Neutralizing antibodies to interferon beta in multiple sclerosis: Analytical evaluation for validation of a cytopathic effect assay

Background: Recent guidelines have recommended the use of validated assays for the measurement of neutralizing antibodies (NABs) to interferon beta (IFN beta) in patients with multiple sclerosis (MS). In an attempt of validation, we studied the analytical performance of a bioassay based on antiviral cytopathic effect (CPE) using WISH cells and the vesicular stomatitis virus (WISH/VSV CPE). Methods: NAB titres measured with the WISH/VSV CPE assay in 63 sera from IFN beta-treated MS patients were compared to those obtained with the reference CPE method using A549 cells and the encephalonnyocarditis virus. Binding antibodies (BABs) were measured using a capture ELISA as a screening test for NABs. Results: No false-negative BAB was obtained in our patients. The between-run coefficients of variation (CVs) determined with log(10) titres of the NIH anti-IFN beta (G038-501-572) yielded good results (<= 10.4%) and within-run variability was excellent (CV:<= 2%). The log(10) titres obtained with both CPE assays were highly correlated (r=0.969 and r=0.884 for anti-IFN beta-1a and anti-IFN beta-1b, respectively). The same patients were found NAB-positive with both CPE assays. Conclusion: Because of its good precision, sensitivity and excellent correlation with the reference CPE method, the WISH/VSV CPE bioassay can be used in the follow-up of IFN beta-treated MS patients. (c) 2006 Elsevier B.V. All rights reserved.