neutralizing), while RGA detects free, neutralizing ADA only. Conclusions Although the assays are fundamentally different, the results show significant concordance between the clinically validated tests performed in different laboratories.

Abstract Background Infliximab (IFX) is a chimeric monoclonal antibody targeting tumor necrosis factor-α, used for the management of autoimmune and inflammatory diseases. Immunogenicity to this protein drug may lead to therapeutic failure. Laboratory testing for serum IFX and antidrug antibodies (ADAs) is available for the evaluation of clinical nonresponsiveness. The purpose of this study was to compare the performance of testing methodologies used by 2 clinical reference laboratories for the quantification of IFX and detection of ADAs. Methods Deidentified serum samples submitted for clinical testing were selected (n = 120) and tested at both sites. A trypsin-based LC-MS/MS assay for IFX and a bridging electrochemiluminescent immunoassay (ECLIA) for ADAs (Mayo Clinic) and a functional cell-based reporter gene assay (RGA) to measure both bioactive drug concentrations and neutralizing ADAs (ARUP Laboratories) were compared. Results In all, 105 samples had measurable concentrations of IFX by both methods and yielded a correlation coefficient (r) = 0.917, slope = 1.028, and intercept = −0.377. One outlier measured <1.0 μg/mL by LC-MS/MS and 37 μg/mL by RGA, which was confirmed to be attributed to the presence of adalimumab. Regarding detection of ADAs, 81 of 120 samples were negative by ECLIA and RGA, whereas 30 of 120 were positive by both methods, resulting in an overall 92.5% agreement. Conclusion Although there are substantial methodological differences in the assays used for detecting IFX and ADAs, results show significant concordance between the clinically validated methodologies performed in different laboratories.